University of Southern California Dissertations and Theses

Continental Slopes Of The World

(USC Thesis Other)

Continental Slopes Of The World

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Content T h is d is se r ta tio n h a s been 65— 12,268 m ic r o film e d e x a c tly a s r e c e iv e d T E R R Y , R ichard D ean , 1 9 2 4 - C O NTINEN TAL SL O PES O F THE WORLD. U n iv e r sity o f Southern C a lifo rn ia , P h .D ., 1965 G eology U niversity M icrofilms, Inc., A nn Arbor, M ichigan CONTINENTAL SLOPES OF THE WORLD by R ich ard Dean T e r r y A D i s s e r t a t i o n P r e s e n t e d to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In P a r t i a l F u l f i l l m e n t of th e R equ irem en ts f o r the Degree DOCTOR OF PHILOSOPHY (Geology) June 1965 UNIVERSITY O F S O U T H E R N CALIFORNIA THE G RA DUATE SC H O O L U N IV ER SITY PARK L O S A N G ELES, C A L IFO R N IA 9 0 0 0 7 This dissertation, written by ......................Richard. Dean .Terry........................ under the direction of h\&....Dissertation Com mittee, and approved by all its members, has been presented to and accepted by the Graduate School, in partial fulfillment of requirements for the degree of D O C T O R OF P H I L O S O P H Y Dean Date J.une^.1.9.6.5 DISSERTATION COM M ITTEE CONTENTS Page ABSTRACT.......................................................................................... 1 INTRODUCTION ...................................................................................................... 3 P r e v i o u s w o r k ...................................................................................... 6 N o m enclature ........................................................................................... 11 T e r r a c e c o r r e l a t i o n ...................................................................... 15 A c k n o w l e d g m e n t s ..................................... 21 JAPANESE ISLANDS.......................... 24 I n t r o d u c t i o n .......................................................... 24 P a c i f i c C oast o f Ja p a n ................................................................ 27 K ii S t r a i t ...................................................................................... 28 K ii S t r a i t to Kumano-Nada S e a ................................ 29 Enshu-Nada S e a ........................................................................... 29 Suruga B a y ................................................................................. . 30 Sagami Bay .. . . ........................................................................... 31 Kamogawa, Boso P e n i n s u l a ................................................ 31 S a n r i k u .......................................................................................................32 Cape S h i r i y a to Cape Erim o, Hoddaido I s l a n d 32 K u s h ir o , Hokkaido ................................................................ 32 A kkeshi A r e a .......................................................... 33 Nemuro S t r a i t .......................... 33 J a p a n S e a ......................_ ....................................................................... 34 N o r th e r n Hokkaido ................................................................ 34 O k u s h ir i I s l a n d to T sug aru P e n i n s u l a . . . . 34 S o u th e r n Hokkaido . 35 N o rth e rn Honshu ...................................................................... 35 Banks n o r t h o f Sado I s l a n d ........................................... 35 N i i g a t a P e r f e c t u r e ................................................................ 36 Toyama B a y ...................................................................................... 36 S a n - i n D i s t r i c t .......................... 36 Yamato B a n k .................................................. ' ............................ 37 Ryuku I s l a n d s ........................................................................... 37 . D i s c u s s i o n .......................................... 37 Bottom d e p o s i t s and g e o lo g i c h i s t o r y ........................... 41 i i Page JAPAN S E A ............................................................................................................... 50 KURILE-KAMCHATKA A R C ............................................................... 55 I n t r o d u c t i o n ........................................................................................... 55 R e s u l t s ........................................................................................................... 58 OKHOTSK S E A ................................ 64 BERING S E A .................................................................................................... . 6 8 ALEUTIAN A R C .......................................................................................................... 7 2 I n t r o d u c t i o n ............................................................................................... 72 R e s u l t s ............................................................................................................... 74 Geology . . . . . 80 WEST COAST OF ALASKA AND CANADA . . . . ..................................... 90 I n t r o d u c t i o n ............................................................................................... 90 R e s u l t s ..................................... 92 O R E G O N .......................................................... 96 I n t r o d u c t i o n ........................................................................................... 96 R e s u l t s ..................................................... 96 Bottom m a t e r i a l s ................................................................................ 102 G e o l o g y .................................................................................................................102 C A L IF O R N IA .................................................................................................................105 I n t r o d u c t i o n .............................................................................................. 105 R e s u l t s ........................................................................................... 105 BAJA CALIFORNIA BORDERLAND . I l l I n t r o d u c t i o n ........................................................................... I l l R e s u l t s . . . . . I l l G e o l o g y .................................................................................................................112 GULF OF C A L IF O R N IA .............................................................................. 116 . I n t r o d u c t i o n .............................................................................................. 116 R e s u l t s ................................................................................................................. 117 CENTRAL AMERICA I n t r o d u c t i o n 124 124 Page WEST COAST OF SOUTH AMERICA....................................................................127 I n t r o d u c t i o n ....................................................................................... 127 R e s u l t s .............................................................................................................128 TIMOR AND NORTHWEST AUSTRALIA...............................................................132 I n t r o d u c t i o n ....................................................................................... 132 R e s u l t s .............................................................................................................135 G e o l o g y ....................................................................................... 143 SOUTHWEST PACIFIC .................................................................................. 150 I n t r o d u c t i o n .............................................. ........................................ 150 R e s u l t s .......................................................................................................151 G e o l o g y .......................................................................................................160 G re at B a r r i e r R e e f ..............................................................160 S o u th e a s t A u s t r a l i a and Western New Zealand . 171 . C eleb es S ea--S ulu Sea ......................................................... 172 HAWAIIAN ISLANDS ....................................................................................... 175 I n t r o d u c t i o n ....................................................................................... 175 R e s u lts . . . ..................................................................................179 D i s c u s s i o n ............................................................................................ 192 Geology .......................................................................................194 OTHER PACIFIC ISLANDS.............................................................................202 C lip p e r t o n I s la n d ............................................................................. 202 Rapa I s l a n d ................................................... ........................................ 203 T a h i t i ....................................... _............................................204 ANTARCTICA.......................................................................................................207 I n t r o d u c t i o n ....................................................................................... 207 R e s u l t s ......................................................................................................208 G e o l o g y .......................................................................................................215 Bottom m a t e r i a l s ......................................... ...................................217 ARCTIC OCEAN .................................................................................................. 221 I n t r o d u c t i o n ....................................................................................... 221 R e s u l t s ............................................................................................................. 222 Bottom m a t e r i a l s ............................................................................. 232 G e o l o g y .......................................................................................................232 iv Page NORWAY........................................................................ 243 I n t r o d u c t i o n ................................................................... 243 R e s u l t s ................................................................................................... 243 O r ig in of C o n t i n e n t a l T errac e .......................................... 247 WESTERN GREENLAND ................................................................................... 254 I n t r o d u c t i o n .................................... 254 R e s u l t s ................................................................... 254 Bottom m a t e r i a l s ......................... 256 G e o l o g y ................................................................................................... 256 GREENLAND-ICELAND ................................................................................... 259 I n t r o d u c t i o n ......................................................................................... 259 R e s u l t s ................................................................................................... 261 WEST COAST OF EUROPE.............................................................................. 267 I n t r o d u c t i o n .................................................................... 267 R e s u l t s ................................................................................................... 268 G e o l o g y ................................................................................................... 271 NORTHWEST COAST OF AFRICA ............................................................... 27 8 I n t r o d u c t i o n ......................................................................................... 278 R e s u l t s .............................................................. 279 G e o l o g y ................................................................................................... 284 GULF OF GUINEA.............................................................................................. 290 I n t r o d u c t i o n ......................................................................................... 290 R e s u l t s ................................................................................................... 290 Bottom m a t e r i a l s .............................................................................. 291 G e o l o g y ................................................................................................... 293 SOUTHWEST AFRICA ......................................................................................... 294 I n t r o d u c t i o n ......................................................................................... 294 R e s u l t s ................................................................................................... 294 Comparison of C o n t i n e n t a l T e rra c e of West C oast o f A f r i c a .......................................................... 296 Geology . ......................................................................................... 298 Bottom m a t e r i a l s .............................................................................. 305 v Page EASTERN CANADA ............................................................................................... 309 I n t r o d u c t i o n .................................................................................... 309 R e s u l t s .................................................................................................... 309 EAST COAST OF THE UNITED S T A T E S ................................................... 314 I n t r o d u c t i o n .................................................................................... 314 R e s u l t s .................................................................................................... 314 BAHAMA PLATFORM........... .................................................................................... 323 I n t r o d u c t i o n ............................................................................................. 323 R e s u l t s .................................................................................................... 323 Tongue of the O c e a n ................................................... 325 Exuma S o u n d ............................................................................... 327 G e o l o g y .................................................................................................... 330 BLAKE P L A T E A U ............................................................................................... 336 I n t r o d u c t i o n .......................................................................................... 336 R e s u l t s .................................................................................................... 336 D i s c u s s io n . . . . * . ................................................................ 339 GULF OF MEXICO............................................................................................... 341 I n t r o d u c t i o n .......................................................................... 341 R e s u l t s .................................................................................................... 341 Bottom m a t e r i a l s ............................................................................... 349 G e o l o g y .................................................................................................... 350 D i s c u s s i o n .............................................................................................. 356 STRAITS OF FLORIDA..................................................................................... 359 I n t r o d u c t i o n .......................................................................... 359 R e s u l t s .................................................................................................... 359 Geology . . . ................................................................................ 362 EAST COAST OF SOUTH A M E R IC A .......................................................... 365 I n t r o d u c t i o n .......................................................................................... 365 R e s u l t s ..................................................................................................... 365 BERMUDA.............................................................................................................. 373 MID-ATLANTIC RIDGE 374 Page GREAT METEOR SEAMOUNT.......................................................................................377 I n t r o d u c t i o n ........................................................................................... 377 R e s u l t s ................................................................................................................. 377 MEDITERRANEAN S E A ..................................................................................................380 I n t r o d u c t i o n ........................................................................................... 380 R e s u l t s ..................................................................................................................380 G e o l o g y ..................................................................................................................382 BLACK SEA ............................................... 1 384 CASPIAN SEA ..................................................... ..... ......................................386 RED S E A .....................................................................................................................387 I n t r o d u c t i o n .......................................................................................... 387 R e s u l t s ......................................................................................................387 G e o l o g y ...........................................................................................................388 \ INDIAN OCEAN ...................................................................................................... 389 I n t r o d u c t i o n ...........................................................................389 R e s u l t s ...........................................................................................................390 Bottom M a t e r i a l s ................................................................................ 398 G e o l o g y ...........................................................................................................399 DISCUSSION ......................................................................................................406 Types o f C o n t i n e n t a l - ' S l o p e s ......................................................406 S h e l f B r e a k s ...........................................................................................408 T e r r a c e s ......................................................................................................411 Large F l a t A r e a s ................................................................................ 413 I n s u l a r S lo p e s . . ...........................................................................414 Bottom M a t e r i a l s . . ................................................................................ 415 S u b s id e n c e of Oceans and S e a s ........................... 416 O r i g i n o f C o n t i n e n t a l S lo p e s ................................................ 421 E a r th q u a k e s and T e c to n ism ........................................................... 425 O r i g i n of C o n t i n e n t s and Ocean B a s in s ........................... 429 I n t r o d u c t i o n ................................................................................ 429 C o n t i n e n t a l D r i f t ...................................................................... 436 Cause of S u b sid en c e . ...........................................................446 C o n c l u s i o n ......................................................................................461 The E a r t h ’ s G e o i d ................................................................................ 463 C o n t i n e n t a l Growth ........................................................................... 466 Economic c o n s i d e r a t i o n s ................................................................. 470 O th e r F a c t o r s ...........................................................................................471 v i i Page GENERAL CONCLUSIONS ................................................................................... 473 A P P E N D IX ......................... 486 I n t r o d u c t i o n ....................................................................................... 486 Evidence of Subsidence .............................................................. 497 REFERENCES CITED ........................................................................................ 586 ILLUSTRATIONS F ig u re Page 1. Echogram o f f P a lo s Verdes Slope . . . . . . . 4 2. Flow Diagram f o r Echogram and P r o f i l e P r o c e s s i n g ......................................................... 7 3. Index Map of Ja p an e se I s l a n d s .................................... 26 4. D i s t r i b u t i o n of T e r r a c e s around Ja p a n e se I s l a n d s ............................................................... 38 5. Depths of T e r r a c e s around Ja p a n e se I s l a n d s . 39 6. Age of Bottom Rocks around Jap anese I s l a n d s ......................................................................................... 42 7. Schem atic P r o f i l e Showing T e c to n ic Development of N o r t h e a s t e r n Honshu and Ja p an Trench s in c e Youngest Neogene . . . . 47 8. D i s t r i b u t i o n of S h e lf B reaks in N orthw est P a c i f i c Ocean ......................................................................... 54 9. P r o f i l e s Across the K u r i l e , Ja p a n , and P h i l i p p i n e Trenches .......................................................... 56 10. C o r r e l a t i o n Diagram of T e r r a c e s on the K u rile-K am ch atk a Trench Slope ................................ 57 11. Bathym etry of N o rth w estern P a c i f i c Ocean . . 59 12. C o r r e l a t i o n Diagram of T e r r a c e s on the A l e u ti a n A r c ......................................................................... 75 13. C o r r e l a t i o n Diagram of T e r r a c e s on the West Coast of A laska and C a n a d a .......................... 91 14. D i r e c t T r a c in g s of Echograms o f f the Coast of O r e g o n .................................................................................... 97 ix Figure Page 15. C o r r e l a t i o n Diagram of T e rra c e s and Other F e a tu r e s o ff t h e Coast of O r e g o n .......................... 98 16. C o r r e l a t i o n Diagram of T e rra c e s and Other F e a tu re s o f f the C oast of C a l i f o r n i a . . . . 106 17. Continuous Seism ic P r o f i l e North of P o in t A rg u e llo , C a l i f o r n i a ......................................... 109 18. Continuous Seism ic P r o f i l e Across A rg u e llo P l a t e a u ........................................................... 110 19. P r o f i l e s Across C o n t i n e n t a l Margins of A u s t r a l i a .........................................................................................134 20. C o r r e l a t i o n of C o n t in e n t a l T errace F e a tu re s Between A u s t r a l i a and Timor I s la n d ..................... 140 21. P r o f i l e s Across G reat B a r r i e r Reef ........................... 161 22. Schematic C r o s s - S e c tio n Across Great B a r r i e r R e e f ....................................................................................165 23. L o ca tio n of Dredge Hauls o f f Hawaiian I s l a n d s ..............................................................................................177 24. Echograms South of O a h u ...........................................................180 25. P r o f i l e s o f f Rapa I s l a n d ...........................................................205 26. P r o f i l e s o f f C lip p e r to n Is la n d ..................................... 205 27. P r o f i l e s o f f T a h i t i ..................................................................... 206 28. C o r r e l a t i o n of T e r r a c e s and O ther F e a tu re s on the C o n t in e n t a l T e rra c e o ff A n t a r c t i c a . 212 29. Comparison o f C o n t in e n t a l S helves of High L a t it u d e L a n d s ...............................................................213 30. Map Showing Ice Removed from A n t a r c t i c a . . . 219 31. G en eral Geology o f A n t a r c t i c a ...................................... 220 32. Bathymetry of the A r c t i c ........................... 223 33. P r o f i l e s Across the A r c ti c Ocean and Norwegian S e a ...............................................................................226 x Figure Page 34. T e c to n ic c h a r t of the A r c t i c .................... 237 35. C o r r e l a t i o n Diagram of F e a t u r e s o f f Norwegian C o n t i n e n t a l T e rra c e ................................... 245 36. D ia g ra m a tic C r o s s - S e c t i o n Between B a f f i n I s l a n d and S c a n d in a v ia ................................ 258 37. Echosounding P r o f i l e s o f f Beeren I s l a n d and S p i t s b e r g e n ........................................................................... 260 38. C r o s s - S e c t i o n a l P r o f i l e o f f E a s t G reenland . . 265 39. P r o f i l e Between S p i t s b e r g e n and G reenland . . 266 40. B athym etry of C o n t i n e n t a l Slope o f f Morocco . 283 41. T e c to n ic Map of A f r i c a ......................... 287 42. E a rth q u a k e A c t i v i t y in Morocco ..................................... 288 43. Average Annual Frequency of E a rth q u a k e s in A f r i c a ............................................... 289 44. E a rth q u a k e A c t i v i t y in South A f r i c a ..................... 299 45. A t t i t u d e of C y c li c E r o s i o n a l Land S u r f a c e s in S o u th ern A f r i c a ..................................... 302 46. Troughs and D e p r e s s io n s Along the L abrador-N ew foundland C o a sts ..................................... 311 47. C o n tin u o u s S e ism ic P r o f i l e Along th e E a st C oast o f the U nited S t a t e s .................................................319 48. C o r r e l a t i o n of S t r u c t u r a l Benches o f f N o r t h e a s t U n ite d S t a t e s ................................................ 320 49. I n t e r p r e t a t i o n of Seism ic R e s u l t s by Heezen, T h arp, and Ewing, 1959 ................................ 321 50. I n t e r p r e t a t i o n of S e ism ic R e s u l t s by Heezen, T harp, and Ewing, 1959 ................................ 322 51. C o r r e l a t i o n o f T e r r a c e s in Tongue of the O c e a n ........................................................................................... 329 52. G e n e r a li z e d Diagram of Blake P l a t e a u ...................... 338 x i Figure Page 53. P r o f i l e s of the F l o r i d a - G u lf C o n tin e n ta l M a r g i n .................................................................................. 343 54. Schematic Diagram of C o n t in e n t a l , O ceanic, and I s la n d S t r u c t u r e s .................................................... 434 55. W ater-Covered C o n t in e n t a l Areas Computed from P a le o g e o g ra p h ic M a p s ................................................451 56. T o ta l Accumulation of M ic r o - m e te o r it i c M a te r ia l on E arth sin c e the P a l e o z o ic . . . 458 x i i TABLES Table Page 1. Mean S h e lf B reaks f o r Okhotsk S e a ............................... 64 2. Approximate S h e lf B reak s, West C oast of A lask a and C a n a d a .................................................................... 93 3. Approximate Depth of S h e lf Breaks in Gulf of C a l i f o r n i a ..................................................................... 118 4. A re a l D i s t r i b u t i o n of Slopes in th e Gulf of C a l i f o r n i a ......................................................................120 5. Depth of C o n t i n e n t a l S h e lf Breaks o f f C e n t r a l America ......................................................................... 126 6. Approximate Depth of S h e lf Break o f f J a v a and B a l i .....................................................................................156 7. Hawaiian I s l a n d s Dredge Samples .................................... 178 8. C o ra ls from Hawaiian I s l a n d s .......................................... 187 9. Depth of S h e lf B re ak s, A n t a r c t i c a ............................... 209 10. Depth o f S h e lf Breaks in N o r th e a s t A t l a n t i c Ocean ......................................................................... 263 11. Mean S h e lf - B r e a k s and Widths o f I n s u l a r S h e lv e s , N orth A t l a n t i c Ocean ..................................... 263 12. The C o n t i n e n t a l S h e lf and O th e r S u r f a c e s o f f the West Coast of E u r o p e ........................................... 273 1 3 . G r a d ie n t s of C o n t i n e n t a l Slope o f f N orthw est A f r i c a .................................................................... 281 14. S h e lf Breaks o f f Niger D e lta ............................291 15. C o n t i n e n t a l Slope G r a d ie n t s and S h e lf Breaks o f f S o uth w estern A f r i c a ..................................................... 295 x i i i Table Page 16. Com parison of C o n t i n e n t a l T e r r a c e o f f West C o a st of A f r i c a ........................................................... 297 17. A pproxim ate S h e l f Breaks o f f E a s t C oast of C a n a d a ...................................................................................... 310 18. A pproxim ate S h e l f B reaks o f f E a s t C oast o f U n ite d S t a t e s ...................................................................... 318 19. A pproxim ate S h e l f B reaks o f f Bahamas and A n t i l l e s .......................................................................... 324 20. D epths of Major B reaks in S lo p e s in Exuma S o u n d ................................................................................ 330 21. D i f f e r e n c e s Between C o n t i n e n t a l S lo p e s N orth and South o f 27° N ................................................ 342 22. Approxim ate S h e l f B reak s in the W estern G u lf of M e x i c o ........................................................................... 345 23. S h e l f B reaks o f f N o r th e r n G u lf of Mexico . . . 346 24. A pproxim ate Depths of S h e l f B reak s o f f E a s t C oast o f South A m e r i c a ...................................... 366 25. C h a r a c t e r i s t i c s of C o n t i n e n t a l S h e lv e s and S l o p e s ...................................................................................... 409 26. E v id en ce used f o r R e c o g n iz in g F a u l t i n g and O ther F e a t u r e s ................................................................ 490 x i v PLATES ( P l a t e s 1-19 and 22-44 a re i n a s e p a r a t e volume) P l a t e Page 1. P r o f i l e s A c ro ss Ja p a n T rench . . . p o c k e t 2. P r o f i l e s A c ro ss Ja p an T rench and Ryuku I s l a n d s ........................................................................... p o c k e t 3. P r o f i l e s A c ro ss th e Sea of J a p a n .............................p o c k e t 4. P r o f i l e s A c ro ss K u rile -K a m c h a tk a Trench . . . p o c k e t 5. P r o f i l e s A c ro ss K u rile -K a m c h a tk a T rench . . . p o c k e t 6. P r o f i l e s A c ro ss A l e u t i a n Arc ............................ . . . p o c k e t 7. P r o f i l e s A cro ss West C oast of A lask a and Canada ................................................................................................ p o c k e t 8. P r o f i l e s A cross C o n t i n e n t a l Slope o f f Oregon . p o c k e t 9. P r o f i l e s A c ro ss C o n t i n e n t a l Slope o f f C a l i f o r n i a ...................................................................................... p o c k e t 10. P r o f i l e s A c ro ss C a l i f o r n i a - M e x i c o B o r d e rla n d . p o c k e t 11. P r o f i l e s A cross G u lf of C a l i f o r n i a ......................... p o c k e t 12. P r o f i l e s A cross C o n t i n e n t a l Slope o f f C e n t r a l A m erica ...................... ........................................... p o c k e t 13. P r o f i l e s A cro ss P e r u - C h i l e Trench ......................... p o c k e t 14. P r o f i l e s Between A u s t r a l i a and Timor .................... p o c k e t 15. P r o f i l e s Between A u s t r a l i a and Timor Showing Major T o p o g rap h ic F e a t u r e s . . . . . p o c k e t 16. P r o f i l e s of C o n t i n e n t a l Slope o f f V ietnam . . p o c k e t xv P la t e Page 17. P r o f i l e s of C o n t i n e n t a l Slope in S o u th w e st P a c i f i c Ocean ............................................................................. p o c k e t 18. P r o f i l e s of C o n t i n e n t a l Slope o f f J a v a and B a l i ...............................................................................................p o c k e t 19. P r o f i l e s o f f A u s t r a l i a and New Z ealan d . . . . p o c k e t 20. K o daco lor P r i n t s of Dredge H auls from H aw aiian I s l a n d s .......................................................................... 185 21. K o daco lor P r i n t of Dredge Haul o f f P e n g u in Bank, Hawaii ................................................................ 186 22. P r o f i l e s a c r o s s C o n t i n e n t a l T e r ra c e o f f A n t a r c t i c a ........................................................................................ p o c k e t 23. P r o f i l e s A c ro ss C o n t i n e n t a l T e r r a c e and O ther F e a t u r e s in A r c t i c Ocean .................................. p o c k e t 24. P r o f i l e s A c ro ss th e C o n t i n e n t a l S lope o f f N o rth e rn Norway ............................................................. p o c k e t 25. P r o f i l e s A c ro ss N orw egian C o n t i n e n t a l T e r r a c e ............................................................................................. p o c k e t 26. Subm arine R e l i e f and F a u l t o f f Norway . . . . p o c k e t 2 7* P r o f i l e s o f f the C o n t i n e n t a l T e r r a c e o f f th e E a s t and West C o a s ts of G re en lan d . . . p o c k e t 28. P r o f i l e s o f f the E a s t C oast o f G re en lan d and I c e l a n d .................................................................. p o c k e t 29. P r o f i l e s of West C o a st of E u r o p e ......................................p o c k e t 30. P r o f i l e s o f West C oast o f E u r o p e ......................................p o c k e t 31. P r o f i l e s o f West C o a st o f E u r o p e ......................................p o c k e t 32. P r o f i l e s A c ro ss R o c k a ll Bank .................................................. p o c k e t 33. P r o f i l e s A c ro ss N o rth w e st A f r i c a .................................... p o c k e t 34. P r o f i l e s A c ro ss Southw est A f r i c a .................................... p o c k e t 35. P r o f i l e s A c ro ss th e C o n t i n e n t a l S lope I n c l u d i n g Grand Banks and F lem ish Cap . . . p o c k e t x v i P la te Page 36. P r o f i l e s Across C o n t in e n t a l Slope of E a s te r n United S t a t e s ....................................................... pocket 37. P r o f i l e s Across Bahamas and L e sse r A n t i l l e s . pocket 38. P r o f i l e s Across C o n t in e n t a l Slope o f f E a s t Coast of South America ..................................... pocket 39. P r o f i l e s Across South Sandwich Trench . . . . pocket 40. Major Topographic F e a tu r e s of the In d ian O c e a n .................................................................................................pocket 41. P r o f i l e s Across C o n t in e n t a l Slopes of the In d ia n Ocean . pocket 42. P r o f i l e s Across I n s u l a r S lop es of In d ia n Ocean I s l a n d s and o f f P e n a n g ........................................pocket 43. P r o f i l e s Across C o n t in e n t a l Slopes o f f E ast A f r i c a .................................................................. pocket 44. P r o f i l e s o ff Labrador and Newfoundland . . . . pocket x v i i ABSTRACT S u rfa c e s of c o n t i n e n t a l s lo p e s d iv id e them selves i n to s i x g e n e ra l ty p e s : tho se w ith d i s t i n c t c o n t i n e n t a l r i s e s ; r e l a t i v e l y s t e e p s lo p e s w ith sm all aprons a t t h e i r b a s e s ; convex-shaped s lo p e s w ith r e l a t i v e l y g e n tl e upper and s te e p lower s l o p e s , o f te n having a sh a rp b reak a t t h e i r b a s e s ; c o n t i n e n t a l s lo p e s te r m in a t in g in a b o r d e r l a n d - l i k e p l a t e a u a t t h e i r b a s e s ; and e x tre m e ly g e n t l e c o n t i n e n t a l slo p e s g rad in g alm ost im p e r c e p tib ly i n to the c o n t i n e n t a l s h e l f and the a b y s s a l sea f l o o r . E s s e n t i a l l y ve c a l c o n t i n e n t a l s lo p e s a ls o e x i s t in re g io n s of r e c e n t a u l t i n g . C o n tin e n t a l slo p e s show a l l g r a d a t io n s between th ese typ es and- ab s o l u t e l y smooth s lo p e s to those having g r e a t i r r e g u l a r i t y along the s t r i k e and dow n-slope. C o n t in e n t a l slo p e s are b e lie v e d to have been formed by fo ur fundam ental methods: f a u l t i n g , f l e x u r i n g , com bination of f a u l t i n g and f l e x u r i n g , and f a u l t i n g (and p o s s i b l y f l e x u r in g ) combined w ith u p b u ild in g on a su b s id in g f o u n d a tio n . T e r r a c e s of d i v e r s o r i g i n s a re common a t a l l d e p th s from those on the c o n t i n e n t a l s h e l f to n e a r the b ases of t r e n c h e s . Many of the t e r r a c e s a re hundreds of k ilo m e te r s in w idth and some can be tr a c e d f o r tho usand s of k i lo m e te r s a t d e p th s f a r g r e a t e r than can be accounted fo r by g l a c i a l l y - c o n t r o l l e d e u s t a t i c se a l e v e l changes. T e r ra c e s u nd ou btedly have been formed by many d i f f e r e n t p r o c e s s e s and no sim ple or s i n g l e o r i g i n i s a p p l i c a b l e f o r a l l . C o n tin e n ta l s h e l f b reak s a re g e n e r a l l y h ig h ly sinuous and i n d i c a t e th a t some agency has f r e q u e n t l y a l t e r e d t h e i r d e p th s s in c e fo rm a tio n d u rin g the Q u a te rn a ry Epoch. In some r e g i o n s s h e l f b re a k s may vary t e n s of m eters in d epth in a r e l a t i v e l y s h o r t d i s t a n c e . Deep s h e l f b reaks are not c o r r e l a t e d w ith g l a c i a t e d r e g i o n s or w ith l a t i t u d e . T e r ra c e s along c o n t i n e n t a l s lo p e s o f te n show p a r a l l e l s i n u o s i t y w ith th e changes in d ep th of s h e l f b re a k s and s u g g e st a g e n e tic r e l a t i o n s h i p between s h e l f edge and t e r r a c e warping. Widespread sub sid ence of oceans and seas in r e l a t i v e l y r e c e n t time undo ub ted ly have had c o n s i d e r a b l e e f f e c t upon the o r i g i n of c o n t i n e n t a l s l o p e s , t e r r a c e s , and many o th e r 1 2 major se a f l o o r f e a t u r e s . While the evidence i s str o n g t h a t su b sid e n c e has o c c u r r e d , a l l a tte m p ts to e x p la in the mechanism have f a i l e d . INTRODUCTION D uring a s t u d y of the P a l o s V erdes S lope o f f S o u th e r n C a l i f o r n i a i n 1955 a t e r r a c e , or change in s l o p e , was n o t ed on numerous echogram s ( F ig u r e 1) (Emery and T e r r y , 1 9 5 6 ). The p e r s i s t e n c e of t h i s f e a t u r e s u g g e s te d an o r i g in by f a u l t i n g , b u t d e t a i l e d e x a m in a tio n of e a r t h q u a k e e p i c e n t e r s f a i l e d t o show any r e c o g n i z a b l e a c t i v i t y a lo n g t h i s s l o p e . E cho so un din g p r o f i l e s e ls e w h e r e o f f S o u t h e r n C a l i f o r n i a C o n t i n e n t a l B o rd e rla n d showed t h a t t e r r a c e s were common, t h e r e f o r e , an e f f o r t was made to check e c h o grams ta k e n in o th e r p a r t s o f the w o r ld . During 1955 and 1956, n e a r l y a th o usand p r o f i l e s were examined a t th e U n i v e r s i t y of S o u th e r n C a l i f o r n i a , Navy E l e c t r o n i c s L a b o r a t o r y , S c r i p p s I n s t i t u t i o n of O ceanography, C o a st and Geo d e t i c S u rv e y , Navy O c e a n o g ra p h ic O f f i c e , Lamont G e o l o g i c a l O b s e r v a t o r y , and th e U n i v e r s i t y of W ash in g to n . A s e a r c h of th e l i t e r a t u r e was a l s o made to l o c a t e p r o f i l e s and r e f e r e n c e s to d e ep t e r r a c e s . E x c e p t f o r a few p r o f i l e s a t Lamont G e o l o g i c a l O b s e r v a t o r y , a l l p r o f i l e s examined d u r i n g t h i s e a r l y p h a se had been t a k e n by equ ip m ent in u se p r i o r to the d e v elo p m e n t o f p r e c i s i o n ech o so u n d in g e q u ip m e n t. S e r i o u s l i m i t a t i o n s 3 P R O F I L E 0 - NO V E R T I C A L E XA GG ER A TIO N ,1000 STATUTE MILE V erticil Eiaggerition — 5 Times F ig u re 1. P r o f i l e s e x te n d in g down the s l o p e , redrawn from echograms. Note the p re se n c e from r i g h t to l e f t o f zones l i m i t e d by dash l i n e s : c o n t i n e n t a l s h e l f , smooth upper s l o p e , u n d u la tin g lower s l o p e , and b a s in f l o o r . ( A fte r Emery and T e r r y , 1956.) r e s u l t e d from t h e sm a ll s c a l e and c u r v i l i n e a r p l o t on e c h o grams (su c h as made by the NMC-2 e c h o s o u n d e r) and r e s u l t s were d i s a p p o i n t i n g . O th e r s e r i o u s p ro b le m s , e x c e p t f o r a few a r e a s , c o n s i s t e d of wide s p a c in g betw een p r o f i l e s ; the te n d e n c y of e x p e d i t i o n s to ig n o re th e s h e l f and s lo p e by f a i l u r e to m o n ito r th e ech o so u n d e r a n d /o r p l o t p o s i t i o n s u n t i l deep w a te r was r e a c h e d ; the te n d e n c y to c r o s s the c o n t i n e n t a l t e r r a c e a t s h a r p a n g le s t h e r e b y making i n t e r p r e t a t i o n o f t e r r a c e s d i f f i c u l t ; c r o s s i n g th e s lo p e w h ile c r u i s i n g a t h ig h s h ip sp e ed s r e s u l t i n g in echograms show ing s l o p e s so s t e e p as to mask any t e r r a c e s t h a t o th e r w is e m ight be p r e s e n t ; and i n a b i l i t y to make d e t a i l e d s t u d i e s along a given slo p e b e ca u se o f poor n a v i g a t i o n a l p r e c i s i o n . Numerous a t t e m p t s were made to j o i n e x p e d i t i o n s when e v e r p o s s i b l e to accum ulate d a t a . Because o f th e s e s e r i o u s l i m i t a t i o n s and the d e a r t h of d a t a , p r e v i o u s a tt e m p t s to stud y d e e p - s e a t e r r a c e s have n o t been s u c c e s s f u l anywhere in th e w o r ld . During the e a r l y p h a se s o f the s t u d y , t e r r a c e s of 600 m to 900 m o n ly were s t u d i e d . As work p r o g r e s s e d , th e scope o f th e i n v e s t i g a t i o n was bro aden ed when p r e c i s i o n d e p th r e c o r d e r echogram s became a v a i l a b l e . I t became ap p a r e n t t h a t d e e p t e r r a c e s were much more common th a n h e r e t o f o r e b e l i e v e d . As a r e s u l t , more th an 600 echograms p h o to g rap h e d i n 1955-1956 t e r m i n a t i n g a t a b o u t 600 m had to be d i s c a r d e d b ecau se th e y d id n o t f a i t h f u l l y p o r t r a y th e t o p o g r a p h i c f e a t u r e s down the com plete s l o p e . An a t t e m p t has been made to u t i l i z e as many o r i g i n a l echogram s as p o s s i b l e , p a r t i c u l a r l y th o s e p e r s o n a l l y c o l l e c t e d , b u t i t has b een n e c e s s a r y to r e l y h e a v i l y upon p u b l i s h e d ech o g ram s, red ra w n p r o f i l e s , and s e a f l o o r d e s c r i p t i o n s . P r o f i l e s ta k e n d u r in g th e I n t e r n a t i o n a l G e o p h y s ic a l Year were p a r t i c u l a r l y h e l p f u l , b u t o f t e n th e s c a l e was so s m a ll t h a t m inor f e a t u r e s could n o t be p ic k e d out on th e r e c o r d s . These a l s o had the d i s a d v a n t a g e of b e in g re d ra w n . Depth u n i t s on redraw n ( o r r e c o n s t r u c t e d ) echograms g e n e r a l l y were c o n v e r t e d to m e t e r s , b u t on some p r o f i l e s or d e s c r i p t i o n s i t was more c o n v e n ie n t to r e t a i n th e s c a l e in f e e t or f a th o m s . In an e f f o r t to s t a n d a r d i z e p r o f i l e s , th e y were p h o t o g r a p h i c a l l y m o d if i e d . A flo w d iag ra m of a p r o c e s s worked ou t d u r i n g t h i s s tu d y i s shown in F ig u r e 2. The d e a r t h of b o tto m sam ples on the c o n t i n e n t a l s l o p e , p a r t i c u l a r l y on w e l l d e f i n e d t e r r a c e s , was an enormous d i s a d v a n t a g e . Wider a p p l i c a t i o n of s e i s m ic p r o f i l i n g e q u i p ment a c r o s s the c o n t i n e n t a l t e r r a c e w i l l m a t e r i a l l y a id in i n t e r p r e t i n g s u b s u r f a c e f e a t u r e s . P r e v i o u s work L i t t l e r e a l e f f o r t (com pared to o t h e r more i n t e r e s t ing t o p o g r a p h i c f e a t u r e s ) has been expended on e c h o so u n d in g and b o tto m sa m p lin g o f the c o n t i n e n t a l s l o p e s . Much g e o p h y s i c a l w ork, how ever, h a s b e en done a c r o s s th e F INA L P L A T E P H OTO GRA PH ED ] INDIVIDUAL PR O F IL E S WITH SAME SCALES VERT EXAG (PA ST E UP) PH OTO GRA PH ICALLY PH OTO GRA PH ICALLY PHOTO GRA PH ICALLY SIZED SIZED SIZED PH OTO GRA PH IC ALLY | ' 1 1 PH OTO GRA PH IC I I REDUCTION OF I VE RTICA L - EXAGGERATION . nr.r CONTINUOUS P R O F IL E TR A CE D SAME SIZE AS PH O TO GRA PH I I r PH OTO GRA PH IC ^ REDUCTION OF VE RTICA L . EXAGGERATION > r _ J I I I ’--------1 1 PH OTO GRA PH IC 1 REDUCTION O F a V E R T IC A L I | EXAGGERATION j PH OTO GRA PH ICALLY SIZED USED “ AS IS* 1 “ 1 1 I PH OTO GRA PH IC REDUCTION O F I V E R T IC A L 1 I EXAGGERATION I H " T RACED PDR INTO CONTINUOUS P R O F IL E CONTINUOUS P R O F IL E TRACED FROM I IN. STRIP PHOTOGRAPH OF PDR (REDUCED SIZE) PHOTOGRAPHICALLY RE DUCED TO IN’ WIDE STRIP T RACED PDR F U L L SCALE | ' | 1 PH OTO GRA PH IC 1 I CHANGE O F I I V E RTICA L I - EXAGGERATION b i t CONTINUOUS IN TEG RA TED P R O F IL E TRACED 600 F T SW E E P PH OTO GRA PH ED 600 FM SW E E P PH OTO G RA PH ED 0 -6 0 0 0 FM S W E E P PH O TO G RA PH E D TRACED EDO (F U L L SIZE) PH O T O G RA PH E D EDO (REDUCED SIZE) PU E L J5H E D 1 ORIGINAL I P R O F IL E S ' ■ PDR ■ ORIGINAL EDO -4 Figure 2. Flow diagram f o r p rocessing echograms and published p r o f i l e s . c o n t i n e n t a l m arg in . F o llow ing th e i n t e r e s t e x p r e s s e d by the a u t h o r , Heezen ( p e r s o n a l com m unication, 1955) i n d i c a t e d t h a t he had o b served t e r r a c e s along th e E a s t C o ast of th e U n ite d S t a t e s and e ls e w h e re in th e A t l a n t i c . His o b s e r v a t i o n s , p u b l is h e d in d e t a i l in 1959 (H eezen, T h arp , and Ewing, 1959) con clu ded t h a t E a s t C o a st t e r r a c e s were th e r e s u l t of o u tc r o p p in g o f v a r i o u s C r e ta c e o u s and T e r t i a r y s t r a t a . C orresp o nd ence w i t h T. S a to i n i t i a t e d a d e t a i l e d stu d y o f t e r r a c e s s u r r o u n d in g J a p a n . Among th e f i r s t a tte m p ts t o stu d y deep t e r r a c e s over a c o n s i d e r a b l e a r e a i s t h a t by Yabe and Tayama (1 9 3 4 ). T h is was done u s in g b a th y m e t r i c c h a r t s long b e f o r e c o n t i n uous echosounding equipm ent was a v a i l a b l e . While o t h e r s t u d i e s , in s e l e c t e d a r e a s such as t h o s e o f f C a l i f o r n i a (Uchupi and Emery, 1 9 6 3 ), and the A l e u t i a n I s l a n d s r e c o g n iz e d the p r e s e n c e of t e r r a c e s or p la n e d o f f p l a t f o r m s a t v a r i o u s d e p t h s , no a tte m p t h a s been made anywhere to stu d y the c o n t i n e n t a l t e r r a c e on a w o rld -w id e b a s i s . In volume 3 of The Sea--T he E a r t h Beneath the S e a , G u ilc h e r (1963) summarized the knowledge of the c o n t i n e n t a l t e r r a c e ( c o n t i n e n t a l s h e l f and s l o p e ) . This b r i e f t r e a t m e n t compared to o t h e r p a r t s of t h i s volume showed, f i r s t , how l i t t l e i s known ab ou t th e c o n t i n e n t a l s lo p e and, se co n d , how l i t t l e a p p a r e n t im p o rta n c e i s a t t a c h e d to i t . R e c e n t l y , D. C. Krause ( p e r s o n a l com m unication, J u l y 1964) i n d i c a t e d t h a t he had r e c o g n i z e d d e ep t e r r a c e s in w i d e l y s c a t t e r e d r e g i o n s i n t h e P a c i f i c . His f i r s t i n t r o d u c t i o n to th e s e t e r r a c e s o f f th e c o n t i n e n t a l b o r d e r l a n d w e s t of B a ja C a l i f o r n i a , M exico, was r e p o r t e d in h i s d i s s e r t a t i o n ( 1 9 6 1 ) . In an u n p u b l i s h e d m a n u s c r i p t d a t e d J u l y , 1964, K rau se s t a t e d : "The c o n t i n e n t a l s lo p e in many r e g io n s of th e P a c i f i c i s b ro k e n i n t o two s e c t i o n s , an u p p e r s l o p e s e p a r a t e d by a d e e p t e r r a c e o r b o r d e r l a n d of d e p t h s betw een 500 and 1 ,5 0 0 f a t h o m s . I have e n c o u n t e r e d th e f e a t u r e in t h e s o u t h e r n c o n t i n e n t a l b o r d e r l a n d w e s t o f B a ja C a l i f o r n i a , M exico, i n th e Bounty r e g i o n e a s t of S o uth I s l a n d , New Z e a la n d , in th e C o r a l Sea b etw een A u s t r a l i a and New G u in e a , in t h e B ism ark Sea n o r t h of New G u in e a , and in th e C e le b e s Sea - S u lu Sea r e g i o n . The c r u s t a l s t r u c t u r e below th e deep t e r r a c e s i s v i r t u a l l y unknown, e x c e p t f o r a s t u d y by Shor and R a i t t (1 9 5 8 ) of th e complex c o n t i n e n t a l b o r d e r l a n d o f f s o u t h e r n C a l i f o r n i a . " So f a r as i s known, t h i s i s t h e o n ly s t a t e m e n t c o n c e r n i n g r e c o g n i t i o n o f d e e p s e a t e r r a c e s a t one l e v e l in w i d e l y s e p a r a t e d r e g i o n s . I t does n o t e x p l a i n t e r r a c e s a t g r e a t e r or l e s s d e p t h s t h a n th e f e a t u r e s e p a r a t i n g th e u p p e r and low er s l o p e s . S a to ( u n p u b l i s h e d ) u n s u c c e s s f u l l y a tt e m p t e d to c o r r e l a t e d e e p t e r r a c e s of Ja p a n w ith o t h e r a r e a s . M urray and o t h e r w o r k e r s r e c o g n i z e d e n o rm o u s ly l a r g e " b e n c h e s " in th e A l e u t i a n T re n c h and c a l l e d a t t e n t i o n to 10 s t e e p e n in g of the g r a d i e n t . L ik e w ise , L ario n o v a (1959) c a l l e d a t t e n t i o n to th e t r a n s i t i o n p o i n t between the upper and lower s lo p e s of t r e n c h e s , which she c a l l e d ’’m a rg in a l r a m p a r t s . ” She s p e c i f i c a l l y m entioned t h e s e f e a t u r e s in th e K u rile-K a m ch a tk a , A l e u t i a n , and P h i l i p p i n e T ren c h es. As work p r o g r e s s e d on th e c o n t i n e n t a l slo pe s tu d y i t became a p p a re n t t h a t t h e e n t i r e spectrum of i n f o r m a tio n b e a r i n g upon th e c o n t i n e n t a l m argin i s i m p o r t a n t . As a con seq uence, w herever p o s s i b l e , g e o l o g i c a l and g e o p h y s ic a l in f o r m a ti o n of the s u rro u n d in g re g io n was s t u d i e d in an e n deavor to u n d e rs ta n d the f o r m a tio n of the c o n t i n e n t a l t e r ra c e and a s s o c i a t e d f e a t u r e s . A d i r e c t outgrow th of t h i s was a c o m p ila tio n of the n a tu r e of the c o n t i n e n t a l m argin , e v id e n c e of s u b s id e n c e , u p l i f t , and s i m i l a r f a c t o r s r e l a t ed to th e o r i g i n of c o n te n e n ts and o c ea n s. T his has been summarized in t a b u l a r form and in c lu d e d as an appendix. The work of O. J e s s e n , a voluminous memoir p u b lis h e d in 1943 e n t i t l e d ’’Die R andschw ellen d e r K o n t i n e n t e , ” was un a v a i l a b l e , b u t a cc o rd in g to Umbgrove ( 1 9 4 7 ), J e s s e n p r o v i d - ed a w e a lth of d a t a on th e c o n t i n e n t a l m a rg in . He gave n u merous examples of r e j u v e n a t e d zones su rro u n d in g c o n t i n e n t a l edges and submarine b a s i n s . He c l a s s i f i e d the t h i c k e n in g s of the c o n t i n e n t a l m argin i n t o t h r e e ty p e s : ( 1 ) w arp ing accompanied by f a u l t s , (2) updoming accompanied by f a u l t s and s l i g h t f o l d i n g , and (3) f o l d i n g and o v e r t h r u s t in g , accompanied by u n d e r t h r u s t i n g of th e se a f l o o r , 11 r e s u l t i n g in a deep se a t r o u g h . I t i s u n f o r t u n a t e t h a t t h i s b a s i c work i s u n a v a i l a b l e and has been ig n o re d by ma r i n e g e o l o g i s t s . A f u r t h e r outgrow th of t h i s stu d y was th e c o n f l i c t t h a t o f t e n e x i s t s between g e o l o g i c a l and g e o p h y s i c a l i n f o r m a tio n . U n t i l more g e o l o g i c a l i n f o r m a ti o n i s g a th e r e d g eo p h y s i c a l d a t a o f t e n w i l l be d i f f i c u l t to r e c o n c i l e . The g e o l o g i s t o f t e n i s a t a d i s a d v a n t a g e b e c a u s e he i s unable to u n d e rs ta n d the m ath em atics o f the g e o p h y s i c i s t s . As Lees (1953) p o i n te d o u t: While g e o p h y s ic a l p r o c e s s e s n e c e s s a r i l y r e q u i r e , fo r t h e i r a n a l y s i s , a l a r g e measure of m a th e m a tic a l t r e a t m e n t , many o f the a n a l y s t s i n d u lg e i n a de g re e of m a th e m a tic a l e x h i b i t i o n i s m which makes a rea so n e d judgment by most g e o l o g i s t s e x tr e m e l y d i f f i c u l t . J e f f r e y s i s w e l l aware of t h i s , but i n s t e a d of t r y i n g to be h e l p f u l he m erely a d v i s e s t h a t . . . t h e g e o l o g i s t sho uld s k i p the m a th e m a tic a l s e c t i o n s and move on. T h is is sim ple a d v ic e , u s u a l l y f o llo w e d , b u t i t means t h a t the g e o l o g i s t must th en a c c e p t as v a l i d th e r e s u l t s of th e e q u a t i o n s . The v a lu e o f th e end r e s u l t of a s e r i e s of e q u a t i o n s , however, depends on th e r e a s o n a b l e n e s s of the a ssu m p tio n s w hich a re p u t in a t the f r o n t en d , and t h i s r e q u i r e s a combined o p e r a t i o n of both g e o l o g i c a l and g e o p h y s ic a l m ind s. Too o f t e n the g e o l o g i s t has been overawed by the assumed a u t h o r i t y of the g e o p h y s i c i s t s and h as i n c o r p o r a t e d t h e i r c o n c e p tio n s in to h i s framework of i d e a s ; and the c y c le i s then made com plete when g e o p h y s i c i s t s q u o te g e o lo g i c a l s u p p o r t in c o n f i r m a t i o n of t h e i r own d e d u c t i o n s . N om enclature Among the se a f l o o r term s used to d e s c r i b e f e a t u r e s which are f l a t (o r p e rh a p s g e n t l y s l o p i n g ) , and which b o r d e r the c o n t i n e n t s a re the f o l l o w i n g : 12 S h elf C o n tin e n ta l s h e l f C o n t in e n t a l t e r r a c e C o n t in e n t a l p l a t e a u C o n tin e n ta l slo p e ♦ B o rderland slope Basin slo p e T errace Deep-sea t e r r a c e P l a te a u ( e . g . , Blake P l a t e a u ) Marginal p l a t e a u ( e . g . , Blake P l a te a u ) P la tf o r m Bench ( e . g . , A l e u tia n Bench) Plane Abyssal p l a i n C o n t in e n t a l r i s e Rise Step A r c h ip e la g ic apron Apron Fan B a r r i e r r e e f ( e . g . , G reat B a r r i e r Reef) S t a i r c a s e ( e . g . , ’’g i a n t s t a i r c a s e ” of H a k k e l’ in A r c t i c Ocean) I t i s obvious t h a t th e s e f e a t u r e s depend upon such f a c t o r s as s i z e , d e p th , shape, l o c a t i o n , p ro x im ity to la n d , 13 and o t h e r f a c t o r s which a r e used a t t h e d i s c r e t i o n of th e a u t h o r . Some term s a re d e s c r i p t i v e ; o t h e r s have a g e n e t i c c o n n o t a t i o n . U n f o r t u n a t e l y , sea f l o o r n o m en c la tu re i s n o t u n ifo rm . Many f e a t u r e s have been d e f i n e d and a re w e l l a c c ep ted p h y s i o g r a p h ic term s (Wiseman and Ovey, 1953; Shep a r d , 1962); o t h e r s have o n ly a l e g a l c o n n o t a t i o n (UNESCO, 1957). Many of the term s which a re of im p o rtan ce in t h i s r e p o r t have not been p r o p e r l y d e f i n e d . In c lu d e d a r e : t e r r a c e , p l a t f o r m , bench, p l a i n , and s t e p . Wiseman and Ovey have d e f i n e d a d e e p - s e a t e r r a c e as n a b e n c h - l i k e f e a t u r e b o r d e r in g an e l e v a t i o n of t h e d e e p - s e a f l o o r a t d e p th s g r e a t e r than 300 f a th o m s ." P l a te a u i s d e f i n e d as "a v e ry e x t e n s i v e but i l l - d e f i n e d e l e v a t i o n of the d e e p - s e a f l o o r , the to p of w hich may be d i v e r s i f i e d by l e s s e r f e a t u r e s of e l e v a t i o n and d e p r e s s i o n . " M arg inal p l a t e a u was d e f i n e d by H eezen, T harp , and Ewing (1959) as "a s h e l f - l i k e f e a t u r e h aving a g r e a t e r d e p th th a n the c o n t i n e n t a l s h e l f and s e p a r a t e d from the c o n t i n e n t a l s h e l f by a low c o n t i n e n t a l s l o p e . " They a r b i t r a r i l y s e t the d e p th l i m i t a t i o n s f o r m a rg in a l p l a t e a u s at d e p th s g r e a t e r th a n 100 fms (200 m) and s h a llo w e r th a n 1,200 fms (2 ,2 0 0 m ). The Blake P l a t e a u i s c i t e d as an example of a m a rg in a l p l a t e a u , and i t was s u g g e s te d by Heezen and Menard (1963) t h a t the C a l i f o r n i a C o n t i n e n t a l B o rd e rla n d m ig h t, in th e f u t u r e , become a m ar g i n a l p l a t e a u a f t e r the b a s i n s became f i l l e d w ith s e d i m ents. So f a r as i s known th e only s e a - f l o o r f e a t u r e 14 em ploying th e term "b ench " i s th e A l e u t i a n Bench. T h is is l o c a t e d a t a d e p th of a p p r o x i m a t e ly 4 ,0 0 0 m on th e A l e u t i a n T re n c h s l o p e . T h is c ou ld a l s o be c a l l e d a t e r r a c e , d e ep - s e a t e r r a c e , p l a t e a u , p l a t f o r m , o r p l a n e . Whenever p o s s i b l e a c c e p te d te r m in o lo g y i s used through out the r e p o r t w i t h th e f o l lo w in g e x c e p t i o n s : (1 ) The term " d e e p - s e a t e r r a c e " i s n o t used a s d e f i n e d by H eezen, T h arp , and Ewing (1 9 5 9 ) , t h a t i s , " a b e n c h - l i k e f e a t u r e . . . a t d e p th s g r e a t e r th an 300 f m s . ” " T e r r a c e " w i l l r e f e r to any more or l e s s d i s t i n c t f l a t or g e n t l y s l o p i n g f e a t u r e a t any d e p th s m a l l e r th a n a p l a t e a u or p l a n e . (2) The term "b en c h " w i l l be e x c lu d e d ( e x c e p t where a f e a t u r e a l r e a d y has been named [such a s the " A l e u t i a n B e n c h " ] ) . (3) " P l a t e a u " and " p l a n e " a re used i n t e r c h a n g e a b l y w i t h the i m p l i c a t i o n t h a t t h e s e a re e x t e n s i v e f e a t u r e s (su c h as the Blake P l a t e a u , Lord Howe R i s e , e t c . ) . Many p r o f i l e s of the c o n t i n e n t a l s lo p e show a r i d g e and d e p r e s s i o n s e q u e n c e . T his c o m b in a tio n i s u n u s u a l l y common and o f t e n can be c o r r e l a t e d from p r o f i l e to p r o f i l e . When t h i s c o n s i s t s of r e l a t i v e l y sm a ll f e a t u r e s , i t i s o f t e n term ed a " t e r r a c e " f o r lac k o f b e t t e r t e r m i n o l o g y . The t r u e shape of t h i s f e a t u r e i s unknown and m ight have a wide v a r i e t y of o r i g i n s . However, th e w i d e - a n g l e e c h o so u n d e r beam masks th e t r u e s h a p e . K rause (1962) r e c e n t l y d i s c u sse d t h i s p ro b lem . P r a t t ( 1 9 6 3 ) , u s in g c o n t i n u o u s s e i s mic p r o f i l i n g e q u ip m e n t, Showed t h a t th e r i d g e and depression 15 top og raph y on G re at Meteor Seamount was u n d e r l a i n by a f l a t s u r f a c e . Thus, w h ile argum ents a g a i n s t the use of " t e r r a c e ” f o r r i d g e and d e p r e s s i o n f e a t u r e s i s w e ll ta k e n , good re a so n s a l s o e x i s t fo r assuming t h a t a t l e a s t some of th e s e f e a t u r e s are r e s t i n g on a more or l e s s f l a t t e r r a c e . T e r r a c e C o r r e l a t i o n T e r r a c e s may take t h r e e g e n e r a l form s: (1) d i s t i n c t t e r r a c e s , (2) changes in s l o p e , and (3) rid g e-a n d -d e p ressio n sequence. Changes in slo p e in c lu d e b o th i n c r e a s e s and d e c r e a s e s in g r a d i e n t . P o s s i b l y o th e r co m b ination s e x i s t . The a b ru p t n e s s of the change in slo p e v a r i e s from b a r e l y d i s c e r n i b l e a l t e r a t i o n s in the p r o f i l e to sharp a n g le s ; g r a d a t i o n s e x i s t between th e s e changes in slope to w e l l - d e fin e d t e r r a c e s . Most t e r r a c e s a re narrow , but a few are e x c e p t i o n a l l y w id e . T e r r a c e s o f f P a l o s Verdes H i l l s and Santa Monica are more than a k i lo m e te r in w id th (s e e F ig u re 1 ). Off Coos Bay, Oregon, i s a t e r r a c e more than n in e k i l om eters in w id th ( F ig u re 14), and even w ider t e r r a c e s e x i s t o f f the A le u tia n and K u rile-K am ch atk a A rcs. S e v e ra l f a c t o r s should be re c o g n iz e d w i t h r e g a r d to submerged t e r r a c e s v e r s u s u p l i f t e d , m a rin e ^ c u t t e r r a c e s . F i r s t i s the problem of view ing or r e c o n s t r u c t i n g the t e r r a c e s from echosounding d a ta (w ith i n h e r e n t problem s of i n d i r e c t d e te r m i n a t i o n s o f shapes and m i c r o - s t r u c t u r e s and n e a r l y a com plete la c k of knowledge of n a v i g a t i o n a l 16 p o s i t i o n s ) . Second i s th e problem of p i c t o r i a l l y i l l u s t r a t i n g t e r r a c e s . Land t e r r a c e s can be shown in g r e a t d e t a i l by use of s u r v e y i n g equipm ent w hereas t e r r a c e s below se a l e v e l c a n n o t be su rv e y e d in s i m i l a r d e t a i l b e ca u se of equipm ent and n a v i g a t i o n a l p ro b le m s. U s u a l l y g r e a t v e r t i c a l e x a g g e r a t i o n i s n e c e s s a r y to show ch an g es alo n g a p r o f i l e . Because of t h i s g r e a t v e r t i c a l e x a g g e r a t i o n ( v a r y i n g from about 5 to n e a r l y 500 t i m e s ) , t h e r e i s a n a t u r a l t e n d ency to make e r r o n e o u s c o n c l u s i o n s a b o u t g r a d i e n t s . T h i r d , e v id e n c e shows t h a t t e r r a c e s have been b r o a d l y downwarped. The f a c t t h a t t e r r a c e s have been warped (s u c h as t h o s e o f f Ja p a n ) does n o t w a r r a n t th e c o n c l u s i o n t h a t such f e a t u r e s are n ot t e r r a c e s and, h e n c e , sh ou ld be given o t h e r nam es. In a d d i t i o n , some s l o p e s may be p a r t i c u l a r l y s t e e p , th e n show a sh a rp d e c r e a s e in g r a d i e n t . These may or may n o t be t e r r a c e s , d e p e n d in g upon t h e i r h o r i z o n t a l e x t e n t ( p e r s i s t e n c e ) and g r a d i e n t s below the s lo p e c h ang e. In o t h e r w ords, i t is assumed t h a t t h e s e a re d i s t i n c t b r e a k s in s l o p e s b u t th e o r i g i n of such f e a t u r e s re m a in s unknown. A lth o u g h i t i s c l e a r l y r e c o g n iz e d t h a t such f e a t u r e s may or may n o t be t e r r a c e s in the t r u e s e n se of th e m eaning, o f t e n th e upper and low er slo p e ch ang es can be c o r r e l a t e d over c o n s i d e r a b l e d i s t a n c e s . An u n u s u a l f e a t u r e o b se rv ed on many echogram s i s a r i d g e and d e p r e s s i o n seq uen ce w hich a lm o st i n v a r i a b l y o c c u r s as a s i n g l e u n i t when the s l o p e i s more or l e s s 17 smooth. The r i d g e s t h a t appear on th e echograms are p r o b ably not mounds ( t h a t i s , w ith a c i r c u l a r o u t l i n e ) but are e lo n g a te and ro u g h ly p a r a l l e l to the s t r i k e of the s lo p e . ( I t would be r e l a t i v e l y r a r e to sound a mound, compared to r i d g e . ) On many s lo p e s , however, t h e r e may be a v a r i e t y of h i l l s , mounds, and v a rio u s ty p es of d e p r e s s i o n s . In a d d i t i o n , mounds and o th e r i r r e g u l a r to p o g ra p h ic f e a t u r e s may occur a t the base of s lo p e s , p ro b a b ly th e r e s u l t of slump in g . Topographic i r r e g u l a r i t i e s f o r each echogram, such as changes in s lo p e s and t e r r a c e s , were recorded on a v e r t i c a l graph so t h a t a la r g e number of s lo p e s could be reduced f o r easy comparison and e v a l u a t i o n . I f the p r o f i l e s are c l o s e ly spaced, f e a t u r e s on the bar g raphs can be c o r r e l a t e d . C o r r e l a t i o n of t e r r a c e s o b v io u s ly i s o b j e c t i v e . In the p r e s e n t stu d y , s i g n i f i c a n t f e a t u r e s such as the s h e l f b re a k , base of the c o n t i n e n t a l s l o p e , and d i s t i n c t t e r r a c e s were p icked from p r o f i l e s and t r a n s f e r r e d to a bar graph. A fte r a l l of the p r o f i l e s were completed f o r a s e c t i o n of the c o n t i n e n t a l slo p e , major f e a t u r e s could be c o r r e l a t e d on a d ja c e n t p r o f i l e s by j o i n i n g l i n e s to th e s e f e a t u r e s . T h is in c lu d e d j o i n i n g s h e l f b rea k s and th e base of the co n t i n e n t a l s l o p e , thus g iv in g s e v e r a l g e n e r a l tren d l i n e s . By working downward from the s h e l f edge and upward from the base of the slo p e , or on e i t h e r s id e of a prom inent t e r r a c e , i t was p o s s i b l e to c o n s t r u c t a r e a s o n a b ly a c c u ra te p r o f i l e of t e r r a c e s in an a re a based upon the d a ta 18 a v a i l a b l e . O ften the d i s t a n c e was g r e a t between p r o f i l e s , making c o r r e l a t i o n l e s s c e r t a i n . Even so , many f e a t u r e s a p p a r e n t l y could be c o r r e l a t e d over s i g n i f i c a n t d i s t a n c e s . I d e a l l y , c lo s e l y - s p a c e d PDR r e c o r d s o b ta in e d by s h ip s having p r e c i s e n a v i g a t i o n a l equipm ent, p ro c e e d in g a t slow speeds and employing narrow-beam t r a n s d u c e r s , would be most e f f e c t i v e in making c o r r e l a t i v e i n v e s t i g a t i o n s . Lacking such s o p h i s t i c a t e d r e f in e m e n ts and n e c e s s a r y sh ip tim e fo r making d e t a i l e d s t u d i e s , t h i s r e p o r t can be i n t e r p r e t e d only as a r e c o n n a i s s a n c e . The d e p th d i s t r i b u t i o n of v a r i o u s to p o g ra p h ic f e a t u r e s was s tu d ie d in d e t a i l on a p p ro x im a te ly 1,850 echograms, not a l l of which are shown h e re . S e v e r a l hundred a d d i t i o n a l echograms could n ot be used because the re c o rd e d s lo p e s were so s te e p t h a t even r e l a t i v e l y l a r g e to p o g ra p h ic f e a t u r e s would n ot show up on the t r a c e . Almost e v e r y slo p e around o cean ic i s l a n d s appeared as n e a r l y v e r t i c a l on the echograms and th e s e n e c e s s a r i l y were o m itte d . S e v e ra l echograms of d e l t a s were examined, b u t t h e s e s lo p e s were so g e n t l e t h a t no to p o g r a p h ic f e a t u r e s could be d e t e c t e d . Gealy (1 9 5 5 ), however, showed t h a t t e r r a c e s and o t h e r f e a t u r e s can be rec o g n ize d on the c o n t i n e n t a l slo p e w est of the M i s s i s s i p p i D e l t a , i n the n o r t h w e s te r n p a r t of the Gulf of Mexico. The absence of t e r r a c e s on an echogram in a given r e gion does n o t n e c e s s a r i l y mean t h a t the f e a t u r e s a re 19 m is s in g i n the e n t i r e a r e a or even i n th e im m ediate v i c i n i t y . Echograms made when the s h i p was c r u i s i n g a t l e s s th a n four k n o t s showed much h i g h e r p e r c e n t a g e s of t e r r a c e s . Of n in e echogram s ta k e n d u r i n g a s p e c i a l s u r v e y of th e P a lo s V erdes Slope ( a v e r a g i n g a b ou t 1,200 m a p a r t ) , fo u r showed w e l l - d e f i n e d t e r r a c e s or changes in s l o p e ( i n c l u d i n g the 1,100 m wide t e r r a c e m en tio n ed a b o v e ) , t h r e e had o n ly m inor changes i n s l o p e , and two had no r e c o g n i z a b l e t e r r a c e s or s lo p e changes e x c e p t t h a t i r r e g u l a r to p o g ra p h y o c c u r r e d below 550 m ( F i g u r e 1 ) . A s i m i l a r c o n d i t i o n e x i s t e d o f f C h a r l e s t o n , South C a r o l i n a in w hich o n ly h a l f of s i x c l o s e l y - s p a c e d p r o f i l e s showed t e r r a c e s o r c h an g e s in s l o p e . U p l i f t e d w a v e -c u t t e r r a c e s on la n d i l l u s t r a t e t h e prob lem c o n n e c te d w ith s p o r a d i c o c c u r re n c e of t e r r a c e s . T e r r a c e s f r e q u e n t l y a re d i s c o n tin u o u s on lan d and on subm arine s lo p e s and as a c o n s e quence f r e q u e n t l y a re d i f f i c u l t to r e c o g n i z e , p a r t i c u l a r l y i f o n ly one or two p r o f i l e s a r e a v a i l a b l e . There i s an added problem o f making p r o f i l e s w i t h an e c h o so u n d e r in the o c e a n . Echosounding hampers th e r e c o r d i n g of sm a ll f e a t u r e s , e s p e c i a l l y when th e d ep th i s g r e a t . The d e p t h , a s r e c o rd e d on an echogram , is th e minimum d e p th w i t h i n th e e c h o - sounder* s sound cone r a n g e . T h is cone may be as much as 65° of a r c . Thus s l i g h t l y g r e a t e r d e p th s (also w i t h i n the range of the cone) a re masked and d e t a i l s of the bo tto m 20 g e n e r a l l y become more obscure as th e d e p th i n c r e a s e s a n d /o r as the bottom g r a d i e n t i n c r e a s e s . A g ra p h ic example of the d i f f i c u l t y i s n o te d o f f o c e a n ic i s l a n d s where the g r a d i e n t of the s lo p e s range from 10° to more than 40° and perh aps average 25°. T h is i s in c o n t r a s t to c o n t i n e n t a l slo p e s which have an average g r a d i e n t of on ly 4 .5 ° f o r the f i r s t 1,000 fms; d e l t a i c c o a s t s which average 1 .5 ° down to 1,000 fms; and f a u l t c o a s t s which average 5 .6 ° (S h ep ard , 1948). Thus, i t i s obvious why echograms tak e n .along the s l o p e s of o c e a n ic i s l a n d s do n o t show to p o g r a p h ic i r r e g u l a r i t i e s . Ship speed i s a n o th e r f a c t o r which c o n t r o l s the deg ree of com p lexity of an echogram. The l a r g e s t number of t o p o g ra p h ic f e a t u r e s on an echogram have been o b ta in e d when the s h ip fo llo w ed a co u rse d i r e c t l y u p - s lo p e a t speeds of l e s s than fo u r k n o t s . No r e a s o n a b le e x p l a n a t i o n i s known why b e t t e r r e c o r d s a re o b ta in e d when going u p - s l o p e ; the exam i n a t i o n of a l a r g e number of echogram s, however, shows t h i s to be so . One p o s s i b l e e x p l a n a t i o n is t h a t th e echosound- e r ’ s tr a n s d u c e r i s t i l t e d s l i g h t l y fo rw ard . In o rd er to o b t a i n a good re c o r d of changes in s l o p e , t e r r a c e s , and o th e r sm all f e a t u r e s i t i s n e c e s s a r y to e x te n d th e time of t r a v e r s e a c r o s s a slo p e and th us expand the echogram. The v alu e of such a p r a c t i c e i s e a s i l y shown by the number of sou nd ing s p o s s i b l e a t v a r i o u s s p e e d s . A sh ip t r a v e l i n g a t 10 k n o ts t r a v e r s e s a p p ro x im a te ly 5 m of h o r i z o n t a l d i s t a n c e each second. By slow ing the s h ip to h a l f t h i s speed and 21 assu m in g a c o n s t a n t sound t r a n s m i s s i o n i n t e r v a l by th e e c h o s o u n d e r , i t i s o b v io u s t h a t th e number o f s o u n d in g s i s d o u b le d and t h e chance of r e c o r d i n g s m a ll t o p o g r a p h i c f e a t u r e s i s g r e a t l y e n h a n c e d . I f the speed i s to o g r e a t or th e s l o p e e x c e p t i o n a l l y s t e e p , th e p r o f i l e w i l l a p p e a r as a v e r t i c a l t r a c e on the echogram and i r r e g u l a r i t i e s , ev en i f p r e s e n t , c a n n o t be r e c o r d e d . Many s l o p e s o f f s o u t h e r n C a l i f o r n i a which w ere t r a v e r s e d a t n i n e k n o ts or more showed no f e a t u r e s a t 500 m, b u t upon slow in g th e s h i p to l e s s t h a n f o u r k n o t s , many n a rro w t e r r a c e s and o t h e r t o p o g r a p h i c f e a t u r e s were d i s c o v e r e d . The PDR r e c o r d i n g u n i t g e n e r a l l y p i n g s a t the r a t e of 6 0 / m i n u t e s - - t h e same as th e s o n a r u n i t to w hich th e PDR i s a t t a c h e d - - t h e r e f o r e , i t seems d e s i r a b l e to slow th e s h i p when c r o s s i n g a s l o p e b e c a u s e many s m a l l f e a t u r e s w i l l be m issed a t th e h i g h e r c r u i s i n g s p e e d . Adams ( 1 9 4 6 ) , Herdman ( 1 9 5 5 ) , Kuenen (1 9 3 5 , 1 9 5 0 ), S c h u l e r ( 1 9 5 2 ) , T o l s t o y and Ewing ( 1 9 4 9 ) , U d i n t s e v (1 9 5 1 , 1 9 5 6 ), and K rau se (1 9 6 2 ) g iv e a d d i t i o n a l i n f o r m a t i o n on e c h o so u n d in g t h a t i s p e r t i n e n t to t h e p r e s e n t s t u d y , p a r t i c u l a r l y th e e f f e c t of so u n d in g s l o p e s , r e f l e c t i o n o f so un d, and i n t e r p r e t a t i o n of ech o g ram s. Acknowledgmen t s The a u t h o r i s g r a t e f u l to K. O. Emery, of th e U n i v e r s i t y of S o u th e r n C a l i f o r n i a (now a t Woods Hole O c e a n o g ra p h i c I n s t i t u t i o n ) , f o r a i d i n g i n many ways to d e t e r m i n e t h e 22 p o s s i b l e e x i s t e n c e of deep t e r r a c e s ; M. Ewing, Lamont Geo l o g i c a l L a b o r a to ry ; H. Gould, U n i v e r s i t y of Washington (now a t E sso P r o d u c t io n R esearch Co., H ouston, T e x a s); H. Menard, F. P. S h e p a rd , T. H. van Andel, and R. F i s h e r of S c r ip p s I n s t i t u t i o n of Oceanography; J . Byrne of the U n i v e r s i t y of Oregon; The D i r e c t o r , L. V. Evans, G. F. J o r d a n , J . Kofoed, R. S. D i e tz , R. M alloy, and M. Y e l l i n of the U. S. C oast and G eod etic Survey; U. S. O ceanographic O f f i c e ; T. S ato of the Ja p a n H y dro g raph ic O f f i c e ; the B r i t i s h N a tio n a l I n s t i t u t e of Oceanography; and J . U l r i c h of K i e l, Germany, f o r making echograms and o t h e r d a t a a v a i l a b l e . G r a t e f u l a p p r e c i a t i o n is a ls o e x p re ss e d to the U. S. Navy f o r making a s h ip a v a i l a b l e f o r the s tu d y of the Hawaiian I s l a n d s and to F. P. Shepard f o r a llo w in g the a u th o r to j o i n an e x p e d i t i o n t o th e G ulf o f C a l i f o r n i a . J . W. Durham, E. A l l i s o n , and H. Johnson p ro v id ed in f o r m a tio n on the age of fa u n a dredged o f f H aw aii. T. S a to , J . Kofoed, D. C. K ra u se , G. A. Rus- nak, and H. Palmer loaned u n p u b lis h e d m a n u s c r ip ts which were e x tr e m e ly u s e f u l . H. N iino t r a n s l a t e d s e v e r a l J a p a n ese p a p e rs and p ro v id e d a d d i t i o n a l i n f o r m a ti o n on Ja p an e se geo lo g y . E. R. Hope, J . N. C a r r u t h e r s and M. K lenova, su p p l i e d s e v e r a l im p o rta n t p a p e rs and r e f e r e n c e s on m arine g e o lo g y unknown to the a u th o r . F i n a l l y , a p p r e c i a t i o n i s e x p re s s e d to my Committee: To Dr. D. S. G o r s lin e (who served as Chairman a f t e r Dr. K. O. Emery moved to Woods Hole O cean og raph ic I n s t i t u t i o n ) , 23 and to D rs. 0 . L. Bandy and R. H. Merriam who a c t i v e l y guided th e f i n a l p r e p a r a t i o n of t h i s d i s s e r t a t i o n . Drs. T. C lem en ts, form er Chairman of the D epartm ent of Geology, and R. T ibby a l s o se rv ed on th e Committee. The a s s i s t a n c e of t h e s e s t a f f members was o f g r e a t im p o rta n c e d u rin g th e long p e r i o d r e q u i r e d to c o l l e c t th e d a t a and to w r i t e t h i s d i s s e r t a t i o n . JAPANESE ISLANDS I n t r o d u c t io n Yabe and Tayama (1 9 3 4 ) were the f i r s t g e o l o g i s t s to c a l l a t t e n t i o n to deep subm arine t e r r a c e s su rr o u n d in g J a pan and w ere a b le to d e f i n e subm arine t e r r a c e s as deep as 700 m. T h e ir e x c e l l e n t stu d y was b ased upon th e exam in a t i o n o f Jap an ese c h a r ts made b e f o r e th e advent o f e c h o - s o u n d in g . More r e c e n t d e t a i l e d e c h o so u n d in g s u r v e y s s i n c e World War I I , em p loy in g DECCA n a v i g a t i o n and p r e c i s i o n e ch o so u n d in g equipm ent have r e v e a le d t h a t some o f Yabe and Tayama's i n t e r p r e t a t i o n s were i n c o r r e c t , l a r g e l y b ec a u se o f the s p a r s e d a t a a v a i l a b l e t o them in th e e a r l y 1 9 3 0 ’ s . The m ost im p o rta n t d e t a i l e d e c h o so u n d in g s u r v e y s made a lo n g the c o n t i n e n t a l s lo p e o f Japan s i n c e World War I I i n c lu d e (F ig u r e 3 ) : Kyushu to Shikoku (Tayama, 1950b) and n o r th e r n Honshu and H okkaido (N asu , 1964; Yo, e t a l , 1 9 5 4 ) . L ocal su r v e y s i n c l u d e : K ii S t r a i t (Tayama, 1 9 4 8 ) , E n shu - Nada Sea (S a t o and H osh in o , 1 9 6 2 ) , Kumano-Nada Sea (Ho- s h i n o , 1961; H oshino and I c h i h a r a , 1 9 6 0 ) , Sagami Bay (M ogi, 1 9 5 5 ) , Suruga Bay (Japan H yd rog ra p h ic O f f i c e C hart 7001; and S a t o , 1 9 6 2 ) , Kamogawa Submarine Canyon (H o sh in o and 24 25 S a to , 1 9 6 0 ), Sanriku C lijim a and Kagami, 1 9 6 1 ), Mogami Bank (Mogi and S a to , 1 9 5 8 ), Toyama Bay (Tayama and Sano, 1 9 5 2 ), and K ushiro Submarine Canyon (Yo, 1953; and S a to , 1 9 6 2 a ). Rather w e l l - d e f i n e d sh a llo w t e r r a c e s occur around J a pan on the c o n t i n e n t a l s h e l f . Japanese g e o l o g i s t s r e c o g n iz e the f o llo w in g t e r r a c e s : ( 1 ) The a b rasion te r r a c e at 10 m to 20 m, (2 ) in te r m e d ia te t e r r a c e a t 50 m (1 20 m), and ( 3 ) the s h e l f edge at 130 m ( i 20 m ). Most workers b e l i e v e th e s e t e r r a c e s were cut during the post-Wurm G la c i a l S ta g e . N iin o (1952) p o in ted out v a l l e y t e r r a c e s ( v a l l e y - i n - v a l l e y t e r r a c e s ) s im ila r t o r iv e r t e r r a c e s in submarine canyons in many l o c a t i o n s surrounding Japan. Tayama (1950b) rep orted te r r a c e s as deep as 1,000 m to 2,000 m o f f Shikoku and Kyushu. I ij im a and Kagami (1 9 6 1 ) d e s crib e d a n c ien t ab ra sio n p la tfo r m s at a depth o f about 2,0 0 0 m o f f Sanriku Coast and dated the age o f submergence o f the p la tfo r m as p o st m iddle P l i o c e n e . F i n a l l y , Taka- h ir o Sato (u n p u b lish e d ) has r e c e n t l y com pleted a stu d y of the t e r r a c e s around the Japanese I s l a n d s . The w r ite r has corresponded w it h Sato s i n c e e a r l y 1961 and has th o ro u g h ly d is c u s s e d w ith him the t e r r a c e s surrounding Japan. The f o l lo w in g d i s c u s s i o n i s based l a r g e l y upon th e above s o u r c e s . In form ation s u p p lie d by Sato was e s p e c i a l l y im p o r t a n t . Many o f the o r i g i n a l r e p o r ts were p r in te d in SEA OF JAPAN OKUSHIRI IS. TSUGARU PENINSUt BUNGO STRAIT NEMURO STRAIT KUNASHIRt IS ^ : SHIKOTAN IS HO KKAIDO AKKESHI KUSHIRO KUSHIRO/x C ERIMO CANYON HAKODATE C. SHIRIYA OGA PENINSULA YAMATA BANK HIMEGAWA MOGAMI BANK CHOKAISHO BANK AMADA SANRIKU 1 - 1 NAGAW Av SACO IS NIIGATA COAST NIIGATA PREFECTURE TOYAMA BAY K ll PENINSULA . FOSSA V ^M AG N A TOKY OKI BANK o HONSHU MIUVA PEN. KAMOGAWA SHIMIZU TOKYO BAY BASO PENINSULA/ ^ / s h ik u k u r SAGAMI ENSHU-NADA SEA KUMANO*NADA SEA K ll STRAIT SARUGA BAY HACHIJO TOSA BAY HYUGA-NADA tTORISHIM A SAN-IN DISTRICT. PACIFIC OCEAN F ig u re 3. Index map of Ja p a n e s e I s l a n d s . 27 Japan ese and were t r a n s l a t e d and made a v a i l a b l e by Sato and H ir o s h i N iin o . Sato was ab le to supply d e t a i l e d d e s c r i p t i o n s o f the t e r r a c e s from b oth p u b lis h e d and u n p u b lish ed sou r c e s . The o n ly o r i g i n a l p r e c i s i o n e ch o so u n d in g s examined were th o s e taken by F. P . Shepard and were made d u rin g a c r u is e to Japan f o r the purpose o f s t u d y in g subm arine can y o n s. E chosou nd ings made on t h i s c r u i s e were taken p a r a l l e l to the s lo p e sou th of Tokyo Bay in an area h e a v i l y i n c is e d w it h submarine c an yon s, h e n c e , t h e s e d a ta were not u s e f u l in the p r e s e n t s tu d y . P u b lish e d p r o f i l e s in c lu d e Japan ese ( P la t e 1, m o s tly from Nasu, 1 9 6 4 ) and R u ssian s o u r c e s ( P la t e 2 ) . ^ I t i s p ro b a b le t h a t both o f th e s e so u r c e s r e c o n s t r u c t e d th e p r o f i l e s from so u n d in g s taken at i n t e r v a l s of s e v e r a l m in u tes and h e n c e , sm a ll d e t a i l s are m iss i n g . Sato o f t e n p r e f e r s to u se the word " p l a i n ” in d e s c r i b ing r e l a t i v e l y f l a t f e a t u r e s ; how ever, the word " te r r a c e " i s used in t e r c h a n g e a b ly th rou gh ou t t h i s r e p o r t . P a c i f i c C oast of Japan Kyushu to Shikoku Between Kyushu and Shikoku the s h e l f break o c cu rs at ■^All la r g e fo ld e d p l a t e s are in a se p a r a te p o c k e t a t th e end of the d i s s e r t a t i o n . 28 a d e p th o f 100 m t o 300 m. Two w e l l - d e f i n e d t e r r a c e s o c cu r in th e a r e a — an upper p l a i n a t 800 m to 1 ,3 0 0 m and a lo w er p l a i n w h ich form s th e f l o o r o f Tosa Sea B a s i n . Tayama (1 9 5 0 b ) c a l l e d the l a t t e r th e "Tosa T e r r a c e . ” Tosa T e rra ce l i e s l a r g e l y 800 m to 1 ,3 0 0 m b u t o f f Kyushu i t r a n g e s from 500 m to 1 ,2 0 0 m. The low er t e r r a c e was named the "Hyuga T e r r a c e ” a f t e r i t s typ e l o c a l i t y , th e b ottom of Hyuga-Nada S e a . Submarine canyons t e r m in a t e on the T osa T erra ce o f f Shikoku a t a d e p th o f about 1000 » * ? w h ile t h o s e o f f Kyushu d is a p p e a r on the Hyuga T e r r a c e . K i i S t r a i t The s h e l f break o c c u r s at K ii S t r a i t a t d e p th s o f 160 m t o 180 m. B etw een 200 m t o 400 m th e c o n t i n e n t a l s l o p e has an a v e ra g e g r a d i e n t o f about 4 ° w h ich i s more o f a g e n t l e s lo p e than a f l a t t e r r a c e . A d e p r e s s i o n o f f K ii P e n in s u la h as a f l a t f l o o r at 1 ,2 0 0 m to 1 ,4 0 0 m i n th e w e s te r n p a r t , and 1 ,5 0 0 m to 1 ,6 0 0 m in the e a s t . The e a s t e r n p a r t a p p ea rs t o be c o n t in u o u s w it h the f l o o r o f Kumano-Nada S e a . Submarine canyons in K ii S t r a i t te r m in a t e on th e f l o o r o f th e d e p r e s s i o n ( i . e . , a t 1 ,2 0 0 m t o 1 ,6 0 0 m ). O ther canyons s t a r t a t th e edge o f t h i s deep t e r r a c e and e x te n d t o the S o u th w est Japan T rench. 2 9 K ii S t r a i t to Kumano-Nada Sea Between K ii S t r a i t and Kumano-Nada Sea, the s h e l f break v a r ie s betw een 50 m to 500 m. Two t e r r a c e s , s i m i la r to th e Tosa and Hyuga T e r r a c e s , are r e c o g n iz e d in the a r e a . A sm a ll p l a i n , lo c a t e d a t 800 m to 1 ,0 0 0 m, p r o b a b ly c o r r e l a t e s w it h the Tosa T e rr a ce . The f l o o r of the Kumano-Nada Sea c o n s i s t s o f an e x c e p t i o n a l l y f l a t f l o o r at 2 ,0 0 0 m and i s th e l a r g e s t t e r r a c e su rroun din g the Japan ese I s l a n d s . Local t e r r a c e s occur at 1 ,5 0 0 m to 1 ,8 0 0 m, and at 2 ,0 0 0 m. L ess w e ll- d e v e lo p e d t e r r a c e s occur a t 2 ,8 0 0 m to 3 ,0 0 0 m, 3,1 0 0 m t o 3 ,8 0 0 m, and in the Southw est Japan Trench a t 4 ,3 0 0 m to 4 ,7 0 0 m. Submarine canyons ter m in a te at a depth o f ap p roxim ate l y 1 ,0 0 0 m, or on t h e w e ll- d e v e lo p e d Tosa T e r r a c e . In the Kumano-Nada S ea , canyons s t a r t at the o u ter edge o f the c o n t i n e n t a l s h e l f and extend to the Kumano-Nada Sea bottom t e r r a c e . Other canyons b eg in at the edge o f Hyuga T errace and r ea c h the bottom o f the Sou thw est Japan T rench. Enshu-Nada Sea In th e Enshu-Nada Sea th e s h e l f break o c cu rs a t d e p th s ranging from 50 m to 300 m. T e r r a c e s a t 400 m to 500 m may o c c u r , b u t s u f f i c i e n t d a ta are la c k in g to make d e f i n i t e c o n c l u s i o n s . W e ll-d e v e lo p e d , w id e sp r e a d , f l a t t e r r a c e s o c cur at d e p th s o f 850 m t o 1 ,3 0 0 m and betw een 1 ,6 0 0 m and 30 1,8 0 0 m. Another t e r r a c e , at 2,0 0 0 m, probab ly i s c o r r e l a t i v e w ith the 1,600-m to 1,800-m t e r r a c e . L ocal t e r r a c e s occur between 2,5 0 0 m and 2,6 0 0 m on the s lo p e s of banks. The lo w e st t e r r a c e i s lo c a t e d at 3 ,5 0 0 m to 4 ,0 0 0 m, the bottom o f the Southw est Japan T rench. Canyons term in a te on the lower 1,600-m to 1,800-m t e r r a c e . Suruga Bay The s h e l f break in the v a c i n i t y o f Suruga Bay o c cu rs at a depth o f 100 m to 300 m. T e r r a c e s, o f te n o f l o c a l c h a r a c te r (b u t s e v e r a l o f la r g e d im e n s io n ), occur between 400 m and 600 m. Another e a s i l y r e c o g n iz a b le te r r a c e o c curs between 800 m and 1,0 0 0 m, and l e s s pronounced l o c a l t e r r a c e s e x i s t at 1,200 m to 1,600 m, and 1,800 m to 2 ,5 0 0 m. The f l o o r of Suruga Bay i s e x c e p t i o n a l l y f l a t and i s composed o f s e v e r a l p l a i n s at d i f f e r e n t dep th s: 1,400 m to 1 .6 0 0 m, 2 ,0 0 0 m, and 2 ,5 0 0 m to 2 ,8 0 0 m. The 1 ,4 0 0 m to 1 .6 0 0 m te r r a c e in the bay head c o in c i d e s w ith th e deep t e r r a c e on the c o n t i n e n t a l s l o p e . Submarine canyons o r i g i n a t e at s e v e r a l depth s such as the c o n t in e n t a l s h e l f , 400 m to 600 m, or 600-m to 1,100-m t e r r a c e s but a l l u s u a l l y term in a te on the bay f l o o r . A few canyons te r m in a te on the 600-m to 800-m t e r r a c e . Submarine canyons in Suruga and Sagami Bays show no r e l a t i o n s h i p to r i v e r s on l a n d . 31 Sagami Bay In the e a s t e r n p a r t o f Sagami Bay the s h e l f break o c c u r s at a depth o f 110 m to 200 m. Four t e r r a c e s have been r e c o g n iz e d : 200 m to 300 m, 300 m to 400 m, 400 m to 500 m, and 700 m to 750 m. Another t e r r a c e , at 500 m to 600 m, o c c u r s as the summit and on the s lo p e of o f f s h o r e ban k s. The 700-m to 750-m t e r r a c e ( l o c a t e d betw een banks and the c o n t i n e n t a l s l o p e ) i s f l a t and w id e sp r e a d . The s h e l f break in the e a s t e r n p a r t o f Sagami Bay o c cu rs a t a depth o f 115 m to 160 m. L o c a l to w id esp read t e r r a c e s occur a t a depth o f 500 m. Sm all t e r r a c e s a t 600 m to 1 ,1 0 0 m occur around the margin of the bottom o f Sag ami Bay. The bottom o f Sagami Bay i s rem arkably f l a t , i n c r e a s in g in depth from 1 ,2 0 0 m to 2 ,6 0 0 m. Submarine can yons te r m in a te on the bay f l o o r ( a t about 1 ,2 0 0 m) and i n c i s e th e 700-m to 750-m t e r r a c e . A ccording to Nasu ( 1 9 6 4 ) , Tokyo Submarine Canyon i s U-shaped and has a w e l l - d e f i n e d f l a t bottom a t 400 m to 500 m. Kamogawa, B5s5 P e n i n s u l a The s h e l f break o c cu rs a t a dep th o f 140 m to 160 m in th e v i c i n i t y of Kamogawa. T e r r a c e s b etw een 500 m to 600 m and 1 ,1 0 0 m to 1 ,2 0 0 m occur in th e e a s t e r n p a r t o f the r e g i o n . The most w id esp read t e r r a c e i s l o c a t e d a t a 32 depth of 2,1 00 m to 2 ,2 0 0 m. Canyons term in ate on t h i s s u r f a c e . The d e e p e st t e r r a c e s occur at 2,7 0 0 m. Sanr iku The c o n tin e n ta l s lo p e o f f Yamada has a g e n t le g r a d ie n t ( 1 ° ) down to 2,200 m. Two d i s t i n c t f l a t t e r r a c e s occur at 900 m and 2,0 0 0 m. At l e a s t f i v e a d d it io n a l t e r r a c e s occur on the s l o p e . A f l a t te r r a c e 7-km w id e , at 1 ,5 5 0 m, and another 8-km wide between 1 ,7 0 0 m and 1 ,8 0 0 m, occurs along the 38° N p a r a l l e l . Cape S h ir iy a to Cape Erimo, Hokkaidd Is la n d The s h e l f break occu rs at a depth of 100 m to 200 m. A te r r a c e (more of a g e n t le s lo p e ) occu rs between 40) m and 600 m. A w idespread te r r a c e i s lo c a te d between 1,000 m and 1,1 0 0 m, and another f a i r l y d i s t i n c t te r r a c e o ccu rs between 2 .0 0 0 m and 2,200 m. K ushiro, Hokkaido The s h e l f break o f f K ushiro occu rs at a depth o f 80 m to 140 m. T erraces occur at 700 m to 1 ,1 0 0 m, 1,4 0 0 m to 2.00 0 m, and 2,000 m to 2,300 m; the s h a llo w e s t c o n s i s t s o f a very g e n t le slo p e r a th er than a f l a t p l a i n . The 1,500-m to 1,900-m te r r a c e i s the w id e s t and b e s t developed in the r e g io n . The d e e p e st t e r r a c e s are sm a ll in area and occur on the s id e of a submarine canyon. 33 A kkeshi Area U n lik e the Cape S h i r i y a to Cape Erimo a r e a , the o f f sh ore topography i s c o m p lic a te d w ith s t e e p o f f s h o r e g r a d i e n t s , p o o r ly d ev e lo p ed t e r r a c e s , and no submarine ca n y o n s. T e r r a c e s do n o t c o r r e l a t e w ith th o se in th e r e g io n to the s o u th . The s h e l f break o c c u r s at a dep th o f 100 m to 200 m. T e rr a ce s at 2 ,0 0 0 m to 2 ,3 0 0 m are pronounced bu t sm a ll in area; th o se a t 3 ,1 0 0 m to 3 ,3 0 0 m and 3 ,6 0 0 m to 3 ,8 0 0 m are l o c a l and o f sm a ll a rea ; the te r r a c e a t 5 ,3 0 0 m i s ob scu re due to la ck of so u n d in g s; th o se deeper than 5 ,5 0 0 m are w e l l - d e v e l o p e d , but d e t a i l s are l a c k i n g . Nemuro S t r a i t The c o n t i n e n t a l s h e l f break around S h ir e to k o P e n in s u la o c cu rs at a depth o f 100 m to 120 m. From the s h e l f break to about 300 m i s a g e n t l e s lo p e w ith i n t e r m i t t e n t ob scu re t e r r a c e s on sp u r s . Other obscure t e r r a c e s occur at 600 m to 1 ,0 0 0 m, or d e e p e r , and are s c a t t e r e d through out the r e g io n ; a t 1 ,7 0 0 m; and on the bottom o f Nemuro S t r a i t at 2 ,0 0 0 m to 2 ,5 0 0 m. Submarine canyons o f f Hokkaido te r m in a te e i t h e r on th e deep t e r r a c e at 2 ,0 0 0 m to 2 ,2 0 0 m (su ch as o f f Cape Erimo) or on a sh a llo w e r t e r r a c e a t 1 ,5 0 0 m to 1 ,9 0 0 m (su c h as o f f T o k a c h i) . T e rr a ce s and s l o p e s above th e s e d e p th s are i n c i s e d w it h can yon s. 34 Japan Sea N orthern Hokkaido The c o n t i n e n t a l s h e l f o f f n o r th e r n Hokkaido v a r i e s in d e p th from 150 m to 250 m. A w id esp rea d t e r r a c e o c c u r s at d e p th s o f 300 m 1:o 500 m. Other t e r r a c e s in c lu d e : a v ery f l a t bottom d e p r e s s i o n a t 800 m; s m a l l , but n o t a b le t e r r a c e s a t 900 m to 1 ,0 0 0 m; g e n t le s l o p e s betw een 1 ,0 0 0 m and 1 ,5 0 0 m; narrow and l o c a l t e r r a c e s at 2 ,1 0 0 m t o 2 ,4 0 0 m; and th e b ottom o f the Japan Sea B a sin at 3 ,3 0 0 m to 3 ,5 0 0 m. O k u sh ir i I s la n d to Tsugaru P e n in s u la The c o n t i n e n t a l s h e l f o f f Honshu and Hokkaido i s c o n tin u o u s e x c e p t fo r a d e p r e s s i o n w e s t o f T sugaru. The s h e l f break o c c u r s a t a d ep th o f 120 m t o 140 m. A g e n t l e s lo p e o c c u r s betw een 200 m and 400 m but i s n o t as d i s t i n c t as deep er t e r r a c e s . The f l o o r o f O k u sh ir i S t r a i t o c c u r s a t a dep th of 800 m to 1 ,0 0 0 m. S im ila r f l a t a r e a s are known e ls e w h e r e ; how ever, b eca u se some o f t h e s e p l a i n s are l o c a l in c h a r a c t e r and are o f t e n o b s c u r e , th e y may be in c lu d e d in th e t e r r a c e s l o c a t e d at d e p th s of 1 ,3 0 0 m to 1 ,4 0 0 m. These are th e most c o n sp ic u o u s and w id esp rea d in th e a r e a . A nother w id e sp re a d t e r r a c e occu rs a t 1 ,8 0 0 m to 1 ,9 0 0 m and a t t a i n s a maximum w idth at 20 km. 35 S o u th e r n H okkaido The f o l l o w i n g t e r r a c e s and t h e i r l o c a t i o n occu r o f f s o u t h e r n H okkaido: 400 m to 500 in w e s t o f Shakotan P e n i n s u l a ; 1 ,3 0 0 m to 1 ,4 0 0 m o f f Oshima P e n i n s u l a and O k u sh ir i I s l a n d ; and 1 ,8 0 0 m to 1 ,9 0 0 m o f f Tsugaru and Oshima P en i n s u l a s . N o r th e rn Honshu The n o r th e r n p a r t o f th e r e g io n has l o c a l t e r r a c e s at 1 ,8 0 0 m to 2 ,0 0 0 m and a w id e sp r e a d t e r r a c e a t 2 ,0 0 0 m to 2 ,5 0 0 m. In the s o u th e r n p a r t o f n o r th e r n Honshu, a d i s t i n c t t e r r a c e o c c u r s a t 800 m t o 1 ,0 0 0 m; a f a i r l y d i s t i n c t t e r r a c e o c cu rs o f f A k ita a t 1 ,3 0 0 m to 1 ,5 0 0 m. Banks N orth o f Sado I s la n d S e v e r a l banks are l o c a t e d n o r th o f Sado I s la n d as w e l l as to th e s o u t h e a s t o f Oga P e n i n s u l a . They are c o n s id e r e d to be o f t e c t o n i c o r i g i n . The s h e l f break o f f Sado I s la n d o c c u r s a t a dep th of 140 m; a t 200 m to 250 m o f f th e N i i g a t a c o a s t ; w h ile th e banks have a d e p th o f about 120 m to 170 m. A t e r r a c e a t 400 m to 500 m can be r e c o g n iz e d t o the so u th and e a s t o f C h okaish o Bank and o b sc u r e t e r r a c e s o c cu r a t about 500 m. In a d d i t i o n , a w e l l - d e v e l o p e d p l a i n e x i s t s , w hich r e p r e s e n t s a d e p r e s s i o n at 500 m to 600 m, bounded by banks and th e i n s u l a r s h e l f o f Sado I s l a n d . 36 T e rr a ce s have been r e p o r te d above t h i s d e p r e s s io n . N i i g a t a P e r f e c t u r e The c o n t i n e n t a l s h e l f break o c cu rs at d e p th s v a r y in g from 50 m to 200 m. Sado S t r a i t c o n s i s t s o f a w id e , f l a t p l a i n a t 500 m and an obscu re t e r r a c e o ccu rs at 500 m to 600 m o f f Himekawa. Other t e r r a c e s or f l a t a r ea s in c lu d e w e ll- d e v e lo p e d t e r r a c e s at 800 m to 1 ,1 0 0 m and w idesp read t e r r a c e s at 1 ,1 0 0 m to 1 ,3 0 0 m above a f l a t d e p r e s s io n b o t tomed a t 1,7 0 0 m to 2 ,0 0 0 m. Toyama Bay O ff Toyama Bay, th e s h e l f break v a r i e s betw een 50 m and 150 m and the c o n t i n e n t a l s lo p e has a g r a d ie n t o f about 7 ° . The area has numerous canyons se p a r a te d by s p u r s . S lo p e s of many spurs r e v e a l l o c a l , n e g l i g i b l e t e r r a c e s . S a n -ln D i s t r i c t The s h e l f break o f f the S a n -in D i s t r i c t i s among the d e e p e s t in Japan and ranges in dep th to 500 m. T e rra ces at 600 m to 900 m appear on both s l o p e s of Oki Bank. A d e p r e s s io n formed by Oki Bank and th e c o n t i n e n t a l s h e l f con s i s t s of a f l a t , g e n t l e s lo p in g d e p r e s s io n d iv id e d i n t o two t e r r a c e s 900 m to 1 ,3 0 0 m and 1 ,5 0 0 m to 1 ,7 0 0 m. Another t e r r a c e at 1 ,3 0 0 m to 1 ,6 0 0 m, and a g e n t l y s lo p in g p l a i n at about 1 ,9 0 0 m, o ccu rs n o r th w e s t o f Oki Bank. Yamato Bank T h is bank has a f l a t summit at 300 m w hich c o r r e l a t e s w it h the deep c o n t i n e n t a l s h e l f o f th e S a n - in D i s t r i c t . Ryuku I s la n d s S e v e r a l p r o f i l e s have been taken in the Ryuku I s l a n d s by th e VITYAZ ( P l a t e 2; p r o f i l e s V 2 5 - 4 , V 2 7 - 5 , and V 3 1 - 1 ) . A l l o f t h e s e p r o f i l e s show e s s e n t i a l l y th e same f e a t u r e s as th o s e o f f the P a c i f i c C oast of Jap an , w it h a major t e r r a c e a t about 2 ,0 0 0 m. D i s c u s s i o n The f o l l o w i n g are th e s i g n i f i c a n t c o n c l u s i o n s co n c er n in g t e r r a c e s su rro u n d in g the J a p a n ese I s la n d s ( F ig u r e s 4 and 5 ) . Four b a s i c f e a t u r e s can be r e c o g n iz e d beyond th e c o n t i n e n t a l s h e l f on the P a c i f i c C oast o f J a p a n : 1 . C o n t in e n t a l s lo p e 2 . 300-m t o 500-m t e r r a c e 3. 800-m to 1 , 300-m t e r r a c e , or th e Upper P l a i n 4. 1,600 -m to 2 ,2 0 0 -m t e r r a c e , or the Lower P l a i n , on w h ich many subm arine can y o n s t e r m in a t e . The d i s t r i b u t i o n o f th e Lower P l a i n i s l e s s w id e sp read than o t h e r p l a i n s or t e r r a c e s , but the two deep t e r r a c e s are d i s t i n c t and c l e a r l y r e c o g n i z a b l e alon g th e \ 38 n □ C O N T IN E N T A L . S H E L F 300- 300M P L A IN U P P E R P L A IN I.UiI PR P L A IN TR1- NCH OR D E E P - F L O O R 0 200 K m 1 --- 1 --- I --- 1 F igu re 4 . D i s t r i b u t i o n of t e r r a c e s around Japanese I s la n d s . (A fte r T. S a to , u n p u b lish e d .) P A C I F I C SID E o i K Y U SH U C . T O I O SU M I S T R A IT T A N E G A S H IM A I. 4 K m . JA P A N SEA SIDE 0 1 2 39 3 K m . K U SH IR O C . E R IM O A T S U B E T S U C . S H IR IY A H A C H IN O E M IY A K O K E S E N U M A K IN K A Z A N I. C . SH IO Y A IS O Z A K I K U JO K U R I K A W O G A N A SU N O SA K I S A G A M I BAY IT O C . i r O z a k i S H IM IZ U C . O M A E Z A K I T E N R Y O A T S U M I P E N . SH IM A P E N . K A T S U U R A C . SH IO N O M ISA K I T A N A B E K II S T R A IT T O S A -B A E B K . C . M U R O T O T O S A B A Y C . A S H IZ U R I B U N G O S T R A IT W/ / A / V/// A I M . i mm I i \ R IS H IR I, R E B U N Y A K U SH IR I, T E U R I IS H IK A R I BAY C . K A M U I O K U S H IR I I . O SH IM A P E N . C . S H IR A K A M I T S U G A R U P E N . F U K A U R A C . n y O d O S A K A T A S A D O I. K A S H IW A Z A K I T O Y A M A B A Y N O T O P E N . W A KA SA B A Y C . K Y O G A S A K I TOT TORI O K I L. I, = IS L A N D P E N . = P E N IN S U L A B K . = B A N K C . = C A P E F i g u r e around ( A f t e r 5 . D ep th s o f t e r r a c e Ja p an ese I s l a n d s . T. S a t o , u n p u b lis h e d . 40 P a c i f i c C o a s t, from the Ryuku I s l a n d s to N o rth e rn Hokkaido. Nasu (1964) p o i n te d out t h a t v i r t u a l l y every p r o f i l e from Honshu and HokkaidS to the Japan and K u r ile Trench shows a f l a t p l a i n , 20 km to more th an 100 km in w i d t h , a t d e p th s ra n g in g from 1,000 m to 3,000 m. He has termed t h i s th e ’’Ja p a n e se P a c i f i c S e a - S h e l f , ” h ence, Nasu has more or l e s s combined s e v e r a l p l a i n s or t e r r a c e s . Most p r o f i l e s ( P l a t e s 1 and 2) show a s h a r p - i n c r e a s e in g r a d i e n t betw een the low e s t t e r r a c e l e v e l and the t r e n c h . The Upper P l a i n has the fo llo w in g c h a r a c t e r i s t i c s : (1 ) i t c o n s i s t s more of a g e n t l y s lo p in g g r a d i e n t r a t h e r than a f l a t t e r r a c e betw een 800 m and 1,300 m; (2 ) i t s d i s t r i b u t i o n i s s p o r a d i c and i t s depth i s v a r i a b l e , and (3) i t s s u r f a c e i s i n c i s e d by submarine canyons. The Lower P l a i n has the fo llo w in g c h a r a c t e r i s t i c s : (1) i t co v ers a wide a r e a ; (2) i t i s commonly l o c a te d b e tween 1,600 m and 2,000 m, e x c e p t o f f South Fossa-Magna and the bottom of Tosa Bay; and (3 ) i t is the s u r f a c e a t which subm arine canyons u s u a l l y t e r m in a t e . The f o llo w in g are the most im p o rta n t geomorphic f e a t u r e s on the Ja p an Sea s id e of the Jap anese I s l a n d s : 1. C o n t i n e n t a l s h e l f 2. 300-m to 500-m t e r r a c e 3. 800-m to 1 , 500-m t e r r a c e ( t h e Upper P l a i n where submarine canyons t e r m i n a t e ) 4. 1 , 800-m to 2,200-m t e r r a c e ( t h e Lower P l a i n ) 41 5. 3 ,2 0 0 -m to 3 , 500-m t e r r a c e (b o tto m of J a p a n S e a ) . I t i s of p a r t i c u l a r i n t e r e s t t h a t su b m arin e cany on s along th e e n t i r e w e s t c o a s t of Ja p a n t e r m i n a t e a t d e p t h s o f 800 m to 1,0 00 m, s e v e r a l th o u sa n d m e t e r s above th e f l o o r of th e J a p a n Sea d e p r e s s i o n . T h is d e p th c o r r e s p o n d s to a w id e s p r e a d t e r r a c e a t t h i s d e p t h . The 300-m to 500-m t e r r a c e d o e s n o t have a p a r t i c u l a r l y w id e s p r e a d d i s t r i b u t i o n , e i t h e r in th e Ja p a n Sea or P a c i f i c C o a s t s ; how ev er, th e 800-m to 1 , 500-m and 1 , 800-m to 2,200-m t e r r a c e s a r e w e l l - d e v e l o p e d in th e Ja p a n S e a . S in c e the d e p t h s of t h e s e l a t t e r t e r r a c e s c o r r e s p o n d to th e d e p t h s of t e r r a c e s on th e P a c i f i c C o a s t , one m ig ht r e a s o n a b l y c o r r e l a t e th e t e r r a c e s on th e two c o a s t s . How e v e r , th e two d e e p t e r r a c e s in th e J a p a n Sea a re f a i r l y f l a t , a re u n i f o r m in c h a r a c t e r , and canyons t e r m i n a t e m o s t l y on th e Upper P l a i n . I f t h i s l a s t c h a r a c t e r i s t i c i s c o n s i d e r e d a l o n e , th e Upper P l a i n in the J a p a n Sea must be c o r r e l a t e d w i t h the Lower P l a i n on t h e P a c i f i c C o a s t . Un f o r t u n a t e l y , d a t a on b o tto m g e o lo g y i s l a c k i n g , t h e r e f o r e , i t i s i m p o s s i b l e t o s p e c u l a t e f u r t h e r on th e c o r r e l a t i o n o f t e r r a c e s ( F i g u r e 5 ) . Bottom D e p o s i t s and G e o lo g ic H i s t o r y F i g u r e 6 shows th e age o f a l l r o c k s d a te d from th e s h e l f and o f f s h o r e r e g i o n . W ith o u t d i s c u s s i n g i n d i v i d u a l b o tto m s a m p le s , b a s i c c o n c l u s i o n s can be sum m arized a b o u t • T TERTIARY FOSSIL OBTAINED FROM B E D R O C K • T " // // n S O F T DEPOSIT O T H " " WHERE SEPARATED SUCH AS GRAVEL • P PLEISTOCENE FOSSIL OBTAINED FROM S O F T B E D ROCK OR SOFT SEDIMENT F ig u r e 6. Age of ro ck s su rro u n d in g J a p a n e se I s l a n d s . ( A f te r N iin o , 1952, and o t h e r s o u r c e s . ) 43 th e c h a r a c t e r and age of th e r o c k s beyond th e c o n t i n e n t a l s h e l f . N iin o (1 9 5 2 ) r e p o r t e d t h a t r o c k s dred g ed from th e s e a f l o o r ’’i n d i c a t e t h a t the ra n g e o f d i s t r i b u t i o n w i t h d e p th of T e r t i a r y s t r a t a i s from sh o re t o below 400 m, and P l e i s to c e n e d e p o s i t s from 100 m t o 300 m. Most of th e P l e i s t o cene d e p o s i t s are r e l a t e d to th e su b m arine t e r r a c e s c a r p of 160 m to 180 m. P o s t - P l e i s t o c e n e d e p o s i t s a re d i s t r i b u te d on b o tto m s s h a l lo w e r th a n 20 m i n d e p t h . ” Basement rock h a s n o t b e e n r e c o v e r e d from th e Kumano- Nada Sea or th e Enshu-Nada S ea. The 2,000-m t e r r a c e o f the Kumano-Nada Sea and the S o u th w e st Ja p a n T ren ch i s c o v e re d by t e r r i g e n o u s b l u e mud c o n t a i n i n g rem ains of d iato m s and r a d i o l a r i a (H osh in o and I c h i h a r a , 1960; Nasu, 1964; and S ato and H o sh in o , 19 62 ). S a to (19 62 b) d e s c r i b e d a 302-cm c o re from th e b o tto m of Suruga Bay. The s u r f a c e c o n s i s t e d of 50 cm of s o f t s e d im ent below which was c le a n sandy g r a v e l and s h e l l d e b r i s . The g r a v e l s were c o r r e l a t e d w i t h P a l e o g e n e , M iocene, and p e rh a p s P l i o c e n e r o c k s on l a n d . In th e Ja p a n Sea, T e r t i a r y age r o c k s a re a l s o common on th e s h e l f and b a n k s . P l i o c e n e r o c k s c ro p o u t i n some c a n y o n s. B u rie d v a l l e y s on lan d n e a r Toyama p r o b a b l y e x te n d e d o f f s h o r e to su bm arine c a n y o n s . The v a l l e y f i l l i s d a t e d as e a r l i e s t P l e i s t o c e n e . Off Onagawa, a d red g e h a u l (JE D S -2-S2) was made a t a depth of 2,330 m (Nasu, 1964). Over 500 p e b b le s and cob b l e s up to 46-cm d ia m e te r ( s i l t s t o n e ) , as w e ll as sand and mud, were c o l l e c t e d . Rocks had o rn am en tatio n s i m i l a r to t h a t produced by wave and wind e ro s io n and by r o c k - b o r in g a n im a ls. L iving and dead f o r a m i n i f e r a in the g r a v e l ma t r i x were normal d e e p - s e a assem b lages. This l o c a l i t y (38° 1 6 . 2 ’ N, 143° 1 1 .8 ' E) l i e s on the tr e n c h slo pe beyond the o u te r margin of the 1 , 500-m to 2,000-m t e r r a c e . Immedi a t e l y west of t h i s l o c a l i t y (38° 03* N, 142° 5 9 ’ E ) , a dredge h a u l (JEDS-4E1) was tak e n on th e f l a t t e r r a c e a t 1,690 m. W ell-rounded se d im e n ta ry p e b b le s were mixed w ith sand and mud. Rocks had o rn a m e n ta tio n s i m i l a r to t h a t p r o duced by wave o r wind e ro s io n and by r o c k - b o r in g a n im a ls. L iving and dead f o r a m i n i f e r a in the g r a v e l m a tr ix were n o r mal d e e p -s e a a sse m b la g e s. A core (JEDS-4-E1; 38° 0 3 ’ N, 142° 59 ’ E, 1,810 m) from t h i s same f l a t t e r r a c e M a ls o showed i t s t e r r i g e n o u s o r i g i n , having abundant c o n te n t of co arse se d im e n t. . . ." (Nasu, 1964). At s t a t i o n JEDS-2-S1 (38° 11.4* N, 143° 12.1* E ), the dredge h aul from 2,350 m c o n ta in e d rounded to a n g u la r p i e c e s of metam orphic, s e d i m entary, and igneous ro c k s . Nasu r e p o r t e d t h a t the angu l a r frag m ents seem to be T e r t i a r y in a g e, s u g g e s tin g bed rock in the a r e a a ls o i s of T e r t i a r y age. One p ie c e of s i l t s t o n e was g iv en a t e n t a t i v e Miocene age by Taro Ka- naya, i n d i c a t i n g a b r a s io n of th e g r a v e l o c c u rre d in p o s t - Miocene tim e. O ff T sugaru S t r a i t a f l a t t e r r a c e o c c u rs a t 1 ,2 00 m, and, a c c o rd in g to Nasu ( 1 9 6 4 ) , t h i s f l a t p l a i n i s the n o r t h e r n e x t e n s i o n of the t e r r a c e o f f Onagawa. A c o re (N 5? 41° 21* N, 141° 53* E) tak en on t h i s f l a t p o r t i o n a t i t s e a s t e r n margin a t a d e p th o f 988 m c o n s i s t e d of mud. However, a n o th e r co re (N 8; 39° 58* N, 143° 4 1 ’ E) taken on th e t r e n c h s l o p e , s l i g h t l y beyond th e e a s t e r n m argin of th e t e r r a c e a t 2,643 m, c o n s i s t e d of sandy m a t e r i a l w ith v e ry f i n e g r a v e l . S t i l l a n o th e r core (N 4; 485 m; 41° 32* N, 141° 38* E) c o n s i s t e d of c a l c a r e o u s s i l t . These few bottom sam ples r e v e a l t h a t c o a r s e se d im e n ts c o n s i s t i n g of sand and g r a v e l a re w id e ly d i s t r i b u t e d on the Ja p a n e s e P a c i f i c S e a - S h e lf and beyond th e o u t e r m argin of t h i s deep p l a i n . I t is p ro b a b le t h a t s i m i l a r sedim ent w i l l be found on th e c o n t i n e n t a l s l o p e s . Nasu (1961 and 1964) c o n s i d e r e d t h r e e p o s s i b i l i t i e s c o n c e rn in g th e o r i g i n of the c o a r s e s e d i m e n ts : (1) submar in e s l i d e s , i n c l u d i n g t u r b i d i t y c u r r e n t s from p r e s e n t - d a y c o a s t s ; (2) i c e r a f t i n g from modern c o a s t s ; or (3) l o c a l subm arine s l i d e s or by o t h e r a g e n c i e s , such as ic e r a f t in g , from the a r e a s of i t s p rim a ry d e p o s i t i o n ( e . g . , from the w id e sp re a d deep t e r r a c e ) . The f i r s t two p o s s i b i l i t i e s a re e l i m i n a t e d b e c a u se l o c a l c o n d i t i o n s m i t i g a t e a g a i n s t e a c h . Nasu co ncluded t h a t th e w id e sp re a d Ja p a n e s e P a c i f i c S e a - S h e lf m ight once have been a f l u v i a l p l a i n , or wave- c u t t e r r a c e o v e r l a i n by c o a rs e s e d im e n ts s i m i l a r to the 46 f l u v i a l p l a i n s and c o n t i n e n t a l s h e lv e s of to d a y , and t h a t i t was l a t e r submerged by c r u s t a l down-warping or by d e f o r m atio n in th e v i c i n i t y of th e Japan and K u r ile T r e n c h e s . T his p e n e p l a n a t i o n p resu m ab ly o c c u r r e d i n p o st-M io c en e tim e . Nasu a ls o su g g e ste d th e p o s s i b i l i t y t h a t th e submar in e canyons cu t i n t o the u p per 1,000 m to 3,000 m, which t e r m in a t e on the d e e p e s t w id e s p re a d p l a i n , took p l a c e d u r ing p e r i o d s of s u b a e r i a l e r o s i o n when th e s h e l f was formed ( F ig u re 7 ) . F i n a l l y , Miocene and p o st-M io c en e age fo rm a t i o n s are e l e v a t e d s e v e r a l th o u sa n d m e te r s in Jap an and c o n s i d e r s submergence of e q u a l m agnitude n ot u n r e a s o n a b l e . I i j i m a and Kagami (1 9 6 1 ) s u g g e s te d t h a t th e Lower P l a i n o f f S a u rik u was d r y la n d in p o s t - E a r l y P l i o c e n e and t h a t the land su b s id e d s i n c e p o s t- M id d le P l i o c e n e or E a r l y P l e i s t o c e n e tim e . In c o n c lu s io n , Nasu p o i n t e d out t h a t in J a p a n , the Eocene has been c o n s i d e r e d a p e r i o d of p e n e p l a n a t i o n , and t h a t from th e Miocene to p r e s e n t , o ro g e n ic movement h as o c c u r r e d alo n g th e J a p a n e s e a r c . The deep p l a i n on the P a c i f i c s id e o f J a p a n , t h e r e f o r e , i s th o u g h t to p o s s i b l y be r e l a t e d to th e f o r m a t io n of th e Ja p an and K u r i l e T ren c h es in L ate Miocene or p o st-M io c e n e tim e . The p r e s e n c e of c o a r s e se d im e n ts a t d e p th s d e ep e r th an the lo w e st t e r r a c e ( a p p r o x i m a t e l y 3,000 m) , i n c l u d i n g the tre n c h f l o o r , must i n d i c a t e t h a t the w id e sp re a d o c c u r re n c e of c o a r s e se d im e n ts on t h e s e p l a i n s may r e p r e s e n t LATE PLIOCENE H SfiiBIlI 100 KM I ii. i. i EARLY PLEISTO CEN E Figure 7. Schematic p r o f i l e s showing t e c to n ic development of n o r th e a s te r n Honshu and Japan Trench since youngest Neogene. V e r tic a l ex aggeration 1 0 :1 .1 . Complicated p re - T e r t i a r y s t r a t a ; 2. P r e - T e r t i a r y a c id ic i n t r u s i v e s ; 3. P r e - T e r t ia r y u l t r a - b a s i c i n t r u - s iv e s ; 3. P r e - T e r tia r y u l t r a - b a s i c i n t r u s i v e s ; 4. Younger s t r a t a ; 6. Younger T e r t ia r y a c id ic i n t r u s i v e s ; 7. Quaternary volcano; J : Japan Sea; D: Dewa Range; 0: Ohu Back bone Range; K: Kitakami P la te a u ; S: JEDS-2-S; T: Japan Trench; H: I n fe rre d southward e x te n sio n o f Hidada Range and i t s metamorphic zone. (A fter Iijim a and Kagami, 1961.) 48 p o s s i b l e so u rc e a r e a s , r a t h e r than c o n s i d e r i n g t u r b i d i t y c u r r e n t s o r i g i n a t i n g c l o s e to s h o r e , as the p r i n c i p a l so u rc e r e g i o n . In the f i n a l a n a l y s i s , so few b otto m sam ples a re a v a i l a b l e beyond the s h e l f , p a r t i c u l a r l y from th e m ajor t e r r a c e s or p f a i n s , t h a t i t i s d i f f i c u l t t o a r r i v e a t any d e f i n i t e c o n c l u s i o n s . In re v ie w in g the l i t e r a t u r e , S a to ( s i n c e he was u n a b le t o draw any c o n c l u s i o n s r e g a r d i n g the w o rld -w id e e x i s t e n c e o f deep p l a i n s or t e r r a c e s ) co n clu d ed t h a t th e p l a i n s s u rro u n d in g Ja p a n are a l o c a l phenomenon. As a d d i t i o n a l e v i d e n c e , he p o i n te d out t h a t the p l a i n s a re a t d i f f e r e n t d e p th s on the P a c i f i c and Ja p a n Sea s l o p e s s u g g e s t i n g l o c a l , d i f f e r e n t i a l c r u s t a l s u b s i d e n c e . Three d i s t i n c t d i s t u r b a n c e s o c c u rre d d u r i n g th e Neo gene i n Ja p a n : (1) f o r m a t io n o f s e d i m e n ta r y b a s i n s in e a r l i e s t Miocene; (2) g e a n t i c l i n a l u p l i f t in l a t e s t M iocene, and (3) g e n e r a l u p l i f t in l a t e P l i o c e n e . Most g e o l o g i s t s a g re e t h a t th e c o n t i n e n t a l s h e l f and t e r r a c e s on th e s h e l f were c u t d u r i n g e u s t a t i c changes in se a l e v e l a s s o c i a t e d w i t h g l a c i a t i o n . I f the Lower P l a i n s submerged in p o s t - L a te P l i o c e n e - - a s i n d i c a t e d o f f S a u rik u and Sagami B ay-- the p l a i n s a r e c o r r e l a t i v e w i t h t h e u n c o n f o r m ity or u p l i f t d u r in g L ate P l i o c e n e . The Upper P l a i n (w hich Sato r e g a r d s as th e o l d e r ) can p r o b a b ly be c o r r e l a t e d w i t h l a t e s t Mio cene u p l i f t . Four d i s t i n c t t e r r a c e s o ccur o f f the Green 49 T u ff re g io n on the Japan Sea s i d e and South Fossa-Magna. I f im portance i s a tta c h e d to u p l i f t (which Sato presum ably does in acco u n tin g f o r the c u t t i n g of l a r g e submarine can y o n s ) , then the Lower and Upper P l a i n s of the P a c i f i c s id e of Japan are c o r r e l a t e d w ith the Upper and Lower P l a i n s , r e s p e c t i v e l y , on the Japan Sea s i d e . The 300-m to 500-m t e r r a c e i s assumed by Sato to have been c u t a f t e r l a t e s t P lio c e n e b u t b e fo r e the l a s t G l a c i a l age. JAPAN SEA The Ja p an Sea i s a broad tro u g h e lo n g a te d in a n o r t h - so u th d i r e c t i o n . I t a t t a i n s a maximum w id th of 1,265 km and h a s a le n g th of 2,032 km from n o r t h to s o u th , the r a t i o of le n g th to w id th being 1 : 6 . The s h e l f i s n arrow , g e n e r a l l y n o t exceeding 26 km, has open embayments and few c lo s e d b a y s . The maximum d e p th s of over 3,500 m are a s s o c i a t e d w ith a n o r t h e a s t e r l y t r e n d i n g tr o u g h . I s o l a t e d e l e v a t i o n s , in c lu d in g p ro b a b le v o l c a n ic p e a k s , r i s e from the f l o o r of th e s e a (Bezrukov and Udintsev, 1953). The mean d e p th of th e s h e l f b reak f o r th e n o r t h w e s t - - e rn p a r t o f the Japan Sea is 136 m, 185 m f o r th e n o r t h e a s t e r n p a r t of Honshu and 149 m between HokkaidS to mid- S a k h a lin I s l a n d ( F ig u r e 8 ). The mean d e p th of th e s h e l f edge f o r th e se a as a whole i s 146 m (Kanayev, 1963). The c o n t i n e n t a l slo p e along the w e s t e r n ( c o n t i n e n t a l ) s id e has an average g r a d i e n t of 8° to 10°, and l o c a l l y re a c h e s 20° to 25°. P l a t e 3 shows t h a t th e lower c o n t i n e n t a l slo p e i s s t e e p e r than th e u p p e r, and no c o n t i n e n t a l r i s e e x i s t s in the Sea o f J a p a n - - a t l e a s t not in the n o r t h e rn p a r t . Deep-w ater se d im e n ts c o n s i s t of s i l t a t th e b ase of 50 the c o n t i n e n t a l s lo p e and c la y s i n th e c e n t r a l t r o u g h . C oarse g r a v e l s occur on the s h e l f and in deep w a t e r . Sands occur l a r g e l y on banks and a t d e p th s up t o 3,000 m, and i n th e s o u th e r n p a r t of th e Japan S ea, sands have a high p e rc e n t a g e of f o r a m i n i f e r a l t e s t s . G l a c i a l - m a r i n e se d im e n ts more or l e s s f o llo w th e t r a c k of d r i f t i n g i c e . D uring m iddle and l a t e P a l e o z o i c tim e a b ro ad geo- s y n c l in e e x i s t e d a t the p r e s e n t s i t e of S a k h a l i n , Jap an and p o s s i b l y t h e n o r t h e r n and c e n t r a l p a r t of th e Ja p a n Sea (B e lo u sso v and R u dich, 1960). During the H e rcy n ian s ta g e a c e n t r a l u p l i f t o c c u rre d a t th e p r e s e n t s i t e of th e Japan Sea, bounded on th e e a s t by a m a rg in a l d e p r e s s i o n c o rre s p o n d in g to th e o u t e r zone of so u th w e st J a p a n . At the s t a r t of the A lp in e c y c l e , t h i s m a r g in a l d e p r e s s i o n was tra n s fo rm e d i n t o th e Mesozoic i n t r a g e o s y n c l i n e . The u p l i f t e d m a s s if o c cu py in g th e Ja p a n Sea was r e p e a t e d l y u p l i f t e d and d e e p ly ero d e d d u rin g the J u r a s s i c . A sou rce i d e n t i f i e d as th e p r e s e n t s i t e o f the Jap an Sea i s c l e a r l y i n d i c a t e d in g e o s y n c l i n e f a c i e s in J a p a n . G e o s y n c li n a l c o n d i t i o n s e x te n d e d to the end of th e Lower C r e ta c e o u s p e r i o d . S tr o n g e v id e n c e p o i n t s to th e d r y land of c o n t i n e n t a l - t y p e c r u s t in th e p r e s e n t s i t e of th e Ja p a n and Okhotsk Seas d u r in g the C r e ta c e o u s and e a r l i e r . Even as l a t e a s the P a le o g e n e epoch th e Jap an Sea ap p ea rs to have been th e so u rc e a r e a o f g r a n i t e . Along the n o r t h w e s t e r n edge of th e f u t u r e Ja p a n Sea a zone of 5 2 a c t i v e v o lc a n is m c o n ti n u e d to e x i s t i n the P a le o g e n e tim e . S u b sid e n c e beg an on a g r e a t s c a l e a t th e s i t e o f th e J a p a n Sea in e a r l y N eogene. By the Miocene epoch the Ja p an Sea was e s s e n t i a l l y d e v e lo p e d as to d a y w i t h i t s p r e s e n t bound a r i e s . A c co rd in g to R u s s ia n g e o l o g i s t s a l l of th e depressions, t h e i r b o r d e r s , i s l a n d a r c s , and b o r d e r i n g t r o u g h s l i e w i t h in a R ecent g e o s y n c l i n a l r e g i o n of t h e rim of A s ia . E v i dence of u p l i f t , downwarps, s u b s i d e n c e , and f a u l t i n g are e v i d e n t . T e r t i a r y age f o l d i n g o c c u r s in the e a s t , in J a pan and S a k h a l i n . Klenova and G e rs h a n o v ic h (1 95 1) and Lavrov (1960) a re among th o s e who c o n s i d e r th e Ja p a n Sea a modern g e o s y n c l i n e . T h is b e l i e f i s b a se d upon v a r i o u s f e a t u r e s such as the c o n f i g u r a t i o n and c o m p o s itio n of th e b o t tom and th e g e o l o g i c a l s t r u c t u r e of th e c o a s t s . For e x am ple, on t h e w est c o a s t of s o u t h e r n S a k h a li n o n ly b e d ro c k i s e x p o se d . A s t u d y of lan d and s e a f l o o r r o c k s has shown t h i s r e g i o n to be composed of Upper C r e ta c e o u s and T e r t i a ry age s e d i m e n ta r y r o c k s and v o l c a n i c s . The r o c k s on land and on th e s e a f l o o r c l e a r l y r e v e a l the p r e s e n c e of a g r e a t s y n c l i n a l s t r u c t u r e which co u ld have formed a t th e end o f th e P l i o c e n e epoch or the b e g in n in g o f P l e i s t o c e n e tim e on th e s i t e of an Upper T e r t i a r y age downwarp. O th e r e v id e n c e of s u b s id e n c e a l s o i s g i v e n by L avrov which to o k p l a c e i n Upper Q u a t e r n a r y tim e . F ig u r e 8. S ch em atic c h a r t o f th e d i s t r i b u t i o n of mean d e p th s (m) f o r the edge of the c o a s t a l s h e l v e s in th e n o r t h w e s t e r n P a c i f i c . The t h i n s o l i d l i n e i s th e edge of the c o a s t a l s h e l f ; th e s t r a i g h t l i n e s show the b o u n d a r ie s of the d i f f e r e n t a r e a s of the s h e l f f o r which the mean e d g e - d e p th was d e te r m i n e d ; th e number o f so u n d in g s from w hich t h i s d e p th was c a l c u l a t e d i s g iv e n i n b r a c k e t s . In th e m iddle o f th e s e a s , the number i s th e mean d e p th of the s h e l f edge f o r t h a t s e a ; i n b r a c k e t s the number of so u n d in g s from w hich t h i s d e p th was c a l c u l a t e d . The b r o ken l i n e shows th e edge of th e a b r a s i o n a l - a c c u m u l a t i o n a l p l a t f o r m s u r f a c e f o r th e V ity a z R id g e. ( A f t e r Kanayev, 1963.) 338.(7 107 (51) K n m r l n s k l G ulf 151(13 ) |— 147411)— 1 V K a m c h a t k a G ulf Krono<;kl Gulf > 140(13 F ig u re 8. KURILE-KAMCHATKA ARC •” I n t r o d u c t i o n A t o t a l of 25 p r o f i l e s are a v a i l a b l e f o r the K u r i l e - Kamchatka Trench ( P l a t e s 4 and 5). Except f o r two incom p l e t e r e p l o t t e d p r o f i l e s (F ig u re 9) based upon Japanese so u rc e s ( D i e t z , 1954), a l l o th e r p r o f i l e s are based upon S o v ie t so u n d in g s. T h ir t e e n p r o f i l e s have a s c a le la r g e enough f o r t e r r a c e c o r r e l a t i o n ( P l a t e 4 and Figure 10). Although R ussian g e o l o g i s t s have s tu d ie d the K u r i l e - Kamchatka Trench in c o n s id e r a b le d e t a i l , few r e p o r t s have been t r a n s l a t e d or are r e a d i l y a v a i l a b l e . A p aper by U d intsev (1955a) i s the b a s i s for the p r o f i l e s used in P l a t e 4; the o r i g i n a l has not been t r a n s l a t e d , t h e r e f o r e U d i n t s e v ’ s i n t e r p r e t a t i o n of the f e a t u r e s rem ains unknown. An a tte m p t was made to i d e n t i f y t e r r a c e s on U. S. Navy b a th y m e tric p l o t t i n g s h e e t s but soundings are s c a rc e and the con tou r i n t e r v a l (100 fms) i s too g r e a t to p ic k out any sm all slo p e f e a t u r e s . Some of the r e f e r e n c e s d e s c r i b i n g the K u r i l e - Kamchatka Trench, Okhotsk Sea, and a d ja c e n t a r e a s in c lu d e 5 5 5 6 KURIL TRENCH KURIL TRENCH V X I 2 JAPAN TRENCH (■ ♦> JAPAN TRENCH PHILIPPINE TRENCH V * 17 F ig u re 9. Redrawn p r o f i l e s a c r o s s the K u r i l e - Kamchatka, J a p a n , and P h i l i p p i n e t r e n c h e s . ( A f te r D i e t z , 1 9 5 4 .) 5 7 K U R I L E - K A M C H A T K A T R E N C H K m - 0 S E A L E V E E — 1 - S C -2 S H E L F B R E A K -3 - 4 c 3 T - 5 - 6 - 7 SC* - - T —8 B R E A K B E T W E E N U P P E R A N D L O W E R S L O P E - 9 B O T T O M O F T R E N C H - 1 0 -11 — 1 2 T = T E R R A C E S C = S L O P E C H A N G E ( I N C R E A S E IN G R A D IE N T : D E C R E A S E IN G R A D IE N T r b - B A S E OR E N D O F P R O F I L E -13 —14 —15 H O R IZ O N T A L D IS T A N C E N O T T O S C A L E F i g u r e 10. C o r r e l a t i o n of t e r r a c e s and o t h e r f e a t u r e s the K u rile -K a m c h a tk a T re n c h s l o p e . on 58 the f o l lo w in g . A few o f th e s e have been t r a n s l a t e d and the source of the t r a n s l a t i o n i s c i t e d : Andreyeva and U d in tse v (1958); Beloussov (1960 and 1962); Bezrukov and U d in tse v (1953-1955); .Boichenko (19 61 ); Chemekov (1 95 7); Goryachev (1 960); I l ’y in (1961); Kanayev (1959 and 1963); Kanayev and L arin a (1959); K ro p tk in , e t a l . (1 95 8): Kuno (19 59 ); L ario n o v a (1959); L indberg (1 9 5 6 ); Muratov (1957); Sysoyev, e t a l . (1958); Tikhomirov (1958); U d in tse v (1954, 1955a, 1955b, 1955c, 1957a and 1957b); Ushakov (1950); Zatonsky e t a l (1961) and Zenkovich (1 9 5 8 ). R e s u Its The K u rile Ridge c o n s i s t s o f a g r e a t double g e a n t i c l i n e and in n er (G re at K u rile Range) and an o u te r r id g e (V ity az Submarine R id g e). I s la n d s and a c t i v e v o lca n o s p r o tru de above the G re at K u r ile from Hokkaido I s la n d to Kam c h atk a P e n i n s u l a and are a s s o c i a t e d w ith g r e a t deep f r a c t u r e s (F ig u re 1 1 ). The o u te r r id g e i s r e l a t i v e l y old ( T e r t i a r y age) and shows no s ig n s of Recent vo lcanism . The in n e r r id g e of the K u r i l e s i s s p l i t i n t o th r e e s e g ments by the deep f r a c t u r e s of Boussole S t r a i t and Kru- z e n s h te r n S t r a i t . The o u te r r id g e is broken in the c e n t e r and more or l e s s d e to u r s around a broad o v e r t h r u s t tongue of th e f l a n k of th e in n e r r id g e which in t h i s s e c t o r i s thought to r e p r e s e n t a s t a b l e c o r e . F u r t h e r e a s t behind the s o u th e r n K u r ile S t r a i t r i s e a number of i s l a n d s of the 59 F ig u re 11. Legend: 1. P a c i f i c F i s h e r i e s I n s t i t u t e D e p re s s io n (992 m ), 2. D e riu g in D e p re s sio n (1 ,7 4 4 m ), 3. I n s t i t u t e of Oceanology Bank (894 m ), 4 . Academy of S c ie n c e s Bank (940 m ), 5. South Trough of Okhotsk Sea (3 ,3 7 0 m ), 6. Outer Ridge of K u r ile I s la n d Arc, 7. K urile-K am ch atk a Trough, and 8. S h ir s h o v Range. W estern Bering Sea B asin i s in m iddle r i g h t . A l e u ti a n Arc j o i n s K urile-K am ch atka Trough a t the Kamchatka P e n i n s u l a . Bowers Bank i s loop to n o r t h of A l e u t i a n T ren c h . Obruchev Swell i s l o c a t e d about 163° to 166° E, 53° N. (Based upon d a t a from Hope, 1956.) 60 L i t t l e K u rile Range. (These c o n ta in the o l d e s t ro ck s in the c h a i n .) The K urile-K am chatk a Arc has a t y p i c a l tr e n c h w ith an a sy m m e tric al c r o s s s e c t i o n along i t s e n t i r e l e n g t h ( P l a t e s 4 and 5 ) . The n o r th w e s te r n s lo p e i s 6 km to 10 km high w h ile the s o u t h e a s t e r n ( a b y s s a l sea f l o o r ) s id e i s on ly 2-km to 5-km h ig h . Trench s l o p e s have an average g r a d i e n t of 7°; the upper p a r t i s 5° to 6° b u t the lower slo p e i s 20° to 25°. L o c a l l y , s lo p e s exceed 30° to 45°. The maximum known d e p th i s 10,542 m (Zatonsky. e t a l ., 1961). Using the 6,000-m i s o b a th the tr e n c h l e n g t h i s 2,200 m and has a w id th of 20 km to 60 km. I t l i e s about 180 km from th e i s l a n d a rc and toward the south i t j o i n s the Japan Trench at an angle of 130° and tow ards Kamchatka S t r a i t to the n o rth i t j o i n s the A le u tia n Trench a t an an g le of 70° a t a d ep th of 5,600 m. As i n d i c a t e d above, the upper s lo p e is more g e n tl e than th e lower s l o p e . C ro ss s e c t i o n a l p r o f i l e s show a more or l e s s V-shape but the f l o o r of the tr e n c h i s f l a t . I t s w idth v a r i e s from 1 km to 20 km, a v erag in g 5 km, and s h o a ls towards the nor t h . U d in ts e v (1955b) and Z ato n sk i. e t a l . (1961) r e p o r t e d t h a t th e tr e n c h slo p e has numerous e s c a r p m e n ts , t e r r a c e s , and canyons. U n f o r t u n a t e l y , the a u th o r s do n o t i d e n t i f y the d e p th or e x t e n t of the t e r r a c e s . 61 A wide t e r r a c e can be tr a c e d on alm ost e v e ry p r o f i l e a t d e p th s ra n g in g from 3,000 m to 4,5 0 0 m ( P l a t e 4 and F i g ure 1 0 ). I t i s a t l e a s t 93-km wide a t some l o c a t i o n s and commonly has a h ig h r i d g e a t i t s seaward edge. P r o f i l e s a t n a t u r a l s c a l e ( P l a t e 4, upper r i g h t ) show t h i s t e r r a c e i s a m ajor f e a t u r e on the t r e n c h s l o p e . The s c a l e is too sm all to d i f f e r e n t i a t e s m a ll e r t e r r a c e s on th e tr e n c h s l o p e . V ity a z Ridge i s f l a t , i s lo c a te d a t a d e p th of about 500 m, and i s an e r o s i o n a l p l a t f o r m ( U d in ts e v , 1955b). In B oussole and K r u z e n s h te r n S t r a i t s i t i s now l o c a t e d below wave base and has been s t r o n g l y downwarped. E r o s i o n a l p l a t f o r m s a lso a re r e p o r t e d around i s l a n d s to d e p th s of 1,200 m. A few l a r g e subm arine canyons occur n e a r B oussole and K ru z e n s h te rn S t r a i t s and in A v ach in sk ay a, K rono^ki, and Kamchatka Bays. Some of the canyons can be t r a c e d i n t o the t r e n c h e s , or to d e p th s of 6 km to 7 km. The canyons in the s t r a i t s a p p a r e n t l y are a s s o c i a t e d w i t h f a u l t s n o r mal to th e tr e n d of th e t r e n c h . Large f a u l t s c a r p s are found a t t h r e e l o c a t i o n s on the n o r th w e s t slo p e (a b o u t 1,500 m) b u t a p p a r e n t l y a re n o t of g r e a t l e n g t h . These f a u l t s a re l o c a t e d n e a r H okkaid5, o f f S h im u s h ir i I s l a n d , and o f f th e s o u t h e r n c o a s t of Kamchatka. U d in ts e v (1955b) c o n s i d e r s the l o n g i t u d i n a l e s c a r p m e n ts , form ing s t e p s , and canyons as h a v in g a f a u l t o r i g i n . E ls e w h e re , f a u l t s c a r p s as h ig h as 800 m and a t l e a s t 500 km in l e n g t h have been d i s c o v e r e d a l t e r n a t i n g w i t h n e a r l y h o r i z o n t a l t e r r a c e s . They a r e known from th e slo p e o f th e A l e u t i a n T r e n c h , n e a r the Komandorski I s l a n d s , and from th e K u rile -K a m c h a tk a Trench n e a r Kamchatka ( U d i n t s e v , 1 9 5 5 c ) . The s o u t h e a s t s lo p e r e p o r t e d l y a l s o has s t e p s , or s t e e p l o n g i t u d i n a l s c a r p s and narrow t r a n s v e r s e canyons ( U d i n t s e v , 1955b, 1 9 5 5 c ). As on th e o p p o s i t e w a l l of th e t r e n c h , th e s e s c a r p s and canyons a re assumed to have a t e c t o n i c o r i g i n . The s h e l f b re a k v a r i e s c o n s i d e r a b l y alo n g th e K u r i l e Arc as i n d i c a t e d in F i g u r e 8. Off Kamchatka P e n i n s u l a th e edge o f th e s h e l f l i e s a t a mean d e p th of 133 m on th e w e st and 145 m on th e e a s t . Off th e n o r t h e a s t s i d e of th e K u r i l e Ridge th e mean d e p th i s 133 m; on th e s o u t h e a s t s i d e i t i s 153 m. For th e r i d g e as a whole th e mean s h e l f b r e a k i s 143 m (b ased upon 359 m e a s u r e m e n ts ) . For th e G r e a t e r K u r i l e Ridge the mean s h e l f b re a k i s 143 m, b u t f o r th e L e s s e r Ridge i t i s m ark ed ly d e e p e r - - 1 6 4 m. The d i f f e r e n c e in d e p th betw een th e n o r t h w e s t e r n and th e s o u t h e a s t e r n edges o f th e s h e l f amounts to 20 m f o r th e G re a t K u r i l e Arc and 87 m f o r th e L e s s e r K u r i l e A rc . Along th e in n e r s i d e o f th e G r e a t e r K u r i l e Arc ( n e x t to O khotsk Sea) the s h e l f b r e a k l i e s a t a n e a r c o n s t a n t d e p t h , b u t on th e o c e a n ic s i d e th e lo w e rin g o f the s h e l f b r e a k in th e c e n t r a l s e c t o r o f the a rc i s d e e p e r compared t o th e n o r t h e r n and s o u t h e r n p o r t i o n s o f th e a r c . T h u s, th e i n n e r r i d g e i s 63 l e s s t i l t e d , p e rh a p s b ecau se th e r e i s n o t as much lo ad in g of the sea f l o o r by the o u t e r v o l c a n ic r i d g e . Most d e p r e s s e d , a c c o rd in g to Kanayev (1 9 6 3 ), a re the s h e l f edges of th o se i s l a n d s which sh a re a common f o u n d a t i o n w ith the o u t e r r i d g e . As p r e v i o u s l y i n d i c a t e d , the V ity az Ridge i s lower in the c e n t r a l p a r t . In the s o u t h e r n s e c t o r of th e V ity az Ridge the p lan e d s u r f a c e has su b sid e d t o a d e p th of 1,220 m. The sunken p a r t s a re s e p a r a t e d from one a n o th e r by s c a r p s , i n d i c a t i n g b lo c k f a u l t i n g on t h i s p a r t of th e r i d g e . Zatonskv, e t a l . (1961) su g g e ste d t h a t " t h e middle s e c t i o n of the K u r i l e Chain r e p r e s e n t s a young, a s c e n d a n t m o r p h o s t r u c t u r e , n o t as y e t having e x p e r ie n c e d u p l i f t and no t having undergone l e v e l i n g o f f and su b seq u e n t d e p r e s s i o n , as one m ight suppose in the c a se of V ityaz R id g e ." A ccording t o Kanayev, the G r e a t e r K u r i l e Ridge has n o t undergone any t e c t o n i c movements su b se q u e n t to the fo r m a tio n o f the a b r a s i o n a l p l a t f o r m , b u t has r e a c t e d to a l l s t r e s s e s t o g e t h e r . Evidence p o i n t s to a g e n e r a l u p l i f t of the G r e a te r K u r i l e Arc. OKHOTSK SEA O khotsk Sea m ea su re s 2,5 00 km n o r t h - s o u t h and 1,200 km i n an e a s t - w e s t d i r e c t i o n . The b a th y m e try o f th e Okhotsk Sea i s c o m p l i c a te d , b ut i s b a s i c a l l y s h a llo w to th e n o r t h where i t form s a wide p l a i n , t i l t e d t o the so u th ( F i g u r e 1 1 ) . Beyond 300 m and 500 m, the b o tto m i s h i g h l y i r r e g u l a r . S e v e r a l b a s i n s and s w e l l s occur in th e s o u t h and one tr o u g h i s 1,744-m d eep ; the maximum d e p th i s 3,370 m. T his l a t t e r tro u g h i s u n u s u a l l y f l a t , has c o m p l e x l y - i n t e r s e c t e d subm arine canyons and r i d g e s , and the tro u g h has b o r d e r i n g s l o p e s as s t e e p as 20° to 30° and r e l i e f of 2,500 m ( U d i n t s e v , 1957 b). A ccording to Kanayev ( 1 9 6 3 ) , th e mean s h e l f b r e a k s f o r th e Okhotsk Sea a re shown in T able 1. T able 1. Depths of Mean S h e l f B re a k s , Okhotsk Sea West Kamchatka P e n i n s u l a 133 m N o rth w est S e c to r 234 S a k h a lin I s l a n d 164 Between S a k h a li n and HokkaidS 211 West K u r i l e I s l a n d s 133 Mean f o r Okhotsk Sea 147 64 65 Okhotsk Sea i s a r e c e n t f e a t u r e which formed o n l y d u r in g the Q u a t e r n a r y e p o c h . T h is was a r e g i o n o f e r o s i o n d u r in g th e P a l e o g e n e epoch (U shakov, 1 9 5 0 ). The n o r t h e r n s h a llo w and c e n t r a l p a r t s of th e s e a a re a r e l a t i v e l y s t a b l e p l a t f o r m a r e a , u n a f f e c t e d by T e r t i a r y age f o l d i n g b u t r e c e n t l y s u b s id e d ( U d i n t s e v , 1 9 5 7 b ). D e riu g e n D e p r e s s io n and P a c i f i c F i s h e r i e s I n s t i t u t e D e p r e s s io n a l s o were formed r e c e n t l y . They a r e r e g a r d e d as m a r g in a l s a g s ( r e l a t i v e to the f o l d s t r u c t u r e s o f S a k h a l i n and K am ch atk a). The d e e p s o u t h e r n tro u g h i s th e o l d e s t downward f l e x u r e and s t i l l i s i n th e p r o c e s s o f s u b s i d i n g . The f l o o r of th e O khotsk Sea i s composed p r e d o m i n a n t l y of mud and sand w i t h many a r e a s o f ro c k y b o tto m . Muds c o v e r th e d e e p e r a r e a s , w h i l e r o c k s , s a n d , and mud a re common on th e s h e l v e s . The r e g i o n b o r d e r i n g the O khotsk S ea, i n c l u d i n g the S i b e r i a n c o a s t and i s l a n d s , h av e s i m i l a r g e o lo g i c h i s t o r y . The m o u n tain r a n g e s a re the r e s u l t o f v o lc a n is m , f o l d i n g , and f a u l t i n g . The ro c k s v a r y i n age from P a l e o z o i c to R e c e n t and i n c l u d e i g n e o u s , m e tam o rp h ic, and s e d i m e n ta r y t y p e s . Almost a l l of th e s h o r e s a re ro c k y and m o u n ta in o u s . M ou ntain g l a c i e r s o f Q u a t e r n a r y age have l e f t t h e i r m ark, i n c l u d i n g f j o r d s a lo n g th e B e rin g Sea c o a s t . The mouths o f a l l r i v e r s a re o b s t r u c t e d by o f f s h o r e b a r s . On S a k h a l i n , th e basem ent i s o f p r e - C r e t a c e o u s age r o c k . A m ajor o r o g e n i c p h a se f o l lo w e d th e d e p o s i t i o n o f 66 P lio c e n e age s e d im e n ts . The p r e s e n t r e l i e f i s due to pene- p l a n t a t i o n , renewed u p l i f t , and b lo c k f a u l t i n g d u rin g the T e r t i a r y p e r i o d . W e ll- d e fin e d marine cut t e r r a c e s , at l e a s t 150 m in e l e v a t i o n , ex tend f a r i n l a n d . The b o rd e rs of Okhotsk Sea are of p l a t f o r m - l i k e s t r u c t u r e . The se a b a s in i t s e l f i s composed of a s e r i e s of broken Mesozoic p l a t e s , f r a c t u r e d by movements d u rin g T e r t i a r y tim e . One of th e s e b lo c k s , surrounded by T e r t i a r y mountain s t r u c t u r e s of S a k h a lin and Kamchatka, i s found d e p re sse d in the c e n t r a l p a r t o f the Okhotsk Sea to a depth of about 1,200 m. I t is on t h i s b lo ck t h a t two submarine e l e v a t i o n s r i s e (Academy of S c ien c es Bank and I n s t i t u t e of Oceanology Bank, Figure 1 1 ). Peaks are d i s s e c t e d by a system of submarine canyons thought to be of s u b a e r i a l o r i g i n (Z aton sk y, e t al,. 1961). The f l a t a re a s below the peaks may r e p r e s e n t a sub a e r i a l r i v e r system o f even more a n c ie n t o r i g i n - - a p e n e p l a i n s u r f a c e developed on lan d (Chemekov, 1957). C o n t in e n t a l - ty p e c r u s t i s g e n e r a l l y c o n sid e re d t o con s i s t of th r e e p r i n c i p a l rock complexes: upper s e d im e n ta r y , and two lower ones: a " g r a n i t i c ” and below t h i s a b a s a l t i c la y e r (See F igure 5 4 ). F u rth e rm o re , c o n t i n e n t a l - t y p e c r u s t is g e n e r a l l y 20 km to 30 km t h i c k , and the p r o p a g a tio n ve l o c i t y of l o n g i t u d i n a l waves i s n ot over 6.0 km /sec. O c ea n ic-ty p e c r u s t commonly c o n s i s t s o f two l a y e r s : a t h in sed im en tary l a y e r (m o stly l e s s th an one km t h ic k but re a c h e s 3 km l o c a l l y ) , and a b a s a l t i c lower l a y e r 5 km to 67 10 km t h i c k . The a v e ra g e p r o p a g a t i o n v e l o c i t y o f t h i s type of c r u s t i s a b o u t 7 k m /s e c . Veytseman, e t a l . (1 96 1) have shown t h a t c o n t i n e n t a l , o c e a n i c , and t r a n s i t i o n a l - t y p e c r u s t s o ccu r in the K u r i l e - Kamchatka t o Ja p a n Sea a r e a . The n o r t h e r n O khotsk Sea i s c o n t i n e n t a l - t y p e c r u s t b u t th e deep d e p r e s s i o n s o p p o s i t e B o u sso le S t r a i t c o n s i s t of a t r a n s i t i o n a l - t y p e c r u s t . D e f i n i t e o c e a n i c - t y p e c r u s t e x i s t s on th e e a s t e r n p a r t o f th e i s l a n d a r c , and e x te n d s i n t o th e O khotsk Sea th ro u g h B o u ss o le and K r u z e n s h te r n S t r a i t s . BERING SEA Most o f the Bering Sea i s sh a llo w in the n o r th bu t a deep w a ter b a s in to the s o u t h i s d iv id e d i n t o two d e p r e s s io n s by a major m ountain c h a in ( t h e S h irsh o v Range) ex te n d in g from Cape O l i n t o r s k i southward almost to the A le u t i a n I s l a n d s (Bezrukov and U d in ts e v , 1953). The r e l i e f of the range i s 2,500-m to 3,000-m h ig h , i t s le n g th i s about 700 Irm, and i t s w idth 150 km to 300 km. Like the Japan Sea and Okhotsk Sea, the c o n t i n e n t a l slo p e of the Bering Sea is 20° to 25° and i s h i g h l y d i s s e c t e d (F ig u re 1 1 ). The f l o o r s of th e s e b a s i n s are n e a r l y f l a t . A canyon more than 4,500-m deep p a s s e s between the Kamchatka and Bering I s la n d , a p p a r e n t l y a c o n t i n u a t i o n of the K urile-K am chatka T r e n c h . Evidence p o i n t s to la r g e r e c e n t su b sid e n c e of Bering Sea d e p r e s s i o n s , the s o u th e r n p a r t being the most a n c i e n t . S h irsh o v Range (which s e p a r a t e s th e d e p r e s s i o n s ) was formed d u rin g T e r t i a r y f o l d i n g , and a l s o l a t e r s u b s id e d . The K urile-K am chatka Trench i s young and i s a c t i v e today. I t s n o r th e r n te rm in a l has r e c e n t l y d i s r u p t e d the c o n n ec tio n between Kamchatka and the Komandorski I s l a n d s and i s advanc ing i n t o th e Bering Sea (Bezrukov and U d in tse v , 1953-1955). 68 69 A ccording to Kanayev ( 1 9 6 3 ) , th e s h e l f b r e a k in th e w e s t e r n p a r t of th e B ering Sea i s 167 m, v a ry in g betw een 99 in to 379 m. The mean s h e l f b r e a k f o r the w e s te r n B e rin g Sea i s 167 m. West of S h i r s h o v Range the mean s h e l f b re a k along th e n o r t h i s 228 m, and in K a r a g in s k i G u lf i t i s 162 m in the n o r th w e s t and 151 m in the s o u t h w e s t. S h e lf b r e a k s on the f a r w e s t e r n end of th e A l e u t i a n r i d g e have a mean s h e l f b re a k of 152 m on th e n o r t h and 147 m on the s o u t h . Kanayev s t a t e d t h a t the e a s t Kamchatka s h e l f h a s u n derg on e d i f f e r e n t i a l t e c t o n i c movements as i n d i c a t e d by th e sunken p a r t s o f an e r o s i o n a l t e r r a c e d e e p e r th an the c o n t i n e n t a l s h e l f . I n c lu d e d a re th e m iddle p a r t s of K rono^ki and Kamchatka G u lfs and the s o u t h e r n t i p of Kam c h a tk a ( I l ’y i n , 1961; Kanayev, 1959; and Kanayev and L a r i n a , 1959 ). As much as 87 m d i f f e r e n c e in the d e p th of s h e l f b rea k o c c u rs in K a r a g i n s k i G ulf (B oichenk o, 19 61 ). During Q u a t e r n a r y g l a c i a t i o n the n o r t h e r n p a r t of th e B e rin g Sea was d ry lan d and was co v ered by i c e . On the b a s i s of sed im en t and f o r a m i n i f e r a l s t u d i e s of c o re s ta k e n in th e b a s i n s of w e s t e r n B e rin g Sea, S a id o v a and L i s i t s y n (1961) c o n clu d ed t h a t the b o tto m o f t h i s r e gion underw ent two p e r i o d s of u p l i f t s m easured in term s of h u n dred s and th o u sa n d s o f m e t e r s d u r i n g the W isco n sin and I l l i n o i a n and s u f f e r e d s u b s id e n c e d u r in g th e H olocene and Sangamon. V o lc a n ic a c t i v i t y i n c r e a s e d s h a r p l y d u r in g 70 p e r i o d s of g l a c i a t i o n . The b a s i n bottoms were u p l i f t e d and the d e p o s i t i o n of g l a c i a l d r i f t of g ra v e l and p e b b le s i n t e n s i f i e d . The l a s t str o n g p e rio d of su bsiden ce occurred a t the beginn ing of the Holocene d u rin g which the re g io n o f the contem porary b a s i n s of the Bering Sea su b s id e d more r a p i d l y than did the c o n t i n e n t a l s lo p e ; t h a t i s , s u b s i dence d e c re a se d tow ards sh o re . The a u th o rs r e p o r t t h a t the Bering Sea has reach ed i t s g r e a t e s t depth s in c e the second h a l f o f the Q u a te rn a ry p e r i o d . The Bering Sea i s bounded on the south by the A leu t i a n Arc and on th e n o r t h by S i b e r i a and A la sk a. T hrough out the n o r th e r n p a r t of th e B ering Sea the s h e l f i s re~ m arkedly smooth and l e v e l . B u f f i n g t o n . e t a l . (1950) r e p o rte d t h a t i t has an averag e slo p e of 5 cm per km and i s tho ug ht to be f l a t t e r than any land f e a t u r e of comparable a r e a . Bogoslof I s l a n d , a v o lc a n ic i s l a n d , i s l o c a te d in the B ering Sea n o rth w e st o f U nalaska I s l a n d . According to Smith (1937) the n a tu r e of th e topography does not su g g e st f a u l t i n g . One f a u l t is su g g e ste d about 56 km n o r t h e a s t of the cone and has a downthrow to the west of 200 m or more, but l i t t l e or no movement o c c u rre d a f t e r the cone was formed. The most amazing to p o g ra p h ic f e a t u r e s a s s o c i a t e d w ith Bogoslof are the i n t r i c a t e stre am p a t t e r n s on i t s submerged s l o p e s . Smith concluded t h a t : (1 ) the to p o g ra p h ic f e a t u r e s have a s u b a e r i a l o r i g i n and (2 ) t u r b i d i t y 71 c u r r e n t s have l a t e r m o d ified th e s t r u c t u r e s . George Shor (1964) r e c e n t l y made a s e r i e s of s e ism ic p r o f i l e s a c r o s s the B e rin g S e a . H is c o n c lu s io n s on t h i s stu d y in v o lv e b o th the Bering S e a , the A l e u ti a n R idge, and Trench: I t i s p o s t u l a t e d . . . t h a t th e A l e u ti a n b a s i n o r i g i n a l l y had the same s t r u c t u r e as the P a c i f i c b a s i n and was p a r t of i t . The A l e u ti a n a b y s s a l p l a i n , i n the P a c i f i c b a s i n so u th o f the A l e u ti a n I s l a n d s , has a s lo p e upward to the n o r t h , im plying t h a t s e d i ment forming the a b y s s a l p l a i n was d e riv e d from a n o r t h e r n sou rce now c u t o f f by th e A l e u t i a n t r e n c h and the A l e u t i a n r i d g e . The A l e u ti a n r i d g e was formed as a l i n e of v o l c a n o e s , which b lo ck ed move ment of sedim ent to the s o u th and caused i t to pond in the A l e u t i a n b a s i n . Because of the l a r g e supply of sed im en ts b ro u g h t by t h r e e g r e a t r i v e r s . . . to t h i s r a t h e r sm all b a s i n , a l a r g e t h i c k n e s s of s e d i ment (and p o s s i b l y v o l c a n i c s ) has accum ulated and has d e p re s s e d the o c e a n ic c r u s t and th e m a n tle . In the b a s i n the w ater dep th i s 1 .3 km l e s s th a n in the P a c i f i c Ocean; the l o w - v e l o c i t y l a y e r s a re 4 km t h i c k e r than n orm al, and the m antle and c r u s t a re d e p re s s e d about 3 km. I f sedim ent c o n ti n u e s to be added to f i l l th e b a s i n to s e a l e v e l and th e c r u s t c o n ti n u e s to s in k b e n e a th i t , th e f i n a l sedim ent t h i c k n e s s would be betw een 14 and 18 km (d epending on i t s d e n s i t y ) , and the d e p th t o m antle would be between, 21 and 25 km below se a l e v e l , v a lu e s n o t uncommon under the c o n t i n e n t a l s h e l f . The a d d i t i o n of t h i s much sed im e n t would p ro b a b ly r e s u l t in com p a c t i o n and m e ltin g of th e base s e c t i o n . The d e n s e r , h ig h e r v e l o c i t y ro ck t h u s c r e a t e d could be i n t e r p r e t e d as the c o n t i n e n t a l g r a n i t i c c r u s t . T his a re a i s t h e r e f o r e , a te x tb o o k example of an i n c i p i e n t c o n v e r s io n or an ocean b a s i n I n t o a con t i n e n t a l m ass. (Emphasis added) ALEUTIAN ARC I n t r o d u c t i o n I n 1955, a p p r o x i m a t e ly 600 p r o f i l e s o f th e A l e u t i a n Arc were examined and p h o to g r a p h e d a t th e C o a st and G e o d e t i c S u rv e y . A ll o f t h e s e echogram s were r e c o r d e d on e c h o - s o u n d e rs w hich had c u r v i l i n e a r p l o t s (su c h as u sed on th e NMC-2 e c h o s o u n d e r ) , t h u s making i n t e r p r e t a t i o n and c o m p a ri son d i f f i c u l t . F u r th e r m o r e , tim e and t e c h n i c a l d i f f i c u l t i e s d id n o t p e r m i t p h o t o g r a p h i n g p r o f i l e s from th e s h e l f b r e a k t o t h e f l o o r of th e A l e u t i a n T re n c h . Most p r o f i l e s t e r m i n a t e d a t a b o u t 1,0 00 m. F i n a l l y , echogram s a t th e C o a st and G e o d e tic S urvey were r e s t r i c t e d t o a few l o c a l i t i e s w hich had been c l o s e l y s u r v e y e d , w h i l e o t h e r A la sk a n r e g i o n s had few o r no p r o f i l e s . As a c o n s e q u e n c e , none of t h e 600 p r o f i l e s were used in th e p r e s e n t s t u d y of th e A l e u t i a n A rc . With the e x c e p t i o n o f one VITYAZ p r o f i l e and t h r e e p r o f i l e s by H u r l e y ( 1 9 6 0 ) , th e o n ly u s e a b l e echogram s were t h o s e made by t h e C o a st and G e o d e tic Survey w h ile s h i p s were e n r o u t e t o and from A la s k a to th e West C o a s t o f th e U n ite d S t a t e s . These p r o f i l e s o f t e n c u t th e c o n t i n e n t a l 72 73 s lo p e a t an a n g l e . An a t t e m p t was made to o b t a i n PDR r e c o rd s made i n r e c e n t y e a r s by th e C o a s t and G e o d e tic S urvey a t c l o s e l y - s p a c e d i n t e r v a l s b e tw ee n A la s k a and H a w a ii; how e v e r , t h e s e r e c o r d s a re s t i l l aboard th e s u r v e y s h i p . Nine PDR r e c o r d s ( l a b e l e d CGS on P l a t e 6) and 14 r e c o n s t r u c t e d p r o f i l e s made a v a i l a b l e by M a rtin Y e l l i n , of the C o a s t and G e o d e tic S u rv e y , were p a r t i c u l a r l y u s e f u l . The l a t t e r are c o r r e c t e d f o r sound v e l o c i t y , as i s t h a t made by th e VITYAZ. S ix a d d i t i o n a l r e c o n s t r u c t e d p r o f i l e s of G ib so n ( 1 9 6 0 ) , l a b e l e d A - l to A -6, f i v e from G a te s and G ibson ( 1 9 5 6 ) , l a b e l e d GG 1 t o GG 5, and s i x from G ibson and N i c h o ls ( 1 9 5 3 ) , l a b e l e d GN 1 to GN 6, were a l s o used ( P l a t e 6 ) . A l l of th e p u b l i s h e d p r o f i l e s a re r e c o n s t r u c t e d and have s c a l e s so sm a ll t h a t o n ly g r o s s f e a t u r e s can be r e c o g n i z e d . These do n o t r e v e a l th e complex to p o g ra p h y a c t u a l l y e x i s t i n g on t h e t r e n c h s lo p e and se e n on p u b l i s h e d b a t h y m e t r i c c h a r t s (G a te s and G ib so n , 1956; and G ibson and N i c h o l s , 1953) or on PDR r e c o r d s . H u r le y (1960) p u b l i s h e d t h r e e r e c o n s t r u c t e d p r o f i l e s w hich a re a l s o shown on P l a t e 6 . B ecause so many of t h e p r o f i l e s a re r e c o n s t r u c t e d and have s m a ll s c a l e s , a c o r r e l a t i o n g ra p h ( F i g u r e 12) u t i l i z ing 39 p r o f i l e s shows o n ly th e g r o s s f e a t u r e s ; how ever, s i n c e the to p o g r a p h y i s e x t r e m e l y i r r e g u l a r , p e r h a p s th e s c a l e i s a d e q u a te . O th er p u b l i s h e d p r o f i l e s o f th e t r e n c h i n c l u d e th o s e 74 by M urray (1941 and 1945) and Menard (1 9 6 4 , p . 1 0 0 ). R e s u l t s The A l e u t i a n A rc , c o m p r is in g th e A l e u t i a n I s l a n d s , th e A l e u t i a n T re n c h , and the A la s k a n P e n i n s u l a (and even f u r t h e r e a s t ) a r e g e n e t i c a l l y r e l a t e d . The A l e u t i a n T rench h a s a maximum d e p th o f a p p r o x i m a t e l y 7 ,6 7 9 m and p a r a l l e l s th e convex s i d e of th e A l e u t i a n I s l a n d s . The A l e u t i a n Ridge r i s e s 3,600 m above t h e B e rin g Sea f l o o r and 5,500 m above the P a c i f i c Ocean s e a f l o o r . I t s t o t a l l e n g t h i s a t l e a s t 3,70 0 km, e x te n d in g from w est of A ttu I s l a n d ( F ig u r e 12) e a s tw a rd where i t s h o a l s and t e r m i n a t e s in two subm ar i n e v a l l e y s b etw een Cape S t. E l i a s and Y a k u ta t Bay (M urray, 1 9 4 1 ). The f o o t of the c o n t i n e n t a l s l o p e ( t h a t i s , th e f l o o r o f the tr o u g h ) o f t e n i s l o c a t e d o n l y 50 km to 100 km seaw ard of th e 200-m i s o b a t h . A p r e v i o u s l y u n r e p o r t e d s e a m ount, n e a r l y t h r e e km h i g h o c c u r s in the b o tto m of th e t r e n c h ( P l a t e 6, p r o f i l e C G S -2). From A ttu to a b o u t Adak I s l a n d , th e b o tto m o f th e t r e n c h l i e s a t s l i g h t l y more t h a n 7 km, and seven p r o f i l e s show i t s maximum d e p t h i s r e l a t i v e l y c o n s t a n t . E a s t of Adak I s l a n d t o about l o n g i t u d e 159° W, th e maximum d e p th o f th e t r e n c h v a r i e s from 6 km to 7 km. E a s t o f 159° W, th e f l o o r o f th e A l e u t i a n T rench a g a i n i s s l i g h t l y more th a n 7 km, s h o a l i n g s l i g h t l y to w a rd s the e a s t . Between Kodiak ALEUTIAN ARC sc UNIMAK SEAMOUNT. WIDE PA C IFIC BETW EEN U PPE R t. B E N C H ^ f SC SEAMOUNT 2300 - 5000 M, -6 HORIZONTAL DISTANCE NOT TO SCALE BOTTOM O F TRENCH Figure 12. C o r r e la tio n of t e r r a c e s and other f e a t u r e s on A leutian Arc, U l 7 6 I s l a n d and Cape S t. E l i a s , th e t r e n c h s h o a l s d i s t i n c t l y , r i s i n g from about 7 ,0 0 0 m to 4 ,1 0 0 m o f f Cape S t . E l i a s ( p r o f i l e A -6 ). The s h e l f edge of the A l e u t i a n Ridge v a r i e s in d e p th from 200 m to 900 m, or more, and i s a b s e n t i n s e v e r a l a r e a s . Pronounced t e r r a c e s o ccu r on t h e s h e l f and upper c o n t i n e n t a l slo p e (G ates and G ib so n, 1956; and S c r u to n , 195 3). The most pronounced deep t e r r a c e on th e c o n t i n e n t a l slo p e i s the s o - c a l l e d A l e u t i a n Bench. I t was f i r s t d e s c ri b e d by Murray (1945) in th e e a s t e r n A l e u t i a n s . G ates and Gibson were u n a b le to d e c id e w h e th er the bench e x i s t e d in the c e n t r a l A l e u t i a n s , b u t i t was r e p o r t e d i n the f a r e a s t e r n p a r t o f the A l e u t i a n Arc by Gibson and N ic h o ls . G a tes and Gibson n o te d t h a t th e A l e u t i a n -Bench was 20 km to 40 km wide in the w e s t e r n p a r t and c o n s i s t e d of two to p o g ra p h ic u n i t s . They s t a t e d t h a t th e i n s i d e of the b en ch , o p p o s i t e the mouths of Murray and Heck Sea V a l l e y s , as w e l l as the base of the convex s l o p e so u th o f K iska and A m chitka, has the a p p ea ra n c e of a r e g i o n of s e d i m e n t a t i o n and s h a llo w e r o s i o n . The o u t s i d e o f th e bench c l o s e s t to the t r e n c h has c o n s i d e r a b l y more r e l i e f w i t h c o n e s, k n o l l s , crude e l l i p t i c a l d e p r e s s i o n s , and b ro ad v a l l e y s . In th e r e g i o n s t u d i e d by G a tes and G ibson , th e y s t a t e d t h a t ’’th e Bench l a c k s marked l i n e a r to p o g r a p h i c f e a t u r e s t h a t f i t the c r i t e r i a f o r s t r u c t u r a l i n t e r p r e t a t i o n . ” Heck and Murray Sea V a lle y s and Rat I s l a n d Canyon t e r m i n a t e a t the i n n e r 77 edge of th e b e n c h , s u g g e s t i n g t h a t th e v a l l e y s may be o f f a u l t o r i g i n and a r e s t r u c t u r a l l y c o n t r o l l e d by th e bench w hich i s a l s o a s t r u c t u r a l f e a t u r e . G ibson and N i c h o l s (1953) s t a t e d t h a t the A l e u t i a n Bench i s h i g h l y i r r e g u l a r i n r e l i e f and s u g g e s te d i t m ight be a r e c e n t s t r u c t u r a l f e a t u r e . The bench i s c o n tin u o u s from as f a r w e st as p r o f i l e s a re a v a i l a b l e (1 7 3 ° 30* E ) . I t seems to c o r r e s p o n d w i t h a wide p l a t f o r m a t a b ou t 3,000 m on th e K u rile -K a m c h a tk a T rench s lo p e ( P l a t e 4 and F ig u r e 1 0 ) . Nowhere d o es i t ap p e a r t o be a l e v e l p l a t f o r m h o r i z o n t a l l y , a lt h o u g h s e v e r a l o f the p r o f i l e s show i t to be f l a t norm al t o th e s l o p e . In many p r o f i l e s i t i s n o t a wide f l a t f e a t u r e so c o n s p i c uous as in M u rra y ’ s p r o f i l e s ( 1 9 4 5 ) , b u t may be r e c o g n iz e d o n ly as an i r r e g u l a r f e a t u r e b u t s t i l l c o r r e l a t i v e w ith a d j a c e n t p r o f i l e s ( F i g u r e 1 2 ) . I t v a r i e s from as deep as 5,000 m to as s h a l lo w as 3,00 0 m in t h e w e s t e r n A l e u t i a n s , and may be even s h a l l o w e r i f i t c o r r e l a t e s w i t h s h a llo w e r f e a t u r e s . The d i s p o s i t i o n of th e b ench a t Unimak, or a t the w e s t e r n t i p o f A la sk a P e n i n s u l a , i s i n c o n c l u s i v e ; i t may bend downward from 4 ,0 0 0 m t o 5 ,0 0 0 m and be r e p r e s e n t ed by any one of a number of f e a t u r e s t h a t can be t r a c e d to Cape S t . E l i a s a t d e p th s of about 5,000 m and 3,0 0 0 m, or i t may c o n s i s t of a w e l l - d e f i n e d and c o r r e l a t i v e f e a t u r e a t d e p th s r a n g i n g from 1 ,0 0 0 m to 3,00 0 m. Where th e bench i s most pronounced in t h e w e s t e r n A l e u t i a n s , i t seems to fo llo w a m ajor to p o g ra p h ic change s e p a r a t i n g the upper and lower tr e n c h slope (F ig u re 12 - heavy l i n e ) . I f t h i s c r i t e r i a i s used f a r t h e r e a s t , th e n the t r e n c h most p r o b a b l y i s r e p r e s e n te d by f e a t u r e s a t about 3,000 m. The A leu t i a n Bench a ls o can be i d e n t i f i e d to the w e ste rn edge of th e c h a r t p rep a red by Gibson and N ic h o ls . Another major to p o g ra p h ic f e a t u r e i s th e P a c i f i c B ig h t, a wide p la tf o r m in the w e s te r n A l e u ti a n s (F ig u re 12, p r o f i l e s GN-1 to a t l e a s t CGS-5). I t i s l e s s co ntin u o u s than the A le u tia n Bench, b u t l o c a l l y i s a pronounced f e a t u r e . From Unimak to Cape S t . E l i a s , th e tr e n c h slo p e has a d i s t i n c t f e a t u r e a t d e p th s of about 1,000 m, deepening to p e rh a p s 2,200 m a t the f a r e a s t e r n p a r t of th e t r e n c h . Another f e a t u r e having v a rio u s to p o g r a p h ic forms can be t ra c e d more or l e s s c o n tin u o u s ly from w est o f Kodiak I s land to Cape S t . E l i a s a t about 1,000 m. While more p r o f i l e s would g r e a t l y improve the accuracy of Figure 12, r e s u l t i n g in major m o d i f i c a t i o n in the shape o f many of the c o r r e l a t i v e f e a t u r e s , s u f f i c i e n t d a t a i s a v a i l a b l e to draw two major c o n c l u s i o n s : (1 ) s e v e r a l d i s t i n c t t e r r a c e s e x i s t , some of w hich can be t r a c e d over g r e a t h o r i z o n t a l d i s t a n c e s , and (2 ) to p o g ra p h ic f e a t u r e s a re not l a t e r a l l y h o r i z o n t a l , s u g g e s tin g w a rp in g . Most d e formed f e a t u r e s seem to be more c l o s e l y r e l a t e d to the s h e l f edge than to the shape of the l o n g i t u d i n a l p r o f i l e of 7 9 the tr e n c h f l o o r . (However, s i n c e the tre n c h i s a re g io n of a c t i v e s e d i m e n ta t io n t h i s means l i t t l e in d e c ip h e r in g the t e c t o n i c h i s t o r y of the A l e u t i a n s . ) That th e tre n c h slo p e i s co m plicated i s a p p a r e n t from th e PDR t r a c i n g s ( p r o f i l e s l a b e le d G ) , s u g g e s tin g t h a t the re g io n has been one of major te c to n is m . Submarine canyons are u n u s u a l ly common on the c o n t i n e n t a l s l o p e , w ith s e v e r a l of the canyons lin e d up w ith d e p r e s s i o n s on the s h e l f . In a d d i t i o n , g r e a t a sy m m etrical tr o u g h s , tr e n d in g a t an angle about 60° to the t r e n c h , o c cur on the n o r th slope of the w e s te r n end of th e A l e u t i a n s . S e v e ra l tro u g h s are 50 km in le n g th and a re s t r a i g h t . Bowers Bank i s an a r c u a t e , submerged rid g e 500-km long t h a t j o i n s the A l e u ti a n Ridge a t l o n g it u d e 180° to the so uth ern m o st p o i n t of the A le u ti a n Ridge and A l e u ti a n Trench (F ig u re 1 1 ). I t r i s e s s t e e p l y from a r e l a t i v e l y f l a t Bering Sea f l o o r a t 3,730 m to d e p th s l e s s than 1,280 m ( N i c h o l s , P e r r y and Kofoed, 1964). The s h a l lo w e s t d e p th i s 119 m. Bowers B asin i s about 200 m deeper th a n the s u r rounding Bering Sea f l o o r on the n o r t h and e a s t of Bowers Bank. Large f l a t a r e a s o ccur on th e Bank upper s u r f a c e and i n n e r s lo p e s a t d e p th s of 500 m, 900 m, and 1,800 m. A l i n e of seamounts to the w est of Bowers Bank forms a con t i n u a t i o n of th e s t r u c t u r e , e v e n t u a l l y c o n n e c tin g n e a r Kam c h a tk a P e n i n s u l a (F ig u re 11). P r o f i l e s seaward of the Trench show sm oother 80 t o p o g r a p h y , w i t h no e v id e n c e o f t e r r a c e s o f c a n y o n s . The c o n s p ic u o u s s w e ll on c l o s e l y spaced p r o f i l e s (A, and 1 t o 14) i s p a r t i c u l a r l y i n t e r e s t i n g . A c c o rd in g to H urley ( 1 9 6 0 ) , t h i s r i d g e or s w e l l , p a r a l e l l i n g the t r e n c h , i s a b s e n t at th e e a s t e r n end o f t h e t r e n c h . T his f e a t u r e a p p e a r s t o be common on th e seaw ard s i d e of a l l t r e n c h e s . G eology The A l e u t i a n I s l a n d s are c h i e f l y of v o l c a n i c o r i g i n bu t some s e d i m e n ta r y r o c k s a re e x p o s e d . C o a ts (1956) and o t h e r s have c o n clu d ed t h a t th e i s l a n d s assumed t h e i r p r e s e n t form and d i s t r i b u t i o n in t h e T e r t i a r y . G a te s and Gibson (1956) summarized th e g e o lo g y of Near I s l a n d s and R at I s l a n d s , t h a t i s , t h e A l e u t i a n s w est of l o n g i t u d e 1 8 0 °. In M esozoic ( ? ) and e a r l y to m id d le T e r t i a r y tim e , v a r i o u s s e d i m e n ta r y r o c k s were l a i d down and were i n t r u d e d by g ab bro and o t h e r ig n e o u s r o c k s , fo llo w e d by a m ajor u p l i f t , e r o s i o n , much f a u l t i n g , and some f o l d in g . In L a te T e r t i a r y tim e , f u r t h e r m arin e s e d im e n ts were d e p o s i t e d and much v o l c a n i c a c t i v i t y o c c u r r e d . Normal f a u l t i n g h a s c o n tin u e d t o the p r e s e n t . L o c a l w a rp in g and o t h e r e v id e n c e shows s e v e r a l f l u c t u a t i o n s of s e a l e v e l r e l a t i v e t o l a n d . The u n c o n f o r m ity s e p a r a t i n g Lower t o M iddle T e r t i a r y ro c k s from Upper T e r t i a r y r o c k s has been o b s e r v e d a lm o st the e n t i r e l e n g t h of the A l e u t i a n Arc and r e p r e s e n t s a 81 major t u r n in g p o i n t in th e g e o lo g ic h i s t o r y of th e r e g i o n . Below the u n c o n fo rm ity , ro ck s a re m o s tly a s p i l i t i c s u i t e o f m arine se d im e n ts , m arine p y r o c l a s t i c s , and p i l l o w l a v a s . Upper T e r t i a r y and Q u a te rn a ry age ro c k s are m o s tly s u b a e r i a l or sh a llo w w a t e r , p y r o c l a s t i c s , and s u r f a c e l a v a f l o w s . G l a c i a l e v iden ce s u g g e s ts the i s l a n d s were about t h e i r p r e s e n t s i z e and shape d u rin g the l a t e P l e i s t o c e n e epo ch. The A le u tia n Arc i s s t i l l t e c t o n i c a l l y a c t i v e , w ith numerous stro n g e a r t h q u a k e s , a c t i v e v o lc a n o e s , and much e v id e n ce of f a u l t i n g . Some f a u l t s have v e r t i c a l d i s p l a c e ments o f s e v e r a l hundred m e te r s . Movement was v e r t i c a l on some and t r a n s v e r s e on o t h e r s . The r e g i o n a l d ip of th e ro c k s i s s t e e p to the n o r t h along the n o r t h c o a s t of A ttu and g e n t l e to the sou th on A g a ttu . According to Gates and G ibson, ’’th e g e o lo g ic and t o p o g r a p h ic ev id e n ce s u g g e s ts t h a t th e c r e s t of the A l e u t i a n R id g e, ex cept f o r the s t r a t o v o lc a n o e s , i s a s u r f a c e of e r o s i o n a c r o s s the top of the Ridge . . E u s t a t i c sea l e v e l changes d u rin g th e P l e i s t o c e n e epoch p r o b a b l y a c count f o r the numerous sh a llo w w a te r t e r r a c e s and u p l i f t e d , m arine c u t t e r r a c e s . G ates and Gibson b e l i e v e t h a t th e n o r t h i n s u l a r slo p e of th e A l e u ti a n Ridge i s p ro b a b ly a g r e a t f a u l t s c a r p m ark ing a fundam ental s t r u c t u r a l e le m e n t. The s lo p e i s rem ark a b ly s t r a i g h t , has a g r a d i e n t of about 15°, and i s 82 c o n s i d e r e d as a p r o b a b l e d i p sloped A lignm ent of v o lc a n o e s along th e e a s tw a r d e x t e n s i o n o f th e n o r t h i n s u l a r s lo p e a p p e a r s to s u p p o r t th e c o n c l u s i o n t h a t th e s lo p e r e p r e s e n t s a f r a c t u r e zone. In c o n t r a s t to th e n o r t h i n s u l a r s l o p e , the s o u th s l o p e i s c o n s i d e r a b l y more complex and i t s o r i g i n more d i f f i c u l t t o e x p l a i n . Much e v id e n c e e x i s t s f o r a f a u l t o r i g i n f o r many of th e l a r g e s e a v a l l e y s . G a te s and Gibson s u g g e s t e d t h a t th e A l e u t i a n Bench may mark a s t r u c t u r a l d i s c o n t i n u i t y , p e r h a p s a t h r u s t zone d i p p in g below th e i s l a n d s . Gunn ( 1 9 4 7 ), West ( 1 9 5 1 ) , and B e n io f f (1954) p r e v i o u s l y p ro p o se d s u c h a t h r u s t f a u l t . Menard (1964) a l s o b e l i e v e s t h a t the A l e u t i a n I s l a n d s have been s u b j e c t e d to b o th n o rm al and w ren ch f a u l t i n g t r e n d i n g p a r a l l e l t o t h e subm arine t r o u g h . He s t a t e s t h a t th e s o u th s lo p e o f the A l e u t i a n Ridge i s o f f s e t l e f t - l a t e r a l l y 80 km to 100 km a t M urray Sea V a l l e y . Menard a l s o b e l i e v e s move ment on the w e s t e r n end of the A l e u t i a n Ridge has s t r a i g h t ened th e a r c . He b e l i e v e s th e b e n c h e s a re th e u p p e r s u r f a c e of f a u l t b l o c k s w hich have moved down i n t o th e t r e n c h es and, as t h e y moved, were r o t a t e d away from th e t r e n c h e s so t h a t th ey have become e x c e l l e n t trjyps f o r s e d i m e n ts . <r ; W o o lla rd , O s te n s o , T h i e l , and B o n in i (1-960) showed t h a t a s t e e p , p o s i t i v e anomaly g r a d i e n t p a r a l l e l s th e A l e u t i a n s t o the s o u t h and s u g g e s t s c r u s t a l t h i n n i n g in t h a t d i r e c t i o n s i m i l a r t o t h a t o b se rv e d a t th e c o n t i n e n t a l 83 b o r d e r s . A ccording to a r e c e n t paper by P e t e r , E l v e r s , and Y e l l i n (1964) m agnetic and g r a v i t y anom alies sou th of C her- ik o f I s l a n d s a c r o s s th e A l e u ti a n T rench i n d i c a t e a f i s s u r e zone in th e c e n te r o f the tren c h and the p re s e n c e of the m antle 4 km below th e tre n c h f l o o r . They a ls o b e li e v e t h a t a d d i t i o n a l f r a c t u r e zones are i n f e r r e d on the so u th e rn (seaw ard) p a r t of th e t r e n c h . The d a t a su g g e st the e x i s t ence of a r i d g e , c o n s i s t i n g of igneous rock under the n o r t h e r n s l o p e . The a u th o rs n o te the e x i s t e n c e of numerous l i n e a r f e a t u r e s ( p a r a l l e l to the a x is of th e tr e n c h ) and b e l i e v e th e s e i n d i c a t e i n t e n s e f a u l t i n g . They b e lie v e the d a ta su p p o rt the th e o r y t h a t the c o n t i n e n t a l margins and tr e n c h e s a re t e n s i o n a l f e a t u r e s and th a t the r i d g e s under the s h e l f and the u p t h r u s t of sedim ents .in to mountain c h ain s are fo rc e d up by h i g h ly a c t i v e magmas. N ic h o ls , P e r r y , and Kofoed (1964) b e l i e v e t h a t Bowers Bank and Basin o r i g i n a t e d along a s e r i e s o f f a u l t s . The main r i d g e of Bowers Bank i s b e lie v e d to be a major r e v e r s e f a u l t b lock t h a t e x te n d s from Pochnoi Canyon to the n o r t h w e s te r n end of the bank. The g e n t l e r (con cave) slope of the bank i s a secondary f a u l t b lo c k t h a t has been t i l t e d up a t the same time the main rid g e was form ed. The a l i g n ment of Murray Canyon and K iska I s l a n d w ith the w e ste rn end of the f a u l t b lock i s more th a n c o in c id e n c e . L ikew ise, Bowers B asin i s a l a r g e down-dropped f a u l t b lo c k , or 84 grab e n . Bowers Bank and a s s o c i a t e d f e a t u r e s i s n e i t h e r a r e gion of a c t i v e volcanisxn nor s e i s m i c i t y . The s h a l lo w e s t a re a s (which are f l a t ) , as w e l l as o th e r f l a t a r e a s along th e f l a n k s of th e r i d g e , a r e p l a t f o r m s which p r o b a b ly were b ev eled by m arine e r o s i o n a t wave base or a re s t r u c t u r a l l y c o n t r o l l e d f e a t u r e s . N ic h o ls , P e r r y , and Kofoed (1964) b e l i e v e the A l e u t i a n I s l a n d s a re e i t h e r a l a r g e r e v e r s e f a u l t or a re a l a r g e g e a n t i c l i n e . The A l e u ti a n Arc i s s t i l l t e c t o n i c a l l y a c t i v e , bu t Bowers Bank and B asin a re n o t . They s u g g e s t t h a t f a u l t i n g , form ing Bowers Basin and Bank, o c c u rre d in the l a t e C re ta c e o u s or e a r l y T e r t i a r y tim e , d u rin g the L a ra - mide Orogeny. Menard (1964) su g g e ste d t h a t a tre n c h may have once e x i s t e d on the convex s id e of Bowers Ridge but has been b u r ie d by s e d im e n ts . In s o u t h e a s t A la sk a , n e a r the r e g i o n of Y a k u tat Bay to Cross Sound, th e r e i s e v id e n c e i n th e p r e s e n t m ountains of r e g i o n a l upwarping of the o rd e r of 1,000 m n e a r the c o a s t . I t i s assumed by P e a c o c k (1935) t h a t t h i s e l e v a t i o n took p la c e in P l i o - P l e i s t o c e n e tim e s . In the C ro ss Sound a r e a , h ig h m ountains c o n s i s t i n g of metamorphic and igneous ro c k s of p r e - T e r t i a r y age b o r d e r th e c o a s t . N orth of C ross Sound, th ro u g h L it u y a Bay and Y a k u tat Bay and beyond, a narrow c o a s t a l p l a i n e x i s t s o u t s i d e the m ountain range which c o n s i s t s o f s t r a t a most p r o b a b ly of P l i o - P l e i s t o c e n e 85 a g e s . In t h e K en ai P e n i n s u l a and Kodiak I s l a n d a r e a , sh a rp t o p o g r a p h i c r e l i e f s u g g e s t s r e c e n t and v i o l e n t p e r i o d s of o r o g e n y . As r e p o r t e d by the C o a st and G e o d e tic S u rv e y , the e l e v a t i o n o f the a x i a l s t r u c t u r e s d e c r e a s e from th e n o r t h e a s t , where e l e v a t i o n s are 3,000 m to about 1,800 m a t the f o o t of Kenai P e n i n s u l a , to 1,2 0 0 m from Kodiak I s l a n d . From th e a x i a l s e r r a t e d r i d g e s t h e e l e v a t i o n s f a l l o f f r a p i d l y ( a s a r u l e ) to w a rd s th e o c e a n . L i n e a t i o n s show a p ro m in e n t n o r t h e a s t w a r d t r e n d p a r a l l e l to th e A la s k a P e n i n - < s u l a and the A l e u t i a n c h a in and s e v e r a l o f th e l a r g e r f a u l t s have been t r a c e d to t h e B e rin g Sea th ro u g h s o u t h e a s t e r n A l a s k a . A l l o f the m ajo r t e c t o n i c u n i t s more or l e s s p a r a l l e l th e p r e s e n t d a y s h o r e l i n e . These a r e , from la n d to w a rd s th e o c e a n , th e T a l k e e t n a g e a n t i c l i n e , Matanus g e o s y n c l i n e , S h e l i k o f t r o u g h , S e l d o v i a g e a n t i c l i n e , and the Chugach M o u n tain s g e o s y n c l i n e . The r o c k s v a ry in age from p e rh a p s P re c a m b r ia n t o Q u a t e r n a r y and i n c l u d e p o s s i b l e ma r i n e M iocene and P l i o c e n e . The Chugach M ountains g e o s y n c l i n e c o n s i s t s of l a r g e l y Upper C r e ta c e o u s age r o c k s , p e r haps as t h i c k as 6 ,0 0 0 m. In r e g a r d t o th e t e c t o n i c s o f t h i s a r e a , K a r l s t r o m (1960) r e p o r t e d as f o l l o w s : " L a t e s t Q u a t e r n a r y movement se e m in g ly was c o n c e n t r a t e d a lo n g the C h u g a c h - S t . E l i a s f a u l t of s o u t h e r n c o a s t a l A l a s k a . E l e v a t e d s t r a n d l i n e s and m arine d e p o s i t s alo n g t h e c o a s t s o u t h of th e f a u l t r e co rd n o t a b l e t e c t o n i c d i s p l a c e m e n t d u r i n g l a t e Q u a t e r n a r y 86 tim e . In c o n t r a s t , the e v id e n c e a lon g th e c o a s t n o r t h of the f a u l t i n d i c a t e s e s s e n t i a l c r u s t a l s t a b i l i t y over th e same tim e i n t e r v a l . ” The P r i n c e W illiam Sound a r e a shows s u b s id e n c e in r e l a t i v e l y r e c e n t time b ut here th e e v id e n c e i s in c o n c lu s iv e s in c e ev id e n ce of r e v e r s a l s in w hich s e v e r a l l o c a t i o n s show emergence a ls o e x i s t . Follow ing th e 1964 e a rth q u a k e in P r i n c e W illiam Sound, th e C oast and G e o d etic Survey P r e l i m i n a r y R eport (USC & GS, 1964) s t a t e s t h a t i t ap pears the r e g i o n on the e a s t s id e of th e f a u l t zone ( t h a t i s , on the e a s t s id e of the Chugach g e o s y n c l i n e ) went up and the w est s id e went down. P a r t s o f Y a k u tat Bay s h o r e l i n e were e l e v a te d 14 m d u rin g a s e r i e s of e a r t h q u a k e s e x te n d in g over a p e r io d of 17 d a y s. C o n s id e r a b le e v id e n c e a l s o shows s u b s id e n c e as i n d i c a t e d by drowned t r e e t r u n k s . T arr and Mar t i n (1906) r e p o r t e d some of the sh o re l i n e changes along the c o a s t of A la sk a and in c lu d e d some o f the o b s e r v a t i o n s made by Vancouver in th e v i c i n i t y of Chalmers Bay in P r i n c e Henry Sound. He commented t h a t he had never seen such a r a p id encroachm ent of th e s e a as had a p p a r e n t l y oc c u rr e d sin c e the v i s i t of o t h e r E n g li s h e x p l o r e r s some seven y e ars e a r l i e r . Jo rd a n (1958) r e l a t e d a r a t h e r i n t e r e s t i n g h i s t o r i c a l account of a form er sh o a l in th e G ulf o f A lask a. F i r s t r e c o rd e d in s t a n c e of t h i s s h o a l , term ed Pamplona Rock, ap p a r e n t l y appeared in 1779. E v id ence shows i t r e p r e s e n t e d a major n a v i g a t i o n a l h a z a rd s in c e a t l e a s t one R u ss ia n s h ip ran aground on th e rock ( o r s h o a l ) . For the n e x t hundred y e a r s i t was se en or rec o rd ed on v a r i o u s c h a r t s ? however, by 1883, the C o ast P i l o t , p r e p a r e d by th e C oast Surv ey, s a i d t h e r e was not s u f f i c i e n t e v id e n ce t o i n d i c a t e t h a t such a s h o a l e x i s t e d and t h e r e f o r e removed i t as a n a v i g a t i o n a l h a z a rd from i t s c h a r t s . C oast and G e o d e tic Survey s h i p s on v i r t u a l l y e v e r y t r i p from or to A lask a in the v i c i n i t y of t h i s h i s t o r i c f e a t u r e have a tte m p te d t o r e l o c a t e Pamplona Rock. D e t a i l e d su rv e y s have been made in th e a r e a and e v id e n c e shows t h a t t h i s fo rm e r s h o a l i s c o n s i d e r a b l y below s e a l e v e l and does n o t r e p r e s e n t a n a v i g a t i o n a l h a z a rd . J o r d a n showed t h a t t h i s form er s h o a l l i e s on a r i d g e which he h as termed the Pam plona S e a r i d g e . I t i s l o c a t e d a p p ro x im a te ly 59° 30' N and 142° 30* W. The s e a r i d g e i s about 28-km long and ap p ea rs to be e x tr e m e l y ro ck y and today l i e s more than 120 m below se a l e v e l . J o r d a n co n clu d ed t h a t Pamplona S e a r id g e i s bed ro ck s t r u c t u r e which was u p l i f t e d i n the complex b u i l d i n g o f the C h u g a ch -S t. E l i a s Range and has fo u n d e re d su b s e q u e n t to i t s d i s c o v e r y . The f o u n d e r in g p r o b a b l y o c c u r r e d g r a d u a l l y , f o r any such g r e a t change or c h an g e s would have been i n d i c a t e d by r e p o r t s of l o c a l e a r th q u a k e s and ts u n a m i s . The absence of such r e p o r t s m ight n o t be c o n c l u s i v e b e cause of the l o c a t i o n (37 km to 55 km) o f f s h o r e from the bend in t h a t u n i n h a b i t e d c o a s t l i n e . L o c a l e a r t h q u a k e s 88 and v o lc a n ic e r u p t i o n s around the rim of the G ulf of A la s ka have o ccu rred f r e q u e n t l y . Foundering a p p ea rs to be i n d i c a t e d by embayments on each s id e of the s e a r i d g e . Gibson (1958) d e s c rib e d a l a r g e tro u g h d i r e c t l y o ff Y akutat Bay seaward of Pamplona S e a r id g e . T h is c o n s i s t s of a t r e n c h p a r a l l e l i n g the A l e u ti a n Trench a t - a d i s t a n c e of 110 km from the tre n c h f o r a d i s t a n c e of 460 km. This i s a f i s s u r e 900 m to 1,300 m deep and f o r the most p a r t i t i s 4-km to 6-km wide over most of i t s d i s t a n c e . This trough e x i s t s at the bottom of the c o n t i n e n t a l slo p e and has a g r a d i e n t of a p p ro x im ate ly 8 m per km. Gibson con c lu d e s i t to be of t e c t o n i c " o r i g i n . He p o i n t s out t h a t i t b o rd e rs the major g e o sy n clin e of th e A le u tia n T rench, and t h a t i t s axis fo llo w s a r e v e r s e curve in co nfo rm ity w ith the tr e n d of the t e c t o n i c elem ents mapped on s h o r e . He s u g g e s ts f u r t h e r t h a t ’’the trough may mark the s o u th e a s t edge of the g e o sy n c lin e of the A le u tia n Trench and t h a t the t h i r d p a r a l l e l e x te n s io n [of the C hugach-S t. E l i a s F a u l t] c o n s t i t u t e s a n o r t h e r l y and e a s t e r l y boundary of the G ulf of A laska T e r t i a r y P ro v in c e and has been mapped from L it y u a Bay to the Copper River D e l t a , and i n f e r r e d to curve to the so uth w est along the c o n t i n e n t a l s h e l f beneath the se a to c ro s s Kodiak Is la n d im m ed iately n o r t h of the s o u th e r n c o a s t l i n e . ” Known i n s t a n c e s of su bsiden ce a t Y akutat Bay are d o c umented fo llo w in g a stro n g earth q u ak e in r e c e n t y e a r s . At 89 Pamplona S e a r i d g e t h e s e may be a s s o c i a t e d w i t h su b s id e n c e n e a r the a x i s ( e x t e n d e d ) o f t h e A l e u t i a n T r e n c h . T h is s u b s i d e n c e , and t h e u p l i f t o f the G u lf o f A la s k a T e r t i a r y P r o v i n c e a lon g the m arg in s of th e g e o s y n c l i n e , would f i t a p a t t e r n of d e f o r m a t i o n c o n s i s t i n g of downwarping i n th e zone of w eakness and h i g h - a n g l e t h r u s t f a u l t i n g along th e m arg in s a t t e n d i n g the l a t e r a l s h o r t e n i n g and f o l d i n g of t h e g e o s y n c l i n e p r i s m . In c e r t a i n l o c a l a r e a s (su c h as V a ld ez ) t h e r e was e v i d e n t i n d i c a t i o n - o f s u b s i d e n c e . For ex am p le, th e r e p o r t e d h a rb o r d e p th s had changed from 10 m t o 40 m and d i v e r s r e p o r t e d deep f i s s u r e s i n th e o f f s h o r e a r e a . WEST COAST OF ALASKA AND CANADA I n t r o d u c t i o n A t o t a l of 26 p r o f i l e s were a v a i l a b l e f o r the w est c o a s t of A laska and Canada, s t r e t c h i n g from Ju n e au , A lask a, to the S t r a i t s of Juan de Fuca. Two p r o f i l e s ( P l a t e 7, p r o f i l e s V 2 9-3 , and V 29-4) were o b ta in e d from VITYAZ c r u i s e s ; th r e e were made by the U n i v e r s i t y of W ashington (UW 199-1, UW 199-4, and UW 1); and the rem aining were ob t a i n e d from v a r io u s C oast and G e o d etic Survey c r u i s e s . P r o f i l e s C -l to C-7 were d e riv e d from Gibson (1960) and were based upon soundings made by the Coast and G e o d e tic S urvey. Nine of the 26 p r o f i l e s were grouped around th e e n tr a n c e to Juan de Fuca. P r o f i l e s by G ibson, VITYAZ, and the U n i v e r s i t y of Washington have been c o r r e c t e d fo r sound v e l o c i t y ; the r e maining p r o f i l e s are u n c o r r e c t e d . With th e e x c e p tio n of p r o f i l e s la b e le d CGS or numbered 90, 91, 98, and 99, r e s p e c t i v e l y , a l l a re r e c o n s t r u c t e d from i n d i v i d u a l sound in g s ; the rem aining are d i r e c t t r a c i n g s of PDR r e c o r d s . T w enty-four p r o f i l e s were used t o c o n s t r u c t F ig u re 13. I t should be n oted t h a t the use of r e c o n s t r u c t e d p r o f i l e s p u ts s e r i o u s l i m i t a t i o n s on i d e n t i f y i n g sm all 90 9 1 ALASKA & CANADA (W EST CO AST) KM u BA SE O F C O N T IN E N T A L S L O P E H O R IZ O N T A L D IS T A N C E NOT T O SC A LE F ig u re 13. C o r r e l a t i o n o f t e r r a c e s and o t h e r f e a t u r e s on the c o n t i n e n t a l slo p e o f t h e w est c o a s t o f A la sk a and Canada. 92 f e a t u r e s . T h is i s p a r t i c u l a r l y t r u e in th e u se of G i b s o n 's p r o f i l e s . At b e s t , P l a t e 7 and F ig u re 13 show m a c ro b a th y - m e t r i c f e a t u r e s . The names of m ajor b a t h y m e t r i c f e a t u r e s and a g e n e r a l b a t h y m e t r i c c h a r t have b e en p u b l i s h e d by McManus ( 1 9 6 4 ) . P i c k a r d (1956) has shown many c r o s s - s e c t i o n a l and l o n g i t u - d irra l s e c t i o n s o f B r i t i s h Columbian f j o r d s . B a n c r o f t ( 1 9 1 3 ) , C a r t e r ( 1 9 3 3 ) , P e a c o c k ( 1 9 3 5 ) , C o c k b ain ( 1 9 6 3 ) , H u r le y ( 1 9 6 0 ) , Menard ( 1 9 6 4 ) , G ibson ( 1 9 6 0 ) , B o stock (1948), Dolmage ( 1 9 2 2 ) , and Toombs (1956) have d i s c u s s e d th e f j o r d s , the s e d i m e n t s , and th e g e n e r a l g e o lo g y o f the. r e g i o n ; o n ly H u r l e y ' s p a p e r shows p r o f i l e s a c r o s s th e c o n t i n e n t a l s l o p e . The o n s h o re and o f f s h o r e g e o lo g y a re e s s e n t i a l l y unknown (C o c k b a in , p e r s o n a l c o m m u n ic a tio n ), as shown by th e f a c t t h a t B a n c r o f t ' s p a p e r i s s t i l l th e b a s i c r e f e r e n c e f o r t h i s r e g i o n . Resu 1 t s The s h e l f b r e a k o c c u r s betw een 150 m and 400 m (T a b le 2 ) . The s h e l f edge may a p p e a r as a d i s t i n c t change in s l o p e , as a g e n t l y ro u n d ed convex s l o p e , or c o n s i s t of a s e r i e s o f s t e p s or r i d g e s n e a r the s h e l f b r e a k . U sing th e 200-m i s o b a t h a s the s h e l f b r e a k , t h e s h e l f i s o n l y 2-km wide a t th e s o u t h e r n end of Queen C h a r l o t t e I s l a n d s , i n c r e a s i n g to 65 km n o r t h o f Dixon E n t r a n c e . I t d e c r e a s e s t o 22 km s o u th of G ross Sound, and from C r o s s Sound to 93 Cape S t . E l i a s i t v a r i e s between 65 km and 102 km. De p r e s s i o n s to 290 m occur on the s h e l f and vary from 120 km to 59 km in w id th (Murray, 1941 and H o lte d a h l, 1958). Table 2. Approximate S h e lf Breaks, West Coast of A laska and Can ad a NORTH LATITUDE DEPTH (m) 58° 200 56° 200 - 250 55° 200 54° 250 - 350 53° 100 - 250 52° 150 49° 250 No t y p i c a l c o n t i n e n t a l r i s e o c c u rs on the West C oast o f N orth America between Juneau to Mendocino S e a sca rp in N o rth ern C a l i f o r n i a . In the n o r t h e r n p a r t of th e Gulf of A la sk a , t h e c o n t i n e n t a l slo p e e i t h e r t e r m in a t e s a b r u p t l y or has a c o n t i n e n t a l r i s e which i s only a few hundred me t e r s high between the base of the slo p e and the a b y s s a l sea f l o o r a t 2,000 m to 3,000 m. The b ase of the c o n t i n e n t a l slo p e u s u a l l y is lo c a te d a t a d epth of 2,500 m to s l i g h t l y l e s s than 3,000 m. The 2,000-fm (3 ,6 0 0 m) con to u r i s l o c a te d 750 km to 800 km from th e c o a s t between Juneau to Mendocino S e a sca rp . At the s c a rp the 2,000-fm 94 i s o b a t h bends s h a r p l y tow ard th e c o a s t ( s e e in d e x c h a r t , . , low er l e f t o f P l a t e 7 ) . Because th e g r a d i e n t i s so g e n t l e seaw ard o f the lower c o n t i n e n t a l s l o p e th e to p o g ra p h y of the f o rm e r c a n n o t t e c h n i c a l l y be c a l l e d a c o n t i n e n t a l r i s e ; f u r t h e r m o r e , h i g h l y i r r e g u l a r to p o g ra p h y o f t e n e x i s t s on the b ro ad p l a t e a u t h a t s t r e t c h e s h u n d re d s of k i l o m e t e r s o f f s h o r e a t d e p th s s l i g h t l y above th e t r u e a b y s s a l s e a f l o o r . T h is i s w e l l i l l u s t r a t e d o f f W ashington ( P l a t e s 7 and, UW 19 9-4) and Oregon ( P l a t e 8, low er p r o f i l e ) . T h is wide p l a t e a u becomes s m o o th e r, w i t h l e s s r e l i e f to w a rd s th e n o r t h , and f i n a l l y d i s a p p e a r s e x c e p t f o r e v id e n c e p r o v id e d by th e 2 ,0 0 0 -fm i s o b a t h . As many as t h r e e t e r r a c e s can be i d e n t i f i e d betw een Juneau and Ju an de Fuca ( P l a t e 7 ) . The s h a l l o w e s t l i e s m o s tly a t a d e p th of a b o u t 600 m, b u t may be as s h a llo w as 400 m and as deep as 1,0 0 0 m. I t i s n o t e s p e c i a l l y w e l l - d e v e lo p e d and i n most r e g i o n s c o n s i s t s o f one or more r i d g e s and d e p r e s s i o n s ; on s e v e r a l p r o f i l e s i t c o n s t i t u t e s a d i s t i n c t f e a t u r e ( P l a t e 7, CGS-3, and 9 1 ) . I t i s i n d i s t i n c t or a b s e n t on most o f G i b s o n ’s p r o f i l e s . A h i g h l y d e v e lo p e d t e r r a c e , n e a r l y c o n ti n u o u s a c r o s s the e n t i r e r e g i o n , o c c u r s a t a b o u t 1,000 m, and r a n g e s from 600 m, where i t p o s s i b l y j o i n s th e 500-m t e r r a c e , to 1 ,5 0 0 m to 1 ,6 0 0 m. T h is t e r r a c e may c o n s i s t of a p r o nounced p l a t e a u su ch a s th o s e shown on p r o f i l e s CGS-3 and CGS-16, b u t more commonly i n v o l v e s a r e g i o n o f i r r e g u l a r to p o g rap h y . I t may p o s s i b l y j o i n sh a llo w e r t e r r a c e s at s e v e r a l l o c a t i o n s . At l e a s t one deep er t e r r a c e e x i s t s a t ap p ro x im ate ly 2,000 m. T his may co rresp o n d to the broad p l a t e a u so c h a r a c t e r i s t i c of t h i s r e g i o n . I f so , i t s d i s t r i b u t i o n i s more w idespread than i n d i c a t e d on P l a t e 7 or F ig u re 13. OREGON I n t r o d u c t i o n T h i r t y - t h r e e more o r l e s s com plete p r o f i l e s and 14 in co m p lete p r o f i l e s a re a v a i l a b l e f o r th e c o n t i n e n t a l t e r r a c e o f f Oregon (B y rn e, 1962, 1963a and 1 9 6 3 b ). The upper 31 p r o f i l e s on P l a t e 8 a re b a sed upon C o a st and G e o d etic Survey s o u n d in g s; th e long p r o f i l e a t th e b o tto m was made by the VITYAZ. A l l sou n d in g s have been c o r r e c t e d f o r sound v e l o c i t y . A l l p r o f i l e s are r e c o n s t r u c t e d . P r o f i l e s in F ig u re 14 a re d i r e c t t r a c i n g s of e c h o grams and a re u n c o r r e c t e d f o r sound v e l o c i t y o r s l o p e . The upper p r o f i l e (A) was made by th e C o a st and G e o d etic S urvey employing an NMC-1 e c h o s o u n d e r . The lower p r o f i l e s , showing d e t a i l s o f th e t e r r a c e a t a p p r o x i m a t e ly 500 ra, a re d i r e c t t r a c i n g s o f PDR echo gram s. P r o f i l e s shown on P l a t e 8 o n ly have been used f o r c o r r e l a t i n g t e r r a c e s ( F i g u r e 1 5 ) . R e s u I t s The s h e l f b r e a k v a r i e s from 100 m t o 350 m. Some of the a p p a r e n t l y d e e p e r s h e l f b r e a k s may be th e r e s u l t of t e r r a c e s a t th e s h e l f ed g e, such a s th o se shown on p r o f i l e s 96 OREGON DEPTHS IN METERS 97 W E S T o r COOS BAY 2000 3 0 0 0 h — 1 1 8 . 6 K i l o m e t e r s 3 0 0 — 4 0 0 — 5 0 0^ 6 0 0 - ' 2 ' S ow 7 0 0 V % 8 0 0 — 3 0 0 C “ V 5 0 0 6 0 0 TOO 8 0 0 3 0 0 4 0 0 * -------- 5 0 0 V — 6 0 0 \ - 7 0 0 "A ST O R IA c a n y o n 4 0 0 - = 5 s 3'- 5 0 0 — ('* 3 ' 6 0 0 - 2 = - 3 0 0 3 0 0 4 0 0 5 0 0 6 0 0 6 0 0 7 0 0 7 0 0 3 0 0 4 0 0 5 0 0 5 0 0 S SIDE ASTORIA CANYON 4 0 0 - N . y « _ • < M « n 5 0 0 w ■ * N 6 0 0 -------- 0 1 4 0 0 5 0 0 6 0 0 7 0 0 • 8 0 0 K ilo m e te rs F ig u re 14. D i r e c t t r a c i n g s of echograms o f f the c o a s t of Oregon. OREGO N KM V E R Y W ID E T E R R A C E rrr rrr SC 7 + 7 B A S E O F C O N T IN E N T A L S L O P E rrr R ID G E A N D D E P R E S S IO N S T O P O G R A P H Y H O R IZ O N T A L D IS T A N C E N O T T O S C A L E Figure 15. C o r re la tio n of t e r r a c e s and oth er f e a t u r e s on the c o n tin e n ta l slope o ff the c o ast of Oregon. i vO 00 9 9 l o c a t e d a t 45° 20* to 45° 4 0 ’ N ( P l a t e 8 ) . A few p r o f i l e s show sm a ll r i d g e s or p r o m o n to r i e s a t th e edge of the s h e l f ( P l a t e 8 and F ig u r e 1 4 ) . A t y p i c a l c o n t i n e n t a l r i s e , such a s e x i s t s o f f th e E a s t C oast of the U n ite d S t a t e s , do es n o t o c cu r o f f O regon. The b ase of the c o n t i n e n t a l s lo p e and t h e d e ep s e a may be r a t h e r a b r u p t or have a wide b e l t of v a r y i n g to p o g ra p h y a t about 2,8 00 m t o 3 ,0 0 0 m b e f o r e th e a b y s s a l se a f l o o r i s re a c h e d a t a d e p th of 3,600 m ( P l a t e 8, lower p r o f i l e ) . The wide bench a t th e b a se o f th e s l o p e was d i s c u s s e d in th e p r e v i o u s s e c t i o n . (See a l s o H u r l e y , 1 9 6 0 .) The c o n t i n e n t a l s lo p e i s h i g h l y i r r e g u l a r , c o n s i s t i n g o f s l o p i n g p l a i n s and r i d g e s w ith r e l i e f o f s e v e r a l h u n d re d m e t e r s . R id g es commonly a re su p e rim p o sed upon p l a i n s or t e r r a c e s ; n e v e r t h e l e s s , i t i s p o s s i b l e to d e l i n e a t e d e f i n i t e t e r r a c e s . By i n c l u d i n g th e r i d g e s , or th e t o t a l ra n g e i n d e p th of t o p o g r a p h i c f e a t u r e s on a p l a i n , r a t h e r l a r g e ra n g e s in d e p t h s f o r g iv en t e r r a c e s r e s u l t . The wide bands shown f o r t e r r a c e s on F ig u r e 15 do n o t n e c e s s a r i l y c o rr e s p o n d w i t h th e w i d e s t or b e s t d e v e lo p e d t e r r a c e s . A p a r t i c u l a r l y d i s t i n c t t e r r a c e o c c u r s a t a p p r o x i m a te ly 500 m. I t can be t r a c e d a lm o st c o n t i n u o u s l y a lon g the e n t i r e Oregon C o a s t. I t v a r i e s b e tw ee n 300 m and 1,70 0 m, th e l a t t e r b e in g e x tr e m e , p r o b a b l y th e r e s u l t o f w a r p in g . T his i s s u g g e s te d a t l a t i t u d e 46° 10* ( P l a t e 8 ) , 100 where the base o f the c o n t i n e n t a l s lo p e shows d i s t i n c t downward d e f l e c t i o n . The t e r r a c e may be f e a t u r e l e s s ( F i g ure 14, G and N), or h i g h l y i r r e g u l a r , w i t h r e l i e f of 150 m to 200 m ( p r o f i l e s B, I , and L ). The 500-m t e r r a c e can be i d e n t i f i e d on th e s i d e s of A s t o r i a Canyon ( p r o f i l e s H and M). This w e ll- d e v e l o p e d t e r r a c e a t t a i n s a w idth o f a t l e a s t 7 km. Where the 500-m t e r r a c e i s wide and f l a t ( p r o f i l e s G and N) i t commonly shows a s t e p of about 50 m below which i s an o th er t e r r a c e a t about 500 m to over 600 m in d e p th . This somewhat de ep e r t e r r a c e i s no t shown on P l a t e 8. I t i s p ro b a b ly t h a t o t h e r i n t e r m e d i a t e and l e s s pronounced t e r r a c e s occur a t g r e a t e r and l e s s e r d e p th s bu t cannot be d i s t i n g u i s h e d because o f the sm a ll s c a l e . In a d d i t i o . , t h e s e p r o f i l e s were r e - p l o t t e d and are n o t d i r e c t t r a c i n g s of echograms and thus p r o b a b ly do n ot show s m a ll e r f e a t u r e s . Another t e r r a c e , g e n e r a l l y l e s s w e ll- d e v e l o p e d ( l o c a te d a t 700 m to 1,300 m d e p th a v e r a g in g about 1,000 m ), a p p a r e n t l y does n o t o ccur along the e n t i r e Oregon C o a st. I t may p o s s i b l y j o i n one or more of the d e ep e r t e r r a c e s , such as 43° 5 0 ’ and 42° 50* ( P l a t e 8 ) . The n e x t d e e p e r t e r r a c e ra n g e s from 500 m to 2,600 m, a v e ra g in g about 1,500 m ( F ig u r e 1 5 ). T his g r e a t e r depth a p p ea rs to be the r e s u l t of downward w arping where i t ap p a r e n t l y j o i n s a d e e p e r t e r r a c e a t 44° 20 *. The t e r r a c e 101 g e n e r a l l y shows a g e n t l y s l o p i n g p l a i n upon w hich a re s u p erim p o sed one or more r i d g e s , g i v i n g th e t e r r a c e a c o n s i d e r a b l e ra n g e in d e p t h . T h is 1 , 500-m t e r r a c e may e x te n d a c r o s s t h e warp a t 44° 2 0 1 or be d e f l e c t e d downward, com m encing a t 43° 0 0 1 . The t h i r d , or f o u r t h t e r r a c e , ( d e p e n d in g upon th e l o c a t i o n ) o c c u rs a t a d e p th of 1,400 m t o 2,00 0 m, a v e r a g in g a b o ut 1 ,7 00 m. T h is o c c u r s s o u th o f 44° 17*. I t may j o i n the 1 , 500-m t e r r a c e a t 44° 17*, p o s s i b l y e x te n d i n g a c r o s s the 1 , 500-m t e r r a c e a t 42° 5 0 ’ . I f s o , i t shows the i n f l u e n c e of w a rp in g a t 42° 20*. G e n e r a l l y , t h i s t e r r a c e i s p o o r l y d e v e lo p e d . The d e e p e s t t e r r a c e i s p o o r l y d e v e lo p e d and a p p e a rs o n ly betw een 44° 17* and 44° 4 0 ' . I t s d e p th ra n g e i s 2 ,0 00 m to 2,400 m. When th e edge of th e s h e l f i s viewed h o r i z o n t a l l y i t shows a c o n s i d e r a b l e v a r i a t i o n i n d e p th ( P l a t e 8 ) . Most of th e t e r r a c e s , i n c l u d i n g th e d e e p e s t , commonly c l o s e l y f o l l o w th e s in u o u s shape of th e s h e l f e d g e. T h is s u g g e s t s , f i r s t , t h a t a l l t e r r a c e s and th e c o n t i n e n t a l s h e l f s u f f e r e d w a rp in g s i m u l t a n e o u s l y ; s e c o n d , w a rp in g o c c u r r e d a f t e r a l l t e r r a c e s were form ed; and t h i r d , i t ap p e a r s h i g h l y u n l i k e l y t h a t the c o n t i n e n t a l s h e l f or th e d e e p e r t e r r a c e s co u ld p o s s i b l y r e p r e s e n t a d e p o s i t i o n a l f e a t u r e - - t h e y must be o f s t r u c t u r a l o r i g i n . T h is i s a g r o s s l y o v e r s i m p l i f i e d c o n c l u s i o n as r e v e a l e d by the 102 r e s u l t s of c o n tin u o u s se ism ic p r o f i l i n g (C urray and Moore, 1964). Bottom M a t e r i a l s Maloney and Byrne (1964) have l i s t e d 138 bottom sam p l e s from the c o n t i n e n t a l t e r r a c e and in c lu d e a wide v a r i e ty of rock ty p e s i n c l u d i n g : l im e s to n e , s i l t s t o n e , s h a l e , d ia t o m it e sa n d s to n e , c o a l , and g r a v e l . Age d e te r m i n a ti o n s have not been made on the r o c k s ; however, rock ty p e s sug g e s t t h a t the geology changes r a t h e r a b r u p t l y along the c o n t i n e n t a l m argin. Geology Snavely and Wagner (1963) have given a b r i e f d e s c r i p t i o n of th e geology of the c o a s t a l r e g io n s of Oregon and W ashington. R e c e n tly , Carey (1958) and Wise (1963) s u g g e sted a h y p o th e s is in v o lv in g g r e a t r i g h t l a t e r a l s h i f t s of c o n t i n e n t a l masses along the n o r t h e r n p a r t of the w est c o a s t of N orth America. This movement would ( a p p a r e n t l y ) e x p la in much of the t e c t o n i c s from n o r t h e r n C a l i f o r n i a to B r i t i s h Columbia. The fo llo w in g d e t a i l s are taken l a r g e l y from Snavely and Wagner*s r e p o r t . T a l i a f e r r o (1943) r e p o r t e d t h a t a l a r g e land mass e x i s t e d o f f C a l i f o r n i a and Oregon which came i n t o e x is te n c e as a r e s u l t of the Nevadian Orogeny and was the major source a r e a f o r the F r a n c i s c a n - K n o x v i l l e . At the 103 b e g in n in g of the T e r t i a r y p e r i o d th e w e s te rn p a r t of O re gon and Washington was th e s i t e of an e u g e o s y n c lin e e x te n d in g from Vancouver I s l a n d to th e Klamath M ountains. The w e s t e r n margin c o n tin u e d f o r some unknown d i s t a n c e o f f s h o r e . During the e a r l y s ta g e of g e o s y n c l i n a l form a t i o n ( i n Eocene tim e ) t h i c k v o l c a n ic e l a s t i c s and p i l l o w flows a ccu m u lated . G eo p h y sical and g e o l o g i c a l mapping i n d i c a t e t h a t th e s e v o l c a n i c s t o t a l 3,000 m to 4,600 m, and 3 p r o b a b ly have a volume of a t l e a s t 110,000 km . The v o l c a n ic ro c k s in c lu d e p i l l o w s t r u c t u r e s and are in te r m in g le d w ith s i l t stone and l i t h i c wackes, c h e r t and G l o b i g e r i n a - b e a rin g b e d s, and c o n g lo m e ra te s . Volcanism extended i n to the P lio c e n e epoch. In m iddle Eocene tim e major u p l i f t o c cu rred so u th of the g e o s y n c l i n e . N o r t h e a s t - t r e n d i n g c u r r e n t r i p p l e marks in the so u th w est p a r t of the g e o s y n c lin e s u g g e s t t h a t the source of some o f th e d e t r i t u s was a h ig h la n d a re a t h a t e x i s t e d w est of the p r e s e n t s h o r e l i n e . Snavely and Wagner s t a t e : ’’Whether o th e r lan d masses along the west b o rd e r of the g e o sy n c lin e stood high enough to supply c o a rs e d e t r i t u s to the b a s i n is c o n j e c t u r a l . However, e a s t - tr e n d in g se d im e n ta ry s t r u c t u r e s found as f a r n o r t h as the Umpqua R iver s u g g e s t t h a t a w e s t e r n land mass may have e x tended a t l e a s t t h a t f a r n o r t h . ” During m iddle Eocene time more th a n 1,520 m o f non marine c o a l - b e a r i n g a rk o s i c sands were d e p o s i te d on a 104 s u b s id i n g a l l u v i a l p l a i n t h a t b o r d e r s th e n o r t h e a s t e r n p a r t of the g e o s y n c l i n e . Downwarping k e p t pace w ith s e d i m e n t a t i o n . The major so urce a r e a a p p e a rs to be from the e a s t . At the b e g in n in g o f l a t e Eocene tim e , a r e a s of l o c a l u p l i f t d iv id e d the g e o s y n c lin e i n t o s e v e r a l b a s i n s and the a x i s of s e d i m e n ta t io n s h i f t e d westward w ith tim e . S h a llo w - w a te r d e p o s i t s e x i s t along th e r e g i o n of the p r e s e n t c o a s t l i n e , b u t f u r t h e r w e s t , tow ards open s e a , o r g a n i c - r i c h t u f - f a c e o u s s i l t s and c l a y s were d e p o s i t e d i n d e e p e r w a t e r . In e a r l y and m iddle O lig o ce n e time m ild r e g i o n a l u p l i f t of the s o u th e r n p a r t of the g e o s y n c l i n e o c c u r r e d , s h i f t i n g the s t r a n d l i n e n o r th w a r d . On th e o t h e r h a n d , su b s id e n c e too k p la c e in the n o r t h e r n p a r t of the g e o s y n c l i n e . D e p o s i t io n c o n tin u e d i n t o the e a r l y M iocene, e s s e n t i a l l y u n i n t e r r u p t e d , b u t in e a r l y m iddle Miocene tim e , o l d e r T e r t i a r y s t r a t a were f o l d e d and f a u l t e d along the g en e r a l l y n o r t h e a s t s t r u c t u r a l tr e n d s of Oregon and along n o r th w e s t t r e n d s in W ashin gton . D uring Miocene and P l i o cene tim es the d e e p e r p a r t s o f the b a s i n l a y w est o f th e p r e s e n t c o a s t l i n e . During l a t e P l i o c e n e time th e Olympic M ountains and th e C o a s t Ranges p r o b a b l y a t t a i n e d t h e i r p r e s e n t e l e v a t i o n s . Contem poraneous s e d i m e n t a t i o n r e p o r t e d ly o c c u r r e d in the n o r t h - t r e n d i n g tro u g h as d e te rm in e d by a g r a v i t y low t h a t l i e s w e st o f the p r e s e n t c o a s t l i n e . CALIFORNIA I n t r o d u c t i o n Uchupi and Emery (1963) and Emery (1 96 0) have summa r i z e d th e knowledge of C a l i f o r n i a , hence o n ly a few a d d i t i o n a l rem arks a re n e c e s s a r y . The v e r t i c a l e x a g g e r a t i o n o f Uchupi and Emery*s p r o f i l e s have been re d u c e d and f o u r a d d i t i o n a l p r o f i l e s have b e e n added ( P l a t e 9 ) . R e s u l t s A w e l l - d e f i n e d t e r r a c e can be t r a c e d a t a d e p th of a b o u t 500 m n o r t h of the c o n t i n e n t a l b o r d e r l a n d ( F i g u r e 1 6 ) . T h is f e a t u r e e v i d e n t l y j o i n s one of th e c o r r e l a t i v e f e a t u r e s o f s o u t h e r n Oregon ( F i g u r e 1 5 ) . The 500-m t e r r a c e e x te n d s from n e a r th e edge of the s h e l f to o v e r 1,200 m. I t ends a b r u p t l y a t the s t a r t of th e c o n t i n e n t a l b o r d e r l a n d n e a r P o i n t A r g u e l l o . However, a c u r s o r y e x am in a t i o n of th e u p p e r edge of the d e ep c o n t i n e n t a l s lo p e a t the seaw ard edge o f the b o r d e r l a n d s t r o n g l y s u g g e s t s t h a t th e 500-m t e r r a c e c o r r e l a t e s w i t h the to p of th e c o n t i n e n t a l s lo p e o f f th e b o r d e r l a n d . Based upon t h i s , p l u s 105 E . SID E G U AD A LU PE IS M E X IC O T O P H O RIZO N TA L DISTA NC E N OT TO SC A LE Figure 16. C o r r e la tio n of t e r r a c e s and other f e a t u r e s on the c o n tin e n ta l t e r r a c e and borderland o ff C a li f o r n ia . 107 E m ery’ s s t u d i e s (1958 and 1960) on th e d e e p e n in g of s h e l f b r e a k s toward th e so u th w e s t and i n a seaw ard d i r e c t i o n , i t i s b e l i e v e d t h a t the c o n t i n e n t a l b o r d e r l a n d r e p r e s e n t s a bro ad downward f l e x u r e . Some f a u l t i n g u n d o u b t e d l y e x i s t s , f o r exam ple, o f f San C lem ente I s l a n d , b u t u n p u b l is h e d con t i n u o u s s e is m ic p r o f i l e s i n d i c a t e t h a t f o l d i n g - - n o t f a u l t - i n g - - h a s been th e p r i n c i p a l o f f s h o r e t e c t o n i c p r o c e s s o f f C a l i f o r n i a . Sedim ents a re a l s o much t h i n n e r in o f f s h o r e b a s i n s than h e r e t o f o r e b e l i e v e d . Uchupi and Emery d a t e th e o r i g i n by f a u l t i n g of th e c o n t i n e n t a l s lo p e as n o t e a r l i e r th an L ate C r e t a c e o u s . A wide and p e r s i s t e n t t e r r a c e o c c u r s a t 1,80 0 m to 1 ,9 0 0 m a lo n g the e n t i r e n o r t h e r n C a l i f o r n i a c o a s t n o r t h of M urray F r a c t u r e Zone (Menard, 19 6 0 ). A c o n tin u o u s s e i s m ic p r o f i l e n o r t h of P o i n t A r g u e ll o ( F i g u r e 17) shows a p e n e t r a t i o n o f a t l e a s t 300 m. T h is p r o f i l e r e v e a l s a t h i c k b l a n k e t of s e d im e n t e v ery w h ere a lo n g th e c o n t i n e n t a l s h e l f , s l o p e , and a b y s s a l s e a f l o o r , s u g g e s t i n g w a r p i n g - - n o t f a u l t i n g . F u r t h e r , e x c e p t l o c a l l y , most s t r a t a ap p ea r h o r i z o n t a l . F a u l t i n g may c o n t r o l the c o n t i n e n t a l s lo p e b u t s u b s e q u e n t s e d i m e n t a t i o n has o b sc u re d i t . Palm er (1965) has made a c o n ti n u o u s s e i s m ic p r o f i l e a c r o s s th e A r g u e ll o P l a t e a u w h ich l i e s a t an a v e ra g e d e p th of 1,00 0 m and shows th e broad concave shape o f th e p l a t e a u ’ s s u r f a c e ( F i g u r e 1 8 ) . Only a t h i n l a y e r o f se d im e n t (a b o u t 80-m t h i c k ) c o v e rs the bedrock s u r f a c e . Sediment a p p e a rs to l i e on a t r u n c a t e d p l a t f o r m . Palmer su g g e ste d t h a t the A r g u e llo P l a t e a u i s a fo u n d ered b lo c k t h a t s u b sid e d d u rin g th e w id e s p r e a d , post-M iocene d i s t u r b a n c e and p o s s i b l y o c c u rre d as r e c e n t l y as p r e - l a t e P l e i s t o c e n e tim e . THIN UNCONSOLIDATED COVER CONSOLIDATED FOLDED TERTIARY BEDROCK BOTTOM ECHO 1 1 SECOND ECHO OF BOTTOM THICK UNCONSOLIDATED SECTION BOTTOM ECHO 7000 8000-F E E T 5 MILES U Figure 17. Continuous seismic p rofile north of Point Arguello, C alifornia. (Courtesy of J. Smith.) 109 ACOUSTIC REFLECTION (ARCER) RECORDS OF DAVIS SEAKNOLL AND ARGUELLO PLATEAU igure 18. Continuous seism ic p r o f i l e across A rguello P la te a u . (Courtesy of H. M P alm er.) m o BAJA CALIFORNIA BORDERLAND I n t r o d u c t i o n Two s o u rc e s of i n f o r m a tio n a re a v a i l a b l e f o r th e Baja C a l i f o r n i a b o r d e r la n d r e g i o n : Uchupi and Emery*s p r o f i l e s (1 9 6 3 ), shown in upper h a l f of P l a t e 10, and f i v e p r o f i l e s from Krause (1964a) shown in lower h a l f of P l a t e 10. This re g io n was the s u b j e c t of two d i s s e r t a t i o n s (Uchupi and K r a u s e ) , t h e r e f o r e , c o n s i d e r a b l e i n f o r m a tio n has been a c cu m u lated. Krause has w r i t t e n s e v e r a l p a p e rs on the r e gion (1961a, 1961b, 1961c, 1964a and 1964g). R e s u I t s V arious f e a t u r e s along the c o n t i n e n t a l slo p e are c o r r e l a t e d on F ig u re 16. T h is shows the c o n t i n e n t a l slo p e edge m a in ta in in g i t s d e p th a t a b o u t 500 m to 1,000 m. To wards Guadalupe I s l a n d i t becomes more o b s c u r e , j o i n i n g w ith a d e ep e r or s h a llo w e r f e a t u r e . South of S a n ta Lucia Bank a t e r r a c e (o r m ajor t e r r a c e ) o c c u rs a t about 2,000 m, deepening somewhat to the s o u t h . S e v e r a l of the b a s i n s a l s o have t h e i r f l o o r s a t about the same d e p th . I t i s a l so n o tew o rth y t h a t San Q u in tin B a sin ( p r o f i l e EF) has a 111 112 broad t e r r a c e a t 2,000 m on b o th s i d e s - - o n the r i s e bound ing C edro s Deep and Guadalupe I s l a n d ( p r o f i l e GH). K rause (1961c) r e p o r t e d t h a t t e r r a c e s o c c u r a t v a r i o u s l e v e l s down to a t l e a s t 1,000 m, b u t th e y c an n o t be c o r r e l a t e d from p l a c e to p l a c e in th e s o u t h e r n b o r d e r l a n d . He t h e r e f o r e a t t r i b u t e s t h e s e f e a t u r e s to more or l e s s i n d e p e n d en t v e r t i c a l movements o f c r u s t a l b l o c k s . D o lo m itiz e d , c a l c a r e o u s ooze was r e t r i e v e d in two or t h r e e p l a c e s n e a r t e r r a c e s , i n c l u d i n g the d e e p e s t . In one i n s t a n c e d o lo m ite e n c l o s e s a n d e s i t e w ith c h i l l e d g l a s s y m a rg in s. Geology The s o u th e r n b o r d e r l a n d i s a few hundred m e te rs d e e p e r th an th e n o r t h e r n b o r d e r l a n d and d i f f e r s in o th e r im p o r ta n t ways (K ra u s e , 1 9 6 4 a ). P r o c e s s e s of f o l d i n g and f a u l t i n g a re e q u a l l y im p o r ta n t b u t i t i s o f t e n d i f f i c u l t to d e t e r mine when f a u l t i n g has o c c u r r e d . K rause h as concluded t h a t ” the b o r d e r l a n d has not deformed as a u n i t . Some b lo c k s have gone up w h ile o t h e r s went dow n.” In g e n e r a l , f a u l t s in the b o r d e r l a n d d e c r e a s e i n number from n o r t h t o s o u th by g r a d u a l l y m erg ing . M agnetic a n o m a lie s of th e s o u t h e r n b o r d e r l a n d are much d i f f e r e n t from th o se of the o c e a n ic c r u s t or m a n tle . Large a n o m a lie s a p p ea r to r e f l e c t some m ajor t e c t o n i c f e a t u r e , p a r t i c u l a r l y l a r g e f a u l t s . Of p a r t i c u l a r i n t e r e s t are th e a n o m a lie s a s s o c i a t e d w ith th e m arg in of the 113 I s u b a e r i a l p o r t i o n of th e c o n t i n e n t which su g g e s ts f a u l t s p a r a l l e l to the c o a s t , t o g e t h e r w i t h la r g e la v a e x t r u s i o n s a t the m argin. These anom alies a re in d i r e c t c o n t r a s t to the c o n t i n e n t a l margin o ff Oregon and n o r th e r n C a l i f o r n i a where no anomaly i s a s s o c i a t e d w i t h the m argin. Krause i n d i c a t e s t h a t the boundary s e p a r a t in g the n o r t h e r n and so u th e rn b o rd e rla n d occurs a t the Santo Tomas f a u l t (about 31° 30 1 N ) . The topography drops 450 m to the so u th and may be o f f s e t l a t e r a l l y f o r 15 km. T h is , and o t h e r e v id e n c e , s u g g e s ts t h a t the n o r t h e r n b o r d e r la n d i s moving west r e l a t i v e to the s o u th e r n p o r t i o n along the S anto Tomas f a u l t , w h ile the P a c i f i c Ocean b a s in i s a s sumed to be moving n o rth w e st r e l a t i v e to the b o r d e r la n d and c o n t i n e n t . Recorded s e i s m i c i t y i s a s s o c i a t e d w ith a f a u l t zone tr e n d in g from I s l a s Las Coronados to B ahia Todos S a n to s, SE-NW f a u l t i n g w i t h in the b o rd e rla n d ( e s p e c i a l l y a tre n d towards San Clemente I s l a n d ) , and the Santo Tomas f a u l t zone. Heat flo w measurements r e v e a l t h a t h e a t flow i n c r e a s e s to the e a s t and p ro b a b ly cau ses th e s t r e n g t h of the c r u s t under the b o rd e rla n d to d e c re a s e by o n e - h a l f the s t r e n g t h of the o cean ic c r u s t t o the west where h e a t flow i s norm al. Seism ic evidence i n d i c a t e s t h a t in the n o r t h e r n b o r d e rla n d a re a the c r u s t t h ic k e n s very a b r u p t l y a t the 114 P a t t o n E scarpm ent to 17 l / 2 km, th e n t h i c k e n s g r a d u a l l y tow ard the c o n t i n e n t . (Most o f th e t h i c k e n i n g o c c u r s in the t h i r d l a y e r . ) In th e v i c i n i t y of B ahia V i s c a i n o Bay, th e c r u s t t h i c k e n s about the same as a t the c o n t i n e n t a l m a rg in , b u t th e t h i r d l a y e r s i g n i f i c a n t l y ch an g es d e p t h . In g e n e r a l , the s o u th e r n b o r d e r l a n d i s p r o b a b l y c o n s i d e r a b ly t h i n n e r than the c r u s t u n d e r the n o r t h e r n b o r d e r l a n d . The r e g io n s may have had d i f f e r e n t h i s t o r i e s which co uld a c c o u n t f o r the d i f f e r e n c e . Krause b e l i e v e s t h a t the c o n t i n e n t a l b o r d e r l a n d was in e x i s t e n c e in Mesozoic tim e but was l i m i t e d in a r e a l d i s t r i b u t i o n u n t i l Miocene tim e . In M iddle Miocene tim e a m ajor d i s t r o p h i s m o c c u r r e d which i n i t i a t e d t h e modern b o r d e r l a n d . S in c e t h a t tim e the r e g i o n has u nd ergo ne d e f o r m a t i o n as w e l l as s e d i m e n t a t i o n in the b a s i n s . Menard (1960) and Krause (1 96 4a) b e l i e v e t h a t the E a s t P a c i f i c R ise p a s s e s under th e N orth Am erican c o n t i n e n t n e a r t h e G ulf of C a l i f o r n i a . The c r e s t o f th e r i s e marks the a s c e n d in g column of a c o n v e c ti o n c e l l and i s a r e g i o n of t e n s i o n a l s p r e a d i n g , r e s u l t i n g in the f o r m a t io n of th e G u lf of C a l i f o r n i a . The e a s t - w e s t s p r e a d i n g o f the c r u s t w i l l have a s h e a r component o f r i g h t l a t e r a l d i r e c t i o n of the San A ndreas f a u l t . A b r o a d , s h e a r zone o c c u rs betw een th e deep se a w e s t of B a ja C a l i f o r n i a and the e a s t ern m ost l a r g e s t r i k e - s l i p f a u l t . B a ja C a l i f o r n i a l i e s w i t h i n th e s h e a r zone and i t w i l l move more slo w ly th an 115 the ocean b a s i n to the w e s t , t h e r e f o r e , s h e a r and t e n s i o n w i l l occur along the P a c i f i c m arg in , th e re b y form ing th e b o r d e r l a n d . The r i d g e s and b a s i n s a re the r e s u l t of a c o m b in atio n of b lo c k f a u l t i n g , s h e a r , and uneven s t r e t c h i n g . GULF OF CALIFORNIA I n t r o d u c t i o n A r e c e n t symposium e d i t e d by T. H. van Andel and G. G. S h o r, J r . , e n t i t l e d Marine Geology of the G ulf of C a l i f o r n i a (American A s s o c i a t i o n of P e tro le u m G e o l o g i s t s Mem o i r 3 ) , i s an e x c e l l e n t summary of t h i s r e g i o n . The a u th o r made a m onth’ s c r u i s e to th e G u lf i n 1962 w i t h F. P . S h ep a rd ; however, th e a r e a i n v e s t i g a t e d was h e a v i l y i n c i s e d by subm arine canyons as shown by S h e p a r d ’ s (1964) d iag ra m s in the s o u t h w e s t e r n p a r t of th e G u lf , h e n c e , no s u i t a b l e e c h o grams o f the c o n t i n e n t a l t e r r a c e and no bottom samples were o b t a i n e d . Numerous a t t e m p t s were made to examine the o r i g i n a l echograms o f th e V e r m i l li o n Sea E x p e d i t i o n w i t h out s u c c e s s . Many p r o f i l e s of th e G u lf have been p u b l i s h e d : Byrne (1 9 5 7 ), Byrne and Emery ( 1 9 6 0 ), C u rra y , and Moore ( 1 9 6 4 ), H a r r i s o n and Mather (1 9 6 4 ), H ild e ( 1 9 6 4 ) , Rusnak, F i s h e r , and Shepard ( 1 9 6 4 ), Shepard ( 1 9 5 0 ) , and van Andel ( 1 9 6 4 ) . Only a few summary rem ark s a re r e q u i r e d h e r e . P l a t e 11 i s r e p ro d u c e d from Rusnak, F i s h e r , and S h e p a r d ’ s p a p e r . 116 117 R e s u l t s S h e l f b r e a k s i n t h e G u lf o f C a l i f o r n i a v a r y from 82 m to 133 m (T a b le 3 ) . Many p r o f i l e s show s e v e r a l s h e l f b r e a k s or t e r r a c e s n e a r th e edge o f th e s h e l f . D i s t i n c t s h e l f b r e a k s a re more common on th e w e s t th a n on t h e e a s t s i d e . The maximum d i f f e r e n c e be tw ee n s h e l f b r e a k s on the w e s t e r n s i d e i s 54 m, b u t more l i k e l y i s o n ly 13 m. On the e a s t e r n s i d e t h e d i f f e r e n c e b e tw e e n s h e l f b r e a k s i s 49 m. T h is g r e a t e r t e c t o n i c a c t i v i t y Cor p e r h a p s more m odi f i c a t i o n by s e d i m e n t a t i o n ) on the e a s t e r n p a r t of th e G u lf may a c c o u n t f o r t h e g r e a t e r ra n g e on th e e a s t s i d e . The s h e l f i s a l s o much w id e r on th e e a s t s i d e . Both s i d e s o f th e G u lf a re bounded by s t e e p c o n t i n e n t a l s l o p e s h a v in g g r a d i e n t s up to 38°; most a r e l e s s th a n o 15 . The s t e e p e r s l o p e s a p p e a r to be more common on th e w e s t s i d e . Subm arine c a n y o n s commonly o r i g i n a t e a t t h e s h e l f b r e a k , or s h o r e w a r d , and e x te n d to th e b a s e o f th e s l o p e , t e r m i n a t i n g in f a n s . S h e p a rd (1 9 6 4 ) c o n c l u d e d , on th e b a s i s o f m o rp h o lo g y , t h a t th e c an y o n s w ere o l d , s u b a e r i a l l y - c u t v a l l e y s subm erged t o t h e i r p r e s e n t d e p t h s (900 m to 1 ,1 0 0 m ) . S h a llo w w a t e r f o s s i l s w ere r e c o v e r e d fro m c o n s i d e r a b l e d e p t h s , a l s o i n d i c a t i n g s u b s i d e n c e . Numerous s e a m o u n ts , k n o l l s , and r i d g e s o c c u r and a p p e a r t o be e n t i r e l y v o l c a n i c , w h e r e a s th e w e s t e r n i s l a n d s 118 are " g r a n i t i c . " Table 3. Approximate Depth of S h e lf Breaks in Gulf of C a l i f o r n i a (from N orth to South)* WESTERN SIDE EASTERN SIDE P r o f i l e No. Depth (m) P r o f i l e No. Depth (m) XII 53 (91) X III 99 X 88 XI 91 VI 91 IX 77 V 95 VIII 95 I I 37 (82) VII 84 IV 88 I I I 133 I 95 *See van Andel (1964, p. 22C ) f o r l o c a t i o n s of p r o f i l e s . Numbers in p a r e n t h e s e s i n d i c a t e seco nd ary , or p o s s i b l y , main s h e l f b r e a k . Much of the n o r th e r n p a r t o f the G ulf i s devoid of s h e l f b re a k s (van Andel, 1964). He s t a t e d (1964, p. 219): The so u th e rn and c e n t r a l p o r t i o n s of the G ulf p o s s e s s w e ll-d e v e lo p e d c o n t i n e n t a l s h e l v e s . On the w e s t e rn s i d e , the s h e l f i s g e n e r a l l y rocky and narrow , w ith a sharp s h e l f - b r e a k between 55 and 45 fms [101 and 82 m] and a s te e p upper slo p e studded w ith h i l l s and p i n n a c l e s . About 30 m ile s [48 km] n o r th of S an ta R o s a l ia the s h e l f widens and the upper slo p e becomes smooth and more g e n t l e . The topography appears de- p o s i t i o n a l in n a t u r e , but no l a r g e d r a in a g e system o c cu rs on the a d ja c e n t la n d . The e a s t e r n s h e l f i s w id e r, ran g in g from a few 119 m il e s o p p o s i t e p r o g r a d i n g d e l t a s to a p p r o x im a te ly 30 m i l e s . The s u r f a c e shows l i t t l e r e l i e f and v e r y g e n t l e s l o p e . S o uth of t h e F u e r t e R iv e r d e l t a , a v e ry i n d e f i n i t e s h e l f - b r e a k o c c u r s a t 100 - 120 fms [180 to 330 m], and th e u p p e r s l o p e i s g e n e r a l l y smooth and g e n t l e . T h is and th e i n t e r n a l s t r u c t u r e i n d i c a t e a slo w ly s u b s id i n g d e p o s i t i o n a l t e r r a c e . O ff the F u e r t e R iv e r d e l t a , the s h e l f i s n a r r o w e r , w ith a sh a rp edge and a somewhat ro u g h upper s l o p e . Rocky i s l a n d s and many v o l c a n i c o u t c r o p s w i t h i n the d e l t a i n d i c a t e a t h i n sed im e n t c o v e r on an i r r e g u l a r s u b s t r a t e . S e v e r a l o bv io u s d e p o s i t i o n a l s h e l v e s o ccu r and van Andel summar i z e d : T hus, i t a p p e a rs t h a t , in c o n t r a s t to th e l a r g e l y w a v e -c u t w e s te r n s h e l f , the e a s t e r n c o n t i n e n t a l t e r r a c e i s p r e d o m in a n tly d e p o s i t i o n a l in n a t u r e . Van Andel d i v i d e s th e s l o p e s below th e s h e l f b re a k i n t o t h r e e c l a s s e s on th e b a s i s of g r a d i e n t as i n d i c a t e d i n T a b le 4. H ence, most of th e g u l f shows a lm o st a f l a t b o tto m . Rusnak, F i s h e r , and S hepard r e p o r t e d : " w e l l - d e v e l o p e d s h e l v e s or t e r r a c e s a re c o n f i n e d l a r g e l y to the e a s t e r n m argin o f the c e n t r a l and s o u t h e r n g u l f . ” The w e s t e r n b o r d e r h a s p r a c t i c a l l y no s h e l f d e v e lo p m e n t, e x c e p t l o c a l l y . None of t h e a u th o r s in th e G u lf of C a l i f o r n i a sympo sium m ention th e d i s t i n c t d e c r e a s e in g r a d i e n t and o c c a s i o n a l l y wide ( > 5 0 km) to p o g r a p h i c f e a t u r e on the e a s t e r n s i d e of the G u l f . I t i s v i s i b l e on p r o f i l e s by Rusnak, e_t al. (1 9 6 4 , P l a t e 1 ); H a r r i s o n and Mathur (1 9 6 4 , p . 8 1 ); and H ild e (1964, p . 12 3). Van A n d e l 's (1964, p. 220) p r o f i l e s t e r m i n a t e a t the b e g in n in g of th e f e a t u r e . Byrne and 120 E m ery ’s (1 9 6 0 ) p r o f i l e s a l s o s u g g e s t the wide t e r r a c e . The b e s t p r o f i l e s are t h o s e by R usnak, F i s h e r , and S hepard b u t th e v e r t i c a l e x a g g e r a t i o n (60 x ) g i v e s a d i s t o r t e d view of the r e l i e f ( P l a t e 1 1 ). T able 4 . A r e a l D i s t r i b u t i o n of S l o p e s in th e G u lf of C a l i f o r n i a SLOPE TYPE PERCENT OF TRACK ( E x c l u s i v e of S h e l f ) N o r t h e r n G u lf (%) S o u t h e r n G u lf (%) < 5° 99 75 5° - 30° 1 24 . 5 > 30° - 0 .5 The f i r s t i n d i c a t i o n of t h e b r o a d , p ro n o u n ce d f e a t u r e on th e e a s t s i d e of th e G u lf i s p r o f i l e P - P ’ o c c u r r i n g im m e d i a t e l y s o u th of the m ajor i n f l u e n c e of d e l t a s e d i m e n t a t i o n . From h e re s o u th a lm o st e v e r y p r o f i l e shows a g e n t l e g r a d i e n t down to a p e r f e c t l y l e v e l , or som etim es i r r e g u l a r s u r f a c e , b elo w w hich i s a s h a r p i n c r e a s e in g r a d i e n t to th e b o tto m o f t h e G u l f . F u r t h e r m o r e , t h e t o p o g r a p h i c f e a t u r e d e e p e n s to t h e s o u t h ; i t o c c u r s on p r o f i l e s P - P ’ to N-N’ a t a b o u t 200 fms (36 5 m) and i n c r e a s e s to 300 fms (550 m) on p r o f i l e L - L ’ and r e a c h e s 700 fms ( 1 ,2 8 0 m) on p r o f i l e I - I ’ , m a i n t a i n i n g t h i s d e p t h t o th e e n t r a n c e o f th e G u l f . O ff M a z a tla n ( p r o f i l e A -A ’ ) i t c o n s i s t s o f a r i d g e - a n d - t r o u g h ty p e to p o g r a p h y w i t h r e l i e f o f s e v e r a l hun dred 121 fath o m s. The o r i g i n of t h i s f e a t u r e i s unknown b ut i t i s r e m in e s c e n t of the to pography in the Red Sea where a d i s t i n c t p l a t f o r m o c c u rs at about 500 m on both s i d e s of the s e a . From i t s seaward edge r e e f s have grown to th e surface. In the G ulf of C a l i f o r n i a i t may r e p r e s e n t one of th e major f a u l t b lo c k s in which one f a u l t o c cu rs somewhere n e ar the c o a s t ( a s su g g e ste d by g r a v i t y and m agnetic d a ta ) and the o th e r p a r t i s l o c a t e d seaward of the p l a t f o r m a t 365 m to 1,280 m where the g r a d i e n t su d d en ly i n c r e a s e s . I t a ls o seems to corresp on d to th e change from c o n t i n e n t a l to o c e a n ic c r u s t as su g g e ste d by H a r r is o n and Mathur (1 96 4). The bottom morphology i s a c o n t i n u a t i o n of th e t o p o graphy of the a d ja c e n t land a r e a s and the g e n e r a l o f f s h o r e f e a t u r e would seem t o be due to s i m i l a r s t r u c t u r a l d e v e l o p ment. The G ulf l i e s between w e stw a rd -d ip p in g f a u l t b lo c k s of Baja C a l i f o r n i a and the w e stw a rd -d ip p in g f a u l t b lo c k s of the Mexican m ain lan d . S h e p a rd ’ s (1950) c o n c l u s i o n t h a t most of the major e sca rp m en ts a re of f a u l t o r i g i n seems i n e s c a p a b le . The g r a v i t y an o m alies d i v i d e the Gulf i n t o t h r e e zones: a prom inent maximum from the G u l f ’ s mouth n o r t h to about 28° N, where a t r a n s i t i o n a re a o c cu rs (which a ls o c o rre sp o n d s to more g r a v i t y s t a t i o n s ) and the g r a v i t y max imum d i s a p p e a r s . Anomalies n o r t h of T ibu ron Is la n d are a t h i r d a r e a . A c e n t r a l Bouguer g r a v i t y maximum of about +100 to 122 +120 mgal c o r r e s p o n d s to the r e g i o n o f d e e p e s t w a te r i n the G u l f . The 0-m g al c o n to u r g e n e r a l l y c o r r e s p o n d s to th e e a s t c o a s t and a n o m a lie s a re s l i g h t l y n e g a t i v e . The w est c o a s t commonly has p o s i t i v e a n o m a lie s w hich may be due t o the n a rro w w est c o a s t s h e l f . T h is seems to i n d i c a t e much s e d i m e n t a t i o n on the m ain lan d ( e a s t ) s h e l f w h ic h a re a b s e n t on th e B a ja C a l i f o r n i a s h e l f ( w e s t ) . The g r a v i t y maximum i n the c e n t e r of the G ulf i n d i c a t e s t h a t d e n s e r r o c k s o c cu r h e r e th an on e i t h e r s i d e , p r o b a b l y i n t e r m e d i a t e betw een c o n t i n e n t a l and o c e a n i c - t y p e c r u s t s . The n o r t h e r n s e c t i o n shows 0-m gal to -20 mgal a n o m a lie s ; c o n s i d e r a b l e se d im e n t f i l l o c c u rs h e r e . H a r r i s o n and Mathur c o n c lu d e d t h a t g r a v i t y and s e i s m ic d a t a i n d i c a t e d t h a t th e s o u t h e r n s e c t o r shows a s l i v e r of c r u s t 100-km wide a t the mouth, t a p e r i n g t o 50 km w est of Guaymas. I t i s b e l i e v e d t h a t t h i s d e n s e r c r u s t in a c o n t i n e n t a l a r e a i s due t o u p w e llin g of d e n s e r m a t e r i a l in a c r a c k as B a ja C a l i f o r n i a p u l l e d away from th e m a in la n d . G i r d l e r (1958) gave a s i m i l a r e x p l a n a t i o n f o r the Red S ea. N orth o f 28° N, H a r r i s o n and Mathur p o s t u l a t e d t h a t th e G ulf p u l l e d a p a r t ( t e n s i o n ) and flow ed by p l a s t i c flo w w i t h o u t f r a c t u r i n g , t h u s c r e a t i n g an i s o s t a t i c a l l y compen s a t e d d e p r e s s i o n . S e ism ic r e f r a c t i o n d a t a i n d i c a t e t h a t th e n o r t h e r n p o r t i o n of th e G u lf h as a s t r u c t u r e l i k e t h a t o f f the s o u t h e r n C a l i f o r n i a b o r d e r l a n d , and the s o u t h e r n s e c t i o n 123 l i k e the E a s t P a c i f i c R is e ( P h i l l i p s , 1 9 6 4 ). M a g n etic p r o f i l e s r e v e a l a c l o s e a s s o c i a t i o n o f t o p o g ra p h y and m a g n e tic a n o m a lie s ( H i l d e , 1 9 6 4 ). N e g a tiv e a n o m a lie s o c cu r over s t e e p s c a r p s . C u rra y and Moore (1964) s t u d i e d the c o n t i n e n t a l s h e l f s o u th of M a z a tla n and showed t h a t t h e u p p e r c o n t i n e n t a l t e r r a c e i s composed o f a se q u e n c e o f wedges o f d e l t a i c s e d im e n ts i n t e r s p e r s e d w i t h o t h e r open s h e l f f a c i e s which g rad e seaw ard i n t o c o n t i n e n t a l s l o p e f a c i e s . Low s t a n d s of s e a l e v e l ( t o -124 m) were r e c o r d e d . The s h e l f b r e a k i s com plex, b u t i s c o n t r o l l e d by P l e i s t o c e n e d e l t a s w hich showed t h a t th e g e n e r a l l y - a c c e p t e d o r i g i n of a w o r ld - w id e s h e l f b r e a k c a u se d p r i m a r i l y by s u r f e r o s i o n d u r i n g s e a l e v e l lo w e r i n g i s o v e r s i m p l i f i e d . CENTRAL AMERICA I n t r o d u c t i o n Heacock and Worzel (1955) have p u b lis h e d e le v e n p r o f i l e s a c r o s s the c o n t i n e n t a l slo p e of Mexico and C e n tr a l America ( P l a t e 1 2 ). Worzel a tte m p te d to l o c a t e the o r i g i n a l echograms w i t h o u t s u c c e s s , hence o n ly e n la rg e m e n ts of the p u b l is h e d p r o f i l e s a re a v a i l a b l e . S e v e r a l a d d i t i o n a l p r o f i l e s were o b ta in e d by S c r ip p s I n s t i t u t i o n of Oceanography o f f Mexico, Panama, and C o sta R ic a , b u t th e s e e i t h e r c u t the slo p e a t an a c u te a n gle or the o r i g i n a l p l o t t i n g s h e e t s could not be l o c a t e d , t h e r e f o r e , th e s e p r o f i l e s were n o t u s e d . W h i t c r a f t (1944) and F is h e r (1961) have d e s c r i b e d the submarine geology b u t do n o t in c lu d e any c o n tin u o u s p r o f i l e s of th e c o n t i n e n t a l s l o p e . R e s u Its S e v e r a l p r o f i l e s c r o s s th e Middle American Trench which l i e s a t a d e p th of about 5,500 m. Beyond the t r e n c h l i e s the a b y s s a l s e a f l o o r , a v e ra g in g about 3,600 m. Many of th e p r o f i l e s show a deep s h e l f b re a k (o r p e rh a p s th e s e 124 125 are wide t e r r a c e s below the s h e l f b r e a k ) a t a d e p th of ap p r o x i m a te l y 900 m. In th e v i c i n i t y of the t r e n c h the on ly n o t a b l e f e a t u r e i s a t a d e p th of ab ou t 3,600 m where th e g r a d i e n t of the c o n t i n e n t a l slo p e e i t h e r d e c r e a s e s or i n c r e a s e s . Cocos Ridge l i e s a t an a v e ra g e d e p th of 1,800 m. Submarine canyons c u t the upper c o n t i n e n t a l s l o p e , e s p e c i a l l y n o r th w e s t of A cap u lco . These e x te n d to 600 fms to 800 fms (1 ,1 0 0 m to 1,460 m) b u t none have been t r a c e d to th e tr e n c h f l o o r ( F i s h e r , 1961 ). E ig h te e n of 24 p r o f i l e s between 97° W, n e a r P o r t An g e le s and the G uatem ala b o r d e r , show a deep t e r r a c e whose edge v a r i e s between 284 m to 366 m. T h is deep s h e l f c o n t i n u e s f a r t h e r w est a t 200 fms to n e a r 95° 1 5 ’ W, so u th of S a l i n a C ruz. From h e r e to 93° 3 0 ’ W the deep t e r r a c e l i e s a t 165 fms to 175 fm s. West o f S a l i n a Cruz the s h a llo w and deep s h e l f b r e a k s a re n a rr o w . S o u t h e a s t of Champerico o n ly th e sh a llo w s h e l f b re a k was found ( F i s h e r , 1961 ). The s h e l f b reak v a r i e s c o n s i d e r a b l y , as i n d i c a t e d in T able 5. From l a t i t u d e 20° N to A capulco a w e ll- d e v e l o p e d t e r ra c e can be i d e n t i f i e d on F i s h e r ' s p l a t e 2, a t 900 m to a b ou t 1,830 m. The g r a d i e n t o f the c o n t i n e n t a l slo p e n o r th w e s t of th e G u lf of T eh u a n te p ec a v e r a g e s 10° to 14°, w i t h a range of 5° to 24°, w h ile s o u t h e a s t of T eh u a n te p ec i t a v e ra g e s 4° to 8°. L o c a l l y , the g r a d i e n t may exceed 3 5 °. The ward sid e of th e tr e n c h s lo p e a v e r a g e s o n ly 1° to 3 °. T able 5. Depth o f C o n t i n e n t a l S h e l f Break REGION DEPTH (m) T re s M arias to M a n z a n illo Acapulco 30 m ile s SE o f A capulco to P o r t Angeles P o r t A ngeles to Guatem ala Border Champerico to G u lf de N icoya 101-110 100-256 119-183 128-165 108-165 126 s e a - WEST COAST OP SOUTH AMERICA I n t r o d u c t i o n Three so u rc e s of in f o r m a tio n were used to p r e p a r e P l a t e 13: (1) p r o f i l e s p u b lis h e d by F is h e r and R a i t t (1 9 6 2 ), (2) one p r o f i l e by the OB, and (3) e i g h t s h o r t p r o f i l e s made by S c rip p s I n s t i t u t i o n of Oceanography. Some of the numbered S c r ip p s p r o f i l e s p e rh a p s are d u p l i c a t e s of F ish er and R a i t t * s p r o f i l e s . For example, p r o f i l e 49 a p p ears s i m i l a r to p r o f i l e H-HT and 51 may be the same as B-B’ . The OB p r o f i l e is r e c o n t r u c t e d ; the rem a in der a re d i r e c t t r a c i n g s of PDR r e c o r d s . O ther p r o f i l e s have been p u b lis h e d by Z e i g l e r , A th e arn , and Small (195 7). Seism ic measurements are r e p o r t e d by F i s h e r and R a i t t (19 62 ); F is h e r and Hess (1 963); Ewing, W orzel, and Shubert (1957); Worzel (1 959); and Ewing, Heezen, and E ric s o n (1 95 9). The g e n e ra l geology of the r e g i o n has been d i s cussed in G e o lo g ic a l S o c ie ty of America Memoir 65 (se e e s p e c i a l l y Muftoz C r i s t i , 1956; and J e n k s , 1956) and by Op- penheim (1 9 47 ). No a tte m p t i s made h e re to d i s c u s s the r e g i o n a l geology or g e o p h y s ic a l i n f o r m a tio n in t h i s r e gion. 127 128 R e s u I t s I t i s o b v io u s from P l a t e 13 t h a t th e P e r u - C h i l e T re n c h has a very i r r e g u l a r s l o p e , p r o b a b l y due i n p a r t to th e p r e s e n c e of su b m a rin e c a n y o n s. The a v e r a g e s l o p e of the n e a r s h o r e p a r t of the t r e n c h v a r i e s from 2 3 / 4 ° to 6 ° , w i t h the g r e a t e s t g r a d i e n t o f f A n t o f a g a s t a . S h e l f b r e a k s , as r e v e a l e d on P l a t e 13, do n o t i n d i c a t e any l a r g e v a r i a t i o n s i n d e p th t h a t are so c o n s p ic u o u s i n most p r o f i l e s around th e w o r l d . C o r r e l a t i o n o f f e a t u r e s on th e s lo p e i s d i f f i c u l t b e c a u se of th e i r r e g u l a r n a t u r e of th e s l o p e . However, i t a p p e a r s t h a t a s l o p e change o c c u rs a t a d e p th of about 1 ,5 0 0 m t o 2,500 m. S e v e r a l p r o f i l e s s u g g e s t t e r r a c e s a t 1 ,0 0 0 m and 2,5 0 0 m. A wide t e r r a c e o c c u rs a t about 2,5 0 0 m on p r o f i l e B-B1, and the OB p r o f i l e shows a pronounced t e r r a c e betw een 1,0 00 m and 1,70 0 m. P r o f i l e s p u b l i s h e d by Z e i g l e r e t a l (1 957) have a s m a l l s c a l e and some p r o f i l e s do n o t e x te n d to s e a l e v e l . Only the g r o s s f e a t u r e s can be d e te r m in e d from t h e s e p r o f i l e s , a d e s c r i p t i o n o f which f o l l o w s : P r o f i l e A- - G u l f o f G u a y q u il. Wide t e r r a c e s b etw een 730 m and 1 ,2 8 0 m? i n c r e a s e in g r a d i e n t a t 1 ,2 8 0 m to 1 ,4 6 8 m; t e r r a c e 9 km wide a t 2,56 0 m t o 2 ,7 4 0 m; b o tto m a t 3 ,9 50 m. P r o f i l e C - - D e p a r t T a l a r a . Below s h e l f b r e a k a 129 d e p r e s s i o n to 1,460 in; a f l a t a r e a a t 915 m to 1,100 m; concave s lo p e below h e re to 5,850 m w ith minor i r r e g u l a r i s t i e s . S l i g h t t e r r a c e a t 3,290 m to 3,660 m. P r o f i l e D— Between 8° to 9° S. P r o f i l e s t a r t s a t 1.460 m; f l a t t e n i n g of minor slo p e at 2,000 m; convex slo p e to 4,570 m; d e c r e a s e i n g r a d i e n t below h e r e ; bottom a t 6,550 m. P r o f i l e E--B etw een 8° to 10° 3 0 T S. P r o f i l e b e g in s a t 1,460 m; s lo p e i s convex to 4,0 20 m where narrow (a b o u t 8-km w ide) t e r r a c e o c c u rs ; g r a d i e n t s t e e p e r to 6,620 m. P r o f i l e F- - A r r i v e C a lla o from NW. D e p re ssio n below s h e l f b reak a t 366 m to 550 m; f l a t t e r r a c e 1,100 m to 1.460 m, 35-kms to 40-kms w ide; t e r r a c e 2,377 m to 2,740 m, 37-km w ide; t e r r a c e 40-km wide a t 3,658 m to 4 ,0 2 3 m; s t e e p g r a d i e n t between 4,023 m and 3,464 m. P r o f i l e G--Leave C a lla o towards SW. Small d e p r e s s i o n and r i s e a t 914 m; f l a t t e r r a c e 47 -km wide a t 600 fms to 800 fms; smooth slo p e betw een 1,645 m to 4 ,0 23 m; sm a ll r i s e a t 3,658 m to 4 ,0 23 m; s t e e p slo p e to 6,090 m. P r o f i l e I - - L a t i t u d e 15° 3 0 T S. G e n tle g r a d i e n t ( t e r r a c e ? ) from s h e l f b reak a t 900 m; slo p e i n c r e a s e s a t 900 m and i s smooth to 3,300 m, where t h e r e i s a f l a t t e r r a c e 10-kms to 12-kms w ide; f l a t t e r r a c e 15-km wide a t 3,660 m; s t e e p g r a d i e n t to 4 ,2 0 0 m; t e r r a c e a t 4,9 40 m; bottom about 5,500 m. P r o f i l e J --From 15° S to 16° S. Upper c o n t i n e n t a l 130 t e r r a c e i s convex from s h e l f b re a k to 1,280 m; l e s s convex slope betw een 900 m to 1,280 m; t e r r a c e 15-km wide betw een 2,750 m to 3,660 m. Ridge and tro u g h a t 3,660 m to 3,840 m. S te e p between 3,66 0 m and 4 ,9 4 0 m. P r o f i l e K— From 16° 30* S to 18° 2 0 1 S. S te e p slo p e beyond s h e l f b reak and 366 m; betw een h e re and 2,000 m concave s lo p e w ith f l a t o u t e r s u r f a c e 24-km w ide; g r a d i e n t s t e e p from 2,000 m to 4,000 m; f l a t t e r r a c e 9-km wide a t 4 .0 0 0 m. G r a d ie n t below 4,00 0 m i s same as 2,000 m to 4.000 m. P r o f i l e L- - 1 9 ° S. P r o f i l e s t a r t s a t 1 ,6 5 0 m. Topo g rap h y i r r e g u l a r ; more or l e s s even g r a d i e n t betw een 2,000 m to 3,300 ra; s te e p g r a d i e n t to 4,7 5 0 m; d e c r e a s e i n g r a d i e n t betw een 4,750 m to 5,550 m; s t e e p g r a d i e n t to 6,600 m. P r o f i l e M- - 2 1 ° 2 0 ' S. P r o f i l e s t a r t s a t 3,100 m, s t e e p to 4 ,2 00 m; t e r r a c e 4 ,2 00 m to 4 ,9 4 0 m; s t e e p g r a d i e n t 4,940 m to 6,400 m where a narrow t e r r a c e ; b ottom about 4 ,1 0 0 fm s, or 7,500 m. P r o f i l e P --Due w est of A n t o f a g a s t a . I r r e g u l a r s u r f a c e to 1,200 m where t e r r a c e i s 11 km w ide; s t e e p g r a d i e n t 2,380 m to 3,100 m where sm all r i d g e and d e p r e s s i o n ; i r r e g u l a r to about 7,50 0 m (bottom ) w i t h s l i g h t s lo p e changes a t 4 ,0 0 0 m, 5,850 m, and 6,770 m. P r o f i l e Q- - 2 4 ° 5 0 ’ . Broken p r o f i l e , t e r r a c e a t 1,650 m; s t e e p g r a d i e n t 1 ,6 5 0 m to 2,75 0 m; concave s lo p e 1,650 131 m to 4 ,7 0 0 m; t e r r a c e ( ? ) b e tw e e n 4 ,0 0 0 m to 4 ,5 7 0 m; smooth s t e e p e r s l o p e 4 ,5 7 0 m to 6 ,4 0 0 m; b o tto m a t 7 ,1 0 0 m. Sum m arizing a v a i l a b l e i n f o r m a t i o n , t h e r e a p p e a r s to be a common t e r r a c e o c c u r r e n c e b etw een th e f o l l o w i n g d e p t h s : 730 m to 1,460 m, 1,650 m t o 2 ,2 0 0 m, and 2,7 5 0 m t o 3 ,6 5 0 m. S e v e r a l t e r r a c e s o c c u r as deep as 4 ,0 0 0 m to 4 ,9 5 0 m. TIMOR AND NORTHWEST AUSTRALIA I n t r o d u c t i o n A ll p r o f i l e s o ff Timor and n o r th w e s t A u s t r a l i a ( P l a t e 14) were made by S c r ip p s I n s t i t u t i o n of Oceanography. E ch ograms used to c o n s t r u c t p r o f i l e s la b e le d vA-1 to vA-13 were made a v a i l a b l e by T. H. van A n d e l. With the e x c e p t i o n of p r o f i l e s vA-11 and vA-12 (which a re EDO ech og ram s), a l l were made u sin g p r e c i s i o n d e p th r e c o r d in g equ ip m en t. O th er p r o f i l e s on P l a t e 14 were made by S c r i p p s I n s t i t u t i o n of Oceanography. P r o f i l e s were made by d i r e c t t r a c i n g of echogram s, u n c o r r e c t e d f o r changes in sh ip speed or sound v e l o c i t y . S in c e e x a c t sh ip speeds a re unknown, n e i t h e r th e bottom g r a d i e n t s nor v e r t i c a l e x a g g e r a t i o n can be giv en p r e c i s e l y ; however, the v e r t i c a l e x a g g e r a t i o n i s a p p ro x im a te ly 16 t i m e s . S h o r t , m issin g p o r t i o n s of p r o f i l e s a re th e r e s u l t of th e s h ip s to p p in g to occupy o c e a n o g ra p h ic s t a t i o n s ( l o s s in t im e ) . Wider gaps are th e r e s u l t of l o s s e s of bottom on the echosounder (no l o s s in t i m e ) . P r o f i l e s are o r i e n t e d on i l l u s t r a t i o n s w ith Timor on the r i g h t and A u s t r a l i a on th e l e f t s i d e . 132 F ig u r e 19. P r o f i l e s of A u s t r a l i a ' s c o n t i n e n t a l m a rg in . ( A f t e r F a i r b r i d g e , 1 9 5 0 .) GERALDTON HOUTMAN'S ABROLHOS ISLANDS W. S .L INDIAN OCEAN N. W. S .L INDIAN OCEAN WEST COAST SHELF MERMAID REEF BROOME NORTH-WEST SH E L FV ' \ \ \ \ \ \ \ \ " " - " ' TROUGHTON I. SAHUL BANK HOLATHURIA BANKS CAPE LONDONDERRY N. W TIMOR SEA SAHUL SHELF w w w w w THURSDAY ISLAND TIMOR W . TROUGH TORRES STRAIT REEFS MURRAY ISLAND GULF OF GULF OF CARPENTARIA PAPUA YONGE REEF IL E . S .L S. W — — — E FE ET CORAL SEA QUEENSLAND SHELF QUEENSLAND TRENCH CAPE CAPRICORN HERON ISLAND HIXSON CAY SWAIN REEFS s.w. 0 - --------------- - i F QUEENSLAND SHELF 60 80 N .B . VERTICAL SCALE EXAGGERATED X 100 100 HORIZONTAL SCALE. 0 20 40 CORAL SEA PLATFORM CAPRICORN TROUGH. ■ * ' \ \ R. W .F . FATHOMS 134 135 A d d i t io n a l p r o f i l e s a re shown on P l a t e 19 ( p r o f i l e V -3 1 -2 ), and F ig u r e 19 which shows p r o f i l e s a c r o s s the c o n t i n e n t a l t e r r a c e in a number of a r e a s o f f A u s t r a l i a . R e s u l ts A trough 2,000-m to 3,000-m deep s e p a r a t e s the i s l a n d of Timor and o t h e r i s l a n d s of the In d o n e s ia n I s l a n d Arc from n o r th w e s te r n A u s t r a l i a (se e c h a r t , lower l e f t of P l a t e 1 4 ). The c o n t i n e n t a l s h e l f o f f n o r th w e s t A u s t r a l i a i s e x c e p t i o n a l l y b ro a d , 100 m or l e s s in d e p th , and has s e v e r a l w e l l r developed t e r r a c e s , many mounds, r i d g e s , and d e p r e s s i o n s . This s h e l f is b e in g s t u d ie d in d e t a i l by van Andel and c o -w o rk e rs , b ut only the g e n e r a l r e s u l t s are known. R e c e n tly van Andel (1964a) d e s c r i b e d the s h e l f as f o l lo w s : The Sahul S h e l f , between n o r th w e s te r n A u s t r a l i a and the Timor Trough, i s of u n u su a l w id th . I t c o n s i s t s o f . a c e n t r a l b a s i n b o rd ere d by two sh a llo w r i s e s e x te n d in g from th e c o a s t to the s h e l f edge, and by one r i s e p a r a l l e l to the s h e l f edge. Superimposed on t h i s r e l i e f i s a system of b an k s, t e r r a c e s , and c h a n n e ls . The f l a t to p s o f banks and t e r r a c e s can be c o r r e l a t e d as s e v e r a l r e g i o n a l s u b h o r i z o n t a l s u r f a c e s . These a l l show e l e v a t i o n s and d e p r e s s i o n s c o r r e s p o n d ing to the b a s in and r i s e s . The upper s u r f a c e s c o n v erge toward the s h e l f edge, the lower s u r f a c e s toward the c r e s t s of th e r i s e s . The s t e p l i k e to po grap hy c l o s e l y resem b les a system of e t c h p l a i n s of p ro b a b le l a t e T e r t i a r y and P l e i s t o c e n e age, d ev elo p ed on the a d j a c e n t la n d . The upper s h e l f s u r f a c e s are c o n s id e r e d th e e x t e n s io n o f these e tc h p l a i n s . T h is r e q u i r e s u p l i f t , w e a t h e r i n g , and d e n u d a tio n of th e s h e l f in the l a t e T e r t i a r y . v The s h e l f was s u b s e q u e n tly deform ed, r e s u l t i n g in the fo rm a tio n of b a s i n and r i s e s , the o r i g i n a l d r a in a g e system m a in ta in e d i t s o r i g i n a l , but now a n te c e d e n t , p a t t e r n . In the P l e i s t o c e n e , the s h e l f slo w ly s u b s id e d , and th e lower r e g i o n a l s u r f a c e s 136 were formed d u rin g g l a c i a l s e a - l e v e l low s t a n d s . The s h e l f was, and s t i l l i s , p r i m a r i l y an a r e a o f se d im e n t- b y p a s s in g , b u t m arine d e p o s i t i o n h as been c o n tin u o u s s in c e th e Upper T e r t i a r y on the c o n t i n e n t a l s lo p e . T h is h i s t o r y of u p l i f t , e r o s i o n , s u b s id e n c e , and ma r i n e t r a n s g r e s s i o n r e p e a t s s i m i l a r , w e l l - e s t a b l i s h e d c y c l e s in th e P re c a m b ria n , P a l e o z o i c and Mesozoic in t h i s b a s i n . This s h e l f has been d e s c r i b e d by Weber ( 1 9 1 9 ), Molen- g r a a f f (1 9 2 9 ), Kuenen (1 9 3 5 ), T e i c h e r t and F a i r b r i d g e ( 1 9 4 8 ) , Davis (1 9 2 8 ), F a i r b r i d g e (1953, 1955, 1957 and 1963), C a r r i g y and F a i r b r i d g e (1 9 5 4 ), van Andel (1 9 6 4 a ), van Andel e t a l (1 9 6 1 ), and o t h e r s . A ll of t h e s e w o rk e rs have s t a t e d t h a t the S ahul S h e l f has a s h e l f b rea k a t a p p r o x i m a te l y 550 m. They have a ls o n o ted t h a t a t o l l s and r e e f s have been b u i l t up to se a l e v e l from th e edge of the s h e l f (s e e P l a t e 14, vA-2 to vA-4, and F ig u re 19). While i t i s t r u e t h a t a t o l l s and r e e f s are w e l l- d e v e lo p e d a t the edge of the s h e l f , th e r e p o r t e d 550-m s h e l f b re a k i s c o n s i d e r e d too d e ep . More commonly, th e s h e l f b re a k i s about 300 m to 400 m. I f the s h e l f b re a k i s l o c a t e d a t th e r e gion of maximum c u r v a t u r e where no d i s t i n c t b rea k o c c u r s , t h i s i s lo c a te d f u r t h e r out beyond th e b a r r i e r r e e f a t d e p th s of 400 m to 500 m. Because of th e g e n t l e se a f l o o r g r a d i e n t and the p r e s e n c e of w e ll- d e v e l o p e d t e r r a c e s on the s h e l f and c o n t i n e n t a l s l o p e , i t i s o f t e n d i f f i c u l t to p r e c i s e l y i d e n t i f y the s h e l f b re a k . S ahul S h e lf i s 350 km o f f Cape L ondo nd erry and i s n e a r l y h o r i z o n t a l in t h i s a r e a . The s h e l f edge v a r i e s from 137 45 m to about 540 m ( C a r r ig y and F a i r b r i d g e , 1954). Most of the in n er s h e l f shows w e l l - d e f i n e d t e r r a c e s (5 m to 9 m; 18 m to 27 m; and 45 m to 54 m) with a d i s t i n c t s t e p com monly o c c u r r in g at about 110 m, s e p a r a t i n g th e s h e l f i n to an in n e r and o u ter s h e l f . C a r r ig y and F a i r b r i d g e have drawn a number of p r o f i l e s a c r o s s th e s h e l f , based upon soundings from c h a r t s , b ut none extend i n t o deep w a te r . The e n t i r e a re a i s p o o r ly sounded and among the l e a s t known a r e a s of the w o rld . As a consequence, the p r o f i l e s made by van A ndel, S c r i p p s , and o t h e r r e c e n t e x p e d i t i o n s are p a r t i c u l a r l y i m p o r t a n t . C oral r e e f s and o r g a n ic banks occur a t the edge of the s h e l f , r a i s i n g from d e p th s of s e v e r a l hundred m eters ( P l a t e 14 and F igure 1 9 ). The a t o l l s r i s i n g from the deep s h e l f edge have the fo llo w in g c h a r a c t e r i s t i c : a l l r i s e from the s h e l f edge from a dep th ran g in g from about 250 m to over 550 m; th ey have the g e n e ra l a n n u la r p a t t e r n of a t r u e o c e a n ic a t o l l ; and most a re f a i r l y l a r g e . Since the e n t i r e r e g io n i s p o o r ly su rv e y ed , w ith only a few a e r i a l p h o to g ra p h s and a few echosounding p r o f i l e s , t h e r e e x i s t s some s p e c u l a t i o n co n c e rn in g the o r i g i n of the s h e l f edge a t o l l s as w e ll as the deep s h e l f b re a k . Since M o le n g raa f, Kuenen, and l a t e r w o rk e rs d id not have c o n tin u o u s echosounding p r o f i l e s , i t i s e asy to u n d e r sta n d t h e i r c o n c lu s io n t h a t a t o l l s a ro se from the edge of 138 the s h e l f and t h a t th e s h e l f b reak o c c u rre d a t 550 m. The c o n t i n e n t a l slope o f t e n app ears to be more or l e s s c o n tin u o u s on e i t h e r s id e o f the r e e f s (s e e e s p e c i a l l y vA-2 to v A - 4 ) , w ith no sharp d em a rk atio n between th e s h e l f and s i ope . To th e n o r t h e a s t , edge r e e f s or a t o l l s a re e i t h e r a b s e n t , or the echograms do not ex te n d c lo s e enough tow ards A u s t r a l i a to p ic k them up; however, a s h e l f edge r e e f can be observed on vA-9. The sou th w est p o r t i o n of the S a h u l C o n t i n e n t a l Slope has a g e n t l e g r a d i e n t more or l e s s f r e e of i r r e g u l a r i t i e s or s i g n i f i c a n t r e l i e f and i s a sy m m e tric a l with r e l a t i o n to the Timor c o n t i n e n t a l slo p e . Toward the n o r t h e a s t , t h i s p a s s e s i n t o a s t e e p e r , i r r e g u l a r c o n t i n e n t a l s l o p e , more or l e s s sy m m etrical in c r o s s - s e c t i o n w ith r e s p e c t to the In d o n e s i a n Arc c o n t i n e n t a l s lo p e . Although i t m ight be t e c h n i c a l l y c o r r e c t to r e f e r to the s o u t h e a s t e r n slo p e o f f Timor I s l a n d as an ’’i n s u l a r s l o p e , " t h i s i s c o n tig u o u s w i t h o th e r i s l a n d s l o p e s and forms a c o n tin u o u s c o n t i n e n t a l s lo p e of the In d o n e s ia n A rc. In a d d i t i o n , t h i s slo p e r e p r e s e n t s the seaward l i m i t of the v a s t South China Sea a r c h i p e l a g o . The c o n t i n e n t a l s l o p e o f f Timor and th e i s l a n d s f u r t h e r n o r t h e a s t o f f New Guinea i s r e l a t i v e l y s t e e p , h i g h ly i r r e g u l a r , w ith r e l i e f up to s e v e r a l hundred m e te r s , and shows few s i m i l a r i t i e s w ith the c o n t i n e n t a l s lo p e o f f 139 n o r t h w e s t e r n A u s t r a l i a . The to p o g rap h y from so u th w e st of Timor I s l a n d t o about the m iddle o f th e i s l a n d (vA-5) i s s i m i l a r , but f u r t h e r n o r t h e a s t the c o n t i n e n t a l s lo p e shows a d i s t i n c t change in c h a r a c t e r . H ere, the a x i s of Timor Trough i s f u r t h e r o f f s h o r e , g iv in g T im o r ’ s c o n t i n e n t a l slo p e a lower g r a d i e n t . In th e n o r t h e a s t e r n r e g io n the c o n t i n e n t a l s lo p e shows a b r o a d , g e n t l y - s l o p i n g p l a i n . Superim posed on t h i s p l a i n are r i d g e s and d e p r e s s i o n s w ith a r e l i e f of s e v e r a l hundred m e te r s . Only one p r o f i l e (vA-4) shows a s h e l f b re a k o f f Timor. Here th e s h e l f b rea k o c c u rs a t l e s s than 50 m. As a means f o r d e f i n i n g t e r r a c e s , d e s p i t e l o c a l i r r e g u l a r i t i e s , red l i n e s have been drawn along the m ajor s u r f a c e s ( h o r i z o n t a l or s t e e p l y d i p p i n g ) sm oothing out i r r e g u l a r i t i e s ( P l a t e 1 5 ). Because th e v e r t i c a l e x a g g e r a t i o n i s a p p ro x im a te ly 16 tim e s , one should n o t c o n s i d e r the p r o nounced s t e p s as r e p r e s e n t i n g high a n g le norm al f a u l t s . On the b a s i s of t h i s p l a t e , as w e l l as P l a t e 14, an a tte m p t has been made to c o r r e l a t e t e r r a c e s on b o th s id e s of the Timor Trough ( F ig u r e 2 0 ). On the A u s t r a l i a n s id e an e x tr e m e ly wide (70 km) t e r r a c e can be se e n a t 400 m to 500 m on vA-1 ( P l a t e 1 5 ). F u r t h e r n o r t h e a s t ( t o a t l e a s t p r o f i l e v A - 5 ) , t h i s t e r r a c e m a i n t a i n s i t s w id th , but c o n s i s t s o f a seaward d ip p in g p l a t e a u , r e a c h i n g a d e p th of 700 m b e f o r e the g r a d i e n t s t e e p e n s . E a s t of th e major change in to p o g ra p h y ( a t vA -7), 140 AUSTRALIAN SIDE TIMOR SIDE BA SE O F TIM O R TR O U G H H O R IZ O N T A L D IST A N CE NOT T O SC A L E F ig u re 20. C o r r e l a t i o n o f c o n t i n e n t a l t e r r a c e f e a t u r e s o f f n o r th w e s te r n A u s t r a l i a and Timor I s l a n d . 141 t h i s d i s t i n c t t e r r a c e a t a p p r o x im a te ly 500 m can be i d e n t i f i e d on a l l p r o f i l e s , b u t i t has a s t e e p e r g r a d i e n t and i s n a r r o w e r . A nother t e r r a c e o c c u r s be tw ee n 800 m and 1,200 m, av e r a g i n g 1,000 m. I t i s l e s s c o n tin u o u s th a n the p r e v i o u s t e r r a c e , but on s e v e r a l p r o f i l e s i t i s d i s t i n c t (s e e P l a t e 15, vA-7 to v A - 9 ) . On p r o f i l e vA-8 i t a t t a i n s a w id th of 20 km. The s u r f a c e of th e t e r r a c e i s i r r e g u l a r n o r t h e a s t of v A -7 . The d e e p e s t t e r r a c e i s l o c a t e d at 1,3 00 m to 1,500 m. I t i s l o c a l but pronounced on a few p r o f i l e s . F e a t u r e s a t t h i s d e p t h , as w e l l as a t 1,000 m, are commonly o b se rv ed as a change in s l o p e , h e n c e , may n o t be a t e r r a c e sensu s t r i c t o . Timor Trough may have a f l a t f l o o r (s e e vA-2 and vA-5) h aving a maximum w id th of 13 km, b u t more commonly i t h a s a V -shaped a sy m m e tric a l p r o f i l e (vA-1 and v A - 8 ) . One p r o f i l e (vA-9) r e v e a l s a r i d g e about 200-m h ig h in the c e n t e r of the t r o u g h . S e v e r a l o t h e r p r o f i l e s have to p o g ra p h y n e a r th e f l o o r w hich a l s o s u g g e s t s r i d g e s a lo n g the s i d e s of th e t r o u g h . P r o f i l e LH-6 was made a t a low a n g le a c r o s s th e S a h u l C o n t i n e n t a l T e r r a c e . T h is shows pronounced f l a t a r e a s a t s e v e r a l d e p th s which have l i t t l e or no r e l i e f . These p r o f i l e s s u g g e s t t h a t su b m arin e canyons a r e a b s e n t alo n g t h i s s e c t i o n of n o r t h w e s t e r n A u s t r a l i a . 142 On the Timor s id e o f the tro u g h , s e v e r a l d i s t i n c t p la t f o r m s can be i d e n t i f i e d , v a ry in g in w id th to 75 km or more (see P l a t e 1 5). Superimposed on th e s e are r i d g e s and d e p r e s s i o n s w ith r e l i e f of s e v e r a l hundred m e te rs . Some of the more prom inent r i d g e s and d e p r e s s io n s can be t r a c e d b e tween s e v e r a l c r o s s - s e c t i o n s , or c o v e rin g l a t e r a l d i s t a n c e s of t e n s of k i l o m e t e r s . S e v e ra l p r o f i l e s show l a r g e b l o c k l i k e h o r s t s upon which are superim posed s m a ll e r r e l i e f f e a t u r e s . A d i s t i n c t t e r r a c e a t d e p th s of 250 m to 600 m, or d e e p e r , can be re c o g n iz e d on most p r o f i l e s t h a t are s u f f i c i e n t l y s h a llo w . On vA-12, t h i s t e r r a c e i s a t l e a s t 25-km w ide. The s u rf a c e of the t e r r a c e i s h i g h ly i r r e g u l a r and has l o c a l r e l i e f up to 100 m. Another l o c a l , pronounced t e r r a c e a c c u rs a t 700 m to 1,000 m. N o r t h e a s t of p r o f i l e vA-3, most p r o f i l e s show a w e l1-d evelo ped t e r r a c e at 1,400 m to 1,700 m. P r o f i l e s to th e so u th w est of p r o f i l e s vA-3 show a s l i g h t f e a t u r e which a l s o s u g g e s ts c o r r e l a t i o n . S t i l l a n o th e r t e r r a c e p o s s i b l y may e x i s t a t about 2,000 m (se e vA-7, vA-9, vA-10, and vA-11), but due to i r r e g u l a r to pography d e f i n i t e c o n c l u s i o n s c a n n o t be r e a c h e d . As p r e v i o u s l y m en tio n ed , many of the s u r f a c e s having h i g h ly i r r e g u l a r to pography can be tr a c e d over c o n s i d e r a b l e d i s t a n c e s . I t is a ls o p ro b a b le t h a t many o f the f e a t u r e s n e ar the f l o o r of the tro u g h are r e l a t e d to p r o c e s s e s t h a t have formed th e Timor Trough i t s e l f . 143 GegJ-g&E E le v a t e d c o r a l r e e f s occur on Timor I s l a n d , as w e l l as on o t h e r i s l a n d s in the E a s t - I n d i a n A r c h ip e l a g o . The i s land c o n s i s t s of ro c k s ra n g in g in age from P erm ian to Re c e n t . One of the most unique d e p o s i t s i s a pu re G l o b i g e r - in a lim e s to n e of Neogene age. R e s tin g on t h i s deep w a te r d e p o s i t are c o r a l r e e f d e p o s i t s of p ro b a b ly Miocene age, fo llo w e d by s h a llo w w a te r t e r r e s t r i a l and m arine d e p o s i t s of P l i o c e n e age. A g raben o c c u rs alo n g the c e n t r a l p a r t of the i s l a n d in which the G l o b i g e r i n a , s h a llo w w a te r r e e f , and t e r r i g e n o u s se d im e n ts were d e p o s i t e d . O ther c o r a l r e e f s occur o u t s i d e t h i s g ra b e n . S t r u c t u r a l and s t r a t i - g r a p h ic e v id e n c e p o i n t s to m ajor u p l i f t s on Timor and n e a r by i s l a n d s . M o le n g ra a ff (1913) s u g g e s te d u p l i f t i s s t i l l c o n t i n u i n g . The c e n t r a l u p l i f t has been somewhat g r e a t e r th an t h a t along th e s o u t h e r n or n o r t h e r n c o a s t a l r e g i o n s . No f r i n g i n g r e e f s are found on e i t h e r th e n o r th w e s t e r n or s o u t h e a s t e r n c o a s t s d e s p i t e the ob vio us l a r g e u p l i f t s t h a t have o c c u rre d on Timor. M o le n g ra a ff e x p la in e d t h i s rem a rk ab le f a c t by p o i n t i n g o u t t h a t b o th c o a s t s a re b o r d ered by l a r g e f a u l t s . Major m ountain r i d g e s are c u t o f f s h a r p l y by c o a s t a l f a u l t s , w i t h no o b v iou s seaward c o n t i n u a t i o n s , e i t h e r as i s l a n d s or s h o a l s . M o le n g ra a ff con- c lu d e s : A ll o b s e r v a t i o n s made along t h i s c o a s t give s u p p o r t to the o p in io n t h a t th e i s l a n d t e r m i n a t e s h e re a g a i n s t 144 a f a u l t fa c in g the Timor Sea . . . I f we accep t the e x is te n c e of these b rea k s, the q u e s tio n a r i s e s : what has been detached towards the n o rth and south? C le a r ly i t must be the sunken b locks of land which are found in the deep b a s in s of the Timor Sea and the Savoe Sea . . . Not only Timor, however, is thus bordered a t both s id e s by deep sea b a s i n s , b ut i t i s a c o in c id e n ce which holds good fo r the m a jo r ity , i f not a l l , - of the i s l a n d s of the e a s t e r n p o r t i o n of the a rc h i p e l a g o , c o n seq u en t ly , the o r i g i n of the deep sea b a s in s and the e l e v a t i o n of the i s l a n d s in the e a s t e r n p o r t io n of the a r c h i p e l ago may be re g a rd e d as a sim u ltan eo u s p ro c e ss between which a g e n e tic c o n n ec tio n must have e x i s t e d . . . The g e n e sis of a d jo in in g sunken and t i l t e d block s must be the r e s u l t of one and the same c r u s t a l movement, which in my opin io n would be the cause of a p r o c e s s of f o l d ing a t g r e a t d e p th s . A b e l t o f l a r g e , n e g a tiv e g r a v i t y anom alies p a r a l l e l s Timor Trough, w ith the g r e a t e s t o c cu rrin g over Timor Isla n d i t s e l f . These n e g a tiv e anom alies c o in c id e w ith a l l the i s land s and submarine r id g e s where stro n g fo ld in g and o v e r t h r u s t i n g of s u rfa c e ro ck s have been found. Presum ably, maximum c r u s t a l s h o r te n in g occu rred du ring the Lower Miocene and P l i o - P l e i s t o c e n e epochs (de Waard, 1954). W esterveld (1955) doubts t h i s l a t e r p e rio d of f o l d in g . According to W esterveld , Timor and a d ja c e n t i s l a n d s belong to the Moluccas Fold System which in clu ded f o ld in g and o v e r t h r u s t i n g p r i o r to the g e n eral Lower Miocene t r a n s g r e s s i o n . D ep o sits of Neogene age were a ls o s t r o n g l y d i s tu rb e d . Vening Meinesz (1954, 1964) has c ro sse d the Timor Trough a t s e v e r a l l o c a t i o n s and has shown t h a t most of the sea f l o o r a d ja c e n t to w e stern A u s t r a l i a i s in i s o s t a t i c e q u il i b r i u m , but the Timor Trough has a zone of e x trem ely 14 5 n e g a t i v e a n o m a lie s. Thus, ev id e n ce i s c o n c lu s iv e t h a t Timor Trough (and a d ja c e n t r e g i o n s ) i s one of g r e a t t e c t o n i c a c t i v i t y , and u p l i f t and su b sid e n c e has been a c t i v e s i n c e the Miocene per i o d . Most of w e s te r n A u s t r a l i a c o n s i s t s of the A u s t r a l i a n S h i e l d , b u t fo u r major se d im e n ta ry b a s i n s on the c o n tin e n t's m argin are f i l l e d up to 1,200 m of p re d o m in a n tly marine ro ck s from Cambrian to T e r t i a r y in age ( T e i c h e r t , 1958). L o c a ll y , th e s e se d im e n ts a re g r e a t l y f a u l t e d and g e n t l y fo ld e d but have not s u f f e r e d major o ro g e n ic c o m pression . F a i r b r i d g e (1955) p o i n te d out t h a t the amount of downwarp i s 1.6 km to 6 .4 km. These b a s i n s c o n tin u e seaward in to d e p r e s s i o n s r e c o g n i z a b le on the c o n t i n e n t a l s h e l f and even the c o n t i n e n t a l s lo p e . The n o r th e r n m o s t b a s i n - - B o n a p a r t e G u lf B a s i n - - h a s 5,380 m of se d im e n t. I t i s shown on P l a t e 14, lower l e f t ; i t s e s t im a t e d seaward p o s i t i o n i s shown w ith a d o t te d l i n e . I t i s assumed t h a t i t s seaward p a r t c o rr e s p o n d s to the major to p o g ra p h ic changes o c c u r r in g a t the p o s i t i o n of p r o f i l e s vA-6 and vA-7. F u r t h e r to th e s o u th w e s t, a t the ap pro xim ate edge of the map b o r d e r , an o th e r major se d im e n ta ry b a s in o c c u r s . Between th e s e two b a s i n s i s pre-C am brian ro ck. The n o r t h e r n p a r t of t h i s s t a b l e , p r e r Cambrian age ro c k , the K im berly Block, c o n t i n ues seaward and the subm arine p o r t i o n i s termed the London d e r r y R ise ( F a i r b r i d g e , 1955). 146 C a r r i g y and F a i r b r i d g e (1 9 5 4 ), T e i c h e r t ( 1 9 5 8 ), and F a i r b r i d g e (1955) have p o in te d out t h a t the West A u s t r a l i a n S h e l f i s not a c o m p a r a tiv e ly r e c e n t f e a t u r e as i s the case f o r most c o n t i n e n t a l t e r r a c e s . Since the P a l e o z o i c e r a i t was p a r t of the A u s t r a l i a n c o n t i n e n t a l m ass. The h i s t o r y of th e c o n t i n e n t and o f f s h o r e r e g io n have had s i m i l a r h i s t o r i e s . In c o n t r a s t to the g r e a t m o b i l i t y , s e i s m i c i t y , and v o lca n ism of the Timor r e g i o n , A u s t r a l i a i s n o te d f o r i t s g r e a t s t a b i l i t y . The t e c t o n i c a c t i v i t y (on the c o n t i n e n t ) , as su c h , c o n s i s t e d of l o c a l l y - s u b s i d i n g b a s i n s which have not been f o l d e d . ■ C a r r i g y and F a i r b r i d g e (1954) n o te d t h a t th e s h e lv e s a re w id e s t and d e e p e s t o p p o s i t e the s e d im e n ta r y b a s i n s on the m ain lan d , w hereas pre-C am b rian r i d g e s , p l a t f o r m s , or p o s i t i v e b lo c k s were r e f l e c t e d on the s h e l f a ls o as narrow , p o s i t i v e f e a t u r e s . F u r t h e r , c o r a l r e e f s and a t o l l s occur o p p o s i t e the younger b a s i n s . T h is s u g g e s t s t h a t th e deep s h e l v e s , s h e l f edge c o r a l r e e f s and a t o l l s , and th e s u b s i d ing b a s i n s on th e m ainland a re r e l a t e d . S tr o n g c i r c u m s t a n t i a l e v id e n c e t h e r e f o r e p o i n t s to s u b s id e n c e alo n g th e n o r t h w e s t e r n A u s t r a l i a n S h e l f . In a d d i t i o n , the s h e l f has been m o d ified by P l e i s t o c e n e e u s t a t i c changes in sea l e v e l as re c o rd e d by d i s t i n c t t e r r a c e s s h a llo w e r than 110 m. Whether the s h e l f was warped w i t h a hinge l i n e n e a r th e p r e s e n t - d a y c o a s t , or i s th e r e s u l t of a s e r i e s o f f a u l t s w ith s t r i k e s p a r a l l e l to th e c o a s t i s p r o b l e m a t i c . Faultin g 147 o r w a rp in g must have o c c u r r e d in r e l a t i v e l y r e c e n t g e o l o g i c t im e . In c o n c l u s i o n , w h i l e s u b s i d e n c e and f a u l t i n g a lo n g th e n o r t h w e s t c o a s t of A u s t r a l i a may a p p e a r to be anom alous in view o f the s t a b l e A u s t r a l i a n s h e l f , e v id e n c e e x i s t s w hich p r o v e s c e r t a i n p a r t s of the c o n t i n e n t and o f f s h o r e a r e a a re r e g i o n s of s u b s i d e n c e . D a v is (1 928) d i s c u s s e d th e S a h u l S h e l f and compared i t w i t h th e Sunda S h e l f . The l a t t e r r e g i o n has a w e ll-k n o w n b a r r i e r r e e f - - t h e G r e a t Sunda B a r r i e r R e e f - - s t r e t c h i n g a lo n g th e e a s t e r n e d g e . D av is c o u ld f i n d no e v id e n c e f o r a b a r r i e r on S ahu l S h e l f . M o l e n g r a a ff (1 9 2 9 ) and th e A us t r a l i a n P i l o t c o n s i d e r e d th e s c a t t e r e d r e e f s and submerged s h o a l s as a "much i n t e r r u p t e d b a r r i e r r e e f . " T e i c h e r t and F a i r b r i d g e (1948) were of th e o p i n i o n t h a t th e s c a t t e r e d i s l a n d s , r e e f s , and s h o a l s o f th e S a h u l S h e l f c o u ld be gro u p ed i n t o s e v e r a l i n t e r r u p t e d s e r i e s . E ch o so u n d in g p r o f i l e s in th e a r e a sounded show t h a t r e e f s , a t o l l s , and i s l a n d s a re n e a r l y c o n t i n u o u s to ( a t l e a s t ) l o n g i t u d e 118° E. Thus, on th e b a s i s o f e c h o s o u n d i n g , a n e a r l y c o n t i n u o u s s h e l f edge b a r r i e r r e e f now seems e s t a b l i s h e d . T e i c h e r t and F a i r b r i d g e ( 1 9 4 8 ) , in d i s c u s s i n g th e s h e l f - e d g e a t o l l s , p o i n t e d out th e d i f f i c u l t y in e x p l a i n i n g t h e i r o r i g i n . S ubm arine e l e v a t i o n s of v o l c a n i c o r i g i n seem u n l i k e l y ; t h e r e g i o n l a c k s v o l c a n is m . I t i s an a s e i s m i c 148 r e g i o n and the a u t h o r s do n o t b e l i e v e th e c o n t i n e n t a l slo p e i s t e c t o n i c a l l y a c t i v e , a s , f o r ex am p le, the J a v a T re n c h . T e i c h e r t and F a i r b r i d g e p r e c l u d e d th e g r e a t d e p th of the p l a t f o r m (300 m to 550 m) as th e r e s u l t of P l e i s t o c e n e e u s t a t i c lo w e rin g of s e a l e v e l , y e t D avis and o t h e r w o rk e rs term the a t o l l s as ''n o r m a l ,” h e n c e , i t must be assumed t h a t " D a rw in ia n s u b s id e n c e " i s e s s e n t i a l . D e s p ite th e o b v io u s s t a b i l i t y of th e A u s t r a l i a n c o n t i n e n t , T e i c h e r t and F a i r b r i d g e a re f o r c e d to c on clud e " t h a t t h e r e may be some sym p a t h e t i c e p e i r o g e n i c movement in th e o ld c o n t i n e n t . . . ." The a u t h o r s s u g g e s te d t h r e e p o s s i b i l i t i e s : (1 ) s u b s id e n c e w ith seaw ard t i l t i n g , ( 2 ) e u s t a t i c s e a l e v e l lo w e r i n g , and (3 ) f a u l t i n g . As a comprom ise, th e y t e n t a t i v e l y s u g g e s t t h a t " s u b s id e n c e has o c c u r r e d , p o s s i b l y in c o n n e c tio n w ith o r o g e n ic a c t i v i t y in the a d j a c e n t E a s t I n d i a n A rc s, which has e x p r e s s e d i t s e l f as a combined t i l t i n g and down f a u l t ing o f th e o u t e r m argin of the A u s t r a l i a n c o n t i n e n t a l s h e l f , so t h a t the c o n t i n e n t a l edge h e re i s now marked by the 30 0 -fath o m l i n e . " Q u a t e r n a r y e u s t a t i c s e a l e v e l ch an ges have made t h e i r mark by th e f o r m a t i o n of a s e r i e s of t e r r a c e s and s h a llo w w a te r r e e f s . Echograms p r o v id e a d d i t i o n a l d a t a n o t a v a i l a b l e to T e ic h e r.t and F a i r b r i d g e . F i r s t , a b a r r i e r r e e f and a t o l l s e x i s t a t th e s h e l f edge which s t r e t c h e s o v e r a d i s t a n c e of h u n d re d s of k i l o m e t e r s beyond a v a i l a b l e e ch o so u n d in g d a t a . Second, many of th e s e s h e l f edge r e e f s and a t o l l s do n o t occur a t p r e c i s e l y the edge of the c o n t i n e n t a l s h e l f . For example, p r o v i l e s vA-3 and vA-4 are l o c a te d on a broad g e n tly s lo p in g p la t f o r m . T h ird , a moat f r e q u e n t l y occurs behind the s h e lf -e d g e r e e f s (s e e p r o f i l e vA-2) and two or more r e e f s may occur n ear the edge of the s h e l f (see p r o f i l e vA-2 and vA-7). F o u rth , the g e n e r a l im p re ssio n of the c o n t i n e n t a l slo p e west of vA-7 i s one of g e n tle downbuckl- ing and c o n s i s t s of a b ro a d , smooth, convex-shaped slope r a t h e r than a concave shape so commonly observed in most p a r t s of the w orld. This r e g io n i s b e lie v e d to be l a r g e l y pre-Cam brian age ro c k . E a s t of p r o f i l e vA-7, the c o n ti n e n t a l slope i s steep, i r r e g u l a r , and has s t e p s . Here, oppo s i t e Bonaparte Gulf B a sin , p o s s i b l e f a u l t i n g may have oc cu rre d in sympathy w ith t e c t o n i c movements w i t h i n the East In d ian I s la n d Arc. Evidence s t r o n g l y su g g e s ts g e n e r a l su b sid ence f o r n o r th w e s te r n A u s t r a l i a and o ff the In d o n esian I s la n d Arc. SOUTHWEST PACIFIC I n tr o d u c t i o n A number of s c a t t e r e d echogram s a re a v a i l a b l e i n the so u th w e st P a c i f i c Ocean, i n c l u d i n g f o u r p r o f i l e s o f f V i e t nam, 12 o f f Ja v a and B a l i , seven from the n e a r Halmahera I s l a n d to New G uinea, and 19 from e a s t e r n A u s t r a l i a and New Z e a la n d . No a tte m p t i s made to d e s c r i b e the l o c a l g e o lo g y o f t h i s v a s t r e g i o n s i n c e i n s u f f i c i e n t echogram s are a v a i l a b le t o make any com p ariso ns w i t h echogram s and the g e o l ogy. Nor i s c o r r e l a t i o n p o s s i b l e b e ca u se o f th e wide s p a c ing of p r o f i l e s . P r o f i l e s were d e r i v e d l a r g e l y from t h r e e s o u r c e s : R u s s ia n (OB and VITYAZ), from v a r i o u s c r u i s e s made by S c r i p p s I n s t i t u t i o n of O ceanography, and s e v e r a l p r o f i l e s from B ro die (1 9 5 2 ). The p r e c i s e l o c a t i o n o f th e fo rm er two are somewhat in d o u b t. OB and VITYAZ p r o f i l e s a re c o r r e c t ed f o r sound v e l o c i t y ; S c r i p p s p r o f i l e s are u n c o r r e c t e d . P r o f i l e s a re n o t a lig n e d in any p a r t i c u l a r o r d e r . S e v e ra l o t h e r p r o f i l e s are shown on F ig u re 21. 150 151 R e s u l t s Four p r o f i l e s o f f Vietnam betw een 13° to 16° N were made n e a r l y p e r p e n d i c u l a r to th e c o n t i n e n t a l s lo p e ( P l a t e 1 6 ). A l l o f th e s e p r o f i l e s show wide t e r r a c e s a t d e p th s o f 300 m to 500 m. S e v e r a l echogram s ( p r o f i l e s 1 and 2) show t e r r a c e s a t b o th d e p t h s . Only p r o f i l e 3 shows no p r o nounced f e a t u r e s a t a d e p th n e a r 500 m. A lth o u g h s e v e r a l echogram s e x te n d t o more than 2,000 m, no c o n c l u s i o n s can be drawn abo ut f e a t u r e s below 500 m. Two p r o f i l e s n e a r M o ra ta i and H alm ahara I s l a n d s show a s t e e p c o n t i n e n t a l s lo p e w ith an i r r e g u l a r r i d g e a t a b o u t 500 m and a t e r r a c e , or r i d g e , a t a d e p th o f about 2,000 m ( P l a t e 17, V-25-5 and V - 2 5 - 8 ) . R e c e n tl y , Marova (1963) d e s c r i b e d th e P h i l i p p i n e T re n c h , i n c o r p o r a t i n g b o t h R u s s ia n and GALATHEA echogram s ( K i i e r i c h , 1 9 5 9 ). U n f o r t u n a t e l y , a l l of th e echogram s a c r o s s th e t r e n c h show o n ly th e low er p o r t i o n s o f th e c o n t i n e n t a l s l o p e . I t i s a p p a r e n t t h a t the P h i l i p p i n e T rench h as many of th e c h a r a c t e r i s t i c s of o t h e r t r e n c h e s , w i t h a g e n t l e u p p e r p r o f i l e and a s t e e p low er p o r t i o n . The mean g r a d i e n t of the s lo p e i s 5° to 6°, b u t the low er s l o p e s are 15° to 30°, and l o c a l l y exceed 35 °. The mean g r a d i e n t o f th e e a s t e r n s l o p e , which i s about 3-km to 5-km h i g h , i s about 4 ° , and l o c a l l y g r a d i e n t s a re 25° to 4 0 ° . Marova p o i n te d o ut t h a t many t e r r a c e s o c cu r on the m id dle and low e r s l o p e s and have w i d t h s v a ry in g from 6 km to 700 km. 152 Such t e r r a c e s a r e l e s s p ro n o u n ce d on th e seaw ard s i d e of th e t r e n c h s l o p e . Off M indanao, a t 3 ,0 0 0 m, i s a t e r r a c e 37-km w id e . S e v e r a l wide t e r r a c e s a t d e p t h s o f 4 ,0 0 0 m t o 6,50 0 m can be o b s e r v e d b u t i n s u f f i c i e n t p r o f i l e s a re a v a i l a b l e to a s c e r t a i n i f t h e s e have any g r e a t h o r i z o n t a l e x t e n t . The a u t h o r i n d i c a t e d t h a t f o l d i n g and f a u l t i n g have a c c o u n te d f o r much o f th e o b s e r v e d to p o g r a p h y . The P h i l i p - p e a n T rench was formed i n th e Upper M esozoic e r a ( p o s s i b l y e a r l i e r ) and th e i n n e r c r e s t o f the P h i l i p p i n e Arch a l s o a p p a r e n t l y h as been in e x i s t e n c e s i n c e th e Upper M e so z o ic . However, the g e o s y n c l i n e i s s t i l l d e v e l o p in g and i s p a r t of t h e g roup of i s l a n d a r c s s t r e t c h i n g n o r th w a r d from I n d o n e s i a . The P h i l i p p e a n T re n c h s h o a l s b o t h to th e n o r t h and s o u t h , a t t a i n i n g a maximum d e p th o f 1 0 ,4 2 7 m. I t i s 1 ,4 4 5 -km lon g and 92-km w id e . S e ism ic i n v e s t i g a t i o n s i n d i c a t e th e t r e n c h i s f i l l e d w i t h 5 km of T e r t i a r y age s e d i m e n t s . The o u t e r c r e s t of th e a r c h as T e r t i a r y and Q u a t e r n a r y s e d im e n ts and a c t i v e v o l c a n o e s . The c o n s e n s u s i s t h a t th e t r e n c h i s c o n n e c te d w i t h a zone o f deep o v e r t h r u s t i n g c au se d by p r e s s u r e of th e c o n t i n e n t a l m a rg in on t h e bed of th e ocean and t r a v e r s e s u n d e r the i s l a n d a r c . E a r t h q u a k e s have i d e n t i f i e d the l o c a t i o n of t h i s f a u l t z o n e . T e r r a c i n g of th e t r e n c h s l o p e i n d i c a t e s t h a t f o l d i n g o f the t r e n c h i s accom panied by num erous f a u l t s (M arova, 153 1963) . P r o f i l e V -25-5 a p p e a r s to e x te n d i n t o the s o u t h e r n p a r t of th e P h i l i p p i n e T rench b e c a u s e i t h a s a s t e e p c o n t i n e n t a l s lo p e and r e a c h e s to n e a r l y 6,0 0 0 m. S e v e r a l s m a ll s t e p s a p p e a r on the s l o p e a t i n t e r v a l s of 500 m to 1 ,0 0 0 m. L a r io n o v a (1 959) r e p o r t e d t h a t t e c t o n i c l e d g e s , i n th e form of a g i g a n t i c s t a i r c a s e , occur on p r o f i l e s of th e P h i l i p - pean Trench ( s e e F ig u r e 9 ) . T h is p r o f i l e , as w e l l as most o t h e r s in th e r e g i o n (V -2 5-3 , - 4 , - 5 , - 6 , - 8 , - 9 , and -10) shows a d i s t i n c t r i d g e a t a d e p th a v e r a g i n g 500 m. A nother s i m i l a r i t y among s e v e r a l p r o f i l e s i s a s l i g h t , or m ajor r i s e beyond the ba se of th e c o n t i n e n t a l s l o p e (V -2 5 -2 , -3 , - 4 , - 5 , -6 , and - 9 ) . On o c c a s i o n , s h o a l i n g beyond th e base of th e s lo p e i s h i g h l y i r r e g u l a r and has c o n s i d e r a b l e r e l i e f (V -25-5 and - 9 ) . P r o f i l e V -2 5 -4 , n e a r A d m ira lty I s l a n d , has a wide t e r ra c e at 2,200 m to 2,400 m, w i t h l o c a l r i d g e s r i s i n g to 1,900 m. Beyond th e wide t e r r a c e th e s lo p e i s v e r y s t e e p to 4 ,5 0 0 m. P r o f i l e V -25-10, b etw een B o u g a i n v i l l e and New I r e l a n d , c o n s i s t s of a s e r i e s of l a r g e r i d g e s and d e p r e s s io n s r i s i n g from more th a n 7 km to n e a r s e a l e v e l . One of the r i d g e s i s t r u n c a t e d a t 500 m to 600 m and c o r r e s p o n d s to a n o th e r wide s t e p a t th e same d e p th n e a r the i s l a n d . Two r i d g e s have common f e a t u r e s a t 1 ,8 00 m to 2 ,2 0 0 m and the n e x t to d e e p e s t r i d g e has a t e r r a c e a t 2,900 m t o 3,200 m. P r o f i l e V -2 5 -9 , so u th of R abaul I s l a n d , c o n s i s t s of a 154 v e ry s t e e p s lo p e betw een 900 m and 8 ,0 0 0 m. The f i r s t b re a k in s lo p e o c c u r s a t about 900 m. A sm a ll t e r r a c e o c c u r s a t 2,1 0 0 m and s e v e r a l minor s t e p s o ccu r a t s e v e r a l o t h e r d e p t h s . The s lo p e i n c r e a s e s i t s g r a d i e n t s l i g h t l y a t 3,900 m. Near th e s o u t h e a s t end of New G u in e a, p r o f i l e V-27-6 shows a convex s lo p e betw een 400 m to 2,000 m. The s lo p e i n c r e a s e s s i g n i f i c a n t l y a t 1,0 00 m and s lo p e changes or t e r r a c e s occur a t ab ou t 2,0 00 m. The slo p e i n c r e a s e s s i g n i f i c a n t l y a t 1 ,0 0 0 m and s lo p e c h an g e s or t e r r a c e s o c cur a t a bo ut 2,000 m and 3,2 0 0 m. P r o f i l e s V -27-2 and -3 o ccur o f f P o r t M oresby, New G u inea. The maximum d e p th a t t a i n e d i s about 2,500 m where th e p r o f i l e s t e r m i n a t e in a l a r g e b a s i n . V -27-2 a p p e a rs to have been made d i r e c t l y down the i n s u l a r s l o p e and shows a v e r y s t e e p s l o p e . V-27-3 i s a d u a l p r o f i l e u p s lo p e ( r i g h t s i d e ) and downslope from P o r t Moresby. The l e f t p a r t o f th e p r o f i l e a p p e a rs to c u t a c r o s s th e c o n t i n e n t a l s l o p e at an a c u te a n g l e . I t r e v e a l s a group o f c h a n n e l s , or r i d g e s and d e p r e s s i o n s , r a n g ing from 500 m to 1,5 00 m. Twelve p r o f i l e s o f f J a v a and B a l i a re shown on P l a t e 18. R. F i s h e r , of S c r i p p s I n s t i t u t i o n o f O cean og raph y, has many a d d i t i o n a l p r o f i l e s a c r o s s the J a v a - S u m a tr a T ren ch b u t t h e s e were n o t made a v a i l a b l e . When t h e s e p r o f i l e s a re p u b l i s h e d and combined w i t h o t h e r s ( P l a t e 1 8 ) , a f a i r l y d e t a i l e d c o r r e l a t i o n d ia g ra m can be c o n s t r u c t e d . A c u r s o r y e x a m in a tio n o f the F i s h e r ’s p r o f i l e s and V-31-6 and -7 155 i n d i c a t e s the t r e n c h s lo p e i s among the most i r r e g u l a r ob served anywhere to d a t e . While i r r e g u l a r i t i e s , in p a r t , can be e x p la in e d by the f a c t t h a t some p r o f i l e s cut the slo p e a t an a n g le , r e v e a l i n g many submarine canyons, many p r o f i l e s t h a t appear normal to th e slo p e show much r e l i e f along the slo p e (su c h as V -3 1 -6 ). S e v e ra l of the p r o f i l e s (V -31-5, -6 , and -7) show ma j o r b re a k s in slo p e g r a d i e n t a t about 3,000 m. Below t h i s d e p th the g r a d i e n t i s much s t e e p e r . V-31-5 a p p a r e n t l y has a slo p e so ste e p t h a t the echosounding re c o rd was l o s t b e low 1,700 m, but a f e a t u r e o c c u rs a t 2,200 m to 2,600 m t h a t a p p a r e n t l y can be c o r r e l a t e d on V-31-5 and -7. Most of the sh a llo w e r p r o f i l e s show t e r r a c e s , slo p e chan ges, or r i d g e s between 500 m and 1,200 m. The edge of the c o n t i n e n t a l s h e l f shows c o n s i d e r a b le v a r i a t i o n in d e p th as i n d i c a t e d in Table 6. Seven p r o f i l e s are a v a i l a b l e f o r the r e g i o n o f f w e s t e rn and so u th w e ste rn A u s t r a l i a ( P l a t e 19, upper h a l f ) . P r o f i l e V-31-2 p r o p e r l y b e lo n g s in the d i s c u s s i o n on n o r t h w e s te r n A u s t r a l i a and Tim or. T h is p r o f i l e shows h i g h ly i r r e g u l a r topography between 1,000 m to 2,000 m, w ith summits a t 1,000 m which cover a c o n s i d e r a b l e h o r i z o n t a l d i s t a n c e . The base of the slo p e o c c u rs a b r u p t l y a t about 3,200 m. A wide t e r r a c e e x i s t s a t 500 m. P r o f i l e V -31-3, between N orth West Cape and Cape I n s p i r a t i o n , i s convex in shape; i t i s r e l a t i v e l y g e n t l e down to about 1,800 m and s t e e p 156 T able 6. Approxim ate Depth o f S h e lf Break o f f J a v a and B a l i 1 PROFILE DEPTH (m) V-31-7 80 21 225 V-31-6 100 20 50 19 200 18 200 V-31-5 200 39 500 ? 38 300 ? 41 50 40 80 below 2,000 m. An i n d i s t i n c t t e r r a c e seems to o ccur a t about 1,100 m. The rem a in d e r of th e s lo p e i s i r r e g u l a r to i t s b a se a t more th a n 5,000 m. Three p r o f i l e s o ccur i n the v i c i n i t y of F re em a n tle (LA-2, V -31-4, and L H - 1 ) . V-31-4 i s the o n ly p r o f i l e t h a t t r a v e r s e s d i r e c t l y up the c o n t i n e n t a l s l o p e ; however, b ecause o f th e bend in i s o b a t h s , LA-2 a ls o may be n e a r l y norm al to th e c o n t i n e n t a l t e r r a c e . P r o f i l e LA-2 shows a t e r r a c e a t a b ou t 700 m and a m ajor i n c r e a s e in the g r a d i e n t a t 1,200 m. A sm a ll t e r r a c e a p p e a rs a t 3,100 1See P l a t e 19 f o r l o c a t i o n . 157 m. The s h e l f may a l s o have a t e r r a c e betw een a b o u t 50 m and 300 m. P r o f i l e V -31-4 i s i r r e g u l a r and th e p r e s e n c e of subm arine canyons i s s u g g e s t e d . The t e r r a c e a t l e s s than 300 m and a t 400 m to 600 m seems t o c o r r e l a t e w i t h t h a t on LA-2. U n lik e th e p r o f i l e to th e n o r t h ( V - 3 1 - 3 ) , a sm a ll c o n t i n e n t a l r i s e i s e v id e n t on p r o f i l e V -31-4. P r o f i l e LH-1 c u t s the c o n t i n e n t a l t e r r a c e a t an a c u t e a n g le r e v e a l ing h i g h l y i r r e g u l a r t o p o g r a p h y , p r o b a b l y the r e s u l t of subm arine c an y o n s. T e r r a c e s may e x i s t a t 500 m to 600 m, 1 ,4 0 0 m, 2,0 0 0 m, 2 ,5 0 0 m, 3,0 00 m, and p o s s i b l y a t l e s s th a n 300 m. S o u th w e st A u s t r a l i a ( p r o f i l e s 11 and 13) has a narrow s h e l f and a s t e e p c o n t i n e n t a l s l o p e . Narrow t e r r a c e s a p p e a r on th e s h e l f and p o s s i b l y a t d e e p e r d e p t h s . Shepard (1 9 6 3 , p. 294) r e p o r t e d a s l o p e o f f s o u t h w e s t e r n A u s t r a l i a of 27°; to th e n o r t h the s l o p e d e c r e a s e s and i s i l e s s th a n 1 o f f n o r t h w e s t e r n A u s t r a l i a . D i e tz (1948) p u b l i s h e d a p r o f i l e o f th e c o n t i n e n t a l s l o p e from th e South A u s t r a l i a n B a s in i n t o Bass S t r a i g h t betw een A u s t r a l i a and T asm an ia. (The p r o f i l e s t a r t s a t 40° 52* S, 142° 3 7 T E and f o l l o w s a c o u rs e of 40° t r u e . ) T his shows a s h e l f b rea k a t 145 m, a s t e e p (6 ° ) u p p e r s l o p e , w i t h a s h a rp d e c r e a s e i n g r a d i e n t t o 2° a t a b o u t 990 m. Below the b r e a k in g r a d i e n t , th e to p o g ra p h y i s i r r e g u l a r and hummocky. D ie tz s u g g e s t e d t h a t th e s h a r p b re a k in g r a d i e n t m ig ht be the r e s u l t of d e t r i t u s t r a n s p o r t e d a c r o s s th e s h e l f , moved down th e 6° s l o p e , and b u i l t up as a wedge of s e d im e n t a t 158 the g e n t l e r angle o f r e p o s e ; the hummock might be a t t r i b u ted to land s l i d e s o r o t h e r mass movements. P r o f i l e s a c r o s s the c o n t i n e n t a l slo p e of s o u t h e a s t A u s t r a l i a t y p i c a l l y show a sh a rp b rea k in t h e s h e l f a t about 100 m; th e lower c o n t i n e n t a l slo p e i s s t e e p e r th a n the upper c o n t i n e n t a l s lo p e and l o c a l l y 15° or more; a sh a rp boundary o c c u rs between the c o n t i n e n t a l slope and the f l o o r of the Tasman Sea w ith no c o n t i n e n t a l r i s e ; a f e a t u r e a t 2,000 m to 3,000 m ap p ea rs to be c o r r e l a t i v e on most p r o f i l e s ; and no submarine canyons are known to o c c u r. Ac c o rd in g to S tand ard (1 9 6 1 ), the averag e g r a d i e n t of the c o n t i n e n t a l slop e b o r d e r in g the Tasman Sea i s 6°. P r o f i l e 35, taken so u th of Cooktown, i s a s h o r t p r o f i l e a c r o s s the u pper p a r t of the c o n t i n e n t a l slo p e seaward of the G re a t B a r r i e r R eef. I t shows a sm all t e r r a c e j u s t below the s h e l f break; and a d i s t i n c t d e c r e a s e in the g r a d i e n t a t about 1,200 m. P r o f i l e s S-6 and S-7 ( P l a t e 19) show s e v e r a l banks and guyots in the Tasman Sea and a c r o s s - s e c t i o n of Lord Howe R is e . The l a t t e r is s e v e r a l hundred k i l o m e t e r s wide and l i e s at an average d e p th of 1,280 m, b u t a l a r g e p a r t l i e s a t d e p th s of 900 m. Only s i x p r o f i l e s a re a v a i l a b l e from the New Z ealand a r e a and are n o t r e p r e s e n t a t i v e of the r e g i o n . OB-1-7 e x te n d s from 5,000 m to l e s s th a n 1,000 m, t e r m i n a t i n g o f f Auckland I s l a n d . U n f o r t u n a t e l y , i t d o es not show a good 159 p r o f i l e o f the New Z e a la n d , or Campbell P l a t e a u , which i s about 500 m ile s w id e . Most o f t h i s l a r g e p l a t e a u l i e s a t a d e p th of about 500 m to 1,500 m (Adams, 1 9 6 2 ). P r o f i l e s V-26-3 and 66, on th e w est s i d e of th e i s l a n d s , show o n ly p a r t of th e c o n t i n e n t a l slo p e and the form er p r o f i l e c u ts the s lo p e a t a h ig h a n g le . V-26-3 shows s e v e r a l t e r r a c e s i n c l u d i n g one at 1,000 m, a marked t e r r a c e a t a b o u t 1,000 m, on one end of th e p r o f i l e , and a marked t e r r a c e a t about 600 m. With the e x c e p ti o n o f p r o f i l e 66, a l l show some f e a t u r e s a t about 1,00 0 m, g e n e r a l l y c o n s i s t i n g of i r r e g u l a r to p o g rap h y a t a bo ut t h i s d e p th . B rodie (1952) o b ta in e d s e v e r a l a d d i t i o n a l p r o f i l e s o f f w e s t e r n New Z ea la n d and b r i e f l y d e s c r i b e d th e m ajor subm ar ine f e a t u r e s . Lord Howe R ise s h o a l s to 460 m to 730 m where i t j o i n s New Z e a la n d , and to p o g rap h y bounded by th e s e 2 d e p th s c o v e rs an a r e a of a t l e a s t (1 3 ,0 0 0 km ) . An e c h o gram was o b ta in e d showing sm ooth, l e v e l t e r r a c e s a t 900 m and 768 m, 9-km and 18.5-km w id e , r e s p e c t i v e l y . At a d e p th of 550 m t h e f l o o r was f l a t f o r a d i s t a n c e of 92 km o f f s h o r e . S e v e r a l sh a rp changes of r e l i e f o c c u r , i n c l u d i n g a peak r i s i n g to 400 m. Beyond h e re the g r a d i e n t i n c r e a s e s u n t i l th e bottom o f the c o n t i n e n t a l slo p e i s rea ch e d a t 869 m. 160 Geology G r e a t B a r r i e r Reef The G re at B a r r i e r Reef i s c o n s i d e r e d a t y p i c a l example (on a l a r g e s c a l e ) of a m o r p h o lo g i c a l f e a t u r e t h a t le d to D a rw in ’ s b e l i e f in th e s u b s id e n c e t h e o r y . Here i s exposed a l i n e of r e e f s , a p p a r e n t l y u n c o n n e c te d w ith l a n d , a f l a t - f l o o r e d s h a llo w la g o o n w ith o c c a s i o n a l p a t c h e s of c a l c a r e ous d e p o s i t s , and a f r i n g i n g r e e f a t t a c h e d to most of the i s l a n d s in th e la g o o n . No d o u b t e x i s t s t h a t the G re a t B a r r i e r Reef i s a prime e x a m p le --a n d the l a r g e s t — of an e p i c o n t i n e n t a l s e a . (See F ig u r e 21 and P l a t e 1 9 ) . 2 The r e e f c o v e rs an a r e a e x c e e d in g 275,000 km , i t s mean d i s t a n c e from th e c o a s t i s 55 km, b u t as much as 160 km in c e r t a i n p l a c e s . The lag o o n b eh in d the o u t e r r e e f i s 18 m to 27 m d e e p , b u t to th e s o u th i t i n c r e a s e s to about 100 m. The G re a t B a r r i e r Reef i s e n t i r e l y of r e e f m a t e r i a l . The r e e f i s n o t alw ays a t the edge of th e s h e l f ; o f t e n i t i s f a r i n l a n d from i t . Nor is th e o u t e r r e e f c o n ti n u o u s as an u n b ro ken c h a i n . A few i s l a n d s e x i s t o f f s h o r e i n the l a goon and c o n s i s t s of th e i d e n t i c a l ro c k s as on the m a in lan d . Ig n o r in g the in n u m e rab le f a c t o r s of r e e f grow th ( s u c h as e c o l o g i c c o n t r o l ) , th e e x i s t a n c e of a l i n e of r e e f s o f f Q u een slan d i s g e o m o r p h o l o g ic a ll y or s t r u c t u r a l l y c o n tr o l le d . EAST WEST LIZARD ISLAND, MAX 1178 FT EM REEF (IN STRIKE OF ROCKY ISLETS) FEET +6Q0 LOOKOUT POINT YONGE REEF 15 fm. 15 fm LAT. 14°40'S. -600 PORT DOUGLAS 6 - 8 fm . LOW ISLES .15 fm . -600 CAPE GRAFTON , BATT REEF INFILLED LAGOON 25 fm . V///////Z////,, ARLINGTON REEF PARTIALLY FILLED LAGOON MICHAELMAS CAY 25 fm . +600- LAT. 16°40'S. FEET ,CAPE CAPRICORN +600 - i 15 fm. 7 / / / / Z / / S , . - 6 0 0 -J 600 F T . • HERON ISLAND 35 fm . N .B . ABSENCE OF OUTER BARRIER LAT. 23 25'S. 60 fm . \ 732 F T . J rt* APPROX: 30 MILES OMITTED EXPLANATION: HORIZONTAL SCALE: 0 2 4 6 8 10 CORAL h FORAMINIFERAL (giggl GLAUCONITIC SAND (UNDIFFERENTIATED) QUARTZ SAND NAUTICAL MILES VERTICAL SCALE EXAGGERATED X 20 HARD BASEMENT (PALEOZOIC GNEISS h SCHIST) Figure 21. C r o s s - s e c tio n a l p r o f i l e s across Great B a r rie r Reef at various l a t i t u d e s . (A fter R. F a ir b r id g e , 1950.) 161 162 F a i r b r i d g e (1950) s t a t e d t h a t the Queensland S h e lf has had a r e l a t i v e deg ree o f s t a b i l i t y through the Recent epoch, or a t l e a s t f o r the l a s t 4,000 y e a r s . The o u t e r b a r r i e r r e e f s are d i v i s i b l e i n t o two s e c t o r s : the n o r t h e r n zone c o n s i s t s of c r e s c e n t i c rib b o n or l i n e a r r e e f s , w hereas the s o u th e rn zone of o u te r r e e f s is d is c o n ti n u o u s and c o n s i s t s of i s o l a t e d p a tc h e s and sm all p l a tf o r m s . R eefs in th e n o r th e r n group l i v e a few hundred m e te rs from the 200-m i s o b a t h , and the 2,000-m i s o b a th l i e s only 8 km from the r e e f . This is a lso t y p i c a l o f the r e e f s of New C aledonia and o f the o th e r mobile b e l t s (Spender, 1930). The o u te r slo p e shows a s t e p at 200 m, w ith s te e p s lo p e s above and below t h i s t e r r a c e . This ste e p f r o n t of the r e e f f r o n t is g e n e r a l l y b e li e v e d to mean t h a t the r e e f grew upward a t a r a p id r a t e . Such double s t e p s are not un iform because of d i f f e r e n t r a t e s of s u b s id e n c e . Shepard (1963) r e p o r te d t h a t a t 22° S, where the s h e l f i s w id e st ( o u t s i d e the r e e f ) , i t has d e p th s of a t l e a s t 400 m. The so u th e rn zone of r e e f s i s d i s c o n t i n u o u s , has su b merged r i d g e s , and the landward s h e l f f l o o r i s about 72 m - - e x c e p t i o n a l l y deep f o r the Queensland S h e l f . The seaward s id e of the o u te r r i d g e , 36 m to 54 m deep, drops on the seaward s id e to 72 m onto a narrow s h e l f , then descends to 200 m. F a i r b r id g e sug gested t h a t the o u te r rid g e may be a drowned o u te r b a r r i e r i n i t i a t e d in e a r l y Wilrm tim e, w hereas the n o r t h e r n zone was formed on a much deeper basement in 163 e a r l y P l e i s t o c e n e or even l a t e T e r t i a r y tim e . In any e v e n t , th e b a se o f the r e e f s t r u c t u r e alm ost c e r t a i n l y i s w e l l below the lo w e s t l i m i t of P l e i s t o c e n e e u s t a t i c se a l e v e l lo w e rin g ; su b s id e n c e must have o c c u r r e d as a r e s u l t . F a i r b r i d g e (1950) h as p o i n t e d out t h a t the R ecent s h e l f se d im e n ts a re m a in ly t e r r i g e n o u s bu t in c lu d e some c a l c a r e o u s m a t e r i a l , t h u s , the c o r a l r e e f s of the G r e a t B a r r i e r complex could n o t grow up from t h e f l o o r of th e l a goon u n der e x i s t i n g c o n d i t i o n s . Smith and I r e d a l e (1924) r e c o g n iz e d beach ro c k a t 120 m along the edge of New South Wales S h e l f and a t t r i b u t e d i t t o e u s t a c is m . W ilkenson (1887) th o u g h t t h i s s h e l f was due to l a t e r T e r t i a r y f a u l t i n g w h ile Hedley (1910) s u g g e s te d i t in v o lv e d a b ro a d asym m etric downwarp of the Tasman B asin and f a u l t i n g . G arden er (1915) a l s o c o n s i d e r e d i t as a t y p i c a l f a u l t s c a r p . Guppy ( 1 8 9 0 ), David (1 9 1 1 ) , J e n se n ( 1 9 1 1 ) , Bryan (1 9 4 4 ), and C o tto n (1949) a l l a t t r i b u t e d the s t e e p (7 ° to 14°) c o n t i n e n t a l s lo p e to f a u l t i n g . The co ncensus i s , a c c o rd in g to F a i r b r i d g e (1 9 5 0 ), t h a t the deep e r o s i o n s u r f a c e w i t h beach ro c k i s lower than P l e i s t o c e n e e u s t a t i c s e a l e v e l changes and p r o b a b l y i s r e l a t e d to w id e sp re a d p e n e p l a n a t i o n w a rp in g and f r a c t u r i n g in l a t e T e r t i a r y tim e . F u r t h e r s u b s id e n c e o c c u rre d as r e c e n t l y as l a t e P l e i s t o c e n e tim e . F a i r b r i d g e f u r t h e r p o i n te d out t h a t th e o u t e r edge of the s h e l f i s f a u l t e d , b u t t h a t the s t e e p s l o p e d i e s out 164 g r a d u a l l y t o th e s o u t h e a s t and i s obscure at Swain Reefs (about 21° 3 0 ’ S). He concluded t h a t the Queensland S h e lf and the Coral Sea are the p ro d u c t of a " g i g a n t i c hinge f a u l t " s lo p i n g down to th e n o r t h and g r a d u a l l y i n c r e a s i n g from a few hundred m e te rs in the s o u t h e a s t to about 2,000 m in the n o r t h e r n s e c t o r of the G re a t B a r r i e r R eef. The G re a t B a r r i e r Reef has been s t u d i e d f o r ov er a c e n t u r y , and w hile th e g e n e r a l n a tu r e of the G reat B a r r i e r R eef i s known, yet the f o u n d a t i o n of the w o r l d ’ s l a r g e s t r e e f complex i s s t i l l unknown. J . Beete J u k e s , n a t u r a l i s t on HMS FLY (18 4 3 -1 8 4 7 ), made th e f i r s t and s t i l l the most v a l i d d e s c r i p t i o n of the G re at B a r r i e r Reef. Ju k es n o ted e v id e n c e of s u b s id e n c e along th e Queensland c o a s t , and a ls o a r e c e n t sm a ll e l e v a - to r y movement, th en w ro te: " A f te r se ein g much of the G re a t B a r r i e r R e e fs, and r e f l e c t i n g much upon them, and t r y i n g i f i t were p o s s i b l e by any means to evade the c o n c l u s i o n s to which Mr. Darwin has come, I cannot h e lp adding t h a t t h i s h y p o t h e s is i s p e r f e c t l y s a t i s f a c t o r y to my mind, and r i s e s beyond a mere h y p o th e s is i n t o the t r u e th e o r y of c o r a l r e e f s . " Jukes then drew a h y p o t h e t i c a l c r o s s s e c t i o n which c l e a r l y su g g ested g r e a t t h i c k n e s s f o r the r e e f . (See F i g u r e 2 2 .) Darwin, in h i s book S t r u c t u r e and O r ig in of C o ral Reefs (1 8 4 2 ), i n d i c a t e d in h i s p o s t u l a t e of su b s id e n c e t h a t he a ls o had " e v e ry re a s o n f o r b e l i e v i n g t h a t t h e r e are now BARRIER R EEF QUEENSLAND Figure 22. Diagram atic cro ss s e c tio n of subsurface s t r u c t u r e of the Great B a rrie r Reef. I t i s g e n e ra lly believed th a t the regio n e a st of Queensland c o n s i s t s of a s e r i e s of f a u l t block s. 166 l a r g e a r e a s g r a d u a l l y s i n k i n g , in th e same manner as o t h e r s a re r i s i n g . When we c o n s i d e r how many p a r t s of th e s u r f a c e o f th e g lo b e have e l e v a t e d w i t h i n r e c e n t g e o l o g i c a l e p o c h s , we must adm it t h a t t h e r e have been s u b s i d e n c e s on a c o r r e spon ding s c a l e , f o r o t h e r w i s e , t h e whole g lo b e would have s w o l l e n . ” I n 1896, A le x a n d e r A g a s s iz made a q u ic k s u r v e y as f a r n o r t h as L i z a r d I s l a n d (1 4 ° 4 0 ’ S ) . He was of th e o p i n io n t h a t the G re a t B a r r i e r Reef c o n s i s t e d o f a t h i n v e n e e r upon a c o n t i n e n t a l p l a t f o r m w hich has b e en s t a t i o n a r y s i n c e th e C r e t a c e o u s p e r i o d . E. C. Andrews r e p o r t e d in 1922 ( a f t e r a d e t a i l e d s t u d y made in 1902) t h a t the r e e f was o f P l e i s t o c e n e age w hich had grown on a p l a t f o r m b e v e l e d o f f by th e s e a d u r i n g th e g l a c i a l p e r i o d ( i . e . , D a l y ’s g l a c i a l c o n t r o l t h e o r y ) . He gave e v id e n c e of d i f f e r e n t i a l movement in w hich th e c o a s t a l a r e a has s u b s i d e d w h i l e th e i n l a n d a r e a h a s r i s e n . L a t e r , C. H ed ley and T. G. T a y l o r gave a d d i t i o n a l e v id e n c e f o r d i f f e r e n t i a l movement a t the end o f th e T e r t i a r y p e r i o d , wi th d e p r e s s i o n in th e e a s t and e l e v a t i o n i n th e w e s t d u r in g w hich tim e ’’m atu re r e e f p l a i n s ” were b u i l t up by th e d e p o s i t i o n o f s e d im e n t b etw een th e m a in la n d and r e e f . R i c h a r d s and H ed ley ( R i c h a r d , 1922, 1923) i n d i c a t e d t h a t "one g e t s th e g e n e r a l b u t d i s t i n c t i m p r e s s i o n o f a f o u n d e r e d c o a s t a l r e g i o n p a r a l l e l to th e e n t i r e l e n g t h s o f the G r e a t B a r r i e r R e e f, and t h a t many o f t h e c o r a l r e e f s 167 between the o u te r b a r r i e r r e e f and the m ainland were once e l e v a t e d and now are subm erged." From Sandy Cape (24 21* S) to Cape C a p ric o rn no high o f f s h o r e i s l a n d s e x i s t , and the " c o a s t shows ev id e n ce of a r e c e n t sm a ll e l e v a t i o n f o l low ing along the c o n s i d e r a b l e d e p r e s s io n along the Queens lan d c o a s t . The c o n t i n e n t a l s h e l f i s here c o n t r a c t e d , and e a rth q u a k e shocks have r e c e n t l y emanated from movements w i t h i n the r e g i o n . " From Cape C a p ric o rn to G lo u c h e s te r Head (19° 5 9 ’ S) d i s t i n c t ev id ence of su b s id e n c e o c c u rs--d ro w n e d m ountain r a n g e s , s t e e p c o a s t , and high p ro m o n to rie s s e p a r a t e d by a lo w - ly in g r e g i o n - - a n d t h i s f a c e s th e g r e a t e s t s h e l f w id th o f f e a s t e r n A u s t r a l i a . S t i l l f a r t h e r n o r t h v o l c a n ic f e a t u r e s are e v id e n t and mark th e t e r m i n a t i o n of th e r e e f . At a p p ro x im a te ly 24° S the w a te r i s too cold f o r c o r a l grow th, y e t the s h e l f i s i d e n t i c a l to t h a t where c o r a l s f l o u r i s h f a r t h e r n o r t h . T h is was r e p o r t e d by T. W. Vaughan in 1917. However, o t h e r w orkers a t t r i b u t e the f u r t h e r s o u th e r n growth to the e f f e c t of muddy w a te r . Vaughan and D aly, l i k e A g a s s i - , b e li e v e d the r e e f was a t h i n v e n e e r, p e rh a p s 60 m to 100 m t h i c k , and was formed s i n c e th e P l e i s t o c e n e epoch. A g a s s iz , G a rd e n e r, and An d r e w s ’ views a l s o s u b s c r ib e d to t h i n c o r a l r e e f . J u k e s , W. M. D a v ie s, S a v i 11e - - K e n t , H edley, and T aylo r b e li e v e d the r e e f to be o f g r e a t t h i c k n e s s . The d i f f e r e n c e in views i s dependent upon th e 168 im p o rtan c e a t t r i b u t e d to s u b s id e n c e as w e ll as th e age a s sig n e d the G re a t B a r r i e r R e e f. Old r i v e r c o u r s e s c an n o t be t r a c e d on the p r e s e n t sea f l o o r such a s was done by M o le n g ra a ff on the Sunda S h e l f . A ttem p ts have been made to e x p l a i n o p e n in g s in the o u t e r r e e f as marking th e o ld e n t r a n c e s to the se a of c o a s t a l r i v e r s which once flow ed a c r o s s t h e s h e l f . T h is seems un l i k e l y in view of th e f a c t t h a t the c h a n n e ls cannot be i d e n t i f i e d and s u f f i c i e n t tim e has e la p s e d f o r r e e f m a t e r i al to c l o s e t h e i r o p e n i n g s - - i f th e r i v e r - o r i g i n were v a l i d . R ich ard and Hedley su g g e ste d t h a t the o p e n in g s were a s s o c i a te d w ith " c o a s t a l v a l l e y s ” of fo u n d e re d s t r i p s on th e edge of which now e x i s t s the G re a t B a r r i e r R e ef. In 1918, B risb a n e s u f f e r e d a s e v e r e e a r t h q u a k e . The e p i c e n t e r was r e p o r t e d l y l o c a t e d e a s t of Bundaberg ( L a t . 25° S ) . Submarine c a b l e s b etw een Bundaberg and New C a l e d o n ia have o f t e n been broken where th e y c r o s s a b a s i n e a s t of B re a k se a S p i t . T h is l a t t e r r e g i o n i s of c o n s i d e r a b l e i n t e r e s t f o r a minor c o n t r o v e r s y e x i s t s about l a r g e s e a f l o o r changes in the a r e a (B ry an , 1 9 3 6 ). (See a p p e n d i x .) Lenox-Conyngham (1925) s t a t e d t h a t th e o u t e r edge, where th e G r e a t B a r r i e r Reef now grows, came i n t o e x i s t e n c e b e f o r e the c o r a l and t h a t th e c o r a l d id n o t c o n s t r u c t i t but m erely too k a d v an tag e o f i t s p r e s e n c e . P a r t of t h i s e v id e n c e l i e s in V aughan’s r e p o r t in 1917 t h a t c o r a l s c a n n o t grow in the cold w a t e r s below 24° S, y e t th e s h e l f has 169 a form i d e n t i c a l to t h a t f a r t h e r n o r t h where re e f-g ro w in g anim als f l o u r i s h . The a u th o r , however, m a in ta in s the a r e a covered by the G reat B a r r i e r Reef i s an a re a of su b s id e n c e . Among the l i n e s of e v id ence are a d e e p ly in d en ted m ainland and c u r i o u s l y i r r e g u l a r i s l a n d s o f f s h o r e . The evidence s u g g e s ts a new c o a s t; t h a t the land has only r e c e n t l y sunk and th e w a t e r s flowed i n t o the embayments. J . S. G ard iner ( in Lenox-Conyngham and P o t t s , 1925, p. 332) noted t h a t a s i t u a t i o n s i m i l a r to t h a t of the G reat B a r r i e r Reef e x i s t s o ff th e c o a s t of B r a z i l . Here the r e e f c o n s i s t s of cemented sand (beach ro c k ) which has a L i t h o - thamniun r i d g e - - b u t no c o r a l r e e f . In a l l p a r t i c u l a r s , as f a r as can be d e te rm in e d , the A u s t r a l i a n and B r a z i l i a n r e e f s are i d e n t i c a l , yet one has no c o r a l r e e f . G ard iner a lso p o in te d to an a re a sou thw est of Ceylon, between G alle and Colombo, where a tro u g h e x i s t s between land and o f f shore b a r r i e r but has no c o r a l r e e f s . A ncient r e e f s e x i s t e ls e w h e re , such as in F i j i , and none are more than a few hundred f e e t t h i c k . F i n a l l y , c e r t a i n f r i n g i n g r e e f s of E ast A f r i c a , i f th e y were submerged 100 m, would look i d e n t i c a l to the G reat B a r r i e r Reef p l a t f o r m . G ardiner con cluded by su g g e stin g t h a t a l l of the P a c i f i c r e e f s are very r e c e n t — 200,000 to 500,000 y e a r s - - a n d were a s s o c i a t e d w ith P l e i s t o c e n e g l a c i a t i o n . I t i s w e ll e s t a b l i s h e d t h a t c o r a l r e e f s are composed of m a t e r i a l much too l i g h t to cause i s o s t a t i c ad ju stm en t as 170 they accum ulate. (See d i s c u s s i o n on Bahama P l a tf o r m and a p p end ix , Bucher and o t h e r s . ) In 1929, J . A. S t e e r s summarized v a r i o u s o p in io n s on th e G reat B a r r i e r Reef and agreed w ith the m a j o r i t y t h a t the r e e f i s the r e s u l t of submergence and t h a t f a u l t i n g has played a p a r t . In 1937, S t e e r s made a n o th e r e x t e n s i v e sum mary on the p h y sio g ra p h y of the G reat B a r r i e r R eef. Yonge (1930) p o in te d out t h a t L ith o th a m n iu n f l o u r i s h e s b e s t where the s u r f b rea k s and cem ents i t s e l f i n t o a s o l i d ra m p a rt. He a ls o showed t h a t the o c c a s i o n a l deep c h a n n e ls through the b a r r i e r a re k e p t c l e a r of m arine growths by t i d a l c u r r e n t s which are n o t l e s s th an e i g h t k n o t s . R ic h a rd s (1940) r e p o r t e d on two b o r i n g s made on the G re a t B a r r i e r R eef. C o ra l extended t o d e p th s of 120 m and 137 m, r e s p e c t i v e l y , where c o a rse t e r r i g e n o u s sand and s e d iment was d r i l l e d f o r a n o th e r 61 m and 85 m, r e s p e c t i v e l y . F a i r b r i d g e (1950) showed the g e n e r a l s t r u c t u r e of the r e e f based upon t h e s e b o r i n g s (F ig u re 2 1 ). Thus, the b o r i n g s f a v o r su b s id e n c e and a re c o n s i d e r a b ly d e e p e r th an can be e x p la in e d by g l a c i a l c o n t r o l . In 1959, a 576-m w e ll was d r i l l e d on Wreck I s l a n d , l o c a te d a t the s o u th e rn end of the G reat B a r r i e r Reef (L at 23° S ) . One hundred s i x t y - t w o m eters of R ecent c o r a l r e e f m a t e r i a l was p e n e t r a t e d , fo llo w ed by T e r t i a r y se d im e n ts from 162 m to 547 m (M ott, 1960). The u n d e rly in g bedrock i s p ro b a b ly P a le o z o ic metamorphic rock s i m i l a r to t h a t on 171 th e m ain lan d n e a r b y ( S t a n d a r d , 1 9 6 1 ). A n o th er w e l l was d r i l l e d on Heron I s l a n d , l o c a t e d 9 .6 km so u th of Wreck I s l a n d . T h is w e l l r e v e a l e d a marked i n c r e a s e in t e r r i g e n o u s m a t e r i a l a t 153 m and was th o u g h t to have been a s s o c i a t e d w i t h the e u s t a t i c change of se a l e v e l of 100 m d u r i n g the l a s t g l a c i a l p e r i o d ( R i c h a r d s and H i l l , 1 9 4 2 ). T h is would i n d i c a t e a p o s t - P l e i s t o c e n e s u b s id e n c e i n t h i s r e g i o n of a b o u t 60 m. In c o n c l u s i o n , w h ile th e basem ent or f l o o r of th e G re a t B a r r i e r R eef s t i l l h a s not been p e n e t r a t e d , good r e a sons e x i s t t h a t s u p p o r t th e g e n e r a l c o n c l u s i o n t h a t the o f f s h o r e s t r u c t u r e i s t e c t o n i c a l l y c o n t r o l l e d . A d ia g r a m m a tic view o f th e p r o b a b l e o f f s h o r e s t r u c t u r e i s s u g g e s te d in F ig u re 2,2. G e o p h y s ic a l i n f o r m a t i o n so f a r h a s n o t p r o v id e d much new i n f o r m a t i o n about th e s t r u c t u r e o f f e a s t e r n A u s t r a l i a . S o u t h e a s t A u s t r a l i a and W estern New Z ea la n d No c o n t i n e n t a l - t y p e c r u s t e x i s t s e a s t of th e p r e s e n t A u s t r a l i a n c o a s t ( O f f i c e r , 1955; and E ib y , 1 9 5 8 ). The c r u s t above t h e M o h o ro v ic ic d i s c o n t i n u i t y a lo n g e a s t e r n A u s t r a l i a r e p o r t e d l y i s 37 km t h i c k , and i s s e p a r a t e d from Tasman B a s in ( w i t h 5-km of c r u s t ) by th e c o n t i n e n t a l s l o p e (D o y le, E veringham , and Hogan, 1 9 5 9 ). The d e e p e s t p a r t of th e Tasman B a sin l i e s a t the w e s t e r n m arg in n e a r the A us t r a l i a n c o n t i n e n t a l s l o p e . V oisey (1959) and S ta n d a rd 172 (1961) have su g g e ste d t h a t th e s e "d eep s" are p o s s i b l y rem n a n ts of an a n c ie n t s o u t h e a s t e r n A u s t r a l i a n tr e n c h which i s n e a r l y f i l l e d w ith sed im en ts and are analogous to the J a p a nese and A le u tia n T ren c h es. Major d i f f e r e n c e s e x i s t b e tween the tr e n c h e s of the North P a c i f i c Ocean and e a s t e r n A u s t r a l i a b ut th e s e a u th o r s b e l i e v e Tasman Basin i s c o n s i d e r a b l y o ld e r than the Ja p an e se and A le u tia n T ren c h es. F u r t h e r , they su g g e st Tasman B asin may r e p r e s e n t the remains of a te c to g e n e ( f o r e deep) a s s o c i a t e d w ith c o n t i n e n t a l grow th. According to t h i s view, the c o n t i n e n t a l slo p e of s o u t h e a s t e r n A u s t r a l i a r e p r e s e n t s the maximum eastw ard growth of the g e o s y n c lin e . C eleb es S e a --S u lu Sea T his r e g i o n has had a g e o lo g ic h i s t o r y much l i k e t h a t in o th e r p a r t s of the P a c i f i c rim in v o lv in g e x te n s i v e C re ta c e o u s v o lca n ism , i n t e n s e L ate Miocene and Q u a te rn a ry o r o geny. The s t r u c t u r a l geology i s the r e s u l t of a complex i n t e r a c t i o n of s t r i k e - s l i p f a u l t i n g , t h r u s t f a u l t i n g , b lock f a u l t i n g , f o l d i n g , v o lca n ism , e r o s i o n , and s e d i m e n ta t io n . Krause (1964d and 1964e) i n d i c a t e d t h a t most of the o ld e r g e o lo g ic in f o r m a tio n of the re g io n i s out o f d a t e , l a r g e l y because of the la c k of good g e o p h y s ic a l and geochem ical d a t a . L e f t l a t e r a l f a u l t i n g in the P h i l i p p i n e I s l a n d s p a r a l l e l i n g the P h i l i p p i n e Trench has been r e c e n t l y observed ( A lle n , 1962). The main f a u l t has been t r a c e d as f a r south 173 as Mati on the n o r t h e a s t c o rn e r of Cape San A g u s tin . Krause s u g g e s te d t h a t t h i s f a u l t c o n t i n u e s a t l e a s t as f a r s o u th as 3° N, or a t o t a l d i s t a n c e of 1,650 km. Good c o r r e l a t i o n e x i s t s between f a u l t i n g and v o lc a n o e s . Krause s t a t e d t h a t ample e v id e n c e e x i s t s of subm arine v e r t i c a l movements in th e r e g i o n in the form of s c a r p s , a b y s s a l p l a i n s a t d i f f e r e n t l e v e l s , p a r t i a l l y - f i l l e d t r o u g h s , t h ic k c o r a l p l a t f o r m s , c o n g lo m e ra te s a t g r e a t d e p t h s , deep t e r r a c e s , e t c . Kuenen (1950) a l s o has c a l l e d a t t e n t i o n to the l a r g e u p l i f t s in s u r r o u n d in g i s l a n d s , such as u p l i f t e d r e e f s a t e l e v a t i o n s of 1,000 m. R e c e n tly , New e l l (1960) q u e s t io n e d th e i n t e r p r e t a t i o n of h i g h l y e l e v a t e d r e e f s as i n d i c a t i n g ip so f a c t o P l e i s t o c e n e u p l i f t . He b e l i e v e s t h a t many are o ld e r th a n P l e i s t o c e n e . The P h i l i p p in e I s l a n d s have been u p l i f t e d g r e a t l y d u r in g the P l i o c e n e ep och. On Ceram, P l i o c e n e age s e d im e n ts o ccu r over 3,000 m above se a l e v e l (Kuenen, 1950). Krause summarizes th e g e ology by s t a t i n g : " R e c e n tly th e h ig h s seem to have g o t t e n h ig h e r and the lows l o w e r ." K rause (1 9 6 4 e ) , i n a su rv e y of Kawio S t r a i t (5 ° N, 125° 2 0 ’ E) so u th of Mindanao, i n d i c a t e d the f l o o r to be i r r e g u l a r . Bottom p h o to g ra p h s from 914 m to 1,229 m showed b o th pahoehoe l a v a and w e ll- r o u n d e d c o n g lo m e r a te . I t was c o n c lu d e d t h a t th e s t r a i t has sunk a t l e a s t 900 m to p e rh a p s over 1,100 m and Krause d a te d the s u b s id e n c e as p ro b a b ly R ecent or Late P l e i s t o c e n e . 174 He a l s o c a l l e d a t t e n t i o n to " c u r i o u s deep t e r r a c e s ” in the C e le b e s and Sulu Seas. T hese were o b se rv e d a t 1,000 fms to 1,5 0 0 fms ( 1 ,8 0 0 m to 2,7 5 0 m) and d i v id e d the c o n t i n e n t a l s lo p e i n t o an upper and lower s l o p e . One t e r r a c e in th e C e le b e s Sea l i e s a t a d e p th o f 2,750 m o f f S i b u tu P a s s a g e and a p p e a rs to be bound on th e s o u t h e a s t by a f a u l t . A d e e p e r , b u t s t r u c t u r a l l y s i m i l a r f e a t u r e a t 3,660 m to 4 ,5 7 0 m, i s th o u g h t to l i e betw een Mindanao and the n o r t h e a s t e r n t r o u g h . These t e r r a c e s may be c o n tin u o u s w ith th o s e o f f J a p a n , K u r i l e - K a m c h a tk a , and A l e u t i a n T r e n c h e s . B a s i l a n S t r a i t ( s o u t h o f Zamboanga and Mindanao) h a s a main p l a t f o r m a t 55 m to 73 m, w ith c h a n n e l s 130 m to 180 m. A d i s t i n c t change in s l o p e o c c u r s on t h e f l a n k s of t h i s r i d g e a t 550 m to 730 m and K rause s u g g e s te d t h a t t h i s i s th e t h i c k n e s s o f th e c o r a l p l a t f o r m h e r e . A 1,800-m to 2,750-m t e r r a c e o c c u r s betw een a tr o u g h i n th e s o u t h w e s t e r n p a r t of th e Sulu Ridge and s l o p e s n o r t h e a s t e r l y . I t seems to c o r r e l a t e w ith a s i m i l a r t e r r a c e on th e o p p o s i t e s id e o f the r i d g e . HAWAIIAN ISLANDS I n t r o d u c t i o n A wide p l a t f o r m in th e Hawaiian c h a in so u th of Oahu i s known from c h a r t s ( F ig u r e 23) b u t bottom sam ples were not re c o v e re d u n t i l a l a r g e dredge h a u l was made by the ARGO in 1961 (Menard, A l l i s o n , and Durham, 1962). This s i n g l e h a u l, w eighing about 100 kg, was ta k e n a t d e p th s of 500 m to 520 m, 10 km so u th w est of H o n o lu lu , and c o n ta in e d a t y p i c a l a n c ie n t r e e f fa u n a . No echosounding p r o f i l e s were p u b lis h e d in t h i s p a p e r; however, i t was r e p o r t e d t h a t t e r r a c e s e x i s t a t d e p th s down to 1,000 m on the s lo p e s of many i s l a n d s and banks in the Hawaiian gro up . In m id-1962, the a u th o r , th rou gh th e a s s i s t a n c e of the U. S. Navy ( i n H a w a ii), was a b le to o b t a i n 13 a d d i t i o n a l dredge h a u ls between Oahu and Maui (F ig u re 23 Table 7 ) . F o r a m in i f e r a and m o llu sc s were s t u d i e d by E. C. A l l i s o n and o s t r a c o d s by J . C. Holden, Departm ent of Geology, San Diego S t a t e C o lle g e (now a t the Coast and G e o d etic S u rv e y ); c o r a l s were s t u d i e d by J . W. Durham, Departm ent of P a l e o n t o l ogy, U n i v e r s i t y of C a l i f o r n i a , B e rk eley ; and c a l c a r e o u s a lg a e by J . H. Johnson, Colorado School of Mines, Golden, C o l o r a d o . 1 7 5 F ig u re 23. Index c h a r t of dredge h a u ls in Haw aiian I s l a n d s . H A W A IIA N ISLANDS CONTOURS IN FATHOMS ^ 5 DREDGE STATION 177 178 T a b le 7 H a w a iia n D r e d g e S a m p l e s S A M P L E NO. L O C A T I O N F R O M D E P T H T O ‘ D E S C R IP T IO N U N IV . C A L I F . S A M P L E NO. U C M B L O C . 1 2 1 ° 9 . 4 ' N 15 7 ° 5 4 . 6 ' W 550 m 2 1 ° 7. 3' N 15 7 ° 5 4 . 4 ’ W 567 m D r e d g e a c r o s s u p p e r p a r t o f i n s u l a r s lo p e . L i g h t ta n o r g a n i c m u d . S c r e e n e d , N o c o a r s e f r a c t i o n . 2 2 0 ° 51. 8 ' N 1 5 7 ° 54. 7 ’ W 622 m 2 0 ° 52. 2 ' N 1 57° 5 3 . 6 ' W 4 3 9 m D r e d g e d u p s lo p e on t e r r a c e . B a s a l t h e a v i ly e n c r u s t e d w ith m a n g a n e se o x id e . One b a s a l t s p e c i m e n h a d c a v i ty f ille d w ith o r g a n i c d e b r i s . S e v e r a l m a n g a n e s e n o d u le s . D e a d r e e f m a t e r i a l . A n im a l b o r i n g s . W t. a b o u t 9 kg. B - 3 52 5 3 2 0 ° 46. 2 ' N 157° 48. 5' W 569 iti 2 0 ° 47.. 1' N 157° 48. 5' W 547 m D r e d g e d o u t e r e d g e of t e r r a c e . A b o u t 14 k g d e a d r e e f m a t e r i a l . S o m e c o r a l s h a v e lig h t coa.tB o f m a n g a n e s e . M a x . s iz e 30 c m . B - 3 5 2 6 4 2 1 ° 1 6 . 2 ' N 1 56° 34. 3' W 512 m 2 1 ° 16. 0' N 1 5 6 ° 34. 1' W 508 m S i m i l a r to d r e d g e No. 3. W t. a b o u t 5 kg ' 5 2 1 ° 1 2 .6 ' N 15 6 ° 24. 1’ W 533 m 2 1 ° 11. 4 ’ N 1 5 6 ° 23. 3' W 530 m G u n n y s a c k p u t in b o tto m of d r e d g e . D re d g e f i l l e d w ith lig h t b r o w n m u d . A f t e r s c r e e n ing, s m a l l n u m b e r of w o r m tu b e s . 6 2 1 ° 1 2 .6 ' N 1 5 6 ° 19. 5' W 6 1 3 m 2 1 ° 1 2 .2 ' N 1 5 6 ° 20. 4 ' W 550 m L i g h t ta n m u d . C o a r s e f r a c t i o n m o s t l y w o r m tu b e s . ' 7 2 0 ° 33. 3' N 1 56° 54. 4 ' N 543 m 2 0 ° 34. 9' N 1 56° 52. 9' W 4 04 m O ne c a l c a r e o u s s p e c i m e n ; w t. a b o u t 1 /2 kg 8 2 0 ° 34. 7 1 N 1 56° 54. 5 1 W 503 m 2 0 ° 34. 3' N 1 56° 55. 8' W 582 m T w o s m a l l c a l c a r e o u s r o c k s ; w t. a b o u t 1 /2 kg. B -3 5 2 7 9 2 1 ° 1. 5' N 1 57° 8. 7' W 503 m 2 1 ° 1. 1' N 1 57° 8. 1' W 530 m S e v e r a l p i e c e s of r e e f r o c k w ith a n i m a l b o r i n g s . C o a t in g s of m a n g a n e s e . S m a ll q u a n tity of g r a y m u d . T o t a l w e ig h t a b o u t 5 k g . B -3 5 2 8 10 2 1 ° 21. 3' N 157° 2 1. 5 1 W 860 m 2 1 ° 20. 9' N 157° 22. 5' W 874 m T w o p i e c e s of c o r a l , a b o u t 10 c m d i a m e t e r , w t. a b o u t 1 /2 kg 11 2 1 ° 2 2 . 8 ’ N 157° 34. 7 ' W 540 m 2 2 ° 23. 1' N 1 57° 33. 8' W 585 m A b o u t 14 k g r e e f r o c k c o n ta in in g m o l l u s k s a n d c o r a l s a n d tw o b a s a l t p e b b l e s . S o m e f r a g m e n t s h a v e m a n g a n e s e c o a t i n g s . B - 3 5 2 9 12 2 1 ° 1 7 . 8 ’ N 15 7 ° 28. 8 ' W 563 m 2 1 ° 19. O' N 1 5 7 ° 29. 7 ' W 590 m A b o u t 68 k g of r e e f r o c k . S i m i l a r to N u m b e r 11. B - 3 5 3 0 13 2 0 ° 59. 5 ' N 1 57° 4 2 . O' W 40 m 2 0 ° 59. 5' N 1 57° 4 1 . 8 1 W 40 m D r e d g e h a u l on liv in g r e e f . P e n g u in B an k . W t. a b o u t 90 kg. B -3 5 3 1 1 7 9 F o llo w in g t h i s s u c c e s s f u l d re d g e by the a u t h o r , F. P . Shepard s u b s e q u e n t l y o b t a i n e d s e v e r a l a d d i t i o n a l sm a ll sam p l e s from deep t e r r a c e s i n the H a w aiian a r c h i p e l a o . ( S h e p a r d ’ s sa m p le s a ls o a r e b e in g s t u d i e d by th e above a u t h o r i t i e s b u t c u r r e n t l y o n ly th e o s t r a c o d i d e n t i f i c a t i o n s have been c o m p l e t e d .) The U. S. Navy made ASR GREENLET a v a i l a b l e f o r d r e d g ing o p e r a t i o n s . Only an NMC-2 e c h o so u n d e r was a v a i l a b l e on t h i s s h i p , t h e r e f o r e no echogram s were o b t a i n e d . N e v e r t h e l e s s , s e v e r a l echogram s made by the C o a s t and G e o d e tic S u r vey show the wide t e r r a c e a t a b o u t 550 m so u th of Oahu ( F i g u r e 2 4 ) . D ie tz and Menard (1 9 5 3 ) , D i e t z , Menard, and H am ilto n ( 1 9 5 4 ) , Emery (1 9 5 5 ) , and H am ilto n (1957) have p u b l i s h e d p r o f i l e s o f f th e Hawaiian c h a in b u t the s c a l e i s much to o sm a ll to be u s e f u l f o r i d e n t i f y i n g t e r r a c e s . R e s u l t s D i e tz and Menard (1953) r e p o r t e d " t h a t a r e m a rk a b ly f l a t t e r r a c e w ith an a b r u p t i n c r e a s e in s l o p e ' s h e l f - b r e a k ’ a t 190 to 220 fath o m s (350 m to 400 m) e x i s t s on the n o r t h e a s t c o a s t of th e i s l a n d of H a w a i i ." The i n s u l a r s h e l f b e yond d e s c e n d s r a p i d l y to a b y s s a l d e p t h s . T h is deep s h e l f has a w id th o f a b o u t 5 l / 2 km and i s c o n f in e d to th e Mauna Kea and K ohala s e c t o r s o f the i s l a n d . T h is c o r r e s p o n d s to th e o l d e s t p a r t o f the i s l a n d as w e l l as b e in g b e s t exposed 180 KAIWI CHANNEL 0 ,5 Km 1 Km F ig u r e 24. P r o f i l e s a c r o s s th e i n s u l a r s h e l f and s lo p e s o u t h of Oahu. 181 on th e windward c o a s t . D ie tz and Menard su g g e st t h a t v o l canoes e lsew h e re on th e i s l a n d have covered t h i s s h e l f by e r u p t i o n s in h i s t o r i c tim e . Only th o se p a r t s where v o l c a n ism has been i n a c t i v e s in c e the G l a c i a l P e r io d have escaped cov ering by l a v a s . In a d d i t i o n , the deep s h e l f has s u b s e q u e n tly s u f f e r e d su b sid e n c e of s e v e r a l hundred m eters ( i . e . , from about 10 m to 400 m ). H o ltsm ark (1949) r e p o r t ed t h a t t h i s deep s h e l f is composed of la v a w ith a few p a tc h e s of v o l c a n ic sa n d s. D ie tz and Menard have concluded t h a t the topography i s n o t c o m p lica te d by the p re s e n c e of o rg a n ic r e e f s . O ther deep t e r r a c e s a re r e p o r t e d a t l e v e l s between 370 m and 750 m, b u t o t h e r s exceed 1,400 m. The most p r o nounced i s the wide t e r r a c e a t about 500 m so u th of Oahu ( F ig u re 2 4). In th e same r e g i o n , a n o th e r t e r r a c e i s su g g e ste d a t about 750 m. Emery’s (1955) p r o f i l e s so u th of th e i s l a n d of Hawaii show t e r r a c e s a t s e v e r a l l e v e l s , i n c lu d in g pronounced f e a t u r e s a t 1,000 m, 1,500 m to 2,000 m, and p e rh a p s o t h e r s a t even g r e a t e r d e p t h s . Kroenke and W oollard (1 9 6 4 ), u s in g s e is m ic p r o f i l i n g equipm ent, found l i t t l e or no sedim ent on P e n g u in Bank. On the i n s u l a r s h e lv e s n o r t h of Molokai C hannel, sedim en t a c cu m u latio n a p p e a rs to be s p o r a d ic and v a r i e s between 100 m and 160 m in t h i c k n e s s . The a u th o r s s u g g e s t t h a t r e e f s a p p e a r to be p r e s e n t on the s h e l f n o r t h of Maui, and the s o u th edge of Penguin Bank, and l i e a t a d e p th of about 182 450 m to 500 m below sea l e v e l . During the a u t h o r ’s U. S. Navy c r u i s e , e x c e l l e n t to p o o r l y - d e f i n e d t e r r a c e s were dredged to d e p th s of n e a r l y 900 m, th u s , w h ile echograms are l a c k i n g , numerous dredge h a u ls have shown an a n c ie n t r e e f i s w id e sp rea d around the Hawaiian I s l a n d s . Excep.t f o r dredge h a u ls 1, 5, and 6 (T able 7) which c o n ta in e d mud o n ly , a n c i e n t r e e f - b u i l d i n g o r g a n ic rem ains were re c o v e re d a t d e p th s ran g in g from a few hundred m eters to n e a r l y 1,000 m. A dredge was l o s t a t 21° 0 . 7 ’ N, 158° 0 . 5 ’ W when i t hung up on hard bottom (u n d o u b te d ly a b a s a l t f lo w ) . No sam ples were re c o v e re d from two a d d i t i o n a l dredge l o c a t i o n s : 21° 2 1 . 4 ’ N, 157° 3 3 . 3 ’ W to 21° 2 2 . 3 ’ N, 157° 3 5 . 0 ’ W; and 21° 2 2 . 7 ’ N, 157° 5 1 . 3 ’ W to 21° 2 3 . 3 ’ N, 157° 5 7 . 0 ’ W. P l a n k t o n i c f o r a m i n i f e r a are no t d i a g n o s t i c f o r a c c u r a t e d e t e r m i n a t i o n s s in c e most range in age from Miocene to Recent (O. L. Bandy, p e r s o n a l com m unication). Most of the m o llu scan fau n a i s unknown from th e f o s s i l r e c o r d , hence i t i s of l i t t l e use f o r age i d e n t i f i c a t i o n . S i m i l a r l y , v i r t u a l l y n o th in g i s known about o s t r a c o d s in the t r o p i c a l P a c i f i c ; t h e r e f o r e , th e s e are of l i t t l e v a lu e f o r age d e t e r m in a tio n s (E. C. A l l i s o n , p e r s o n a l com m u nicatio n). Durham and Johnson have p ro v id e d a d d i t i o n a l b a s i c i n fo r m a tio n on th e 13 dredge h a u ls made by the w r i t e r in 1962. Kodacolor p h o to g rap h s were made of the e n t i r e dredge h a u l w h ile th ey were f r e s h ( P l a t e s 20 and 2 1 ). At s t a t i o n 183 t h r e e , an e x c e l l e n t a sse m b la g e of r e e f m a t e r i a l was r e c o v ere d from a d e p th of 547 m to 569 m. N earb y, h a u l number one was made beyond ( d e e p e r th a n ) th e t e r r a c e s u r f a c e , u p - s lo p e from 622 m to 439 m. H ere, o l i v i n e b a s a l t e n c r u s t e d w i t h up to one c e n t i m e t e r o f manganese o x id e was r e c o v e r e d a lo n g w i t h r e e f m a t e r i a l a l s o e n c r u s t e d w i t h m anganese. Mud was a l s o o b t a i n e d a t a n o th e r deep l o c a t i o n (No. 6 ) , b u t no r e e f m a t e r i a l from 613 m to 550 m. At s t a t i o n 10 ( t h e d e e p e s t s t a t i o n ) , two p i e c e s o f c o r a l were o b t a i n e d from a d e p th of 860 m to 874 m. Assuming t h a t th e c o r a l s from s t a t i o n 10 a r e n ot t a l u s ( t h e y a p p e a r f r e s h and u n w o rn --s e e P l a t e 20, No. 1 0 ) , the a n c i e n t r e e f e x te n d e d to d e p th s much g r e a t e r than t h e ARGO sample ( i . e . , 500 m to 520 m); how e v e r , the s h a rp b rea k i n slo p e s o u th o f Oahu seems to be the low er b o un dary f o r th e r e e f iri t h i s r e g i o n b e c a u se b a s a l t was the p r i n c i p a l m a t e r i a l d red g ed beyond th e s h e l f edge. In some a r e a s , R ecent d e p o s i t s a p p a r e n t l y c o v e r o l d e r r e e f s , p a r t i c u l a r l y on the r a i n y s i d e s of the i s l a n d and c l o s e to s h o re where r u n o f f i s g r e a t e s t . Dredge sam p les of r e e f m a t e r i a l a re t y p i c a l l y cream - c o lo r e d t o d u l l w h i t e , m o d e r a te l y l i t h i f i e d , w i t h s p o r a d i c , t h i n c o a t i n g s of manganese and f e r r i c i r o n o x i d e s . B o r in g s by o r g a n is m s , such as p h o la d s and o t h e r p e le c y p o d s , a re common b o t h in r e e f and b a s a l t m a t e r i a l . C a v i t i e s o f t e n a re p a r t l y f i l l e d w i t h m i s c e l l a n e o u s c a l c a r e o u s m a t e r i a l , c l a y , and p l a n k t o n i c f o r a m i n i f e r a . Some sp ecim ens a r e P l a t e 20. Dredge h a u ls from H aw aiian I s l a n d s . See F ig u re 23 and T able 7 f o r l o c a t i o n . S c a le i s i n d i c a t e d by l i g h t m e te r . Sample number i s i n d i c a t e d in u pp er r i g h t c o r n e r . See t e x t fo r d e s c r i p t i o n . A ll p h o to g ra p h s ta k e n d i r e c t l y a f t e r c o l l e c t i n g . P h o to g r a p h s a re much d a r k e r (b ro w ner) th an o r i g i n a l . Manganese and f e r r i c i r o n s t a i n s a re com mon, b u t are e s p e c i a l l y pronounced on l a r g e p i e c e of m a t e r i a l on number 12. Burrowings a l s o v i s i b l e on many s p e c i mens . P l a t e 20. Dredge h a u l s from H aw aiian I s l a n d s . P la te 21. Dredge sample from Penguin Bank, a l iv in g r e e f . Depth 40 m. Most c o ra ls are P o r i t e s l o b a t a . Scale in d ic a te d by l i g h t m eter. P h o to graphs taken immediately a f t e r c o l l e c t i n g . 186 Table 8. Corals From the Hawaiian Isla n d s STATION NUMBER CORALS h : < d O ' O H v O D C o o u e I < a S c a n c n 8 11 12 13 c < u o < L > P i Acropora s p . , cf _ Acropora s p . A. A streopora sp. C o sc m are a (?) n. sp. a f f . F A. e ch inate (Dana) Fungia n. s p . , L e p ta s tr e a b o tta e L e p ta s tre a n . s p . L e p ta s tr e a n. sp. s c u t a r i a (Milne Edwards and A, a f f . L. purpurea Lamarck Haime) (Dana) B, a f f . L. t r a n s v e r s a Klunzinger L e p to s e ris h a w aiien sis Vaughan L e p t o s e n s s p ., c f . scabra Vaughan L e p to s e r is n. sp. A. L e p to s e ris n. sp. B. L e p to s e ris n. sp. C. L e p to s e r is n . s p . D. Montipora v erru co sa Lamarck Montipora sp. A Montipora s p . indet Pavona n. sp. A, c f . P. g ig an tea V e r r i l l Pavona n. sp. B, cf Pavona n. sp. C P la ty g y ra n. sp. P o c illo p o r a molokensis Vaughan P o c i llo p o r a sp. i n d e t . P o r i t e s lo b a ta Dana P. duerdeni Vaughan x x X ? X X X X X X X X X ? X 00 -v] Table 8. Corals From the Hawaiian Isla n d s (Continued) STATION NUMBER CORALS B-8691 "Argo" Sample 2 3 8 9 11 12 GO Recent P o r i t e s sp. in d e t. Indeterm inable co ral X X X X i - 1 0 0 0 0 189 r o u n d e d . C o r a ls in seven of the sam ples ( 2 , 3, 8, 9, 11, 12, and 13) have been s t u d i e d by J . Wyatt Durham. N in e te e n c o r a l s have been i d e n t i f i e d (T able 8 ). Of t h e s e , one (Mo n t i p o r a v e r r u c o s a ) o c c u rs on ly in sample 13, of Recent c o r a l s from P eng uin Bank. The sample dred ged by the ARGO (Samples B-8691, T able 2) i n c l u d e s s i x s p e c i e s n o t r e c o g n iz e d in any of the 13 o t h e r d redge h a u l s . I n c lu d in g the ARGO sam ple, 24 f o s s i l s p e c i e s ( i n a d d i t i o n to i n d e t e r m i n a b le m a t e r i a l in sample No. 9) were r e c o g n iz e d by Durham. Of th e s e 24, only fo u r are r e f e r a b l e (two w ith some d o u b t) to s p e c i e s now l i v i n g in the a r c h i p e l a g o ; ten s p e c i e s ap p e a r to be new; the o t h e r te n cannot be a d e q u a te ly e v a l u a te d u t i l i z i n g the specimens a v a i l a b l e . Based upon d e p th s from which sam ples were c o l l e c t e d f o r th e purpose of d a t i n g , i t i s assumed t h a t a l l samples came from the same submerged t e r r a c e . C o l l e c t i v e l y , t h e r e f o r e , a t l e a s t 41 per c e n t of the c o r a l s r e c o v e r e d are e x t i n c t . On the b a s i s of p e r c e n ta g e v a lu e s of W ells (1954a, p. 6 1 1 ), t h i s s u g g e s t s a Miocene ( sensu l a t u ) a g e. I f the sam ples a re c o n s id e r e d i n d i v i d u a l l y , then sample No. 11, w ith 42 p e r cent e x t i n c t , would appear to be th e o l d e s t , but a l s o of Miocene age. Sample number 3 i s the on ly sample c l o s e l y comparable to the ARGO sam ple, p r o b a b ly r e p r e s e n t i n g the same f a c i e s , w ith f o u r of the e i g h t s p e c i e s i d e n t i c a l . 190 Sam ples 11 and 12 a p p e a r to r e p r e s e n t t h e L e p t o s e r i s zone ( f a c i e s ) o f W ells (1 9 5 6 b , p . 3 9 9 ), c h a r a c t e r i z e d by an abundance of s p e c i e s o f L e p t o s e r i s . A c c o rd in g to W e lls , t h i s zone o c c u r s a t d e p t h s o f 90 m to 160 m in the M a r s h a l l I s l a n d s . Vaughan (1 9 0 7 , p . 35 and 40) had p r e v i o u s l y n o te d t h i s zone as th e ’’i n t e r m e d i a t e z o n e ” i n the H a w aiian I s l a n d s , betw een d e p t h s o f 45 m and 185 m. From t h e s e d a t a i t w ould a p p e a r t h a t when th e c o r a l s found in t h e s e two s a m p le s were a l i v e , t h a t th e p o r t i o n of the t e r r a c e where th e y were growing was a t d e p t h s o f a t l e a s t 45 m, and more p r o b a b l y 90 m. The a sse m b la g e in sam ple number 3 s u g g e s t s d e p t h s of l e s s th a n 45 m, b u t th e number of s p e c i e s r e p r e s e n t e d i s i n a d e q u a t e to make an a s s e s s m e n t o f g r e a t e r r e f i n e m e n t . The A c ro p o ra r e p r e s e n t e d in t h i s sam ple i s d i f f e r e n t from t h a t in the ARGO sa m p le , b u t th e m a t e r i a l i s i n a d e q u a t e f o r s p e c i e s d e t e r m i n a t i o n . O th er sa m p le s c o n t a i n to o few c o r r a l l i n e s p e c i e s t o make any e c o l o g i c e v a l u a t i o n s e x c e p t t o i n d i c a t e t h a t th e y a re a l l h e r m a ty p i c t y p e s . L iv in g f a u n a from P e n g u in Bank (No. 13) has a p oor s p e c i e s r e p r e s e n t a t i o n ; most o f th e sp e c im e n s a r e r e f e r a b l e to P o r i t e s l o b a t a ( P l a t e 2 1 ) . P o c i l l o p o r a was d e a d , b a d l y m u t i l a t e d , and b o r e d . L e p t o s e r i s i s r e p r e s e n t e d by one s m a l l and d i s t o r t e d s p e c im e n . A c c o rd in g to Durham, t h i s sam ple a f f o r d s a v e ry p oor r e p r e s e n t a t i o n o f the l i v i n g 191 fa u n a of the i s l a n d s . Because of th e p a u c i t y of c o r a l s p e c i e s , age a s s e s s ment i s d i f f i c u l t . L ik e w is e , o s t r a c o d e s s t u d i e d by Holden ( i n p r e s s ) do no t c o n t r i b u t e s i g n i f i c a n t in f o r m a ti o n o t h e r than d a t a a lr e a d y p u b l is h e d by Menard, A l l i s o n , and Durham (1 9 6 2 ). A l l i s o n h a s n o t com pleted h i s s t u d i e s on f o r a m i n i f e r a and m o ll u s c s , b u t in g e n e r a l , th e 13 sam ples a re d a te d the same as the ARGO sample ( i . e . , M io cen e). In a d e s c r i p t i o n of t h e ARGO sam ple, p l a n k t o n i c f o r a m i n i f e r a G l o b i g e r i n o i d e s q u a d r i l o b a t u s (=G. t r i l o b u s a u c t . ) p l e x u s was used by the a u th o r s as p o s s i b l e e v id e n c e f o r a lo w e r age l i m i t of e a r l y Miocene. However, Bandy (1964; and p e r s o n a l com m unication) a s s i g n s t h e s e f o r a m i n i f e r a to a P l i o c e n e - P l e i s t o c e n e (? ) age. Hence, a Miocene age i s n o t p ro v e n . A l l i s o n ( p e r s o n a l com m unication) i n d i c a t e d t h a t on the b a s i s o f s c a r c e p l a n k t o n i c f o r a m i n i f e r a , sam ples 2 and 7 are p r o b a b ly p o st-M io c e n e . (A dred g e sample by Shepard o f f Kauai a l s o was d a te d as p o s t - M i o c e n e . ) Samples 1, 8, and 12, as w e ll as th e ARGO sam ple, co u ld be th e same age (or ages) or s l i g h t l y o l d e r . The re m a in in g sam ples have even l e s s d i a g n o s t i c f o r a m i n i f e r a . E ig h t s l i d e s o f c a l c a r e o u s a l g a e , r e p r e s e n t a t i v e of the d red g e sa m p le s, were s t u d i e d by J . H a rla n Jo h n s o n . The s l i d e s had many sp e cim en s, a lth o u g h r e p r e s e n t i n g o n ly a few s p e c i e s . Of 31 sp ecim en s, 25 b e lo n g e d to a s i n g l e s p e c i e s 1 9 2 - - L ith o p h y llu m ( D e r m a to lith o n ) p a p il l o s u m ( Z a n .) F o s l i e - - and the o th e r s i x r e p r e s e n t e d two a d d i t i o n a l s p e c i e s . Three were L ithotham nium b e t i e r i Lemoine and th e o t h e r t h r e e b elong to an u n d e s c r ib e d s p e c i e s of the genus P s e u d o - l i t h o p h y l l u m . L. p a p illo s u m i s a v e ry t h i n e n c r u s t i n g form , c o n s i s t i n g of c o u n t l e s s p l a n t s which may grow s u p e r imposed to make th ic k c r u s t s or i r r e g u l a r n o d u l a r m asse s. Jo h n so n s t a t e d t h a t the f i r s t two named s p e c i e s are c h a r a c t e r i s t i c of th e Upper Miocene, a lth o u g h t h e y exten d i n t o the lo w e st P l i o c e n e . D i s c u s s io n Although in c o m p le te , the p a l e o n t o l o g i c d a t a s u g g e s t t h a t the sam ples c o l l e c t e d by the ARGO, F. P. S h e p a rd , and the w r i t e r a re from a w id e sp re a d t e r r a c e s u r r o u n d i n g the H aw aiian a r c h i p e l a g o . As y e t , the shape o f t h i s t e r r a c e i s u n d e f i n e d . In many r e g io n s i t may n o t even be a t e r r a c e . The a n c i e n t r e e f may have been a b a r r i e r r e e f or a f r i n g i n g r e e f . That i t was w id e sp re a d has now been e s t a b l i s h e d b u t i t s l a t e r a l e x t e n t i s unknown and i t s d e p th l i m i t s have not been d e te rm in e d th ro u g h d r e d g in g . P u b l i s h e d p r o f i l e s by Emery (1955) so u th and s o u t h e a s t of the i s l a n d of Hawaii show t e r r a c e s a t about 1,000 m, as does a p r o f i l e by H am ilton (1957) n o r t h e a s t o f Oahu. Men a rd , A l l i s o n , and Durham (1962) a l s o s t a t e d t e r r a c e s a t about 1,000 m are w id e sp re a d in the H aw aiian a r c h i p e l a g o . 193 T hese d a t a s u g g e s t such f e a t u r e s a re w i d e s p r e a d . F r a g i l e , u n b ro k e n , or unworn c o r a l sp e c im e n s have b een r e c o r d e d from d e p t h s of 860 m to 874 m and i t i s b e l i e v e d t h a t t h e s e sp e c im e n s were in s i t u and n o t p a r t of a t a l u s d e p o s i t . R e t r i e v a l of s e v e r a l p i e c e s o f o l i v i n e b a s a l t s o u th of H o n o lu lu betw een d e p t h s of 622 m to 439 m, t o g e t h e r w ith s m a ll q u a n t i t i e s o f r e e f m a t e r i a l h e a v i l y e n c r u s t e d w i t h manganese o x i d e , s u g g e s t t h e l i v i n g r e e f d id n o t r e a c h as d eep as t h i s i n t h i s a r e a . S in c e no r e c o v e r e d r e e f sp e c im e n s a p p e a r to have been f r e s h l y b r o k e n o f f th e a n c i e n t r e e f , a l l a p p e a r w e a t h e r e d , have numerous a n im al b o r i n g s , and some sp e cim en s a re w e l l - r o u n d e d , no c o n c l u s i o n can be r e a c h e d w h e th e r r e c o v e r e d r e e f m a t e r i a l was t r a n s p o r t e d or in s i t u . On t h e p o s i t i v e s i d e , w i d e l y - s p a c e d , r a n d o m l y - c o l l e c t e d r e e f m a t e r i a l , some on f l a t t e r r a c e s , s t r o n g l y s u p p o r t s th e b a s i c c o n c l u s i o n t h a t th e r e e f m a t e r i a l i s l a r g e l y ill s i t u . I f t r u e , th e r e e f i n c e r t a i n p a r t s of th e i s l a n d group o c c u r s a t l e a s t as deep as 874 m. A lth o u g h th e age o f t h i s o ld r e e f h as n o t been com p l e t e l y r e s o l v e d , a Miocene ( o r p o s s i b l y e a r l y P l i o c e n e a g e ) i s s u g g e s t e d . The f o s s i l a s s e m b la g e , w e a th e r e d n a t u r e , and p r e s e n c e of anim al b o r i n g s s u g g e s t s e v e r a l e n v ir o n m e n ts r a n g i n g from e x p o s u r e to a tm o s p h e r ic c o n d i t i o n s , l i t t o r a l , and c o r a l r e e f g ro w th a t 45 m to 90 m, p o s s i b l y as g r e a t as 184 m b e low s e a l e v e l . 194 A f t e r a r e l a t i v e lo w erin g w ith r e s p e c t to p r e s e n t sea l e v e l of hundreds of m e te r s , e x ce p t where th e r e e f i s co v ered by P l i o c e n e and Q u a te rn a ry age se d im e n ts (m o stly c lo s e to sho re and on the r a i n y s id e of the i s l a n d s where r u n o f f is g r e a t e s t ) , the r e e f has been e s s e n t i a l l y a non- d e p o s i t i o n a l e n v iro n m en t. T his i s proven by c a v i t y f i l l in g s which c o n ta in m arl (which a re o n ly p ro b a b ly s l i g h t l y o ld e r than the r e e f ro ck ) and by d e p o s i t s of manganese and f e r r i c iro n and no cover of Recent se d im e n ts . Sediment by p a ssin g thus seems to be e s t a b l i s h e d f o r i n s u l a r s h e lv e s as in the case of many c o n t i n e n t a l s h e l v e s . Menard, A l l i s o n , and Durham (1962) concluded t h a t the Hawaiian r e g io n has had a c o m p lic a te d h i s t o r y w ith i n t e r m i t t e n t v o lca n ism , f o r m a tio n of p l a t f o r m s or p l a i n s a t sea l e v e l , and bo th l o c a l and r e g i o n a l su b s id e n c e They c o n cluded t h a t a s h a llo w p l a t f o r m capped w i t h a c o r a l r e e f e x i s t e d a t the p r e s e n t s i t e ( s o u th of Oahu) d u rin g the Mio cene and the t e r r a c e h as s u b s e q u e n tly been drowned to a depth of about 500 m. Such a c o n c l u s i o n , i f t r u e , o b v i o u s ly must be ex te n d ed to in c lu d e th e t e r r a c e and r e e f s o c c u r r i n g so w id e ly in th e Hawaiian a r c h i p e l a g o . Geology The Hawaiian I s l a n d s a re the above se a l e v e l p o r t i o n of a much l a r g e r s t r u c t u r e i n v o lv i n g the Hawaiian R idge, Hawaiian S w e ll, Hawaiian Deep, and the H aw aiian Arch. 195 Betz and Hess (1942) were the f i r s t to r e c o g n iz e th e g e n e r al submarine s t r u c t u r e of the r e g i o n , b u t S to ck s (1 9 5 0 ), Bezrukov and U d in tse v (1 9 5 5 ), D ie tz and Menard (1 9 5 3 ), D i e tz , Menard, and H am ilton (1 95 7), and H am ilton (1957) were able to c l e a r l y d e f i n e the geomorphic f e a t u r e s . The Hawaiian Ridge i s a v o lc a n ic s t r u c t u r e about 3,000-km long which in c lu d e s ( o f c o u rs e ) th e v a r i o u s b a s a l t i c i s l a n d s in the Hawaiian Chain. The Hawaiian Ridge i s superim posed on a 1,100-km wide, w e s t - n o r t h w e s t , e a s t - s o u t h e a s t tre n d in g g e n t l e sw e ll of the ocean f l o o r . A d jacen t to the Hawaiian Ridge l i e s th e Hawaiian Deep, formed by the d e p re s s io n between the r id g e and the a r c h . N o r t h e a s t and n o rth of Oahu, t h i s i s o u t l i n e d by the 2,700 -fatho m ( 4 ,9 3 8 m) i s o b a t h , but e a s t of Oahu, Maui, and Ha- i w a ii the deep i s lower in d e p th than 3,000 fathom s (5 ,4 8 6 m). The deep s h o a l s around th e sou th end of Hawaii u n t i l , on the so u th w est s i d e of t h i s i s l a n d to Oahu, i t i s d e l i n e a te d by the 2 ,5 0 0 -fath o m ( 4 ,5 7 2 m) i s o b a t h (H am ilto n, 1957). The Hawaiian Arch b e g in s a t the a x is of the. deep and r i s e s g r a d u a l l y away from the deep and i s w e ll d e f in e d by th e 2 ,9 0 0 -fa th o m (5 ,3 0 0 m) i s o b a t h . T h is c o n to u r swings in a l a r g e h o rs e s h o e -s h a p e d bend around H aw aii. The arc h i s 445-km wide o f f Oahu, 280 km n o r t h e a s t of H aw aii, 390 km so u th w e st of H aw aii, and 410-km wide so u th w e st o f M olokai. The a rc h i s a sy m m e tric a l, b e in g s t e e p e r tow ards the i s l a n d s 196 ( 0 ° . 1 5 ’ vs 0° . 0 6 ’ ) . In a d d i t i o n , r e l i e f o f 275 m to 460 m due to s m a ll h i l l s , o c c u r s on to p of th e a r c h . A c co rd in g t o H a m ilto n , a l l echogram s of th e a r c h show f a u l t i n g alo n g th e c r e s t . D i e tz and Menard (1953) n o te d t h a t the r e l i e f betw een th e b o tto m of the deep to th e to p of th e a r c h o f f Oahu i s 945 m and o f f H aw aii 630 m, b u t o f f M olokai i t r e a c h e s 1,100 m. The H aw aiian S w ell i s a b r o a d , low, e l o n g a t e d r i d g e of th e se a f l o o r upon which a l l of th e p r e v i o u s l y d e s c r i b e d f e a t u r e s ( a s w e l l as se am o u n ts) are su p e rim p o s e d . D ie tz and Menard ( 1 9 5 3 ) , u s in g th e 3 ,0 00 -fm ( 5 ,5 0 0 m) i s o b a t h as a r e f e r e n c e datum , showed the s w e ll to be about 1,100 km to 1 ,3 0 0 km wide w ith an a m p litu d e of a b ou t 550 m and maximum d e p r e s s i o n a t the lim b of about 200 m. I t must be c o n c lu d e d t h a t th e f e a t u r e s d e s c r i b e d - - t h e r i d g e , d e e p , and s w e l l - - a r e g e n e t i c a l l y r e l a t e d . E v iden ce shows t h a t th e r e g i o n i s composed of b a s a l t , w ith v o l c a n i c a c t i v i t y moving p r o g r e s s i v e l y from n o r t h e a s t to w a rd s the s o u t h e a s t . C u r r e n t l y , v o l c a n i c a c t i v i t y i s r e s t r i c t e d to th e i s l a n d of Haw aii and p o s s i b l y i n c l u d e s some subm arin e v o lc a n is m . S t e a r n s (1946) and S t e a r n s and Mac Donald (1946) have s t a t e d t h i s i s l a n d may have formed as r e c e n t l y as l a t e P l i o c e n e . However, i f a deep t e r r a c e c o r r e l a t i v e w i t h t h a t a l r e a d y d i s c o v e r e d to th e n o r t h w e s t o f f Oahu and o t h e r i s l a n d s a l s o o c c u r s around H a w a ii, such a r e c e n t age though i t has by e x t r u s i o n has been (W ils o n , (1955) f au 11 . posed f a u l t i n g , f a u l t s below the i s l a n d group owes i t s o r i g i n system of c o n v e c tio n c u r r e n t s , might break the r i s e under m antle to (1 9 6 0 ). of b a s a l t The (1953) to v o l c a n ic s Hawaiian Arch in tu r n i s b u l g e . D ie tz ( i n H am ilton , movement in the Hawaiian emergences are due f o r the Ham ilton (1957) noted t h a t Bay on the e a s t c o a s t of r a p i d s u b s id e n c e . A l- the c h a in was formed f a u l t , no ev id e n ce such a f a u l t and Emery e x t e n s i o n of a are not a s s o c i a t e d w ith sup- concluded t h a t t r a n s c u r r e n t e x i s t and s u g g e s ts t h a t the r i f t i n g b ro u g h t about by a I t i s assumed t h a t c u r r e n t s a b r u p t l y where c u r r e n t s f r e s h s u r f a c e s of the as proposed by Hess l o c a l l a r g e o u tp o u rin g s 200 km. D ie tz and Menard g r e a t load of The a d ja c e n t r e l a t e d e l a s t i c t h a t th e dom inant and t h a t c h a n g e . Kaneohe to fa n and i n d i c a t e s w id espread and long been supposed t h a t of la v a along a l a r g e a x i a l p r e s e n t e d to prove the e x i s t e n c e of 1963). Surveys by H am ilton (1957) s o u t h e a s t and sou th of Hawaii show no C e r t a i n l y e a rth q u a k e s Wilson (1963) i s l a n d s do not to c r u s t and r i f t i t m id-ocean r i d g e s exposing h y d r a t i o n and a l t e r a t i o n Such a th e o ry would mean ic la v a from d e p th s up to Hawaiian Deep was a t t r i b u t e d by c r u s t a l d e p r e s s i o n caused by the t h a t comprise the i s l a n d c h a in . th ou gh t to be a 1957) b e l i e v e s re g io n i s submergence most p a r t to e u s t a t i c subm arine canyons n e a r Oahu lead d i r e c t l y down 198 d e l t a f e a t u r e s below 1,100 fm to 1,500 fm (2 ,0 0 0 m to 2,800 m). According to H am ilton, th e s e d e p th s appear to be much too g r e a t f o r any p r e v i o u s l y p o s t u l a t e d e s t i m a t e s of subm ergence. Of p a r t i c u l a r s i g n i f i c a n c e i s the c o in c id e n c e of a deep o f f Oahu 550 m deeper than the a r c h - - t h e same d epth as the w id esp read submerged t e r r a c e . Kroenke and Woolard (196 4), u t i l i z i n g s e is m ic p r o f i l ing equipm ent, e n cou ntered c o n s i d e r a b le sediment t h i c k n e s s es w i t h in deeps both n o r th and south of the Hawaiian s w e l l . Sediment t h ic k n e s s was found to be g r e a t e r in the n o r th e r n deeps w ith a t l e a s t 620 m to 770 m of sedim ent compared w ith 100 m to 200 m of sediment so u th of the s w e l l . They noted t h a t both n o rth and so uth of the sw ell the sediment t h ic k n e s s i n c r e a s e s as the base of the swell i s approached. Sub-bottom topography beneath the sed im ents c o n tin u e s to d ip toward the sw ell u n t i l the base of the slo p e i s e n c o u n te re d . I t was suggested t h a t " t h i s subsedim ent c o n f i g u r a t i o n i n d i c a t e s p r o g r e s s i v e downwarping of the c r u s t on both s id e s of the s w e ll, because as th e is la n d p la t f o r m was b u i l t , i t responded to i s o s t a t i c e q u il i b r i u m f o r c e s . Slumping of v o lc a n ic flows appear to mask most of the base of the s w e l l . " ¥ . Arching and upw elling of la v a a p p a r e n t l y produced an e x c e s s iv e load on the E a r t h r s c r u s t and as a consequence the r e g io n has i s o s t a t i c a l l y s u b s id e d . S e v e ra l l i n e s of e v id e n c e seem to s u p p o r t t h i s t h e s i s . F i r s t , the e x i s t e n c e o f a moat (d e e p ) s u rr o u n d in g th e r i d g e g iv e s a s t r o n g im p r e s s i o n o f s u b s id e n c e . Moats s u r r o u n d in g seam ounts much s m a l l e r in s i z e than t h e Hawaiian c h a in have been observed in many p a r t s of the w o rld . Second, th e w id e sp re a d t e r r a c e a t a p p ro x im a te ly 550 m, d a te d as Miocene or younger, can be e x p la in e d e i t h e r as the r e s u l t of a e u s t a t i c change in sea l e v e l or s u b s id e n c e . The c o in c id e n c e of the d e ep , l y i n g a t a d e p th of 550 m, is in rem a rk ab le agreem ent w ith the p r e s ent d e p th of the t e r r a c e , s u g g e s t i n g a g e n e t i c r e l a t i o n s h i p . A e u s t a t i c change of sea l e v e l of the o r d e r of 550 m has n o t been p ro v e n , b u t c an n o t be r u l e d o u t . T h i r d , g r a v i t y a n o m a lie s a p p a r e n t l y a re in good agreem ent w i t h l o c a l and r e g i o n a l s u b s id e n c e caused by o v e r l o a d i n g . Vening Meinesz (1934) c o n clu d ed t h a t the H aw aiian I s l a n d s c an n o t have any r o o t of l a r g e d im en sio n b e c a u s e , i f such a r o o t were p r e s e n t , r e g i o n a l g r a v i t y a n o m a lie s would be l a r g e r . C u r r e n t l y , Hawaii i s a p a r t i a l l y uncom pensated load on the E a r t h ’ s c r u s t . M einesz b e l i e v e d t h a t the c r u s t has n o t been b u c k le d and t h a t the i s l a n d s a re e s s e n t i a l l y an e n o r mous a c c u m u la tio n of v o l c a n i c s r e s t i n g on th e s e a f l o o r . W oollard (1 9 5 9 ), on the b a s i s o f g r a v i t y , a l s o co nclu ded t h a t Oahu i s a p i l e of v o l c a n i c s t h a t has undergone e x t e n s iv e i s o s t a t i c s u b s id e n c e . A lth ou gh e v id e n c e i s i n c o n c l u s i v e , su b s id e n c e a p p a r e n t l y was a t t e n d e d w i t h o u t c o a s t a l b o rd e r f a u l t s . W oollard (1951) c o n s i d e r e d su b s id e n c e 200 r e s u l t e d from downward f l e x u r e of th e E a r t t ^ s c r u s t and amounted to b etw een 8,00 0 f t and 10 ,6 0 0 f t ( 2 ,4 0 0 m to 3 ,2 0 0 m ) , and t h a t a l l s u b s i d e n c e r e s u l t e d from downward f l e x u r e o f th e c r u s t . F o u r t h , a c c o r d i n g to S t e a r n s ( 1 9 4 6 ) , b o r e - h o l e d a t a on Oahu shows s u b s id e n c e as g r e a t as 355 m. S e ism ic r e f r a c t i o n p r o f i l e s a c r o s s Oahu show r o c k s w i t h a low s e i s m i c v e l o c i t y ( 3 . 1 k m /s e c ) e x t e n d i n g down t o about 700 f t (250 m ) . T h is h a s b e e n i n t e r p r e t e d by Furum oto, Thompson, and W oollard (1 9 6 4 ) as c o r a l f i l l i n g in a fo rm e r la g o o n . F i f t h , s u b s id e n c e i s a l s o s u g g e s t e d by th e f a c t t h a t a t r a n s i t i o n o c c u r s from a t o l l s i n th e n o r t h w e s t e r n p a r t o f the H a w a iia n S w e ll to v o l c a n i c i s l a n d s to w a rd s th e sou t h e a s t . A c c o rd in g to S t r a n g e , M a l a h o f f , and W o o llard (1 9 6 4 ) t h e r e i s marked p a r a l l e l i s m b e tw ee n th e g e o l o g i c a l p a t t e r n o f th e H a w a iia n I s l a n d s and t h e o f f s h o r e b a t h y m e t r i c t r e n d s , m a g n e tic and g r a v i t y d a t a . The a u t h o r s s t a t e : T hese o b s e r v a t i o n s s u g g e s t t h a t th e t e c t o n i c s e t t i n g o f th e H aw aiian I s l a n d s i s g o v e rn e d by two c r u s t - a l t e c t o n i c t r e n d s . One t r e n d s t r i k e s e a s t - w e s t and i s a s s o c i a t e d w i t h the M olokai f r a c t u r e zo n e; th e o t h e r s t r i k e s n o r t h w e s t - s o u t h e a s t j u s t s o u t h of th e i s land of H a w aii and i n t e r s e c t s t h e e a s t - w e s t t r e n d a lo n g the a x i s o f th e H aw aiian s w e l l on th e i s l a n d of M o lo k a i. The g e o p h y s i c a l t r e n d s o r i g i n a t e a t s e a , where t h e y can be a s s o c i a t e d w ith l i n e a r su b m a rin e t o p o g r a p h y , and c r o s s the i s l a n d s w i t h o u t any m ajor d e f l e c t i o n s . Between th e i s l a n d s o f M o lo kai and Oahu, a s h a r p t r a n s i t i o n from e a s t - w e s t t r e n d s to n o r t h w e s t - s o u t h e a s t t r e n d s o c c u r s . A s i m i l a r t r a n s i t i o n o c c u r s n o rth w a rd on t h e i s l a n d o f K auai and i s r e f l e c t e d in th e s t r i k e o f the v o l c a n i c r i f t s y s te m . Land and o f f s h o r e g r a v i t y d a t a s u p p o r t t h e m a g n e tic o b s e r v a t i o n s , show t h a t t h e s e a n o m a lie s a r e r e l a t e d 201 to c a l d e r a s , c e n t e r s of v o lc a n is m , and d ik e complexes and u s u a l l y have no a s s o c i a t i o n w ith the p r e s e n t - d a y c o a s t l i n e or the s t r i k e of the Hawaiian s w e l l . From the ev iden ce . . . i t a p p e a rs t h a t any l a t e r a l d i s p lacem ent of the c r u s t has been a lo n g the e a s t - w e s t f r a c t u r e system w ith d i s p l a c e m e n t o f the n o r th s id e toward the e a s t . One of the m ajor problem s a p p e a rs to be an e x p l a n a t i o n o f the o v e r a l l range of u p l i f t and s u b s id e n c e t h a t has t a k en p la c e i n the Hawaiian I s l a n d s s in c e e a r l y T e r t i a r y p e r i od. T e r r a c e s as deep as 1,300 m are known which have an a p p a re n t Miocene age. At l e a s t seven u p l i f t e d marine t e r r a c e s , m o stly of P l e i s t o c e n e age, occur a t e l e v a t i o n s as high as 326 m. The i s l a n d s have been u p l i f t e d and have i s o s t a t i c a l l y submerged r e l a t i v e to se a l e v e l on numerous o c c a s i o n s . They a lso have been eroded d u rin g p e r i o d s of e u s t a t i c changes in se a l e v e l . Evidence seems to i n d i c a t e a minimum t o t a l range r e l a t i v e change in e l e v a t i o n of 1,600 m sin c e the Miocene epoch, b ut what, p a r t s were due to i s o s t a t i c ad j u s tm e n ts and e u s ta c is m at p r e s e n t i s d i f f i c u l t to a s s e s s . OTHER PACIFIC ISLANDS L i t e r a l l y hundreds of echograms of s m a ll or i s o l a t e d i s l a n d s , i n c l u d i n g a t o l l s , were examined; however, the r e corded i n s u l a r s lo p e s on th e m a j o r i t y o f the i s l a n d s a p pe ared so s t e e p t h a t they were u s e l e s s in t h i s i n v e s t i g a t i o n . N e v e r t h e l e s s , s e v e r a l i s l a n d s were of p a r t i c u l a r i n t e r e s t i n c lu d in g T a h i t i , Rapa, and C l i p p e r t o n . C l i p p e r t o n I s l a n d C l i p p e r t o n i s the on ly a t o l l in th e e a s t e r n P a c i f i c (10° 19* N, 109° 1 3 ’ W). In r e c e n t y e a r s , s e v e r a l e x p e d i t i o n s have stopped s t o study the sh a llo w w ater p a r t s of the a t o l l , i n c lu d in g s e v e r a l d e e p -w a te r d r e d g e s , b u t no d e t a i l e d o f f s h o r e su rv e y s a re known. The land s u r f a c e c o v e rs 2 2 1 .2 km form ing a c o n tin u o u s lagoon of 8 .2 km . The i s l a n d i s a normal a t o l l e x ce p t on the s o u t h e r n p a r t where a p a r t ly p h o sp h a tiz e d rock o f a l k a l i n e t r a c h y t e 200-m long and 30-m high o c c u r s . L a c ro ix d e s c r i b e d t h i s rock as a p ^ le a n dome b e n ea th the lag o o n . The lagoon i s 106-m (58 fm) deep, an e x c e p t i o n a l depth which Davis (1928) a t t r i b u t e d to s u b s i d e n c e . I t i s presumed t h a t one c y c le of v o lca n ism o c c u rr e d d u rin g the T e r t i a r y p e r i o d . G r a v ity measurements 202 203 show a p o s i t i v e anomaly between 130 mgal to 140 mgal over th e i s l a n d . S e v e r a l p r o f i l e s made by S c r i p p s T s h i p s c lo s e to th e i s l a n d r e v e a l s e v e r a l w e l l- d e v e l o p e d t e r r a c e s a t s e v e r a l d e p th s ( F i g u r e 2 6 ). The o u t e r p a r t of the s h e l f i s h i g h l y i r r e g u l a r , g iv in g a s t r o n g im p re s s io n of o r g a n ic r e e f s . Most p r o f i l e s show a m ajor t e r r a c e , a l s o w ith i r r e g u l a r i t i e s , a t d e p th s between 200 m to 500 m. O ther f e a t u r e s o c cur on th e s t e e p , i n s u l a r s lo p e bu t do not show th e c o r r e l a t i o n o f the s h a l lo w e r f e a t u r e s . Rapa I s l a n d Rapa I s l a n d is one of the two most s o u t h e r l y i s l a n d s in th e A u s t r a l group. I t s d im e n sio n s a re 9 km by 11 km and 633 m h ig h . I t i s an eroded c a l d e r a , h a v in g a deep bay which p e n e t r a t e s to the c e n t r a l c o r e . Rocks c o n s i s t p r i n c i p a l l y of o l i v i n e b a s a l t . On the w est s i d e of T abuai Bay, a b l u f f of l im e s to n e e x te n d s from below sea l e v e l to 30 m above, form ing a " s k i n ” about 6-m t h i c k over th e v o l c a n i c r o c k s . S in c e th e i s l a n d was form ed, i t has been s u b j e c t e d t o a r e l a t i v e r i s e and d e p r e s s i o n o f 30 m. Deep e r o s i o n of v a l l e y s i n d i c a t e s c o n s i d e r a b l e s u b s id e n c e . The i n s u l a r s h e l f i s 55-m deep and 2-km to 11-km w ide. No r e e f s s u r round the i s l a n d . R apa’ s i n s u l a r s lo p e i s s te e p , and on one p r o f i l e a l e d g e , or narrow i r r e g u l a r t e r r a c e , o c c u r s a t 300 m ( F i g u r e 2 5 ). 204 T a h i t i T a h i t i i s a v o lc a n ic cone ( p l u g ) m easuring 40 km by 33 km and is 2,233-m h ig h . The p lu g c o n s i s t s c h i e f l y of n e p h e lin e m onzonites and t h e r a l i t e s , w h ile the rem aind er of the i s l a n d i s d o m in a n tly b a s a l t . R e efs occur c o m p le te ly around the i s l a n d , and form er r e e f s a re a t the base o f 300 m c l i f f s . Two p r o f i l e s e n t e r i n g P a p e e te show an i r r e g u l a r slo p e (F ig u re 2 7 ). F ig u re 25. Echograms of Rapa I s l a n d F ig u r e 26. Echograms of C l i p p e r t o n I s l a n d . 206 1 K m F igu re 27. Echograms of T a h i t i ANTARCTICA I n tr o d u c t i o n P r o f i l e s a c r o s s th e c o n t i n e n t a l t e r r a c e were made by the OB d u r i n g 1957 and 1958 and one o t h e r c r u i s e ; one p r o f i l e was made by D ie tz (1948; p r o f i l e H - l ) ; t h r e e by L epley (1964; p r o f i l e s L - l to L - 3 ) ; t h r e e by S h o ji and S ato (1959; p r o f i l e s SS-1 to S S -3 ); and a s e r i e s by Roos (1937) in the Ross Sea s e c t o r . A ll of t h e s e p r o f i l e s have been r e p l o t t e d ( P l a t e 2 2 ). OB and Roos* so u n d in g s a re c o r r e c t e d f o r sound v e l o c i t y ; a l l o t h e r so u n d in g s a re b e l i e v e d to be u n c o r r e c t e d . R o o s’ p r o f i l e s , w h ile based upon e c h o s o u n d i n g s , are sp o t so u n d in g s. C o r r e l a t i o n of p r o f i l e s ( a s w e l l as a t t e m p t s to p ic k out sm a ll f e a t u r e s ) i s d i f f i c u l t b ecau se of the sm a ll scale, i r r e g u l a r to p o g rap h y , and high a n g le s w ith which many c r o s s the c o n t i n e n t a l t e r r a c e . C o r r e l a t i o n i s i n h i b i t e d f u r t h e r by th e wide s p a c in g of th e p r o f i l e s and f r e q u e n t c o u rs e changes r e q u i r e d w h ile m aneuvering in i c e . The sm all num ber of p r o f i l e s compared to a c o a s t l i n e l e n g t h of more than 22,400 km, and f o r th e re a s o n s a l r e a d y g i v e n , make a l l c o n c l u s i o n s t e n t a t i v e . 207 208 R e s u l t s The c o n t i n e n t a l t e r r a c e around A n t a r c t i c a has been th e s u b j e c t o f d i s c u s s i o n f o r about 65 y e a r s . EREBUS and TER ROR made so u n d in g s to th e e a s t o f V i c t o r i a Land which showed d e e p e r th a n normal s h e l f b r e a k s , but i t was Henryk A rc to w sk i ( 1 8 9 9 ), of th e A n t a r c t i c a BELGICA E x p e d i t i o n , who f i r s t c a l l e d a t t e n t i o n to the f a c t t h a t A n t a r c t i c a had a s h e l f b re a k a t d e p th s d e e p e r th a n th e w o rld a v e r a g e . He made a s e r i e s o f so u n d in g s o f f A le x a n d e r Land (83° W) and s t a t e d th e s h e l f b re a k o c c u r r e d a lo n g th e 3 0 0 -fath o m (540 m) i s o b a t h . (T h is i s a p p ro x im a te b e c a u s e of th e s p a r s e so u n d in g s w hich were a v a i l a b l e . ) A rc to w sk i (1944) r e p o r t e d t h a t i n th e r e g i o n of th e B e l g i c a D r i f t th e s h e l f b re a k o c c u rs a t 600 m to 700 m. The d e p th of s h e l f b re a k s s u r r o u n d i n g A n t a r c t i c a a re sum m a riz e d in T able 9. DISCOVERY I I s u r v e y s s u g g e s t t h a t a s h e l f i s a lm o st c o m p l e t e ly a b s e n t in the A t l a n t i c s e c t o r (Herdman, 1932, 1948) b u t t h a t i t i s wide a lo n g th e Palm er P e n i n s u l a , in th e W eddell and B e l l i n g s h a u s e n S e a s , and i n a few o t h e r a r e a s . Few p r o f i l e s have been made c o m p le te ly a c r o s s th e s h e l f in any r e g i o n , l a r g e l y b e c a u se of o p e r a t in g d i f f i c u l t i e s . Flem ing (1952) b r i e f l y re v ie w e d th e subm arine t o p o g rap h y s u r r o u n d i n g A n t a r c t i c a and i n c lu d e d a p h y s i o g r a p h i c d ia g r a m , b u t gave few d e t a i l s on th e c o n t i n e n t a l t e r r a c e . 209 T able 9. Approximate Depth of S h e l f Breaks', A n t a r c t i c a AREA DEPTH (m) Gunnerus Bank (34° E) 500 - 600 Lutzow-Holm Bay (39° E) 300 - 400 Mackenzie Sea (73° E) .500 Davis Sea (91° E) 400 - 700 S h ack leto n S h e l f - I c e (97° E) 400 - 430 Budd C oast (113° - 116° E) 300 - 500 Banzare C o ast (125° E) 350 C la r i e Coast (134° E) 300 - 450 C la r ie C oast (135° E) 450 A delie Coast (142° E) 1000 (? ) George V. C oast (147° - 150° E) ' 400 - 500 Oates C oast (161° - 146° E) 450 - 500 Ross Sea 250 - 700 ( ? ) S u lz b e rg e r Bay (153° - 163° W) 300 - 525 E le p h an t I s la n d (57° 450 B e lg ic a D r i f t 600 - 700 Ewing and Heezen (1956) i d e n t i f i e d the m ajor p h y s io g r a p h ic f e a t u r e s of the A n t a r c t i c Ocean and in c lu d e d a d iagram showing th e edge of the s h e l f . More r e c e n t l y (1 9 6 2 ), the American G e o g ra p h ic a l S o c i e t y has is s u e d a l a r g e c h a r t of A n t a r c t i c a , in c lu d in g to po grap hy below the ic e cap and ic e s h e lv e s (See P l a t e 22, upper l e f t ) . T h is map shows the 210 i r r e g u l a r shape of the s h e l f edge as w e l l as s e v e r a l l a r g e b a s i n s and tro u g h s below se a l e v e l under th e i c e . Ford (1 964) has made a s i m i l a r map ( F ig u r e 30). No average s h e l f b rea k can be given because of the commonly i r r e g u l a r n a t u r e of th e o u te r s h e l f edge; n e v e r t h e l e s s , i t i s obvious from Table 9 and F ig u re 28 t h a t the s h e l f b r e a k is c o n s i d e r a b l y deeper than th e world a v e ra g e . Based upon a v a i l a b l e p r o f i l e s , the s h e l f edge i s most com monly l o c a te d a t about 450 m, a lth o u g h l o c a l l y i t may be as sh allo w as 150 m, and p o s s i b l y as deep as 1,000 m. The c o n t i n e n t a l t e r r a c e has a s t r i k i n g s i m i l a r i t y to t h a t of Norway (compare F ig u re 29 and P l a t e 22) and many of the f e a t u r e s o f o th e r high l a t i t u d e la n d s ( i n p a r t i c u l a r , a c lo s e p a r a l l e l arrangem ent of th e shape of the s h e l f edge and the base of the c o n t i n e n t a l s lo p e and deep d e p r e s s i o n s on th e s h e l f p a r a l l e l to th e c o a s t ) . The sh a llo w p a r t of p r o f i l e OB 5 7 /8 -1 1 is p a r a l l e l to the c o a s t and shows the i r r e g u l a r n a t u r e o f the s h e l f s u r f a c e . O ther p r o f i l e s , such as OB-2-6 and OB 5 7 /8 - 9 , give su p p o rt to the c o n c lu s io n t h a t most o f A n t a r c t i c a ’ s s h e lv e s a re i r r e g u l a r . A p r o f i l e by D ie tz (1948, 1952) made a c r o s s the c o n t i n e n t a l t e r r a c e ( H - l) has been h i g h l y quoted as b e in g t y p i c a l of A n t a r c t i c a . I t now a p p e a rs t h a t the Mackenzie Sea a r e a (72° to 73° E) i s e x c e p t i o n a l , f o r no o t h e r r e g io n where p r o f i l e s are a v a i l a b l e show a c o n t i n e n t a l t e r r a c e 211 w ith such a smooth and g e n tl e g r a d i e n t . Another common high l a t i t u d e f e a t u r e i s s h e lv e s which slope towards the land r a t h e r than the t y p i c a l seaward s lo p in g s h e l f ( P l a t e 22, P r o f i l e s L - l and V I I I ) . Although many c r o s s i n g s of the c o n t i n e n t a l t e r r a c e in A n t a r c t i c a have been made, o f t e n at c o n s i d e r a b le a n g le , th e p resen c e of t y p i c a l submarine canyons i s s t i l l un decided . Herdman (1932) showed a number of r e - e n t r a n t s o f f South G eorgia I s la n d which s u g g e s ts submarine canyons. The major problem s are the s p a rse number of sounding l i n e s p lu s o th e r re a s o n s p r e v i o u s ly enumerated making i t d i f f i c u l t to d e l i n e a t e canyons. The A u s t r a l i a n sh ip AURORA (1911) made soundings o f f the A delie Coast a t 140° E and showed a moat 720 m below se a l e v e l (500 m r e l i e f ) on the c o n t i n e n t a l s h e l f . Since th e n , d e p r e s s io n s p a r a l l e l to th e s h e l f have been sounded in many a re a s ( P r o f i l e s L - l , L -2, and ZL-2, P l a t e 22, show th e s e m o a ts). A n t a r c t i c voyages on the COMMANDANT CHARIOT (d u rin g 1949-50), Zhivago and L i s i t z y n (1 9 5 7 ), and L ip le y (1964) have noted th ese i n n e r - s h e l f d e p r e s s i o n s . Zhivago and L i s i t s y n (1957) r e p o r t e d t h a t the Davis Sea has complete a l t e r a t i o n s of d e p r e s s i o n s and e l e v a t i o n s w ith r e l i e f of 200 m to 300 m. These f e a t u r e s are o r i e n t e d p a r a l l e l to the edges of the c o n t i n e n t a l s h e l f . The in n e r s h e l f tro ug h i s a l s o o r i e n t e d p a r a l l e l to the c o a s t , and a t t a i n s d e p th s of 900 m to 1,400 m and i s 7-km to 22-km 212 ANTARCTICA HO RIZO N TA L DISTANCE N O T TO SCALE F ig u re 28. C o r r e l a t i o n of t e r r a c e s and o t h e r f e a t u r e s on th e c o n t i n e n t a l t e r r a c e of A n t a r c t i c a . 213 sv N B to o too too A iEl SIV too too. 300 N £ TURHAVtK ISLAND, U4W OW N £ C MAKKOVIIr, LABRADOR I BRIO HARBOUR ISLAND . LABRADOR 0 to o too 3 0 0 N W HARAM ; M ORS, NO RW AY NW p p . P LIO C E N E P LE ISTO C E N E M i P R E -T E R T IA R Y 0 10 NAUTICAL M U E S D E P TH S IN FATHOM S too- too - 40 0 - F U Q LtirO JU PE T, NORW AY S B F igure 29. Comparison of c o n t i n e n t a l sh e lv e s in high l a t i t u d e a r e a s . Note the "moats" or deeps on the s h e l f . Compare w ith P l a t e 22, L - l , L-2, and ZL-2. (A f te r O. H o l t e d a h l, 1958.) (See a ls o F igure 4 6 .) 214 w ide. Seco nd ary f e a t u r e s i n th e f l o o r of the tr o u g h c o n s i s t of d e p r e s s i o n s d iv id e d by s t e p p e d , or smoothed c r e s t s , u s u a l l y a sy m m e tric al in sh a p e . Like the main tr o u g h , t h e i r s l o p e s n e a r e s t the c o n t i n e n t a re v e r y s t e e p , w h ile th o se f a r t h e r away from th e c o a s t are more g e n t l e . One e x p e d i t i o n r e c o r d e d a g r a d i e n t of 8° on th e s o u t h e r n s l o p e . An o t h e r d e p r e s s i o n f u r t h e r s o u t h , n a rro w e r and l e s s deep (840 m ), a ls o h as an asym m etric sh a p e . Zhivago and L i s i t s y n a ls o s t a t e d t h a t the r e l i e f of the Davis Sea and th e c o n t i n e n t a l s h e l f e a s t o f the Shack- l e t o n S h e lf i c e ’’has s t r o n g l y d i s j o i n t e d f e a t u r e s . ” They b e l i e v e t h i s to p o g ra p h y , w ith r e l i e f of 200 m to 300 m, r e p r e s e n t s the "submerged r e l i e f of a m ountainous c o u n t r y , w hich has been s u b j e c t e d to the a c t i o n o f a n c i e n t g l a c i e r s , b u t where th e d i s j u n c t i v e d i s t u r b a n c e s s t i l l rem ain a c t i v e . F a u l te d s t r u c t u r e s are only s l i g h t l y cov ered by t e r r i g e n o u s d e p o s i t s . " They b e l i e v e t h a t many h i l l s and d e p r e s s i o n s (which a re rounded or c u rv e d ) a re r e l i c g l a c i a l form s made when the i c e s h e e t s p re a d o u t over the s h e l f . The s t r o n g l y d i s j o i n t e d f e a t u r e s and th e y o u t h f u l a p p ea ra n c e of the s h e l f f e a t u r e s n e a r the c o a s t g iv e the im p r e s s io n t h a t the s h e l f was o n ly r e c e n t l y immersed. F a r t h e r o f f s h o r e , s e d i ments have changed th e h i l l y s h e l f i n t o wavy p l a i n s . In g e n e r a l , th e s h e l f i s sm oother as th e d i s t a n c e from the c o n t i n e n t i n c r e a s e s . D ie tz (1948) r e p o r t e d a p r o b a b l e f a u l t e sc a rp m e n t 215 about 480 km o f f P r i n c e s s Ragnhild C oast (35° E ) • This o c cu rs on th e e a s t s id e of a sp u r, and has a 44°- slo p e angle between 1,980 m to a t l e a s t 4,860 m (1 ,1 0 0 fm to 2,700 fm). A f o re d e e p may e x i s t . D ie tz s t a t e d t h a t t h i s escarpm ent can only be e x p la in e d by e i t h e r f a u l t i n g or a sh a rp f l e x u r e in the E a r t h ’s c r u s t . P r o f i l e s taken by th e OB o f te n show l a r g e block s t r u c t u r e s wi:th r e l i e f up to 600 m on the s lo p e (se e P l a t e 22; OB 5 7 / 8 - 6 ) . These s t r u c t u r e s were found n o r t h of Knox C oast, S a b rin a C oast, Banzare Land, and the D’U r v i l l e Sea. In a d d i t i o n , the b ase of v o lc a n ic B a lle n y I s l a n d s (OB 57/8- 16) i s a l s o of the same type r e l i e f and su g g e st t h a t i t r e p r e s e n t s la rg e r i f t s . Geology R e c e n tly Ford (1964) reviewed the geology of A n t a r c t i c a , hence, i t is u n n e ce ssa ry to go i n to d e t a i l h e r e . F i g u re 30 shows A n t a r c t i c a with the ic e removed and F ig u re 31 p o r t r a y s the g e n e r a l geology. U n f o r t u n a t e ly , th e r e i s no in f o r m a tio n about o f f s h o r e geology and t h i s can o n ly be i n f e r r e d from the land geology. E a s t A n t a r c t i c a is Precam brian S h i e l d , h i g h e s t along the b o r d e r s of the V i c t o r i a Land, Queen Maud Range, and H o rlic k Mountains where i t i s over 3,000 m in e l e v a t i o n , dro p ping g r a d u a l ly to about 1,000 m toward the c o a s t s . These ra n g e s are c u t o f f a b r u p t l y form ing the A n t a r c t i c 2 1 6 H o r s t, and a graben. T h is graben s t r e t c h e s from the Ross Sea to B e llin g s h a u s e n Sea and i s bound on th e n o r t h by th e E d se l Ford, E xecu tiv e Committee, and Kohler Ranges. As e a r l y as 1912, Gregory c a l l e d t h i s yet unproved graben the " A n t a r c t i c R i f t V a l l e y . " R e c e n tly i t was renamed Byrd B a s i n . F a u ltin g i s common along the h o r s t and graben ( F i g ure 31) . P r o f i l e s a c r o s s the f r o n t o f the Ross Ice S h e lf , b e tween Cape Colbeck and Cape C r o z ie r , show d e p th s g e n e r a l l y deeper than 500 m and o f f Ross I s la n d they are 850 m. An o t h e r p r o f i l e a c ro ss the i c e f r o n t at the Bay of Whales, ta k e n in Ja n u a ry 1935, shows the f l o o r to be about 500 m to 600 m. B e n tle y , C ra ry , O ste n so , and T h ie l (1960) have p u b lis h e d a c h a r t showing the rock s u r f a c e s below sea l e v e l . Byrd Basin ran g e s to 2,500 m in d e p th n o r t h of the H o rlic k M ountains. Most of t h i s b a s i n , ly in g between the Ross Sea and B e llin g s h a u s e n Sea, i s deeper than 500 m. A tro u g h a ls o ex ten d s along the e n t i r e w e s te rn and so u th e rn boundary of the Ross Ice S h e l f . A trough w ith d e p th s g r e a t e r than 1,000 m below sea l e v e l e x te n d s from the edge o f th e F i l c h n e r Ice S h e lf to the m ountains a t lo n g itu d e 85° W. West A n t a r c t i c a i s about o n e - t h i r d the s i z e of the e a s t e r n P recam brian s u b - c o n t i n e n t . The w estern s e c t i o n c o n s i s t s of r e l a t i v e l y young r o c k s , e s s e n t i a l l y a c o n t i n u a t i o n of the grand loop of i s l a n d s and submerged r i d g e s 217 c a l l e d the S c o t i a A rc, and c o n t i n u e s up to th e Andes. I t i n c l u d e s a t l e a s t one a c t i v e v o lc a n o . V o lc a n ic and marine s e d im e n ta ry se q u en c es as young as l a t e T e r t i a r y age are p r e s e n t . Thus, w e s t e r n A n t a r c t i c a c o n s i s t s of the t y p i c a l c i r c u m - P a c i f i c f o l d b e l t s . A n t a r c t i c a i s an a s e is m ic r e g io n e x c e p t f o r a few e a r t h q u a k e s i n the S c o t i a Arc. S e i s m i c - a c t i v e r e g i o n s o c cur along the v a r io u s subm arine r i d g e s such as t h a t stre tc h ing from E a s te r I s l a n d to the Ross Sea, and a n o th e r from A u s t r a l i a and Tasmania tow ards the Ross Sea. A ccording to Sykes (1 9 6 3 ), e a r th q u a k e s have been r e c o r d e d as f a r as o 65 S, but he d id not con du ct a th o ro u g h s e a r c h f o r A n t a r c t i c sh o c k s. Ewing and Heezen (1956) r e p o r t e d a number of a d d i t i o n a l e a r th q u a k e s on the P a c i f i c s id e of Palm er P e n i n s u l a a t the app rox im ate s h e l f ed ge, but none from c o n t i n e n t a l A n t a r c t i c a . The im po rtance of the land geology i s s i m i l a r t o th a t o f A u s t r a l i a and s e v e r a l o th e r a r e a s where a n c i e n t c r y s t a l l i n e ro ck s and T e r t i a r y se d im e n ts occur and where g r e a t s t a b i l i t y and m o b i l i t y e x i s t c o i n c i d e n t a l l y . The r e g i o n has a deep s h e l f b re a k around th e e n t i r e c o n t i n e n t , i g n o r ing ro c k t y p e , age, or s t a b i l i t y . Bottom M a t e r i a l s As m ight be e x p e c te d , bottom m a t e r i a l s s u r r o u n d in g A n t a r c t i c a a re unique b e ca u se of a c o m b in a tio n o f many 218 f a c t o r s (no s tr e a m s ; v i r t u a l l y a l l t e r r i g e n o u s m a t e r i a l i s of g l a c i a l o r i g i n ; e s s e n t i a l l y no ch em ical w e a th e rin g ; r i c h o rg a n ic l i f e , e t c . ) . Bedrock has been dredged from 350 m and much s e s s i l e ben th o s has been c o l l e c t e d . Boulder g r a v e l i s w id e ly d i s t r i b u t e d and i s th o u g h t to r e p r e s e n t u n d e rw ater m o rain es of Q u a tern ary age. Banks on the s h e l f are i n t e r p r e t e d as mor a in e s dumped by th e extended g l a c i e r s of th e Ice Age (Maw- son, 1935; Howard, 1950; and T a y l o r , 1930). S e v e r a l l i n e s of ev id e n ce su g g e s t t h a t P l e i s t o c e n e g l a c i a t i o n d e p o s i t i o n on the A n t a r c t i c c o n t i n e n t a l s h e l f was r a t h e r slow. * OCEAN n o • i v W E S T ANTARCTICA I E A ST ANTARCTICA Physiographic Diagram oj Antarctica with Ice Cover R em oved. This map is slightly modified from a US Geological Survey map (1962) of the bedrock surface, unadjusted for isostatic uplift. Hachures show continental slope and m ajor m ountain areas; stippled regions are above s»a level. In alphabetical order, num bered features are as follows; (1) Adelie Coast, (2) Alexander Island, (S) A m ery Ice Shelf, (4) Am undsen Sea, (6) Beardmore Glacier, (6) Cape Adare, (7) D enman Glacier, (8) Edsel Ford Ranges, (9) Eights Coast, (10) Ells worth Land, (11) Ellsworth M ountains, (12) Falkland Islands, (18) George V Coast, (14) Ilorlick M ountains, (15) Luttow -H olm Bay, (16) M cM urdo Sound, (17) M ount Sandow, (18) Pensacola M ountains, (19) Queen M aud Range, (20) Ross Ice Shelf, (21) Scotia Arc, (22) Shackleton Range, (23) South Georgia, (24) South Orkney Islands, (26) South Shetland Islands, (28) Southern Prince Charles M ountains, (27) Thiel M ountains, (28) Theron M ountains, (29) Victoria Land, and (SO) W hitmore Mountains. F i g u r e 30. Map showing i c e removed from A n t a r c t i c a showing the s u b - g l a c i a l t o p o g r a p h y . ( A f t e r F o rd , 1964) f 7 3 - iO O m ,( 2 | i t ' / / l? S -2 0 0 m , ( 9 | B T f lm y O t) 5 0 0 my (5) (-**•' QuMnMau* Lund b*di UDB»r p u c a m t m i l i i.rf on> 320-630my(S) \ L Q « |f P a I ■ • l i l t t - ^A m try Fm." / 400-l800m y ' H /cuntr-' ■ * 0 “ * ° v I A . I. •», y s ++.. (13) ♦ S N X , X v * ) , ♦ / j ? / i f / MtSondow . f / J / »tJSS£!l .460- ‘ P * V 6 1 S m y — f - 9 0 ° E W3I0- 5lOmy ’ /i< j\ ’ I520my -H20m y / :£6(»0-730m,(2) 1040*1060 m y (2 Q Shtlf SondttoM 430-l000my (1 9 ) BOO km 1530-1540 my (2) 340-760 my (9) 320-600m y 450*9,0^7<3) k e y t o s y m b o l s F o u iti, Hochuret indicate down-dropped tide, v V v\ v ] Cenoioic volcanic rocks, Devonian to Jurassic sedimentory rocks and associated Jurassic diabase and basalt. Sedimentary rocks of uncertoin o g e —in part, at least, late Precom brian to early Paleozoic. * S g jw [ 7 Z 7 Deformed a n d variably m eta m o rp h o se d sedim entary rocks, m ostly of lots P recom brian to e a rly Mesozoic oge (mostly Paleozoic to Mesozoic in west A n tarctica, where voleonic reeks a re included locally). Gneissic ro ck s , m ostly of Precombrian age. Granitic rocks, ranging g reatly in age. Geologic Sketch Map oj Antarctica. Symbol orientations show general structural trends; arrows show regional plunge directions of fold axes. Numbers show approximate ranges of radiometric ages, with the number of dates within each range given in parentheses. Compiled from numerous sources. F ig u re 31. G e n era l geology of A n t a r c t i c a . ( A f t e r Ford, 1964) ARCTIC OCEAN I n t r o d u c t i o n I n f o r m a t io n on th e c o n t i n e n t a l m argin o f th e A r c t i c O cean, l i k e i t s A n t a r c t i c c o u n t e r p a r t , i s s c a n t y . One of the most o bv io u s r e a s o n s i s th e d i f f i c u l t y of making c o n t i n u o u s e c h o so u n d in g r e c o r d s th r o u g h i c e . Some o f th e a v a i l a b l e p r o f i l e s were made by d r i f t i n g i c e s t a t i o n s so t h a t the t r a c k i s random ( P l a t e 2 3 ) . Hope (1959) and O ste n so (1962, 1964) t h o r o u g h l y sum m arized th e g e o p h y s i c a l and g e o l o g i c a l l i t e r a t u r e b u t th e geomorphology o f the c o n t i n e n t a l m argin i s v i r t u a l l y u n known. Hakkel* (1957) has d i s c u s s e d th e c o n t i n e n t a l t e r r a c e b u t n e i t h e r the o r i g i n a l or t r a n s l a t i o n i s a v a i l a b l e (E. R. Hope, p e r s o n a l c o m m u n ic a tio n ). R e f e r e n c e s t h a t b r i e f l y d i s c u s s the c o n t i n e n t a l t e r r a c e or A r c t i c ( geology i n c l u d e : B u f f i n g to n e t a l (1 9 5 0 ) , C a r s o l a (19 54 , 1955), Car s o l a , e t a l . ( 1 9 6 1 ) , Cromie ( 1 9 6 0 ), F ish er, e t a l . ( 1 9 5 8 ) , G o rdien ko and L a k tio n o v ( 1 9 6 0 ) , LaFond ( 1 9 5 4 ) , D ie tz and Shumway ( 1 9 6 1 ) , H a k k e l ’ ( 1 9 5 8 ) , H unkins (1 9 5 9 , 19 6 3 ), Hunkins, e t a l . ( 1 9 6 2 ) , L a k tio n o v ( 1 9 5 9 ) , Nansen ( 1 9 0 4 ) , O s te n so (1 9 6 2 , 19 6 4 ), Panov (1 9 4 3 , 1948, 1952, 1955, 1957, 221 222 1 9 5 9 ), Saks, e t a l . ( 1 9 5 5 ) , Shaver and Hunkins ( 1 9 6 4 ) , V o l kov ( 1 9 6 1 ) , and Weber ( 1 9 6 3 ). Only 17 p r o f i l e s a re a v a i l a b l e o f t h e c o n t i n e n t a l s l o p e in th e A r c t i c B a s i n . P r o f i l e s J - J * and K-K* a re from Weber (1963) and in c l u d e g r a v i t y a n o m a lie s along the s e c t i o n s . These p r o f i l e s s t a r t from E l l e f R in g n e s s I s l a n d and P e a r y C h ann el, r e s p e c t i v e l y , and c u t a c r o s s Meighhen I s lan d . The g e n e r a l f e a t u r e s o f th e A r c t i c Ocean and bathym e t r y are shown i n F i g u r e 32 ( a f t e r O s te n s o , 1964). R e s u I t s The A r c t i c Ocean i s u n iq u e b e c a u s e o f th e e x t r e m e l y wide c o n t i n e n t a l s h e l v e s , but th e w id th v a r i e s g r e a t l y . G o rd ien k o and L a k tio n o v (1960) r e p o r t e d t h a t th e c o n t i n e n t a l s h e l f b o r d e r i n g the A r c t i c B a sin i s n o t everyw here d e v e lo p e d . Off A la sk a and G re e n la n d , t h e s h e l f i s 100-km to 200-km w id e ; th e E a s t S i b e r i a n S h e l f , B a r e n t s S e a , and Kara S ea S h e lv e s ran g e from 500 km t o 1,700 km in w i d t h . N orth o f E lle s m e r e I s l a n d i t i s a b o u t 100-km w ide. The c o n t i n e n t a l s h e l f b re a k n o r m a lly o c c u r s a t a d e p th of 200 m. N o rth o f A la s k a the s h e l f b r e a k o c c u rs a t 63 m and the g r a d i e n t of th e c o n t i n e n t a l s lo p e r a n g e s from 1 .5 ° ° o to 4 . However, s l o p e s a s s t e e p as 23 have b e e n r e p o r t e d n o r t h o f A la s k a ( F is h e r , e t a l .. 1958; G o rd ien k o and L a k t i o n o v , 196 0). Off n o r t h e r n Chukchi and B e a u f o r t Seas th e 1 40* 120* 10 0 * 90* 60* U niversity of F ig u re 32. B athy m etric C hart of A r c t i c Ocean. ( A f te r N. A. O sten so , 1964) ^59637357260763165 999999999996999 224 c o n t i n e n t a l s lo p e d ro p s o f f s t e e p l y i n t o the P o l a r B asin to d e p th s over 4,000 m. Roots (1962) r e p o r t e d t h a t in th e a r e a ly in g o f f s h o r e o f th e Canada B asin from Meighen I s l a n d and E l l e f R in g n ess I s l a n d , and w ith the a r c h i p e l a g o in S v e rd ru p C hannel, P e a ry C hannel, H a s s e l Sound, and p a r t o f P r i n c e G u s ta f A dolf Sea, the c o n t i n e n t a l s h e l f l i e s at a r e l a t i v e l y g r e a t d e p t h , w i t h a w idth of about 150 km and a g e n t l y , u n d u l a t i n g s u r fa c e t h a t b r e a k s s h a r p l y to a smooth c o n t i n e n t a l s l o p e . The c o n t i n e n t a l s lo p e n o r t h of th e L ap tev Sea r e a c h e s up to 18°. Most o f the p r o f i l e s ( P l a t e 23 and F ig u r e 33) show s e v e r a l f e a t u r e s below the s h e l f b r e a k . These in c lu d e a s t e e p upper s lo p e in w e s t e r n B e a u f o r t Sea, g e n t l e u p per s lo p e in the c e n t r a l B e a u f o r t S ea, g e n t l e lower s l o p e , and a f l a t f l o o r of the Canada B a s in . On p r o f i l e F a t e r r a c e o c c u rs a t a d e p th s l i g h t l y more t h a n 1,460 m; on G i t i s 2,00 0 m; on H s e v e r a l i r r e g u l a r i t i e s o c c u r , the f i r s t b e in g a t 1,65 0 m; and on I ab ou t 1,800 m. The low er s lo p e has a g r a d i e n t of o n ly 1° 9 ’ (on p r o f i l e s F and G ) . The NAUTILUS p r o f i l e ( P l a t e 23, upper r i g h t ) a l s o shows a d i s t i n c t u pper c o n t i n e n t a l s l o p e , a t e r r a c e a t 900 m, and an i r r e g u l a r g e n t l e lower s l o p e . P r o f i l e s J and K show a p ro m in e n t t e r r a c e a t about 500 m. S e v e r a l o t h e r p r o f i l e s a ls o show a p ro m in e n t f e a t u r e a t 500 m to 2,00 0 m. I t i s i n t e r e s t i n g to n o te t h a t F ig u re 33. P r o f i l e s a c r o s s th e A r c t i c Ocean and the N or wegian Sea. The two A r c t i c Ocean p r o f i l e s a re s p e c u l a t i v e i n t e r p r e t a t i o n s of s c a t t e r e d so u n d in g s. The i n d i v i d u a l sou ndings are i n d i c a t e d as s h o r t v e r t i c a l l i n e s along th e upper m argin of each p r o f i l e . P r o f i l e s IV and V are p l o t ted from the e a r l y (1937-8) c o n tin u o u s echo soundings pub l i s h e d by Boyd. The e a s t e r n h a l f of p r o f i l e I I I is based on c o n tin u o u s echo so un din gs w h ile the w e s te rn h a l f i s p l o t t e d from d i s c r e t e so un din gs (by Boyd 1948) ( A f t e r Heezen and Ewing, 1961). ARCTIC OCEAN AND NORWEGIAN SEA B ft , i irrn I Lama zooo 3 0 0 0 £ 1000 mrTTTm iii BorrftnH S h ill 1000 3 0 0 0 S o lt i b T Q f tn 1000 2000 3 0 0 0 B oyd 0 9 4 3 ) O f f - iS 2 « J * b « 1000 2000 3 0 0 0 Boyd 0 9 4 6 ) 1000 L o m « A. Boyd Bonh I O O O 2000 3 0 0 0 B o yd 0 9 4 3 ) SCALE IN NAUTICAL MILES VERTICAL EXAGGERATION 4 0 : 1 F ig u re 33. 227 Chukchi Cap, Nansen R idge, and p o s s i b l y th e Lomonosov R id g e, are b e v e le d a t about th e same d e p t h . S e v e r a l c r o s s i n g s have been made of Chukchi Cap, e s p e c i a l l y d r i f t i n g ic e s t a t i o n s ( P l a t e 23; Hunkins. e t a l . . 1962; Shaver and H u n k in s, 1964; and Crom ie, 1960). The s h a l l o w e s t d e p th of Chukchi Cap i s 246 m, i s ro u g h ly 150 km in d ia m e t e r a t the 500 m d e p th c o n t o u r , and h a s a m a r g i n a l d e p r e s s i o n . S i m i la r d e p r e s s i o n s have been o b se rv e d in th e c o a s t a l r e g i o n of many h i g h l a t i t u d e a r e a s ( A n t a r c t i c a , Norway, G re e n la n d , L a b r a d o r , A la s k a , e t c . [ F i g u r e s 29 and 4 6 ] ) . The cap r i s e s s t e e p l y from th e f l o o r of the a b y s s a l s e a , and has a t r u n c a t e d and d i s s e c t e d top w i t h r e l i e f o f 5 m to 30 m, s u g g e s t i n g s u b a e r i a l or g l a c i a l p l a n a t i o n (H unkins, e t a l .. 1962; D i e t z and Shumway, 1 9 6 1 ). I t i s sim i l a r in shape t o Flem ish Cap (Heezen and Ewing, 1 9 6 1 ). A s m a l l e r b u t s i m i l a r f e a t u r e named N orthw ind Seahigh i s l o c a t e d to the s o u t h e a s t o f Chukchi Cap ( F is h e r, e t a l .. 1958). D ie tz and Shumway s u g g e s te d t h a t Chukchi Cap i s an o u t l i e r of th e c o n t i n e n t a l s h e l f and p r o b a b l y of s i m i l a r r o c k , w h ile Heezen and Ewing (1 961) c o n s i d e r e d th e Cap to be a " s e m i- d e ta c h e d p i e c e of c o n t i n e n t a l s h e l f . " Hunkins. e t al. (1962) and Shaver and Hunkins (1964) s u p p o r t the c o n c l u s i o n t h a t a lth o u g h the Cap i s s e p a r a t e d from th e c o n t i n e n t a l s h e l f , i t i s c o n t i n e n t a l in c h a r a c t e r and h a s in some man n e r become d i s a s s o c i a t e d from th e main c o n t i n e n t a l s h e l f . Alpha Ridge (te rm e d C e n t r a l A r c t i c R ise by D i e t z and 228 Shumway, 1961) l i e s n o r t h of the N orth American s id e and s u b - p a r a l l e l to the Lomonosov R idge. I t has a minimum d e p th of about 1,400 m, v a r i e s c o n s i d e r a b l y in d e p th , and i s about 900-km lo n g . The r i d g e j o i n s the c o n t i n e n t a l s h e l f a t e i t h e r end by broad t r i a n g u l a r p l a t e a u s . Hunkins e t a l (1962) su g g e ste d t h a t th e c r e s t of the r i d g e c o n s i s t s of a re g io n of f a u l t b l o c k s . D ie tz and Shumway (1961) noted t h a t the f l a n k s are a b r u p t, about 600-m h ig h , and are presumed to be f a u l t e s c a rp m e n ts . Lomonosov Ridge has a summit d e p th m o stly betw een 900 m and 1,450 m, a minimum d e p th of about 504 m, and a m axi mum s i l l depth of 1,650 m. The r i d g e e x te n d s 1,800 km from the c o n t i n e n t a l s h e l f n o r t h of E lle sm e re I s l a n d to New S i b e r i a n I s l a n d s , and has a w idth of 60 km to 200 km. The r id g e has a r e l i e f of more th a n 3 km. The south f l a n k i s a s c a r p w ith a d e c l i v i t y of 13°; th e n o r th slo p e i s l e s s s t e e p . D ie tz and Shumway concluded t h a t the summit was p laned by s u r f a c t i o n . Lomonosov Ridge a p p e a rs to be a fo ld e d range and not a v o lc a n ic r i d g e . However, H a k k e l’ (1958) has s t a t e d v o l c a n ic a c t i v i t y i s a s s o c i a t e d w ith the Ridge . The SKATE and NAUTILUS c r o s s e d the m id - A t l a n t i c r id g e p ro v in c e which c o n s i s t s of a seamount p r o v in c e in the A rc t i c Ocean. Topography here has a r e l i e f of about 1,000 m. H a k k e l’ (1958) shows the reg ion between New S i b e r i a n I s l a n d s and Chukchi Sea as a " g i a n t s t a i r c a s e ” (Hope, 229 1 9 5 9 ). These s t e p s have been shown to be common in many p a r t s of th e w o rld . E s s e n t i a l l y , H a k k e l’ i n t e r p r e t s h i s " s t a i r c a s e r e g i o n " as a s e r i e s of f a u l t - t e r r a c e s or b e n c h e s . Hope (1959) su g g e s te d t h a t " th e f l o o r of the H y perborean B asin has been formed by th e su b s id e n c e of an enormous oblong b lo c k , along r o u g h ly p a r a l l e l l i n e s of f r a c t u r e : the f r a c t u r e s form the c o n t i n e n t a l s lo p e on the N orth American s id e and th e ’s t a i r c a s e ’ on t h e S i b e r i a n s i d e . " As an a l t e r n a t i v e he p o i n t s ou t t h a t the p a r a l l e l r i d g e shown on H a k k e l’ s map m ight be caused by d e f o r m a ti o n of s u r f a c e l a y e r s d u r in g s u b s id e n c e of the b a s i n or by th e f o l d e d basem ent p a t t e r n of the H yperborean p l a t f o r m which has been p r e s e r v e d from e r o s i o n by subm ergence. (More r e c e n t c h a r t s do not show H a k k e l ’s s t a i r c a s e s t r u c t u r e . ) Heezen and Ewing (1961) s u g g e s te d t h a t th e E a s t S i b e r ian c o n t i n e n t a l slo p e may c o n s i s t o f a f e a t u r e s i m i l a r to the Blake P l a t e a u (which they term a " m a r g in a l p l a t e a u - m a r g in a l escarpm ent com plex") or b o r d e r l a n d - l i k e as e x i s t s o f f s o u t h e r n C a l i f o r n i a . The r e g i o n o f f the Mackenzie D e l t a a ls o s u g g e s t s a m a rg in a l p l a t e a u , b u t t h i s - - t h e B e a u f o r t P l a t e a u - - d i f f e r s from th e Blake P l a t e a u by h a v in g an u p tu r n e d e d g e . S i m i l a r p l a t e a u s are r e p o r t e d o f f E lle s m e re I s l a n d and n o r t h of Wrangel I s l a n d . I n s u f f i c i e n t c o n tin u o u s echogram s e x i s t to a s c e r t a i n w h ether a c o n t i n e n t a l r i s e i s w id e s p re a d in the A r c t i c 230 Ocean. The p r o f i l e made by the NAUTILUS o f f A laska shows a c o n t i n e n t a l r i s e ; o t h e r p r o f i l e s o f f A laska and w e ste rn Canada a ls o show a c o n t i n e n t a l r i s e . Other a re a s are l e s s c l e a r , as fo r example, o f f B a ren ts Sea, S p i t s b e r g e n , e t c . ( F ig u r e s 33 and 37). The p r o f i l e s o f f P o i n t Barrow ( P l a t e 23, A and B) show a s t e e p 2 3 ° - c o n t i n e n t a l slo p e w ith no c o n t i n e n t a l r i s e . B a re n ts Sea covers a l a r g e a re a and con s i s t s o f a s e r i e s of d e p r e s s io n s ly in g m o stly between 100 m and 300 m (Klenova, 1960). Ahlman (1933) p o in te d out the p ro b a b le im portance of b lo ck f a u l t i n g in the B aren ts Sea which b e s t e x p la in s the submarine f e a t u r e s . Submarine canyons i n c i s e the c o n t i n e n t a l t e r r a c e bu t t h e i r d i s t r i b u t i o n s are unknown. S e v e ra l occur n o r th of P o i n t Barrow, in the B a re n ts and Kara Seas, and o f f the Canadian A r c ti c A rc h ip e la g o . B arents Sea i s c o n sid e re d by Klenova (1960) to be a p l a t f o r m - t y p e sea and has a broad c o n ta c t w ith th e ocean. The major p o r t i o n l i e s a t d e p th s not exceeding 300 m; in the c e n t r a l d e p re s s io n o n ly the d e p th i n c r e a s e s to 400 m, and in the w e stern tre n c h b o rd e rin g the G reenland Sea i t d e c r e a s e s to 500 m. Klenova s t a t e d t h a t d e p r e s s io n s and s lo p in g sea f l o o r f e a t u r e s , having a n o r t h w e s t e r l y t r e n d , are a ssig n e d to i n h e r i t a n c e from P re ca m b ria n f o l d i n g s . In the w e ste rn r e g io n , t r a c e s of Lower P a l e o z o ic s t r u c t u r e s remain on banks and in the tr e n c h e s of the Greenland Sea. T e r t i a r y movements occur in the n o r t h e r n s e c t i o n of th e 231 B a re n ts Sea c o rre sp o n d in g to s e c t i o n s of the B a re n ts Sea P l a i n which began to sag in the J u r a s s i c p e r i o d . The s a g ging presum ably was accompanied by f r a c t u r e s and b a s a l t i c e r u p t i o n s , c o n tin u in g i n to the Q u a te rn a ry p e rio d and s t i l l c o n tin u in g today in c o n n ec tio n w ith th e fo rm atio n of the deep d e p r e s s io n s of the A r c ti c Ocean. Recent f r a c t u r e s occur in many p l a c e s : on th e Kola P e n i n s u l a , Finmarken, Novaya Zemlya, the c o a s t of Franz J o s e f Land and S p i ts b e r g e n A rc h ip e la g o , west end of Goose S h o al, in pre-Novaya Zemlya Trench, and e lsew h e re. According to Klenova, the B a re n ts Sea S h e lf fo rm a tio n c o in c id e d w ith low ering of the N orth A t l a n t i c and A r c t i c Oceans, but subsid en ce was v a r i a b l e in d i f f e r e n t r e g i o n s . T e rra c e s are pronounced a t 180 m to 220 m and the mean i s 200 m. Another sh a llo w e r t e r r a c e a l s o o c cu rs a t 70 m, e s p e c i a l l y in th e s o u t h e a s te r n p a r t of the sea. The 200-m t e r r a c e i s a ssig n e d by Klenova to th e maximum lo w erin g sea l e v e l d u rin g the P l e i s t o c e n e epoch. The 70-m to 100-m t e r r a c e s a re a t t r i b u t e d to the l a s t p e rio d of g l a c i a t i o n . As the n o r th e r n s e c t i o n of the A t l a n t i c Ocean sub s i d e d , forming the Greenland Sea, Norwegian Trench, the d e p r e s s i o n o f the A r c tic B asin, and the S t r a i t s of Franz J o s e f Land in l a t e T e r t i a r y tim e, movement was r e f l e c t e d in the B a ren ts Sea P l a i n . F r a c t u r e s and su b sid e n c e oc cu rred th ro u g h o u t the r e g io n , e v i d e n t l y as e a r l y as m id -Q u atern ary p e r i o d . 232 Bottom M a t e r i a l s Among the i n t e r e s t i n g bottom sedim ents of the A r c ti c B asin are sm o o th -ro lle d p e b b le s found in g r e a t q u a n t i t i e s a t a l l d e p th s , in c lu d in g th o se exceedin g 3,000 m. They were d is c o v e re d d u rin g the 1 9 5 0 -1 9 5 1 d r i f t s t a t i o n which moved along the n o r t h e r n p a r t of A laska (Anonymous, 1954). Burkanov ( i n S c h e id e g g e r, 1963, p. 32) r e p o r te d t h a t c o re s taken from the Lomonosov Range re v e a le d " g l a c i a l and i n t e r g l a c i a l d e p o s i t s r e m in is c e n t of those on the p r e s e n t c o n ti n e n t of A s i a . " I t was con clu ded , t h e r e f o r e , t h a t the Lomonosov Range, in whole or in p a r t (or a t the minimum), was above but s u b s e q u e n tly submerged to a mean d e p th of 1,000 m. However, w ith o u t more in f o rm a tio n i t i s d i f f i c u l t to a s s e s s what p a r t of t h i s g l a c i a l d e b r i s was r a f t e d by ic e f l o e s , ( C a r s o la , 1954a; Hunkins, 1959, 1960; Schwarz- acker and Hunkins, 1960). I t i s notew o rthy t h a t only ice i s l a n d s - - w h i c h are r a r e - - c a r r y l a r g e amounts of g r a v e l a t p r e s e n t (H unkins, 1959). Geology I t should be obvious t h a t the geology must be d e t e r mined l a r g e l y from t e r r e s t r i a l f e a t u r e s . H a k k e l’ r e p o r te d t h a t in 1957 a t o t a l of o n ly 3,000 soundings had been made. The number of bottom samples p ro b a b ly d id not exceed t e n p er cent o f t h i s number. 233 The A r c t i c Sea f l o o r geology ( F ig u r e 34) i s i n t i m a t e l y r e l a t e d to bottom topography and many of the s t r u c t u r a l e l ements on c o a s t a l lan d s are sim ply e x te n s i o n s i n t o the A r c t i c Basin ( E a r d l e y , 1948, 1954 and 1961; B elo ussov , 1954; Saks, e t a l ., 1955; Panov, 1952, 1955, 1957; O s te n s o , 1962; E. R. King, e t a l .. 1964; Hope, 1959). In the e a r l y P a l e o z o ic e r a , C aled on ian f o l d i n g o c c u rre d in S c a n d in a v ia , the G reenland Sea, S p i t z b e r g e n , N an sen ’ s S i l l , and n o r t h e a s t G re en lan d . E ast of th e Low er P a l e o z o ic zone of f o l d i n g , a r i g i d b lo ck c o n tin u e d n o r t h ward from the E a s t European P l a t f o r m . I t extend ed over the B a re n ts Sea, the e a s t e r n p a r t of S p i t z b e r g e n , Franz J o s e f Land, and the n o r t h e r n p a r t of the Kara Sea. At th e end of the P a l e o z o i c e r a , f o l d i n g extended over the U ra l-T ie n s h a n a r e a , Novaya Zemlya, Teimyr P e n i n s u l a , S e v ern aya Zemlya i n t o the A r c t i c Ocean, and s u r f a c e d on the o t h e r s id e in n o r t h e r n G reenland and E lle s m e re Land. Upper P a l e o z o ic f o ld s t r u c t u r e s p ro b a b ly occupy the bottom of the w e s te rn p a r t o f the A r c t i c B a sin , i n c l u d i n g the n o r t h p o l a r r e g i o n . Throughout the Mesozoic e r a a v a s t r e g i o n in n o r t h e a s t e r n A sia and A laska was f o l d e d , r e s u l t i n g in the V erk hoyansk, C hersk, Gydan, and Chukchi r a n g e s , and the Brooks Range in A la sk a . The f o l d s of the Verkhoyansk Range have been tr a c e d to the bottom of the L aptev Sea, thence to the w e s te r n p a r t o f the New S i b e r i a n A r c h ip e la g o , and as a 234 n a t u r a l e x t e n s i o n of th e subm arine Lomonosov Range. The f o l d s o f the L onjpnosov Range c o n ti n u e to E lle s m e re Land. R u ssian s o u r c e s have r e p o r t e d o t h e r m ountain r a n g e s , n o t as l a r g e as the Lomonosov Range, " c o n s t i t u t e l a r g e u p l i f t s of the b o t to m ." I t i s b e l i e v e d t h a t a m o un tain system of more a n c i e n t f o l d i n g alm ost p a r a l l e l s and i n t e r s e c t s the Lomono sov Range a t an angle o f 60° to 120°. S e v e r a l of th e s e r i d g e s have been t r a c e d from the Chukchi Sea to the v i c i n i t y of N an sen ’ s Ridge betw een S p i t z b e r g e n and G re e n la n d , a d i s t a n c e of 2,500 km. These ran g e s or r i d g e s a re s e p a r a t e d from each o t h e r by n a rro w , deep t r o u g h s . The Lomonosov Range i s p a r a l l e l to th e B a r e n t s - K a r a c o n t i n e n t a l s l o p e , and i s th o u g h t to e x te n d along th e f a u l t l i n e which t e c t o n i c a l l y r u p t u r e d when the Lomonosov Range was formed i n the Mesozoic or T e r t i a r y (A n ., 1954). The o th e r more a n c i e n t f o l d s on th e deep p a r t s of the A r c t i c Ocean a p p a r e n t l y form a c h a in of e l e v a t i o n s and r i d g e s e x te n d in g p a r a l l e l to th e North American c o n t i n e n t a l s h e l f . The s e a f l o o r s t r u c t u r e in the e a s t e r n d e p r e s s i o n of the A r c t i c B asin i s s t i l l n o t c l e a r . The r e g i o n seems to have m issed b e in g f o l d e d d u rin g Mesozoic tim e . As a r e s u l t , R u ss ia n g e o l o g i s t s have pro p o se d t h a t a s o l i d b u t t r e s s , the s o - c a l l e d "H yperborean S h i e l d , ” i s l o c a t e d in the r e g i o n of deLong I s l a n d s , n o r t h o f th e E a s t S i b e r i a n Sea, n o r t h e r n A la s k a , and i n t o the B e a u f o r t Sea, p e rh a p s j o i n i n g up w i t h the G re e n la n d -C a n a d ia n p l a t f o r m . A nother F ig u r e 34. T e c t o n i c c h a r t o f th e A r c t i c . ( A f t e r A tla so v , e t a l .. 1964) KEY TO FIGURE 34. P la tfo rm b lo ck s w ith unevenly developed M eto-Cenozolc s u p e r s tr u c tu r e :- 1 - R ussian p la tfo rm ( l a - Feodora b lo c k ), Z - N orth American p la tfo rm (b a s in s : 2a - Hudson, Zb • P as, 2c - L a n c a ste r, 24 - V ic to ria , 2e - D av ie), 3 - B est S ib e ria n p la tfo rm . P la tfo rm b lo ck s w ith p redom inantly developed Meao-Cenoxolc s u p e r s tr u c tu r e s t - w est S ib e ria n p la tfo rm , 5 - B aren ts-B a re p la tfo rm , S - H yperborean p la tfo rm . ] A rchaean and F ro tero zo lc f o ld system s I 7 - B a ltic s h ie ld , 8 - Greenland-Canada s h ie ld , 9 - E a s t S p itsb e rg e n m a ss if, 10 - Anaber m a ssif, 11 - S h a ts k i's m a ssif, 12 - H erald Is la n d m a ss if. I B a lk a lld e s :- | 13 - Y en isei R idge, I t - N orth B aik al u p la n d s, 15 - T l n n - B ear Is la n d , 16 - N o rth ea st G reenland - E llesm ere la n d . [ 1 C aled o n id es: - II 17 - Norway and th e B arents Sea, 18 - West S p itsb e rg e n , 19 - E a s te rn G reenland, Z0 - N orthern G reenland and th e PUrry Is la n d s , 21 - N o rth ern rim o f th e Canadian A rchipelago and th e B eau fo rt suboceanlc r id g e , 22 - C o rn w allis and A xel H eiberg Is la n d s , 23 - Anadyr-Semsrd m a ssif (PreC esfcrian- C aled o o lan ), 24 - Severnaya Z em lla, 25 - Lomonosov suboceanlc rid g e and th e N orth P la te a u , 26 - M endeleyev [Alpha] suboceanlc r id g e . H e rcy n id es:- 27 - U ra l - Hovaya Zem lla re g io n . l a t e r B ercy n ld es:- 28 - Taim yr - Severnaya Zem lla re g io n . M esozoldes:- 29 - Yana-Xblym system , 30 - New S ib e ria n and Chukchi system , w ith th e Brooks ra n g e , 3 1 - Nevadan and Iaram id s o f c e n t r a l A lask a. A lp la ld e s (r e c e n t n a tu re g e o s y n c lla e s ) :- 32 - n u c b a tk a , Koryak uplands and A lask a. I * 1 1 I II r r r r M rm g so ey n cllaal d e p re ssio n s and downwarps:- 33 - le a r y (R - S ), 34 - E llesm ere - Devon (B - D ), 35 - N orth A laska (C r - N), 36 - S verdrup (Ca - P g ), 37 - K olym a-Indigirka (Ct • P g ), 38 - Kbrkodon-Onalon (Cm - P g ), 39 - Anadyr-Seward (C rx - P g ), 40 - New S ib e ria n (C r* - N ), 41 - C anada-B eaufort (D - Q ), 42 - M ck en zle (Cm - Q ). M arginal downwarps:- 43 - Kola (R ), 44 - C la -U ra lla n (C* - T ), 45 • C ls-N ovozeolian (Ca - T ) , 46 - cla-Talm srr ( J + C r), 47 - C ls-V erkhoyan ( J + C r). G reenland-O khotsk vol canog en lc b e l t (C r - P g ): - 48 - M e ld s o f b a s ic and In te rm e d ia te e ffu s iv e ro ck s ( a - G reenland, b - A rc tic , c - O khotsk-Chukchl. Oceanic d e p re ssio n s 49 - I m la g e r , 50 - L abrador, 51 - G reenland, 52 - S c u th -Ic e la n d , 53 - N orth Ic e la n d , 54 - Norwegian, 55 - L ofoten, 56 - Hansen, 57 - Assmdsen, 58 - West B ering, 59 - E a st B ering, 60 - N o rth e a st d e p re ssio n o f th e M c lf ic Ocean. Oceanic tr o u g h s :- 61 - B a ffin , 62 - M urvln, 63 - Lena, 64 - Ice lan d -G reen lan d , 65 - Ir e la n d , 66 - P se ro e -S c o tlsn d , 67 - S t . Anna, 68 - TIHRO. M id-oceanic rid g e s and e le v a tio n s : - 69 - R elk jan e s, 70 - Ic e la n d - Jan Mtyen, 71 - Mona, 72 - K hlpovich, 73 - Schm idt, 74 - S h irsh o v , 75 - Obruchev. Is la n d a r c s : - 76 - A le u tia n , 77 - X h ach a tk a-B tflle? JO ceanic tre n c h e s : 78 - A le u tia n , 79 - K k rile . R egional zcnes o f re c e n t f a u ltin g . 236 237 m I % m F igu re 34, 238 name f o r t h i s i s the E a s t S i b e r ia n P l a tf o r m . T his Hyper borean S h ie ld i s e s s e n t i a l l y th e n u c le u s f o r E a r d l e y ’s "A ncient A r c t i c a . " No Cenozoic (A lp in e) f o l d i n g is known in the A r c ti c Basin or in a d ja c e n t land a r e a s . However, the w e ste rn deeps and the e x te n s io n of the m id - A tl a n t i c Ridge i s a se ism ic re g io n . Saks e t a l (1955) su g g e ste d t h a t the w e s t ern A r c ti c Ocean d e p r e s s io n i s of a g e o s y n c l i n a l n a t u r e . The e a s t e r n p a r t of the A r c tic i s an a se ism ic r e g io n , has no v o lc a n o e s , nor is i t an a re a o f m assive sediment a c c u m u latio n . T h is su g g e sts t h a t t h i s p a r t of the A r c tic Sea f l o o r i s a r i g i d b lo c k , presum ably p a r t of the P recam brian S h i e l d . Thus, the C e n tr a l A r c ti c Basin i s composed of th r e e s t r u c t u r a l e le m e n ts: (1) the P a le o z o ic p la tf o r m near Europe (European B a s in ), c r e a t e d by Lower and Upper P a l e o z o ic f o l d i n g , ( 2 ) the Mesozoic fo ld s t r u c t u r e s of the Lomo nosov Range, and (3) the Hyperborean p la tf o r m (a b a s in e x ten d in g towards A laska) of p o s s i b l e P recam brian age. The A r c ti c Basin could not have formed e a r l i e r than the development of Mesozoic f o l d i n g and the fo rm atio n of the Lomonosov Range. The f o l d in g was preceded by a geo s y n c l i n a l phase. At the end of the Mesozoic e r a , s i m u lt a n e o u sly ( o r n e a r l y so) w ith o ro g en ic p r o c e s s e s in th e Lomo nosov Range, su b sid en ce o c cu rred over the e n t i r e deep -w ater p a r t of the A r c ti c Ocean (Saks, e t a l ., 1955). At the b e g in ning of the T e r t i a r y p e r i o d , se as b o r d e r in g the A r c t i c were 239 d ry ; the sea b a s in p e r se e x i s t e d only a t the s i t e s of th e d e e p -w a te r d e p r e s s i o n s . A ccording to Obruchev (1 9 5 2 ): On the n o r t h and e a s t of the Taimyr P e n i n s u l a , at th e b e g in n in g of the Q u a te rn a ry p e r i o d , d ry land ex tended northw ard c o n s i d e r a b l y f a r t h e r th a n a t p r e s e n t , and the p r e s e n t - d a y i s l a n d s of Severnaya Zemlya, the i s l e t s a t the mouth of the Katanga R iver and the whole New S i b e r i a n a r c h ip e la g o are rem nants of t h i s la n d , of which th ey formed i t s h ig h e r p a r t s . I t p r o b a b ly took in a l l the p r e s e n t c o n t i n e n t a l s h e l f of t h i s p a r t of the A r c t i c Ocean. I t was covered w ith tu n d r a and wooded t u n d r a , and i n h a b i t e d by mammoths, the f o s s i l rem ains of which have been found in abundance on the New S i b e r i a n I s l a n d s . When th e d r y land began to s in k and was floo ded by the s e a , th e s e a n im a ls took refu g e on the h e i g h t s ; f o r i n s t a n c e , G re a t L ia k h o v sk i I s l a n d might be c a l l e d a cem etery of mammoths, from the num b e r of t u s k s of t h e s e b e a s t s which have been found t h e r e . In a d d i t i o n to the deep b a s i n s , o t h e r submerged a r e a s i n c lu d e the Kara and G reenland S eas, th ro u g h w hich, u n t i l the m iddle of the T e r t i a r y p e r i o d , s t r a i t s co nn ected the A r c t i c B asin w ith se a s in s o u th e r n E u r a s i a w ith the A t l a n t i c Ocean. These s t r a i t s were r e s p o n s i b l e f o r b r i n g in g about a mild c lim a te in t h i s r e g io n d u r in g the T e r t i a r y p e r i o d . F orm ation of th e ocean b a s i n s in the c e n t r a l A r c t i c began in the T r i a s s i c p e rio d as a r e s u l t of the s h a t t e r i n g and s in k in g o f p l a t f o r m s t r u c t u r e s . West (1951) d a t e s the s t a r t of th e su b sid e n c e in l a t e C a r b o n if e r o u s tim e, t h r u s t ing towards the A l e u t i a n s as i t s u b s id e d . Mesozoic s e d i ments were d e p o s i t e d in th e s h a t t e r e d P a l e o z o i c s t r u c t u r e s , s u b s id e n c e of the edges of the Canadian A r c t i c A rc h ip e la g o p l a t f o r m , and Mesozoic marine t r a n s g r e s s i o n s from the 240 n o r t h , in the n o r t h e r n p a r t o f t h e USSR, and in N o rth Amer i c a . The Lomonosov Range was form ed a t t h i s tim e . The n e x t s t a g e was g r e a t s u b s id e n c e of th e E a r t h ’ s c r u s t in th e c e n t r a l A r c t i c d u r i n g th e T e r t i a r y p e r i o d . E a r d le y concluded t h a t , a lt h o u g h th e b re a k u p of A r c t i c a b e gan d u r in g P a l e o z o i c tim e , th e b a s i n s a c q u i r e d t h e i r p r e s ent g r e a t d e p t h s d u r in g th e T e r t i a r y p e r i o d . T h is in v o lv e d v e r t i c a l movements am ounting to 7 ,6 0 0 m alo n g the c o a s t of G r e e n la n d , and c o n t r o l l e d or m o d if ie d the p r e s e n t c o a s t l i n e s of the Canadian A r c t i c A r c h i p e l a g o , G r e e n la n d , and S p i t z b e r g e n . T h is was accom panied by enormous e f f u s i o n s of b a s a l t alo n g the f r a c t u r e zone. The l a s t s t a g e of s u b s i d ence o c c u r r e d d u r in g the Q u a te r n a r y p e r i o d when the s h e l v e s were subm erged. O l i v e r , Ewing, and P r e s s (1 9 5 5 ) r e p o r t e d t h a t th e A rc t i c Ocean d id n ot t r a n s m i t the Lg p h a s e , t h e r e f o r e c o n c lu d e d th e A r c t i c B a s in was o c e a n i c . H u nk in s (19 63 ) has show n t h a t fo r w ater d e p th s g r e a t e r th a n 2 ,0 0 0 m, the s o l i d c r u s t i s betw een 6 km and 15 km t h i c k . I t i s c o n clu d ed t h a t th e d e e p e r b a s i n s a re u n d e r l a i n by a c r u s t s i m i l a r to t h a t found b e n e a th ocean b a s i n s of s i m i l a r d e p th in o t h e r p a r t s of th e w o r l d . No c o n t i n e n t a l l a y e r i s p r e s e n t as r e q u i r e d by a s u b s id e n c e t h e o r y . H ence, w h i l e E a r d l e y (1 96 1) c o n c u rs w ith th e g e n e r a l c o n c l u s i o n s re a c h e d by S o v i e t g e o l o g i s t s on th e h i s t o r y o f the A r c t i c B a s in , th e a b sen c e o f c o n t i n e n t a l c r u s t l e a d s him to r e j e c t th e s u b s id e n c e th e o ry . 241 He a lso does not b e l i e v e the Lomonosov Range i s a f o ld b e l t , u n l e s s the f o ld b e l t and a d j a c e n t r i f t b a s in are s e p a ra te d by a c o n s i d e r a b le time i n t e r v a l . K in g .e t a l .(1 9 6 4 ) have examined g r a v i t y and m agnetic d a t a . G ra v ity d a ta y i e l d s a t h i c k n e s s of 2 km to 7 km un der the deep b a s i n s and 15 km to 25 km fo r r i d g e s . Large m agnetic anom alies over the Canadian c o n t i n e n t a l s h e l f and over Chukchi Cap and Alpha Ridge su g g e st f a u l t c o n t r o l . The magnetic d a t a p ro v id e co n v in cin g e v id ence t h a t the f l o o r of the A r c ti c Ocean on the N orth American sid e of the Lomonosov Range is formed by a la r g e sunk en b lo c k , or b lo c k s , of c o n t i n e n t a l m a t e r i a l , a la r g e p a r t p ro b ab ly c o n s i s t i n g of a Precam brian complex sim i l a r to t h a t of the p r e s e n t s h i e ld a r e a s . (King, e t a l , 1964) Magnetic d a t a a ls o show the E u r a s ia n b a s in i s u n d e r l a i n by m a t e r i a l c o n s id e r a b ly d i f f e r e n t from a c o n t i n e n t a l c r y s t a l l i n e complex; i t is more t y p i c a l of deep sea b a s i n s . This i s a s e i s m i c a l l y - a c t i v e r e g io n , p ro b a b ly an e x te n s i o n of the M id -A tla n tic Ridge (Heezen and Ewing, 1961). However, S o v ie t g e o l o g i s t s r e j e c t t h i s in fa v o r of a s u b s id in g geo s y n c l i n a l trough (Saks, e t a l ., 1955). The o b j e c t i o n to su b sid e n c e on th e b a s i s t h a t o c e a n ic c r u s t may e x i s t in the A r c t i c Basin does n o t appear to be a con vin cin g argument in view o f the f i n d i n g o f o c ea n ic c r u s t in o th e r a re a s which have been shown c o n v in c in g ly to have su b sid e d in l a t e T e r t i a r y tim e; f o r example, the Sea of J a pan and the Okhotsk Sea (B eloussov and Rudich, 1960; Mura to v , 1957; Tikhominov, 1958; Sheynmann, 1959). Removal of 242 c r u s t a l m a t e r i a l from th e b ase of s u b s id e d b a s i n s or b l o c k s c an n o t be ig n o re d ( G i l l u l y , 1955, 1963; B e lo u s so v , 1955; H ess, 1955; K i n g , e t a l , 1964 ). E a r d l e y ’s o b j e c t i o n to a f o ld e d range (Lomonosov) in an ocean b a s in a l s o seems weak f o r th e same r e a s o n . F u rth e r m o r e , K i n g , e t a l . ( 1 9 6 4 ) have p o i n te d out t h a t s e is m ic r e s u l t s (b ased on the Lg s t u d i e s , R a y le ig h , and Love w ave d a t a ) a re s u s p e c t . C arey (1958) p r e s e n t e d a t h e o r y w hich is based upon f o r m a t io n of the A r c t i c B asin by t e n s i o n a l r i f t i n g which i s d i r e c t l y r e l a t e d to c o n t i n e n t a l d r i f t . K i n g .e t a l . (1964) len d s u p p o r t f o r t h i s r i f t i n g p r o c e s s . Shaver and H unkins (1964) b e l i e v e t h a t of th e two t h e o r i e s of A r c t i c B a sin o r - i g i n s - - v e r t i c a l su b s id e n c e and h o r i z o n t a l m o v em en ts--th e l a t e r h y p o t h e s i s i n v o lv i n g an e x p a n d in g E a r t h b e s t f i t th e f a c t s c o n c e rn in g the o r i g i n of Chukchi Cap. NORW AY I n t r o d u c t i o n The Norwegian c o n t i n e n t a l t e r r a c e has been s t u d i e d in d e t a i l by Nansen (1 9 0 4 ), O la f H o l t e d a h l (1940 and o t h e r p a p e r s ) , and Hans H o l t e d a h l ( 1 9 5 5 ). P r o f i l e s f o r n o r t h e r n Norway p u b l is h e d by O. H o l t e d a h l a re ta k e n m o s tly a t l e s s than 300 m ( P l a t e 2 4 ). In mid-1963 Hans H o lte d a h l r e p o r t e d ( p e r s o n a l co m m u nicatio ns) t h a t no a d d i t i o n a l work had been done s i n c e he p u b l is h e d h i s p a p e r in 1955. No o r i g i n a l echosounding p r o f i l e s were o b t a i n e d f o r t h i s r e g i o n . Resu1 t s The d e p t h of th e s h e l f b re a k i n the S to re g g a r e g i o n ( P l a t e 25) v a r i e s from 130 m to 270 m over a d i s t a n c e of 120 km. The ba se of th e c o n t i n e n t a l s lo p e i s n o t c l e a r l y d e f i n e d ; however, i f t h i s i s ta k e n as th e b ottom of the s t e e p s lo p e beyond the edge of the s h e l f , i t o c c u rs a t d e p th s ra n g in g from 240 m to 480 m, a v e r a g in g about 270 m. T h is s lo p e som etim es h a s a g e n t l e g r a d i e n t (a b o u t 1°) and the s u r f a c e i s o b s c u r e . More commonly i t i s w e ll p r o nounced and has g r a d i e n t s v a ry in g from 16° to 25°. 243 244 V a r i a t i o n s in the d e p th of s h e l f b re a k and th e base of the c o n t i n e n t a l s lo p e , as w e l l as o th e r f e a t u r e s and t h e i r c o r r e l a t i o n , can be r e a d i l y observed on the v e r t i c a l bar graph ( F ig u re 3 5). Where p r o f i l e s are a v a i l a b l e the c o n t i n e n ta l t e r r a c e o ff Norway i s shown to be co m p licated by d e p r e s s i o n s and o th e r i r r e g u l a r i t i e s common to h ig h l a t i tu d e s , making c o r r e l a t i o n d i f f i c u l t . Hence, th e r e s u l t i n g i l l u s t r a t i o n i s r a t h e r c o m p lic a te d . In a d d i t i o n to the r e l a t i v e l y s t e e p c o n t i n e n t a l s l o p e , s e v e r a l o th e r e sc a rp m e n ts occur in the r e g i o n , the most pronounced of which i s l o c a te d o f f S te in m a re n . I t s upper edge i s i r r e g u l a r , vary in g in d epth from 480 m to 600 m, and the low er base ( a l s o i r r e g u l a r ) ra n g e s in dep th to 770 m. A s t e e p slo p e o c c u rs in the so uth ern m o st a re a a t 620 m to more th a n 770 m. A s t i l l deeper e sc a rp m e n t, having a g r a d i e n t of about 18°, i s r e p o rte d between 1,570 m and 1,670 m. A number o f t e r r a c e s can be i d e n t i f i e d b u t o f t e n merge w ith o th e r t e r r a c e s or s lo p e s h o r i z o n t a l l y and v e r t i c a l l y and so are d i f f i c u l t to c o r r e l a t e . In a d d i t i o n , the t e r raced s u r f a c e s cover c o n s i d e r a b l e v e r t i c a l ra n g e and com monly show a marked p a r a l l e l i s m w ith th e shape of th e s h e l f edge. In the so u th e rn m o st a r e a a wide t e r r a c e ra n g in g in d e p th from 140 m to 350 m o c cu rs on the c o n t i n e n t a l s l o p e . A sm a ll escarpm ent occu rs above and below the t e r r a c e . A n a rr o w e r, and o f t e n b a r e l y r e c o g n i z a b le t e r r a c e ra n g e s in d e p th from 240 m to 300 m o c c u rs a few k i l o m e t e r s f u r t h e r •NORTHERN MOST AREA NORTHERN BAY AREA SOUTHERN BAY AREA SOUTHERN MOST AREA HEADLAND AREA XIV XV XI vin m VI vu IV -0 CONTINENTAL SHELF SEA LEV EL - J 0 0 / BASE OF CONTINENTAL SLOPE SH ELF EDGE SH ELF EDGE -2 0 0 VE] s m a l l ;. -3 0 0 -4 0 0 -5 0 0 -6 0 0 S TE EP p * \ \ SLOPE SC- -7 0 0 T -------- SC ' 5 < = G E N T L E S l- n p >800 -9 0 0 S C 1 ST E E P SLOP -1000 P T = TERRACE SC 4 - SLO PE CHANGE (INCREASE IN GRADIENT) SC t = SLOPE CHANGE (DECREASE IN GRADIENT) At -1100 N O R W A Y END OF PR O FILE hlSPQ METERS Figure 35. C o r r e la tio n of t e r r a c e s and o th er f e a t u r e s on the c o n tin e n ta l slope o ff Storegga reg io n , Norway. co Ln 82 472964572452 246 n o r t h , m erging i n t o th e b o tto m of th e c o n t i n e n t a l s l o p e a t b o th e n d s . (See F ig u re 35) A n o th e r n arro w t e r r a c e o c c u r s below t h i s f e a t u r e a t 330 m to 400 m and i s in p a r t the base of the c o n t i n e n t a l s l o p e . The b a se of th e c o n t i n e n t a l s l o p e from th e h e a d la n d a r e a to the n o r t h e r n m o s t a r e a a l s o h a s a t e r r a c e a t i t s b a s e . T e r r a c e s below th e b a se of the c o n t i n e n t a l s l o p e can be c o r r e l a t e d over c o n s i d e r a b l e d i s t a n c e s but i t i s d i f f i c u l t to d e f i n e p r e c i s e l y what may be term ed t e r r a c e s s i n c e th e o n ly d i s t i n c t i o n betw een f e a t u r e s a re v a r i a t i o n s in g r a d i e n t s . In the s o u th e r n m o s t a r e a ( p r o f i l e s 1 to 8 ) , f o r exam ple, th e g r a d i e n t s o f the s l o p e s a re g e n t l e , y e t a num b e r o f d i s t i n c t s u r f a c e s can be i d e n t i f i e d . On p r o f i l e 3, a d i s t i n c t f e a t u r e o c c u r s b etw een 300 m and 420 m; below t h i s i s a v e r y g e n t l e s l o p e to 530 m; f l a t a r e a s o c c u r a t 520 m and 580 m to 610 m. With th e e x c e p t i o n of th e d e e p e s t f l a t a r e a , a l l o f the o t h e r s u r f a c e s have c o n s i d e r a b l e h o r i z o n t a l e x t e n t . The t e r r a c e im m e d ia te ly below the c o n t i n e n t a l s lo p e can be t r a c e d th r o u g h o u t t h e e n t i r e r e g i o n . Below t h i s , the very g e n t l e s l o p e can o n l y be i d e n t i f i e d in th e s o u th e r n m o s t a r e a ; w h ile i n the n o r t h e r n m o s t r e g i o n , a g e n e r a l l y d i s t i n c t t e r r a c e o c c u r s b e tw ee n 450 m and 620 m, b ut g e n e r a l l y c o v e r s o n ly a n a rro w ra n g e in d e p t h . A lso in t h i s a r e a i s a t e r r a c e a t 410 m to 500 m w i t h a n a rro w ran g e d e p t h . F ive p r o f i l e s c r o s s the c o n t i n e n t a l s l o p e and r e a c h 247 3,200 m ( P l a t e 25, lower r i g h t ) . The v e r t i c a l e x a g g e r a t io n i s 462 tim e s , t h e r e f o r e , a l l minor f e a t u r e s a re o b sc u re d . The most s i g n i f i c a n t f e a t u r e i s a d i s t i n c t break in the slo p e a t a d e p th of a p p ro x im a te ly 1,400 m. O rig in of C o n t in e n t a l T e rra c e Nansen (1904) was th e f i r s t to d e s c r i b e c o n t i n e n t a l t e r r a c e s in g e n e r a l and the Norwegian a r e a in p a r t i c u l a r . He summarized the o r i g i n of the Norwegian c o n t i n e n t a l t e r rac e as f o l lo w s : During long p r e - g l a c i a l p e r i o d s the s h e l f a re a was dry land and underwent a g r e a t d e a l of d i s s e c t i o n , c h i e f l y a tm o sp h e ric e r o s i o n . In th e co urse of t h i s time the main f e a t u r e s of the s h e l f took form: v a l le y s were carved by r i v e r s in two main d i r e c t i o n s , one l o n g i t u d i n a l , alm o st p a r a l l e l to th e c o a s t , . a n d one t r a n s v e r s a l , r o u g h ly a t r i g h t a n g le s to the form e r , th e s e d i r e c t i o n s b eing c o n t r o l l e d by th e g e o l o g i c a l s t r u c t u r e . During p e r i o d s o f r e l a t i v e l y h ig h e r e l e v a t i o n of the la n d , the now-submerged l o n g i t u d i n a l f j o r d s of th e s h e l f were eroded down to a b a s e - l e v e l about 400 m to 500 m below pr.esent s e a - l e v e l . As th e d i s s e c t e d lan d became submerged, an i n t e r s e c t e d c o a s t w ith deep subm arine f j o r d s a r o s e , to be s u b s e q u e n tly c u t back c o m p a r a tiv e ly e a s i l y by the j o i n t a c t i o n of m arine d e n u d a tio n and s u b a e r i a l e r o s i o n . The uneven s h e l f th u s formed has s in c e to a l a r g e e x t e n t been f i l l e d in by marine d e p o s i t s and g l a c i a l d r i f t , e s p e c i a l l y in i t s o u te r r e g i o n s . The submerged v a l l e y s were t o a g r e a t e r or l e s s e r e x t e n t r e p e a t e d l y r e o pened by g l a c i e r s and by a tm o sp h e ric e r o s i o n d u rin g p e r i o d s of e l e v a t i o n . Nansen su g g e ste d t h a t the c o n t i n e n t a l s h e l f was a t l e a s t 300 m h ig h e r in c o m p a r a tiv e ly r e c e n t g e o lo g ic time th en now lo c a te d , and d u rin g t h i s p e r i o d of h ig h e r e l e v a t i o n the l e v e l of the b a r r i e r s o f the subm arine f j o r d s was 248 d e v e lo p e d . He f u r t h e r s t r e s s e d th e resem b lan c e of the r e g io n s o f f L o ffe n and V e s t e r a l e n and th o s e o f f S0ndm0r- Romsdalen t o the s o u th . In t h e s e a r e a s the s h e l f b r e a k o c c u rs n e a r the c o a s t (18 km to 87 km). In the n o r t h e r n r e gion the c o n t i n e n t a l s lo p e i s a b r u p t w ith g r a d i e n t s of 50° 3 0 ’ to 20°. F a r t h e r so u th i t i s l e s s s t e e p , w ith a g r a d i en t of 3° 2 5 ’ between 150 m and 780 m. Nansen a ls o p o in te d ou t t h a t " t h e L o f te n - V e s te ra 'le n I s l a n d s and the Spfndm^r-Romsdalen c o a s t , the two h i g h e s t and most m ountainous p o r t i o n s of the Norwegian c o a s t w ith the s t e e p e s t s l o p e s , have th e most r e g u l a r l y d e v elo p ed c o n t i n e n t a l s h e l v e s , w i t h the s h a l l o w e s t w a t e r , e x h i b i t in t h i s r e s p e c t a s t r i k i n g d i f f e r e n c e from the r e s t of the Norwegian c o a s t . ” Nansen d e s c r i b e d numerous narrow v a l l e y s which c u t i n t o the c o n t i n e n t a l t e r r a c e down the s lo p e to a t l e a s t th e 800-m c o n to u r . He b e l i e v e d t h e s e canyons were c u t by s u b a e r i a l e r o s i o n , i n d i c a t i n g t h a t the s h e l f was once l o c a t e d a t t h i s e l e v a t i o n above se a l e v e l . As e a r l y as 1875, H ellan d w ro te t h a t i n some c a s e s subm arine f j o r d s were c o n t i n u a t i o n s of i n l a n d f j o r d s . He concluded t h a t th e f j o r d s were f i l l e d w ith i c e d u r in g the P l e i s t o c e n e ep o ch , and t h a t th e land must have been s i t u ate d r e l a t i v e l y h i g h e r th a n a t p r e s e n t , o th e r w is e th e ic e to n g u es would have b een broken by the s e a . Ahlmann (1919, p . 159) a l s o n o te d the s i m i l a r i t y 249 betw een la n d and submerged f j o r d s and c o n c lu d e d t h a t the c h a n n e ls must have been formed by s u b a e r i a l e r o s i o n a l p r o c e s s e s a t a p e r i o d when th e la n d was h i g h e r . As an exam p l e , B r e is u n d d ju p e t was c u t by i c e , b u t was o r i g i n a l l y formed by f l u v i a l e r o s i o n when the s h e l f l a y 200 m to 300 m h ig h e r t h a n p r e s e n t sea l e v e l . Shepard (1931) c i t e d Norway to e x e m p li f y g l a c i a l subm arine t r o u g h s . Since 1929 0 . H o l t e d a h l h a s d i s c u s s e d th e subm arine g e o lo g y o f f Norway. He h a s em phasized t h e e x i s t e n c e " o f a w e l l - d e f i n e d bou nd ary zone betw een th e S c a n d in a v ia n land mass and the s h e l f a r e a w hich i s d e l i n e a t e d e i t h e r as a l o n g i t u d i n a l m a r g in a l d e p r e s s i o n or as a d i s t i n c t seaw ard s l o p e o u t s i d e th e uneven ro ck y r e g i o n ( P l a t e 2 6 ). T hese f e a t u r e s , l i k e th e d e p r e s s i o n of th e Norwegian Channel o f f the s o u t h e r n and s o u t h w e s t e r n p a r t s of Norway, a re m a r g i n a l f r a c t u r e l i n e s alo n g w hich the to p o g ra p h y has been c a rv e d o u t , m ain ly d u r in g p e r i o d s when s e a l e v e l s were low er th a n a t p r e s e n t . " These t e c t o n i c f r a c t u r e l i n e s a re c o n s i d e r e d to have a c l o s e r e l a t i o n s h i p to the r e l a t i v e l y r e c e n t , l a t e T e r t i a r y u p l i f t o f th e la n d m ass. E viden ce of t h i s c o n c l u s i o n i s a l s o c i t e d from th e su b m a rin e f e a t u r e s o f f th e c o a s t s of S p i t z b e r g e n , G r e e n la n d , L a b r a d o r , A l a s k a , and S c o t la n d ( H o l t e d a h l , 1958; See F ig u r e 29 and 4 6 ) . T r a n s v e r s e subm arin e c h a n n e ls w hich c r o s s th e s h e l f a re r e g a r d e d by O. H o l t e d a h l as the d i s t a l p a r t s o f p r e u p l i f t s u b a e r i a l l y - c u t r i v e r v a l l e y s , rem odeled by g l a c i a l 250 e ro s io n d u rin g the P l e i s t o c e n e epoch ( H o lte d a h l, 1952). He c o n sid ere d numerous submarine f e a t u r e s as o r i g i n a t i n g a t the ic e f r o n t , r e q u i r i n g a r e l a t i v e sea l e v e l change of 300 m. He concluded (1940) t h a t "the c o n t i n e n t a l slo p e must be regarded as a zone of d i s l o c a t i o n of th e f i r s t o r d e r , form ing a boundary between the E u r a s i a t i c lan d b lo ck and the o cean ic b a s i n , w h i l s t the l i n e s of d e p r e s s io n b o rd e rin g the S can d in av ian land mass and the s h e l f re g io n must belong to a f r a c t u r e zone of more l o c a l c h a r a c t e r . " Evers (1937) o b je c te d to O. H o l t e d a h l ’s i n t e r p r e t a t i o n of f a u l t i n g , and e x p la in e d th e sudden seaward slo p e as an underw ater s t e e p s t e p l i k e d e c l i v i t y of a "piedmont p l a i n . " H o lte d a h l (1940) p o in te d out t h a t newer c h a r t s (showing deep m argin al d e p r e s s io n s w ith tr e n d s p a r a l l e l to the mar g i n a l slope and having s t r a i g h t or s l i g h t l y curved p lan views over g r e a t d i s t a n c e s ) give s t r e n g t h to s t r u c t u r a l c o n t r o l . Tanner (1938), Sederholm (1913) and o t h e r s a ls o b e l i e v e t h a t the r e l i e f of Fennoscandia i s the r e s u l t of f a i r l y r e c e n t u p l i f t of 1,000 m to 2,000 m along w e ste rn f a u l t l i n e s . F le x u re movements are a ls o im p o r ta n t. G reg ory (1 91 3), in d i s c u s s i n g f j o r d o r i g i n by f a u l t i n g ( a view no longer b e l i e v e d ) , p o in te d out t h a t " th e f j o r d d i s t r i c t s of the w orld are a l l p l a t e a u s , which have been s h a t t e r e d by a P lio c e n e or p o s s i b l y sometimes a l a t e r u p l i f t . " He a s c rib e d g l a c i a l e r o s i o n o n ly a very m oderate r o l e . 0. 251 H o lte d a h l p o in te d out how d i f f i c u l t i t i s to prove and f o l low f j o r d f r a c t u r e s , a ltho ug h the young (C enozoic) age fo r the f a u l t i n g i s r e c o g n iz e d . Other w r i t e r s have su g g e ste d the Norwegian f j o r d p a t t e r n s are of P a l e o z o ic age or o l d e r . I t i s n otew orthy t h a t the f r a c t u r e p a t t e r n s along the Nor wegian c o a s t advocated by O. H o lte d a h l ( P l a t e 26) can be t r a c e d , unbroken, f o r c o n s id e r a b le d i s t a n c e , hence, must be younger than the f j o r d f r a c t u r e s , i f p r e s e n t . F e a tu r e s s i m i l a r to Norway are reco g n ized by O. H o lte d a h l (1940, 1952, and 1955) o ff South America (C a ld e n iu s , 1932), A la s ka, L ab ra d o r, G reenland, S p i t s b e r g e n , and S c o tla n d (F ig u r e s 29 and 46; P l a t e s 22 to 27). The Norwegian Channel, a d e p r e s s io n a t l e a s t 800-km in l e n g t h , and 60-km to 80-km wide, p a r a l l e l s the c o a st and i s made of old c r y s t a l l i n e rocks (see P l a t e 2 6 ). T his e x t r a o r d in a r y d e p r e s s io n , up to 700-m deep in i t s e a s t e r n h a l f , can only be i n t e r p r e t e d as a re g io n of su bsiden ce con t r o l l e d by f a u l t i n g (b u t m odified by g l a c i a t i o n ) . I t t e r m in a tes a b r u p t l y in the O s lo f jo r d d i s t r i c t . A lthough the re g io n shows l i t t l e se ism ic a c t i v i t y t o day, two e p i c e n t e r s d u rin g t h i s c e n tu r y were lo c a te d in the Norwegian C hannel. C r u s t a l u n r e s t in t h i s zone d u rin g the Neogene i s i n d i c a t e d by a s e r i e s of v olcano s t h a t s t r e t c h e d from Denmark to Norway a c r o s s the Norwegian C hannel. Hans H o lte d a h l a ls o c o n s i d e r s th e a b ru p t and i r r e g u l a r s h e l f b re a k , w ith r e l i e f of s e v e r a l hundred m e te r s , 252 g r a d i e n t s of 25°, and o th e r s t e p - l i k e arrangem ent of the slo p e at g r e a t e r d e p th s ( p a r t i c u l a r l y in the headland a re a ) as i n d i c a t i v e of f a u l t i n g (F ig u re 3 1 ). He summarized by s t a t i n g : ’’the c o n t i n e n t a l slo p e must be re g a rd e d as a zone of r e c u r r e n t f a u l t i n g , the main e scarp m en ts being major f a u l t s c a rp s and the a re a s betw een them zones of minor d i s - loc a t i o n s ." The i r r e g u l a r i t i e s of the M0re-Romsdal a re a cannot be e x p la in e d by f a u l t i n g a lo n e . S u b a e r i a l and m arine e ro s io n a l t e r e d the upper c o n t i n e n t a l t e r r a c e d uring e u s t a t i c low e rin g of sea l e v e l . U n q u e stio n ab ly , d i f f e r e n t i a l e r o s io n has played a l e a d in g r o le in the o r i g i n o f topography. However, i f the bays are the r e s u l t of s u b a e r i a l and marine e r o s io n during e u s t a t i c changes in sea l e v e l , th e r e l a t i v e low ering would have to be n e a r l y 800 m. Such a low ering was advocated by Nansen (1 9 0 4 ). H. H o lte d a h l d e n ie s e v i dence f o r such a low stand of sea l e v e l . G l a c i a l e r o s io n a ls o is e lim in a te d by H. H o lte d a h l as a cause f o r t h i s s in c e i t would a ls o r e q u i r e a r e l a t i v e low ering of se a l e v e l of 700 m to 800 m. Thus, the bays owe t h e i r o r i g i n to some o th e r p r o c e s s . In the bay are as H. H o lte d a h l observed a marked change in g r a d ie n t a t a d ep th of 400 m to 460 m, i n d i c a t i n g the slo p e i s s t e e p e r above and more g e n tl e below t h i s d e p th . I f t h i s change in g r a d i e n t i s i n d i c a t i v e of a low se a l e v e l s t a n d , i t would be in agreement w ith Nansen who p o in te d out 253 t h a t the b o tto m of th e major subm arine f j o r d s of the Nor wegian c o n t i n e n t a l t e r r a c e are commonly s i t u a t e d a t 400 m to 460 m, and l o c a l l y to 500 m. Nansen, t h e r e f o r e , s u g g e s te d t h a t t h i s r e p r e s e n t e d th e a p p ro x im ate b a se l e v e l of e r o s i o n when land was r e l a t i v e l y h i g h e r . T his th e o ry was given g r e a t e r s u p p o rt when f j o r d s in o t h e r r e g i o n s were found to co rre sp o n d to th e s e d e p t h s . O. H o l t e d a h l (1940) con clu ded t h a t when g l a c i e r s c ro s s e d the s h e l f , th e r e l a t i v e sea l e v e l sto od 300 m to 400 m lower than a t p r e s e n t . This would mean t h a t the s h e l f would have to be about 400 m h ig h e r ( r e l a t i v e l y s p e a k in g ) than p r e s e n t d u rin g deep c u t t i n g d u r in g th e P l e i s t o c e n e epoch. The ba se of the c o n t i n e n t a l slo p e a t about 270 m i s the most c o n s i s t e n t f e a t u r e of the M0re-Romsdal r e g i o n . H. H o lte d a h l c o n s id e r e d t h i s as a p o s s i b l e l e v e l o f a form er sta n d of sea l e v e l . In s u p p o r t of t h i s t h e o r y , he p o i n te d to e v id e n c e in o th e r a r e a s along the Norwegian c o a s t p r o v ided by Ahlmann (1919) and O. H o l t e d a h l ( 1 9 4 0 ) . The d e p r e s s i o n s , along b o th t h e i r l o n g i t u d i n a l and t r a n s v e r s e s e c t i o n , show a base l e v e l of about 270 m. H. H o l t e d a h l a l s o t e n t a t i v e l y s u g g e s t s a n o th e r s u b s e q u e n t se a l e v e l lo w e rin g of 400 m to 500 m below p r e s e n t sea l e v e l based upon deep d e p r e s s i o n s along s e v e r a l p a r t s of the Norwegian c o n t i n e n t a l s l o p e . WESTERN GREENLAND I n t r o d u c t i o n Many r e c o n s t r u c t e d p r o f i l e s were p u b l i s h e d in U. S . C o a s t Guard B u l l e t i n No. 19 as a r e s u l t of the M arion and G e n e r a l Greene E x p e d i t i o n s ( P l a t e 27) b u t no d e s c r i p t i o n o f b a th y m e tr y i s g i v e n . Rvachev (1 9 6 3 ) made a s p e c i a l su rv e y of s o u th w e s t G re en lan d b u t th e p r o f i l e s t e r m i n a t e a t abo ut 400 m to 500 m. O ther R u s s ia n s o u r c e s , i n c l u d i n g th e b a t h y m etry o f f w e s t e r n G r e e n l a n d , i n c l u d e : I g n a t ' e v ( 1 9 5 6 ) , L i t v i n ( 1 9 5 9 ) , L i t v i n and Rvachev ( 1 9 6 2 ) , and M azaro v ich ( 1 9 5 2 ) . Rvachev (1 96 3) and D i b n e r , K ry lo v , S edova, and Vakar (1 9 6 3 ) d e s c r i b e d a u n iq u e b o tto m sam ple on th e G re e n la n d s h e l f . R e s u l t s S h e l v e s aro u n d G re e n la n d a re n o t o r i o u s l y i r r e g u l a r w h ich i s common in g l a c i a t e d r e g i o n s w here g l a c i a l , s u b a e r i a l , and m arin e p r o c e s s e s combine to form su b m a rin e t o p o g ra p h y t h a t i s d i f f i c u l t to d e c i p h e r ( P l a t e 2 7 ) . Ic e and g l a c i a l l y - d e p o s i t e d f e a t u r e s form b a n k s , w h i l e i c e c a r v e s ou t d e p r e s s i o n s . 254 255 A ccording to Rvachev the s h e l f o f f s o u th w e s t G reen lan d g r a d u a l l y narrow s from n o r t h to s o u t h ; 130 km to 170 km in the n o r t h to 74 km in the s o u t h . The s h e l f b r e a k i s over 200 m a t Disko Bay, 100 m a t about 67° N, and 160 m to 180 m a t the s o u th w e s te rn p a r t of G re e n la n d . Where th e s h e l f b reak i s about 200 m the upper c o n t i n e n t a l s lo p e i s 3° to 5° ( P l a t e 27, lower l e f t , p r o f i l e s 1 and 2 ) . When the s h e l f has a g e n t l e g r a d i e n t i t s s h e l f b re a k i s 240 m to 360 m ( p r o f i l e s 5 and 6 ). S outh of 64° N ( s o u th o f a r i s e ) a s t e e p (1 0° to 15°) upper c o n t i n e n t a l s lo p e s t a r t s a t d e p th s of 60 m to 100 m ( p r o f i l e 9 ). A ll of the s o u t h e r n p r o f i l e s have a s h e l f d epth of 100 m to 125 m, b u t t h e i r s h e l f b r e a k s l i e a t 230 m to 240 m and have s t e e p (10° to 15°) upper c o n t i n e n t a l s l o p e s . The Greenland s h e l v e s have t y p i c a l m oats p a r a l l e l to sho re s i m i l a r to th o se d e s c r i b e d in Norway, A n t a r c t i c a , L abrad o r and e ls e w h e r e . No f e a t u r e s can be d e te rm in e d from the o t h e r h i g h l y e x a g g e ra te d r e p l o t t e d p r o f i l e s ( P l a t e 27, A to G ) . The s h e l f b rea k o f w e s t e r n G reenland i s c o n s i d e r a b l y s h a llo w e r th an A n t a r c t i c a which a v e r a g e s about 450 m. The e a s t c o a s t o f G re en lan d has a s h e l f b r e a k betw een 60 m to 360 m ( s e e n e x t c h a p t e r ) . The s h a l lo w e r d e p th s are b e l i e v e d to be due to d e p o s i t s o f g l a c i a l m arine d e p o s i t s l y ing on a d e e p e r s h e l f p l a t f o r m . For exam ple, D avis Bank on 256 the A n t a r c t i c s h e l f was shown t o have as much as 200 m of se d im e n ts on th e s h e l f . I t i s p o s s i b l e , t h e r e f o r e , t h a t G reenland s h e l v e s a l s o may have c o n s i d e r a b l e t h i c k n e s s of g l a c i a l d e p o s i t s and the bedrock s u r f a c e of the s h e l v e s , t h e r e f o r e , may be much d e e p e r . Bottom M a t e r i a l s As e x p e c te d , bottom m a t e r i a l s v a ry g r e a t l y on th e s h e l f and s i o p e . C oarse se d im e n ts occur in th e c o a s t a l r e - g ion s w h ile sa n d s, g r a v e l s , and rock occur on th e s h e l f . Muddy sands e x te n d to d e p th s of 300 m to 400 m, and in some a r e a s 500 m to 700 m. Geology G reenland i s b a s i c a l l y a c r y s t a l l i n e s h i e l d of P recam b r i a n age b ut i t was i n t r u d e d d u r in g th e P a l e o z o i c e r a and T e r t i a r y p e r i o d . B a s a l t i c l a v a flow s of T e r t i a r y age are w id e s p re a d and v o lc a n is m was a s s o c i a t e d w ith f a u l t i n g and v e r t i c a l movements w hich l a r g e l y d e te rm in e d th e shape of th e c o a s t s ( F i g u r e 3 6 ). S t u d i e s s u g g e s t t h a t G reenland i s in a s t a t e of i s o s t a t i c e q u i l i b r i u i n . C a l c u l a t i o n s i n d i c a t e t h a t as th e g l a c i a l load i s removed th e lan d l e v e l must r i s e about one- t h i r d of the ic e t h i c k n e s s t h a t has m e lte d in o r d e r to m a in ta in e q u i l i b r i u m . Hence, as u n lo a d in g h a s o c c u r r e d i t has been r e f l e c t e d i n an i s o s t a t i c l i f t i n g which may have a f f e c t e d the s h e l f . T h is may have caused the sharp r e l i e f , m oats, c o a s t a l f a u l t i n g , and u p l i f t e d m a rin e - c u t t e r r a c e s . While the g e n e ra l c h a r a c t e r of w est G reenland is l i k e oth er g l a c i a t e d r e g i o n s , i t shows a y o u th f u l r e l i e f w ith very s t e e p s l o p e s . This i s a t t r i b u t e d in l a r g e measure to the t e c t o n i c c o a s t a l f a u l t s , which in tu rn may have a c c e n tu a te d the r e l i e f by i s o s t a t i c a d ju s tm e n ts . WEST BAFFIN LAND BAFFIN RIFT r 3000 M GREENLAND ^ ICECAP EAST SCANDINAVIA ATLANTIC RIFT L3000 M Figure 36. Diagramic c r o s s - s e c t i o n between B a ffin Island and Scandinavia. co cn oo GREENLAND- ICELAND I n t r o d u c t i o n The number o f p u b l is h e d p r o f i l e s o f f the e a s t c o a s t of G reen lan d and I c e la n d i s l i m i t e d . In f a c t , the o n ly c o n t in u o u s e ch o so u n d in g s a v a i l a b l e are th o s e made by German i n v e s t i g a t o r s d u rin g the IGY ( D i e t r i c h , 1959) and U l r i c h (1960, 1962, 1963). S e v e r a l r e c o n s t r u c t e d p r o f i l e s by Dan i s h i n v e s t i g a t o r s a l s o a re a v a i l a b l e , and a p r o f i l e by Rus s i a n i n v e s t i g a t o r s c r o s s e s N a n se n ’ s S i l l ( L a k tio n o v , 1959, and Volkov, 1 9 6 1 ). B o u rc a r t (1938) p u b l is h e d a b r i e f d e s c r i p t i o n of t h e w est c o a s t o f G reenland and I c e la n d (sum m arized in T able 1 2 ). Boyd (1935) made ech osou nd ing p r o f i l e s ( s e e P l a t e 28) and Sp'drck (1933) has p r e p a r e d a b a t h y m e tric c h a r t of Franz J o s e f F j o r d . H o lte d a h l (1955) has p u b l is h e d f o u r p r o f i l e s o f f Beeren I s l a n d and S p i t s b e r g e n ( F ig u r e 3 7 ). R e c e n t l y , H a l l e r and Kulp (1962) d e s c r i b e d th e geo lo g y of E a s t G r e e n la n d . However, s i n c e so few echogram s a re a v a i l a b l e , o n ly a b r i e f d e s c r i p t i o n o f the r e g i o n i s n e c e s s a r y . 259 260 Or m s w - 200- - -6 0 0 - - - 8 0 0 -- - 1000- - - 1 2 0 0 - - -1 4 0 0 - - SPITZBERGE -1600-■ -1 8 0 0 - - - 2000 - - - 2 2 0 0-- -2 4 0 0 - - BEE REN ISLAN, -2 6 0 0 -2 8 0 0 -3 0 0 0 -3 2 0 0 200 N au tica l 1 L miles V ertical e x a g g e ra tio n 462 tim es. 100 F ig u r e 37. E ch osou nd in g p r o f i l e s o f f B eeren I s l a n d and S p i t z b e r g e n . ( A f t e r H. H o l t e d a h l , 1 9 5 5 .) 261 R e s u l t s Two s e r i e s of p r o f i l e s are a v a i l a b l e f o r th e e a s t c o a s t of G re e n la n d . One group i s based upon sp o t sou n ding s ( P l a t e 27) and the o th e r i s composed of p r e c i s i o n echograms by U l r i c h ( P l a t e 2 8 ). Both s e r i e s show an i r r e g u l a r s h e l f and upper slope w ith one or more l o n g i t u d i n a l d e p r e s s i o n s . Local r e l i e f on the s h e l f i s up to 100 m ( P l a t e 2 8 ). Lon g i t u d i n a l d e p r e s s i o n s are 300-m or more d eep. A r id g e of s l i g h t r e l i e f commonly o c cu rs along th e edge of the s h e l f g iv in g i t a warped a p p e a ra n c e . S h e lf b r e a k s occur a t 200 m to 300 m. The upper c o n t i n e n t a l slo p e i s s t e e p and may be e i t h e r s t r a i g h t and smooth, concave, or convex. Below about 1,500 m th e c o n t i n e n t a l slo p e meets the c o n t i n e n t a l r i s e showing a change in g r a d i e n t . A r i s e or rid g e of about 500 m o f te n o c c u rs a t th e j u n c t u r e of the c o n t i n e n t a l slo p e and c o n t i n e n t a l r i s e . The west I s l a n d i c c o n t i n e n t a l s h e l f and s lo p e appear to be s i m i l a r to G r e e n l a n d ’ s e a s t c o a s t ( P l a t e 27, p r o f i l e X). U l r i c h (1960) made 54 p r o f i l e s a c r o s s the R eykjanes R idge. The c r e s t of th e r i d g e i s s h a llo w e r th an 1,000 m and i s e x tre m e ly i r r e g u l a r , t y p i c a l of the m id - A t l a n t i c R idge. . The a u th o r found no c e n t r a l r i f t zone su g g e ste d by Heezen on the R eykjanes R idge. 26 2 P r o f i l e s o f f Beeren I s l a n d and S p i t s b e r g e n show a s h e l f b r e a k a t d e p th s r a n g in g from 200 m to 300 m ( F i g u r e 3 7 ) . S e v e r a l o f th e p r o f i l e s show f e a t u r e s a t d e p th s of 1 ,2 0 0 m and lo w er; how ever, th e g r e a t v e r t i c a l e x a g g e r a t i o n and sm a ll number o f p r o f i l e s p r e c l u d e s and d e f i n i t e c o n c l u s i o n s . E x t e n s i v e , r e l a t i v e l y s h a l l o w - w a t e r t e r r a c e s o c c u r in the n o r t h A t l a n t i c , s o u th w e s t I c e l a n d , F a e r o e s - S h e t l a n d - H e b r id e s g ro u p s, and I r e l a n d ( V a s i l ’ yev, 1 9 6 4 ). T e r r a c e d e p th s and w id th s a re summarized in T a b le s 10 and 11. The mean s h e l f b re a k in t h i s r e g i o n i s 231 m. A c co rd in g to V a s i l ’ yev, w ith the e x c e p t i o n of s o u t h e r n I r e l a n d , th e s h e l v e s show a common g e n e t i c g l a c i a l c h a r a c t e r . S h e lv e s t h r o u g h o u t the r e g io n have low su bm arine h i l l s 2,000-m to 3,100-m wide a t th e b a s e , 900 m a t the to p , a h e i g h t of 20 cm to 22 cm, and have a mean d e p th of 166 m. T hese f e a t u r e s were a t t r i b u t e d to th e plow ing a f f e c t of i c e s h e e t s . C ob b les d red g e d from the r e g i o n a re m o d e r a t e l y smoothed b u t s o f t - r o c k p e b b le s a re w e l l p o l i s h e d . F l a t t e n i n g i s i n s i g n i f i c a n t . I t was c o n clu d ed t h a t th e p e b b l e s a re p r o b a b l y o f " h y d r a u l i c - g l a c i a l - p e l a g i c " o r i g i n . A wide t e r r a c e o c c u r s o f f th e w est c o a s t of S p i t z b e r - gen ( F i g u r e 3 9 ) . L a k tio n o v (1959) showed t h a t Nansen S i l l , s u p p o s e d ly o c c u r r i n g in t h i s r e g i o n , i s n o n - e x i s t e n t . T able 10. Depth of S h e lf Breaks in N o r th e a s t A t l a n t i c Ocean. ( A f t e r V a s i l ’ yev, 1964.) LOCATION DEPTH ( m) WIDTH (km) 140 7 .2 H eb rid es 155 7 .8 158 4.6 154 3.6 S h e tla n d I s . 157 6 .5 160 5.4 Table 11. Mean S h e l f - b r e a k s and Widths of the I n s u l a r S h e lv e s , North A t l a n t i c Ocean. ( A f te r V a s i l ’yev, 1964.) LOCATION DEPTH (m) WIDTH (km) S h e tla n d 165 91 H ebrides 220 95 I r e l a n d 222 111 F aeroes 250 69 Ic e la n d 282 70 264 One of the most i n t e r e s t i n g f e a t u r e s of th e e a s t G reenland c o a s t , near Scoresby Sound e x te n d in g fo r 800 km, i s a marked f l e x u r e of b a s a l t flow s ( F ig u r e 38). According to Wager and Deer (193 8), Wager (1947 ), and Lees (1953) th e s e flow s show a d i s t i n c t downward f l e x u r e along th e c o a s t and a t the re g io n o f maximum f l e x u r e (near the p r e s e n t c o a s t l i n e ) dense dike swarms o ccu r. 265 D EN SE DIKE SW ARM V /\ M ETA M O R PH IC SA M E H O R IZO N T A L A N D V E R T IC A L F ig u re 38. Lavas o ff the e a s t c o a s t of Greenland d ip about 3° below sea l e v e l , b u t the g r a d i e n t i n c r e a s e s near the c o a s t to about 10°. Dike swarms occur where th e l a v a s show a m axi mum f l e x u r e . These c h a r a c t e r i s t i c s c l o s e l y fo llo w the p r e s e n t c o a st l i n e . The f l e x u r e and d ik e swarms are a s s o c i a t e d w ith an a b ru p t seaward t i l t of the c r u s t ( A f te r Wager, 1938). 2 6 6 ?*6£a ^ C a m p V S * * n - oexcfGN Figure 39. Bottom p r o f i l e between S p itsb e r g e n and Green land . (A fter L ak tion ov, 1 9 5 9 .; WEST COAST OF EUROPE I n t r o d u c t i o n The b a th y m e try , s u r f a c e , and s u b s u r f a c e g eo lo g y of the B r i t i s h I s l e s have been s t u d i e d by many i n v e s t i g a t o r s f o r more th an a c e n t u r y . T h is a r e a has p e rh a p s been i n v e s t i g a te d n e a r l y as c o m p le te ly as th e E a s t C oast of the U n ited S t a t e s . Some o f the r e c e n t p a p e r s on th e r e g i o n i n c l u d e : Day, 1959; H adley, 1964; H i l l , 1956; B e r t h o i s and B r e n o t , 1960; F r a n c i s , 1962; Heezen, T h arp , and Ewing, 1959; Heezen and L aug hto n, 1963; W h i t t a r d , 1962; B la c k , 1962; B renot and B e r t h o i s , 1962; C u rry , M a r t i n i , S m ith , and W h i t t a r d , 1962; B o u r c a r t , 1938; Browne and Cooper, 1949; B u lla r d and G a s k e l l , 1941; C ooper, 1948 and 1952; Donovan, e t a l .. 1961; H o l t e d a h l , 1935 and 1952; W. B. R. King, 1949 and 1950; P r a t j e , 1951; R obinson, 1952; T in g, 1937, and o t h e r s . A t o t a l o f 56 p r o f i l e s a re a v a i l a b l e f o r the w est c o a s t of Europe ( P l a t e s 2 9 - 3 2 ) . Many d i f f e r e n t s o u r c e s were u sed i n c l u d i n g Heezen, T h a rp , and E w ing ’s ( P l a t e 29, H p r o f i l e s ) ; OB p r o f i l e s ; B r i t i s h I n s t i t u t e of O ceanography (D p r o f i l e s ) ; U l r i c h ( P l a t e 32) f o r R o c k a ll Bank, o t h e r 267 268 German p r o f i l e s (L p r o f i l e s ) , and p r o f i l e s by B ren o t and B e r t h o i s ( P l a t e 3 1 ) . While th e l o c a t i o n f o r most o f th e p r o f i l e s a re known, o n ly the a p p ro x im a te l o c a t i o n o f th e l a t t e r p r o f i l e s a r e known. B o u r c a r t (19 38 ) has g iv e n a d e s c r i p t i o n of v a r i o u s t o p o g r a p h i c f e a t u r e s alo n g the w e st c o a s t of Europe find A f r i c a (T a b le 12) . A p p ro x im a te ly 25 echogram s of the r e g i o n s o u th of t h e . B r i t i s h I s l e s were c o p ie d a t th e B r i t i s h I n s t i t u t e of O ceano grap hy ; however, t h i s r e g i o n i s h e a v i l y i n c i s e d by su bm arin e canyons and the echo gram s, t h e r e f o r e , were n o t used in the p r e s e n t s t u d y . The h i g h l y i n c i s e d c o n t i n e n t a l s lo p e betw een 45° N, 2 ’ W to 48° N, 1 1 ’ W can be se e n in F i g u r e 2 o f th e p a p e r by H ad ley ( 1 9 6 4 ) . H adley a l s o p ub l i s h e d a number of a d d i t i o n a l p r o f i l e s a c r o s s the c o n t i n e n t a l s lo p e s o u t h of the B r i t i s h I s l e s ( n o r t h e r n p a r t of Bay o f B i s c a y ) . R e s u I t s P r o f i l e L - l - 1 ( P l a t e 29) i s b e tw ee n I c e l a n d and S c o t l a n d . I t shows th e i r r e g u l a r bo ttom to p o g ra p h y betw een t h e s e two r e g i o n s — a s t e e p , i r r e g u l a r c o n t i n e n t a l s l o p e o f f I r e l a n d , th e dom e-shaped f e a t u r e of B i l l B a i l e y ’ s Bank, and a sm ooth, concave c o n t i n e n t a l s lo p e o f f S c o t l a n d . A n oth er p r o f i l e c r o s s e s th e c o n t i n e n t a l s lo p e a t an an g le and a l s o shows a concave s l o p e . 269 Two p r o f i l e s occur o f f I r e l a n d (L -2-9 and D - 3 - 1 ) . P r o f i l e L -2-9 r e v e a l s a s t e e p c o n t i n e n t a l slo p e w ith no c o n t i n e n t a l r i s e and a sm all slope change or minor t e r r a c e at 1,000 m. This t e r r a c e , or slope change, a lso i s v i s i b l e on D -3-1. Both p r o f i l e s c ro s s a co rn e r of R ock all Bank. R ock all Bank ( P l a t e s 32 and 31) c o n s i s t s of two major f l a t a r e a s - - a b o u t 500 m and a v a s t p l a t e a u a t about 1,400 m. A l a r g e number of p r o f i l e s c ro s s the c o n t i n e n t a l slope from s o u th e rn I r e l a n d to France (se e index map, P l a t e 29). P r o f i l e s L -2 -8 , 12, D - l / 2 - 2 , H - l , H-2, H-3, and o t h e r s show a prom inent t e r r a c e between 1,200 m (D l / 2 - 2 ) to 2,800 m (12 and D - 3 - 2 ) . The c o n t i n e n t a l slope of the Bay of B iscay i s s t e e p , having a g r a d i e n t from 3° to 6° ( P l a t e 29, H-4; P l a t e 30, D - 3 - 5 ; OB-5 7/8-16A; and OB 5 7 / 8 - 1 ) . The so u th e rn slo pe is p a r t i c u l a r l y s t e e p , is i n c i s e d by submarine canyons, and i s tho ug ht to be a major f a u l t sc a rp ( P l a t e H-4A and H-4B). < * A la r g e t e r r a c e , named Meriadzek T e rra c e by Day (1959), l i e s a t 47 l / 2 ° N, 8 l / 2 ° W, c o v e rs an a r e a of 1,300 km^, and l i e s a t a depth of 1,800 m to 2,200 m. Below the t e r rac e on t h r e e s i d e s i t has s te e p (6° to 27°) c l i f f s (s e e F igu re 3, p r o f i l e GG1 of Haley, 1964). The c o n t i n e n t a l slo p e above the t e r r a c e i s more g e n tl e than e ls e w h e re . Hadley attem p ted to l o c a t e o th e r t e r r a c e s bu t r e p o r t e d he could not l o c a t e them, and i f th ey e x i s t e d were l e s s 270 than 18-km long and 4-km wide. Heezen, e t a l . (1 95 9), how e v e r , in d ic a t e d t h a t M the c o n t i n e n t a l slope i s broken by a prom inent bench or m a rg in a l p la te a u a t 1,000 fms to 1,200 fms [1,800 - 2,200 m ]." H i l l ’ s (1956) c h a r t shows t h i s prom inent bench exten ds f o r more than 1,700 km along the c o n t i n e n t a l margin from 45° N to 60° N. In a d d i t i o n , the c o n t i n e n t a l slo p e from th e s h e l f break to the prom inent bench e x h i b i t s sm a lle r benches and changes in slo p e . Heezen and c o lle a g u e s su g g e st t h a t many of th e s e w i l l be c o r r e l a t i v e when more p r o f i l e s are a v a i l a b l e . P r o f i l e s C -16-2, H-6, C -16-3, and H-7 a re lo c a te d o f f P o r tu g a l and Spain. These r e v e a l a s t e e p c o n t i n e n t a l slo p e w ith p o s s i b l e narrow t e r r a c e s a t s e v e r a l d e p th s . Many banks occur o f f the n o rth w e s t c o a s t of I r e l a n d - - P o r c u p in e , R o c k a ll, Rosemary, B i l l B a i l e y , Lousey, e t c . The banks are t y p i c a l l y s t e e p - s i d e d and f l a t - t o p p e d and r e semble g uy ots. Porcup ine and R o c k a ll are e lo n g a te d in a n o r t h e a s t - s o u t h w e s t d i r e c t i o n , whereas the Rosemary, George B lig h , and Faeroe Banks are c i r c u l a r in p la n (Robinson, 1952). Tops of banks vary from 180 m f o r P o rc u p in e Bank, to 110 m to 128 m on R ock all Bank; o t h e r s are s h a llo w e r. A ll o f th e s e banks belong to North A t l a n t i c t h u le a n igneous p ro v in c e of T e r t i a r y age. E x te n siv e dred ging has shown the banks are p red o m in an tly b a s a l t . 271 Geology G r e e n .e t a l .(1 8 9 7 ) and Charco, e t a l . (1922) have d e s c r i b e d R o c k a ll Bank. Green d e s c r i b e d R o c k a ll as "a p o r t i o n of a g r e a t i n t r u s i v e s h e e t of ig n eo u s ro c k , now l y in g in an u n d iv id e d p o s i t i o n upon s t r a t i f i e d m a sse s, which are seen on the so u th w e st s i d e of the r o c k . ” A t r a w l from 164 m re c o v e r e d ” a most u n e x p ec te d a s s o r t m e n t of s h a llo w w a te r s h e l l s , e v i d e n t l y long s in c e d e a d , ” as w e l l as v o l c a n i c p e b b le s and g r a v e l and "must be a r e l i c of a m ountainous i s l a n d . ” Davis (1928) s t a t e d t h a t " i t can h a r d l y be e x p l a i n e d w ith o u t s u b s i d e n c e . ” Dangeard (1929) r e p o r t e d t h a t d r e d g in g u n d e rta k e n by C h arco t in 1921-1927 showed t h a t ro ck s were l a r g e l y a n g u la r b a s a l t . Cole (1910) found t h a t 80 per c e n t of the bottom • specim ens were o l i v i n e g a b b ro . I t is c o n clu d ed by Robinson t h a t th e bank i s e s s e n t i a l l y a submerged b a s a l t p l a t e a u . R o c k a ll i t s e l f is g r a n i t e p o rp h y ry . V ast a r e a s o f f w est S c o tla n d and N o rth e rn I r e l a n d are n e a r l y f l a t and c o n s i s t s o f b a s a l t flo w s . For exam ple, an echogram due s o u th of the W y ville Thompson Ridge, which l i e s 600 m above the s e a f l o o r , i s h i g h l y i r r e g u l a r and i s assumed to have a d i f f e r e n t o r i g i n . Dredging showed i t to be composed of a m ix tu re of s u b - a n g u l a r fra g m e n ts embedded in a sandy b o u ld e r c l a y . I t i s s u g g e s te d t h a t t h e s e were d e p o s i t e d by an ice s h e e t t h a t moved n orthw ard from S c o tla n d to j o i n w ith the 27 2 S c a n d in a v ia n i c e . H ence, W y ville Thompson Ridge i s th o u g h t t o be a g i g a n t i c end m o raine. (See i l l u s t r a t i o n by R o b in son, 1952, p . 7 2 .) H i l l and Laughton (1954) made a s e r i e s o f s e is m ic r e f r a c t i o n p r o f i l e s o f f th e s o u t h e r n p a r t of the B r i t i s h I s l e s , betw een 47° to 50° N, which showed t h a t t h e r e i s no i m p o r ta n t deep s t r u c t u r a l d i f f e r e n c e s between th e e a s t e r n A t l a n t i c b a s i n , the A t l a n t i c , and P a c i f i c ( H i l l , 1957) while the t y p i c a l c o n t i n e n t a l deep s t r u c t u r e i s m arkedly d i f f e r e n t . P r o f i l e s a c r o s s th e c o n t i n e n t a l t e r r a c e a re s i m i l a r to th o s e o f f the e a s t c o a s t of th e U. S. The basement s l o p e s g r a d u a l l y se aw ard , and i f e x t r a p o l a t e d seaward i t would merge w ith the a b y s s a l se a f l o o r ( B u l la r d and Gas- k e l i , 1941 ). Table 12. The C o n tin e n tal S helf and Other Surfaces of the West Coast of the A t l a n t i c Ocean (A fter B o urcart, 1938) SURFACES REGION 0-200 m 200-500 m 500-1000 m 1000 m Coast of Greenland Scoresby Sound Coast of B l a s s e v il l e and Angmassalik SE Greenland Jean Mayen Island North Coast South Coast Very Narrow Well developed Well developed - Slope d e c lin e s to 1200-2000 m Well developed - 200-500 m p la te a u is elongated and narrows toward the SE; i t appears to be the same as t h i s on the W co ast of Iceland but i t d e c lin e s as a g e n tle slope to 2000 m Narrow small r i s e and steep d e c le v ity to 1500-2000 m Narrow c o n tin e n ta l s h e lf and slope plunges qu ick ly to 2000 m P re se n t Iceland North Coast P re se n t P re se n t - Long, continuous, and pointed to the south. Does not have abrupt slope to g reat depths. Well developed - R e -e n tra n ts in s h e lf (200-500 m) which seem to show c o n tin u a tio n of f j o r d s co Well developed on open sea sid e of North Cape o CO Table 12. (Continued) REGION 0-200 m 200-500 m 500-1000 m 1000 m Iceland (Cont.) North Coast (Cont.) South Coast P re se n t Faeroes Island Well developed Rockall Bank Well developed (min depth 21 m ) Well developed e n t i r e l y along the n o rthern co ast with the W p a r t e s s e n t i a l l y joined with th a t of Green land; e s p e c i a l l y on SE which i s u nited with th a t of the Faeroes (which are on the c o n tr a r y ) , are s e p a r ated from Scotland by depths of 1200-1500 m P re se n t - To SW an im portant 500-m plateau which, i t seems, i s a continuous p r o j e c ti o n of B reidi Fjord. To SE numerous p r o j e c tio n s of 500 m p latea u are con tinuous with F jords e x is ti n g today. 200-500 m p l a teau are w ell-developed to SW, but is n o n -e x is ta n t to SE (except fo r former submarine f j o r d s ) . Drops ab ru p tly to 1500 m. Wide-joined in the N with the 200-500 m p latea u of I c e l a n d . E s p e c ia lly w ell developed near SW where i t is a very wide-spread platform of 0-200 m w ith lo c a l highs of 88 m P re se n t - No s t r a i g h t slopes to g rea t dep th s. Well developed (except to E) Wide (except to SE) to -o ■ f* Table 12. (Continued) REGION 0-200 m 200-500 m 500-1000 m 1000 m NW of Scotland West of Ireland Porcupine Bank Well developed - Comprises the Orcades, Shetland, Hebrides; steep slope to 1500-2000 m Well developed West Entrance to Channel West Coast of France Well developed to 2000 m - To W of the Bank very steep slope P re se n t - To the SE, abru pt, de scending to- 4000 m Well developed to La Grande and P e t i t e ; steep g ra d ie n t to 2000 to 4000 m Cape Brenton Trench North Coast Spain Coast P o rtu g a l Well developed - Rise then steep d e c le v ity to 1200-2000 m Small - Steep slope from s h e l f to 3000 m Moderately well P re se n t - Between Douro and Tage Rivers developed to -o Table 12. (Continued) REGION 0-200 m 200-500 m 500-1000 m 1000 m I n l e t W of G i b r a l t a r Coast Morroco Coast M auritania Towards Cape Blanc Cape Blanc to Dakar West Coast A fric a Dakar to Monrovia P re se n t P resen t - Connects with p la te a u in M editerranean P re se n t - Gentle slope to g reat depths Narrow - Widens to the N of Cape Juby P la te au w ith in v i c i n i t y of 400 m, dropping ra p id ly 1500 m or more F a i r l y wide Appears to be p r e s e n t, but r e a l l y is not v i s i b l e w ith in the N coast region Well developed - Rapid drop to g ie a t depth; N of Cape Vert 0-200 m becomes narrower and almost d isa p p ea rs Poorly developed between Cape Blanc and Cape Vert P re se n t - Gentle g rad ie n t except at Cape Vert where the topography i s ver y rough Wide P re se n t W of French Guinea; elsewhere the drop is co -o O ' Table 12. (Continued) REGION Dakar to Monrovia (C ont.) L ib e r ia Coast Ivory Coast Gold Coast Dahomey-Nigeria Niger D elta E q u a to r ia l A frica Congo Angola SW A fric a 0-200 m Nar row 200-500 m 500-1000 m 1000 m rapid from 0-200 m Narrow - Sudden drop to 2000 m 1500 m iso b a th almost to coast Well developed a t Cape of Three P o i n t s , dropping immediately to 5000 m Narrow - Drops r a p id ly to 2000 m Narrow Moderately wide P resen t Not p re s e n t Narrow Not p re s e n t - Rough topography F a i r l y wide ( o f f Spanish Guinea) Narrow Presen t - 1500-2000 m iso b a th s n e a rly touch coast P re se n t - E s p e c ia lly w ell developed in f r o n t of Orange River P re se n t - E s p e c ia lly S of Orange River; descends to g rea t d ep th s. 277 NORTHWEST COAST OF AFRICA I n t r o d u c t i o n Twelve of th e 17 p r o f i l e s o f f n o r t h w e s t A f r i c a a re ta k e n from Heezen, e t a l . ( 1 9 5 9 ) . They have a v e r t i c a l e x a g g e r a t i o n of 40. For c o n v e n ie n c e , H e e z e n 's p r o f i l e s a re g rou ped ; however, s e v e r a l o t h e r p r o f i l e s occur betw een t h e s e . A d d i t i o n a l p r o f i l e s were t a k e n by the DISCOVERY ( P l a t e 33, D 1 /2 - 3 and - 4 ) , CRAWFORD (C 16-5 and C 5 7 - 2 ) , and the OB (OB 5 7 / 8 - 2 ) . A ll of t h e s e l a t t e r p r o f i l e s have a v e r t i c a l e x a g g e r a t i o n o f 100. H e e z e n ’ s p r o f i l e s a re b ased m o s tly upon PDR s o u n d in g s , b u t i t i s n o t known w h e th er the p r o f i l e s were r e c o n s t r u c t e d or a re d i r e c t t r a c in g s of echogram s. The o t h e r p r o f i l e s are r e c o n s t r u c t e d . I t sh o u ld a ls o be n o ted t h a t th e s c a l e s of th e low er f o u r p r o f i l e s a re d i f f e r e n t from th o s e a b o ve. Because of th e sm a ll s c a l e , i t i s d i f f i c u l t to p i c k ou t m inor t o p o g r a p h i c f e a t u r e s on H e e z e n ’ s p r o f i l e s . The d i f f i c u l t y i n com paring s l o p e s w i t h d i f f e r e n t v e r t i c a l e x a g g e r a t i o n s , as w e l l as a s c e r t a i n i n g g r a d i e n t s on s t e e p s l o p e s , are w e ll i l l u s t r a t e d on P l a t e 33; p r o f i l e s D l / 2 - 3 and D 1 /2 - 4 o c c u r betw een H e e z e n ’ s p r o f i l e s , y e t 278 279 th e form er a p p ea r to have a s t e e p e r g r a d i e n t th an H e ez en ’ s . The above 14 p r o f i l e s a re u n c o r r e c t e d f o r sound v e l o c i t y ; DISCOVERY, CRAWFORD, and OB a re c o r r e c t e d f o r sound v e l o c i t y . R e s u l t s The most c o n sp ic u o u s f e a t u r e along n o rth w e s t A f r i c a i s the wide p l a t e a u a t a p p r o x im a te ly 3,000 m. O ff M a u r i t a n i a , t h i s p l a t e a u has been termed the "Cape Verde P l a t e a u . " I t can be i d e n t i f i e d on H-8, - 9 , and -10 e i t h e r as a p l a i n or by a sh a rp i n c r e a s e in g r a d i e n t a t a p p ro x im a te ly 3,500 m. The p l a t e a u i s f u l l y d e v elo p ed s t a r t i n g w ith D l / 2 - 3 o f f Morocco and l o s e s i t s i d e n t i t y n o r t h o f D akar. I t i s b a r e l y v i s i b l e on C 1 6 -5 . P r o f i l e s n o r th and so uth o f the Canary I s l a n d s (D l / 2 - 3 and D l / 2 - 4 ) a re u n a f f e c t e d by t h i s v o l c a n i c i s land group. These p r o f i l e s show th e t e r r a c e betw een 2,500 m to 3,400 m as a s e a w a r d - s l o p i n g , i r r e g u l a r p l a i n w ith a g r a d i e n t of 0 . 2 ° . On th e s e p r o f i l e s the t e r r a c e i s about 175-km in w i d t h . T e r r a c e s a t a p p ro x im a te ly 500 m o ccu r on e i g h t of H e e z e n ’ s 12 p r o f i l e s . They do no t a p p ea r on the more v e r t i c a l l y - e x a g g e r a t e d p r o f i l e s ; h e n c e , no d e f i n i t e c o n c l u s i o n s r e g a r d i n g the p re s e n c e or absence can be drawn from th e l a t t e r . A d i s t i n c t and o c c a s i o n a l l y wide t e r r a c e o c c u r s a t 1,000 m to 1,400 m. I t can be i d e n t i f i e d on n in e I 280 p r o f i l e s . P r o f i l e OB 5 7 /8 - 2 c u t s a c r o s s th e c o n t i n e n t a l s lo p e o f f S i e r r a Leone and L i b e r i a r e v e a l i n g th e p r e s e n c e o f c a n y o n s. A ltho ug h s e v e r a l o t h e r p r o f i l e s c u t the c o n t i n e n t a l s l o p e a t an a n g l e , canyons do n o t a p p ea r to be p ro n o u n ce d . A l i n e drawn a c r o s s th e top of r i d g e s s u g g e s t s a common l e v e l of t r u n c a t i o n ( p r o f i l e OB 5 7 / 8 - 2 ) . P r o f i l e s H-8 to H-10 are l o c a t e d a t th e e n t r a n c e to the S t r a i t s of G i b r a l t a r . The g r a d i e n t i s more g e n t l e a t th e S t r a i t s th a n f u r t h e r s o u t h , a v e r a g in g o n ly 1°. The b o tto m i s i r r e g u l a r w i t h r e l i e f of 100 m or more, and t e r r a c e s t h a t can be c o r r e l a t e d s u g g e s t exposed bedrock o f f G i b r a l t a r . A t e r r a c e a t a p p r o x i m a t e ly 900 m to 1,200 m i s d i s t i n c t and has a g r a d i e n t of o n ly 1 4 ’ t o 2 4 ’ . A ccording to K rause ( 1 9 6 4 f ) , an e a s t - w e s t t r e n d i n g f r a c t u r e zone has been d i s c o v e r e d and named the G uinea f r a c t u r e zon e. I t o c c u r s o f f S i e r r a Leone (8° ’ to 9° N). The t o p o g r a p h i c , l e f t - l a t e r a l d i s p l a c e m e n t r e p o r t e d l y i s ab ou t 230 km and can be t r a c e d from th e edge of th e c o n t i n e n t a l s h e l f edge 850 km se aw ard . T able 13 l i s t s th e g r a d i e n t s o f th e c o n t i n e n t a l s lo p e o f f n o r t h w e s t A f r i c a . No subm arine canyons e x i s t betw een 32° 4 0 ’ N and 35° N and th e s l o p e i s s t r a i g h t ov er most o f t h i s d i s t a n c e . A c h a r t ( F i g u r e 40) p u b l i s h e d by Gougenheim (1959) b etw een ^ o 30 N t o 35 N, shows a s t e e p , more or l e s s even s lo p e 281 te r m in a tin g r a t h e r a b r u p t l y a t 2,000 m, which G u ilc h e r (1963) termed the c o n t i n e n t a l r i s e . No canyons occur in the a re a between 33° to 35°, but a wide ( a p p ro x im a te ly 55 km) r e - e n t r a n t w ith a f l a t f l o o r and p a r a l l e l s i d e s , s i m i l a r to the tro ug h r e p o r te d by C reager (1958) in the Bay of Campeche ( i n the Gulf of M exico), e x i s t s o f f Rharb p l a i n . G u ilch e r c o n sid e re d t h i s "a sunken a re a in the R if f o r e la n d a c ro s s which th e c o a s t c u t s . ” Topography o f f the R if c h a in i s c o n s id e r a b ly more i r r e g u l a r than o ff the Meseta as f a r sou th as 33° N. I t i s even more c o m p lica te d from Cape Can- t i n to Agadin, w ith many canyons or d e p r e s s i o n s . B o u rc art (1938 and o th e r p a p e rs ) b e l i e v e s the c o n t i n e n t a l margin o ff Morocco i s an example of m arginal f l e x u r e . Table 13. G r a d ie n ts of C o n t in e n t a l Slope o f f N orthw est A f r i c a LOCATION UPPER CONTINENTAL SLOPE LOWER CONTINENTAL SLOPE S t r a i t s of G i b r a l t a r 1° 0 . 6 ° - 1 .1 ° Morocco 3° - 6° 1 .5 ° S panish S ahara 1 .5 ° - 4° 1° - 1 .5 ° M a u r ita n ia O J • 00 o 0 .5 ° Sengal 2° - 3° o oo * o 1 0 o cn • o S i e r r a Leone 5° 0 .5 ° F ig u re 40. Bathym etry of c o n t i n e n t a l slo p e o f f Morocco. ( A f t e r A. Gougenheim, 1959.) 283 7 ° W J6r) jtA B A TV ; —< < S . CASABLANCA ) u * t i d k 4.000'S. COTE ATtANTIOUE OU UAROC L E V E B A T H Y M E T R I Q U E u a c u ti da ISS2 i U SS par Ic Sirvict Hydrographiqua 4a la Manna 7 °W .(G r.) 284 B o u r c a r t ’s d a t a on the w est c o a s t of A f r i c a i s summa r i z e d in Table 12. He s t a t e d t h a t a p l a t e a u in the v i c i n i t y of 400 m o c c u rs o f f the c o a s t of Morocco, and a 200 m to 500 m s u r f a c e ap p ea rs to be p r e s e n t o f f Cape Blanc, M a u r i ta n ia ; i s a b s e n t from Cape Blanc to Dakar; p r e s e n t from Dakar to M onrovia; narrow o f f L i b e r i a ; a b s e n t o f f from the Iv ory C oast to the v i c i n i t y o f the N iger D e l t a ; and at the l a t t e r r e g i o n i t i s p r e s e n t b u t narrow . Geology The Cape Verde P l a t e a u i s r a t h e r i r r e g u l a r (s e e H -18 ), s u g g e s t i n g t h a t i t i s not a d e p o s i t i o n a l p l a i n . The p r e s ence of o f f s h o r e v o l c a n i c i s l a n d s , as w e ll as innum erable seam ounts, a l s o s u p p o r ts t h i s c o n c l u s i o n . The A tla s M ountains s t r e t c h i n g a c r o s s Morocco a l s o i n clu d e th e Canary I s l a n d s . This range c o n s i s t s of C aledon- ia n f o l d s . A t e c t o n i c map of A f r i c a made by M azarovic (1952) shows a r i f t along the s h o r e l i n e of Spanish S a h a ra , and from B a r t u r s t , S e n e g a l, to M a u r i ta n ia a t a p p ro x im a te ly 19° N ( F ig u r e 4 1 ) . The c o a s t a l r e g i o n o f f Morocco and Senegal (Cape Verde) i s s e i s m i c a l l y a c t i v e ( F i g u r e s 42 and 4 3 ). Cape Verde I s l a n d s r i s e from d e p th s of 3,500 m to 4 ,0 0 0 m. They are composed b a s i c a l l y of v o l c a n i c r o c k , b ut P re c a m b ria n , M esozoic, and Eocene se d im e n ts on s i x o f the t e n - p r i n c i p a l i s l a n d s s t r o n g l y su g g e s t t h a t th e y were once 285 co nnected to the A f r ic a n c o n t i n e n t . E rim esco (1963) b e l i e v e s t h a t the c o n n e c tio n may have been m a in ta in e d u n t i l as r e c e n t as th e P l e i s t o c e n e epoch. The p l a t e a u on which the Azores a re l o c a te d c o v e rs 2 2 52,000 mi (179,000 km ) and i s bounded on the so u th w e st sid e by a s te e p s lo p e about 1,100 m h ig h ( T o ls to y and Ewing, 1949). Ridges on the Azores p l a t e a u are s e p a r a t e d by broad v a l l e y s . Using c l a y , Hans Cloos (1939) showed e x p e r i m e n t a l l y t h a t the ty pe of to pography t y p i f y i n g the Azores p l a t e a u can be e x p la in e d in term s of doming of the E a r t h ’ s c r u s t form ing f r a c t u r e s p a r a l l e l to the lo n g e s t dim ension of the domed s e c t i o n (NW-SE). Subsequent e x t r u s i o n of magma thro ug h f i s s u r e s would account f o r NW-SE r i d g e s . A gostinho (1936) lik e w is e b e l i e v e s the major to p o g r a p h ic f e a t u r e s of the Azores p l a t e a u a re due to e x t r u s i o n along NW-SE f r a c t u r e s . The bulge in th e rid g e i s a t t r i b u t e d to th e i n t e r s e c t i o n of two m ajor subm arine r i d g e s : N-S tre n d of th e m id - A t l a n t i c Ridge and the E-W tre n d of the G reat Banks, Milne Bank, the A z o res, and the banks w est of G i b r a l t a r . A s i m i l a r o r i g i n of the Azores p l a t e a u was proposed f o r the c e n t r a l p a r t of Ic e la n d by Hawkes (1938 and 1941) who c o n s id e r e d i t a grab e n . Major o u tp o u rin g s of b a s a l t o c cu rred i n I c e la n d and Azores in l a t e T e r t i a r y to Recent tim e and the o t h e r in m iddle or e a r l y T e r t i a r y p e r i o d . Form ation may th u s have 286 o c cu rred d u rin g th e A lpine o r o g e n ie s . 0 10 - 2 0 J V J V Pre-C am brian foundation of the African plateau w ith out- crops K / y u Zones of shallow subsidence of th e pre-C am brian foun- dation 1 ^ Zones of deep subsidence of the pre-C am brian foundation |- g g g ;[ C aledonian folds w ithin the plateau l-= — ~l Hercynun folds F ig u re 41. T e c to n ic map of I’ Slp-I cape folds A f r i c a . ( A f t e r A. I! ; • . 1 The foredeep of K aroo' M a z a r O V l J l f , 1 9 5 2 ) Alpine folds [°0° B °| M esopotamian and Syrian foredeep P rincipal rifts 288 iraltoH M oaag' •d^aqlanaa\ F ig u r e 42. E a rth q u a k e a c t i v i t y in M orocco. D o u b l e - r u l e d a r e a s a re d e s t r u c t i v e e a r t h q u a k e s ; c lo s e d v e r t i c a l r u l e d l i n e s a r e r e g i o n s of s t r o n g e a r t h q u a k e s , and w id e -s p a c e d v e r t i c a l l i n e s a re r e g i o n s of weak e a r t h q u a k e s T Heavy b l a c k l i n e s w i t h b a r b s a re f a u l t s . ( A f t e r A. S i e b e r g , 1 9 3 2 .) 289 Tschad,-8ecken oSokttra ID \K om «rm •tQ Entisorfirn Z.Krenkef 1S21. 0 , o r 1 i n s e v e r a l y e a r s o r u n k n o w n E 2 2 U p t o 5 a y e a r o n 6 t o 1 0 d o . f T T U n i 1 1 t o 2 0 d o . C Z 3 3 2 1 t o 5 0 d o . E 2 3 5 1 t o 1 0 0 d o . H 4 4 1 U I Q v e r 1 0 0 d o . F i g u r e 43. Average a n n u a l f r e quency of e a r t h q u a k e s i n A f r i c a . ( A f t e r E. K r e n k e l, 1 9 2 3 .) GULF OF GUINEA I n t r o d u c t i o n Only n i n e e c h o s o u n d in g p r o f i l e s a re a v a i l a b l e from th e G u lf o f G u in e a ; a l l a re o f f th e N ig e r D e l t a ( P l a t e 3 3 ) . Buchanan (1 8 8 7 ) d e s c r i b e d th e to p o g r a p h y f o r a p o r t i o n o f t h e G ulf r e g i o n b u t h i s s o u n d in g s a r e s p a r s e l y s c a t t e r e d . R e s u l t s Betw een S i e r r a Leone and P o r t o Novo ( a b o u t 95 km w e s t o f L a g o s ) , 14 l e a d - l i n e so u n d in g p r o f i l e s w ere made by Buchanan. The s h e l f r e p o r t e d l y i s 22-km to 28-km w id e , f l a t u n t i l a d e p t h o f 55 m, when th e d e p t h i n c r e a s e s r a p i d l y to 183 m (100 f m ) . The s l o p e th e n becomes c o n s i d e r a b ly s t e e p e r , r e a c h i n g a maximum g r a d i e n t b etw een 364 m (200 fm) and 730 m (400 f m ) . I t i s l e s s s t e e p b e tw ee n 910 m and 1 ,8 3 0 m (500 fm to 1 ,0 0 0 f m ) , and a f u r t h e r s t e e p e n in g f r e q u e n t l y o c c u r s a t 3 ,3 00 m ( 1 ,8 0 0 f m ) . Buchanan s u g g e s t e d a " l a w " : th e s l o p e to th e e a s t s i d e of th e p r i n c i p a l p o i n t s , on h e a d l a n d s , i s alw ays much s t e e p e r th a n t h a t on i t s w e s t s i d e . S h e l f b r e a k s f o r n i n e p r o f i l e s by A lle n and W e lls 290 291 (1 9 6 2 ), betw een a p p ro x im a te ly 3° 3 0 ’ E to 8° are shown in T ab le 14. Table 14. Depth of S h e lf Breaks o f f Niger D e l ta PROFILE NUMBER APPROXIMATE LONGITUDE DEPTH OF SHELF BREAK (m) 1 3° 2 7 ’ E 166 2 4° 36* 134 3 5° 14 ’ 134 4 5° 33 ’ 117 5 5° 5 0 ’ 146 6 6° 2 7 ’ 200 7 7° 6 ’ 137 8 7° 3 4 ’ 137 9 7° 5 9 ’ 110 Bottom M a t e r i a l s A ccording to A lla n (1 9 64 ), th e open s h e l f o f f the N ig er D e l ta , e x te n d in g from the 41-m c o n to u r to the s h e l f edge, i s p re d o m in a n tly c la y and s i l t . N o n - d e p o s itio n e n v iro n m e n ts of Holocene age e x i s t on the o u t e r s h e l f . Slope d e p o s i t s are alm ost e x c l u s i v e l y g r a y i s h g re e n , anim al d i s t u r b e d , s i l t y c l a y s . At one s t a t i o n a mass of s h e l l y q u a r t z sand was r e t r i e v e d from a d e p th of 468 m. A lle n s u g g e s t s t h a t t h i s d e p o s i t may have s l i d down th e s lo p e from a n o n - d e p o s i t i o n a l environm ent a t th e edge of the 292 s h e l f . A llen and W ells (1962) d e s c r i b e d narrow l i n e a r dead c o r a l ban ks, m a s s i f s , or t h i c k e t s on th e s h e l f to d e p th s of 88 m. The c o i a l s a re n o n - r e e f forms and l i e on the upper s u r f a c e of o l d e r sa n d s. Some of the banks are p a r t l y or w h o lly b u rie d by younger s i l t s and c l a y s . S im ila r c o r a l banks, or t h i c k e t s , are known from the e a s t e r n A t l a n t i c , from Norway ( T e i c h e r t , 1958), where th e y occur as f a r n o r th as 70°, and range in d ep th from 200 m to 300 m. They a ls o have been d e s c r i b e d o f f I r e l a n d so u th to the Bay of B isc a y , where they have been dredged a t 180 m to 200 m. S m a lle r p a tc h e s o f f I r e l a n d occur a t 200 m to 450 m, and a few at 1,200 m. I t i s presumed t h a t s i m i l a r c o r a l bank s are con- tin u o u s from I r e l a n d along the P o r tu g u e s e Coast to Morocco. Off th e l a t t e r re g io n th ey have been re c o v e re d from 110 m to 112 m, and 600 m to 1,500 m. In a d d i t i o n , s i m i l a r c o r a l banks have been d e s c r i b e d by Ludwick and Walton (1957) from the Gulf of Mexico a t d e p th s of 83 m to 137 m. Moore and B u l l i s (1960) a ls o d e s c r i b e d s i m i l a r banks a t 450 m to 550 m on the c o n t i n e n t a l slo p e in th e G ulf of Mexico, t h u s , such c o r a l t h i c k e t s on banks are r a t h e r w id e s p re a d . A llen and W ells b e l i e v e th e Niger D e l ta c o r a l banks were formed d u r in g a low sta n d in se a l e v e l ending about 3,900 y e a r s ago. These p r o f i l e s reach on ly to about 1,000 m so many of th e more im p o rta n t f e a t u r e s are m is s i n g . The upper c o n t i n e n t a l s lo p e i s broken by a number of s t e p s or t e r r a c e s bu t few can be c o r r e l a t e d . T e r r a c e s on the c o n t i n e n t a l s h e l f a re obv iou s on s e v e r a l p r o f i l e s . On a t l e a s t t h r e e p r o f i l e s ( 3 , 7, and 8) a t e r r a c e o c c u rs a t about 330 m. Geology S la n sk y (1958) showed t h a t in the r e g i o n of Dahomey and Togo the se d im e n ta ry b a s i n and basem ent c o n s i s t of a s e r i e s of seaw ard d ip p in g r o c k s , much l i k e t h e s e in th e G u lf C oast r e g i o n of t h e U nited S t a t e s . T h is r e g i o n in the G ulf of Guinea i s t h e r e f o r e c o n s i d e r e d a m a r g in a l f l e x u r e o f g r e a t age. A llen (1964) and A lle n and W ells (1962) a ls o showed t h a t th e Niger D e l t a has been the s i t e of sed im en t a c c u m u la tio n s i n c e th e C r e ta c e o u s p e r i o d . Loading h as r e s u l t e d in a downwarp a t th e c o n t i n e n t a l m argin . SOUTHWEST AFRICA I n t r o d u c t io n P r o f i l e s o f f th e s o u t h w e s t c o a s t o f A f r i c a ( P l a t e 34) were made by CRAWFORD and ATLANTIS o f Woods Hole O ceano g r a p h i c I n s t i t u t i o n and by th e OB. Sound v e l o c i t y c o r r e c t i o n s have b e en made on th e CRAWFORD and ATLANTIS p r o f i l e s . I t i s n o t known w h e th e r s lo p e c o r r e c t i o n s or sound v e l o c i t y c o r r e c t i o n have been a p p l i e d to the R u s s ia n (OB) p r o f i l e s . A ll p r o f i l e s have been r e c o n s t r u c t e d and a re n o t d i r e c t t r a c i n g s of echogram s. Because of th e s m a ll number o f p r o f i l e s a v a i l a b l e ( a c t u a l l y c o v e r in g o n ly f i v e a r e a s ) , r e s u l t s a re somewhat i n c o n c l u s i v e . R e s u l t s The s h e l f b re a k a lo n g t h e s o u t h w e s t e r n A f r i c a n c o a s t i s much d e e p e r th a n th e n o r t h w e s t e r n A f r i c a n c o a s t . The a p p ro x im a te s h e l f b r e a k s from n o r t h to s o u th a re shown in T ab le 15. Over most of t h i s p a r t o f A f r i c a , th e s h e l f b re a k i s 300-m to 400-m i n d e p t h , or a b o u t the same d e p th as A n t a r c t i c a or n o r t h w e s t e r n A u s t r a l i a , two a r e a s h a v in g th e d e e p e s t known s h e l v e s . 294 295 T able 15. C o n t i n e n t a l Slope G r a d ie n ts and Depth of S h e l f Breaks o f f S o u th w e ste rn A f r i c a GRADIENT CONTI NENTAL SLOPE Upper _ Lower DEPTH OF SHELF BREAK (m) Gabon 2° 0 .3 ° 200 Angola ( N o rth e rn ) 5° 0 .1 ° 400 Angola ( S o u th e rn ) 4° 0 .3 ° -------------- South West A f r i c a 2° o • o 300 - 350 Cape of Good Hope 5° 0 .1 ° 350 P r o f i l e s o f f Capetown appear to be somewhat d i f f e r e n t from th o se f u r t h e r n o r t h . A d i s t i n c t f l a t a r e a i s v i s i b l e a t 2,200 m on a p r o f i l e made by the OB (OB 1-3) and i s v i s i b l e as a minor f e a t u r e on A 247-7, b u t i s m issin g on C 247-8. OB 5 7 /8 -3 t r a v e r s e s th e c o n t i n e n t a l slo p e a t an an g le so t h a t c a u t i o n must be e x e r c i s e d in u s in g t h i s fo r c o n c lu s iv e e v id e n c e ; n e v e r t h e l e s s , t h i s p r o f i l e i s u s e f u l f o r i t shows the c o n t i n e n t a l slo p e h ere l a c k s canyons. More s i g n i f i c a n t t e r r a c e s app ear a t 2,000 m, 2,300 m to 2,800 m, 3,000 m to 3,200 m, and 3,800 m to 4,200 m. F u r t h e r , i t shows a wide f l a t a re a a t 500 m. P r o f i l e C 247-8 shows a f l a t t e r r a c e a t 4,200 m to 3,200 m, b u t o t h e r p r o f i l e s seem to i n d i c a t e t h a t t h i s i s the d e p th where the c o n t i n e n t a l slo p e and c o n t i n e n t a l r i s e m e e t. 296 A l a r g e (200 km t o 500 km), dome-shaped f e a t u r e a t a d e p th of 1,000 m to 2,000 m p r o t r u d e s o f f the s o u t h e r n t i p o f Capetown (OB 5 7 / 8 - 4 , and OB 1 - 4 ) . A r i d g e l i e s a t the b ase o f t h i s dome-shaped f e a t u r e a t a d e p th of a p p r o x im a te l y 4 ,0 0 0 m. A p u b l i s h e d p r o f i l e by Needham (1962) a c r o s s the c o n t i n e n t a l t e r r a c e at a p o s i t i o n a p p r o x im a te ly where the words "Cape o f Good Hope" appear on the in d e x map o f P l a t e BB i s e x c e p t i o n a l l y smooth and u n l i k e A 247-7 or the o t h e r p r o f i l e s to the s o u th . Needham’ s p r o f i l e shows a s l i g h t d e c r e a s e on th e slo p e g r a d i e n t a t about 1,7 00 m and f u r t h e r d e c r e a s e in g r a d i e n t n e a r th e b a se of t h e c o n t i n e n t a l s l o p e . Com parison of C o n t i n e n t a l T e r r a c e of West C o a st of A f r i c a Even though so u th w est A f r i c a has few er r e p r e s e n t a t i v e p r o f i l e s , i t a p p e a rs t h a t m ajor d i f f e r e n c e s e x i s t between t h i s re g io n and n o r t h w e s t A f r i c a (T ab le 1 6 ). G e n e r a l l y , th e c o n t i n e n t a l s lo p e i s n o t a smooth, con t i n u o u s p r o f i l e t h a t i s so c h a r a c t e r i s t i c of th e e a s t c o a s t o f t h e U n ited S t a t e s . I t c o n s i s t s of one or more s t e p s (C 57-4 and OB 2-3 ) or r i d g e s (C 60 -2, A 247-10, C 6 0 - 4 ) . The o n ly smooth c o n t i n e n t a l slo p e i s o f f W alvis Bay (A 2 4 7 - 9 ) , b u t a d j a c e n t p r o f i l e s show r i d g e s (o r l e s s l i k e l y , i s o l a t e d v o l c a n i c p e a k s ) . P r o f i l e A 247-10 p r o b a b l y c u t s a c r o s s W alvis R idg e, w h i l e A 247-9 i s to th e s o u th of 297 the r i d g e . Where r i d g e s or i s o l a t e d peak s o c c u r , such as on A 247-10 and C 6 0 -4 , th e convex shape of th e c o n t i n e n t a l s l o p e , i n c l u d i n g the c o n t i n e n t a l r i s e , has an u n i n t e r r u p t e d slo p e on b o th s i d e s of the o b s t r u c t i o n . T h is s u g g e s t s t h a t the r i d g e s or peaks have had no d i r e c t i n f l u e n c e on th e c o n t i n e n t a l slo p e and a re s e c o n d a ry f e a t u r e s . T able 16. Comparison o f C o n t i n e n t a l T e r r a c e s o f f West C oast of A f r i c a . N orthw est A f r i c a S outhw est A f r i c a Normal s h e l f b re a k a t 90 m Deep s h e l f b re a k - 200 m to to 145 m 400 m Upper c o n t i n e n t a l s lo p e has Lower c o n t i n e n t a l s lo p e has g e n t l e r g r a d i e n t s t e e p e r g r a d i e n t Lower c o n t i n e n t a l slo p e Lower c o n t i n e n t a l s lo p e 0 .3 ° to 1 .5 ° 0 . 1 ° to 0 .3 ° D i s t i n c t t e r r a c e s a t Few t e r r a c e s , not d i s t i n c t s e v e r a l d e p th s or w id e sp re a d Pronounced t e r r a c e a t T e r r a c e s a t 3,000 m to 3,800 3,000 m m r e c o g n iz e d on most p r o f i l e s T e rra c e a t 500 m T e rr a c e a t 500 m a b s e n t b u t s h e l f b re a k a t 200 m to 400 m T e r ra c e a t 1,000 m to T e r ra c e a t 1,0 00 m o n ly a t 1,400 m Cape Town S e i s m i c a l l y a c t i v e S e i s m i c a l l y a c t i v e C o a s ta l f a u l t i n g C o a s t a l f a u l t i n g Submarine canyons do not appear t o be p a r t i c u l a r l y dense alo n g t h i s p a r t of the c o a s t , a lth o u g h th e y 298 u n q u e s t i o n a b l y o c c u r . In f a c t , th e Congo i s one o f the most famous su b m a rin e c a n y o n s . The most p ron ou nced f e a t u r e a lo n g t h e c o n t i n e n t a l s l o p e i s l o c a t e d a t 3,0 0 0 m to 3,8 0 0 m, a v e r a g i n g a b o u t 3.200 m. I t t a k e s s e v e r a l fo rm s : o f f Gabon i t c o n s i s t s o f a s t e p w i t h a r i d g e ( o r p e a k ) a t i t s o u t e r e d g e ; o f f n o r t h e rn A ngola i t c o n s i s t s o f i r r e g u l a r to p o g r a p h y be tw ee n 2 .2 0 0 m to a b o u t 3,000 m where th e s lo p e t e r m i n a t e s i n a s t e e p ( 4 ° ) d e c l i v i t y ; f u r t h e r s o u t h i t c o n s i s t s of a d i s t i n c t t e r r a c e , t o 300 km w id e ; or t h e f e a t u r e may be n o t h ing more th a n a change i n s l o p e g r a d i e n t (OB 2 - 3 ) . I f th e same f e a t u r e o c c u r s o f f C apetow n, and i s c o r r e l a t i v e w i t h the p r o f i l e s to th e n o r t h , i t l i e s a t a d e p t h o f 4 ,0 0 0 m or m ore. From Gabon (C 6 0 -2 ) to the n o r t h of W a lv is Bay, a s lo p e change o c c u r s a t a b o u t 2,200 m, r e s u l t i n g in a d e c r e a s e i n g r a d i e n t , and g e n e r a l l y i s a s s o c i a t e d w i t h th e 3,000 m to 3,800 m f e a t u r e . Off th e Congo, th e c o n t i n e n t a l s l o p e r a r e l y e x c e e d s Geology Major f a u l t s alo n g th e c o a s t have b e en r e p o r t e d , i n c l u d i n g an e a s t - w e s t f a u l t from L i b e r i a t o N i g e r i a ; from B r a z z a v i l l e , Congo to m id -A n g o la ; a c r o s s the e n t i r e c o a s t o f S o uth West A f r i c a ; and a c r o s s t h e s o u t h e r n c o a s t of Un io n of S o u th A f r i c a ( F i g u r e s 41 and 4 4 ) . Most o f th e c o a s t 2 9 9 W O 2 0 0 9 0 9 * 0 0 S Q O k m Zppj fonttm W o r m b o d W m Grocttbntein f r a n t f o k t ti o O t k MM I 0/»w /*uri/ a k w e h a fo n d . Q r n c t f o n f f t 1 I S /b n th iN t G ‘ detschuonafaridi Meftktnq Mbobont Bfthj/htn K u t ' S X R j A m r M o f n * i i i i i fhetretkf* Vryheui Ladysmith Kurv/non Kroonstod oik fonttir Ktm toerky "ULn,, B I orond ft lubruche P /ffsk a D u r b a n '- Kokstod G a r e i s M il + Middtlburgh 1111 G m a f f te in e f Viktona West Port."St. J o h n — ,— — _ ; •;.v : ;';vv:; Jo A&e-Bruih 1 1 1 nop-orutn ' I l x ^ t o o ? ctiiobfth Dtarb A S/eberg F ig u r e 44. E a r th q u a k e a c t i v i t y in S outh A f r i c a . See c a p t i o n f o r F ig u re C f o r k e y . S t i p p l e d a r e a s o f f s h o r e a re subm arine banks and r i d g e s . ( A f t e r A. S i e b e r g , 1 9 3 2 .) 300 s t r e t c h i n g from L i b e r i a to th e Union of South A f r i c a i s s e i s m i c a l l y a c t i v e (F ig u r e s 43 and 4 4 ). Krige (1926) p o in te d out t h a t i n t e r m i t t e n t emergence has a f f e c t e d A f r i c a s in c e e a r l y T e r t i a r y tim e s . The e v i dence c o n s i s t s of e x te n s i v e u p l i f t e d m arine t e r r a c e s a t 1,200 m, 750 m, and 300 m to 250 m, as w e l l as l e s s p r o nounced t e r r a c e s a t 140 m to 110 m and 75 m to 50 m. The l a s t th r e e t e r r a c e s are covered in p a r t by m arine Mio- P lio c e n e se d im e n t. In a d d i t i o n , he c o n s i d e r s the emergence was s u f f i c i e n t to expose Agulhas Bank in whole or in p a r t (betw een Cape Town and P o r t E l i z a b e t h ) ; p o s s i b l y th e 400- fathom (720 m) i s o b a th c o n s t i t u t e d the c o a s t l i n e . Krige b e li e v e d the emergence must have o c c u rre d between l a t e T e r t i a r y and l a t e P l e i s t o c e n e , f o r drowned r i v e r e s t u a r i e s are f i l l e d w ith P l e i s t o c e n e or Recent d e p o s i t s . Emergence has a ls o l e f t s t r a n d marks and r i v e r t e r r a c e s a t 15 m to 18 m and 6 m. Dixey (1928) a ls o concluded t h a t r a t h e r r e c e n t g e o lo g i c a l movement has g r e a t l y a f f e c t e d v a r io u s p a r t s of the w est c o a s t of A f r i c a , and S i e r r a Leone, in p a r t i c u l a r . He s a i d : An u p l i f t , p r o b a b ly P l e i s t o c e n e , i s i n d i c a t e d in S i e r r a Leone by the c o a s t a l p l a i n , the smooth c u rv e s of the c o a s t , and th e r e j u v e n a t i o n of the r i v e r s . The u p l i f t was prec ed e d by a deep submergence, d u r in g which a wide p la t f o r m was c u t i n t o the m ountain p a s s . R e ju v e n a tio n of the r i v e r s i s shown in the gorges they have cut i n t o the c o a s t a l p l a i n , and on t h e i r rocky beds above the g o rg e s . The g o rg e s are an 301 i m p o r t a n t f e a t u r e in the s c e n e r y of the Colony; most o f them c u t o n ly P l e i s t o c e n e b e d s , b u t some expose th e u n d e r l y i n g n o r i t e . The c o a s t a l p l a i n i s more o r l e s s c o n tin u o u s a l l around the C olony. . . . below s e a l e v e l in t h e F r e e town a r e a i s a t h i c k developm ent of c l a y s . .' . . A s e r i e s of r a i s e d ben ch es can be t r a c e d . . . . frojn 35 f e e t to 325 f e e t above s e a l e v e l . A l l e x ce p t th e o l d e s t i n d i c a t e only b r i e f p a u se s i n the u p l i f t . South A f r i c a has no t been invaded by the s e a e x c e p t on i t s f r i n g e s s i n c e e a r l y J u r a s s i c tim e . The la n d s c a p e has r e s u l t e d from e r o s i o n d u r in g s i x m ajor p e r i o d s of e r o s i o n and d e p o s i t i o n . Each c y c le was f o llo w e d by u p l i f t and w arping (L. C. King, 1955; D ixey, 1956i; and B a i l e y , 1964). M ajor s c a r p s 300 m or more i n h e i g h t a t t e s t to u p l i f t and e r o s i o n on the s o u t h , w e s t, and e a s t c o a s t s of South A f r i c a ( F i g u r e 4 5 ) . The e a r l i e s t s u r f a c e i s Gondwana of J u r a s s i c and e a r l y C r e ta c e o u s age. A c co rd in g to King ( 1 9 5 3 ) , p r e - Gondwana la n d s c a p e was covered by enormous b a s a l t i c flow s in th e T r i a s s i c p e r i o d . These flo w s o c c u r r e d i n the P a ra n a B a s in of S outh Am erica, the K a o k o v e ld , and the D ra k e n s b e rg , e x te n d in g to the Lehombo in th e e a s t and p r o b a b ly to Queen Maud Land in th e A n t a r c t i c . E r o s i o n s t a r t e d on t h i s d u rin g th e J u r a s s i c , c o n ti n u i n g i n t o e a r l y C r e ta c e o u s tim e . The Gondwana s u r f a c e ex te n d ed f a r to s e a from a l l s o u t h e r n co n t i n e n t s s i n c e th e Gondwana la n d s c a p e i s s t r o n g l y warped down at the c o n t i n e n t a l m a r g in s , d i s a p p e a r i n g b e n e a th more r e c e n t m arine s e d im e n ts in the A t l a n t i c and In d ia n O ceans. King ( 1 9 5 0 ) ‘s t a t e d t h a t t h i s s u r f a c e has been i d e n t i f i e d in 302 I’ OST.G O ND W A NA W NDSCAPF. j (Uld-CraUcaoua) G O N D W A N A LANDSCAPE (Juraaalc and Early C A N D POST - G O N D W A N A (Mld-Cratac. VICTOR* FALLS CYCLE (Uld-TarUary) . ,A FK tCA N CYCLE (Early Tartiaryt CONTINENTAL TERRACE F ig u re 45. A t t i t u d e of c y c l i c e r o s i o n a l land s u r f a c e s in s o u th e rn A f r i c a . A t l a n t i c Ocean on l e f t and In d ian Ocean on r i g h t s id e of i l l u s t r a t i o n . (M odified A f t e r L. C. King, 1956.) 303 South America, A f r i c a , I n d i a , and A u s t r a l i a . C o n t in e n t a l beds of C retaceou s age are w id e sp rea d . In m id -C retaceou s tim e, the lan d scap e stood a t an e l e v a t i o n of about 600 m, a t which p e rio d an a b ru p t m o n o c lin a lly upward t i l t o ccurred along the c o a s t s r e s u l t i n g in a new c y c le of e r o s i o n . Maximum u p l i f t was p e r i p h e r a l to th e c o a s t s 160 m to 240 m in la n d with the s u r f a c e slo p in g from t h i s zone seaward on one s id e and towards a c e n t r a l c o n t i n e n t a l d e p r e s s i o n on the o t h e r . One hundred m eters of Senonian- Eocene age marine sed im ents were d e p o s i te d on the seaward downwarped p l a n e . In l a t e C re ta ce o u s time a new e r o s i o n c y cle was i n i t i a t e d . T h is c y c l e , as w e ll as a l l su bsequ ent c y c l e s , follow ed the f i r s t c y c le of p e r i p h e r a l u p l i f t 160 km to 240 km from the c o a s t (F ig u re 4 5 ). Q u a te rn a ry move ments are a ls o e v id e n t. These e v e n ts have r e s u l t e d in heavy lo a d in g o f f s h o r e by the d e p o s i ti o n of sedim ents eroded in the re g io n between the zone of a rc h in g and the se a w h ile the i n t e r i o r re g io n has s u f f e r e d r e l a t i v e l i g h t d e n u d a tio n and s l i g h t l o a d in g . Hence, i s o s t a t i c resp on se has been g r e a t e s t in the c o a s t a l r e g i o n , w ith la r g e u p l i f t s landward and d e p r e s s io n some d i s t a n c e seaward. The zone arched must be a t l e a s t 400 km wide. The- t o t a l w id th of i s o s t a t i c rebound i s e s tim a te d a t 550 km by King (1956) and 890 km by Gunn (1 9 49 ). King (1956) s t a t e d i s o s t a t i c re c o v e ry was e s t a b l i s h e d a f t e r each e r o s i o n a l p h a se: a t the Gondwana ( e a r l i e s t 304 C r e t a c e o u s ) , post-Gondwana ( l a t e C r e t a c e o u s ) , A f r i c a n ( l a t e O l i g o c e n e ) , and V i c t o r i a F a l l s ( e a r l y P l i o c e n e ) . No marked r e c o v e r y i s y e t e v i d e n t s in c e the Congo c y c l e ( P l e i s t o c e n e e p o c h ) . The h i n g e - l i n e o f u p l i f t moved p r o g r e s s i v e l y seaward w ith each su c c e e d in g c y c le because s e d im e n ts were d e p o s i t e d beyond the c o n t i n e n t a l t e r r a c e . A g r e a t escarpm ent about 200 km i n l a n d on the s o u t h e r n (Cape R egion) and e a s t c o a s t s of South A f r i c a , c o r r e s p o n d ing to th e r e g i o n of a r c h i n g , has been s t u d i e d by H a le s and Gough (1959 and 1960). G r a v it y m easurem ents from th e c o a s t i n la n d a c r o s s t h i s e sca rp m en t show an 80-mgal anomaly in the v i c i n i t y of th e e s c a r p m e n t. A b e l t of p o s i t i v e anoma l i e s o c c u rs i n l a n d , and i t i s s t r o n g l y s u g g e s te d t h a t p o s i t i v e a n o m a lie s occur seaw ard . The a u t h o r s b e l i e v e t h a t the s tr o n g n e g a t i v e anomaly r e p r e s e n t s t h e g r a v i t y a f f e c t of the c o m p en satio n of th e to p o grap hy removed by e r o s i o n . In any e v e n t , the r e g i o n shows s t r o n g e v id e n c e of u p t h r u s t , as a l r e a d y p o i n te d out by King. Brock (1955) has a l s o p o i n te d out the p r i n c i p a l mode of d e fo r m a ti o n in A f r i c a in v o lv e s n e a r l y v e r t i c a l f r a c t u r e s . H a les and Gough b e l i e v e t h a t th e b e l t s of p o s i t i v e anomaly are i n d i c a t i v e of a more or l e s s e l a s t i c upw arping o f th e c r u s t caused by p e r i p h e r a l u p t h r u s t i n g . The seaward b e l t of p o s i t i v e an o m alies o f f s h o r e may be e x p la in e d in p a r t by d e p o s i t i o n of s e d im e n ts o f f s h o r e b u t t h e explanation 305 i s not v a l i d fo r the p o s i t i v e anom alies landward of the e s carpm ent. Bottom M a t e r i a l s Needham (1962) c o l l e c t e d more than 900 ro ck s and f r a g ments from th e se a f l o o r o f f Cape of Good Hope. The l a r g e s t rock r e t r i e v e d weighed 2,270 kg (from 342 m ), w hile the rem ainder ranged in w eight from about 57 kg to l e s s than one gram, and were c o l l e c t e d a t d e p th s of 3,000 m to 3,300 m ( a p p r o x im a te ly ) . Needham c o n sid e re d th e rocks r e m arkable fo r t h e i r abundance and l i t h o l o g i c a l v a r i a t i o n . Although he did n ot make l i t h o l o g i c a l com parisons of v a r i ous sou rce a r e a s , he concluded t h a t the rocks are e r r a t i c s r a f t e d from A n t a r c t i c a . In a d d it i o n to ro c k s , pumice and more than 500 c e ta c e a n e a rb o n e s, some h e a v i l y e n c r u s te d w ith manganese, were a ls o c o l l e c t e d w ith ro c k s . Some rock specimens are n oted fo r t h e i r n e ar p e r f e c t ro u n d in g . Some g l a c i a l f a c e t t i n g ( f l a t t e n e d ) o c c u r s , but s t r i a t i o n s are n o t too co n sp icu o u s. C o n sid e rin g the d i s t r i b u t i o n of s i m i l a r d e p o s i t s e l s e where where g l a c i a t i o n a n d /o r ic e r a f t i n g did no t o c c u r, Needham’s h y p o th e s is of an A n t a r c t i c source may or may not be v a l i d . I t must be concluded t h a t the o r i g i n of such d e p o s i t s i s s t i l l p r o b le m a tic , but evidence s u g g e s ts t h a t c o n t i n e n t a l warping and f a u l t i n g may be a more l o g i c a l ex p l a n a t i o n . S t u d i e s by American, Ja p a n e se , R u ssian , and / 306 F re n c h g e o l o g i s t s have shown t h a t such d e p o s i t s a re by no means r a r e or u n i q u e . For e x am p le , B o u r c a r t (1 9 3 8 ) r e p o r t e d w e l l - r o u n d e d b o u l d e r s , a s l a r g e as 50 cm to 60 cm, o r i e n t e d in g r a v e l s t r i p e s p a r a l l e l t o th e c o a s t to d e p t h s as g r e a t as 400 m. These were n o t l o c a t e d where p r e s e n t day r i v e r s co u ld t r a n s p o r t and d e p o s i t them in such a f a s h i o n , n o r c o u ld th ey be a t t r i b u t e d to ic e r a f t i n g . S e v e r a l m a rin e g e o l o g i s t s have s t u d i e d s e d i m e n ts o f f l a r g e r i v e r s , s u c h as the Congo, w here c a b l e s have b ro k e n as a r e s u l t of a l l e g e d t u r b i d i t y c u r r e n t s . S in c e t r a n s p o r t a t i o n and d e p o s i t i o n i s c l o s e l y r e l a t e d to th e r i v e r s , n o t h i n g a p p e a r s to be u s e f u l to the p r e s e n t i n v e s t i g a t i o n . The r a t h e r p e c u l i a r - s h a p e d dome o f f Capetown a p p e a r s to be a seaw ard c o n t i n u a t i o n of the s o - c a l l e d " e p s i l o n " s t r u c t u r e of Brock ( 1 9 5 5 ) . In t h i s r e g i o n Cape Younger g r a n i t e s , C e d e rb e rg T r e n d s , N o r t h - e a s t e r l y T r e n d s , and Cape F o l d i n g j o i n . Major f a u l t s a r e l a r g e l y p a r a l l e l to s h o r e , a lt h o u g h n e a r th e c o a s t , i n t h e n o r t h - e a s t e r l y T r e n d s , and a re p e r p e n d i c u l a r t o th e c o a s t . S ince t h e tim e when c o n t i n e n t a l d r i f t was f i r s t p r o p o s e d , o p p o n e n ts to t h i s t h e o r y have d isa v o w ed th e e x i s t ence of ah a l l e g e d f i t of S o u th A m erica i n t o t h e a n g le of A f r i c a . J e f f r e y s (1 9 2 9 ) in p a r t i c u l a r h a s s t a t e d th e m i s f i t i s a b o u t 15° and t h a t th e c o a s t s of S o u th A m erica and S outh A f r i c a c a n n o t be b r o u g h t w i t h i n h u n d re d s of k i l o m e t e r s o f e a c h o t h e r w i t h o u t d i s t o r t i o n . L ee s (1 9 5 3 ) a l s o 307 l i s t e d t h i s as an o b j e c t i o n to c o n t i n e n t a l d r i f t . C arey (1955a and 1959) has shown t h a t when the 2,000-m i s o b a t h is used the f i t i s almost p e r f e c t . An o v e r la p o c cu rs a t the N iger d e l t a b u t t h i s can be e x p la in e d by d e l t a f o r m a t io n . The 2,000-m i s o b a t h i s about h a l f way down the c o n t i n e n t a l s l o p e , and g e n e r a l l y s p e a k in g , n o th in g o u t s t a n d i n g ap p ea rs a t t h i s d e p th along most of the c o n t i n e n t a l slo p e of South A f r i c a . The Congo River h a s c u t a ch an nel th ro u g h s o f t C r e t a ceous and T e r t i a r y s e d im e n ts on th e c o a s t a l p l a i n to a max imum depth of about 1,650 m and a w id th of 26 km. V eatch and Smith (1939) s t a t e d t h a t at l e a s t two s t a g e s of e r o s i o n occur in th e re g io n : one i s p o st-M iocen e or even l a t e P l i o c e n e or e a r l y P l e i s t o c e n e , and the o th e r i s Recent in age. They b e l i e v e t h a t the ev id e n ce i n d i c a t e s a r e l a t i v e low ering of se a l e v e l , r a t h e r than a l o c a l e l e v a t i o n of the l a n d . I f so , they h y p o th e s iz e a sea l e v e l lo w e rin g of about 3,300 m. Veatch (1935) r e p o r t e d t h a t over 3,000 m of T e r t i a r y and l a t e C re ta ce o u s age se d im e n ts r e s t on a seaward s lo p in g p e n ep lan e c u t in m id -C re ta c eo u s tim e . "The p r e s e n t Congo h y d ro g ra p h ic b a s i n i s e n t i r e l y post-M iocene and owes i t s o r i g i n to the u p l i f t and w arping of the Miocene P e n e p l a i n . " R i f t f a u l t i n g o c cu rred in l a t e T e r t i a r y a n d /o r P l e i s t o c e n e time . Agulhas Bank, o f f the t i p of South A f r i c a , has been 308 d e s c r i b e d by W e llin g to n (1 9 5 5 ) . He r e p o r t e d t h a t i t c o n s i s t s e s s e n t i a l l y of b e v e le d Cape System f o l d s of P a l e o z o i c age, and i s o v e r l a i n w ith T "T ertiary and R ecent s e d im e n ts . W e llin g to n s u g g e s te d t h a t the bank may have b e en a f f e c t e d to some e x t e n t by t e c t o n i c f o r c e s t h a t t h r u s t i n la n d from the s e a . 0 EASTERN CANADA I n t r o d u c t ion So f a r as i s known, th e e a s t c o a s t of Canada has no t been su rv e y ed u s in g modern e c h o so u n d in g eq u ip m en t. The few p r o f i l e s o f f B a f f i n I s l a n d a re th o s e made by th e U. S. C oast Guard ( B u l l . No. 19) ( P l a t e 4 4 ) . F u r t h e r s o u t h , from L a b ra d o r to Nova S c o t i a , th e f o l lo w in g p r o f i l e s a re a v a i l a b l e : H eezen, T h arp, and Ewing (1959) (marked H ), B r i t i s h I n s t i t u t e of O ceanography ( p r o f i l e D ) , and R u ss ia n e x p e d i t i o n p r o f i l e s l a b e l e d L ( P l a t e 3 5 ). U l r i c h made f i v e p r o f i l e s o f f F le m is h Cap a v a i l a b l e . H eezen, T h a r p , and Ewing (1959) have d e s c r i b e d th e p r o f i l e s so u th of Newfoundland th e th e g e o lo g y and g e o p h y s i c a l s t r u c t u r e have been d i s c u s s e d in in n u m e ra b le p a p e r s . R e s u I t s P r o f i l e s a c r o s s D a v is S t r a i t r e v e a l b o th U -shaped and V -shaped c r o s s - s e c t i o n s ( P l a t e 44, 1, 2, 4 and 5 ) . The s h e l f b re a k i s p o o r l y d e f i n e d b e c a u se o f th e c o n s t r u c t e d p r o f i l e s ; s e v e r a l p r o f i l e s show s h e l f b r e a k s a t l e s s th a n 100 m compared to the much d e e p e r s h e l f b r e a k s o f f G r e e n land . No m oats a re v i s i b l e on t h e s e p r o f i l e s . 309 310 T able 17. Approxim ate S h e l f B r e a k s -- E a s t C oast Canada GENERAL AREA SHELF BREAK* (m) r 2 140 3 400 B a f f i n I s l a n d < 4 100 H 200 m I 340 R e s o l u t i o n I s l a n d ^ 570 ’K 220 L 180 L a b ra d o r < M 260 -N 280 *D 290 . L -2 -7 350 P 240 Q 300 ? H -l 275 R 300 H-2 270 Newfoundland and J S 200 Grand Banks ' T 120 L -2 -6 270 H- 3 110 U 100 V 40 ? H-4 90 W 70 H-5 90 X * 100 ""H-7 144 H-8 91 Nova S c o t i a < H-9 110 H-10 128 H - l l 205 L -2 -4 400 10 350 F lem ish Cap < 11 300 [L -2 -5 200 * S h e l f b re a k h e r e may or may n o t be r e a l b e c a u s e of m o a ts. Some o f th e d e e p e r b r e a k s i n s lo p e a re the seaw ard and d e e p e s t p a r t s of i r r e g u l a r c o a s t a l to p o g r a p h y . See p l a t e s 44 and 35 f o r l o c a t i o n s . 311 A • S I T U A T I O N n o 3 5 0 * N / N E W F O U N D L A N D • FAULT LINES ( M o ifi/ o tto r d m g le Frcto/w c Mop * t C onw fa) ■ INFERRED (rr-a/tr) FAULT ZONES •n ttit t / t t l f a r t* ig u r e 46. Trough and d e p r e s s i o n s along th e L a b ra d o r- ewfoundland C o a st, and i n f e r r e d f a u l t s . (A f te r H o l t e d a h l , 1958.) 312 F u r t h e r s o u t h , o f f L a b r a d o r, the s h e l f b r e a k i s h i g h l y v a r i a b l e (T a b le 1 7 ) . P ronounced m oats s i m i l a r to th o s e o f f G r e e n la n d , Norway, and A n t a r c t i c a ( H o l t e d a h l , 1958) o c c u r . Some of t h e s e t r o u g h s , p a r a l l e l to th e c o a s t , have a r e l i e f o f n e a r l y 750 m and commonly have a seaw ard s i l l a t a b o u t 200 m ( F i g u r e s 29 and 4 6 ) . The s h e l f has an a v erag e w id th o f 130 km o f f L ab rad or and i n c r e a s e s to 370 km o f f New fo u n d la n d . A l a r g e number o f p r o f i l e s have b e e n made a c r o s s Grand Banks ( P l a t e 44, p r o f i l e s Q to X; and P l a t e 3 5 ). The Grand Banks s h e l f v a r i e s in w id th from 220 km to 530 km ?nd has l o c a l r e l i e f o f 90 m t o 200 m. The s h e l f b r e a k s a re i n v a r i a b l y d e e p , of th e o rd e r of 200 m to 300 m (T ab le 1 7 ) . The c o n t i n e n t a l s lo p e has a g r a d i e n t of a b o u t 30° and i s s t e e p e r to the n o r t h . P r o f i l e s o f f N ew foundland and Nova S c o t i a t y p i c a l l y have a concave c o n t i n e n t a l s l o p e and a d i s t i n c t c o n t i n e n t a l r i s e . P r o f i l e s have many i r r e g u l a r i t i e s ; how e v e r , t h e s e do n o t ap p ea r to c o r r e l a t e from p r o f i l e t o p r o f i l e . Most p r o f i l e s show a marked b r e a k betw een 1,0 0 0 m and 2,000 m and some a r e wide ( P l a t e H -6 ). F le m ish Cap i s a dom e-shaped o u t l i e r e a s t o f Grand Banks ( P l a t e 3 5 ) . I t has a r e l a t i v e l y smooth s u r f a c e and a somewhat i n d i s t i n c t s h e l f b rea k a t 200 m to 400 m. The o u t l i e r has a more rounded u p p e r s h e l f b r e a k on i t s n o r t h e a s t e r n s i d e and h a s a more marked s h e l f b r e a k to w ard s the s o u t h e a s t . Between th e s h e l f b r e a k and a b o u t 900 m th e g r a d i e n t i s about 3°. Below 3,000 m th e g r a d i e n t d e c r e a s e s . P r o f i l e s 7, 8, and 9 ( P l a t e 35) show a sm all t r e n c h a t a b o u t 3,000 m a t the base of the c o n t i n e n t a l slo p e where i t j o i n s the c o n t i n e n t a l rim . O f f Nova S c o t i a th e upper c o n t i n e n t a l s lo p e has a g r a d i e n t of about 2° and a low er s lo p e g r a d i e n t of l e s s than 1 l / 2 ° . Many subm arine canyons a r e s u g g e s te d on th e p r o f i l e EAST COAST OF THE UNITED STATES I n t r o d u c t i o n L ik e th e s o u t h e r n C a l i f o r n i a r e g i o n , t h e E a s t C o a st of the U n ite d S t a t e s has been e x t e n s i v e l y s t u d i e d . Heezen, T h a rp , and Ewing (1959) have p u b l i s h e d many p r o f i l e s a c r o s s th e c o n t i n e n t a l s lo p e ( P l a t e 3 6 ) . A few a d d i t i o n a l p r o f i l e s have been added, s e v e r a l by Woods Hole (A and C p r o f i l e s ) and the B r i t i s h I n s t i t u t e o f O ceanography (D p r o f i l e ) . In a d d i t i o n , Jo rd a n h a s made s e v e r a l p r o f i l e s a t a l a r g e r s c a l e ( i n s e r t , P l a t e 3 6 ) . With t h e e x c e p t i o n o f J o r d a n ’ s p r o f i l e s , a l l o t h e r s a re r e c o n s t r u c t e d or a re d i r e c t t r a c i n g s of p r e c i s i o n e c h o s o u n d i n g s . S in c e t h i s r e g i o n has been t h o r o u g h l y d e s c r i b e d in th e l i t e r a t u r e , o n ly a few comments a re deemed n e c e s s a r y . R e s u l t s Heezen, e t a l . (1959) c l e a r l y r e c o g n i z e d the e x i s t e n c e o f d e ep t e r r a c e s along th e e a s t c o a s t ( F i g u r e 4 8 ) . ( S h a l low t e r r a c e s have long been known from v a r i o u s l o c a t i o n s on th e c o n t i n e n t a l s h e l f . ) Heezen, e t a l . (1 9 5 9 ) r e p o r t e d t h a t v a r i o u s b e n c h e s a lo n g th e c o n t i n e n t a l s l o p e a r e o u t c r o p s of 314 315 T e r t i a r y and C r e ta c e o u s age r o c k s w hich have a n o t i c e a b l e seaw ard d i p . T h is s u g g e s t s t h a t b e d s a r e t r u n c a t e d seaw ard and t h a t v a r i o u s age r e s i s t a n t r o c k s from n a t u r a l r e s i s t a n t b e n c h e s s e p a r a t e d by s c a r p s w here l e s s r e s i s t a n t ro ck have been w e a th e re d away. While much e v id e n c e was p r e s e n t e d to p ro v e t h i s c a s e , c o n t i n u o u s s e i s m i c p r o f i l e s in some e a s t c o a s t r e g i o n s have shown t h a t s t r a t a a re n o t t r u n c a t e d alo n g th e seaw ard edge as r e q u i r e d by the t h e o r y . An example o f such a p r o f i l e i s shown in F i g u r e 47. H e re , s u b s u r f a c e s t r a t a a re more or l e s s p a r a l l e l to t h e s e a f l o o r s u r f a c e . ( O b v i o u s l y , much a d d i t i o n a l s t u d y i s r e q u i r e d to b e t t e r d e f i n e and u n d e r s t a n d th e b e n ch e s and t e r r a c e s and w h e th e r th e y d o , in f a c t , r e p r e s e n t o u t c r o p s of T e r t i a r y and o l d e r s t r a t a . ) Moore and C u rra y (196 3b ) a l s o showed t h a t o f f N o r f o l k ” the s e d i m e n ta r y p r is m o f the c o n t i n e n t a l t e r r a c e i s se e n t o be d e p o s i t i o n a l in o r i g i n w i t h o u t b u i l d i n g or p r o g r a d i n g by s e d i m e n t a t i o n on the c o n t i n e n t a l s l o p e and r i s e , and u p b u i l d i n g by c o n t i n e n t a l s h e l f and p a r a l i c s e d i m e n t a t i o n . These t h i c k s e c t i o n s of s h e l f and p a r a l i c s e d i m e n ts r e q u i r e t h a t r e g i o n a l s u b s id e n c e of th e t e r r a c e h a s o c c u r r e d d u r i n g d e p o s i t i o n . ” An ESP p r o f i l e o f f Newport shows s e d i m e n t a r y ro c k u n i t s c ro p p in g o ut on th e u p p e r c o n t i n e n t a l s l o p e . T h is i s i n c o n t r a s t t o th e downbending of s t r a t a o f f N o r f o l k . The a u t h o r s b e l i e v e t h a t s l i d e s may d i s p l a c e l a r g e m asses down s l o p e . 316 A second a re a of i n t e r e s t i s the n a t u r e of the c o n t i n e n t a l m argin. G e o p h y sic a l, g e o l o g i c a l , and b a th y m e tr ic s t u d i e s along th e e a s t c o a s t have been t h o r o u g h ly i n v e s t i g a te d . A s e r i e s of se ism ic r e f r a c t i o n p r o f i l e s made by Ewing and a s s o c i a t e s may be i n t e r p r e t e d in s e v e r a l ways. Engelen (1963) has e x p erim en ted w ith the s e is m ic r e s u l t s and concluded t h a t the observed s t r u c t u r e can be e x p la in e d by a s e r i e s of f a u l t s along the c o n t i n e n t a l m argin ( F i g u r e s 49 and 50). I t i s obvious t h a t such f a u l t i n g could a ls o accou nt f o r the w id espread o c c u rre n c e of t e r r a c e s . Drake, Ewing, and S u tto n (1959) review ed the g e o p h y s i c a l s t r u c t u r e of the e a s t c o a s t and showed the p r e s e n c e of two se d im e n ta ry t r o u g h s , one under the s h e l f and th e o th e r in deep er w a ter n e a r the base of the c o n t i n e n t a l s l o p e . The s h e l f tro u g h has been d r i l l e d and c o n s i s t s of 5,185 m of se d im e n ts d e p o s i te d in s h a llo w w a te r . The d e e p e r w ater tro u g h has up to 9,100 m of s e d im e n ts , i s l o c a te d o f f Grand Banks, and t h i n s toward the ocean b a s i n . G i l l u l y (1964) has examined D rake, Ewing, and S u t t o n ’ s d a t a and c o n clu d ed : (1 ) N e arly a l l se d im e n ts in th e s e d e p r e s s i o n s a re T r i a s s i c and younger in age, or were d e p o s i t e d in the l a s t 225 m i l l i o n y e a r s , (2) The f a c t t h a t c o n t i n e n t a l c r u s t i s r e ta i n e d under th e b a s i n s goes f a r toward p ro v in g the r e a l i t y of a form er ’'A p p a la c h ia ." The s h e l f was emergent d u r in g P a l e o z o ic time and was a so u rc e f o r the A p p a la c h ia n geosyn- c l i n e , (3) Sedim ent a c c u m u la tio n on the s h e l f would not 317 d e p r e s s the s h e l f i s o s t a t i c a l l y b ecause of sedim ent lo a d - i n g ; some s u b c r u s t a l p r o c e s s must have b r o u g h t about the subm ergence. The s h e l f does n o t owe i t s o r i g i n p r i m a r i l y to su b sid e n c e under a load of sedim ent d is c h a r g e d from s h o r e . I s o s t a t i c a d ju s tm e n t s , t h e r e f o r e , are d i f f i c u l t to e x p l a i n , (4) For former A p p a la c h ia to have su b sid e d the s i a l i c c r u s t b en eath i t must have th in n e d and t h i s must have in v o lv e d a mass t r a n s f e r , not a ph ase change. S h e lf b re a k s along the e a s t c o a s t vary c o n s i d e r a b l y from about 45 m to 180 m (T able 1 8 ). Warping of th e c o n t i n e n t a l s h e l f margin was su g g e ste d by Veatch and Smith ( 1 9 3 9 ) . 318 Table 18. Approximate S h e l f Breaks E a s t Coast U nited S t a t e s SHELF BREAK (m) GENERAL AREA 10 8 Maine 180 H-12 C-16-1 110 135 H-13 A-247-16 130 M a s s a c h u s e tts and H-14 126 New York V and S 148 H-15 180 H-16 90 H-17 90 Vir g i n i a 10 8 H-18 135 H-20 90 N orth C a r o li n a H-21 45 H-22 South C a r o lin a H-23 72 72 H-24 72 F l o r i d a H-25 90 CONTINENTAL SLOPE CONTINENTAL SHELF 2 0 NAUTICAL MILES Figure / v . Continuous seismic p iofile along east coast of United States. S. T. Knott, Woods Hole Oceanogzaptic Institution) FATHOMS OFF CAPE HATTER AS OFF CAPE MAY 200 THENT 400 CASTLE HAYNE 600 800 1000 T u s c a l o o s a 1200 1400 Nautical Miles 25 20 1600 Figure 48. — Cor relation of structural benches off northeast United States (After H eezen.et al.. 1959) Soundings by Coast and Geodetic Survey; 35° 30 ’N. — 38° 30 ’N 3 2 0 321 67 FATHOMS^___________________ 15 NAUTICAL MILES 2600 2700 2600 LOWER CONTINENTAL HILLS. (FIG. 4, PL. 3. HEEZEN ET A l.1959) INTERPRETED AS BLOCK FAULTED TOPOGRAPHY. J O _I2 CO L l8 KILOMETERS W 25 "4 K I I Figure 49. I n t e r p r e t a t i o n o f s e is m ic r e s u l t s by Heezen, Tharp, and Ewing, e t a l.. 1959. (A fte r E n gelen , 1 9 6 3 .) 322 NAUTICAL MILES h i iiiS j W 6 i ll! in; iiliiiiin iii rSf I K S SStSS •S]i<<«<I<I W 16 .10 u _22 KILOMETERS ' \ ^ ' ' / T . t - -1 < V- *1 *1 -7 V " '_ * • * t- • W 33 ■U N C O N SO LID A TED " SED IM ENTS A N D SEDIMENTARY R O C K S . (U PPER C R ETA C EO U S A N D Y O U N G E R RO CK S.) "C O N S O L ID A T E D " SEDIMENTARY RO CK S. (EARLY A N D M IDDLE-CRETACEOUS RO CK S.)r . ' c , " , ! a a BASEMENT. O C E A N IC CRUST. F ig u r e 50. I n t e r p r e t a t i o n of s e i s m ic r e s u l t s by Heezen, T harp and Ewing, e t a l .. 1959. ( A f t e r E n g e le n , 1 9 6 3 .) BAHAMA PLATFORM I n t r o d u c t i o n P r o f i l e s a re a v a i l a b l e from Heezen, T h a rp , and Ewing (1 9 5 9 ) , Woods Hole O cean o g rap h ic I n s t i t u t e ( P l a t e 37, A- p r o f i l e s ) , The B r i t i s h I n s t i t u t i o n o f O ceanography, DISCOVERY ( D - p r o f i l e s ), and 21 p r o f i l e s from E m i l i a n i (1 9 6 5 ). R e s u l t s Bahama Bank, or p l a t f o r m , i s a s h o a l a r e a 720-km long and 270-km w id e , s o u t h e a s t of F l o r i d a and n o r t h o f Cuba, v\h ich t a p e r s b l u n t l y a t bo th ends; i t i s bounded on a l l s i d e s by a s t e e p subm arine e s c a r p m e n t. T h is e sca rp m en t d e sc en d s p r e c i p i t o u s l y to more th a n 3,600 m on th e e a s t and 550 m to 2,700 m on th e w e s t. The p l a t f o r m t r e n d s n o r t h - 2 n o r t h w e s t , c o v e r s about 130,000 km , and i s 9-m to 11-m d e e p . In a d d i t i o n to th e 20 p r i n c i p a l i s l a n d s and t h o u san d s o f sm a ll cays l o c a t e d along th e p l a t f o r m m a rg in s , g r e a t subm arine c h a n n e ls form deep ocean r e - e n t r a n t s i n t o th e s h a llo w b an k s, i n c l u d i n g Tongue o f th e Ocean (TOTO), Exuma Sound, and P ro v id e n c e C h a n n e ls . The s h e l f b r e a k f o r 323 324 the Bahamas and A n t i l l e s i s shown in Table 19. T able 19. Approxim ate S h e l f Breaks Bahamas - A n t i l l e s GENERAL LOCATION* SHELF BREAK (M e te rs ) Grand Bahamas I s l a n d H-27 45 E l e n t h e r a I s l a n d H-28 90 Dominican R ep u b lic H-30 180 H-32 90 H-33 90 P u e r t o Rico and A -247-15 60 V i r g i n I s l a n d s A-247-13 50 H-34 90 *See P l a t e 37 f o r L o c a tio n s E m i l i a n i ' s , from so u th of G re at Abaco to th e s o u t h e r n end of San S a lv a d o r I s l a n d ( P l a t e 3 7 ), show the r e l a t i v e l y p r e c i p i t o u s s lo p e of the Bahama P l a t f o r m , ra n g in g from the s h e l f b re a k to the a b y s s a l sea f l o o r a t n e a r l y 5-km d e p t h . The s h e l f commonly i s a narrow p l a t f o r m c o v ered w ith c a r b o n a te sands w i t h growing p a tc h e s of r e e f m a t e r i a l . The s h e l f v a r i e s from 2 km (and som etim es i s l e s s th a n 1-km w ide) to 10 km in w id th , e . g . , o f f n o r t h e a s t end of E l e u t h e r a . S h e l f b r e a k s are u s u a l l y d i s t i n c t and a v e ra g e 65 m. The s t e e p c o n t i n e n t a l s lo p e between th e s h e l f and the m argin of th e Blake-Bahama a b y s s a l p l a i n i s b e l i e v e d to 325 c o n s i s t o f hard c a r b o n a te r o c k . Lower p a r t s o f th e s l o p e s o f te n appear to be cov ered by t a l u s d e b r i s . Average g r a d i e n t from the s h e l f b re a k to the base of the slo p e ra n g e s from 14° to 28°, b u t some s l o p e s exceed 30°. On P r o f i l e 18 the g r a d i e n t i s 3 9 .7 ° . The s t e e p e s t slo p e i s > 4 0 ° ( P r o f i l e s 17 and 18) and i s l o c a t e d o f f San S a lv a d o r I s l a n d . E m i l ia n i s u g g e s ts t h a t th e s e c o n t i n e n t a l s l o p e s p r o b a b ly c o n tin u e below th e a b y s s a l p l a i n . On some p r o f i l e s the t r a n s i t i o n o f the slo p e to the p l a i n i s s h a r p ; in o t h e r s i t is t r a n s i t i o n a l . Many of th e p r o f i l e s have a d i s t i n c t t o p o g r a p h ic change a t about 1 km to 2 km ( P r o f i l e s 2, 5, 6, 8, 9, 10, and 11) which may c o n s i s t o f a r e g i o n of i r r e g u l a r t o p o g raphy or a marked change in g r a d i e n t . Many o f the p r o f i l e s commonly have a concave upper s l o p e , a s t e e p m iddle s l o p e , and e i t h e r a d e c r e a s e d or s h a r p l y - i n c r e a s e d lower slo p e g r a d i e n t . Tongue o f the Ocean Tongue of the Ocean i s a c o n t i n u a t i o n of one o f th e two major r e - e n t r a n t s or c h a n n e ls in th e Bahama Banks, and i n c i s e s the l a r g e s t of th e s h o a l s t r u c t u r e s (G re a t Bahama Bank). TOTO i s long (128 km) and narrow (3 2 km) and h a s a somewhat c i r c u l a r s o u t h e r n p o r t i o n 64 km in d i a m e t e r . The c h a n n e l c o n t i n u e s i n t o N o r t h e a s t P r o v id e n c e Channel and p ro c e e d s e v e n t u a l l y i n t o th e deep s e a . Andros I s l a n d b o r d e r s TOTO on the w est and s h a l lo w f l a t banks o ccu r on the so u th and e a s t . The s o u t h e r n p a r t of th e c h a n n e l t e r m in a te s in a c u l - d e - s a c a bo ut 1,350-m deep and has a U- shaped p r o f i l e . N orthw ard, th e c h a n n e l p r o f i l e i s more V- shaped and i s 1,800-m d e ep . The c e n t r a l c h an n e l f l o o r s l o p e s g r a d u a l l y (a b o u t 0° 1 9 ’ ) from th e c e n t e r of the c u l - d e - s a c to the b e g in n in g of N o r t h e a s t P r o v id e n c e C hannel. TOTO c o n t a i n s no s i l l b u t the N o r t h e a s t P r o v id e n c e Channel has one where i t ^joins w i t h the S t r a i t s of F l o r i d a ( a t 660 m). The w a l l s of TOTO a re smooth and s t e e p a v e r a g i n g 15° t o 20° in the upper 360 m to 550 m. Below h e re th e g r a d i - » e n t i s l e s s s t e e p (1 0° to 20°) but i s s t e e p e r in the n o r t h e rn than in the s o u t h e r n p a r t o f th e c h a n n e l. Large g u l l i e s a re common in the w a l l s b ut th e c u l - d e - s a c is somewhat sm oother (Busby, 1962b). A number o f c r o s s - s e c t i o n a l p r o f i l e s of TOTO have been p u b l is h e d (Busby, 1962a, 1962b, 1962c, and 1963; Lee, 1951; G oedicke, 1960; and R e i t z e l , 19 5 9 ). P r o f i l e s by Busby (1962a and 1962b) have a l a r g e , v e r t i c a l e x a g g e r a t i o n and s m a ll s c a l e . The o n ly d i s c e r n i b l e f e a t u r e s a re the b r e a k s in s lo p e a t about 500 m. S ix p r o f i l e s e a s tw a r d of Andros I s l a n d show e x c e l l e n t t e r r a c e s a t about 500 m. Bare rock w a l l s o ccur betw een 25 m to 183 m and a t g r e a t e r d e p t h s sand and g r a v e l are p r e s e n t (A rm stro n g , 1953). 327 R e i t z e l (1959) made a s p e c i a l su rv e y on th e e a s t e r n w a l l of TOTO n e a r G reen Cay (2 4 ° N). The w a l l has a g e n e r a l n o r t h w e s t - s o u t h e a s t t r e n d , i s s t e e p , ru g g e d , and i s c o n cave upward. Two marked b r e a k s a re r e p o r t e d on n e a r l y a l l c r o s s t r a v e r s e s - The u pper i s an o f t e n i l l - d e f i n e d b r e a k t h a t v a r i e s in d e p t h b u t a p p e a rs to mark a r e a l p h y s i o g r a p h i c change w i t h a r a p i d i n c r e a s e b o th i n s l o p e and l o c a l r e l i e f . The low er b re a k i s a d i s t i n c t f e a t u r e , though s m a l l , and r e p o r t e d l y i s p r o b a b l y c o n ti n u o u s a l l a lo n g th e su rv e y ed p a r t of th e w a l l . I t u s u a l l y o c c u r s n e a r 1,335 m and s e p a r a t e s th e f l a t f l o o r from a g e n t l y r i s i n g r e g i o n w ith 9 m or l e s s l o c a l r e l i e f . Exuma Sound lExuma Sound i s l o c a t e d e a s t o f TOTO and c o v e r s a b o u t o 1 1,6 5 0 km , i s 200-km lo n g , and l e s s th a n 93 km a t i t s w i d e s t p o i n t . U n lik e TOTO, which d e e p e n s from 1,2 8 0 m in th e s o u th to 1,830 m i n th e n o r t h , Exuma Sound d e ep e n s to th e so u th from abo ut 1,460 m w e st of E l e u t h e r a to 2,195 m i n the s o u t h e a s t n e a r C o n c ep tio n I s l a n d (where i t j o i n s the a b y s s a l sea f l o o r ) . A c co rd in g to S i e g l e r ( 1 9 6 1 ) , the s i d e s l o p e s a re s t e e p , a v e r a g in g about 6° on th e w e s t e r n s i d e and 8 .5 ° on the e a s t e r n s l o p e . In th e s o u th e r n m o s t a r e a l o c a l s l o p e s r e a c h 11° to 12°. The bottom i s f l a t - f l o o r e d w i t h no r e l i e f e x c e e d in g 7 3 . m. T e r r a c e s o c cu r on w a l l s ( F i g u r e 5 1 ) . F ig u r e 51. C o r r e l a t i o n of T e r r a c e s in Exuma Sound. ( A f t e r L ee, 1 9 5 1 .) PRO FILE NO. 17 PROFILE NO. 39 HAW KS B A L L R O C K 0 5280 S H IP C H A N N E L C ) 5280 10560 15840 21120 264 0 0 31680 10560 15840 21120 D IS T A N C E 800 800 1200 1200 T E R R A C E 1740 F T 1800 1800 T E R R A C E 2340 F T 2400 2400 T E R R A C E 2340 F T 3000 T E R R A C E 3000 F T 3000 T E R R A C E 3600 F T \ T E R R A C E 4140 F T T E R R A C E 3 6 0 0 F T 3600 3600 42 0 0 - 4200 200 0 0 25000 30000 15000 15000 10000 20000 10000 5000 50 0 0 5000 5000 C O R R E L A T IO N - T E R R A C E S fc G R A D IE N T C H A N C E S - E X U M A P R O F IL E S 40 P R O F IL E NO, 4 9 47 4 6 4 5 4 4 19 20 3 22 23 2 4 2 5 2 6 27 600 600 1200 1200 1800 1600 - 2400 2400 3000 3000 3600 3600 4200 4200 C H A N G E O F G R A D IE N T TH U S: — • T E R R A C E S THUS: 329 330 S i e g l e r c a l l e d a t t e n t i o n to t h e n o t a b l e b r e a k s i n th e s l o p e ; p e r h a p s h a l f th e s e c t i o n s have a f i r s t b r e a k a t a b ou t 400 fm s. T h is b r e a k i s found on th e w e s t e r n s l o p e of a l l p r o f i l e s n o r t h o f th e A d d e r le y Cay--Hawks N e s t P o i n t S e c t i o n . The s e c t i o n s showing t h i s b r e a k and t h e d e p t h w here i t o c c u r s a re i l l u s t r a t e d i n T a b le 20. T ab le 20. D ep th s of M ajor B reak s i n _________ S lo p e s i n Exuma Sound______ SECTION OF OCCURRENCE DEPTH (m) S a d d le Cay - P o w e ll P o i n t 585 Wemyss B ig h t - H a w k s b il l Cay 658 N. Tip H a l l s Pond Cay - SE P o i n t 768 H arvey Cay - A l l i g a t o r P o i n t 695 G a l l o i t Cay - due W o f Cove S e t t l e m e n t 777 A d d e rle y Cay - Hawks N e st P o i n t 841 Geology S c h u c h e r t (19 35 ) s u g g e s t e d t h a t A ndros I s l a n d once f a c e d th e open A t l a n t i c and l a t e r a s u s p e c t e d v o l c a n i c e a s t e r n r e g i o n p o r t i o n o f G r e a t Bank grew up b e f o r e i t , l e a v i n g Tongue o f th e Ocean b e tw e e n . Hess (1933 and 1959) p o s t u l a t e d a t e r r a i n of g e n t l y f o l d e d s e d i m e n t a r y r o c k s more t h a n 4,200-m t h i c k upon w hich a t r e l l i s d r a i n a g e p a t t e r n d e v e lo p e d when i t was above s e a l e v e l . A b r i e f , r a p i d subm ergence drowned th e r i v e r v a ll e y , 331 f o l lo w e d by slow su bm erg ence; re e f's grew upw ards from th e s i d e s o f th e v a l l e y s fo rm in g b a n k s , t h u s , p r e s e r v i n g the d r a i n a g e f e a t u r e s . W ith c o n t i n u i n g s u b s i d e n c e , most s e d i m e n t a t i o n was c o n f i n e d b e h in d r e e f s , p r e s e r v i n g th e v a l l e y s . T u r b i d i t y c u r r e n t s i n t e r m i t t e n t l y s p r e a d o u t s e d i m ents i n the v a l l e y s and k e p t " r i v e r " c h a n n e l s op en , d r a i n ing them from th e s h a l l o w e r a r e a s to 4 ,5 7 0 m where t h e y d e bouched i n t o th e open o c e a n . In 1952, E r i c s o n , Ewing, and H eezen c o n c l u d e d , on th e b a s i s of l i t h o l o g i c a l and p a l e o n t o l o g i c a l d a t a i n c o r e s , t h a t t u r b i d i t y c u r r e n t e r o s i o n may be l a r g e l y r e s p o n s i b l e f o r e x c a v a t i o n . However, th e Miami U n i v e r s i t y (1 9 5 8 ) s t a t e d t h a t th e r e g i o n l a c k s a s o u r c e of l a r g e q u a n t i t i e s of s e d im e n t n e g a t i n g the p o s s i b i l i t y of t u r b i d i t y c u r r e n t e r o s i o n f o r c r e a t i o n of TOTO. The Miami U n i v e r s i t y r e p o r t s u g g e s t e d t h a t th e c h a n n e l o r i g i n a t e d t h r o u g h some ty p e of b lo c k f a u l t i n g . W o rz el, Ewing, and Drake (1 9 5 3 ) c o n c lu d e d t h a t most o f t h e g r a v i t y a n o m a lie s can be e x p l a i n e d by s i m p le e r o s i o n of th e d e e p - w a te r p o r t i o n s w i t h o u t c o m p e n s a ti o n , o r a l t e r n a t e l y , c o n s t r u c t i o n of th e s h a l l o w - w a t e r p o r t i o n s w i t h o u t r e g i o n a l c o m p e n s a tio n . N ew ell (1 9 5 5 ) combined t h e s e and s u g g e s t e d t h a t th e deep c h a n n e l s a re m a i n l y th e r e s u l t o f c o n s t r u c t i o n a l p r o c e s s e s t h r o u g h d i f f e r e n t i a l d e p o s i t i o n and b y p a s s i n g . (N e w e ll a l s o e x p l a i n e d th e s t e e p West F l o r i d a E sc a rp m e n t t h r o u g h r e e f g r o w t h .) 332 T alw ani, W o rz el, and Ewing (1959) e x p la in e d low o b served g r a v i t y an om alies by assuming 1 km to 4 km of l i g h t m a t e r i a l . While sm all t h i c k n e s s may be th e r e s u l t of s e d i m e n ta tio n , such an e x p l a n a t i o n f o r th ic k d e p o s i t s i s t e n u ous. An a l t e r n a t i v e view i s d o w n f a u lt i n g - - g r a b e n fo r m a tio n - - w i t h f a u l t s assumed to c o rre sp o n d w ith the o u t l i n e of the d e p r e s s i o n s . D ow nfaulting low ers l i g h t e r m a t e r i a l in the do w nfaulted b lo c k to th e same l e v e l as h e a v ie r m a t e r i a l on the s i d e s , t h u s , c a u sin g th e anomaly. S e d im e n ta tio n of low d e n s i t y m a t e r i a l would a c c e n t u a t e the anomaly. Talwani e t al s t a t e d t h a t n e i t h e r e r o s i o n o f th e c h a n n e ls nor u p b u i l d ing o f banks by o rg a n ic growths would e x p l a i n th e anoma l i e s . Hess (1 9 5 9 ), on the o th e r hand, concluded t h a t d e t r i - t a l sedim ent f i l l i n g v a l l e y s i s l e s s th an d e t r i t a l and chem ical sedim ents on the banks which would account f o r the p r e s e n t g r a v i t y f i e l d . In a d d i t i o n , he b e l i e v e d the form a t i o n of p a r a l l e l graben s e p a r a t e d by h o r s t s of a p p ro x im a te ly e q ual w id th s seems m e c h a n ic a lly u n l i k e l y . He a l s o f i n d s i t d i f f i c u l t to u n d e rs ta n d how the s t r u c t u r e s were formed, p r e s e r v i n g h o r i z o n t a l a t t i t u d e s of the l a y e r s bo th under banks and in down-dropped b lo c k s ; i t would be n e c e s s a r y to assume f a u l t s a re young. T e r t i a r y r o c k s a re c u t on th e ban ks. The re g io n i s a s e i s m i c , which a rg u e s a g a i n s t young f a u l t i n g (Lockheed C a l i f o r n i a C o ., 1961; and J a c o b s , Rus s e l l , and W ilson, 1959). P o s s i b l y they are old graben w i t h 333 r e c e n t s u b s id e n c e of the f o u n d a t i o n w ith an upgrowth on ban k s. Hess concluded t h a t m arine e r o s i o n pro d u ce s a v a l le y w ith an in n e r gorge o r c h a n n e l ru n n in g down the middle and a c o n t i n e n t a l slo p e in one d i r e c t i o n . H e s s ’ h y p o t h e s is i s su p p o rte d by th e p re s e n c e of 50 m to 150 m of P l e i s t o c e n e age lim e s to n e on New P r o v id e n c e and Andros I s l a n d s , w hereas the f l o o r of TOTO i s e i t h e r b a r e , or i s covered only a few m eters t h i c k and i s u n d e r l a i n by u n c o n s o lid a te d T e r t i a r y ( p r e - g l a c i a l age) c h a lk se d im e n ts (S h o n tin g , 1963). Busby (1962b) r e p o r t e d t h a t the f l a n k s of TOTO are s t e e p (1 5° to 20°) and have b a re rock w a l l s to 180 m to 360 m; below h ere the bottom o f the c h an n e l slo p e i s g e n t l e and has a sedim ent b l a n k e t . Sedim ents are alm ost e n t i r e l y CaCO^. Busby c o n clu d es t h a t t u r b i d i t y c u r r e n t s o r i g i n a t e in upper c h a n n e ls , flow down th e s l o p e , and d i s t r i b u t e s e d iment on the ch an n el f l o o r . P h o to g ra p h s r e v e a l rock o u t c ro p s on the c h an n e l f l o o r at 1,850 m. Also p r e s e n t a re p e b b le s and c o b b le s , ev id e n ce of lim e s to n e s o l u t i o n , b u r rowing o rg an ism s, and o s c i l l a t i o n r i p p l e m arks. These e x clu d e f o rm a tio n of the observed f e a t u r e s by t u r b i d i t y c u r r e n t s or slum ping. Busby (1962a) co nclud ed t h a t the f e a t u r e s can only be e x p la in e d by a s u b a e r i a l t h e o r y . He sug g e s te d TOTO was formed by " g r a d u a l s u b s id e n c e , b ro u g h t about by d e p o s i t i o n o f m a t e r i a l on the p rom inen ces bounded by the chan nel . . . or downdropping of the ch an n el f l o o r 334 by f a u l t i n g can be a p p l i e d . " S u b a e r i a l e r o s i o n and s u b s i d ence o f about 1,800 m i s im p lie d . D e sp ite the rock o u t c ro p s , Goedicke (1 96 0), in a s e is m ic survey of TOTO b a s i n , found' s e v e r a l deep r e f l e c t i n g h o r iz o n s b u t no basem ent. S i e g l e r (1959, 1961) and Miami U n i v e r s i t y (1959) b e lie v e the a re a i s d o w n fa u lte d , p ro b a b ly in p r e - C r e ta c e o u s tim e. A major break in slo p e was no ted a t a d e p th of about 700 fms and was tho ug ht to mark a h i a t u s in s e d i m e n ta t io n . T his b reak in slo p e su p p o rts the p o s t u l a t e of a graben. The trough a l s o has a f l a t f l o o r w ith s t e e p s i d e s which are marked by a s t e p - l i k e d e s c e n t . The f l a t n e s s i s b e lie v e d to r e f l e c t u n d e rly in g d e e p ly b u rie d p r e - C r e t a c e o u s s t r u c t u r a l p a t t e r n . A c l i f f - l i k e escarpm ent b o r d e r s the sh a llo w m a rg in a l p l a t f o r m of the i s l a n d s and banks th ro u g h o u t the Bahamas (Newell and Rigby, 1957). On the e a s t e r n s id e of Andros I s l a n d t h i s "rim escarp m ent" e x te n d s from about 22 m to 29 m down to about 180 m, below which the g r a d i e n t d e c r e a s e s . A th earn (1963) su g g e ste d t h a t t h i s escarpm ent a ls o b o r d e r s the e n t i r e TOTO. Newell and Rigby (1961) c o n s i d e r t h i s c l i f f th e r e s u l t of v e r t i c a l growth of r e e f lim e s to n e d u r ing the P l e i s t o c e n e e u s t a t i c sea l e v e l lo w e rin g . Armstrong (1953) r e p o r t e d b a re rock below t h i s c l i f f to d e p th s down to about 250 m, below which he found g r a v e l s composed m o stly o f Halimeda and sandy g r a v e l s . C a lc a re o u s muds occur below 550 m (Busby, 1965; A th e a rn , 1963). 335 A th e arn d i s c o u n t s t h e o r i g i n o f TOTO by f a u l t i n g ( F i e l d , 1931; S i e g l e r , 1959; T a lw a n i, 1960; and T alw ani. e t al.. 1960) because the m a r g in a l s l o p e s a t n a t u r a l s c a l e are n o t r e p r e s e n t a t i v e of f a u l t b lo c k m ountain s l o p e s . He p r e f e r s H e s s ’ t h e o r y , p a r t i c u l a r l y in view of e v id e n c e of r e g i o n a l su b s id e n c e of 4,6 0 0 m ( E a r d l e y , 1951; I l l i n g , 1954; and N ew e ll, 1959). S h o n tin g (1963) rev iew ed v a r i o u s t h e o r i e s and c o n c lu d e d : ". . . i t i s p r o b a b ly s a f e to say t h a t t u r b i d i t y c u r r e n t s do o c cu r somewhat p e r i o d i c a l l y in th e Tongue. I n d e ed , i t i s p o s s i b l e t h a t th e y a re r e s p o n s i b l e f o r s c o u r in g o u t the Tongue in i t s p r e s e n t c o n f i g u r a t i o n ; however, the f r e q u e n c y of o c c u r r e n c e of m ajor d i s t u r b a n c e s i s p r o b a b ly low, i . e . , g r e a t e r th an one hundred y e ar p e r i o d s . " In c o n c l u s i o n , th e o r i g i n o f th e m ajor d e p r e s s i o n s in the Bahama P l a t f o r m s t i l l i s d i s p u t a b l e b e ca u se of c o n f l i c t i n g e v id e n ce and i n t e r p r e t a t i o n . BLAKE PLATEAU I n t r o d u c t i o n S e v e ra l PDR and o t h e r echogram s t h a t c r o s s the Blake P l a t e a u have been o b ta in e d from Woods Hole ( P l a t e 3 6 ). P r a t t and Heezen (1964) have d i s c u s s e d the g e n e r a l c h a r a c t e r of th e p l a t e a u and are the m ajor so u rc e of the f o l l o w ing i n f o r m a t i o n . R e s u I t s The Blake P l a t e a u i s a bro ad f l a t a r e a c o v e r in g about 2 127,000 km . I t s e p a r a t e s th e Bahama Banks p r o v i n c e , com posed of c a l c a r e o u s d e p o s i t s , from th e m ainland s h e l f and the c o a s t a l p l a i n p ro v in c e to th e n o r t h , composed of t e r r i g e n o u s s e d im e n ts . The p l a t e a u ’ s d e p th ra n g e s from 600 m in th e n o r t h to 1,200 m on the s o u t h e a s t , a v e r a g in g about 850 m. The s i g n i f i c a n t a s p e c t of th e Blake P l a t e a u i s i t s i n t e r m e d i a t e s t r u c t u r a l f e a t u r e betw een th e s h e l f and the a b y s s a l s e a . P r a t t and Heezen d i v i d e the r e g i o n i n t o seven p h y s i o g r a p h ic p r o v i n c e s , b u t o n ly th e g e n e r a l n a t u r e of the p l a t e a u and i t s c o n t i n e n t a l s lo p e a re of i n t e r e s t h e r e . The c o n t i n e n t a l slo p e r e p o r t e d l y i s ’’c h a r a c t e r i z e d by 336 337 a smooth p r o f i l e and a com plete l a c k o f i n c i s i n g canyons or o t h e r i r r e g u l a r i t i e s . The b re a k from the [ c o n t i n e n t a l ] slo p e t o th e bro ad s u r f a c e o f th e Blake P l a t e a u i s a b ru p t e x c e p t tow ards th e n o r t h e r n end where th e Blake E scarpm ent merges w i t h th e s lo p e and th e P l a t e a u t a p e r s o u t . ” The w e s t e r n p a r t has numerous d e p r e s s i o n s b u t i s q u i t e f l a t and f e a t u r e l e s s tow ards th e e a s t . Blake E scarp m en t i s so s t e e p t h a t i t i s d i f f i c u l t to o b se rv e any f e a t u r e s ; i t i s n o t c o m p le te ly s t r a i g h t f o r a pro m in ent h e adland p r o j e c t s out and a s t e e p - w a l l e d canyon c u t s a c r o s s th e slo p e a t 27° N. At t h e ba se of the e s c a r p m ent, between 26° and 36° N, i s a c lo s e d d e p r e s s i o n which a t t a i n s a maximum d e p th of 5,046 m, and on the so u th i s op p o s i t e N orth w est P ro v id e n c e Channel of the Bahama P l a t f o r m . Bottom sam ples i n d i c a t e t h a t th e Blake P l a t e a u i s a c o n t i n u a t i o n o f th e Bahama Bank c a r b o n a t e p r o v i n c e and i n c lu d e s p a r t of F l o r i d a P e n i n s u l a . I n d u r a t e d sam ples taken from the e sca rp m en t and th e p l a t e a u r e v e a l e d t h a t th e l a t t e r ( s u r f a c e and s u b s u r f a c e ) i s of c a r b o n a t e c o m p o s itio n . These sam ples range i n age from C r e ta c e o u s to Miocene. A g e n e r a l c r o s s - s e c t i o n of the o u t e r p a r t of the Blake P l a tea u summarizes p e r t i n e n t f e a t u r e s , i . e . , s t r a t i g r a p h y , t o po g rap h y , and s u b s u r f a c e s t r u c t u r e ( F i g u r e 5 2 ). P r a t t and Heezen b e l i e v e t h a t p ro m in e n t changes in s lo p e alo n g th e e sca rp m en t mark l i t h o l o g i c c h an g e s. 338 M E T E R S C O R E D A T A F R O M E R IC S O N , E W IN G A N D H E E Z E N , 195 2 B L A K E E S C A R P M E N T , O U T C R O P B E N C H E S 1000 - M IO C E N E e o c e n e - o l i g o c e : 2000 U P P E R C R E T A C E O U S 4 . 19 3000 4 0 0 0 6 . 1 K m /S c c 5 0 0 0 A G E VS D E P T H F ig u r e 52. G e n e r a li z e d d iag ra m of t h e Blake P l a t e a u . O u t c ro p bench es on t h e Blake E scarpm ent a re shown. P r a t t and Heezen b e l i e v e the m ajor bench a t 2,500 m marks th e b ase of th e upper C r e ta c e o u s o u t c r o p . They assume t h a t slum ping has c a r r i e d C r e ta c e o u s and p o s t - C r e t a c e o u s sedim ent down the s t e e p lower e sc a rp m e n t b u t sam ples a t t r i b u t a b l e t o the lower two l a y e r s have n o t b een o b t a i n e d . Miocene age s e d i m ents which c ro p o u t on th e o u t e r p o r t i o n s o f the Blake P l a t e a u a re co v ered by a t h i n l a y e r o f manganese o x id e . ( A f t e r P r a t t and Heezen, 1964; Seism ic r e f r a c t i o n d a t a from N a f e . e t a l .) 339 The i n v e s t i g a t o r s c o n clu d e by p o i n t i n g o u t the f o l l o w ing : f i r s t , th e i n f l u e n c e of th e G ulf Stream (o r F l o r i d a C u r r e n t) has been an im p o rta n t i n f l u e n c e on to p o g rap h y and s e d i m e n ta t io n ( P r a t t , 1962). Second, the Blake P l a t e a u is n o t s i g n i f i c a n t l y d i f f e r e n t from the Bahama P l a tf o r m : both have a s t e e p o u t e r e sc a rp m e n t; th e deep Bahama C han nels are s i m i l a r in d e p th and have common c o m p o sitio n and s i m i l a r s u b o r d i n a te f e a t u r e s such as the Blake Nose and San S a l v a dor Bank. T h i r d , '’s u r f a c e sa m p le s, w e l l d a t a , and s e is m ic v e l o c i t i e s r e v e a l a c c r e t i o n o f a t l e a s t 4 ,0 0 0 m of c a r b o n a te ro ck in the r e g i o n , and i t seems a p p a r e n t t h a t the t o pography should be r e l a t e d to f e a t u r e s c h a r a c t e r i s t i c of c a rb o n a te banks or r e e f s , r a t h e r th an t e r r i g e n o u s s h e l v e s . " Discu ssion. I f th e Blake P l a t e a u and Bahama P l a t f o r m a re e s s e n t i a l ly one s t r u c t u r a l e n t i t y , and bo th were formed by o r g a n ic a c c r e t i o n ( a l s o pro po sed by N ew ell, 19 55 ), th e n su b s id e n c e of th e b l o c k ( s ) , or th e sea f l o o r as a w h o le , i s im p e ra tiv e . Deep b o r i n g s on the Bahama P l a t f o r m to 4,9 0 0 m showed t h a t t h i s g r e a t t h i c k n e s s of c a l c a r e o u s m a t e r i a l was d e p o s i t e d in s h a llo w w a t e r . A c c r e t i o n , or b u i l d - u p of c a l c a r e o u s ma t e r i a l from th e d e p th of the e x i s t i n g a b y s s a l sea f l o o r , does not f i t the f a c t s . Another q u e s t i o n which d e s e r v e s c o n s i d e r a t i o n i s : d id c a l c a r e o u s m a t e r i a l grow or accumu l a t e on a p r e - e x i s t i n g p l a t f o r m b e ca u se the p l a t f o r m was t h e r e , or i s the p l a t f o r m the s o l e r e s u l t of o r g a n ic growth? In a d d i t i o n , would s i m i l a r c o n d i t i o n s p r e v a i l o f f F l o r i d a , i . e . , be a r e g i o n of c a r b o n a te a c c u m u la tio n i f t h e r e was no p l a t f o r m t h e r e in th e f i r s t p l a c e ? R ecovery of Miocene from the s u r f a c e of Blake P l a t e a u i n d i c a t e s the r e l a t i v e old age of i t s s u r f a c e , t h u s , i n d i c a t i n g a m ajor h i a t u s . I t i s t h e r e f o r e con cluded t h a t ( 1 ) the B lake P l a t e a u and the Bahama P l a t f o r m have been u n d e rg o in g s u b s id e n c e f o r a long p e r i o d of g e o lo g ic time and t h a t c a r b o n a t e s ( p r e c i p i t a t e s and r e e f grow th) have e i t h e r k e p t pace w ith s u b s i d ence (Bahama Bank) or su b s id e n c e was so r e l a t i v e l y a b ru p t t h a t r e e f b u i l d i n g could not keep pace (B lake P l a t e a u ) ; (2 ) la c k of s i g n i f i c a n t a c c u m u la tio n s of p o st-M io c e n e d e p o s i t s on the s u r f a c e of the Blake P l a t e a u does not' n e c e s s a r i l y mean t h a t the s t r o n g c u r r e n t s o f th e G u lf Stream have k e p t i t s s u r f a c e swept c l e a n . In d e e d , many s h e l f a r e a s w i t h weak c u r r e n t s ( a s o f f C a l i f o r n i a ) a re a r e a s of n o n - d e p o s i t i o n and a l s o have Miocene age ro c k s ex p o sed . While s t r o n g c u r r e n t s u n d o u b te d ly do c o n t r i b u t e to n o n d e p o s i t i o n , t h i s does n o t in i t s e l f e x p l a i n the deep d e p th of th e Blake P l a t e a u . GULF OF MEXICO I n t r o d u c t i o n The n o r t h e r n and n o r t h e a s t e r n p a r t s of the G ulf of Mexico have b een s t u d i e d in c o n s i d e r a b l e d e t a i l b u t l i t t l e i s known about th e w e s t e r n and s o u t h e r n p o r t i o n s , e x c e p t l o c a l l y . J o r d a n (19 51 , 19 5 2 ), and J o r d a n and S te w a r t (1959) have d e s c r i b e d th e w est c o a s t of F l o r i d a . C o u n t le s s p a p e r s have been w r i t t e n about th e c o n t i n e n t a l t e r r a c e o f f th e M i s s i s s i p p i D e l t a , b u t e x c e p t f o r G e a l y ’ s (1955) f u n d a m e n ta l a r t i c l e , S t e t s o n ( 1 9 5 3 ) , and s e v e r a l p a p e r s by Ewing and a s s o c i a t e s , th e c o n t i n e n t a l s l o p e has been l a r g e l y i g n o r e d . C re a g e r (19 53 , 1958) d e s c r i b e d Campeche Bank and Campeche Bay. Ewing, W orzel, E r i c k s o n , and Heezen ( 1 9 5 5 ) , Ewing, E r i c s o n , and Heezen ( 1 9 5 8 ) , and M i l l e r and Ewing (1956) have p u b l i s h e d many s m a l l - s c a l e p r o f i l e s . Many echogram s were examined in 1955 a t th e o f f i c e s of th e C o a st and G e o d e tic Survey b u t o n ly a few a r e a s were sounded in d e t a i l and r e c o r d e d on an NMC-2 e c h o s o u n d e r . R e s u l t s Jo rd a n (1951) and J o rd a n and S te w a r t (1959) p o i n t e d 341 342 ou t t h a t th e c o n t i n e n t a l s lo p e o f f w e s t e r n F l o r i d a h as a 1,200-m e sc a rp m e n t w ith 35° s l o p e s ( a v e r a g i n g 28°) between 1,45 0 m and 2,900 m ( F i g u r e 5 3 ) . The maximum s lo p e i s 50°. The e sca rp m en t e x te n d s th e f u l l l e n g t h o f w e s t e r n F l o r i d a , t u r n i n g e a s t a t 24° 3 0 ’ N. The c o n t i n e n t a l slo p e ch ang es c h a r a c t e r i s t i c s a t 27° as f o l l o w s : T ab le 21. D i f f e r e n c e s Between C o n t i n e n t a l S lo p e s N o rth and South of 27° N NORTH OF 27 o SOUTH OF 27 Upper s lo p e (180 m to 1,100 m) i s b ro ad and sm o oth ly s lo p i n g Top o f e sc a rp m e n t i s g e n e r a l l y a t 1,460 m S c a rp i s r e l a t i v e l y smooth and has a sim p le NW-SE tr e n d Upper s l o p e i s < l / 2 as wide and i s i n t e r r u p t e d by lon g b r e a k s in s lo p e Top of s lo p e i s g e n e r a l l y a t 1,80 0 m to 2,20 0 m S c a rp i s marked by a b r u p t o f f s e t s and embayments At d e p th s betw een 365 m and 730 m the g r a d i e n t a v e r - nO j_ i 1 o ages 3 to 11 . In a d d i t i o n to the P o u r t a l e s T e r r a c e , many t e r r a c e s e x i s t above th e e s c a rp m e n t but i n s u f f i c i e n t c l o s e l y - s p a c e d p r o f i l e s a re a v i l a b l e f o r c o r r e l a t i o n . Because o f th e i r r e g u l a r u p p e r c o n t i n e n t a l s l o p e , i t i s n o t p o s s i b l e to p r e c i s e l y d e f i n e th e s h e l f b r e a k . I t i s e v i d e n t , however, th e th e s h e l f b r e a k v a r i e s c o n s i d e r a b l y , i n d i c a t i n g p o s t c u t t i n g movement. 3 4 3 W 1X00 D e p th s in Fathoms V o rtic a l X2S P ro file * a re x p a rn i p ro p o rtio n ate !) m latitodi- Thf> a re adjuM rd norm al t o t h r niupr D aahrd line* d r lm r a te *l<ip*' rh a n f ru and break* 1B00 F ig u r e 53. P r o f i l e s of th e F l o r i d a - G u l f c o n t i n e n t a l m a rg in . ( A f t e r J o r d a n , 1962) 344 Dome-like s t r u c t u r e s have been r e p o r te d from the con t i n e n t a l s h e l f and upper slo p e a t d e p th s of 110 m to 175 m (J o rd a n , 1951; Jordan and S te w a r t, 1961; and J o rd a n , Mal lo y , and Kofoed, 1964). They are c o n sid e re d r e e f growths s i m i l a r to th o se d e s c r ib e d by Ludwick and Walton (1957) or might be a lg a l k n o l l s . Gealy (1955) has d e s c r ib e d the c o n t i n e n t a l slo p e in the n o r th e r n Gulf of Mexico and in c lu d e s s e v e r a l score of r e c o n s t r u c t e d p r o f i l e s from echograms. The c o n t i n e n t a l s h e l f b reak s e a s t of the M i s s i s s i p p i D e lta are shown in Ta b le 23. These vary from about 50 m to 119 m, showing the c o n s id e r a b le v a r i a t i o n in the s h e l f b re a k , due in p a r t to p o s t - c u t t i n g , warping and f i l l i n g , and to growth of r e e f s . West of the M i s s i s s i p p i D e lta to th e Rio Grande the s h e l f is about 83-km wide and has an av erage s h e l f break of about 137 m; l o c a l l y i t is n e a r l y 200 m. S te ts o n (1953) r e p o r t e d the s h e l f b rea k s from the w e ste rn Gulf in T able 22. Off Campeche Bank the s h e l f b reak i s about 155 m, but commonly i s 100 fms to 120 fms (C reag er, 1958; S t e t s o n , 1953; and Ludwick and Walton, 1957). R e l i e f on the c o n t i n e n t a l slo p e i s measured in hu nd reds, or even th o u sa n d s, of m e te rs . The c o n t i n e n t a l slo p e ex ten d s to a d epth of about 3,100 m. The g r a d i e n t ran ges from 1° to 1° 30 ’ but l o c a l l y exceeds 45°. 345 Table 22. Approximate S h e l f Breaks in the Western Gulf of Mexico* West 128 - 137 m 128 128 91 - 119 119 110 155 (T e rra c e a t 256) 165 (T e rra c e a t 192) East 192 *See S t e ts o n , 1953 f o r l o c a t i o n . 346 Table 23. S h e lf Break N o rth e rn G u lf o f Mexico* STAT [ON STAT I ON STAT I ON STATION NUMBER M NUMBER™ M NUMBER M NUMBER M 1 107 9 69 16 91 23 88 2 101 10 64 17 91 24 90 3 69 11 69 18 91 27 82 4 69 12 97 19 91 29 107 5 73 13 91 20 91 1 110 6 77 14 91 21 88 2 110 8 71 15 95 22 91 3 110 4 108 32 95 41 110 51 82 5 110 33 93 42 101 52 80 6 113 34 90 44 62 53 69 7 119 35 66 45 84 54 82 8 115 36 82 46 71 55 82 9 112 37 49 47 46 56 64 10 110 38 88 48 53 57 84 11 112 39 91 49 66 58 55 31 101 40 108? 50 69 59 58 *For l o c a t i o h see Ludwick and Walton (1957) Ewing, E r i c s o n , and Heezen (1958) c l a s s i f y the c o n t i n e n t a l s l o p e s of th e G u lf of Mexico i n t o t h r e e (and p o s s i b l y f o u r ) t y p e s , a l l of which d i f f e r from t h o s e of th e A t l a n t i c Ocean- Off wide c a l c a r e o u s p l a t f o r m s , such as the West F l o r i d a or Campeche, th e s lo p e i s made up of two s e g m en ts: ( 1 ) a g e n t l y s l o p i n g u pper p o r t i o n from th e s h e l f b r e a k (a b o u t 130 m) to a p p r o x i m a t e ly 1,800 m and (2 ) a p r e c i p i t o u s low er slo p e ( s c a r p ) w hich d ro p s to th e a b y s s a l p l a i n . O ff b o th of t h e s e ty p e s o f p l a t f o r m s a c o n t i n e n t a l r i s e i s a b s e n t . The second ty p e i s l o c a t e d o f f Texas and L o u i s i a n a . I t a l s o c o n s i s t s o f two p a r t s : (1 ) a w id e , u p p e r rugged p o r t i o n w i t h a g e n t l e a v e ra g e seaw ard g r a d i e n t and (2 ) a p r e c i p i t o u s lower s c a r p . The n a rro w s h e l v e s around Cuba and c e n t r a l Mexico may form a s e p a r a t e c a t e g o r y . The f o u r t h ty p e i s r e p r e s e n t e d by th e u p per M i s s i s s i p p i Cone. H e re, th e c o n t i n e n t a l s h e l f and s l o p e i s f a i r l y smooth and c o n tin u o u s low g r a d i e n t , w i t h o u t th e t w o - f o l d d i v i s i o n i n th e above c l a s s e s . S ig s b e e Scarp i s l o c a t e d a t th e b a se of th e c o n t i n e n t a l s lo p e and i s a t l e a s t 630-km lo n g . I t i s 1,460-m h ig h and has. an a v e ra g e g r a d i e n t of a t l e a s t 12° a t i t s w e s t e r n e n d, d e c r e a s i n g b o t h in h e i g h t and s t e e p n e s s to th e e a s t . S ig s b e e E scarpm ent s t a r t s more or l e s s s o u th o f Corpus C h r i s t i , p a r a l l e l s the c o a s t , a nd i n t e r s e c t s th e West F l o r i d a Slope n e a r De S o to Canyon a t an a n g le of 6 0°. Above t h e S ig s b e e S c a rp a zone about 90-km wide and 1,000-m 348 deep e x te n d s th e le n g t h of the c o n t i n e n t a l s lo p e . I t i s n o tew o rth y t h a t most o f G e a l y 's p r o f i l e s show a t e r r a c e or somewhat i r r e g u l a r to po grap hy at a dep th of about 550 m. Sigsbee Deep i s bounded by s c a r p s of g r e a t l a t e r a l e x t e n t and v e r t i c a l r e l i e f ; Gealy concluded t h a t th e s e must be f a u l t s c a r p s . The s lo p e s were a ls o m o d ified by slumping and p o s s i b l y s u b a e r i a l e r o s i o n . The p a r t played by each of th e s e p r o c e s s e s or a g e n c ie s i s d i s c u s s e d by G ealy. Between the s h e l f b re a k and the zone of tro u g h s i s a zone of hummocky topography c o n s i s t i n g m o stly of sm all h i l l s and d e p r e s s i o n s . The M i s s i s s i p p i Trough c u ts i n t o th e c o n t i n e n t a l s h e l f and s lo p e . I t is about 37-km wide and 550-m deep. T rea d w ell (1949) d e s c r i b e d th e r e g io n in the n o rth w e s t G u lf; u n f o r t u n a t e l y , a copy of h i s r e p o r t could not be o b t a i n e d . S t e t s o n (1953) b r i e f l y d e s c r i b e d t h i s r e g i o n . C reag er d e s c r i b e d the b a th y m etry of the Bay of Campe che re g io n and in c l u d e s s e v e r a l p r o f i l e s a c r o s s the c o n t i n e n t a l t e r r a c e o f f the west and n o r t h c o a s t s of th e Yucatan P e n i n s u l a and o ff V e rac ru z. The s h e l f b re a k commonly o c c u rs a t 180 m bu t i s as sh a llo w as 73 m. From the s h e l f b reak to 3,100 m the g r a d i e n t a v e ra g e s 10° 4 5 ’ ; below here the g r a d i e n t d e c r e a s e s as i t g rad e s i n t o the a b y s s a l sea f l o o r . O ff the " v o l c a n i c r e g i o n " th e upper c o n t i n e n t a l s lo p e i s s t e e p and concave to 700 m to 1,200 m. The g r a d i e n t o f the upper slo p e i s 349 8° 1 1 T below which i t i s only 1° 3 0 T. Most p r o f i l e s show a d i s t i n c t f e a t u r e ( t e r r a c e , pronounced d e c r e a s e in g r a d i e n t , or sm all r i s e ) a t about 1,450 m. Three t e r r a c e s are i d e n t i f i e d by C re a g e r: 1,240 m to 1,350 m having a g r a d i e n t of 0° 4 1 ’ ; 1,650 m, is f l a t f o r 6.7 km; and a t 1,900 m, f l a t f o r 12.6 km. S l i g h t t e r r a c e s are observed on o t h e r p r o f i l e s a t 1,755 m, 1,700 m, 1,880 m, 1,975 m, and 2.270 m. I t i s i n t e r e s t i n g to o bserv e t h a t M i l l e r and E w ing’ s p r o f i l e s show a common b reak a t about 800 fms to 1,300 fms in w id e ly -s p a c e d r e g i o n s : o f f Campeche Bank, F l o r i d a E s carpm ent, Texas, and L o u is ia n a . Bottom M a t e r i a l s The changes a t 27° N o f f w e s te r n F l o r i d a are a t t r i b u ted to a d i f f e r e n c e in l i t h o l o g y : n o n - c l a s t i c , m o stly c a r b o n a te ro ck s to th e s o u th , and c l a s t i c se d im e n ta ry ro ck s to the n o r t h ( P r e s s l e r , 1947). S t e t s o n (1951) dredged two sam ples of hard lim e sto n e and one of s o f t lim e s to n e from th e o u te r s lo p e ; a bottom p h o to g rap h a t 2,012 m showed ro c k . J o rd a n (1952) a ls o o b ta in e d p h o to g ra p h s a t the c r e s t of th e s c a r p which s u g g e s ts exposed ro c k . A dredge haul 74 km e a s t of the M i s s i s s i p p i R iver mouth, a t d e p th s of 420 m to 510 m, r e v e a le d the p re s e n c e of a t h i c k and w id esp read d e e p -w a te r r e e f (Moore and Bul- l i s , 1960). S im ila r d e e p -w a te r r e e f s have been r e p o r t e d o f f the V irg in I s l a n d s , Grenada (538 m ), th e w est end of 350 P u e r t o Rico (1 ,6 0 0 m ), P o rc u p in e Banks, and e lsew h ere (Moore and B u l l i s , 1960; and A llen and W e lls, 1962). C ores from the Campeche Scarp have y ie ld e d o n ly l im e sto n e and d o lo m ite . Geology Most a u t h o r i t i e s agree t h a t s t e e p e sc a rp m e n ts such as those o f f w e s te rn F l o r i d a are of f a u l t o r i g i n ( P o o l, 1940; Kidd, 1939; F is k , 1944; Weaver, 1951; T re a d w e ll, 1949; S h e e t s , 1947; G ealy, 1955; Moody, 1950; Kofoed and J o r d a n , 1964; J o r d a n , 1950, 1951, 1952, and 1962; Lyons, 1957; S t e t s o n , 1951; E a r d le y , 1954; S u ess, 1880; Jo rd a n and Stew a r t , 1961; and o t h e r s - - s e e A ppendix). Jo rd a n d a te d the f a u l t i n g as p o s t - C r e t a c e o u s . Minor f a u l t s a re a l s o s u g g e ste d a t o th e r d e p t h s . The g e o p h y s i c i s t s tak e e x c e p tio n to a t e c t o n i c o r i g i n bu t c o n f l i c t i n g e v id e n ce i s in v o lv e d ; Newell (1959) su g g e ste d t h a t c o r a l r e e f s form th e s c a r p s . The G ulf of Mexico is known to be t e c t o n i c a l l y u n s t a b l e and has sub sid ed or t i l t e d ( E a r d l e y , 1951; see a ls o Ap p e n d ix ) and i s e s s e n t i a l l y an a c t i v e g e o s y n c lin e ( G la e s s n e r and T e i c h e r t , 1947). N e t t l e t o n (1952) r e p o r t e d about 12,000 m of upper J u r a s s i c and p o s t - J u r a s s i c sed im en ts a t the p r e s e n t shore l i n e . W ells have p e n e t r a t e d n e a r l y 5,000 m of upper Cenozoic se d im e n ts d e p o s i t e d in sh a llo w w ater ( F i s k , 1953). Over 1,200 m of Q u a te rn a ry se d im e n ts have been d e p o s ite d n e a r th e D e l t a , and p o s t-W is c o n s in se d im e n ts 351 alone are 180-m t h i c k . F is k con cluded t h a t b u r i e d t r e n c h e s of P l e i s t o c e n e r i v e r s on th e G ulf C o a s t a l P l a i n i n d i c a t e a sea l e v e l low ering of 450 f t . These b u r ie d c h a n n e ls r e p o r t e d l y show no ev id ence of w arping or t i l t i n g . I f th e M i s s i s s i p p i Trough was cut by s u b a e r i a l e r o s i o n d u rin g the P l e i s t o c e n e epoch when se a l e v e l was lo w ered , then a d i s c r e p a n c y r e s u l t s f o r the tro u g h which i s a t l e a s t 550-m deep and can be tr a c e d to a t l e a s t 1,800 m; t h u s , downwarping i s i m p l i e d . Antoine and Ewing (1963) showed t h a t s u b - s u r f a c e beds o f f G a lv e sto n c o n tin u e to d ip in a seaward d i r e c t i o n to a p o i n t about 60 km o f f s h o r e where an u p tu r n in g of the s t r a t a i s o b se rv ed . T h is i s i n t e r p r e t e d to i n d i c a t e the p re s e n c e of a prom inent r id g e or u p l i f t in th e de ep e r l a y e r s which form th e s o u th e r n boundary of the g e o s y n c l i n e , s e p a r a t i n g i t from the Sigsbee S c a rp . Ewing, A n to in e , and Ewing (1960) r e p o r t e d t h a t the g e o s y n c lin e i s bounded on the so u th by a rid g e about 185-km w ide, the s o u th e r n edge of which i s a p p ro x im a te ly c o i n c i d e n t w ith the 1,500 fm ( 2 .7 km) c o n to u r . They c i t e a d d i t i o n a l ev id e n ce t h a t the r id g e was cuased e i t h e r by f o l d i n g of o l d e r se d im e n ts or by u p l i f t of the t r o u g h or tr e n c h which had become f i l l e d . F u r t h e r , they su g g e st t h a t t h i s rid g e m ight be a c o n t i n u a t i o n of the A p palachian system which t r e n d s toward a t t h i s p o i n t a t l e a s t as f a r so uth as M i s s i s s i p p i . A ntoine (1963) and A ntoine and H arding (1963) have 352 o b ta in e d o f f s h o r e s e is m ic m easurem ents betw een Panama C i ty and Mobile Bay. Combining th e s e d a t a w ith th o se of w e l ls d r i l l e d n e a rb y , th ey have p l o t t e d the d e p th of the base of the Upper C r e ta c e o u s . A d i s t i n c t tro u g h e x i s t s so u th of the c o a s t l i n e where n e a r l y 4,80 0 m of se d im e n ts have a c c u m ulated s in c e the C re ta c e o u s . T h is tro u g h s h o a l s b o th to the n o r th (lan d w ard ) and to the so u th (to w ard s th e deep s e a ) , about 75 km to 95 km o f f s h o r e . The a x is i s ro u g h ly a lig n e d to t h a t of the Gulf C oast g e o s y n c l i n e . T his i s s i m i l a r to the s e ism ic ev id e n ce so uth of Texas (A n toine and Ewing, 1963). Antoine and Ewing (1963) made a se ism ic t r a v e r s e a- c r o s s the so u th w e s te rn p a r t of the F l o r i d a s h e l f and r e p o r te d the fo llo w in g r e s u l t s : ( 1 ) The T e r t i a r y and Upper C re ta c e o u s se d im e n ts t h i n from th e edge of the s h e l f and from the s h o r e l i n e toward the c e n t e r of the s h e l f and (2) the Lower Mesozoic and P a l e o z o ic se d im e n ts app ear to form a l e n t i c u l a r body w ith a t h i c k n e s s of a p p ro x im a te ly 4 km ne ar th e c e n t e r of th e s h e l f . U n f o r t u n a t e l y , n o th in g could be d e te rm in e d about the F l o r i d a Escarpm ent from th e s e d a t a . Moore and C urray (1963a) have made s e v e r a l ESP r e c o r d s a c r o s s the c o n t i n e n t a l t e r r a c e in th e n o r t h w e s t e r n p a r t of th e G ulf of Mexico. These r e c o r d s r e v e a l n e a r l y f l a t , p a r a l l e l beds of P l i o c e n e and Q u a te r n a r y s t r a t a , o f te n broken by f a u l t s . Some of th e f a u l t s re a c h th e se a s u r f a c e ; o t h e r s can be t r a c e d to n e a r l y 1,000 m. Both u p a rc h in g and 353 downwarping are i n d ic a t e d in surveyed a r e a s . Creager concluded t h a t d i a s t r o p h i s m , v o lca n ism , and slumping have played a p a r t in the o r i g i n of topography of the Campeche and Yucatan r e g i o n s . C reager (1958) b e l i e v e s the c o n t i n e n t a l slope in th e Western Bay i s the r e s u l t of d ia s tr o p h i s m , has been l i t t l e m o dified by s e d i m e n ta tio n , and has a smooth, concave upper s l o p e . The lower slo p e i s broken by a s e r i e s of t e r r a c e s which he a t t r i b u t e s to f a u l t i n g . In th e Southern Bay, the c o n t i n e n t a l slope ap p e a rs to be a p ro d u c t of u n s t a b l e se d im e n t. The upper con t i n e n t a l slo p e is smooth and convex which C reager a t t r i b u t e s to s e d i m e n ta tio n . The lower slo p e i s h ig h ly i r r e g u l a r . Topography of th e c o n t i n e n t a l slo p e in the E a s te r n Bay may be the r e s u l t of f a u l t i n g or c a rb o n a te d e p o s i t i o n on a v o l c a n ic basement. The c o n t i n e n t a l slo p e i s s t e e p , s t r a i g h t , and may i n t e r s e c t a f a u l t on land. Gealy b e l i e v e s t h a t much of the su b sid e n c e o ff s h o re could have taken p la c e d urin g the Q u a te rn a ry p e r io d b e cause of the th ic k L ate T e r t i a r y se d im e n ts. The r a t e of subsiden ce could have been g r e a t e r on the lower p a r t of the c o n t i n e n t a l s l o p e , accounting f o r t i l t i n g toward the Sigsbee Deep, w hile i r r e g u l a r sub sid en ce would r e s u l t in i r r e g u l a r i t i e s on the c o n t i n e n t a l s lo p e . Ewing and c o lle a g u e s s t a t e d t h a t th e Sigsbee Scarp ap p e a r s to be a s e is m ic . T h e r e fo r e , th e a u th o r s su g g e st an o r i g i n based upon a p r o c e s s inv olved in u n c o n s o lid a te d 354 sedim ents and n o t c o n t r o l l e d by t e c t o n i c a c t i v i t y in the basem ent. The m ag netic d a t a of M i l l e r and Ewing (1956) a p p a r e n t l y su p p o rt t h i s c o n c l u s i o n f o r no an om alies occur over the s te e p s l o p e . M i l le r and Ewing (1956) made a m agnetic su rv e y of the Gulf of Mexico and in c lu d e p r o f i l e s a c r o s s the West F l o r i d a E scarpm ent. M agnetic anom alies r e p o r t e d l y were n o t l i n e a r but r a t h e r were 9 km to 37 km in d ia m e te r and up to 400 gammas in a m p litu d e . The boundary between the two ty p es of f i e l d s ( lim e s t o n e p la tf o r m and th e deep se a b a s i n ) is sh a rp and c o in c id e s w ith th e s t e e p e sca rp m en t. A ccording to M i l l e r and Ewing, coverage was s u f f i c i e n t to show t h a t th e anom alies are not l i n e a r , hence they concluded t h a t no la r g e normal f a u l t o c cu rs h e re in t h e basem ent ro c k . They su g g ested t h a t th e l a r g e an o m alies could r e s u l t from b a s i c v o lc a n ic cones now b u r ie d by as much as two m ile s of c a l c a re o u s s e d im e n ts . Other u n p u b lis h e d s t u d i e s i n d i c a t e t h a t s i m i l a r c o n d i t i o n s e x i s t in the n o r t h e a s t e r n p a r t of th e Gulf of Mexico. R e g a r d l e s s , stro n g m agnetic anom alies o c cur a t the edge of Campeche Banks and th e F l o r i d a E sc a rp - men t . No l a r g e , l i n e a r , p o s i t i v e m agnetic a n o m a lie s such as th o se found o f f the e a s t c o a s t of th e U nited S t a t e s have been found along the G ulf of Mexico b u t some e vid ence i n d i c a t e s t h a t th e y may occur ne ar th e s h o r e l i n e of Texas and L o u is ia n a . T h is g iv e s f u r t h e r s u p p o r t to th e view t h a t the 355 s h e l f here c o n s i s t s of a s e r i e s of t h i c k se d im e n ts o v e r l y ing a t h i n c r u s t a l column e s s e n t i a l l y th e same as t h a t found s e i s m i c a l l y under th e deep b a s i n . E w in g .e t a l . (1955) and M i l l e r and Ewing (1956) have concluded from m agnetic and s e is m ic i n v e s t i g a t i o n s t h a t most o f th e s h e l f o f f Texas and L o u is ia n a c o n s i s t s of a t h i c k se d im e n ta ry l a y e r b u i l t up over a c r u s t of the same type as found in the c e n t e r of the b a s i n and t h a t t y p i c a l c o n t i n e n t a l type c r u s t does n o t appear u n t i l near the s h o r e l i n e (A n to ine and Ewing, 1963). S i m i l a r c o n c lu s io n s have been re a c h e d u sin g Lg o b s e r v a t i o n s ( P r e s s and Ewing, 19 5 2). G r a v ity an om alies su g g e st t h a t much of the c o n t i n e n t a l s h e l f c o n s i s t s of a t h i c k column of se d im e n ts over a t h i n o cean ic type c r u s t (Worzel and S h u r b e t, 1955a, 1955b). Ewing, E r i c s o n , and Heezen (1958) have concluded t h a t n e i t h e r g e o p h y s ic a l nor s e d im e n ta r y d a t a su p p o rt t h e o r i e s based upon r e c e n t su b sid e n c e o f th e c o n t i n e n t a l c r u s t to g r e a t d e p t h s , as has been su g g e ste d by Greenman and LeBlanc (1956) and o t h e r s . These a u th o r s s u g g e s t t h a t v e r t i c a l f a u l t i n g of 1,500 m to 3,000 m r e s u l t e d in g r e a t su b sid e n c e of the G u lf of Mexico which o c c u rre d d u r in g the l a s t 10,000 to 20,000 y e a r s . As a r e s u l t of t h e i r c o n f l i c t i n g views Ewing, E r ic s o n , and Heezen (1958) s t a t e d : ’’The a p p l i c a t i o n of the t u r b i d i t y - c u r r e n t co ncep t to a n c i e n t se d im e n ts may l e s s e n th e need f o r wide o s c i l l a t i o n s o f se a l e v e l , l a r g e and r a p i d v e r t i c a l movements, and huge h y p o t h e t i c a l 356 c o n t i n e n t a l s o u rc e s of s e d im e n t, such as A p p a l a c h i a .” D is c u s s io n S e v e ra l f a c t o r s have been ig no red by the g e o p h y sic ists. F i r s t , la r g e f a u l t s do e x i s t in the G ulf of Mexico, v e r i f i e d by many d r i l l e d w e l l s , and r e c e n t l y by c o n tin u o u s s e is m ic p r o f i l i n g (Moore and C u rray, 1963a). These f a u l t s a re r e a l yet most of th e n o r t h e r n p a r t of the Gulf i s an a s e is m ic r e g i o n . S tron g s e ism ic a c t i v i t y has been re c o rd e d in the w e ste rn G u lf. O c c a s io n a l s t r o n g e a r th q u a k e s do o c cur in a p p a r e n t l y n o n -s e is m ic r e g i o n s ( e . g . , the C h a r le s t o n e a r t h q u a k e ) . P r i c e (1951) p o s t u l a t e s the G ulf Coast f a u l t ing ( o f f T exas, e t c . ) may have been of a lo w -en ergy t y p e , u s u a l l y n o t re c o rd e d by o b s e r v a t o r i e s . Weaver (1955) s t a t e d : "the n o r t h s id e of the Gulf of Mexico i s n o t an e a rth q u a k e r e g i o n , b u t t h e r e i s e v id e n c e of some movement t h e r e . Data which are no t r e s t r i c t e d i n d i c a t e t h a t one w ell-do cum ented f a u l t has a d o w n - t o - t h e - c o a s t movement of f i v e in c h e s in the l a s t 14 y e a r s . ” P r i c e (1951) a l s o r e p o r te d t h a t p r e v i o u s shocks in the r e g i o n of th e Bay of Campeche have gone u n n o tic e d . Second, g e o p h y s i c i s t s a p p a r e n t l y cann ot agree among th em se lv e s b ecause of the g r o s s assu m p tio n s t h a t o f t e n are r e q u i r e d f o r p r o p e r g e o l o g i c a l i n t e r p r e t a t i o n . Ewing and a s s o c i a t e s i n d i c a t e t h a t the Gulf i s a t y p i c a l o c e a n ic b a s i n , m o d ified by the a d d i t i o n o f 7-km s e d im e n ts . This i s a 357 b a s i c argument f o r the perm anency o f ocean b a s i n s and a g a i n s t d o w n f a u l t i n g . The m ag n e tic s t u d i e s by M i l l e r and Ewing (1956) a tte m p te d to show t h a t w h ile an o m alies o c c u rr e d on e sc a rp m e n ts o f f F l o r i d a and Campeche, th e s e were n ot l i n e a r , b u t c i r c u l a r - - p r o b a b l y v o l c a n i c p e a k s . As C re ag e r (1958) p o in te d o u t , a c o n to u r i n t e r v a l of 100 gam mas was u s e d , y e t th e r e p o r t e d i n s t r u m e n t e r r o r was about 350 gammas! A f u r t h e r i n d i c a t i o n of th e c o n f l i c t i n g e v id e n c e i s L y o n s’ (1957) s t a te m e n t t h a t : "The G u lf i s w e l l o u t of i s o s t a t i c e q u i l i b r i u m , and t h a t a d d i t i o n a l lo a d in g of s e d i ments i n the f u t u r e w i l l cause i t to fo u n d e r more . . G. P. W oollard (1949) a n a ly z e d g r a v i t y v a lu e s around the w orld and c o n c lu d e d : "No sweeping s t a t e m e n t s can be made c o n c e rn in g any u n i v e r s a l d i f f e r e n c e betw een th e c r u s t b e n e a th t h e oceans and the c o n t i n e n t s from g r a v i t y d a t a a l o n e . " U n t i l g r a v i t y d a t a i s t i e d down more c l o s e l y th e e n t i r e c o n c e p t of i s o s t a s y i s s u s p e c t (L e e s, 1 9 5 0 ). The use o f Lg p hase in the A r c t i c in d e f i n i n g t h a t b a s i n as o c e a n ic a p p a r e n t l y was q u e s t i o n a b l e , f u r t h e r i n d i c a t i n g con fused i n t e r p r e t a t i o n ( s e e d i s c u s s i o n on th e A r c t i c ) . The m ag n e tic f i e l d i s u n ifo rm over l a r g e a r e a s of th e G u lf of Mexico. The re a s o n f o r t h i s i s d i f f i c u l t to e x p l a i n . T h i r d , g e o p h y s i c a l " e v id e n c e " t h a t th e G u lf has alw ays been an ocean b a s i n d i r e c t l y c o n f l i c t s w ith d e t a i l e d 358 g e o l o g i c a l mapping t h a t s t r o n g l y s u p p o r t s fo rm er lan d m asses where oceans now e x i s t . T h is i n c l u d e s th e G u lf of M exico, as w e l l as th e Ja p a n and O khptsk S e a s, and p r o b a b l y th e A r c t i c Ocean. George Shor (1964) has r e p o r t e d t h a t the B e rin g Sea i s a c l a s s i c example of th e c o n v e r s io n of an ocean b a s i n i n t o a c o n t i n e n t a l mass. F o u r th , t h e a tte m p t of some a u t h o r s to e x p l a i n a p p a r e n t l y anomalous m arine d e p o s i t s as th e s o le r e s u l t of t u r b i d i t y c u r r e n t s and disav ow in g s u b s id e n c e of ocean b a s i n s or form er land m asses in a r e a s where t h e r e a re now a b y s s a l d e p th s and o c e a n i c - t y p e s t r u c t u r e c o m p le te ly f a i l t o e x p l a i n c o a r s e c o n g lo m e ra te s ( n o t f i n e g r a i n s e d im e n ts and sa n d s) such as th o se d e p o s i t e d in th e Congo B asin o f A f r i c a and a l l u v i a l - d e p o s i t e d b r e c c i a s such as the San O nofre in S o u th ern C a l i f o r n i a . H ere, th e s o u r c e s were c l e a r l y from sea toward land and the lan d mass was o f g r e a t s i z e . Nor does i t e x p l a i n th e so u rc e a r e a s of i c e movements, a ls o from a seaward d i r e c t i o n . I t a p p e a rs t h a t some g e o l o g i s t s and g e o p h y s i c i s t s a re h i d in g behind a g e o lo g i c p r o c e s s ( t u r b i d i t y c u r r e n t s ) t h a t i s supposed to be th e answer to a l l g e o l o g i c a l p r o c e s s e s and so lv e a l l m y s t e r i e s ! Because of q u e s t i o n a b l e d a t a i t i s no t p o s s i b l e to s p e c u l a t e f u r t h e r on the o r i g i n of th e c o n t i n e n t a l s l o p e s or th e numerous t e r r a c e s in th e G ulf r e g i o n . STRAITS OF FLORIDA I n t r o d u c t i o n Hurley, et__al. (1962) and H u rley (1964) r e c e n t l y summa r i z e d the major b a th y m e t r i c f e a t u r e s of the S t r a i t s of F l o r i d a . O ther im p o rta n t p a p e rs a re c i t e d below . The Ba hama P l a t f o r m i s c o n s id e r e d s e p a r a t e l y a lth o u g h i t o b v io u s ly to u ch e s upon th e S t r a i t s of F l o r i d a . A r e c e n t b i b l i o g r a p h y th o ro u g h ly c o v e rs C arib b ean g e o logy (F in k , 1964). The g e n e r a l c h a r a c t e r of the S t r a i t s i s d i s c u s s e d f i r s t , th en some of the d e t a i l s of P o u r t a l e s T e r r a c e by Jo rd a n and S te w a rt ( 1 9 6 1 ), and J o r d a n , M alloy, and Kofoed (1964) are rev ie w ed . R e s u l ts The S t r a i t s o f F l o r i d a i s the l o n g e s t of s e v e r a l c h a n n e l s in th e Bahama P l a t f o r m r e g i o n . The f l o o r of the n o r t h e r n S t r a i t s has a d e p th of about 730 m, a g e n t l e g r a d i e n t - - ! m/km--from about 27° 3 0 1 N to as f a r so u th as 25° 30* N where th e S t r a i t s f l o o r (o r v a l l e y ) e m p tie s onto an a b y s s a l p l a i n a t 845 m. Between 25° 3 0 1 N and 24° 2 0 ’ N the l o n g i t u d i n a l p r o f i l e i s l e v e l . The slo p e s t e e p e n s ( 4 .0 m/km) and becomes more i r r e g u l a r . I t i s b e l i e v e d t h a t 359 360 t h i s g r a d i e n t c o n tin u e s i n to the Gulf of Mexico. Side s l o p e s of the F l o r i d a S t r a i t s vary g r e a t l y in c h a r a c t e r . On the F l o r i d a sid e th e y are g e n tl e t e r r a c e s , d i f f e r i n g from l o c a t i o n to l o c a t i o n , w hile th o se on the Bahama sid e are s t e e p and i r r e g u l a r . T e r r a c e s occur near the base a t d e p th s of 270 m and about 350 m. In the s o u t h w estern p a r t a t e r r a c e a ls o ap p ea rs between 180 m and 275 m. S o u th e a s t o f Key Largo the slo p e i s s i m i l a r to t h a t in the n o r t h e r n re g io n except f o r a smooth b ut s t e e p e r s e c t i o n from a b o u t 365 m to 550 m. A t e r r a c e occu rs here between 180 m to 275 m. I r r e g u l a r i t i e s about 20-m hig h are tho ug ht to i n d i c a t e rock o u t c r o p s . In f a c t , bedrock p ro b a b ly i s w idespread in the S t r a i t s , but in p l a c e s where topography i s rounded, a t h i n cover o f sediment perhaps o v e r l i e s the bedrock. S tro n g c u r r e n t s of the Gulf Stream , exceeding 200 cm /sec, u n q u e s tio n a b ly account f o r much of the bottom f e a t u r e s . H urley and a s s o c i a t e s b e li e v e t h a t submarine e r o s i o n and f a u l t i n g are the two major su g g ested o r i g i n s f o r the S t r a i t s . The so u th e rn S t r a i t s of F l o r i d a i s w ider and c o n s i d e ra b l y more i r r e g u l a r than the n o r t h e r n S t r a i t s (H u rley , 1964). A d i s t i n c t t r a n s i t i o n occurs between the two r e gions in v o lv in g t h i c k , n e a r l y f l a t - l y i n g c a rb o n a te ro cks o ff F l o r i d a and the f a u l t e d , f o ld e d , and in tr u d e d ro ck s o f f 361 Cuba. The a x i a l v a l l e y of th e S t r a i t s i s s t e e p e r th an f a r t h e r n o r t h , a v e r a g in g 5 m/km. At Cay S a l Bank, the l o n g i t u d i n a l p r o f i l e s t e e p e n s u n t i l a t 85° W the d e p th r e a c h e s 3,500 m. The F l o r i d a s i d e o f th e S t r a i t s i s g e n t l e and smooth; the s o u th e r n s id e i s s t e e p and i r r e g u l a r . T e r r a c e s occur a t 90 m and 460 m, e x te n d in g from M arquesas to Cape F l o r i d a . T h is t e r r a c e , named P o u r t a l e s , which e x te n d s along the e a s t c o a s t of F l o r i d a , l i e s a t d e p th s of 180 m to 260 m. H urley has ex te n d ed th e name P o u r t a l e s T e r r a c e to in c lu d e th e t e r r a c e s between 82° 2 1 1 W and 26° 3 0 ’ N a t d e p th s from 165 m to 238 m, and th o s e o f f the F l o r i d a Keys t o as much as 310 m to 330 m. H u rle y (1964) con clu ded t h a t t o p o g r a p h ic f e a t u r e s p r o b a b ly are the r e s u l t of m arine e r o s i o n . He has shown t h a t bottom c u r r e n t s , moving from t h e s o u th w ith v e l o c i t i e s o f 25 c m /se c, o c c a s i o n a l l y r e v e r s e in d i r e c t i o n . E viden ce a l s o p o i n t s to a t h i n sedim en t co v er ( H u rle y , 1963; and H u r le y and F in k , 1963). Thus, w h ile th e im p o rtan c e of c u r r e n t e r o s i o n i s p ro v e d , th e f u n d a m e n ta l s t r u c t u r e o u t l i n i n g the S t r a i t s of F l o r i d a s t i l l i s unknown. J o r d a n and S t e w a r t (1961) and J o r d a n , M alloy , and Kofoed (1964) s t u d i e d the P o u r t a l e s E scarpm ent and T e r r a c e i n c o n s i d e r a b l e d e t a i l so u th of the F l o r i d a Keys. The p r i n c i p a l f e a t u r e s a r e : (1 ) on th e e a s t e r n end of th e 362 t e r r a c e a n o r t h e a s t t r e n d i n g band of complex k a r s t t o p o g r a phy i s eroded i n t o what a p p e a rs to be an a n c i e n t sand s p i t w hich i s p a r t l y f a u l t - c o n t r o l l e d ; (2 ) in the c e n t e r of the t e r r a c e i s a r e l a t i v e l y f e a t u r e l e s s p l a i n ; ( 3 ) on th e w e s t e rn end of the t e r r a c e a re g i a n t s i n k h o l e s , f i v e o f which are l o c a t e d along P o u r t a l e s E scarp m en t; and ( 4 ) a number of o f f s e t s , v a l l e y s , and tr o u g h s occur along the s o u t h e r n m ar gin o f th e t e r r a c e . P o u r t a l e s T e rra c e i s more th a n 185-km lo n g , has a max- 2 iirium w id th o f 32 km, and c o v e rs an a r e a o f about 2,600 km . The t e r r a c e b e g in s a lon g the 180-m (100 fm) i s o b a t h and e x te n d s seaward t o 275 m where i t t e r m i n a t e s a t the P o u r t a l e s Escarpm ent which form s the edge o f th e t e r r a c e . In a d d i t i o n to the s h a llo w e s c a rp m e n t, a n o th e r d e e p e r one has been found by J o r d a n and S te w a rt a t a d e p th of about 1,280 m to 1,460 m, and was named M i t c h e l l Escarpm ent by them. I t i s about 130-km long and has a 20° s l o p e . A l a r g e group of v a l l e y s have t h e i r h e ad s a t a b ou t 550 m and e x te n d beyond 1,650 m. Geology The l i t h o l o g y of the t e r r a c e i s p r e d o m in a n tly lim e s t o n e , in p l a c e s e n c r u s t e d w ith p h o sp h a te m i n e r a l s , c o r a l gro w th, and i r o n o x id e s t a i n i n g . Sed im en ts c o n s i s t of c a r b o n a te s i l t s and c l a y s . The youngest r o c k s on th e t e r r a c e a re o f Miocene a g e . 363 Bush (1 9 5 1 ) d e s c r i b e d a ro c k sample o b t a i n e d below P o u r t a l e s E scarpm en t (686 m; 24° 1 0 T N, 81° 3 1 T W). The specim en was c a l c a r e o u s ro c k and d a te d as Lower Miocene c o r r e l a t e d w i t h the C h ip o la f o r m a t io n of n o r t h e r n F l o r i d a . He s t a t e d th e specim en was d e p o s i t e d a t 55 m, s u b s e q u e n t l y » r a i s e d above s e a l e v e l , th e n low ered to i t s p r e s e n t d e p t h . G o r s l i n e and M i l l i g a n (1 96 3) d e s c r i b e d b o tto m sam ples from alo n g the m arg in o f P o u r t a l e s T e r r a c e from d e p th s of 238 m to 516 m. The r e c o v e r e d sam ples were m o s tly p h o s p h o r i t e and d a te d as Miocene o r l a t e Miocene a g e. J . W. K ofoed, G o o d e ll, and Yon (1960) p r o j e c t e d Miocene fo rm a t i o n s on la n d o f f s h o r e and th e s t r a t a a re a t a b o u t th e same d e p th as th e t e r r a c e . T h is s u g g e s t s th e t e r r a c e i s o f Mio cene age and was once exposed to s u b a e r i a l w e a t h e r i n g . Kofoed and J o r d a n (1964) d e s c r i b e d the u pper c o n t i n e n t a l slo p e about 83 km w est o f Dry T o r t u g a s . Here two m ajor f a u l t s c a r p s occur norm al to th e c o n t i n e n t a l s l o p e betw een a b o u t 165 m and 100 m. The g r a d i e n t o f th e s c a r p s v a ry from 13° to 49° and a re up to 220-m h i g h . They c o n c lu d e d t h a t the r o c k s a re p r o b a b l y of Miocene age. P o u r t a l e s T e r r a c e shows l o c a l e v id e n c e o f s t e p f a u l t in g . As a r e s u l t , J o r d a n and S te w a rt b e l i e v e P o u r t a l e s E s c a rp m e n t, as w e l l as M i t c h e l l E sc a rp m e n t, a r e of f a u l t o r i g i n . In r e g a r d to th e o r i g i n of the numerous subm arine c a n y o n s, J o r d a n and S t e w a r t p o i n t e d o ut t h a t c u r r e n t s a re much to o s w i f t f o r any sedim ent to a cc u m u late b e f o r e t r i g g e r i n g a t u r b i d i t y c u r r e n t . The a u t h o r s c o n clu d ed t h a t th e o r i g in s of t h e s e v a l l e y s a re u n r e l a t e d to c o n d i t i o n s e x i s t i n g i n th e S t r a i t s to d a y b u t were formed by t u r b i d i t y c u r r e n t s i n th e p a s t . They a l s o r u l e d o u t a t e c t o n i c o r i g i n . J o r d an, M a llo y , and K ofoed, on th e o t h e r han d, c o n clu d ed t h a t the P o u r t a l e s E scarpm ent was formed by p o st-M io c e n e f a u l t ing w hich p re c e d e d s u b a e r i a l e x p o su re of th e t e r r .a c e , r e s u l t i n g in the f o r m a t i o n o f s i n k h o l e s a lo n g the s c a r p by s u r f a c e w a te r l e a c h i n g . S u b se q u e n t s u b s id e n c e and e u s t a t i c t r a n s g r e s s i o n drowned the t e r r a c e a t 180 m to 290 m. The s t r o n g F l o r i d a C u r r e n t has p r e v e n t e d sed im e n t from accumu l a t i n g , t h e r e b y p r e s e r v i n g th e k a r s t to p o g r a p h y . EAST COAST OF SOUTH AMERICA I n t r o d u c t i o n A t o t a l of 14 p r o f i l e s a re a v a i l a b l e f o r th e e a s t c o a s t of South A m erica. Two s o u r c e s were a v a i l a b l e - - R u s - s i a n (OB) and Woods Hole O c e a n o g ra p h ic I n s t i t u t i o n ( P l a t e 38, p r o f i l e s l a b e l e d A and C ) . No a tt e m p t i s made to d i s c u s s the geology o r g e o p h y s i c a l c o n d i t i o n s o f f t h i s c o a s t b e c a u se o f th e d e a r t h of p r o f i l e s , as w e l l as the l a c k o f i n f o r m a t i o n on geolog y and g e o p h y s i c a l c o n d i t i o n s . S hepard (1 9 6 3 ) h as shown how l i t t l e i s known a b o u t the c o n t i n e n t a l s lo p e o f f South America f o r he d e v o te d l e s s th an h a l f a page of h i s book to t h i s r e g i o n . Heezen and Tharp (1961) have p u b l i s h e d a p h y s i o g r a p h i c d iag ram of the S outh A t l a n t i c Ocean t h a t i s u s e f u l in i n t e r p r e t i n g f e a t u r e s . R e s u l t s D epths of s h e l f b r e a k s a lo n g the e a s t c o a s t o f South A m erica vary from a b o u t 50 m to 150 m (T a b le 2 4 ) . However, th e l i m i t e d number of p r o f i l e s and wide s p a c in g do es n o t a llo w d raw in g any d e f i n i t e c o n c l u s i o n s o t h e r th an t h a t th e 365 366 s h e l f has a s h a l l o w e r s h e l f b r e a k th a n S o uth A f r i c a . T h i s may or may n o t be o f s i g n i f i c a n c e i n c o n s i d e r i n g c o n t i n e n t a l d r i f t . T a b le 24. A pp ro xim ate D epth of S h e l f B r e a k s - - E a s t C o a s t of S o u th Am erica* PROFILE NUMBER SHELFBREAK (m) C - 57-1 100 ( ? ) A -247-19 50 A -247-3 70 C -5 7 -3 50 A -247-12 60 A -247-4 70 C -5 7 -5 50 ( ? ) A -247-5 > 1 0 0 A -247-6 190 C -6 0 -3 > 1 50 A -2 4 7 -17 150 A -2 4 7 -18 150 F a l k l a n d I s l a n d s 160 - 180 *See P l a t e 38 f o r l o c a t i o n A v a i l a b l e i n f o r m a t i o n d e r i v e d from c h a r t s s u g g e s t s t h a t t h e s l o p e s o f f m ajor r i v e r s ( o f f V e n e z u e la , th e G u i- a n a s , and B r a z i l ) have a g e n t l e s l o p e such as e x i s t s o f f t h e M i s s i s s i p p i d e l t a . S o u th o f Cape Roque th e s l o p e s a re 367 s t e e p e r f o r 2,8 00 km. Here the g r a d i e n t i s about 4° t o 20°, c o n s i d e r a b l y above th e a v e r a g e . Shepard (1963) s t a t e d t h a t t h i s a p p e a rs to be th e l o n g e s t s t r e t c h in t h e w orld w ith c o n s i s t e n t l y s t e e p s l o p e s . With the e x c e p t i o n of the r e g i o n n e a r R e c if e ( a t the b u lg e of B r a z i l ) , where a l i n e a r group of i s l a n d s and banks o c c u r s , th e c o n t i n e n t a l s l o p e a p p e a r s to be r e l a t i v e l y sm o o th . P r o f i l e C -5 7 -1 , o f f B r i t i s h G u ia n a, c r o s s e s th e s lo p e a t a l a r g e a n g le b u t r e v e a l s a concave s lo p e down to 300 m beyond which i s a l a r g e f l a t topped seamount b e v e le d o f f a t 1 ,1 0 0 m. I t s seaward s lo p e i s r e l a t i v e l y smooth and t e r m in a t e s a b r u p t l y in G u ian a B asin a t 4 ,5 0 0 m. A s l i g h t d e p r e s s i o n a l s o a p p e a rs a t the base of th e s l o p e . Minor t e r r a c e s o ccu r on the c o n t i n e n t a l s lo p e a t about 600 m and 2,200 m. P r o f i l e C -60-1 i s o f f th e Amazon R iv e r and shows a s t e e p e r g r a d i e n t than t h a t o c c u r r i n g o f f th e M i s s i s s i p p i R iv er d e l t a . In f a c t , t h i s p r o f i l e d o es n o t have the a p p e a r a n c e of a d e l t a c o n t i n e n t a l s l o p e . I t has a c o n t i n e n t a l r i s e b e g in n in g a t 3,0 00 m and s e v e r a l p ron ou nced r i d g e s or v o l c a n i c p eaks p r o t r u d e above the c o n t i n e n t a l r i s e . P r o f i l e s A -247-19 and A -264-3 show th e h i g h l y i r r e g u l a r to p o g ra p h y a c r o s s a group of banks and i s l a n d s at about 4° S. None of the f e a t u r e s a p p ea r to c o r r e l a t e from one p r o f i l e to a n o t h e r . S e v e r a l of the banks a re p la n e d 368 sm o o th ly a t 100 m. P r o f i l e C -57-3 i s more n o rm a l to th e c o a s t and r e v e a l s a s t e e p c o n t i n e n t a l s l o p e down to 5 km and h a s e s s e n t i a l l y no c o n t i n e n t a l r i s e ; i t i s more o f a s h o r t s t e p . T h is i s a l s o t r u e o f A -2 4 7 -1 2 , w h ic h i s l o c a t e d n e a r b y . T h is l a t t e r p r o f i l e i s s i m i l a r to C -5 7 -2 i n t h a t b o th a l s o have a marked t e r r a c e o f 1 ,0 0 0 m to 1 ,2 0 0 m. On p r o f i l e A -2 4 7 -4 , l o c a t e d f u r t h e r s o u t h , t h i s 1,000-m t e r r a c e i s a l s o p r e s e n t b u t has more r e l i e f and i s w i d e r . A seam ount p r o v i n c e o c c u r s on th e c o n t i n e n t a l r i s e . I t i s b e l i e v e d t h a t th e t e r r a c e i s e s s e n t i a l l y c o n t i n u o u s from Cape C a lc a n h a r to a b o u t 16° S, or a d i s t a n c e o f more t h a n 1 ,2 0 0 km. P r o f i l e A -246-5 c o n s i s t s of two m ajor s t e p s - - a t a b o u t 2 ,0 0 0 m and 4 ,1 0 0 m. Both o f t h e s e p l a t e a u s a re wide and have r e l i e f o f a few hu n d red m e t e r s . The u pp er c o n t i n e n t a l s l o p e i s concave and s t e e p w i t h no d i s c e r n i b l e f e a t u r e s . P r o f i l e s A -247-6 and C -6 0 -3 a re c l o s e t o g e t h e r y e t a re d e c i d e d l y d i f f e r e n t i n s h a p e . Both t r a v e r s e t h e c o n t i n e n t a l s l o p e a t a v e ry low a n g l e ; (OB 5 7 / 8 - 1 4 ) shows th e a b se n c e of su b m a rin e canyons o f f U ruguay as w e l l as a b y s s a l h i l l s . While s e v e r a l f l a t a r e a s s u g g e s t t e r r a c e s , th e o r i e n t a t i o n o f th e p r o f i l e s p r e c l u d e s any c o n c l u s i o n s . The c o n t i n e n t a l r i s e seems to be w e l l - d e v e l o p e d and s h a r p l y i n t e r s e c t s the c o n t i n e n t a l s l o p e a t a d e p t h of a b o u t 2 ,9 0 0 m. The METEOR d i s c o v e r e d a l a r g e s w e l l betw een 30° S to 40° S (named Rio G rande do S u l S w e ll) i n the e a s t e r n 369 p r o j e c t i o n o f the m i d - A t l a n t i c Ridge ( S t o c k s and Wust, 1 9 3 5 ). I t r i s e s from 3,000 m to 4 ,0 0 0 m to 700 m t o 600 m. The B r a z i l i a n B a s in l i e s to th e n o r t h and the A r g e n t i n e Ba s i n to th e s o u t h . P l a t e a u s on th e top of th e Rio G rande do S u l S w e ll a r e c o n s i d e r e d to be l a v a flo w s ( D e la n e y , 1 9 6 2 ). P a r t of t h i s p l a t e a u can be seen on p r o f i l e OB 5 7 / 8 - 1 4 . A t e r r a c e a t a p p r o x i m a t e l y 500 m on th e c o n t i n e n t a l s l o p e c o r r e s p o n d s r o u g h ly w i t h the c o n t i n e n t a l s l o p e bounding th e p l a t e a u . From h e re s o u t h the 500-m t e r r a c e i s d i s c o n t i n u ous and v a r i e s from a b o u t 550 m to 365 m. O t h e r d e e p e r t e r r a c e s a r e even more d i s c o n t i n u o u s . P r o f i l e A-247-17 a l s o c u t s th e s lo p e a t an a n g l e , b u t in g e n e r a l shows more i r r e g u l a r i t i e s th a n th e p r e c e d i n g , more n o r t h e r n s e c t i o n . Marked c h an g e s in s l o p e o c c u r a t 900 m, 2 ,0 0 0 m, and 2 ,9 0 0 m. Below h e r e a somewhat i r r e g u l a r c o n t i n e n t a l r i s e o c c u r s . A -247-18 i s the most s o u t h e r l y p r o f i l e i n th e s e r i e s and r e f l e c t s many of th e c h a r a c t e r i s t i c s of p r o f i l e A -2 4 7 -1 7 . A s l o p e change o c c u r s a t a b o u t 800 m and a r i d g e and d e p r e s s i o n i s l o c a t e d a t a b o u t 1 ,9 0 0 m to 2 ,1 0 0 m. The e n t i r e slo p e h a s a d i s t i n c t concave s h a p e . O ff A r g e n t i n a a s e r i e s of t e r r a c e s ( s t a i r c a s e s t r u c t u r e ) i s h i g h l y c o n s p ic u o u s ( s e e Heezen and T h a r p f s p h y s i o g r a p h i c d i a g r a m ) . C. W. Holm es, o f th e U n i v e r s i t y o f F l o r i d a , h a s w r i t t e n a b r i e f d e s c r i p t i o n o f the S o u th Sandwich T rench b a se d 370 upon 12 c r o s s i n g s made by the USNS ELTAIN ( P l a t e 3 9 ). The d e e p e st p a r t of the tr e n c h ( > 7 , 3 0 0 m) i s lo c a te d in the n o r th e r n p a r t of the a rc . In t h i s s e c t i o n the g r a d i e n t of the n o r t h e r n slope i s 3°. F u r th e r south the tre n c h becomes narrow er and s lo p e s are s t e e p e r . South of about 57° S the tr e n c h has an upper g r a d ie n t of about 1° 2 0 ’ and a lower slo p e of 3° 30 ’ . Although i n t e r p r e t a t i o n of the p r o f i l e s i s d i f f i c u l t because they are incom plete and the o r i e n t a t i o n a c ro s s the slop e is unknown, s e v e r a l i n t e r e s t i n g to p o g ra p h ic f e a t u r e s are a p p a re n t. R e l a t i v e l y f l a t a re a s occur a t 1,800 m to 2,750 m on s e v e r a l p r o f i l e s . A wide t e r r a c e a ls o o ccu rs a t a d e p th of about 1,370 m on p r o f i l e SG-7. Most p r o f i l e s show a r e l a t i v e l y g e n tle upper slope and a s t e e p e r lower slop e beginning at about 2,750 m to 3,650 m. The o u te r (seaw ard) p a r t of the tre n c h w a ll i s u n u s u a lly rugged (se e p r o f i l e s 10 and 1 1 ), and on s e v e r a l p r o f i l e s the to p of the o u te r edge f l a t t e n s out and c o rre sp o n d s to a t e r r a c e or ma jo r slo p e change on the tr e n c h s lo p e . While i t is d i f f i c u l t to make any d e f i n i t e c o n c lu s io n s re g a rd in g the p r o f i l e s because a l l c r o s s the c o n t i n e n t a l slo p e a t v a rio u s a n g le s , i t would a p p ea r, n e v e r t h e l e s s , t h a t the n o r th e r n c o n t i n e n t a l s lo p e s are much s t e e p e r and have more i r r e g u l a r topography on the s lo p e and on th e up per c o n t i n e n t a l r i s e . Ewing (196 3) and Ewing, Ludwick, and Ewing (1963, 371 1964) have made a s e r i e s of s e is m ic p r o f i l e s a c r o s s the A r g e n tin e c o n t i n e n t a l t e r r a c e and b a s i n . A ll of th e s e p r o f i l e s are to o sm all to be u s e f u l . However, the s u b s u r f a c e d a t a i s of i n t e r e s t . O ff Bahia B lan c a, a t a d e p th of 3 km (where the p r o f i l e b e g i n s ) , about 1 km to 2 km of sedim ent has accum ulated on the c o n t i n e n t a l r i s e . On the s h e l f b e tween B ahia Blanca to Buenos A ire s f o u r groups of sedim en t a r y ro cks ( r e f l e c t o r s ) could be i d e n t i f i e d : R e c e n t- P lio cen e-M io cen e (0.5-km to 1-km t h i c k ) , Lower Miocene- C re ta c e o u s ( ~ ' 1 .5 km), Upper P a l e o z o i c , and Lower Paleozoic. The basement (P re c a m b ria n ) n e a r l y r e a c h e s the s u r f a c e in one r e g i o n . One or more major se d im e n ta ry b a s i n s e x i s t e d in th e o f f s h o r e re g io n in which 6-km of sed im en t accumu l a t e d . A ll of th e p o s t- P r e c a m b r ia n r o c k s e x te n d seaward an i n d e f i n i t e d i s t a n c e . The P a l e o z o ic r o c k s , however, ta p e r out n ear the c o a s t or a s h o r t d i s t a n c e o f f s h o r e . P a l e o z o ic r o c k s , which are th ic k o n sh o re , t h i n , or t a p e r out com p l e t e l y ( e s p e c i a l l y the lower P a l e o z o i c ) below the c o n t i n e n t a l r i s e . The f i r s t la y e r ( R e c e n t-P lio c e n e -M io c e n e ) a p p e a rs to th ic k e n a t the base of the c o n t i n e n t a l r i s e . The Lower M io c en e -C retac eo u s l a y e r a v e ra g e s 1 .5 km on the c o n t i n e n t a l s h e l f and re a c h e s a maximum of 2.5 km a t the to p of the c o n t i n e n t a l r i s e e a s t of Rio de l a P l a t a . Of p a r t i c u l a r i n t e r e s t i s the e x i s t e n c e of two e l o n g ated b a s i n s o r i e n t e d a p p ro x im a te ly p e r p e n d i c u l a r to the 3 7 2 p r e s e n t s h o r e l i n e . They are a b o u t 425-km lo n g , 220-km w ide, and (m ost im p o r ta n t) c r o s s the s h e l f w ith o u t c lo s in g a t th e seaward end. The A rg e n tin e B a sin , l o c a te d seaward of the c o n t i n e n t a l t e r r a c e a t d e p th s of more than about 2,600 fms, has a c cumulated more se d im e n ts than t h a t found in any o th e r ocean b a s i n . H o r i z o n t a l l y - l a y e r e d se d im e n ts a t t a i n t h i c k n e s s of 2.5 km and o v e r l i e a t y p i c a l l y rough basem ent. The b a s in has been e x c e p t i o n a l l y f r e e from d e f o r m a ti o n , e x c e p t broad c r u s t a l w arp in g , th ro u g h o u t the p e rio d of d e p o s i t i o n of the se d im e n ts . BERMUDA Although about f i f t e e n p r o f i l e s of Bermuda were exam i n e d , the echograms showed a s lo p e so s t e e p t h a t no f e a t u r e s co uld be d i s c e r n e d on th e s l o p e s . However, Chave, S a n d e rs , H e s s l e r , and Neumann (1962) made a su rv e y to the s o u t h e a s t of Bermuda, o f f C a s t l e H a rb o r, and r e p o r t e d the slo p e to be d i v i d e d i n to t h r e e d i s t i n c t b a th y m e t r i c zones: (1 ) the r e e f t r a c t , (2) the s t e e p u pp er i n s u l a r s lo p e from 18 m to 730 m, and (3 ) the t e r r a c e d g e n t l e slo p e below 730 m. The g r a d i e n t of th e s lo p e below 18 m o f t e n ex ceed s 4 5 °, and i s r e p o r t e d l y v e r t i c a l l o c a l l y . S edim ents a re a b sen t from much of the upper s lo p e and rock i s commonly re c o v e r e d . Below 730 m, where th e s lo p e i s more g e n t l e - -about 8° 3 0 ’ — the se a f l o o r i s t e r r a c e d . T hree d i s t i n c t t e r r a c e s occur on th e e a s t s id e of th e a r e a i n v e s t i g a t e d a t 823 m, 1,554 m, and 1,830 m, r e s p e c t i v e l y . A b o rin g on Bermuda ( P i r s s o n , 1914) re a c h e d th e v o l c a n ic p l a t f o r m a t 431 m, and had Miocene and Eocene f o r a - m i n i f e r a above the b a s e . P i r s s o n d a te d the v o lc a n is m as T r i a s s i c , b u t i t may be l a t e r and c o ntem peran eo us w ith v o l canism in th e C a rib b e an I s l a n d Arc. 373 MID-ATLANTIC RIDGE T o l s t o y and Ewing ( 1 9 4 9 ) , T o l s t o y ( 1 9 5 1 ) , and H eezen, T h a rp , and Ewing (19 59 ) have d e s c r i b e d t e r r a c e s on th e mid- A t l a n t i c R idg e. E a s t of a seamount l o c a t e d a t 35° 1 2 ’ N, 45° 3 3 ’ W, th e bo tto m f l a t t e n s a t 2 ,5 00 fms ( 4 ,5 7 0 m) and re m a in s a t t h i s d e p th f o r about 65 km. Along 31° N, a n o th e r 2 ,5 0 0 -fm f l a t s t r e t c h o c c u r s n e a r a h ig h peak (3 1 ° N, 45° 3 0 ’ W). These mark th e b e g in n i n g o f a number of such t e r r a c e s . T o l s t o y and Ewing in u s i n g th e term " t e r r a c e " i n d i c a t e th e y do n o t wish to convey any o r i g i n to t h e s e f e a t u r e s , w h ile H eezen, T h arp, and Ewing (1959) term ed t h e s e ” i n te r m o n ta n e b a s i n s . " Many su ch t e r r a c e s b o r d e r the m i d - A t l a n t i c Ridge a t d e p th s betw een 1,60 0 fms ( 2 ,9 0 0 m) to over 2,250 fms ( 4 ,1 0 0 m ). T h is r e g i o n o f t e r r a c e s betw een 1 ,6 00 fms to 2,5 0 0 fms s o u t h of the A zores was term ed the " t e r r a c e d zone" by T o l s t o y and Ewing. T o l s t o y (1 9 5 1 ) i n d i c a t e d t h a t two ty p e s o f t r a n s i t i o n s e x i s t betw een s u c c e s s i v e t e r r a c e s ; some a re s e p a r a t e d by a s t e p , w ith no i n t e r v e n i n g p e a k , w h e re a s in the o t h e r a p e a k , or hump, o c c u r s on th e o u t e r edge of th e h i g h e r t e r r a c e . One a r e a i n v e s t i g a t e d showed t e r r a c e s a lo n g b o t h s i d e s 374 375 of the m i d - A t l a n t i c Ridge (h u n d re d s of m ile s a p a r t ) a t the same d e p t h s . Seism ic s t u d i e s showed t h e s e t e r r a c e s ' t o have 300 m or more sed im en t on t h e i r s u r f a c e s w hereas the r i d g e i t s e l f has no sedim ent c o v e r. I t was co n clu d ed t h a t the t e r r a c e s a r e , or have been, a r e a s of g r e a t e r d e p o s i t i o n . The most rem ark able t e r r a c e s in term s of num bers, w i d t h s , and l e n g t h s are a t d e p th s of 2,250 fms, 2,150 fms, 2,100 fms, 1,950 fms, 1,850 fms, 1,800 fms, 1,750 fms, and 1,600 fms. The most numerous were th o se a t 2,250 fms, 2,050 fms, 1,950 fms, 1,850 fms, and 1 ,8 0 0 fms. The e a s t e r n , or i n n e r deep, has a d e p th of 2,550 fm s, has a f l a t b o tto m , and marks th e s t a r t of th e t e r r a c e d zone. P o s s i b l y t h i s i s the f i r s t (o r d e e p e s t ) t e r r a c e . Because o f th e s p a c in g of t r a c k s th e h o r i z o n t a l e x t e n t of t e r r a c e s could n o t be a s c e r t a i n e d ; however, s u f f i c i e n t d a t a were a v a i l a b l e to s u g g e s t t h a t the t e r r a c e s have g r e a t c o n t i n u i t y , e . g . , s e v e r a l t e r r a c e s can be t r a c e d ' f o r a t l e a s t 180 km. W hile most t e r r a c e s , a re n e a r l y h o r i z o n t a l , some a re t i l t e d . Some t e r r a c e s a l s o a re b o r d e r e d on th e o u t e r edge by peaks 90 m to s e v e r a l h u n d red s of m e te r s in h e i g h t . O th e rs a re e n c lo s e d on b o th s i d e s by s t e e p w a l l s w ith s lo p e s of 30° to 35°. S i m i l a r t e r r a c e s w ith g r e a t h o r i z o n t a l e x t e n t a re a ls o r e p o r t e d o f f the c o a s t of N orth A f r i c a betw een 1,60 0 fms and 2,500 fms ( T o l s t o y and Ewing, 1 9 4 9 ). The main p a r t o f the m i d - A t l a n t i c Ridge i s n o t a b l e f o r 376 i t s a b sen ce o f t e r r a c i n g . I t c o n s i s t s e s s e n t i a l l y of a s e r i e s of r i d g e s t r e n d i n g NE to SW. D redging on the f l a n k o f a s t e e p r i d g e a lo n g th e n o r t h w e s t edge o f a 3 ,1 0 0 -fm t e r r a c e r e t r i e v e d a l a r g e b lo c k o f p r o b a b l e C enozoic age m a n g a n e s e - e n c r u s te d l i m e s t o n e . ♦ GREAT METEOR SEAMOUNT I n t r o d u c t i o n No a tte m p t i s made to i n c l u d e a l l o f th e seam ounts in th e A t l a n t i c Ocean or in o t h e r o c e a n s . However, G r e a t Me t e o r Seamount has r e c e i v e d s p e c i a l a t t e n t i o n by P r a t t (1 9 6 1 , 1963) and i t h as a p l a t f o r m n e a r l y tw ic e the s i z e of Bermuda. R esu 1t s The seamount i s l o c a t e d in t h e n o r t h e a s t A t l a n t i c Ocean (3 0 ° 0 0 ’ N, 28° 3 0 ’ W) and i s the s o u th e r n m o s t s e a mount in a c h a i n e x te n d in g from th e A zores P l a t e a u . The summit s u r f a c e of G r e a t M eteor m e a su re s 67 km by 37 km and h as an a r e a of ab ou t 1,450 km (com pared t o Bermuda’ s p e d - e s t a l of 815 km ) . The minimum d e p t h i s 269 m, b u t b road a r e a s of th e summit s u r f a c e o ccur a t 283 m to 292 m. The s u r f a c e i s re m a r k a b ly sm ooth. The b r e a k s in s l o p e are a b r u p t a t a b o u t 300 m and th e s i d e s l o p e s p lu n g e s t e e p l y t o d e p th s e x c e e d in g 4 ,2 0 0 m. The s i d e s o f th e seamount have an a v e ra g e g r a d i e n t o f a b o u t 12° down to a p p r o x i m a t e ly 2 ,1 9 5 m. Below t h i s d e p th th e s l o p e d e c r e a s e s and 377 378 g r a d u a l l y g r a d e s i n t o t h e a b y s s a l s e a f l o o r . Below th e s h a r p b r e a k i n s l o p e of th e f l a t summit i s a s e r i e s o f t e r r a c e s . P r a t t (1 9 6 3 ) r e p o r t e d : Not o n ly i s th e d e p th of the summit edge n e a r l y u n ifo r m , b u t a l s o the d e p th of th e l o w e s t t e r r a c e , or b re a k t o th e s t e e p s i d e s l o p e , i s c o n s i s t e n t a t 549 m to 585 m. The i n t e r m e d i a t e t e r r a c e s a re d i f f i c u l t to c o r r e l a t e w i t h each o t h e r . . . However, t h e s e d a t a do seem to be a c o n c e n t r a t i o n o f t e r r a c e l e v e l s a t about 457 m. A s e i s m ic p r o f i l e a c r o s s one o f th e t e r r a c e s [ b e low t h e summit] shows an a c c u m u la tio n of m a t e r i a l on the o u t e r edge of a f l a t , s h a r p l y n o tc h e d t e r r a c e s u r f a c e . The i r r e g u l a r n a t u r e of th e t e r r a c e s m ight be due to the grow th o f r e e f s or o f f s h o r e b a r s on an o t h e r w i s e f l a t w a v e -c u t s u r f a c e . P h o to g r a p h s o f the b o tto m and d re d g e h a u l s on th e e a s t s i d e of the seamount r e v e a l th e p r e s e n c e of p r o b a b l e c a l c a r e o u s ro ck down t o a b o u t 567 m --th e l e v e l o f th e lo w e s t t e r r a c e . Commonly c a l c a r e o u s and o t h e r ro c k s show s o l u t i o n h o l e s and ra g g e d edges and a re p a r t l y co vered by u n c o n s o l i d a te d s e d i m e n t. G r a n i t e b o u l d e r s ( b e l i e v e d to be e r r a t i c s ) were r e c o v e r e d from 420 m and 649 m on th e n o r t h e a s t s i d e o f the seam ount ( P r a t t , 1 9 6 1 ). S i m i l a r c a l c a r e o u s r o c k s have b e en d red g e d e ls e w h e r e on the f l a n k s o f th e seam o un t, i n d i c a t i n g the p r e s e n c e o f o t h e r c a l c a r e o u s r o c k s or l i m e s to n e w hich seem to be d i s t r i b u t e d c o m p l e t e ly around the seam o u n t. The lim e s to n e c o n s i s t s of cemented b e n t h i c and p e l a g i c s p e c i e s o f f o r a m i n i f e r a and p t e r o p o d s of Miocene a g e. V o lc a n ic ro c k s have b e en p h o to g ra p h e d and r e c o v e r e d i n d re d g e h a u l s . 379 On the b a s i s of a v a i l a b l e d a t a P r a t t (1963) p r o p o s e s t h r e e p o s s i b l e i n t e r p r e t a t i o n s to e x p l a i n the observ ed c h a r a c t e r i s t i c s : 1. Wave p l a n a t i o n and r e l a t i v e se a l e v e l f l u c t u a t i o n s o c c u rre d d u r in g the M iocene, and Miocene se d im e n ts were d e p o s i t e d d i r e c t l y on th e t e r r a c e s and on the f l a t to p of the p l a t f o r m . 2. Sea l e v e l was r e l a t i v e l y low ered in p o st-M io c en e time and c u t the t e r r a c e s and p lan e d th e to p ; t h a t i s , the summit f e a t u r e s were c u t i n t o Miocene d e p o s i t s . 3. Sea l e v e l was e u s t a t i c a l l y lowered d u r in g the P l e i s t o c e n e from a p o s i t i o n n e a r the p r e s e n t summit s u r f a c e to form t e r r a c e s . T h is would i n d i c a t e a P l e i s t o c e n e lo w e r ing o f a p p ro x im a te ly 183 m and a ls o im p l i e s th e seamount has sunk, p o s s i b l y i s o s t a t i c a l l y , to i t s p r e s e n t d e p th d u r ing P l e i s t o c e n e and Recent tim e . MEDITERRANEAN SEA I n t r o d u c t i o n No a tte m p t w i l l be made h e re to in c lu d e a d e t a i l e d stu d y of the M e d ite r r a n e a n Sea because of a la c k of e c h o grams and the f a c t t h a t the l i t e r a t u r e i s e i t h e r in a f o r e ig n language or i s n o t r e a d i l y a v a i l a b l e . The b e s t r e c e n t summary of the b a th y m e try and marine geology i s by Gon ch arov and M ikhailov (1 9 6 3 ). A number of echograms made by th e Woods Hole Oceano g ra p h ic I n s t i t u t i o n were examined b u t most of th e s e were in the v i c i n i t y of I t a l y . R e s u l t s The main f e a t u r e s in the w e s t e r n M e d ite r ra n e a n are two l a r g e c lo s e d s y n c l i n e s - - t h e A l g i e r o - P r o v i n c e and Tyrrhenian. (These a re s i m i l a r to th e Black Sea, so uth Okhotsk Sea, and Ja p a n e se s y n c l i n e s in which t h i c k d e p o s i t s accum ulate over v a s t p l a i n s . ) Each of the M e d ite rra n e a n s y n c l i n e s a re s u r rounded by com plexly, d i s j o i n t e d , and s t e e p c o n t i n e n t a l s l o p e s , f r e q u e n t l y w i t h t e r r a c e s . The most complex and s t e e p e s t c o n t i n e n t a l s l o p e s occur in the v i c i n i t y of young 380 381 m o u n t a i n s - - t h e A t l a s , and where t h e B a l e a r i c I s l a n d s , the P y r e n e e s , and th e Alps M a ritim e s m ee t. I t i s s i g n i f i c a n t t h a t n ot one of t h e s e r a n g e s can be f o llo w e d f o r any d i s ta n c e along the b o tto m . R o s f e l d e r (1955) s t a t e d t h a t the c o n t i n e n t a l s l o p e a lo n g th e A t l a s M ountain c o a s t a v e ra g e s 6 ° , the s h e l f i s n a rro w , and the c o n t i n e n t a l t e r r a c e i s h e a v i l y i n c i s e d w ith can y o n s. V o lcanoes a re l o c a t e d i n the T y r r h e n i a n Sea along th e c o n t i n e n t a l s l o p e . In the e a s t e r n M e d i te r r a n e a n i s a complex arc formed by th e i s l a n d s of C r e te and Rhodes and c o n t i n u i n g i n t o Greece and T u rkey . Troughs a s s o c i a t e d w ith t h e a rc appear t o be p a r t o f a r i f t system e x t e n d in g f o r a d i s t a n c e of a t l e a s t 1,500 km. T h is i s a r e g i o n o f h ig h s e i s m i c i t y . The t r o u g h s have a V-shaped c r o s s s e c t i o n and re a c h d e p th s of 4 km to 5 km. The s l o p e s a s s o c i a t e d w i t h the tr o u g h s a re p r e c i p i t o u s . Two ty p e s of c o n t i n e n t a l s l o p e s a re d i f f e r e n t i a t e d in the A fr o - A r a b ia n p l a t f o r m - - a s t e e p , unconform ed s lo p e p r o b a b ly c o n n e c te d w i t h r i f t s and th e g e n t l e s l o p e s of th e p l a t f o r m ’ s submerged e d g e s . The f i r s t type o c c u rs a lo n g th e c o a s t of S y r i a and Lebanon and w est from th e A ra b ia n G u lf to the G u lf of S i d r a . The second i s l o c a t e d o f f E g y p t, where s e d i m e n t a t i o n i s a c t i v e , and i n th e Sea o f S i d r a . Off Lebanon, from S y r i a to T u rkey , th e s l o p e s a re a b o u t 1 0°. Shepard (1963) r e p o r t e d t h a t many i r r e g u l a r i t i e s 382 e x i s t in th e n a t u r e o f f a u l t t r o u g h s . The Sea of Marmora i s n o t a b l e f o r i t s s t e e p n o r t h e r n d e p r e s s i o n a lo n g w hich ru n s a f r a c t u r e , a c o n t i n u a t i o n on th e s e a f l o o r of th e N orth A n a t o l i a n f a u l t . T h is can be t r a c e d in the e a s t e r n h a l f of th e s e a as a t r o u g h . F u r t h e r m o r e , th e f r a c t u r e i s c l e a r l y marked in th e n o r t h e r n b a s i n of th e Aegean S ea. The c e n t r a l and s o u t h e r n p a r t s of the Aegean Sea have no c o n t i n e n t a l s h e l f . Goncharov and M ik a ilo v r e p o r t t h a t th e u n d e rw a te r f o u n d a t i o n s of i n d i v i d u a l i s l a n d s , g ro u p s of i s l a n d s , and a l s o th e m a j o r i t y of th e d e p r e s s i o n s have the f e a t u r e s of a b lo c k f a u l t s t r u c t u r e . In th e n o r t h e r n p a r t of th e A d r i a t i c Sea two t e r r a c e l i k e f e a t u r e s have b e e n i d e n t i f i e d : a t 200 m and 300 m to 360 m. Geology G oncharov and M ik h a ilo v d e s c r i b e th e b a s i c s t r u c t u r e of the M e d i te r r a n e a n Sea as f o l l o w s : The M e d i te r r a n e a n is. a lm o st e n t i r e l y l o c a t e d w ith the a l p i n e g e o s y n c l i n a l b e l t . The whole zone i s a complex c o m b in a tio n of i n d i v i d u a l r i g i d m a s s i f s of d i f f e r e n t ages and s t r u c t u r e s of a l p i n e age. W ith in i t s l i m i t s a re e x t e n s i v e r e g i o n s of h ig h s e i s m i c i t y and m a n i f e s t a t i o n s of R ecen t v o lc a n is m . M o r p h o l o g i c a l l y , the M e d i te r r a n e a n i s d i v i d e d s h a r p l y i n t o two r e g i o n s : a w e s t e r n and an e a s t e r n . The m orphology of th e w e s t e r n p a r t i s c l e a r l y c au se d by the developm ent of t h e a lp i n e g e o s y n c l i n a l in the M e so -C e n o z o ic . T h is p a r t i n c l u d e s the A l g i e r o - P ro v e n ce B a sin w i t h th e A lb oran Sea, th e T y r r e n i a n Sea and the A f r i c o - S i c i l i a n [ P e n t e n l l a r i a n ] C h a n n e l. 383 The l a r g e s t forms of bottom r e l i e f in the e a s t e r n p a r t are d eterm ined by the complex i n t e r - r e l a t i o n b e tween the s t r u c t u r a l elem en ts o f the n o r th in the zone of young f o l d i n g [th e A d r i a t i c , the Aegean and the Sea of Marmora] and of the so u th e rn r e g io n s a d ja c e n t to the a n c ie n t A fric o -A ra b ia n s h e l f . According to B eloussov (1962, p. 679), l a r g e e le v a t e d lan d s e x is te d in the Mesozoic and Paleogene in the w e ste rn p a r t of the M e d ite rra n e a n . I t has been i n f e r r e d from s t u d i e s on e l a s t i c s t h a t d ry land was lo c a te d west of the Apen- n in e P e n in s u la and n o r th of A l g e r i a and T u n i s i a . This land sub sid ed at t h e c lo s e of the T e r t i a r y and b eg in n in g of the Q u a te rn a ry p e r i o d s . A la r g e land mass a ls o was th e source of g r a n i t e in the e a s t e r n M e d ite rra n e a n . BLACK SEA Follow ing s tr o n g e a r th q u a k e s in 1927 in the Crimean r e g i o n , the bottom was c a r e f u l l y sounded and was found to c o n s i s t of a s te e p slo p e w ith d i s t i n c t s t e p s ( L a rio n o v a , 1959). A rkhangelsky (1927, 1930, and 1932) c a l l e d a t t e n t i o n to th e s e s t e p s along the s o u th e r n s h o r e s and showed t h a t led g e s e x i s t e d s e v e r a l hundred m eters below the s u r f a c e which, in some c a s e s , were i n c l i n e d tow ards the land and were re m in e s c e n t of s t e p - f a u l t s . A rkhangelsky s t u d i e d the se d im e n ts and found them crumpled and d i s l o c a t e d as th e y s l i d down the slo p e as l a n d s l i d e s . He r e p o r t e d t h a t "such l a n d s l i d e s occur in th e c la y e y sh o re s o f r i v e r s in th e s p r in g and in r a i n y weather.” T h is was th o u g h t to be th e f i r s t o b s e r v a t i o n o f such phe nomena in a se a . V. P. Zenkovich has s t a t e d t h a t l a n d s l i d e s occur by the p r o c e s s of a c c u m u la tio n of s i l t s t r a t a which become t h i c k e r and h e a v i e r . F i n a l l y , the w eight i s s u f f i c i e n t t h a t th e mass overcomes f r i c t i o n and s l i d e s down the s l o p e . A rkhangelsky s t a t e d t h a t l a n d s l i d e s may occur w ith o u t any v i s i b l e c a u se , b u t i n most c a se s f o llo w e a r t h q u a k e s . Black Sea se d im e n ts have a h ig h o r g a n ic c o n t e n t 384 385 because of a hydrogen s u lp h id e zone below 200 m. Bottom s e d im e n ts on le d g e s a t d e p th s to 800 m c o n s i s t of f i n e c la y e y sand w ith s h e l l s . The s h e l l s are very old and o r i g i n a t e d in sh a llo w w a t e r , " c o n s e q u e n tly th e s h e l l - f i s h l iv e d in s h o a ls ne ar shore and only l a t e r were removed to g r e a t e r d e p th s as a r e s u l t of f a u l t s . ” L i t t o r a l g r a v e l and f o s s i l s were r e t r i e v e d from a depth of 1,800 m (A rkh an gelsky and S tra k h o v , 1938). A rkhangelsky showed t h a t subm arine l a n d s l i d e s may o c cur on s lo p e s as g e n t l e as 2° b ut more compact se d im e n ts are s t a b l e on s l o p e s w ith g r a d i e n t s e x ce ed in g 10°. Zenkovich (1958, p . 39) i l l u s t r a t e d the s t e p s on the c o n t i n e n t a l slo p e of th e Black Sea and showed major t e r r a c e s a t a bo ut 300 m and 1,000 m. Submarine canyons i n c i s e the s h e l f ; a l l app ear o f f r i v e r s . The canyons have a g r a d i e n t of 7 °, are eroded i n t o r o c k , and extend to 600 m to 700 m ( K a p lin , 1961). The e v id e n c e , t h e r e f o r e , i s somewhat c o n fu s in g as to w hether the d i s t i n c t t e r r a c e s in the B lack Sea a re l a n d s l i d e , t e c t o n i c , or e r o s i o n a l f e a t u r e s . I t i s n o te w o rth y t h a t R ussian g e o l o g i s t s b e l i e v e t h a t the B lack Sea d e p r e s s io n d id not e x i s t a t th e end o f th e P l i o c e n e ; i t was formed d u rin g the Q u a te r n a r y . This s u g g e s ts t h a t te c to n i s m i s a c t i v e h e re . CASPIAN SEA A pollov ( 1 9 5 6 ), L ario n o v a (1 9 5 9 ) , and Klenova have r e p o r t e d t h a t the c o n t i n e n t a l s h e l f along the s o u t h e r n sh o re of th e Caspian Sea r e p r e s e n t s an example o f t e r r a c e le d g e s r e s u l t i n g from f a u l t i n g . Such t e c t o n i c t e r r a c e s can be co n ce aled by such p r o c e s s e s as s e d i m e n t a t i o n , s o l i f l u c t i o n , or s l i d i n g of lo o se masses tow ards th e base of the c o n t i n e n t a l s l o p e . T h is r e s u l t s in lo w e rin g the g r a d i e n t o f the c o n t i n e n t a l s lo p e or th e base of t e r r a c e s and p ro b a b ly i s more pronounced in s e i s m i c a l l y - a c t i v e r e g i o n s . Lebedev (1961) i n d i c a t e d t h a t th e Caspian Sea s h e l f v a r i e s g r e a t l y . I t s w idth r a n g e s from 11 km to 77 km; th e g r a d i e n t v a r i e s from 3 ’ to 1 2 ’ and th e s h e l f b re a k ran g e s from 50 m to 135 m, a v e ra g in g 97.5 m. I t i s e v i d e n t t h a t t h i s in la n d se a has a s h e l f b rea k and i s below c u r r e n t wave b a se . A p p a r e n tly , the t e c t o n i c a c t i o n has deform ed t h i s s h e l f as in th e open s e a . 386 RED SEA I n t r o d u c t i o n No echogram s a re a v a i l a b l e f o r th e Red Sea; in f a c t , only a few s m a l l - s c a l e p r o f i l e s a re known ( N e s t e r o f f , 1955). The most r e c e n t summary of the r e g i o n i s by Sw artz and Arden ( 1 9 6 0 ). R e s u I ts The most s i g n i f i c a n t f e a t u r e r e v e a l e d in c r o s s - s e c t i o n a l p r o f i l e s a c r o s s the Red Sea a re th e w e l l - d e f i n e d t e r r a c e s or wide p l a t f o r m s s e p a r a t e d by s t e e p s c a r p s . Most of the major p l a t f o r m s a re p a i r e d , t h a t i s , t h e y occur on both s i d e s of the Red Sea. The f i r s t p l a t f o r m l i e s m o stly a t d e p t h s of 60 m to 80 m, from which c o u n t l e s s r e e f s r i s e and p r o v id e h i g h l y i r r e g u l a r to p o g r a p h y . T h is p l a t f o r m i s r e l a t i v e l y narrow compared to th e p l a t f o r m a t d e p th s of 500 m to 900 m. From th e s u r f a c e of t h i s deep p l a t f o r m many c o r a l e d i f a c e s have grown to th e p r e s e n t s e a s u r f a c e . These r e e f s a re r e m i n i s c e n t of the s h e l f edge r e e f s t y p i f i e d by the Sahul S h e l f of n o r t h w e s t A u s t r a l i a ( T e i c h e r t and F a i r b r i d g e , 1948). 387 ''■ v ' Geology There a p p e a rs to be l i t t l e argument t h a t th e Red Sea i s f a u l t c o n t r o l l e d . The o pening of th e p a ar form ing th e Red Sea s t a r t e d in the C r e ta c e o u s and was w e l l- d e v e l o p e d by lower Eocene tim e. I t s opening was accompanied by e f f u s i o n of b a s a l t s . ( B a s a l t i c flow s a c t u a l l y began i n the C r e t a c eous p e r i o d . ) S u b sid e n c e o c c u r r e d from the b e g in n in g of the o pening s t a g e s of dev elo pm ent b u t was w e l l- d e v e l o p e d in Miocene tim e (S w artz and A rden, 1960). As r i f t s formed and b lo c k s s u b s i d e d , r e e f s formed along the h ig h p a r t s of the t i l t e d b l o c k s ; as su b s id e n c e o c c u r r e d , the r e e f s c o n tin u e d to grow upward. R e l a t i v e l y r e c e n t s u b s id e n c e i s i n d i c a t e d by t h e p r e s e n c e of w e l l - p r e s e r v e d o y s t e r s on v e r t i c a l w a l l s down to a t l e a s t 300 m as o b se rv ed by Ja c q u e s C o steau from h i s d i v i n g s a u c e r . INDIAN OCEAN I n t r o d u c t i o n U n t i l th e I n t e r n a t i o n a l G e o p h y s ic a l Year and th e I n t e r n a t i o n a l Indi.an Ocean E x p e d i ti o n (w hich has been t a k i n g p l a c e f o r the l a s t s e v e r a l y e a r s ) v th e In d ia n Ocean r e p r e s e n te d the g r e a t e s t unknown r e g i o n o f th e w o rld o c e a n s. A lth o u g h c o u n t l e s s c r o s s i n g s have been made u t i l i z i n g p r e c i s i o n e c h o so u n d in g e q u ip m e n t, few p r o f i l e s a re a v a i l a b l e f o r s t u d y a t th e p r e s e n t tim e . Many r e s e a r c h e r s have b e en r e l u c t a n t to r e l e a s e echogram s u n t i l th e y have p u b l is h e d t h e i r r e s u l t s . S p a rs e and w i d e ly - s p a c e d echogram s to n o t p e rm it a d e t a i l e d d i s c u s s i o n of c o n t i n e n t a l and i n s u l a r t e r r a c e s in the I n d i a n O cean. Because o f t h e i n t e r n a t i o n a l i n t e r e s t i n the I n d i a n Ocean s e v e r a l r e c e n t s o u r c e s o f i n f o r m a t i o n have become a v a i l a b l e . These i n c l u d e an e x c e l l e n t b i b l i o g r a p h y on a l l p h a s e s of o c e a n o g ra p h y (Y e n ts c h e t a l , 1 96 2); a summary of th e g e o lo g y s u rr o u n d in g th e I n d i a n Ocean (P e p p e r and E v e r h a r t , 1 9 63 ); and a p h y s i o g r a p h i c d iag ra m of th e s e a f l o o r (H eezen, p u b l i s h e d by th e G e o l o g i c a l S o c i e t y of A m e ric a ) . The g e n e r a l b a th y m e try and se a f l o o r names have been 3 89 390 p u b l i s h e d by S to c k s ( 1 9 6 0 ). A lth o u g h th e b a th y m e tr y i s now o u t of d a t e i n c e r t a i n r e g i o n s , S t o c k ’ s c h a r t i s b a s i c a l l y v a l i d ( P l a t e 4 0 ) . F iv e echogram s a re a v a i l a b l e o n ly f o r e a s t A f r i c a a t Z a n z ib a r and Mombasa (K eny a). O ther p r o f i l e s were o b t a i n e d o f f C eylon, and fo u r alo n g th e east, c o a s t of I n d i a ( P l a t e s 4 1 - 4 3 ) . In a d d i t i o n , t h e r e a re two PDR p r o f i l e s from P e n an g , K u a la, s e v e r a l o f f t h e e a s t c o a s t of M a d ag a sc ar, and a number of I n d i a n Ocean I s l a n d s . Four s o u r c e s of i n f o r m a t i o n were u t i l i z e d ; S c r i p p s I n s t i t u t i o n o f O ceanography (LA and LH n o t a t i o n s ) , VITYAZ and OB c r u i s e s , th e .John M urray E x p e d i t i o n (JM ), and ANTON BRUNN (AB). The l a t t e r was made a v a i l a b l e by E. C. LaFond. S c r i p p s ’ p r o f i l e s a re d i r e c t t r a c i n g s of PDR ech og ram s, ANTON BRUNN p r o f i l e s are p h o t o g r a p h e d , w h i l e a l l o t h e r p r o f i l e s a re r e c o n s t r u c t e d . R e su 1 t s The r e g i o n betw een 27° S to 17° S, c o n s t i t u t i n g the w e s te r n p a r t o f Mozambique C h a n n e l, has b een d e s c r i b e d by Duncan in an u n p u b lis h e d m a n u s c r i p t (1963) b u t he d o e s n o t i n c l u d e any b o tto m p r o f i l e s . From 27° S to 22° ^ th e c o n t i n e n t a l s h e l f i s n a rro w , r a n g in g from l e s s th a n 7 .5 km to 83 km, a v e ra g in g 18 km to 46 km. No su bm arin e canyons a re known in th e r e g i o n , or as f a r n o r t h as 10° S . Between 22° and 17° th e s h e l f c o n s i s t s o f a wide c o a s t a l p l a i n and 391 c o n t i n e n t a l s h e l f , r e a c h i n g a maximum w i d t h of 165 km o f f B e i r a . T h is r e g i o n i s p a r t o f the a d v a n c in g Zambezi R iv e r d e l t a . I t c o n t a i n s s m a ll t e r r a c e s a t th e edge o f th e s h e l f . F ro m .17° S to a bo ut 10° S the s h e l f i s o n ly 4-km to 28-km wide and i s i n c i s e d by 25 m ajor su b m a rin e c a n y o n s . L iv in g b a r r i e r r e e f s a re p r o f u s e in t h i s a r e a and a r e c u t by th e c a n y o n s . Canyons t e r m i n a t e in th e ra n g e of 730 m t o 2 ,0 1 0 m w i t h the g r e a t e s t c o n c e n t r a t i o n a t 1,650 m. T h ree PDR r e c o r d s (LA-4, LA-5, and LA-13) and two p r o f i l e s by VITYAZ (V -3 1 -1 5 and -1 6 ) a re a v a i l a b l e f o r Z a n z i b a r and Mombasa ( P l a t e 4 2 ) . In a d d i t i o n , p r o f i l e s by th e Jo hn M urray e x p e d i t i o n a l s o i n c l u d e th e c o n t i n e n t a l t e r r a c e o f f Z a n z ib a r and Pemba I s l a n d s . A l l o f t h e s e p r o f i l e s c u t th e c o n t i n e n t a l t e r r a c e a t an a n g l e , herice , c a u t i o n must be e x e r c i s e d in i n t e r p r e t i n g r e s u l t s . T h is p a r t of th e c o a s t i s a g e n t l y c u r v i n g embayment a b o u t 650-km lo n g and i s i n d e n te d 130 km. A c co rd in g t o F a r q u h a r s o n ( 1 9 3 6 ) , n o r t h o f t h i s bay t h e 2,000-m and 4 ,0 0 0 -m c o n t o u r s l i e a b o u t 50 km and 1,85 0 km, r e s p e c t i v e l y , from th e c o a s t . Between 3° S and 9° S, t h e s e same i s o b a t h s l i e 180 km and 390 km from the m a i n l a n d . S o u th of 9° S th e 2 ,0 0 0 m c o n to u r a g a i n a p p r o a c h e s to w i t h i n 55 km of the c o a s t . The i s l a n d o f Pemba i s s e p a r a t e d from th e m a in la n d by a t r o u g h a b o u t 900 j n d e e p a t th e s o u t h e r n end and 360 m a t th e n o r t h e r n en d . A c h a n n e l w i t h s i m i l a r d e p t h s e x i s t s b e tw e e n Latham I s l a n d and th e c o a s t . 392 Most of th e s e p r o f i l e s show a w e ll- d e v e lo p e d t e r r a c e a t 1,000 m, and s e v e r a l of th e p r o f i l e s a ls o su g g e s t one a t 300 m to 500 m. One of the un iqu e f e a t u r e s of th e c o n t i n e n t a l t e r r a c e n o r t h of Mozambique i s th e very long (more th an 380 km) g e n tl y concave c o n t i n e n t a l s lo p e ( P l a t e 42, V -3 1 -1 6). Kovylin (1961) shows a p r o f i l e 75 km n o r t h of Z an zib ar which i s 630-km in l e n g t h . Seism ic s h o t s a t 110-km i n t e r v a l s i n d i c a t e t h a t se d im e n ts l e s s than 500-m t h ic k are alm ost everywhere alo n g the p r o f i l e , g r a d u a l l y d e c r e a s i n g in t h i c k n e s s tow ards th e a b y s s a l sea f l o o r . The c o n t i n e n t a l s h e l f of M adagascar i s m o stly n arro w , a v e ra g in g 24 km, b ut i s 180-km wide o f f the n o r t h e a s t c o a s t and 90-km wide o f f th e s o u th e r n c o a s t . P r o f i l e s o f f Tama- ta v e ( P l a t e 41, p r o f i l e s V-31-13 and -14) show a s t e e p , i r r e g u l a r c o n t i n e n t a l s l o p e . Submarine canyons are p r o b a b ly p r e s e n t . The upper slo p e i s e s p e c i a l l y s t e e p w h ile th e lower s lo p e i s l e s s s t e e p , w ith r e l i e f up to one k i l o m e t e r . P r o f i l e s V-31-13 and JM-1 show a c o n t i n e n t a l r i s e . P r o f i l e JM-2 ( P l a t e 42) made from th e s o u t h e r n t i p of th e i s l a n d , shows a convex s lo p e ; the upper s lo p e i s g e n t l e w h ile the lower slo pe i s s te e p and t e r m i n a t e s a b r u p t l y on a f l a t p l a i n a t a d e p th of 1,600 m above M ascarene B a sin . P r o f i l e JM-2 a ls o s u g g e s ts a m ajor t e r r a c e down to about 500 m. The g r a d i e n t seaward o f f Pemba I s l a n d (JM-3) i s low and smooth e x c e p t f o r a h i l l (or r i d g e ) s e v e r a l hundred m e te rs h ig h . On the e a s t s id e o f Pemba Channel (w est of 393 Pemba I s l a n d ) the s l o p e i s i r r e g u l a r w i t h pronounced t e r r a c e s a t 600 m and a t about 800 m. S e v e r a l echograms are a v a i l a b l e f o r o t h e r In d ia n Ocean i s l a n d s and a c r o s s m id -ocean r i d g e s . In c lu d e d a re e c h o grams o f f K e rg u elen I s l a n d ( P l a t e 41, p r o f i l e s LA-19, LA-20, and O B -2 -5), l o c a t e d to th e s o u th of th e a re a c o v ered in th e in d ex c h a r t . K e rg u e le n I s l a n d has a smooth i n s u l a r s h e l f , p e rh a p s b e ca u se the i s l a n d i s l o c a t e d f a r to the so u th in the P r e v a i l i n g W e s t e r l i e s . The i n s u l a r slo p e i s c o n s i d e r a b l y more g e n t l e th a n most i s l a n d s , b u t t h i s may be due in p a r t to t r a v e r s i n g the s lo p e o b l i q u e l y . Most of the o th e r i n s u l a r s l o p e s a re s t e e p b ut o f te n show v a r i o u s ty p e s of t o p o g r a p h ic i r r e g u l a r i t i e s a t s e v e r a l d e p t h s . P r o f i l e s a c r o s s th e m id-ocean r i d g e (OB 2 -5 ) and a c r o s s S e y c h e l l e s A r c h ip e la g o (V -3 1 -1 7 , LA-11, and LA-3) are somewhat s i m i l a r i n sh a p e . T y p i c a l l y , the upper slo p e i s s t e e p and the lower s lo p e (more th a n 1 km to 2 km) i s g e n t l e and i r r e g u l a r . Two p r o f i l e s e x te n d from Penang in the S t r a i t of M alacca ( P l a t e 41, p r o f i l e s LA-8 and - 9 ) . These show a d i s t i n c t s h e l f b re a k and a w id e , somewhat i r r e g u l a r b ottom a t 1,000 m to 1,500 m b e f o r e c r o s s i n g the r i d g e ( a t about 250 m) n o r th w e s t o f Sum atra. Echograms of o t h e r i n s u l a r s l o p e s a re shown on P l a t e 43. Three d i f f e r e n t a t o l l s (JM-8 to JM-10) have d i s t i n c t 394 t e r r a c e s a t ab ou t 300 m to 400 m and a d e c r e a s e in g r a d i e n t a t a b o u t 1,300 m. Four p r o f i l e s t r a v e r s e th e s h e l f and s lo p e o f f so u th w e st C e y lo n . E x c e p t f o r p e r h a p s LA-18, a l l p r o f i l e s c u t th e i n s u l a r s l o p e a t an a n g l e . P r o f i l e s V -31-8 and V -3 1 -9 , l o c a t e d f a r t h e s t s o u th on C e y lo n , s u g g e s t t h a t the i n s u l a r s lo p e i s v e ry s t e e p , w h ile LA-17 and LA-18 show a more g e n t l e s l o p e . However, th e l a t t e r two p r o f i l e s are d i r e c t t r a c i n g s of PDR r e c o r d s w h ile the VITYAZ p r o f i l e s are r e p l o t t e d have have a d i f f e r e n t v e r t i c a l e x a g g e r a t i o n . A c c o rd in g to S hepard ( 1 9 6 3 ) , the e a s t e r n p e n i n s u l a of I n d i a has s l o p e s of 4° to 6 ° , and o f f C eylon a re m o s t ly g r e a t e r th a n 10°. The s l o p e s a re c u t by a few c a n y o n s . A m ajor subm arine canyon, T r in c o m a le e , e n t e r s th e o n ly s i g n i f i c a n t bay on th e e a s t c o a s t of C e y lo n . The canyon c u t s th ro u g h hogbacks of P r e c a m b ria n g n e i s s and q u a r t z i t e (Adams, 1929; and S h e p a rd , 19 6 3 ). P r o f i l e LA-18 c r o s s e s t h e m id - I n d i a n Ridge w hich i s b e v e le d f l a t , w i t h no r e l i e f a t 900 m to 1,00 0 m. The i n s u l a r s lo p e o f f the e a s t e r n M aldive I s l a n d s i s s t e e p , and no f e a t u r e s on the s l o p e can be i d e n t i f i e d e x c e p t f o r a m ajor change i n s lo p e a t about 1,100 m (V-31-11). P r o f i l e LH-3, a l s o o f f s o u th w e s t I n d i a , shows a s t e e p u p per s l o p e , a t e r r a c e a t 1 ,5 0 0 m, and a d e c r e a s e in g r a d i e n t b e low t h i s d e p t h . P r o f i l e V-31-10 t r a v e r s e s th e m i d - I n d i a n Ridge a t an 395 o b l iq u e an g le and r e v e a l s th e i r r e g u l a r to p o g r a p h y of th e r i d g e , b u t s u r p r i s i n g l y , th e r e l i e f nowhere e x c e e d s a few hu n d red m e t e r s - The s i n g l e e x c e p t i o n i s th e v o l c a n i c ( ? ) peak b e tw ee n 3 ,7 0 0 m and 2,800 m. None o f th e o t h e r p u b l i s h e d p r o f i l e s o f m id -o c ea n r i d g e s a re so d e v o id o f r e l i e f . A lth o u g h i n t e r p r e t a t i o n must be c a u t i o u s , s e v e r a l wide f l a t a r e a s o c c u r on th e o b l i q u e p r o f i l e - - a t 1,400 m, 2,00 0 m t o 2,2 0 0 m, 3,0 0 0 m to 3,200 m, and 3 ,5 0 0 m to 3,800 m. P r o f i l e V -31-12 t r a v e r s e s th e c o n t i n e n t a l t e r r a c e a t a low a n g le b u t r e v e a l s a s t e e p u p p e r , and g e n t l e r , b u t i r r e g u l a r , c o n t i n e n t a l s l o p e b e g in n i n g a t a b o u t 2,1 0 0 m. P r o f i l e s V -31 -18 and V -3 1 -1 9 , o f f Bombay, show a g e n e r a l convex s l o p e b u t d i s t i n c t d i f f e r e n c e s e x i s t b etw een p r o f i l e s . P r o f i l e V -31-18 i s s m o o th e r, h a s a m ajor b r e a k b e tw ee n the u p p e r and low er s l o p e s marked by a f e a t u r e a t 2 ,5 0 0 m, and h a s a sm a ll c o n t i n e n t a l r i s e . P r o f i l e V -31-19 i s i r r e g u l a r a lo n g i t s e n t i r e c o u r s e and h a s no c o n t i n e n t a l r i s e ; j o i n i n g of s lo p e and d e e p - s e a i s a b r u p t . B oth p r o f i l e s seem t o have c o r r e l a t i v e f e a t u r e s a t 500 m and 3 ,5 0 0 m. The p r e s e n c e o r a b sen c e may be due in p a r t to the s h a l l o w e r w a t e r o f th e A ra b ia n Sea t o t h e n o r t h . F a r t h e r o ut in the A r a b ia n b a s i n , b o t h p r o f i l e s show a h o r s t - l i k e f e a t u r e . No d i s c e r n a b l e f e a t u r e s can be a s c e r t a i n e d from o f f Bombay i n p r o f i l e JM -11, made by th e Jo h n M urray E xpedition. 3 9 6 The p r o f i l e o f f P o i n t M a lin d i shows wide f l a t a r e a s a t a b o u t 3 ,0 0 0 m, 3,800 m, and 4 ,0 0 0 m to 4 ,5 0 0 m. S hepard (1 963) i n d i c a t e s th e c o n t i n e n t a l s l o p e s o f f w e s t e r n I n d i a a re n o r m a l ly a b o u t 2° t o 3°. P r o f i l e AB-2 i s more t y p i c a l o f I n d i a ’ s e a s t c o a s t , c o n s i s t i n g o f a smooth c o n v e x -s h a p e d p r o f i l e (Rao and La Fond, 1 9 5 4 ). A t e r r a c e o c c u r s a t 120 m and a n o t h e r d i s t i n c t one i s v i s i b l e b e tw ee n 270 m to 280 m, b u t th e s lo p e i s o t h e r w i s e sm ooth. Canyons or an i r r e g u l a r p l a i n e x i s t s betw een 700 m and 880 m, h a v in g r e l i e f o f abo ut 250 m. Be cau se d e t a i l s of the to p o g ra p h y a r e l a c k i n g i t i s n o t p o s s i b l e to draw d e f i n i t e c o n c l u s i o n s a bo ut th e n a t u r e o f th e s l o p e . P r o f i l e AB-3 shows a gene r a l l y - s m o o t h , convex s l o p e w i t h a p r o m in e n t t e r r a c e a t 100 m and one a t 550 m on the s h e l f . No d i s t i n c t s h e l f b r e a k e x i s t s , u n l e s s l o c a t e d a t 550 m. P r o f i l e s AB-4 and AB-2 show c l a s s i c a l su b m a rin e c a n y o n s. P r o f i l e AB-4 i n c l u d e s a p o r t i o n of th e c o n t i n e n t a l s lo p e ( t o about 800 m ) . The s h e l f b r e a k on th e l a t t e r p r o f i l e i s a b o u t 110 m, and s e v e r a l n a rr o w t e r r a c e s o c c u r a t 500 m and 600 m. Rao and La Fond (1954) p u b l i s h e d t h r e e r e c o n s t r u c t e d p r o f i l e s a c r o s s the c o n t i n e n t a l s h e l f a s d e e p a s 700 m n e a r 17° 3 0 ’ N. S h e l f b r e a k s o c cu r a t 96 m, 95 m, and 108 m. Each p r o f i l e shows s m a ll p i n n a c l e s a few m e t e r s in e lev ation 397 near the s h e l f edge and minor i n d i c a t i o n s of t e r r a c e s 137 m to 183 m. The c o n t i n e n t a l slope has an average g r a d i e n t of about 2° 4 6 ’ and the s h e l f 0° 15 ’ . The Bay of Bengal ( P l a t e 43) is p a r t i c u l a r l y famous f o r i t s b a th y m e tric s i m p l i c i t y and the "Swatch of No G ro u n d "--th e Ganges Submarine Canyon. Beyond the edge of the s h e l f , the o ff s h o r e g r a d i e n t s te e p e n s , then d e c r e a s e s ag ain g r a d u a l l y , r e s u l t i n g in a smooth southward slo p in g p lan e w ith a g r a d i e n t of only 2 m per km ( D ie tz , 1953; and La Fond, 1957). I t i s concluded by D ie tz t h a t t h i s uniform slo p e i n d i c a t e s the " se a f l o o r here has been t e c t o n i c a l l y s t a b l e for a long p e rio d of time and t h a t the i n i t i a l t e c t o n i c i r r e g u l a r i t i e s have been l a r g e l y masked by s e d im e n ta t i o n . The u n ifo rm g r a d i e n t su g g e s ts th a t the g r a d ie n t is d eterm ined by the p r o f i l e of e q u il i b r i u m of some se a f l o o r p r o c e s s . " D ie tz su g g e s ts t u r b i d i t y c u r r e n t s might f u l f i l l the re q u ir e m e n t. The deep sea f l o o r c o n s i s t s of g l o b ig e - r i n a ooze n o r th t o about 17° N, but f a r t h e r n o r th the b o t tom i s t e r r i g e n o u s m a t e r i a l . At l e a s t s i x major canyons occur on the Andhra C oast. P r o f i l e AB-1 i s l o c a te d near the head of the Bay of Bengal ( P l a t e 43, p r o f i l e s AB-1 to AB-4). The bottom slo p e b e tween 1,100 m to 280 m i s r e l a t i v e l y g e n t l e and has a s l i g h t l y concave shape. The upper p a r t of the slo p e is hummocky and has a prom inent r i s e a t 850 m, having a r e l i e f of 20 m, below which i s smooth topo grap hy , presum ably 398 r e p r e s e n t i n g a d e p o s i t i o n a l s u r f a c e . The s h e l f b r e a k o c c u rs a t 190 m and a t e r r a c e about 1,000-m wide o c c u rs im m e d i a t e ly below the s h e l f edge a t 300 m. Bottom M a t e r i a l s No known bottom sam ples have b een c o l l e c t e d from th e c o n t i n e n t a l s l o p e s a lth o u g h r i d g e s and d e e p - s e a d e p o s i t s have been sam pled. A c co rd in g to V. N. M al’ t s e v ( 1 9 5 9 ) , the b o tto m between the s o u th e rn c o a s t of A f r i c a and A n t a r c t i c a i s of v o l c a n i c o r i g i n . I t c o n s i s t s of v a s t l a v a f i e l d s , m assiv e m ou ntain s of "welded b a s a l t , " u p l i f t e d b lo c k s of b a s a l t , h i l l s , and s t e p - l i k e b l o c k s . M a l’t s e v b e l i e v e s t h a t the r e g i o n was s u b j e c t e d to t e n s i o n and u p l i f t which formed the C ro z e t O ceanic P l a t e a u and the K e rg u e la n -G a u s sb e rg Range (se e a l s o Bezrukov, 1963). R ie d e l (1951) r e p o r t e d t h a t no T e r t i a r y - a g e r a d i o l a r - i a n s were o b t a i n e d in any o f the c o r e s c o l l e c t e d by the Swedish D e e p -s e a E x p e d i t i o n in the I n d i a n Ocean. He c o n clu d e d t h a t no major changes in th e to p o g ra p h y of the s e a f l o o r have r e s u l t e d in the r e d i s t r i b u t i o n of s e d im e n ts . T h is i s in c o n t r a s t to the w e s t e r n P a c i f i c which was a r e gio n of c o n s i d e r a b l e d i a s t r o p h i c a c t i v i t y a t the c l o s e of the T e r t i a r y p e r i o d , r e s u l t i n g in r e d i s t r i b u t i o n o f T e r t i ary s e d im e n ts . Herman (1963) h as s t u d i e d s e v e r a l deep ( 2 ,7 7 0 m and 399 2,950 m) c o re s tak e n from a c o n t i n e n t a l r i s e a bo ut 925 km s o u t h e a s t of Cape Town. These c o re s were d ated as C r e t a c e o u s, P a le o c e n e , and P l e i s t o c e n e a g e s . C o n d itio n s su g g e s t a d i f f e r e n t environm ent d u r in g d e p o s i t i o n of o l d e r s e d i ments in deep broad b a s i n s w ith no s t r o n g bottom c u r r e n t s . Recent sedim ents were removed due to s tr o n g c u r r e n t s . I n d u r a t i o n of o ld e r sed im en ts i s p r o b a b ly the r e s u l t of com p a c t i o n , not d i a g e n e s i s ( c e m e n t a t i o n ) . The r e g i o n p r o b a b ly has s u f f e r e d p o s t - P a l e o c e n e t e c t o n i c u p l i f t . According to Kovylin (1 9 6 1 ), most p a r t s of the In d ia n Ocean are l e s s th a t 200-m t h i c k . Geology Pepper and E v e r h a r t (1963) r e c e n t l y gave an e x c e l l e n t summary of the geology of the l a n d s b o r d e r i n g the In d ian Ocean, t h e r e f o r e , a d e t a i l e d d i s c u s s i o n i s u n n e c e s s a r y h e r e . The major c o n c lu s io n s c o n c e rn in g the c o a s t a l r e g i o n are of im p o rtan c e , however. Evidence of f a u l t i n g and w arp ing a re w id e s p re a d . (A d e t a i l e d breakdown of th e c o a s t s b o r d e r i n g the In d ia n Ocean i s summarized in the A p p e n d ix .) The In d ian Ocean i s b o rd e re d by t h r e e major s h i e l d s , a l l of which a re r o u g h ly t r i a n g u l a r in shape and composed p re d o m in a n tly of igneous and metamorphic ro c k s of Precam- b r i a n and l a t e r ages. The In d ia n S h i e ld i s on th e n o r t h , the A u s t r a l i a n S h ie ld i s on the e a s t , and the A f r i c a n S h ie ld i s on the w e s t. O ther P re ca m b ria n metam orphic ro ck s 400 occur on Madagascar in the S e y c h e lle s A rc h ip e lag o and in e a s t e r n Burma. Cloos (1948) s t a t e d : I t seems from e a r l y g e o lo g ic a l time the c r u s t has been d iv id e d i n t o p oly go nal f i e l d s or b lo c k s of con s i d e r a b l e t h ic k n e s s and s o l i d a r i t y and t h a t t h i s p r i mary d i v i s i o n formed and o r i e n t e d l a t e r movements. He concluded t h a t the p a t t e r n s can be observed on land as w e ll as on the sea bottom . Krenkel (1925-1928) o u tlin e d r i g i d b a s in s and in te r v e n i n g mobile b e l t s of e a r l y age on the A fric a n c o n t i n e n t . He tr a c e d the s t r u c t u r e i n t o the ocean, showing r i d g e s and b a s i n s . Cloos reached a s i m i l a r c o n c lu s io n . Dixey (1956) s a i d : A f r i c a c o n s i s t s o f a g r e a t s h i e l d which to a la rg e e x te n t assumed i t s p r e s e n t l i m i t s in the e a r l y to m i d - J u r a s s i c . . . r e a d i l y d i v i s i b l e i n t o a number of b a s i n s s e p a r a te d by s w e lls , minor s h i e l d s , or p l a te a u s . Movement, l a r g e l y v e r t i c a l , follow ed P recam b rian tren d l i n e s ( B a ile y , 1961, 1964). I n d i a ’ s P recam brian s h i e l d was g r e a t l y f r a c t u r e d d u r ing Archean time but h a s remained a s t a b l e b lo ck and has not been a f f e c t e d by f o l d i n g since the c lo s e of the Precam b r i a n , however, i t has been warped and p o s s i b l y was t i l t e d to the e a s t (Pepper and E v e r h a r t , 1963). V e r t i c a l move ments have r e s u l t e d in normal and b lo ck f a u l t i n g on the margins of the p e n i n s u l a . H i l l s (1947) r e p o r t e d the major e x i s t i n g to p o g ra p h ic f e a t u r e s o f the p e n i n s u l a , i n c lu d in g the c o a s t l i n e and i t s b o rd e rin g e a s t e r n and w e s te rn 401 m ou ntain s, are d i r e c t l y r e l a t e d to th e g r a in of the Indian Shie Id . I n d ia has a c o a s t l i n e ap p ro x im ate ly 9,250 km in le n g t h , i s rem arkably uniform and s t r a i g h t , w ith few deep i n d e n t a t i o n s . The lack of h a rb o rs in e s p e c i a l l y n o t i c e a b l e on th e e a s t (Coromandel) c o a s t . This c h a r a c t e r i s t i c i s a ls o tr u e of A f r i c a and w e s te rn A u s t r a l i a . " C o n t in e n t a l d r i f t i s t s " b e l i e v e t h a t the r i g i d masses r e p r e s e n t remnants of Gonwanaland which broke d u rin g l a t e C re ta c e o u s tim e, the c o a s t a l reg io n being the edge of the broken c o n t i n e n t . An o th e r c h a r a c t e r i s t i c ' of I n d i a ’ s o f f s h o r e a re a i s the sm all number of i s l a n d s . The sea f l o o r g r a d i e n t i s more a b ru p t c l o s e r to shore and on the w e ste rn (A rab ian ) re g io n o f f shore than on the e a s t c o a s t . The l a t t e r reg io n i s p a r t i c u l a r l y f l a t and sandy. Krishnaswany (1954) i n d ic a t e d t h a t the c o a s t s of I n d i a belong e s s e n t i a l l y to the A t l a n t i c type and a re non-embayed, r e e f l e s s , and c o n t i n e n t a l in n a t u r e . (E x c e p tio n s , of c o u rse, e x i s t such as the Malabar c o a s t . ) Both c o a s t a l p l a i n s were formed by deep e ro s i o n of a n c ie n t ro c k s . I t i s r e p o rte d t h a t the edges of b o th c o a s ts s im u l ta n e o u s ly sank slow ly or dipped beneath the se a. B urrard (1916) i n d i c a t e d t h a t p lu m b -lin e d e f l e c t i o n s i n d i c a t e t h a t the c o a s t a l s t r i p s mark the zone o f s u b - c r u s t a l weakness p a r a l l e l to the c o a s ts and were su b s e q u e n tly f i l l e d by r i v e r - b o r n e d e b r i s . M orrison s t a t e d : 402 The e v id e n ce o f p r e s e n t c o n f i g u r a t i o n , confirm ed by t r a d i t i o n , p o i n t as to an a n c i e n t submergence of a v a s t e x t e n s i o n of the c o n t i n e n t on the w e st. O ther E n g lis h g e o l o g i s t s have c on curred w i t h t h i s view. For example, Fermor ( i n B u r r a r d , 1916, and Krishnaswamy, 1954) s a id t h a t the E a r th movements which " le d to the fo u n d erin g of the Deccan T raps over which i s now the A r a b i an Sea" a ls o a f f e c t e d the c o a s t a l b e l t by p r e s e r v i n g a b lo c k of sm all w idth a t an i n t e r m e d i a t e l e v e l between the g r e a t d e p r e s s e d , submerged r e g i o n to the w est and the g r e a t e l e v a t e d p l a t e a u of the Deccan T raps to the e a s t . According to M ed icott and B lan d fo rd ( i n W. M. D av is, 1928, p. 52 8-529), the p e n i n s u l a o f I n d i a i s p a r t of a much l a r g e r lan d mass of m oderate r e l i e f and a l t i t u d e t h a t was c o v ere d by enormous la v a flow s ( th e Deccan T rap s) in the C r e ta c e o u s p e r i o d . On the w e s t, th e l a v a flow s r i s e above c o a s t a l low land s by c l i f f s 610 m to 1,220 m h ig h . I t i s concluded t h a t the Deccan l a v a s were u p l i f t e d in the T e r t i ary w h ile the A rabian Sea f l o o r was d o w n fa u lte d d u rin g l a t e C re ta c e o u s tim e . The e a s t c o a s t of I n d i a has pronounced e v id e n c e of a r e l a t i v e lo w ering of the se a l e v e l , m o stly of sm all m agni tu d e . The w est c o a s t i s more complex; however, the K a t h i a war C o ast, p a r t i c u l a r l y th e Rann of C utch , shows u n m is ta k a b le ev id e n ce of lan d u p l i f t . Rann of Cutch i s of i n t e r e s t because an e arth q u ak e in 1897 r e s u l t e d in the u p l i f t of a l a r g e b lock of land ( th e A lla h Bund), t o g e t h e r w ith nearby 403 s u b s id e n c e . Morgan and M c l n ti r e (1959) r e p o r t e d t h a t the w est s i d e o f the Ganges D e lta i s a r e g io n o f su b sid e n c e due to f a u l t i n g ; t i l t i n g a ls o a p p e a rs to have ta k e n p l a c e . K rishnan (1959) c o n s i d e r s the e a s t c o a s t s of South A f r i c a , M adagascar, and I n d ia took t h e i r p r e s e n t shape ( a f t e r d r i f t i n g a p a r t ) toward th e end of th e J u r a s s i c or e a r l y C re ta c e o u s time by a s o u t h e r l y e x t e n s i o n of the Mozambique R i f t and by s e p a r a t i n g Madagascar from I n d i a . A f t e r the Miocene t r a n s g r e s s i o n and an u p l i f t , the c o a s t was f a u l t e d downward d u rin g the P l i o - P l e i s t o c e n e epochs and the f a u l t extended i n t o the P e r s i a n G ulf r e g i o n . Thus, K rishn an b e l i e v e s the f i n a l shape of the In d ia n Ocean o c c u rre d d u rin g the T e r t i a r y , s i m u lt a n e o u s ly w ith the ou tflo w of the g r e a t Deccan l a v a flo w s, as w e ll as th e f o r m a t io n of the H im ala yan Mountain system and t h e i r e x te n s i o n westward i n t o P e r s i a and S y r i a , and e astw a rd i n t o I n d o n e s i a . S e y c h e l le s A rc h ip e la g o c o n s i s t s o f numerous c o r a l a t o l l s and sand cays of r e l a t i v e l y r e c e n t age. The i s l a n d s a re b a s i c a l l y of c o n t i n e n t a l o r i g i n , b e in g composed l a r g e l y 2 of g r a n i t e . The M a h e -P ra s lin group c o v e r s 258 km in a r e a and r i s e s from a c e n t r a l bank, ly in g m o stly a t d e p th s 1e s s 2 than 60-m deep and c o v ering about 55,000 km . T h is group of i s l a n d s i s alm ost e n t i r e l y P re ca m b ria n age h o rn blend e g r a n i t e , a p p a r e n t l y the core r e g i o n o f a g r a n i t e b a t h o l i t h (Baker and M i l l e r , 1963). Wall ro c k s of the b a t h o l i t h e v i d e n t l y l i e on S e y c h e l le s Bank or beyond the i s l a n d s . 404 D o l e r i t e and b a s a l t d i k e s o ccu r on a l l g r a n i t i c i s l a n d s of P r e c a m b ria n and T e r t i a r y a g e s . S e ism ic work shows t h a t g r a n i t e u n d e r l i e s c o r a l r e e f s to a c o n s i d e r a b l e d e p t h , h e n c e , th e S e y c h e l l e s I s l a n d s a re a r a t h e r uniq ue f e a t u r e in the I n d i a n Ocean in t h a t the c r e s t i s g r a n i t e o f P re c a m b ria n age. The h o r i z o n t a l e x t e n t of t h i s c o n t i n e n t a l - t y p e c r u s t i s as y e t u n d e te rm in e d . The a g es of th e g r a n i t e s a re s i m i l a r to the a g e -ra n g e o f the Mozambique b e l t of the e a s t e r n p a r t o f A f r i c a and M adagas c a r . T h is has le d Baker and M i l l e r to s p e c u l a t e t h a t "The S e y c h e l l e s may have o r i g i n a t e d d u r i n g th e f r a g m e n t a t i o n o f Gondwanaland by c o n t i n e n t a l d r i f t . " They p o i n te d ou t t h a t E a s t A f r i c a and Mozambique show e v id e n c e of i n t e r m i t t e n t d o w n f le x u r in g of th e Mozambique p a r a g e o s y n c l i n e l o c a t e d alo n g the Mozambique Channel and in th e Somali B a s i n , from Kayroo ( l a t e C a r b o n i f e r o u s - P e r m i a n ) to l a t e T e r t i a r y a g e s . They s u g g e s t t h a t the e a s t e r n p a r t of t h e c o n t i n e n t of A f r i c a once e x te n d e d as f a r e a s t as the M ascarene R id g e . In s u p p o r t of t h i s , t h e y p o i n t to the c o n t r a s t of the se a f l o o r to p o g ra p h y o f th e A ra b ia n Sea and e ls e w h e r e in the I n d ia n O cean. The E a s t A f r i c a n and Lebombo S w e lls on one s i d e , and the M ascarene Ridge on th e o t h e r , p o s s i b l y r e p r e s e n t m a r g in a l u p l i f t s of t h i s p a r a g e o s y n c l i n a l zone. G e n e r a l l y s p e a k i n g , th e s t r u c t u r a l h i s t o r y of th e r e g io n b o r d e r i n g the n o r t h e r n p a r t of t h e I n d i a n Ocean i n volved v e r t i c a l and h o r i z o n t a l movements r e s u l t i n g in 405 upw arping and downdropping a lo ng norm al f a u l t s ( s e e Appen d i x ) . R i f t s o c c u r r e d in e a s t e r n A f r i c a and w e s t e r n A r a b ia and b lo c k f a u l t i n g i n p e n i n s u l a r I n d i a and in w e s t e r n and s o u t h e r n A u s t r a l i a . P e p p e r and E v e r h a r t have s t a t e d : O u ts id e th e s h i e l d s , s a g s or f o r e d e e p s formed by downwarping of th e c r u s t and l a t e r f i l l e d w i t h s e d i ments have in some p l a c e s been s u b s e q u e n t l y f o ld e d and t h r u s t f a u l t e d by p r e d o m i n a n t l y h o r i z o n t a l s t r e s e s i n t o g r e a t r e g i o n a l a r c s , as in th e H im alayas and th e i s l a n d c h a in of I n d o n e s i a . DISCUSSION Types o f C o n tin e n ta l S lo p es From a geomorphic p o i n t of view, no u n i v e r s a l type of c o n t i n e n t a l slo p e e x i s t s . Some c o n t i n e n t a l s lo p e s have pronounced r i s e s , such as th o se along the e a s t c o a s t of th e U nited S t a t e s ; o th e r s lo p e s have no such g r a d a t i o n a l f e a t u r e . In g e n e r a l , c o n t i n e n t a l r i s e s appear to be a c h a r a c t e r i s t i c of the A t l a n t i c Ocean, and w h ile th ey occur in o th e r o c e a n s, they are by no means " t y p i c a l " c o n t i n e n t a l s lo p e f e a t u r e s . Some s lo p e s end a b r u p t l y as do th o se in th e Jap an Sea ( P l a t e 3 ). Here the lower p a r t of the c o n t i n e n t a l slo p e a c t u a l l y i n c r e a s e s in g r a d i e n t . The same i s t r u e of the c o n t i n e n t a l s lo p e s o f f e a s t A u s t r a l i a in the Tasman Basin ( P l a t e 1 9 ). Many c o n t i n e n t a l s lo p e s show a convex p r o f i l e , as f o r example, o f f w e s te r n A u s t r a l i a ( P l a t e 1 4 ). In some a re a s a b ro a d , n e a r l y low c o n t i n e n t a l b o r d e r la n d e x i s t s a t the base of th e c o n t i n e n t a l s l o p e . T his may be e i t h e r smooth or i r r e g u l a r and th e t r u e a b y s s a l se a f l o o r i s lo c a te d a c o n s i d e r a b le d i s t a n c e seaward of the c o n t i n e n t a l s l o p e . The re g io n o f f w e s te rn Canada and O re gon shows such an i n t e r m e d i a t e f e a t u r e ( P l a t e s 7 and 8 ). 406 407 Some g e n t l e c o n t i n e n t a l s l o p e s o c c u r where t h e r e i s p r a c t i c a l l y no c o n t i n e n t a l s h e l f and the c o n t i n e n t a l s l o p e g r a d e s i n t o a deep b a s i n . One example i s l o c a t e d i n th e I n d i a n Ocean n o r t h o f Z a n z ib a r ( P l a t e 4 2 ) . The o p p o s i t e o f t h i s ty p e i s a p r e c i p i t o u s s l o p e , so s t e e p t h a t t h e e c h o s o u n d e r h a s d i f f i c u l t y i n r e c o r d i n g th e b o tto m . Most i n s u l a r s l o p e s f a l l i n t h i s c a t e g o r y , as w e l l as some of the c a l c a r e o u s - b u i l t c o n t i n e n t a l s l o p e s (B lak e P l a t e a u , West F l o r i d a E s c a r p m e n t, e t c . ) . C o n t i n e n t a l s l o p e s may be p e r f e c t l y smooth alo n g th e s t r i k e of th e s l o p e , and p o s s i b l y down s l o p e as w e l l , w h ile o t h e r s a r e h i g h l y i r r e g u l a r . T rench s l o p e s commonly show r e l a t i v e l y g e n t l e u p p e r and s t e e p lower s l o p e s ( P l a t e s 2 and 5 ) . Some c o n t i n e n t a l s l o p e s a re h i g h l y i n c i s e d w i t h s u b m a rin e c a n y o n s; o t h e r s a r e f r e e of them. No a p p a r e n t p a t t e r n g o v e rn in g th e p r e s e n c e or a b se n c e of c an y o n s in a p a r t i c u l a r r e g i o n h as been n o t e d . Some c o n t i n e n t a l s l o p e s commence w here th e s h e l f b r e a k i s s h a l l o w ; o t h e r s b e g in from s t e e p s h e l f b r e a k s , or s e a ward o f deep o f f s h o r e p l a t e a u s such as the G r e a t B a r r i e r R eef or th e Blake P l a t e a u . I t must be c o n c lu d e d , t h e r e f o r e , t h a t c o n t i n e n t a l s l o p e s p r o b a b l y were n o t formed a t the same tim e ; t h e y do n o t s h a r e a common o r i g i n , no r a re p r e s e n t day p r o c e s s e s o p e r a t i n g on ( o r below ) th e s l o p e s e v e ry w h e re th e same. 40 8 Evidence p o i n t s to a r e l a t i v e l y y o u th fu l age of most c o n t i n e n ta l s lo p e s . Because e x a c t o r i e n t a t i o n of p r o f i l e s i s unknown no g e n e r a l summary of c o n t i n e n t a l s h e l f and slo p e g r a d i e n t s , a r e a s , e t c . , can be g iv en . However, George K e lle r (1963) has provided un p u b lish ed s t a t i s t i c s which summarize e x i s t ing knowledge of the c o n t i n e n t a l t e r r a c e based upon i n f o r m ation o b ta in e d from c h a r t s (Table 2 5). S h e lf Breaks Whenever c lo s e l y - s p a c e d p r o f i l e s are a v a i l a b l e a c ro ss the c o n t i n e n t a l or i n s u l a r s h e l f edge, the s h e l f b rea k com monly shows a sinuous p r o f i l e . Based upon a v a i l a b l e in f o r m a tio n , waves can a c t i v e l y erode to d e p th s of about 10 m ( D i e t z , 1963, 1964b; Moore and C u rray , 1964). The only l o g i c a l o r i g i n f o r most c o n t i n e n t a l s h e lv e s i s wave p l a n a t i o n or c o n s t r u c t i o n by s e d i m e n ta tio n , or a com bination of these... S h e lf b re a k s o f te n are l o c a te d a t d e p th s c o n s id e r a b ly de ep e r than can be e x p la in e d by P l e i s t o c e n e g l a c i a l e u s t a t i c changes in sea l e v e l . Maximum g l a c i a l low ering i s g e n e r a l l y c o n s id e re d to be about 131 m ( C h a r le s w o r th , 1957, p. 1354-1355) which i s v i r t u a l l y the same as the s t a t i s t i c a l average d e p th of s h e l f b rea k s (S hep ard, 1963). T his s t a t i s t i c a l average i s d i f f i c u l t to f in d in n a t u r e . (Compare s h e l f b re a k s in v a r ious oceans and s e a s , Table 2 5 .) Some s h e lv e s are very / / V J / & / / £ f i / £ A/ / c A / / ° A / / ^ / ■ $ ? / 4 / A / £ AREA / £ / * / ^ / ^ / V / / $ / $ * /A / V / 9 / 7 / / / A 4 > / k} O / Q l A / 4 / / / f f / i A A < ? A / # A /// * ° / / / ■S'/ r ? / i f / 7 / / / A + r / k / ^ M $ U / i f g £ / * / * £ * > / < / 4 ? / « 3 A , / M y , AW /r° 7 7 7 & / < . « / A T W / o « ■ / Ti / v /A A / V / * / ' i 0 * / / T / / < v / < / / V 4 // / 7 / / y A r / - / 9 r / v / / / # / / / / / i / ^ /y 7 A / * 7 7 * ’7 / / Ay / / 7 / / / * / T $ / / ^ / n f c / A/ * / Ay A 4 W g /A 2 3 / / e , / 7 / A A / / ^ / g / g m x ’ / ^ » / / AAAy /£ A i.y aA a a AAyAv M / ' i / r / £ / A t / 4 t a / a * ^ /A A / / £ $ / / $ * / 4 f i , £ / u / C & / £ / J / £ / A / / * / 0 / k y t A / / / / / i s / / / / / f / * / / / / £ / § / & / / / * / ** / ^ / / / ^ /A /«£■// / ’ /■£/* / / / / ^ / £ / / / / $ / $ / 4 / ^ / / * > / « y / / />/ ^ / g? / Q / A $ / Q r / / * 3 / ^ / s T /A / ^ / / 0 / 0 / T / / / A4 A4 / ° / / - f / i f / i f / $ / + / $ I $ / £ / ,T / £ / ' * / £ / s s / & / y / . / & / § / ° / ° / V / r / fit / A /A / r * / £ / £ / k} / kj I < / / V / ? / T / r / t/ t/ ^ / * ARCTIC OCEAN 5-840 256 50-200 87 0 ° l '8" * 15-450 1 38 500-2000 1529 o O * 660 4102000 0 ° 1 0 ’ 0°52' o ° r . i ° 9 ’ 0 ° 8 ‘-5 °2 0 ' ATLA NTIC OCEAN SUBSIDIARY SEAS NORTH SEA 3-370 176 40-100 69 o ° i- 24 2.900 6-210 66 140-1500 517 0U27' 91,100 50 174600 0U15 ’ 0U22* 0u I ’ - r 5 4 - 0U 6 ‘- 1w54 ‘ G REENLA ND AND NORWEGIAN SEAS 7-220 56 100-500 213 0U13 ’ 107.500 10-420 151 500-2000 1514 O u 34‘ 294000 870 75 3,400 0U15’ l d8 ’ 0u r - 0 u49' 0U1 1 '-7 U58- DAVIS STRA IT AND B A FFIN BAY 6-145 57 100-500 205 O'-T 2 ’ 140.500 14-295 110 500-1800 1245 0U39' ZAOfoOO 470 20C&00 0UI 7 ’ 0U49' 0W 3 '- 0 < J57' 0U17’- I lj34’ G ULF O F MEXICO 2-154 57 10-100 44 o 'A i 157.000 17-228 128 BOO-2000 1760 0 °46' 353,300 810 449,200 0C *5’ 1°9' o ° r - o ° i 8 ' 0 ° 2 6 '- 6 ° 3' CARIBBEA N SEA 1-125 23 40-100 95 0°1 4' 101500 10-382 1 34 2000-3700 2576 1 ° 4 ' 30 3p00 1450 801.800 1°44‘ 2U18’ 0 ° 2 ' - 5°4 3’ 0°1 8 '-1 2°25 NORTH ATLA NTIC 1-240 54 10-500 114 0 °7 ' 334000 5-566 143 200-4300 2237 0°5 11 664p00 1796 13(pIUO0 0°35- I °24 0°1 • - 10°48 0 ° 5 5 ° 4 3' NORTH ATLANTIC AND SUBSIDIARY SEAS 1-370 63 10-500 129 0 ° 7 ’ 1,155,400 5-566 99 1 30-4 300 1764 0 °57' ’ 162p00 1672 1W 96P00 0° 36’ 1 °2 4 ’ o ° r - i o ° 4 8 0 ° 5 ’- 1 2°25* SOUTH ATLA NTIC 1-415 79 100+ 100 0°4 ’ 246k500 25-540 I 34 1000-3000 1973 0 ° 4 8 ’ 418 J00 2237 10^77,400 0°1 3' I ° 6 ' 0°1■-1° 5 4 ’ 0° 16 ‘ - 3° 1 2 * NORTH AND SOUTH ATLA NTIC (LESS SUBSIDIARY SEAS) 1 .415 62 10-500 109 0 ° 6 ‘ 1.202200 5-566 140 200-4 300 2171 0 ° 5 1' 2714/bO O 1972 244,9 3.700 0°28- I ° 1 9 1 0 ° ! '- 1 0°48 0°5 -5 °4 ] ■ T O TA L ATLA NTIC 1 -415 55 10-500 100 0 °6 ' 1.46)100 5-566 138 20 0 -4 )0 0 2203 0°52- 3,670,900 1881 2t>,B 7 3,400 0°3Q- 1 °2 8 ' 0 ° r - 1 0 ° 4 8 0°5 .I2 ° 2 5 - M EDITERRAN EAN SEA 1-195 19 100-200 98 0wl 8 ’ 149.800 1-300 34 1B0-2400 1059 1 °1 9' 294^00 810 7 32^00 1°2- 2°l 0 ' O r -5 ° 4 3 - 0°2 - I7 ° 4 5 ' RED SEA 2-90 27 100+ 100 0 ° U ' 5 3800 10-90 34-* 500+ 500 0 °4 0 ' 68.300 270 1 31,000 0° 37' 1 °5 ' 0 ° 4 2 ° 5 2 ‘ 0 ° 1 5 1. 2°17' INDIAN OCEAN 2-200 49 100-300 100 0a 8' 71)9.300 15-420 98 500-3500 1905 I 0 ) ’ 1.753,500 2170 2 3 ,7 56,700 0°2 )' 1 ° ) 5 ' 0 ° 1 •-5 ° 4 2 ’ 0 ° ! 8 - S °4 )' PA C IFIC OCEAN SUBSIDIARY SEAS BERING SEA 2-465 1 23 100 + 100 0d 3- 199,100 J 2-255 1 14 2000 + 2000 0°58' 17Bp00 7<10 t.70^00 0U2 1 ' l d 38' 0 ° ! ’ - 2^51 ' 0 ° 8 '- 8 ° 5 J ' SEA O F OKHOTSK 1 -540 143 100-300 155 0 °4 ' 419,900 4-150 S3 500-1800 888 0°46 ’ I 3)^00 460 4t' 3,500 0 °33' 2°0' 0 ° !- S ° 4 3‘ 0°T I ' - I < 1° I 7 1 SEA O F JA PA N 3-210 33 100- 300 IIS 0°1 2' 79,200 6-68 76 400-1000 1 160 0°49’ 18 3,400 740 2P4?00 0°JO ’ 2° 34’ 0 ° 2 ’- 1 ° 5 5 • p ° j r - 8 0s v YELLOW AND EAST CHINA SEAS 120-695 396 100-500 1 36 0 ° P 261.600 IB S -390 2 36 3000 + 1000 0 °4 2 ’ 1 15,700 1 30 340,300 0 °2 ' 0 d4 4 ‘ 0 ° r .0 ° 4 5 * C l°25-0O5 j ’ SOUTH CHINA SEA 7-600 196 100 + 100 0 °2 ' 447,300 40 - 3 35 2(16 2000 + 2000 0°5 2' 4 7 0 ;0 0 Q00 lp720OO 0 ° 8 ’ 0 ° 4 ! ' 0d 1 -0 d4O- 0< 3 , o-._»°4 J- NORTH PACIFIC 1 -1 OS 30 IOU-200 114 0 °l V 29HJ300 7-255 47 IOOO-SOPO 24 3 3 2°4<l' 00 2110 24/07,5(10 1°0' l044' 0‘ >»-.S°43* Pd 34’- 1 2dr ‘ NORTH PACIFIC AND .SUBSIDIARY SEAS ] -600 75 ion-3on 1 18 0 °5 ' 1,70 5,900 4 - US 71 400-5000 1 <170 ] wl('- 1549,70(1 JO,.,. 27050,000 ! °4 • 3° 3 4 ( 10 ' ’ . 5 '* 4 3' 0d! 3 -'.Ov 5 l- SOUTH PACIFIC 1 - ISO 27 inn - 2iio 101 » °l )• 157,100 17 - III 20 1 22 1600.4(1(10 2571 r 'l t p 1.4 2 (1 ,1 00 2128 1*1074,500 0°4 J* 2° 20' ,t" ; .5 J4 f •2 d 'i' -s'-'jo NOR T il AND SOUTH PACIFIC n . r . s s s u b s i d i a r y s e a s ) li. w,5 2« lllfl 2 IH 1 1 O H ll” ! I' -IS 3,3(10 7- 10.'O 75 l to o -sn o o 25 | 1 1 °5p ’ l.isjp o o 2118 4 3,37 2)»00 i»°40’ 3°! 3 O * ’.*! -S°4 2’ O'*! 0 ‘ -1 2J f ' T O T A L PACIFIC II.60S 7 / inn son 114 Ol,S' 1/35,-,1ml 1- 10 .’0 ’•I mo soon 2150 1 "l T- 2,H 4/00 20 »' 4 1 ^ 1 •4,500 O^ig- 2° » !» ■ ..v - V - Table 25. C h a r a c te r is t i c s of Con t i n e n t a l Shelves and S lo p e s.(A fte r K e lle r, 1963). N O T AIM-1.K A B I .K r j n It A N O N 409 410 s h a l lo w , s u g g e s t i n g r e c e n t u p l i f t ; o t h e r s h e l v e s c o v e r i n g g r e a t h o r i z o n t a l d i s t a n c e s exceed 500 m in d e p t h . The s i n u o u s n a t u r e of th e s h e l f edge i s i n t e r p r e t e d as i n d i c a t i n g l o c a l w arping b r o u g h t a b o u t p r i n c i p a l l y by r e l a t i v e s u b s id e n c e of the ocean b a s i n s and v e r y p r o b a b l y by c o i n c i d e n t a l onsho re u p l i f t . However, t h i s i s o v e r s i m p l i f i e d f o r c o n tin u o u s s e i s m ic p r o f i l e s i n d i c a t e c u t - a n d - f i l l p r o c e s s e s on th e c o n t i n e n t a l m argin have r e s u l t e d in r a i s ing the d e p th of s h e l f b re a k by s e d i m e n t a t i o n or lo w e rin g i t by e r o s i o n . I t may a l s o be deep as a r e s u l t o f n o n d e p o s i t i o n and s u b s i d e n c e . T h is was g r a p h i c a l l y p o i n t e d out by C u rra y and Moore ( 1 9 6 4 ) . Some deep s h e l v e s a re a t t r i b u t e d to i c e l o a d i n g , as i n A n t a r c t i c a , b u t t h i s c e r t a i n l y c a n n o t be the e x p l a n a t i o n f o r deep s h e l v e s in no n g l a c i a t e d r e g i o n s , as o f f n o r t h w e s t A u s t r a l i a or s o u th w e s t A f r i c a . F u rth e r m o r e , Daly (1951) h a s p o i n t e d ou t t h a t K e rg u e le n I s l a n d and th e F a e ro e I s l a n d s do n o t a p p e a r to have caused downwarping of lan d u n d e r lo a d ( s e e P l a t e s 41 and 22, P r o f i l e OB 5 7 / 8 - 1 6 ) . Problem s r e l a t i n g to i c e lo a d i n g and u n lo a d in g are f a r from s im p le ; in f a c t , t h e r e i s some e v id e n c e which o b v i a t e s the n e c e s s i t y o f t h i s p r o c e s s to e x p l a i n c e r t a i n o b se rv ed f e a t u r e s . For exam ple, Hans S t i l l e (1955) has p o i n te d ou t t h a t F e n n o s c a n d ia has been a r i s i n g complex s i n c e e a r l y g e o l o g i c tim e . The e x p l a n a t i o n t h a t th e most r e c e n t r i s e i s due to i s o s t a t i c r e bound by d e g l a c i a t i o n i s c o n s i d e r e d by S t i l l e to be sim p ly 411 an a d d i t i o n a l f a c t o r in th e g e n e r a l c o n ce p t of upwarping which has been going on for 200 m i l l i o n y e a r s . Many Rus s i a n g e o l o g i s t s a l s o q u e s t i o n the w id e ly a c c e p te d t e n e t s of i s o s t a t i c rebound ( Z h e l i n , M eshcheryakov, G z o v s k i i , K r e s t - n ik o v , and R e i s n e r , in S c h e id e g g e r , 1963). No e v id e n c e was found to le a d to th e c o n c l u s i o n t h a t s h e l f - d e p t h s a re r e l a t e d to l a t i t u d e as p o s t u l a t e d by E a rd - le y (1 9 6 4 ). Many t e r r a c e s below the s h e l f b re a k a re w arped, f r e q u e n t l y showing a s i n u o s i t y p a r a l l e l i n g the s h e l f edge v a r i a t i o n s . T e r r a c e s T e r r a c e s , b e n c h e s , or f e a t u r e s w ith o t h e r names (b u t of s i m i l a r c o n n o t a t i o n ) a re w id e sp re a d a t a l l d e p th s on c o n t i n e n t a l and i n s u l a r s l o p e s , on the s i d e s of g u y o ts and seam ounts, m id-ocean r i d g e s , and o t h e r e l e v a t e d se a f l o o r f e a t u r e s . While t e r r a c e s have been re c o g n iz e d and many can be c o r r e l a t e d over g r e a t h o r i z o n t a l d i s t a n c e s , v i r t u a l l y n o th in g i s known about t h e i r o r i g i n f o r few d a t a a re a v a i l a b le from which to work. Some t e r r a c e s u n d o u b te d ly are t e c t o n i c w h ile o t h e r s a re the r e s u l t of e u s t a t i c s e a l e v e l c h an g e s, s e d i m e n t a t i o n , l a v a f l o w s , and p r o b a b l y o t h e r c a u se s no t y e t c l e a r l y u n d e r s t o o d . I t has been p ro v en t h a t many t e r r a c e s and f l a t a r e a s were p la n e d o f f by m arine e r o s io n a t d e p th s no g r e a t e r than 10 m to 20 m, th en submerged 412 r e l a t i v e to p r e s e n t sea l e v e l . Some of the most p e r s i s t e n t t e r r a c e s o ccur on t r e n c h s lo p e s and c o n s i s t of a g e n t l e upper and s te e p lower g r a d i e n t . This f e a t u r e can be t r a c e d a c r o s s th e e n t i r e N orth P a c i f i c Ocean from the P h i l i p p i n e Trench to A la sk a . I t may a ls o co rre sp o n d to w e ll- d e v e lo p e d t e r r a c e s along th e w est c o a s t of North America. T his change in s lo p e i s p o s s i b l y due to t h r u s t i n g but i t s o c c u rre n c e over v a s t d i s t a n c e s i s d i f f i c u l t to u n d e r s ta n d . L ik e w ise , th e wide and le n g t h y benches of the A l e u tia n Trench a re an enigma and p e rh a p s r e p r e s e n t a re g io n where th e M ohorovicic d i s c o n t i n u i t y e i t h e r cro ps o u t, r e p r e s e n t s a major phase change between o c e a n ic and c o n t i n e n t a l type m a t e r i a l , a n d /o r i s a major t h r u s t f a u l t as f i r s t proposed by Lake ( 1 9 3 1 ). He made use of the sim ple g e o m e tr ic a l f a c t t h a t an arc of a g iven c u r v a t u r e i s o b ta in e d when a t h r u s t p l a n e c ro p s o u t a t a s u i t a b le angle of i n c l i n a t i o n on the s u r f a c e of the g lo b e. T h i s , p e r h a p s , i s the b e s t e x p l a n a t i o n f o r the pronounced change in s lo p e along the enorm ously long d i s t a n c e s on tr e n c h s l o p e s . I t a ls o r e c e i v e s su p p o rt from the d i p - s l i p f a u l t n a tu r e of e a r th q u a k e e p i c e n t e r s . Such a c lo s e r e l a t i o n cannot be d i s c a r d e d l i g h t l y as b ein g m erely f o r t u i to u s . C o n t i n e n t a l s h e lv e s were formed by s e v e r a l p r o c e s s e s , in c l u d i n g e r o s i o n . These and many o t h e r t e r r a c e s a t moder a t e d e p th s and even those hig h above se a l e v e l can be 413 a t t r i b u t e d d i r e c t l y to m arine p l a n a t i o n . How f a r below s e a l e v e l e u s t a t i c c h an g e s l e f t t h e i r mark i s n o t known and t h i s rem a in s one of th e fu n d a m e n ta l p ro b le m s c o n f r o n t i n g g e o l o g i s t s . Only g l a c i a l l y - c o n t r o l l e d s e a l e v e l h a s been s t u d i e d - - o r even c o n s i d e r e d - - b u t t h i s i s n ot the e n t i r e p i c t u r e f o r i t i g n o r e s o t h e r p o s s i b l e c a u s e s of e u s t a t i c c h a n g e s . As B u l la r d (1964, p. 19) so c o g e n t l y p u t i t c o n c e r n in g q u e s t i o n s o f mechanisms and t h e o r y : The E a r t h i s so c o m p lic a te d a body and the c o n d i t i o n s w i t h i n i t so f a r from th o s e of th e l a b o r a t o r y t h a t i t i s u n d e s i r a b l e to ask to o soon: ’ I s t h i s p r o c e s s p o s s i b l e ? ’ There a re many phenomena, such as t h u n d e r s t o r m s , ic e a g e s , and the E a r t h ' s m a g n e tic f i e l d t h a t u n d o u b te d ly o c cu r b u t which', i f th e y had not been o b s e r v e d , would p r o b a b l y n o t have been p r e d i c t e d by p h y s i c a l t h e o r y . I t i s u s u a l l y b e s t to d e c id e on the e x i s t e n c e of a phenomenon in the l i g h t of the known f a c t s , or of a r e a s o n a b l e e x t r a p o l a t i o n of them, and to lo o k f o r a mechanism and a p h y s i c a l t h e o r y . . . . T here a p p e a rs t o be good r e a s o n s t o s u s p e c t t h a t sea l e v e l has n o t always been s t a b l e and i n v a r i a b l e e x c e p t f o r g l a c i a l ( c l i m a t i c - c o n t r o l l e d ) l o w e r i n g s . L arge F l a t A reas R e l a t i v e l y f l a t r e g i o n s c o v e r v a s t p a r t s of th e sea f l o o r , i n c l u d i n g the B la k e , C am p b e ll, and Lord Howe P l a t e a u s and R o c k a ll Bank. Such r e g i o n s o f t e n show u n m i s t a k a b le i n d i c a t i o n s of m arin e p l a n a t i o n . W hether th e y were e ro d e d a t t h e i r p r e s e n t l e v e l d u r i n g a form er lower e u s t a t i c s ta n d i n sea l e v e l and have rem ained more o r l e s s s t a b l e , or were once more e l e v a t e d , p la n e d o f f , and s u b m erged, i s p r o b l e m a t i c . E ch oso un ding and d r e d g i n g d a t a s u g g e s t s t h a t many o f t h e s e v a s t p l a t e a u s were s u b a e r i a l l y e ro d e d and r e l a t i v e s u b s id e n c e has o c c u r r e d s i n c e p l a n a t i o n . Some p l a t e a u s c o n s i s t of g r e a t l a v a f l o w s . S eas and i s l a n d g ro u p s o f r e l a t i v e l y s h a l lo w d e p t h s c o v e r i n g g r e a t a r e a s , as w e l l as numerous r i d g e s , u n d o u b t e d l y a p p ly to t h i s s tu d y b u t were beyond t h e scope of t h i s i n v e s t i g a t i o n . They i n c l u d e such r e g i o n s as th e G ulf of P a r i a , B a l t i c , W h ite, and N orth S e a s , P e r s i a n G u lf , s e a s b etw een the Sunda I s l e s , M olucca, G u lf of Siam, Yellow S e a , G u lf o f T a r t a r y , s e a s betw een New G uinea and A u s t r a l i a - - t o name a f e w - - p l u s i s l a n d a rc r i d g e s , as w e l l as e x t e n s i v e b ank s and p l a t e a u s . I n s u l a r S lo p e s I n s u l a r s l o p e s have c e r t a i n c h a r a c t e r i s t i c s in common w i t h c o n t i n e n t a l s l o p e s b u t i n s u l a r s l o p e s of o c e a n i c i s l a n d s u n d o u b t e d l y have d i f f e r e n t o r i g i n s . E v id e n c e p o i n t s to a v o l c a n i c o r i g i n f o r o c e a n ic i s l a n d s . On some i s l a n d s t h i s v o l c a n i c o r i g i n i s v i s i b l e ( e . g . , th e H aw aiian c h a i n ) b u t many i s l a n d s in warm w a t e r s , such as Bermuda, th e v o l c a n i c b a se i s h u n d re d s or th o u s a n d s of m e t e r s below p r e s e n t day s e a l e v e l . I n s u l a r s l o p e s o f t h e s e o c e a n i c i s l a n d s may be t r a c e d d i r e c t l y to v o l c a n is m , u p b u i l d i n g of r e e f m a t e r i a l , or i n o t h e r i n s t a n c e s th e s l o p e s may c o n s i s t of in p a r t 415 or whole o f t a l u s . M o d i f i c a t i o n s t h e s e s l o p e s u n d e rg o as v o l c a n i c r o c k s a re e x t r u d e d and b u i l t up from th e a b y s s a l se a f l o o r , m o d if ie d by o r g a n i c g ro w th , or d u r i n g u p l i f t and s u b s id e n c e i s a s u b j e c t t h a t h as r e c e i v e d b u t l i t t l e i n v e s t i g a t i o n . Some i s l a n d s , se a m o u n ts, and g u y o ts show t e r r a c e s a lo ng t h e i r f l a n k s b u t most i n s u l a r s l o p e s a re so p r e c i p i to u s t h a t e c h o so u n d in g r e c o r d s a s l o p e to o s t e e p to d i s c e r n f e a t u r e s , even i f p r e s e n t . Bottom M a t e r i a l s The number of b o tto m sam ples c o l l e c t e d or d e s c r i b e d from th e c o n t i n e n t a l s lo p e i s l i m i t e d so few c o n c l u s i o n s can be re a c h e d a bo ut th e age or l i t h o l o g y of c o n t i n e n t a l s l o p e s . Most of th e ro c k s d r e d g e d , as w e l l as i n d i r e c t i n f o r m a t i o n such as p r o j e c t i o n o f w e l l d a t a o f f s h o r e , i n d i c a t e s th e u p p e r c o n t i n e n t a l s l o p e c o n s i s t s m a in ly o f Ceno- z o ic age r o c k s of m id d le and u p p e r T e r t i a r y and Q u a t e r n a r y a g e s . However, o l d e r r o c k s a l s o have been r e c o v e r e d . L o c a l l y , b a s i n s may have form ed n e a r th e p r e s e n t c o n t i n e n t a l s lo p e so t h a t a lm o s t any age ro c k e v e n t u a l l y may be r e c o v e r e d . The o l d e s t r o c k s a re of P r e c a m b r ia n a g e : c r y s t i l - l i n e r o c k s a lon g S e y c h e l l e s Ridge i n t h e I n d i a n O cean, a r e p o r t e d t r i l o b i t e - b e a r i n g r o c k from t h e M i d - A t l a n t i c R id g e, and P r e c a m b r ia n age r o c k s from th e H y p e rb o re a n p l a t form in the A r c t i c B a s i n . These a r e e x c e p t i o n a l f o r most 416 ro ck s dredged from th e tops of g u y o ts , and from the deep sea f l o o r are C re ta c e o u s and younger (Menard and H am ilton, 1963; R id e l , 1963). According to p ro p o n en ts of c o n t i n e n t a l d r i f t , the breakup of c o n t i n e n t s o ccu rred in C re ta ce o u s time; however, some eviden ce p o i n t s to d i s r u p t i o n in P e r m o - T r ia s s ic tim e. Hence, rocks o ld e r than th e s e d a te s may be rec o v ere d from r i f t - f o r m e d c o n t i n e n t a l s l o p e s . Subsidence of Oceans and Seas Strong e v iden ce of w idespread su b sid e n c e of ocean b a s i n s and seas i s documented in the Appendix. Some of the major evidence i s summarized h e re : (O b v io u sly , th ese have a d i r e c t b e a rin g on the n a tu r e o f the c o n t i n e n t a l s l o p e . ) 1. D e ta ile d mapping of c o a s t a l and o f f s h o r e a re a s of the world commonly show ev id e n ce of f a u l t i n g , w ith or w ith o u t f l e x u r e along the c o n t i n e n t a l m argin. 2. B ath ym etric e v id e n c e , d r e d g in g , c o r i n g , his-* t o r i c a l d a t a , and g e o p h y sic a l i n v e s t i g a t i o n s of the se a f l o o r , o f t e n t i e d in w ith land geology, p o in t to r e l a t i v e l y r e c e n t submer gence of se a s and ocean b a s i n s or o th e r sea f l o o r f e a t u r e s l a r g e and sm a ll. Major f r a c tu r e zones on the sea f l o o r o f t e n show marked changes in r e l a t i v e r e l i e f . O ther evidence 417 of r e l a t i v e s u b s id e n c e a l s o has been n o te d . C o n c lu s iv e e v id e n c e e x i s t s of f e a t u r e s which could o n ly have been formed s u b a e r i a l l y or in s h a llo w w a t e r : k a r s t to p o g ra p h y , f e a t u r e s formed by l i t t o r a l a n im a ls , w e l l rounded c o b b l e s , beach , and sho re ic e f e a t u r e s . 3. E x is te n c e of seam o un ts, g u y o ts , a t o l l s , r e e f - b u i l t i s l a n d s , or g r e a t banks and p l a t e a u s and o t h e r s t r u c t u r e s show su b s id e n c e m easured in th o u sa n d s o f m eters s i n c e th e C re ta c e o u s per iod . 4. On the b a s i s of v a r i o u s l i n e s o f ev id e n ce such as p a le o g e o g r a p h y , t r a c e s of ic e move m ents, and d e t a i l e d g e o lo g ic mapping, deep w a te r now e x i s t s where m ountainous a r e a s or la r g e land masses once s t o o d . O ften such e v i dence i s in c o n t r a d i c t i o n w ith g e o p h y s i c a l h y p o t h e s e s . 5. C o n t in u a t io n of m ajor s t r u c t u r a l e le m e n ts i n t o ocean d e p r e s s i o n s s u g g e s t s f a u l t i n g , r i f t i n g , s u b s id e n c e , e t c . 6. G e o p h y sic a l s t u d i e s of many m a r g in a l se a s show c o n t i n e n t a l - t y p e s t r u c t u r e , s u g g e s t i n g s u b s i d ence . A nother m ajor a r e a - - p a l e o n t o l o g i c a l - - i s n o t c o n s i d ered h e r e . I t should be o b s e r v e d , however, t h a t on the 418 b a s i s of ind epen den t evidence in v o lv in g g e o l o g i c a l mapping and g e o p h y s ic a l s t u d i e s , many of the assumed land b r id g e s and form er land c o n n e c tio n s made by p a l e o n t o l o g i s t s take on new meaning. The c lo s e c o r r e l a t i o n s of some f r e s h - w a t e r f i s h in the Dutch E ast I n d ie s a re d i f f i c u l t , i f not impos s i b l e , to e x p la in w ith o u t assuming former land c o n n e c tio n s (M o le n g ra aff and Weber, 1919). Another im p o rta n t o b s e r v a t i o n i s t h a t sh a llo w w a te r m a rin e , f r e s h - w a t e r , and t e r r e s t r i a l e n v io rn m en ts have more k in d s of l i f e than the a b y ssa l m arine en v io rn m en t. Only one P a l e o z o ic r e l i c t anim al (Neo- p i l i n a ) is known from the a b y s s a l zone of the ocean. P e r c e n t a g e - w i s e , the a b y s s a l fau na having a known g e o lo g ic re c o r d c o n s i s t m o stly of T e r t i a r y t y p e s . Menzies and Im- b r i e (1958) have concluded t h a t a b y s s a l fau n a i s r e l a t i v e l y r e c e n t ( g e o l o g i c a l l y s p e a k i n g ) . Hence, i t should n o t be concluded t h a t p a l e o n t o l o g i c a l e v id e n ce i s in c o n f l i c t w ith the c o n c l u s i o n s . They o f t e n c o r r a b o r a t e , but too o f te n p a l e o n t o l o g i c a l d a t a s u f f e r from g r e a t e r d i v e r s i t i e s in p o s s i b l e s o l u t i o n s t o a given s i t u a t i o n . P a l e o c l i m a t i c c o n d i t i o n s a re even more s u s p e c t because i t i s g e n e r a l l y b e lie v e d t h a t th e a n g u la r v e l o c i t y o f the E a r t h ’ s r o t a t i o n has been h ig h e r and t h a t th e g e n e r a l a f f e c t s of c e n t r i f u g a l a c c e l e r a t i o n s a f f e c t ocean c u r r e n t s and c l i m a t e . Hence, i n t e r p r e t a t i o n s of p a l e o c l i m a t i c e v i dence i s h ig h ly d e b a t a b l e . F u rth e rm o re , c li m a t e a f f e c t s f l o r a and fa u n a , th us compounding u n c e r t a i n t i e s . 419 S e v e r a l f u n d a m e n ta l q u e s t i o n s a r i s e . C o n s i d e r in g th e m u l t i t u d e o f form er la n d c o n n e c t i o n s and e v id e n c e o f moun t a i n o u s t e r r a i n which have d i s a p p e a r e d , t h r e e c h o i c e s seem open: c o n t i n e n t s moved v e r t i c a l l y ( s u b s i d e d ) , h o r i z o n t a l l y , or moved b o th v e r t i c a l l y and h o r i z o n t a l l y . I f r i f t i n g , f a u l t i n g , and f l e x u r i n g are the p r i n c i p l e o r i g i n s o f c o n t i n e n t a l m a r g in s , w h at, t h e n , cau se d t h e s e b a s i c a l l y t e c t o n i c f e a t u r e s ? L i t t l e i s known a b o u t th e amount of s u b s id e n c e b e ca u se e s s e n t i a l l y no r e f e r e n c e datum i s known. Menard and H a m il ton (1963) s t a t e d t h a t th e P a c i f i c B a sin in M iddle C r e t a c eous tim e was a t l e a s t 3,2 0 0 m deep in the v i c i n i t y of th e M i d - P a c i f i c M ountains and t h a t th e P a c i f i c Ocean h as e x i s t e d in about i t s p r e s e n t form and d e p th s i n c e the C r e t a c eo u s. H. Ladd, however, h a s s t a t e d t h a t the P a c i f i c i s la n d a r e a may have been a g i g a n t i c a r c h i p e l a g o in C r e t a ceous and T e r t i a r y tim e s ( d i s c u s s i o n i n Menard and H a m il to n , 19 6 3 ). T his i s in c o n f l i c t w ith t h e p r e c e d i n g view . H a m ilto n (1957) s t a t e d t h a t the o v e r a l l s i n k i n g , a s i n d i c a t e d by th e g u y o t s , would amount to a 30 p e r c e n t i n c r e a s e in volume i n 100 m i l l i o n y e a r s . Kuenen (1 95 4) e s t i m a t e d the r a t e o f s u b s id e n c e a t 20 m p e r m i l l i o n y e a r s , w h ile W ilson (1962) gave a rang e o f 4 m to over 50 m p e r m i l l i o n y e a r s . C e r t a i n R u ss ia n g e o l o g i s t s s u p p o r t the t h e o r y o f s u b s id e n c e of ocean b a s i n s , e s p e c i a l l y th e A t l a n t i c and A r c t i c 420 Oceans w hich a r e c o n s i d e r e d s u b s id e d ocean m asses and s t i l l e x h i b i t many t r a c e s of o r i g i n a l c o n t i n e n t a l s t r u c t u r e s and s u b a e r i a l f e a t u r e s . (S a k s , 1958; Saks, e t a l ., 1951; Panov, 1955; and B e lo u s so v , 1 9 5 5 ). W estern g e o l o g i s t s have a t ta c k e d t h i s and o t h e r s i m i l a r v iew s. E. R. Hope ( 1 9 6 2 ) , in a re v ie w of S o v ie t l i t e r a t u r e , s t a t e d : In the W est, the p r e v a i l i n g o p in io n h a s been t h a t th e d eep ocean b a s i n s are p r i m o r d i a l , and t h a t the d i f f e r e n c e s betw een c o n t i n e n t a l and ocean c r u s t are p r i s t i n e , fu n d a m e n ta l and i r r e c o n c i l i a b l e . C onse q u e n t l y in some q u a r t e r s th e S o v i e t d o c t r i n e h a s been a s c r i b e d to sim p le i g n o r a n c e of W estern r e s u l t s . T his s u s p i c i o n , how ever, i s c l e a r l y u n fo u n d e d . Ac c o r d in g to Panov, th e t h e s i s of a r a d i c a l d i f f e r e n c e b etw een o c e a n ic and c o n t i n e n t a l c r u s t was s e t f o r t h in the S o v ie t Union j u s t as e a r l y as i n the West and Panov in 1952 r e f e r s to i t w ith a p p r o v a l . But as seen by B e lo u s so v , Panov and S a k s, th e d i f f e r e n c e i s n o t n e c e s s a r i l y p r i m o r d i a l , and t h e r e i s no sim p le c r u s t a l dichtom y of o c e a n ic v e r s u s c o n t i n e n t a l ; b e tween the e x tre m e s t h e r e i s an e x t e n s i v e i n t e r m e d i a t e c a t e g o r y (w hich w i l l i n c l u d e ’m e d i t e r r a n e a n ’ and ’m a r g i n a l ’ s e a s ) . The f a v o r e d p o s i t i o n o f the s u b s id e n c e t h e o r y , in the S o v i e t U nion, may in p a r t be due to the a u t h o r i t y o f B e lo u s s o v , b u t i t a l s o u n d o u b te d ly i s a g e n u in e r e sponse to the new i n f o r m a t i o n produced by the i n t e n s iv e S o v i e t A r c t i c e x p l o r a t i o n in r e c e n t y e a r s . The A r c t i c Ocean i s r e g a r d e d as too complex to be c l a s s i f i e d ’ o c e a n i c . ’ . In th e W est, t h i s same i d e a has r e c e n t l y been d e v e lo p e d by O s te n s o ( 1 9 6 2 ) . In p a r t i c u l a r i t a p p e a rs t h a t th e f l o o r s of the A r c t i c b a s i n s a re d i f f e r e n t : i f b o t h of them a re ’ o c e a n i c , ’ th e n ’ o c e a n i c ’ has more th a n one m eaning. The Nansen (E u ro p e an A r c t i c ) B a sin i s s t r o n g l y s e i s m i c , w h ile the ’H y p e r b o r e a n ’ B a sin i s q u i t e a s e i s m i c ; th e Nansen B asin i s m a g n e t i c a l l y q u i 6 t , w h i l e th e H y p erb o rean B a s in is i n t e n s e l y d i s t u r b e d ( O s t e n s o ) . The d i f f e r e n t c h a r a c t e r of th e two b a s i n s h a s long s i n c e been p o s t u l a t e d , on t e c t o n i c e v id e n c e . . . Hy p e r b o r e a n P l a t f o r m , a r e s i s t a n t b lo c k or c r a t o n fo rm ing th e f l o o r of the H yperborean B a sin , i s fundam en t a l i n the S o v i e t g e o l o g i c a l l i t e r a t u r e . . . I f such a r e s i s t a n t b lo c k c a n n o t be r e c o n c i l e d w i t h a c r u s t o f o c e a n ic t h i c k n e s s , th e n i t seems we may have to 421 invoke l i t h o s p h e r i c r a t h e r th a n c r u s t a l s t r u c t u r e to e x p l a i n i t . As f o r th e f l o o r of the A t l a n t i c O cean, t h e r e i s e v id e n c e t h a t i t s m arine s e d i m e n ta r y c o v e r i s com par a t i v e l y y o u t h f u l . O r i g i n of C o n t i n e n t a l S lo p e s D i r e c t e v id e n c e of c o n t i n e n t a l s l o p e o r i g i n o b v i o u s l y i s m i s s i n g . A lth o u g h th o u s a n d s of echogram s a c r o s s c o n t i n e n t a l s l o p e s a re now a v a i l a b l e , the o r i e n t a t i o n of most p r o f i l e s w ith r e s p e c t to th e t r e n d of th e s l o p e ( i . e . , a lo n g i t s s t r i k e ) i s g e n e r a l l y l a c k i n g . Nor i s i t alw ays known or p o s s i b l e to d e te r m i n e w h e th e r some of th e d i s c o n t i n u i t i e s on echogram s a re the r e s u l t of subm arine c a n y o n s, t e r r a c e s , or o t h e r to p o g r a p h i c f e a t u r e s . Only th o se r e g io n s where th e c o n t i n e n t a l t e r r a c e has been c a r e f u l l y c h a r t e d and th e e x a c t o r i e n t a t i o n of th e echogram i s known can any m ajor c o n c l u s i o n s be drawn w ith r e s p e c t to s lo p e c h a r a c t e r i s t i c s ( g r a d i e n t s , p r e s e n c e or ab sen ce of t e r r a c e s , e t c . ) . Hence, g r e a t c a re must be e x e r c i s e d in draw in g any m ajor c o n c l u s i o n s c o n c e rn in g th e c h a r a c t e r i s t i c s of s l o p e s . T his i s the r e a s o n th e w r i t e r has a v oided any a tt e m p t t o draw m ajor c o n c l u s i o n s based upon one, on w i d e l y - s p a c e d p r o f i l e s , or h as n ot made c o r r e l a t i o n g ra p h s where i n s u f f i c i e n t echogram s were a v a i l a b l e . While d i r e c t e v id e n c e f o r c o n t i n e n t a l s lo p e o r i g i n i s l a c k i n g , and most t h e o r i e s a re s p e c u l a t i v e , s e v e r a l c o n v e r g e n t l i n e s of e v id e n c e p o i n t to f o u r or more b a s i c 422 o r i g i n s : (1 ) f a u l t i n g , (2 ) f l e x u r e ( o r downwarped c o a s t s ) , ( 3 ) c o m b in a tio n of f a u l t and f l e x u r e , and ( 4 ) f a u l t (and p o s s i b l y f l e x u r e ) combined w i t h u p b u i l d i n g of c a r b o n a t e r e e f m a t e r i a l . Under f l e x u r e a re i n c l u d e d c l e a r l y seaw ard d ip p in g s t r a t a , a p p a r e n t l y warped downward w ith or w i t h o u t accompanying f a u l t s . An example i s the Gulf C oast Geosyn- c l i n e where u p b u i l d i n g and o u t b u i l d i n g by s e d im e n ts occur on a s u b s id i n g b a s i n s l o p e . The f l e x u r e in t h i s c a se o c c u r r e d a f t e r the s t r u c t u r e fo rm ed. Under f a u l t i n g a re i n c lu d e d r i f t - f o r m e d c o n t i n e n t a l s l o p e s . The c o n t i n e n t a l s l o p e r e g im e , o f c o u r s e , i n c l u d e s no t o n ly th e o u t e r p r o f i l e seen on an echogram , b u t i t a l s o must i n c l u d e th e u n d e r l y i n g fu n d am e n ta l ( p e r h a p s d eep ) t e c t o n i c s t r u c t u r e . Rock s t r u c t u r e , d i r e c t i o n of f o r c e s , and s i m i l a r f a c t o r s p r o b a b ly a r e of c o n s i d e r a b l e im p o rta n c e in d e te r m i n i n g w h e th e r f l e x u r e or f a u l t i n g o c c u r s . An o f f s h o r e a r e a may move downward l e a v i n g the lan d e l e v a t e d , or c o n v e r s e l y , th e land may become e l e v a t e d (bowed up, or u p - f a u l t e d ) , l e a v i n g the seaw ard b lo c k at a lower l e v e l . In a d d i t i o n , i t i s p r o b a b l e t h a t some c o n t i n e n t a l s l o p e s are t h e r e s u l t of a b u i l d - u p of c a r b o n a t e ( r e e f ) m a t e r i a l on a d o w n f a u lte d or f l e x u r e d b l o c k . Thus, w h ile the c o n t i n e n t a l s l o p e may be s t e e p and c o n s t r u c t e d of r e e f - b u i I d i n g o r g a n is m s , r e l a t i v e downward movement is a p r e r e q u i s i t e to upward c o n s t r u c t i o n on to p of a s u b s i d i n g b l o c k . A r e l a t i v e e u s t a t i c r i s e i n se a l e v e l , w h ile th e c o n t i n e n t a l b lo c k rem ained s t a t i o n a r y , 423 seems u n l i k e l y in view o f d i r e c t e v id e n c e of th o u sa n d s of m e te rs of s h a llo w w ater r e e f m a t e r i a l on top of w id e ly s e p a r a t e d b lo c k s such as th e Blake P l a t e a u , Bahama P l a t f o r m , and p o s s i b l y the West F l o r i d a E sc a rp m e n t. Such a e u s t a t i c r i s e in s e a l e v e l would be u n i v e r s a l l y o b s e r v e d . Hence, e v id e n c e s t r o n g l y s u g g e s t s t h a t c o n t i n e n t a l s l o p e s , d i r e c t ly or i n d i r e c t l y , a re th e r e s u l t of r e l a t i v e m ovem ents--up- l i f t i n g of land w ith or w i t h o u t o f f s h o r e s u b s id e n c e . S e d im e n ta tio n u n d o u b te d ly has been i n s t r u m e n t a l in the c o n s t r u c t i o n o f some c o n t i n e n t a l s l o p e s . I f an ocean b a s i n slo w ly s u b s i d e s , se d im e n ts may b u i l d upward and outw ard as the b a s i n s u b s i d e s . The r e s u l t i n g s t r u c t u r e c o n s i s t s of a s e r i e s of n e a r l y p a r a l l e l bed s w hich show a seaward d i p . S u b sid en c e was the p r i n c i p a l i n f l u e n c i n g f a c t o r in the f o r m ation o f c o n t i n e n t a l s l o p e s of a s u b s i d i n g b a s i n . Moore and C u rray (1963a and 1964) showed t h a t in the n o r t h w e s t G u lf of Mexico, the s t r u c t u r e i s formed by sim ple sedim en t a r y u p b u i ld i n g and o u t b u i l d i n g w i t h accompanying s u b s i d e n c e . T his i s an example of a g e o s y n c l i n e in th e making. One of D i e t z ’ (1 964a) e x p l a n a t i o n s on d o w n - f le x in g along a c o n t i n e n t a l m argin was t h a t " th e se a f l o o r a t the base of th e c o n t i n e n t a l s lo p e i s f i r s t loaded w ith a s e d i m entary apron fo rm ing a c o n t i n e n t a l r i s e . T h is in t u r n i s o s t a t i c a l l y p u l l s down the a d j a c e n t c o n t i n e n t a l s l o p e , assum ing t h a t th e E a r t h ’ s c r u s t a d j u s t s i t s e l f r e g i o n a l l y ” . The load would have to be g r e a t to d i s p l a c e the more 424 dense u n d e r l y i n g sima, or to make the r e g i o n s u b s i d e . Un d e r t h i s p o t u l a t e one would e x p e c t r e g io n s w ith pronounced c o n t i n e n t a l r i s e s to p o s s e s s some of th e d e e p e s t s h e l f b r e a k s ; t h i s i s not o b s e r v e d . I t i s now g e n e r a l l y b e l i e v e d t h a t in a s u b s id in g g e o s y n c lin e o r b a s i n , se d im e n ts accumu l a t e b ecau se th e b a s in i s t h e r e b u t th e se d im e n ts do n o t cause th e b a s i n to i s o s t a t i c a l l y s u b s i d e . (F o r exam ple, se e Bucher, 1952; a b s t r a c t in A p p e n d ix .) The same would be~ t r u e in t h e case of D i e t z ’ e x p l a n a t i o n , hen ce, sedim ent a c c u m u la tio n on the c o n t i n e n t a l r i s e would n o t p u l l down the c o n t i n e n t a l slo p e u n l e s s t h i s a r e a a l r e a d y was a r e gion o f s u b s id e n c e . S e d i m e n ta tio n can no t be th e p r im a ry cause of the f o r m ation o f a g e o s y n c l i n e , such as in th e G ulf of Mexico, but the a c c u m u la tio n of s e d im e n ts w i l l a c c e l e r a t e and i n c r e a s e the s u b s id e n c e of th e u n d e r l y i n g c r u s t (Rittmann, 1956). I f x i s th e t h i c k n e s s of the s e d im e n ts , d t h e i r d e n s i t y (a b o u t 2 . 3 ) , and D the d e n s i t y of the d i s p l a c e d s u b c r u s t a l magma (ab o u t 3 . 3 ) , the s u b s id e n c e , S, caused by the load of the s e d im e n ts i s th e n : S = - x 0 . 7 x . D As the f a c i e s of the g e o s y n c l i n a l se d im e n ts rem a in s e s s e n t i a l l y c o n s t a n t , the t o t a l s u b s id e n c e , S, must be n e a r l y e q u a l to x. S, th e n , must be n e a r l y e q u a l to x. Emery ( i n D i e t z , 1964b) has r e p o r t e d t h a t s u b -b o tto m 425 echos along the E a st Coast of the U nited S t a t e s i n v a r i a b l y show the c o n t i n e n t a l slo p e e x te n d in g b e n ea th the c o n t i n e n t a l r i s e se d im e n ta ry p rism . T his i n d i c a t e s t h a t th e c o n t i n e n t a l r i s e i s a s e p a r a t e and more y o u t h f u l d e p o s i t i o n a l f e a t u r e and i s not sim ply an e x te n s i o n of the c o n t i n e n t a l slo p e regim e. C urray (1965) r e c e n t l y s t a t e d : The s t r u c t u r a l framework of th e c o n t i n e n t a l t e r r a c e o ff n o r t h e r n and c e n t r a l C a l i f o r n i a has been found, by means of a c o u s t i c r e f l e c t i o n , to c o n s i s t of t h i c k a cc u m u la tio n s of s h e l f and slo p e d e p o s i t s over and behind a basem ent h ig h , l o c a l l y known to be g r a n i t i c . Where t h i s high i s d e e p ly b u r i e d , a wide con t i n e n t a l r i s e or fan has formed. Large s c a l e s l i d i n g h as l o c a l l y m odified s t e e p e r p o r t i o n s of th e s l o p e . T h is s t r u c t u r e d i f f e r s in d eg re e of developm ent, not in b a s i c k in d , from the e a s t c o a s t of th e U nited S t a t e s . I t i s n o tew o rthy t h a t most of the w o r l d ’ s m ajor r i v e r s d r a i n i n t o the A t l a n t i c Ocean and t h a t the d r a in a g e empty ing i n t o the A t l a n t i c f a r exceeds a l l o th e r land a r e a s of the w o r ld . T h is may acc o u n t, a t l e a s t in p a r t , f o r the b e t t e r developed c o n t i n e n t a l r i s e s in th e A t l a n t i c Ocean. One would a ls o e x p ec t t h a t se d im e n ts would be t h i c k e r in the deep A t l a n t i c f o r the same r e a s o n . The ob se rv ed v a lu e s a re about l / 2 km in the P a c i f i c Ocean vs more than 1 km f o r the A t l a n t i c Ocean. E a rth q u a k e s and T ectonism Many a tte m p ts have been made to match e a r th q u a k e s w ith p o s s i b l e a r e a s o f f a u l t i n g , i n c l u d i n g the c o n t i n e n t a l s l o p e , th e c o n c lu s io n bein g t h a t a r e a s la c k in g ev id e n ce of 426 s e i s m i c i t y are n ot t e c t o n i c a l l y a c t i v e , hence some non- t e c t o n i c e x p la n a t i o n must be s o u g h t. I t i s b e l i e v e d t h a t such a p r a c t i c e of i d e n t i f i c a t i o n of f a u l t i n g , or tecton ism , on t h i s b a s i s is e n t i r e l y un w arran ted and le a d s to e r r o n eous c o n c l u s i o n s . I t i s p r o b a b le t h a t slow movement, or c re e p , goes on w ith o u t any n o t i c e a b l e d e t e c t i o n on seism o g ra p h s . Many a re a s lack ad equ ate se ism o g ra p h s , hence e a r th q u a k e s ( u n l e s s of l a r g e m agnitude) occur and are no t r e c o r d e d . Orowan (1960, 1964a, and 1964b) has concluded t h a t w ith the e x c e p tio n of se ism ic f a u l t i n g in a t h in u p per l a y e r (^'-'10 km), e a r th q u a k e s a re c re e p f r a c t u r e s . Gutenberg and R i c h t e r (1949) have shown the d i s t r i b u t i o n of e a r th q u a k e s around the w orld. In the P a c i f i c r e g io n e a r th q u a k e s are a s s o c i a t e d w ith the c o n t i n e n t a l mar g i n s . T his i s not the g e n e r a l case f o r the A t l a n t i c and I n d ia n Oceans. In t h e s e oceans most s e is m ic a c t i v i t y i s a s s o c i a t e d w ith t h e m id-ocean r i d g e s and the i s l a n d a r c s . As p o in te d out e a r l i e r , the c o n t i n e n t a l s lo p e s are somewhat d i f f e r e n t in d i f f e r e n t o c e a n s. The most pronounced d i f f e r ence i s t h e p re s e n c e of w e ll- d e v e lo p e d c o n t i n e n t a l r i s e s in the A t l a n t i c Ocean. While sh a llo w - to d e e p - f o c u s e a r th q u a k e s a re a s s o c i ated w ith the c o n t i n e n t a l margins of th e P a c i f i c Ocean, they are not a s s o c i a t e d w ith the m argins of o t h e r oceans and se a s e x ce p t where i s l a n d a r c s o c c u r. Two p o i n t s are im p o r ta n t h e re : (1 ) the lac k o f f a u l t i n g along a •427 c o n t i n e n t a l m argin does n o t n e c e s s a r i l y mean t h a t f a u l t i n g or t e c t o n i c a c t i v i t y i s n o t ta k i n g p la c e on a very low o r d e r (below th e t h r e s h o l d o f s e is m o g r a p h s ) , and (2) th e low s e i s m i c i t y a s s o c i a t e d w ith most c o n t i n e n t a l m a r g in s , e x c e p t th e P a c i f i c Ocean and i s l a n d a r c s , s u g g e s t s t h a t th e s e ty p e s of m argins have a d i f f e r e n t mechanism of f o r m a t i o n . In the d i s c u s s i o n of the n o r t h e r n Gulf of Mexico, an a s e is m ic a r e a , P r i c e (1951) r e p o r t e d a w e ll-d o c u m e n ted c ase o f movement along a f a u l t of f i v e in c h e s in 14 y e a r s . Gu te n b e rg c a l l e d a t t e n t i o n to movement ov er a p e r i o d of a few y e a r s in Los A ngeles b a s i n o i l f i e l d s s u f f i c i e n t to s h e a r o f f c a s i n g s w ith o u t any r e c o rd e d s e is m ic d i s t u r b a n c e . Some s e is m ic r e g i o n s show l i t t l e a c t i v i t y over long p e r i o d s . R i c h t e r has s t a t e d t h a t on ly about 40 h i s t o r i c a l e a r th q u a k e s have been accompanied by exposed f a u l t b r e a k s a lon g which m easurem ents have been made. The E a st A f r i c a n r i f t s show e v id e n c e of g r e a t v e r t i c a l d i s p l a c e m e n t s . I n s t r u m e n t - r e c o r d e d shocks o c c u rre d i n 1910 and 1912, y e t over the n e x t 35 y e a r s major shocks were r a r e (G u ten b e rg and R i c h t e r , 1951). Large shocks have a l s o o c c u r r e d in a se is m ic r e g i o n s : 1663 in Canada; 1811-1812 in th e c e n t r a l M i s s i s s i p p i V a lle y ; 1886 in C h a r l e s t o n ; and c o n s i d e r a b l e shocks in s o u t h e a s t e r n Canada in 1925 and 1935. Suess s p e c u l a t e d t h a t the b i b l i c a l legend of th e D e l uge was based upon the o c c u rr e n c e of a tsun am i w hich i n u n d a te d p a r t of Mesopotamia in p r e - B i b l i c a l t i m e s . The 428 b i b l i c a l legen d re s e m b le s d e s c r i p t i o n s found in B a b y lo n ia n docum ents a p p a r e n t l y w r i t t e n betw een 330 B. C. and 260 B. C. These m a n u s c r i p ts d e s c r i b e d a l a r g e e a r t h q u a k e and tsu nam i which d e s t r o y e d numerous c i t i e s in C h a ld e a and w hich a p p a r e n t l y was c e n t e r e d in the A ra b ia n Sea and was accompanied by e x t e n s i v e t o p o g r a p h i c c h a n g e s . The t h e o r y o f S u e ss has been s e v e r e l y c r i t i c i z e d by t a k i n g i n t o a c c o u n t th e low s e i s m i c i t y of the P e r s i a n G ulf r e g i o n . How e v e r , th e A ra b ia n Sea e a r t h q u a k e of November 1945 h a s , in some way, j u s t i f i e d S u e s s ’ t h e o r y showing t h a t even though s e i s m ic f r e q u e n c y i s v e ry low in t h i s a r e a , th e e a r th q u a k e i n t e n s i t y o c c a s i o n a l l y can be q u i t e h i g h . In f a c t , th e v i o le n c e o f th e A ra b ia n e a r t h q u a k e ( e p i c e n t e r in the A rab ian Sea a t the e n t r a n c e to th e P e r s i a n G u lf ) was com parab le to t h a t of the San F r a n c i s c o e a r th q u a k e of 1906. The accompa n y in g d e s t r u c t i o n co uld be a f u r t h e r p r o o f of th e Suess t h e o r y ( T e r r y , 196 5 ). While the o c c u r r e n c e of l a r g e shocks can be used as p o s i t i v e e v id e n c e of f a u l t i n g and t e c t o n i c a c t i v i t y , the c o n v e r s e - - a b s e n c e o f e a r t h q u a k e s - - c a n n o t be used to r u l e o u t l a t e n t , d o rm an t, or slow c r e e p . The im p o rta n c e of t h i s , o f c o u r s e , i s t h a t many r e g i o n s can and have u n d e r gone u p l i f t or s u b s id e n c e i n c l u d i n g th e c o n t i n e n t a l m a rg in , unaccom panied by e v id e n c e of r e c o r d e d s e i s m i c i t y . 429 O r ig in o f C o n t in e n t s and Ocean B asins I n t r o d u c t i o n V i r t u a l l y a l l of our p r e v io u s knowledge of th e E a rth was based upon d e t a i l e d s t u d i e s of t e r r e s t r i a l E a r t h . Only in th e l a s t two d ecades have any r e a l c o n t r i b u t i o n s been d e riv e d from the o ceans, y e t i t i s the o cean s, even more than the c o n t i n e n t s , which hold the s e c r e t s of the E a r t h ’ s h i s t o r y . The r e a s o n s a r e , f i r s t , because the oceans cover n e a r l y t h r e e - q u a r t e r s of E a r t h , and s e c o n d ly , a l a r g e p a r t of the c o n t i n e n t s i s composed of marine se d im e n ts . While p r o c e s s e s o p e r a t in g in the two e n v iro n m en ts may have been d i f f e r e n t d u r in g d i f f e r e n t g e o lo g ic t i m e s , i t is b e l i e v e d t h a t t e c t o n i c p r o c e s s e s are s i m i l a r . The d a t a d e riv e d e x c l u s i v e l y from examining echograms i s l i m i t e d . However, a d d i t i o n a l in f o r m a tio n such as d r e d g in g , c o r i n g , stu d y of d e t a i l e d b a th y m e tr ic c h a r t s , s e ism ic and o th e r g e o p h y s ic a l i n f o r m a t i o n , c o a s t a l g eolo gy , p a le o - magnetism , and s i m i l a r t o p i c s l e a d s to s e v e r a l p e r t i n e n t b u t n o t n e c e s s a r i l y c o n c l u s i v e f a c t s . Most d a t a co n ce rn in g the ocean b a s i n s o b ta in e d b e fo r e World War I I were based upon s p a rc e i n f o r m a ti o n , w ith v i r t u a l l y no g e o p h y s ic a l and l i t t l e geochem ical d a t a . C o n c lu s io n s n e c e s s a r i l y were based l a r g e l y upon s u p p o s i t i o n . In the p a s t two decades c o u n t l e s s new d i s c o v e r i e s have r e s u l t e d from the use of newer te c h n iq u e s made on w o rld-w id e e x p e d i t i o n s . As a 430 consequence, many o l d e r , alm o st f o r g o t t e n t h e o r i e s are now ag ain i n vogue. Among th e s e are c o n t i n e n t a l d r i f t , an e x panding E a r t h , p o l a r w a n d erin g , and mass d is p la c e m e n t of the E a r t h ’s i n t e r i o r caused by c o n v e c tio n c u r r e n t s . The o r i g i n a t o r o f each of th ese i s l o s t in a n t i q u i t y . Most ev id e n ce f o r su b s id e n c e i s r e i t e r a t i o n s of con c l u s i o n s reached by many a u t h o r s , b e g in n in g over a c e n tu r y ago, b u t which have been l a r g e l y ignored f o r v a r i o u s r e a so n s . However, when a l l of th e d i v e r s e e v id e n c e i s p r e s e n t t o g e t h e r and documented by c o u n t l e s s f i e l d w o rkers (a s in the Appendix) i t is hard to ig n o re the overwhelming e v i dence of s u b s id e n c e . Orowan (1964) observed t h a t u n t i l r e c e n t l y geology la y somewhere between the p e rio d of astronom y of K e p ler and Newton, when the laws of p l a n e t a r y m otion were known b u t t h e i r p h y s i c a l laws were n o t . In m arine g e o lo g y , the d i s covery of m id-ocean r i d g e s (which a c t u a l l y have long been known), high h e a t flow s on th e r i d g e s , g u y o ts, and the r e l a t i v e youth of the se a f l o o r c o m p le te ly changed the u n d e r s t a n d in g of oceans and c o n t i n e n t s . A f u r t h e r advance, a c c o rd in g to Orowan, was new knowledge about the p r o p e r t i e s of s o l i d s . One o f the rem ain ing i n s o l u b l e d i f f i c u l t i e s in marine geology i s the i n a b i l i t y to v e r i f y by e x p erim en t and o b s e r v a t i o n . I t i s n o t th e purpose h e re to re v ie w a l l of the r e c e n t advances in m arine geology because of la c k of sp a c e . More 431 im p o r t a n t , the s u b j e c t i s sim ply too broad to cover and t h e r e a re s t i l l to o many unknowns. Since c o n t i n e n t a l s lo p e s form th e n a t u r a l boundary b e tween oceans and c o n t i n e n t s th ey have a d i r e c t b e a rin g on the o r i g i n of th e s e f i r s t o rd e r f e a t u r e s as w e ll as many of the s m a lle r E a r th f e a t u r e s . D e t a i le d echosounding has r e v e a l e d the f a c t t h a t the sea f l o o r has m ajor s t r i k e - s l i p (o r t r a n s - c u r r e n t ) f a u l t s w ith d im ension s s u f f i c i e n t l y l a r g e to give c o n s i d e r a b le c red en ce t o th e c o n t i n e n t a l d r i f t t h e o r y . These f a u l t s , p a le o m a g n e tic d a t a , w o r I d - c i r c l i n g t e n s i o n c ra c k s forming an a p p a r e n t c o u n te r - c l o c k w is e movement of the e n t i r e ocean b a s i n s , m id-ocean r i d g e s w i t h high h e a t flo w , and s i m i l a r o b s e r v a t i o n s i n d i v i d u a l l y do not r e s u l t in an in dep end ent s o l u t i o n to th e o r i g i n of c o n t i n e n t s and ocean b a s i n s . C o l l e c t i v e l y , the o b s e r v a t i o n s and ev id e n ce u n d o u b ted ly have s i g n i f i c a n t meaning. I t must be a d m itte d t h a t c o n fu sio n and c o n t r a d i c t o r y ev id e n ce s t i l l e x i s t s w hich have not been a d e q u a te ly r e c o n c i l e d . Hence, no sim ple or c o n c lu s iv e s ta te m e n t i s a tte m p te d h e r e . Two major p h i l o s o p h i e s have long p e r s i s t e d c o n cern ing the permanence of oceans and c o n t i n e n t s . The o l d e r domi n a n t sc h o o l has long b e li e v e d in the permanency of oceans and c o n t i n e n t s ("p e rm a n e n t” o b v io u s ly i s a r e l a t i v e te rm ). I t i s p ro b a b le t h a t most g e o l o g i s t s to day s u b s c r i b e to the g e n e r a l b e l i e f t h a t c o n t i n e n t s have always been c o n t i n e n t s 432 and ocean b a s i n s have always been ocean b a s i n s ; however, i t i s a d m itte d t h a t th e c o n t i n e n t s o c c a s i o n a l l y are in u n d a te d by the ocean w ith o u t l o s i n g t h e i r i d e n t i t y as t e r r e s t r i a l f e a t u r e s ( i . e . , " c o n t i n e n t a l ty p e " s t r u c t u r e ) . Geosyn- c l i n e s are t y p i c a l ex am p les, f o r h ere enormous t h i c k n e s s e s o f sh a llo w w ater m arine se d im e n ts a ccu m u late in a s u b s id i n g b a s i n , l a t e r to be f o l d e d and u p l i f t e d i n t o a major moun t a i n r a n g e . E p i c o n t i n e n t a l s e a s a l s o cover l a r g e p a r t s of the c o n t i n e n t s upon o c c a s i o n . A g e n e r a l i z e d diagram of the b a s i c d i f f e r e n c e s betw een o ceans and c o n t i n e n t s are shown in F ig u re 54. In 1888, Edward Suess s u g g e s te d t h a t ocean b a s i n s were r e l a t i v e l y y o u t h f u l g e o lo g i c f e a t u r e s . S u e s s ’ e v id e n c e was l a r g e l y ig n o red and the t h e o r y of permanency of oceans and c o n t i n e n t s won fa v o r which i t e s s e n t i a l l y r e t a i n s to d a y . A few d i s s e n t i n g v o ic e s have been h e a r d , p a r t i c u l a r l y from E uropeans and g e o l o g i s t s who have s t u d i e d th e s o u t h e r n hem i s p h e r e in d e t a i l . G e n e r a l l y s p e a k in g , American g e o l o g i s t s have now a c c e p te d the r e l a t i v e l y y o u t h f u l age of o cean s and s e a s , y e t s t r o n g o p p o s i t i o n i s e x p r e s s e d on one hand c o n c e r n i n g c o n t i n e n t a l d r i f t , w h ile p ro p o n e n ts of s p r e a d i n g of c o n t i n e n t s and ocean b a s i n s , of p a le o m a g n e tic e v id e n c e of p o l a r w a n d e rin g , e t c . , can be r e a d i l y fo u n d . E v iden ce f u r th e r shows h o r i z o n t a l movements measured in hun dred s of k i l o m e t e r s , as w e l l as v e r t i c a l d i s p l a c e m e n t s of th e o r d e r of s e v e r a l thousand m e te r s , are a c c e p t a b l e . Nor i s i t F i g u r e 54. S c h e m a tic d iag ra m of c o n t i n e n t a l , o c e a n i c , and i s l a n d s u b s u r f a c e s t r u c t u r e . V e l o c i t y and d e n s i t y l a y e r s a re a v e ra g e f o r d i f f e r e n t ocean a r e a s . The d e p th o f MOHOLE i s a p p ro x im ate o n l y , and th e d e e p e s t o i l w e l l does n o t r e a c h deep c o n t i n e n t a l - t y p e c r u s t ( i . e . , d e ep s i a l ) . C O N T I N E N T A L S T R U C T U R E OCEANIC STRUCTURE •5 uj A 10 Oh ISLAND STRUCTURE o J MOHOLE 9400 M , D EEPEST OIL W ELL 7678 M TEST HOLES TO 5450 M t CONTINENTAL SHELF SEA LEVEL OCEAN 1.5 K m /S ec OCEAN BASIN SI AL (G R AN ITIC-TYPE CRUST) CRUST (DENSITY 2.67) VOLCANIC LOAD m am MOUNTAIN ROOT MANTLE D E E P CRUST VARIES FROM 3. 6 TO 7. 0 K m /S ec. SEDIMENT 1 MOHOROVICIC DISCONTINUITY (MOHO) G enerally assu m ed velocity) / / / / / / / / / / SECOND LAYER (5. 07 K m /Sec. P ro b ab ly igneous) ' / / / / / / / MANTLE (7. 9 -8. 2 Y ///////////, THIRD LAYER K m /S ec ) y / ^ y y / / Y / / Y / , D EE P CRUST-OCEANIC 'C R U ST (6. 69 K m /S ec. , P ro b ab ly basalt) 30 TO 60 Km (b a s a l t ; . . . / A m a n t l e (DENSITY 3. 27) R. D. TERRY /N O T 435! i I d i f f i c u l t to b e l i e v e t h a t some i s l a n d s , a t o l l s , seam ounts, and guyots have s u b s id e d th o u san d s of m e te rs sin c e the C re ta c e o u s p e r i o d . As r e c e n t l y as the end of World War I I , fo llo w in g the d i s c o v e r y o f g u y o ts , i t was th o u g h t t h a t th e s e were p lan e d o f f in P recam b rian tim e. Also c r e d i b l e and a c c e p ta b le is the e vid ence of l o c a l f a u l t i n g , w a rp in g , and su b sid e n c e along the c o n t i n e n t a l m argin and i n s u l a r s l o p e s . ’ When th e s e d i v e r s e l i n e s of ev id e n ce are put t o g e t h e r problem s and s k e p t ic is m n a t u r a l l y r e s u l t . F i r s t , i t seems i n c r e d i b l e t h a t e n t i r e ocean b a s i n s have formed or su b s id e d r e l a t i v e l y r e c e n t l y and t h a t a r e a s now occupied by oceans and se as on ly a s h o r t time ago were the s i t e s of m ountainous t e r r a i n s . In some i n s t a n c e s , i t i s t h e o r iz e d t h a t c o n t i n e n t a l - t y p e c r u s t has d i s a p p e a r e d a l t o g e t h e r and o n ly o c e a n ic - ty p e c r u s t now e x i s t s in i t s p la c e . A lthough major ev id ence p o i n t s to th e y o u t h f u l age of the o c ea n s, s e v e r a l s e r i o u s d i f f i c u l t i e s a r i s e , among them t h e source of the w ater and how the w ater m a in ta in e d about th e same f r e e b o a r d as su b sid e n c e o c c u r r e d ; what was the cause of the su b sid e n c e in the f i r s t p l a c e ; and how c o n t i n e n t a l - t y p e c r u s t was c o n v e rte d i n t o o c e a n ic - ty p e c r u s t ? These are only a few of the fun dam ental q u e s t i o n s which cannot as y e t be a d e q u a te ly answered. Before c o n clu d in g t h i s s e c t i o n the r e l a t i v e s h a llo w n e s s of the oceans might be em phasized. C o nsider the 4 3 6 r e l i e f as i t would ap pear on a f i v e - f o o t d ia m e te r g lo b e . The M arianas Trench would be only 0.09 in c h e s deep and the average d epth of th e P a c i f i c Ocean would be b a r e l y d i s c e r n - ab le ( 0 .0 2 i n c h e s ) . In f a c t , the ocean b a s i n s on a whole would have about th e same outward c o n v e x ity as the E a r t h ’ s su r f ace . C o n t in e n t a l D r i f t I t is b e l i e v e d t h a t the e v id e n c e p r e s e n t e d h e re i s not a d v e rse to th e th e o r y of c o n t i n e n t a l d r i f t . R e l a t i v e l y r e c e n t deepening of oceans and se a s i s in g e n e r a l agreem ent w i t h c o n t i n e n t a l d r i f t . C o n v e rse ly , major v e r t i c a l move ments could take p l a c e w ith o u t h o r i z o n t a l s h i f t s of c o n t i n e n t s . I f c o n t i n e n t a l d r i f t is assumed to be v a l i d , then some c o n t i n e n t a l s l o p e s presum ably are b a s i c a l l y r i f t s c a r s . One of J e f f r e y ’ s (1929, and l a t e r ) major c r i t i c i s m s of c o n t i n e n t a l d r i f t was t h a t the c o n t i n e n t s sim p ly d id n o t m atch. Du T o it (1927) concluded t h a t the " p h a s a l v a r i a t i o n " in the s t r a t a shows th a t the South American and A f r i can c o a s t s never to u ch e d , nor were t h e i r c o n t i n e n t a l s h e l v e s ev er in c o n t a c t ; th ey must have been s e p a r a t e d by a gap of 250 to 500 m i l e s . The d i f f e r e n c e in fo r m a tio n s on o p p o s i t e c o a s t s would appear to be c o n s i s t e n t w ith a much w id e r gap (G reg ory, 1930 ). Carey (1955 and 1958) showed t h a t th e 2000-m i s o b a t h of the South American and A f r ic a n 437 c o a s t s a lm o st p e r f e c t l y m atch. T his would im ply, f i r s t , t h a t e s s e n t i a l l y no change had o c c u rr e d along the c o n t i n e n t a l s l o p e s s i n c e d i s r u p t i o n o f the c o n t i n e n t s from a s i n g l e b l o c k . The two s i d e s , once f i t t e d t o g e t h e r , i s the s i m p l e s t and most obv io us e x p l a n a t i o n and no o t h e r has been o f f e r e d to e x p l a i n t h i s r e l a t i o n s h i p . Second, the geo lo g y of the two c o a s t s i s d i f f e r e n t , a lth o u g h s i m i l a r i t i e s e x i s t in the g e n e r a l geology ( M a r tin , 1 9 6 1 ). C o n t i n e n t a l s h e l v e s of b o th A f r i c a and South America a re narrow and the d i s t a n c e from the c o a s t to the 2,000-m i s o b a t h i s not g r e a t . The so u th w est A f r i c a n c o a s t has a s h e l f b rea k c o n s i d e r a b l y d e e p e r than th e e q u i v a l e n t S outh American c o a s t . In a d d i t i o n , the g e o lo g ic h i s t o r y of S ou th A f r i c a has had a long h i s t o r y of p e r i o d i c downwarping o f f s h o r e and u p l i f t i n g a s h o r t d i s t a n c e in la n d ( F ig u r e 4 5 ). These f a c t o r s p e rh a p s are of l i t t l e s i g n i f i c a n c e b e ca u se they m o stly p o s t - d a t e the assumed break up of th e c o n t i n e n t s . B u lla r d and M il le r are a t t e m p t i n g to use a computer a t Cambridge to d e te rm in e the b e s t p o s s i b l e '’f i t s ” betw een p i e c e s of c o n t i n e n t s t h a t may have once been jo in e d or were in c l o s e p r o x i m i t y . R e s u l t s so f a r r e p o r t e d l y show re m a rk a b le f i t s in th e n o r t h e r n h em isph ere a t the 500-fin i s o b a t h . The same i s t r u e o f South America and A f r i c a . Some " h o l e s ” e x i s t , one of which i s in the North A t l a n t i c Ocean, b u t t h i s m ight be accou nted f o r ( " p lu g g e d " ) u s in g R o c k a ll Bank ( S t u b b s , 1964). 438 I f th e s e f i t s are v a l i d (and the eye and c a l c u l a t i o n s show the land a re a s do f i t ) , then the only l o g i c a l (and s i m p le s t ) c o n c lu sio n i s t h a t c o n t i n e n t a l d r i f t o ccurred and t h a t some—but not a l l - - c o n t i n e n t a l s lo p e s b a s i c a l l y are major r i f t f e a t u r e s . Two f a c t s must then be a c c e p te d : (1) d i s r u p t i o n o ccu rred r e c e n t l y ( g e o l o g i c a l l y sp e a k in g ) o r, i f r e l a t i v e l y " o l d , n then the c o n t i n e n t a l s lo p e s have e s s e n t i a l l y remained unm odified by e r o s i o n , s e d im e n ta tio n , w arp in g , or d i a s t r o p h i s m ; in s h o r t , they are a unique g e o l o g i cal f e a t u r e of un u su al s t a b i l i t y and i n a c t i v i t y . Evidence shows th ese are n ot t y p i c a l c h a r a c t e r i s t i c s of c o n t i n e n t a l s l o p e s , hence, r i f t i n g must have o c cu rred r e l a t i v e l y r e c e n t l y . Most evidence p o i n t s to a breakup in p o s t - C retaceou s time a lth ou gh p aleo m ag n etic d a ta d a te the b e g i n ning of d i s r u p t i o n in P e r m o - T ria s s ic tim e, (2) the regio n between the f i t s - - t h e deep ocean b a s i n s - - i s an are a of con s i d e r a b l e su b sid ence and d a te s from the p e rio d of r i f t i n g . The age and p ro b a b ly th e r a t e of su b sid en ce are d i r e c t l y r e l a t e d to r i f t i n g . This means t h a t sea f l o o r f e a t u r e s in th e s e r i f t - f o r m e d b a s i n s , s e a s , e t c . a ls o p o s t d a te r i f t ing . C o n t in e n t a l s h e lv e s commonly appear to be r e g io n s of n o n - d e p o s itio n or of sedim ent b y - p a s s i n g . The same i s t r u e of many c o n t i n e n t a l s lo p e s sin c e C re ta c e o u s and T e r t i a r y age sed im en ts ( p a r t i c u l a r l y Miocene age ro c k s ) are e x tre m e ly common, hence, i t might not be u n re a so n a b le to conclude 439 t h a t th e c o n t i n e n t a l m argins have more or l e s s m a in ta in e d t h e i r b a s i c c h a r a c t e r i s t i c s fo r a c o n s i d e r a b l e le n g t h of g e o lo g ic tim e. Bucher (1939) s t a t e d t h a t " th e mature t o pography of th e c o n t i n e n t a l s lo p e s is so f r e s h t h a t i t is e i t h e r a c t i v e l y form ing now or has been fas h io n e d by ’ y e s t e r d a y . ’ " The mid-ocean r i d g e s (1) appear to be t e n s i o n a l f e a t u r e s ly in g about mid-way between c o n t i n e n t s ; (2) show no ev id e n ce of being fo ld e d ra n g e s ; (3) show s tr o n g e viden ce o f f a u l t i n g ; (4) are composed of v o l c a n i c s ; (5) a re a s s o c i a te d w ith sh allo w fo c u s e a r t h q u a k e s ; ( 6 ) o c c a s i o n a l l y have p a i r e d t e r r a c e s on e i t h e r s id e of the rid g e and g e n e r a l l y sy m m etrical p r o f i l e s ( T o ls to y and Ewing, 1949; T o l s t o y , 1951); (7) o f t e n show u n m is ta k a b le s i g n s of having once been s h a llo w e r ( e . g . , show ev id e n ce of s u b a e r i a l e r o s i o n , have g u y o ts) (H ess, 1954); (8 ) have th e h ig h e s t h e a t flow v a lu e s anywhere in the w orld; and (9) the age of the o c ea n ic i s l a n d s r e p o r t e d l y i n c r e a s e s w ith i n c r e a s i n g d i s t a n c e from th e r i d g e s (W ilson, 1963a and 1963b). A c e n t r a l r i f t v a l l e y has been w id e ly i d e n t i f i e d w ith m id-ocean r i d g e s s u g g e s tin g h o r i z o n t a l movement (Heezen, 1960). Evidence was r e c e n t l y p r e s e n t e d to show t h a t I c e land , c o n s id e re d p a r t of the s u b a e r i a l p o r t i o n of the Mid- A t l a n t i c Ridge, was s p r e a d in g a p a r t (B odvarsson and W alker, 1964; S tu b b s, 1964; and L e s s in g , 1965). The c r u s t and man t l e under the r i d g e s are f u n d a m e n ta lly d i f f e r e n t from those 440 under c o n t i n e n t a l m ountain system s. The l a t t e r have s i a l i c r o o t s and are s e p a r a te d from the m antle by the M ohorovicic d i s c o n t i n u i t y . Hess (I9 6 0 ) b e l i e v e s th e r i d g e s are e l e v ated by t h e r m a l l y - l i g h t , deep r o o t s which o b t a i n a d d i t i o n al buoyancy from l i g h t p r o d u c ts of therm ochem ical r e a c t i o n s such as s e r p e n t i n e . Because of the high h e a t flow under the r i d g e s , i t has been su g g e ste d t h a t th e s e are s i t e s of c o n v e c tio n c u r r e n t s (H ess, 1960; D i e t z , 1961a, 1961b; and B u l l a r d , 1964). R ittm ann (1956) has c a l c u l a t e d th e therm al s t r u c t u r e of the c o n t i n e n t a l m argins of the P a c i f i c and A t l a n t i c Oceans. The two r e g io n s are d i f f e r e n t because the P a c i f i c c r u s t i s t h in n e r than the c o n t i n e n t a l c r u s t . At a depth of about 75 km the te m p e ra tu re of the magma beneath the P a c i f ic Ocean i s about 700° C h ig h e r than t h a t b e n e a th th e c o n t i n e n t ; in the A t l a n t i c Ocean i t i s on ly about 120° C. Rittm ann b e l i e v e s t h a t the g r e a t h o r i z o n t a l te m p e ra tu re g r a d i e n t beneath the P a c i f i c margins causes p o w erfu l sub- c r u s t a l c o n v e c tio n c u r r e n t s which are r e s p o n s i b l e f o r the t r e n c h e s , g e o s y n c l i n e s , and o ro g e n ic c y c l e s . On the o th e r hand, the h o r i z o n t a l te m p e ra tu re g r a d i e n t s a re s m a lle r b e n e ath the A t l a n t i c Ocean. H o r i z o n t a l s u b c r u s t a l c u r r e n t s occur here a ls o but th e s e are to o weak to cause m ountain b u i l d i n g . R ittm ann i n d i c a t e d t h a t c o n s i d e r a b l e su b sid e n c e has o c cu rred in the A t l a n t i c Ocean and might be c o n s id e re d s i m i l a r to t h a t of a g e o s y n c lin e . Hence, the d i f f e r e n c e 441 between the two t y p e s . o f c o a s t s i s a q u a n t i t a t i v e one w ith re g a r d to th e i n t e n s i t y o f s u b c r u s t a l c u r r e n t s and i s due d i r e c t l y to th e d i f f e r e n c e s in th e c o n s t i t u t i o n of the E a r t h ’ s c r u s t . Wegener e n v is io n e d s i a l i c m a t e r i a l ( c o n t i n e n t s ) p u sh ing th ro u g h a se a of sima ( t h e o c e a n s ) . He p o s t u l a t e d t h a t the o r i g i n a l c o n t i n e n t a l f r a g m e n ta ti o n r e s u l t e d in move ment, n o t by an expanding E a r t h , but as ’’s h i p s of s i a l f l o a t i n g upon a b a s a l t i c l a y e r . " T h is c o n c e p t was long h e ld in d i s r e p u t e . In f a c t , i t was p e rh a p s one of th e most overwhelming argum ents a g a i n s t W egener’ s c o n t i n e n t a l d r i f t h y p o t h e s i s . Orowan (1960, 1964a, and 1 964b), how ever, has shown t h a t t h i s and many m is c o n c e p tio n s were the r e s u l t of lack of b a s i c knowledge of th e p r o p e r t i e s of r o c k s . He has concluded t h a t the c o n t i n e n t s a re not f i r m l y anchored to the m an tle and t h a t c o n t i n e n t s are m o b ile . MacDonald (1963) a l s o has c o n c lu d e d , on the b a s i s of the shape of the E a r t h , t h a t t h e r e i s a s o f t l a y e r in the u p per m a n tle , h en ce, s u b s t a n t i a l e v id e n c e e x i s t s which s u p p o r t s W eg e n er's p o s t u l a t e , as w e ll as an ex pan din g E a r t h . In D i e t z ' (1961) h y p o t h e s i s of sea f l o o r s p r e a d in g th e c o n t i n e n t s n e v e r move th ro u g h the sim a: " t h e y e i t h e r move along w ith i t o r sta n d s t i l l w h ile the sima s h e a r s between them ." In o th e r w ords, ocean b a s i n s a re a c t i v e w h ile the c o n t i n e n t s a re p a s s i v e - - the o p p o s ite of W egener’ s h y p o t h e s i s . Suppose the c o n t i n e n t s were to d r i f t . Where would th e r u p t u r e s most l i k e l y o c c u r - - a lo n g the median l i n e or along the m argins of the c o n t i n e n t s a t th e t r a n s i t i o n of the con t i n e n t s and ocean b a s i n s ? T his might be argued in s e v e r a l ways. F i r s t , the t r a n s i t i o n zone presum ably i s a re g io n of w eakness, hence, maximum en echelo n r i f t i n g , s e i s m i c i t y , and volcanism most l i k e l y would occur he re along the c o a s t s . The a l t e r n a t i v e is t h a t the c o n t i n e n t s are s t i c k ing to , and being dragged a lo n g , by the d r i f t i n g c o n ti n e n t along the e n t i r e c o n ta c t zone (E rim esco, 1963). On the o th er hand, g e o p h y sic a l s t u d i e s of bo th the e a s t c o a s t of the U. S. and the w est c o ast o f Europe have shown t h a t the c o n t i n e n t a l margins are q u i t e s i m i l a r . T h is su g g e s ts th a t both had a common o r i g i n . In view of the c o n t i n e n t a l d r i f t th e o ry t h i s p ro b ab ly means t h a t the c o n t i n e n t s moved away from each o th e r and r u p t u r in g o c cu rred midway between the s e p a r a t i n g c o n t i n e n t s . This was f i r s t sug gested by T aylor (1 9 1 0 ). In o th e r words, the reg io n now occupied by the mid-ocean r i d g e s i s the l o c a l e where the c o n t i n e n t s once were j o i n e d . S u b seq u en tly , land a re a s ( s i a l ) moved in e i t h e r d i r e c t i o n away from the reg io n of the m id-ocean r i d g e s . A d i f f i c u l t y i s en co u n tered h e re f o r A f r i c a i s surrounded by mid-ocean r i d g e s which would mean t h a t t h i s c o n t i n e n t would have to move s e v e r a l d i r e c t i o n s a t once ( e a s t and w e st) to account f o r the r i d g e s ! Orowan (1964b) has d is c u s s e d c o n v ec tio n c u r r e n t s on the b a s i s of the most u p - t o - d a t e knowledge on the p r o p e r t i e s of rocks- His s t u d i e s , as w e ll as MacDonald’ s (1 9 6 3 ), have led to the c o n c lu s io n of the i m p r o b a b i l i t y of c o n v ec tio n c u r r e n t s e x c e p t p o s s i b l y in the upper p a r t of the m an tle. The o th e r a l t e r n a t i v e i s t h a t most of the heat flow i s d e riv e d from high r a d i o a c t i v i t y from g r a n i t e ( l a c k ing in o c e a n ic - ty p e c r u s t ) . F u rth erm o re, th e h e a t flow of the c o n t i n e n t s and oceans i s about the same. Orowan has concluded t h a t w ith o u t c o n v e c tio n , c o n t i n e n t a l d r i f t i s e s - s e n t i a l l y _ i m p o s s i b l e u n l e s s the c o n t i n e n t s moved as r i g i d m asses, t o g e t h e r with the d e p le te d p a r t of th e mantle under them. As Orowan (1964b) has p o in te d o u t: ’’The e f f e c t i v e e x c lu s io n of c o n t i n e n t a l d r i f t , however, is a grave d i f f i c u l t y of the n o -c o n v e c tio n h y p o t h e s i s . ” The eviden ce c i t e d i s sim ply too g r e a t to ig n o re . The major o b j e c t i o n s in the p a s t were in ad e q u ate knowledge of the m echanical p r o p e r t i e s o f s o l i d s but t h i s r e c e n t knowledge f a v o r s the d r i f t h y p o t h e s i s (Orowan, 1964a). Adherence to " f i x e d ” c o n t i n e n t s does not e x p la in the c o u n tl e s s d a t a which can be e x p la in e d r a t h e r sim ply w ith the d r i f t h y p o t h e s i s . Orowan (1964b) p o in te d out the d i f f i c u l t y in a t t r i b u t i n g m id-ocean r i d g e s to ascen din g c u r r e n t s where t h in s e d im ents o f f e r only a modest h e a t - i n s u l a t i o n and where r a d i o a c t i v e - g e n e r a t e d h e a t from g r a n i t e i s a b s e n t. He s u g g e ste d t h a t t h i s anomalous s i t u a t i o n might be e x p la in e d i f the hot ascending columns s t a r t e d , f o r example, 500 m i l l i o n y e a rs ago, b e fo re the c o n t i n e n t s d i s r u p t e d , and s t i l l e x i s t 444 today as a consequence of th erm al i n e r t i a in s p i t e of changed c o n d it i o n s on th e E a r t h ’ s s u r f a c e . A major problem con cerns the median d i s t r i b u t i o n of the r i d g e s . I f the r i d g e s are due to r i s i n g hot d i k e s , as su g g ested by Orowan (1964b), they may have a s e l f - c e n t e r i n g mechan ism . I f they were c l o s e r to one a d ja c e n t c o n t i n e n t than to the o t h e r , th e i s o s t a t i c a l l y uncompensated load [ o f v o l c a n ic s ] they dump upon t h a t s id e would be h ig h e r per u n i t are a than the load they p la c e on the o th e r sid e o f the ocean f l o o r ; the r a t e of sub sid ence o f the ocean f l o o r would be g r e a t e r where a c o n ti n e n t i s c l o s e r , and the r e s u l t i n g h o r i z o n t a l spread of the m antle u n d e rn e a th would tend to push the h o t d ik e away from th e c l o s e r c o n t i n e n t . The P a c i f i c m argin, with i t s se ism ic s h e a r p l a i n d i p ping 30° to 60° below the c o n t i n e n t s , s t r o n g l y su g g e s ts a t h r u s t from the s e a or d i p - s l i p f a u l t i n g . Orowan (1964a) s t a t e d t h a t s t r i k e - s l i p f a u l t i n g r e q u i r e s only a f r a c t i o n of the s t r e s s needed fo r comprehensive d i p - s l i p f a u l t i n g and may dominate over a s h o r t p e rio d of tim e. However, d i p - s l i p f a u l t i n g with a s t r i k e - s l i p ’ s component sup erim posed i s su g g e ste d . In g e n e r a l , i f ascending hot d i k e s are r e s p o n s i b l e f o r the m id-ocean r i d g e s where h e a t flow i s up to e i g h t tim es the normal v a lu e , then ascen ding c u r r e n t s in the A t l a n t i c Ocean move upw ard, r e s u l t i n g in a h o r i z o n t a l component t h a t moves the c o n t i n e n t a l b lo c k s away from the ascend ing r e g io n (m id-ocean r i d g e s ) at a r a t e of about one c m /y r . C o in c i d e n ta l to t h i s h o r i z o n t a l movement i s th e movement of the 445 b lo ck ( i n t h i s case N orth and South America) so t h a t d i p - s l i p f a u l t i n g o c c u rs along t h e P a c i f i c m argin. The on ly d e sce n d in g c u r r e n t is th a t a s s o c i a t e d w ith the d i p - s l i p plane. The same g e n e r a l c h a r a c t e r i s t i c seems to be a s s o c i a te d w ith i s l a n d a rc s in the P a c i f i c and e ls e w h e r e . The c o n t i n e n t a l s lo p e s on e i t h e r sid e of a c o n t i n e n t , hence, would be expected to be d i f f e r e n t ; one would be b a s i c a l l y a r i f t s c a r , the o th e r a f a u l t , or f le x e d c o a s t , w ith a d i p - s l i p f a u l t s u r f a c e below. T h is i s in g e n e r a l agreement w ith o b s e r v a t i o n s . F i r s t , s t r u c t u r e s , i n c l u d i n g mountain ran ges along the A t l a n t i c c o a s t s , f r e q u e n t l y are cut o f f a b r u p t l y at the c o n t i n e n t a l m argin whereas m ountain ranges and o th e r s t r u c t u r e s a re p a r a l l e l to th e P a c i f i c c o a s t . Second, the b o rd e rs of the P a c i f i c Ocean have a s e ism ic d i p - s l i p p l a n e , whereas in the A t l a n t i c Ocean none e x i s t s and the c o n t i n e n t a l margin i s l a r g e l y a s e i s m i c . F u r t h e r more, t h i s c o r r a b o r a t i n g eviden ce a f f o r d s a d d i t i o n a l e v i dence o f m o b il i ty of c o n t i n e n t s . As su b sid e n c e o ccu rred and r i d g e s formed the u n d e r l y ing sima must have m ig ra te d ; a t r a n s f e r of d e e p - s e a t e d ma t e r i a l must be i n v o lv e d . No major magmatic e x t r u s i o n or i n t r u s i o n can take p la c e (on land or a t se a ) w ith o u t mass d is p la c e m e n t a ls o o c c u rrin g in the m an tle. L a r g e - s c a l e su b sid e n c e a ls o i n d i c a t e s a l t e r a t i o n in the m asse s. I t has O been e s t im a t e d t h a t th e mid-ocean r i d g e s c o n t a i n 5 x 10 - 5 O - 2 • km of v o lc a n ic rock , and a t l e a s t 4 x 10 km of rock must 446 have been withdrawn from the P a c i f i c Ocean s in c e i t sub sid e d in p o s t - C r e ta c e o u s tim e. In f a c t , c o n s i d e r a b l y more th an 4 x 10^ km^ m ig ra te d e lsew h e re from below the P a c i f i c Ocean (E rim esco, 1963). Evidence s u g g e s ts t h a t most o f the v a s t o u tp o u rin g s of b a s a l t were sp read l a r g e l y in the ocean b a s i n s . Large p o r t i o n s of the Ind ian Ocean f l o o r are b e l i e v e d to c o n s i s t of b a s a l t and Menard (1964) has e s tim a te d t h a t Darwin Rise alone c o n ta in s 10 m i l l i o n km of b a s a l t - - f a r more th an any s i n g l e mass seen on la n d . Ind eed, th e s e submarine b a s a l t i c masses ( i n c l u d i n g I c e l a n d ) dwarf a l l land flo w s. The t r a n s f e r of sima below the m antle might w e l l be e x p la in e d by an analogy w ith the Basin and Range P ro v in c e and the u p l i f t e d Colorado P l a t e a u . G i l l u l y s t a t e d (1963, p . 159): My p e r s o n a l p r e f e r e n c e . . . i s t h a t the Basin Range f a u l t s are the r e s u l t of l a t e r a l t r a n s f e r of c r u s t a l m a t e r i a l from b e n e a th the p r o v in c e to the a r e a of the p l a t e a u . Both t h i s movement and the f o r m a tio n of th e s i l i c e o u s la v a s may be co n n ected w i t h e x t r a o r d i n a r y h e a t flow because of s u b - c r u s t a l cur r e n t s . Cause of Subsidence Evidence of s u b s id e n c e i s w o rld -w id e , t h e r e f o r e a w orld -w id e cause must be in v o lv e d . Three p o s s i b i l i t i e s seem p o s s i b l e : a s h r i n k i n g E a r t h , an expanding E a r t h , and c o n v e c tio n c u r r e n t s . The l a t t e r have a l r e a d y been d i s cu sse d . 447 A c o n t r a c t i n g E a rth t h e o r e t i c a l l y might account f o r the su b sid e n c e of ocean b a s i n s and u p l i f t o f land m asses. C e r t a i n l y f o ld and t h r u s t s t r u c t u r e s are much e a s i e r to e x p l a i n as a consequence of c o n t r a c t i o n in the E a r t h ’ s c r u s t . Sonder (1939, p. 39) proposed a p o s s i b l e c o n t r o l over the development of i s l a n d a rc s by old e s t a b l i s h e d lin e am e n t p a t t e r n s i n h e r e n t in a c o n t r a c t i n g E a rth w ith an e l a s t i c a l ly a n i s o t r o p i c c r u s t . De S i t t e r (1959) i n d i c a t e d t h a t c o n t r a c t i o n o f f e r s the b e s t e x p la n a t i o n f o r the g r e a t c i r c u m - P a c i f i c and M e d i te r ranean o ro g en ic b e l t s occupying two m u tu a lly p e r p e n d i c u l a r g r e a t c i r c l e s . The s h r i n k i n g con cept i s based upon a h i s t o r y o f E a r th c o o lin g from a h o t o r i g i n and as c o o lin g p r o ceeded c r u s t a l s h o r t e n in g o c c u rre d crum pling m ountain ran ges in a re a s of w eakness. The main cause of c o n t r a c t i o n was g e n e r a l l y assumed to be c o o lin g of E a r t h . T h is may have been t r u e in i t s e a r l y h i s t o r y b ut i t does not appear to be a c t i v e to d a y . More im p o r ta n t i s g r a v i t a t i o n a l com p a c t i o n of t e r r e s t r i a l m a tte r and i t s phase c o n v e rs io n s (Khayin, 1957). C o n t r a c ti o n m a n i f e s ts i t s e l f by a r e d i s t r i b u t i o n , or t r a n s f e r of m a t t e r . In clu d e d h e re i s the d i f f e r e n t i a t i o n of m a t e r i a l form ing g r a n i t e s which co ncen t r a t e r a d i o a c t i v e s u b s ta n c e s under downwarps and produce in v e r s i o n which in t u r n r e s u l t s in th e f o r m a tio n of young mountain ra n g e s. T h is i s b a s i c a l l y the combined b e l i e f s of Beloussov and van Bemmelen as proposed by Khayin. 448 In d i s c u s s i n g th e c o n t r a c t i o n t h e o r y , R ubin (1 9 6 4 ) i n d i c a t e d t h a t c r u s t a l movement t a k e s p l a c e by c o n t r a c t i o n of th e E a r t h ’ s s u r f a c e due t o c o m p re s s io n o f the E a r t h ’ s i n t e r i o r . Rubin m en tio n ed t h a t s e v e r a l m u t u a l l y in d e p e n d e n t c a l c u l a t i o n s do show a c o n t r a c t i o n of th e t e r r e s t r i a l r a d i us of 5 cm p e r c e n t u r y i n th e mean. C e r t a i n R u s s ia n g e o l o g i s t s have p o s t u l a t e d t h a t t e r r e s t r i a l c r u s t , under th e a c t i o n of g r a v i t y , s l i d e s or c r e e p s a lo n g the s l o p e s of th e M ohorovic’i c d i s c o n t i n u i t y . G r a d i e n t s as low as 2° to 3° a re c o n s i d e r e d s u f f i c i e n t f o r such s l i d i n g s . I t i s presum ed t h a t h o r i z o n t a l p r e s s u r e s c au se a d e p r e s s i o n of th e M o h o ro v ic ic d i s c o n t i n u i t y and a t such s i t e s c r u s t a l t h i c k e n i n g o c c u r s ( R y b in , 1 9 6 4 ). Rybin b e l i e v e s t h a t h o r i z o n t a l d i s p l a c e m e n t s o f 30 km in 100 m i l l i o n y e a r s i s e n t i r e l y p o s s i b l e . Here t h e a u t h o r t a k e s e x c e p t i o n to s l i d i n g of the c r u s t o v e r th e s u b s t r a t u m (s im a ) as a d v o c a te d in c o n t i n e n t a l d r i f t . S e is m ic s t u d i e s i n d i c a t e t h a t the s u b s t r a t e i s more r i g i d th a n th e c r u s t . How e v e r , l o n g - t e r m slow f lo w , o r c r e e p , w i t h the h ig h ro ck t e m p e r a t u r e and p r e s s u r e s i s p r o b a b l e . The a u t h o r b e l i e v e s t e n s i o n a l f o r c e s o c c u r b e h in d a s l i d i n g p a r t in th e c r u s t , w h i l e g l o b a l s h r i n k a g e o f the E a r t h s e t s up th e c o n d i t i o n s f o r c r u s t a l s l i d i n g in t h e f r o n t a l r e g i o n . T h us, t h i s h y p o t h e s i s d e p en d s upon a c c e p t a n c e o f E a r t h ’ s c o n t r a c t i o n f o r o p e r a t i o n , y e t Rybin s t a t e s t h a t u n i v e r s a l c o n t r a c t i o n of th e c r u s t i s n o t n e c e s s a r y . In e s s e n c e , t h e a u t h o r i s 449 c o n c e rn e d w i t h c r u s t a l s h o r t e n i n g in g e o s y n c l i n e s ( b u t n o t p l a t f o r m s , e p i c o n t i n e n t a l s e a s , e t c . ) . A c o n t r a c t i n g E a r t h would s o lv e r a t h e r n i c e l y the p rob lem s of a c c o u n tin g f o r th e volume o f s e a w a t e r , f o r i t i s presumed t h a t the ocean b a s i n s would s u b s id e d u r i n g c o n t r a c t i o n . An ex pan din g E a r t h is a l e s s o b j e c t i o n a b l e t h e o r y in many r e s p e c t s f o r i t f i t s many more f a c t s th a n th e c o n t r a c t i n g E a r th t h e o r y . I t i s no t p c ;- s ib le to t r a c e th e o r i g i n a t o r of the e x p an din g E a r t h h y p o t h e s i s , b u t c e r t a i n l y W. de S i t t e r , 1917, A. Friedm an, 1922, and G. L e m a i t r e , 1927, forshadow ed e x p a n s io n b e f o r e i t was p o s t u l a t e d m ath e m a t i c a l l y . H i l g e n b e r g (1933 and 1962) a l s o was a m ajor c o n t r i b u t o r f o r he pro po sed t h a t th e o ceans and c o n t i n e n t s owe t h e i r r e l a t i v e p o s i t i o n s to a c o n seq u e n ce of f r a g m e n t a t i o n by an e x p an d in g ( d i l a t i n g ) E a r t h and made one of the most c o n v in c in g a n a l y s e s . In h i s book he showed E a r t h a t s e v e r a l d i a m e t e r s . As the d i a m e t e r i n c r e a s e d , th e A t l a n t i c Ocean form ed; N orth and South A m erica moved away from Eu rope and A f r i c a . C arey (19 58 ) and S c h e id e g g e r (1 961) r e p rod uced H i l g e n b e r g ’ s g lo b e s and t h e s e g iv e a r a t h e r im p r e s s i v e argum ent in f a v o r of an ex pan din g E a r t h . Heezen (1 95 9, 1960, and 1962) s u g g e s te d t h a t an e x p a n d in g E a r t h m ight be the answer t o some of th e o b s e rv e d s e a f l o o r f e a t u r e s , p a r t i c u l a r l y th e m id -o cean r i d g e s and c e n t r a l r i f t v a l l e y s . 450 A ccording to a d v o c a te s of an expanding E a r t h h y p o t h e s i s , ex p an sio n would r e s u l t i n an i n c r e a s e in v o l c a n i c a c t i v i t y . I t i s p o s t u l a t e d t h a t t h i s v o l c a n i c a c t i v i t y has formed th e m id-ocean r i d g e s . U n f o r t u n a t e l y , v o lc a n is m has no t in c r e a s e d th ro u g h o u t g e o lo g ic time (E rim e s c o , 1 9 6 3 ). Much d i s c u s s i o n has been g iven to an expanding u n i v e r s e , w hich, of c o u r s e , was th e b a s i c r e q u ire m e n t o f the th e o r y o f g e n e r a l r e l a t i v i t y as fo r m u la te d by E i n s t e i n . The g r a v i t a t i o n a l c o n s t a n t i s c r i t i c a l in the exp anding E a r th p o s t u l a t e . I t is re a so n e d t h a t i f the u n i v e r s e is expanding,, i f the v e l o c i t y of r e c e s s i o n i s assumed to be c o n s t a n t , and i f the t o t a l mass in th e u n i v e r s e is a ls o c o n s t a n t , th en the g r a v i t a t i o n a l c o n s t a n t would have to d e c r e a s e l i n e a r l y w ith the age o f the u n i v e r s e . The e x p a n s io n of the u n i v e r s e i s r e f l e c t e d in the red s h i f t in the v i s i b l e s p e c t r a and, a c c o rd in g to th e b a s i c t h e o r y , i s a pu re Doppler e f f e c t . Egyed (195 6a, 1956b, and 1956c) has s t a t e d t h a t geo l o g i c a l o b s e r v a t i o n s c l e a r l y show t h a t the volume of the h y d ro sp h e re has grown th ro u g h o u t g e o l o g i c a l tim e , amounting t o about f o u r p e r c e n t s i n c e th e Cambrian p e r i o d ( F ig u r e 5 5 ). I f E a r t h were s h r i n k i n g , the a v e ra g e d e p th o f the oceans must have i n c r e a s e d and th e c o n t i n e n t s would become e v e r i n c r e a s i n g l y co v ered by w a t e r . I f th e volume of E a r th has rem ained c o n s t a n t , the amount of w a t e r - c o v e r e d a r e a s i s i n f l u e n c e d m o s tly by o ro g e n ic movements, but over a long I W A TE R -C O V E R ED AREAS IN 10 KM 70 (A F T E R T. M. STRAHOW) 40 30 - 20 MESOZOIC CENOZOIC PALEOZOIC 0 ■ 300 200 100 500 400 W A T E R -C O V E R E D A R E A S IN 10 KM 60 - (A F T E R H. & G. TERM IER) 50 40 30 20 - 10 - PALEO ZO IC MESOZOIC CENOZOIC 0 400 100 300 200 500 MILLION YEARS MILLION YEARS Figure 55. Water-Covered C o n tin e n tal Areas Computed from Paleographic Maps. 451 452 p e rio d of tim e, remain e s s e n t i a l l y c o n s t a n t . The source o f the water t h a t f i l l s the s u b s id in g b a s in s is a fo rm id ab le o b s t a c l e to e x p la in f o r not on ly i s the .q u a n tity of water v a s t , but evidence p o i n t s to a r a t h e r r e c e n t sub sid en ce i n d i c a t i n g a r a p id change in f r e e b o a r d . While i t might be a c c e p ta b le to assume t h a t the volume of w ater has v a rie d w i t h i n sm a ll l i m i t s , l a r g e volume changes p ro b ab ly would s u b s t a n t i a l l y a f f e c t l i f e . One of the most s e r i o u s d i f f i c u l t i e s ( a p p a r e n t l y ) i s the s i m i l a r i t y of body f l u i d s of a l l anim als ( in c lu d in g man) with the com position of sea w ater (T e rry , in p r e s s ) . T his s t r o n g l y im p lie s t h a t the volume of sea w a te r, w ith i t s c o n s t a n t r a t i o of s a l t s , has v a r ie d l i t t l e sin c e l i f e began on E a r t h . Whether t h i s i s a v a li d c o n c lu s io n i s unknown. Some f i l l i n g of the ocean b a s i n s may be the r e s u l t of w ith d raw a l of water from the c o n t i n e n t s . U n f o r t u n a t e ly , w a ters t h a t cover (or once covered) t e r r e s t r i a l p a r t s of E a rth were l a r g e l y e p i c o n t i n e n t a l s e a s , hence, the volume of w ater was sm all. F u rth e rm o re , th e r e does not appear to be a c o r r e l a t i o n between t r a n s g r e s s i o n s and r e g r e s s i o n s w ith su b sid e n c e of ocean b a s in s and se as a lth ou gh some cy c l i c a f f e c t has been suggested fo r sea l e v e l (Grabau, 1934). In Upper C re ta ce o u s tim e, in f a c t , the oceans expanded and deepened w hile t h e r e was a sim u lta n eo u s marked flo o d in g of the c o n t i n e n t s . I t i s p o s s i b l e t h a t as new w ater i s added to the sea 453 t h a t i t s co m p o sitio n always c l o s e l y approxim ated t h a t o f se a w a te r . As a r e s u l t , sea w ater has r e t a i n e d i t s r a t i o o f s a l t s th ro u g h o u t g e o lo g ic time d e s p i t e th e a d d i t i o n of new w a t e r . The o t h e r a l t e r n a t i v e i s t h a t the volume of wa t e r has remained e s s e n t i a l l y th e same and E a rth has changed shape th e re b y r e d i s t r i b u t i n g the w a t e r . Hess (1954) does not b e l i e v e the q u a n t i t y of w ater has rem ained c o n s t a n t s in c e P recam brian tim e. He s u g g e s te d some r e l a t i o n s h i p b e tween the depth of the Moho under the c o n t i n e n t s has been d i r e c t l y r e l a t e d to sea l e v e l . (See A pp en dix.) A number of w ork ers b e l i e v e t h a t the volume of w ater in the oceans has remained more or l e s s c o n s t a n t d u r in g g e o lo g ic tim e , w h ile o t h e r s have concluded the amount o f w a te r has slo w ly i n c r e a s e d . Rubey (1 9 5 1 ), Kulp (1 9 51 ), and o t h e r s b e l i e v e t h a t the hyd ro sp here has come from the i n t e r i o r of the E a rth th ro u g h o u t g e o lo g ic tim e . In f a c t , i f the p r e s e n t r a t e of w ater r e l e a s e d from the i n t e r i o r has remained c o n s ta n t th ro u g h o u t g e o lo g ic tim e , the c a l c u l a t e d w a te r i s ad equ ate to account f o r the p r e s e n t hy d ro sp h ere (Kulp, 1951 ). F u rth e rm o re , i f t h i s i s t r u e (and the e v i dence seems to su p p o rt such a c o n c l u s i o n ) , the g r a n i t o i d and metamorphic ro ck s which u n d e r l i e th e c o n t i n e n t s have l ik e w i s e a ls o g r a d u a l l y d e v e lo p e d . The work of Rubey, K ulp, and Bucher (1950) seems to p ro v id e a l l th e n e c e s s a r y i n g r e d i e n t s f o r h y d ro sp h ere and c o n t i n e n t a l c r u s t t r a n s f o r m ation and f o r m a tio n . 454 In the in dep end ent s t u d i e s by Strahow (1 9 4 8 ), H. T e r- m ie r, and G. Termier ( 1 9 5 2 ), which have been d i s c u s s e d in d e t a i l by E gyed, i t was shown t h a t land a re a s have been p r o g r e s s i v e l y covered w ith l e s s and l e s s w a ter w ith g e o lo g ic time (F ig u re 55). T his can be a t t r i b u t e d to s e v e r a l c a u se s i n c lu d in g an expanding E a r t h , a e u s t a t i c drop in r e l a t i v e sea l e v e l , a slow r e l a t i v e r i s e in the land a r e a s ( e p e r i o g e n i c movements) so t h a t th e y are l e s s s u b j e c t e d to f l o o d i n g , a d e c re a s e in w ater volume, and p e rh a p s s e v e r a l o t h e r p o s s i b l e e x p l a n a t i o n s . F l i n t (1947) concluded t h a t the average h e i g h t of the c o n t i n e n t s has in c r e a s e d about t h r e e tim es s in c e middle T e r t i a r y time i n d i c a t i n g e p e i r o - g e n ic movements have been o p e r a t i v e . Can i t be assumed t h a t the ocean b a s i n s remained unchanged d u rin g th ese o ro - g a n ic p e r i o d s ? On the b a s i s of Strahow and Term ier and T e r m ie r ’ s d a t a , Egyed concluded t h a t t h i s i s ev id e n ce t h a t E a r t h ’ s r a d i u s has i n c r e a s e d . U t i l i z i n g Term ier and T e r m ie r ’ s d a t a , the r a d i u s i n c r e a s e d 0.66 mm/yr, and 0 .4 mm/yr u sin g S tra h o w ’s d a t a . T his a v erag e s 0 .5 mm/yr d u r in g th e p a s t m. y. Egyed and S te g en a (1958) and Egyed (1961) s t a t e d the minimum r a t e of ex pan sio n i s 0 .3 mm/yr, based upon computa t i o n s from p h y s i c a l d a t a . Holmes ( i n Egyed, 1961) d e t e r mined the an nu al r a d i u s i n c r e a s e was 0 .4 mm/yr, based upon e n t i r e l y d i f f e r e n t p r i n c i p l e s . Egyed (1956b) c a l c u l a t e d t h a t s e a l e v e l was about 455 550 m h i g h e r 500 m i l l i o n y e a r s ago, u s i n g S tr a h o w ’ s d a t a , w h ereas i t was 275 m d u r i n g th e l a s t 400 m i l l i o n y e a r s u s ing T erm ie r and T e r m i e r ’ s d a t a . Egyed (19 60 ) e x p la in e d c o n t i n e n t a l d r i f t as " n o th in g more than th e f o r m a t io n of new ocean b a s i n s along th e gap ing r i f t s w hich came t o e x i s t betw een the c o n t i n e n t s . In t h a t c a s e , i t was no t n e c e s s a r y f o r th e c o n t i n e n t s to have moved w ith r e s p e c t to the m a n tle , as an e x p a n s io n of the m an tle as a whole must have ta k e n p l a c e , w i t h the s u b s t a n c e s of th e s u b c r u s t a l e a r t h - s h e l l s s u r g i n g to f i l l the n ew ly-fo rm ed f i s s u r e s . " C arey has s t a t e d the E a r t h ’s a r e a has i n c r e a s e d about 40 to 45 p e r c e n t s i n c e th e P a l e o z o i c , w i t h a d r i f t i n g a p a r t o f c o n t i n e n t s . D i c k e , in s u p p o r t of an expanding E a r t h , b e l i e v e s t h a t th e E a r t h ’ s g r a v i t a t i o n a l c o n s t a n t must have d e c r e a s e d by ab ou t 13 p e r c e n t in th e l a s t 4 .5 x 10^ y e a r s . P a le o m a g n e tic d a t a do n o t s u p p ly an in d e p e n d e n t s o l u t i o n to the problem s of c o n t i n e n t a l d r i f t ; how ever, the d a t a o f f e r a means to check and e v a l u a t e d i s p l a c e m e n t s . F u r t h e r m o r e , th e p a le o m a g n e tic d a t a ap p ea r to s u p p o r t g l o b a l e x p a n s io n b u t do n o t g iv e any c o n c l u s i v e e v id e n c e co n c e r n i n g p o l a r s h i f t (Van H i l t e n , 196 4). Van H i l t e n c a l c u l a t e d th e r a d i u s o f th e E a r t h from p a le o m a g n e tic d a t a and c o n c lu d e d t h a t E a r t h h as ex p an ded . F u r t h e r m o r e , e x p a n s io n was more in l i n e w ith C arey (1958) 456 and H e ez en ’ s (1959) e s t i m a t e than the s m a ll e r v a lu e s of Egyed (1 9 6 3 ), or th e very l a r g e v a lu e s p o s t u l a t e d by H i l - genberg (1 9 6 2 ). C a r e y ’ s e s t im a t e d g l o b a l e x p a n sio n amounted to an i n c r e a s e in s u r f a c e a r e a amounting to 40 to 45 p e r c e n t s in c e the P e rm ia n , or about 5 mm/yr d u r i n g t h i s p e r i o d . Thus, E a r t h ’s r a d i u s d u r in g the Perm ian p e r i o d was 0 .8 3 of t o d a y ’ s r a d i u s . K. M. C reer (1964a, 1964b) on th e b a s i s of p a le o m a g n e tic r e c o n s t r u c t i o n s of the c o n t i n e n t s , s u g g e s t s a s i m i l a r r a t e of e x p a n s io n . Ward (1963) examined p a le o m a g n e tic d a t a f o r th e Devo n i a n , P e rm ia n , and T r i a s s i c from Europe and S i b e r i a . These y i e l d e d e s t im a t e d r a d i i r e s p e c t i v e l y f o r th e s e p e r i o d s of 1 .1 2 , 0 .9 4 , and 0 .9 9 tim es the p r e s e n t r a d i u s . These are n o t s i g n i f i c a n t l y d i f f e r e n t from t h e p r e s e n t r a d i u s nor e v id e n c e f o r or a g a i n s t E gyed’ s p o s t u l a t e d two p e r c e n t i n c r e a s e s in c e the P a l e o z o i c . Van H i l t e n (1964) concluded t h a t th e g l o b a l e x p a n sio n d id not a f f e c t the c o n t i n e n t s , so t h a t th e s e k e p t t h e i r r e s p e c t i v e s i z e s , and the oceans in between were e n l a r g e d . T h is i s in agreem ent w ith the g e n e r a l t h e o r y of c o n t i n e n t a l d r i f t , s p r e a d in g of ocean b a s i n s , e t c . However, th e c o n t i n e n ts were n o t e n t i r e l y u n a f f e c t e d and Van H i l t e n b e l i e v e s t h a t the " o r a n g e - p e e l ” a f f e c t e d the s u r f a c e in v o lv i n g r a d i a l t e a r s in th e edge of the c o n t i n e n t s . C a p t. V. G. Sm alley , of the AFRCRL’ s P h y s i c s 457 L a b o ra to ry , r e c e n t l y e stim a te d t h a t an average of 10,000 to n s /d a y of m e t e o r i t i c m a t e r i a l f a l l s on E a r th . Fred Whip p le (1952) e s tim a te d the i n f a l l one o rd e r of magnitude s m a lle r than S m a lle y ’s. The t h ic k n e s s of m ic r o - m e t e o r i t i c m a t e r i a l t h a t would cover E a rth s in c e the beginn ing of the P a le o z o ic has been c a l c u l a t e d u sin g Smalley and W hipple’ s e s t im a t e s and p l o t t e d in g ra p h ic form (F ig u re 56). A wide band of d e n s i t y was used, bu t even i f l i g h t t u f f a c e o u s - l i k e m i c r o - m e t e o r i t i c m a t e r i a l i s in v o lv e d , the accum ulation in 550 m il l io n y e a rs would r e p r e s e n t a r a t h e r i n s i g n i f i c a n t q u a n t i t y of m a t e r i a l and of no consequence i n s o f a r as i n c r e a s in g the s i z e of E a r t h . Erimesco (1963) a lso has c r i t i c i z e d the problems of age d e te r m i n a ti o n s and how they a f f e c t the c o n c lu s io n s reached using p aleom agn etic d a t a . Runcorn (1964) p o in te d out t h a t L y t t l e t o n (1963) su g g e sted a d e c re a se in the moment of i n e r t i a of 30 p e r c e n t 9 d u rin g the p a s t 3 x 10 y r s . Runcorn had e a r l i e r sug gested a change with time of the E a r t h ’s moment of i n e r t i a , th u s , both a u th o rs b e li e v e t h a t the moment of i n e r t i a was g r e a t e r in the p a s t than a t p r e s e n t . On the o th e r hand, the e x panding E arth theory of Egyed and o t h e r s p r e d i c t e d t h a t the « moment o f i n e r t i a in c re a s e d with tim e. J . W. Wells (1963) su g g ested t h a t the d a i l y growth r in g s on the e p i t h e c a of c o r a l s can b e re c o g n iz e d , th e re b y a s c e r t a i n i n g the l e n g t h of days in th e P a le o z o ic and o th e r c £ U in < J z o H w & o o < U h o H X o t-H W X 12 104 TONS/DAY ACCRETION 10 (According to V. G. Smalley) 8 6 103 TONS /DAY ACCRETION I (According to F. Whipple) 4 2 0 600 500 200 300 400 100 ASSUMED DENSITY OF MICRO-METEORITIC MATERIAL (lb /ft3) Figure 56. T o tal accumulation of m ic ro -m e te o ritic m a te ria l of d i f f e r e n t d e n s i t i e s in 550 m illio n years on the Earth*s su rfa ce based upon i n f a l l according to two a u t h o r i t i e s . Thickness of d e p o s its on the E a r t h ’ s surface i s shown along the o rd in a te . 458 459 g e o lo g ic p e r i o d s . I t i s re p o r te d t h a t the f i n e e p i t h e c a l growth r i d g e s of Middle Devonian f o s s i l c o r a l s number about 400 p e r year i n s t e a d of about 360 as in the modern r e p r e s e n t a t i v e s of th e s e c o r a l s . They are p ro b a b ly d i u r n a l growth l i n e s . Hence, the Devonian year had about 400 day s, or the le n g th of day was about 22 of our p r e s e n t h ou rs. This agrees w e ll with i s o to p e d a te s f o r the Devonian (385 to 405 m il l io n y e a rs B. P . ) and a len g th e n in g of the day by 1 to 2 m il l is e c o n d s per c e n tu ry (Munk and MacDonald, 1960). Runcorn con clud ed , on the b a s i s of the sp a rse d a t a a v a i l a b le , t h a t th e s e d a ta are opposed to the l a r g e expansion v a lu e s p o s t u l a t e d by Carey and H eezen. However, if_ g r a v i t y v a r i e s - - a s some adv ocates b e l i e v e - - t h e n t h i s problem needs r e a p p r a i s a l . One of the p o s s i b l e mechanisms t h a t has been proposed to account f o r an expanding E a rth i s a simple r e l e a s e of the g r a v i t a t i o n a l com pression of the E a rth due to a decrease in the g r a v i t a t i o n a l c o n s t a n t . For C a re y ’ s p o s t u l a t e d ex- p a n sio n g r a v i t y would have to d e c r e a s e one p a r t in 10 / y r , and f o r Egyed’ s e s t i m a t e , one p a r t in 109/ y r (D icke, 1957; P e e b le s and D icke, 1962). The d e n s i t y of th e E a r t h ’s i n t e r i o r must d e c r e a s e , no t the d e n s i t y of the s u r f a c e . According to Dicke (196 2), e x p a n sio n may ta k e p lac e in two ways: ’’te n s io n c ra c k s may open to be f i l l e d w ith i n t r u s i o n s from th e i n t e r i o r , or e x t e n s iv e magmatic e x t r u s i o n s from v olcano es and s u rf a c e 460 f u s io n could cause the i n t e r i o r o f the Earth to leak out through the c r u s t , to form a new s u r fa c e . The leakage might be at the rate n e c e s s a r y to bring about the needed e x p a n sio n ." He e s t im a t e s th a t i f the second mechanism dom i n a t e s , the t o t a l la v a extruded must, on an average, t o t a l 9 km'Vyr. No r e l i a b l e data i s a v a i l a b l e but one e s tim a te was one km'Vyr, ° r too sm all by one order o f m agnitude. I f the t o t a l mass above the M ohorovici6 d i s c o n t i n u i t y was d e riv ed from such e x t r u s i o n s t h i s would a ffo r d an upper lim i t , or 1 .8 km'Vyr ( d e n s i t y 3 .3 g / c m V . T h is i s only one- f i f t h the amount needed. Only 0 .0 1 2 km'Vyr of magma i s needed to f i l l t e n s io n c r a c k s, assuming they are 10-km d e e p . P e e b le s and Dicke (1962) have concluded t h a t the r e le a s e of the g r a v i t a t i o n a l com pression of E a rth due to a d e c r e a s in g g r a v i t a t i o n a l com pression of the E arth would not lead to the la r g e exp ansion s re q u ire d by C ra ry , Heezen, or Egyed. The upper l i m i t i s roughly 10 tim es and 100 tim es g r e a t e r f o r Egyed and Carey, r e s p e c t i v e l y , than can be a c counted f o r . Cook and E a rd le y (1961) a lso have p o in te d out s e r i o u s d i f f i c u l t i e s in an expanding E a r th , and Kanaswich % and Savage (1963) s t a t e d r a d i o a c t i v e e v iden ce i s opposed to changes in g r a v i t y . Cox and D oell (1961) i n d i c a t e d t h a t the E a r t h ’ s r a d i u s now i s about the same as in Perm ian time but th ey re c o g n iz e c e r t a i n e r r o r s t h a t might allo w an 461 e x p a n s io n of th e o r d e r t h a t Egyed p o s t u l a t e d . They s t a t e d th e e v id e n c e d e f i n i t e l y i s opposed to the amount t h a t C arey s u g g e s t e d . S c h e id e g g e r (1961) h as p o i n t e d o u t a n o th e r m ajor p r o b lem of an expanding E a r t h . An i n c r e a s e in d i a m e t e r by a f a c t o r of two would r e s u l t in an i n c r e a s e in s u r f a c e a r e a of f o u r . An i n c r e a s e in r a d i u s a l s o p r o d u c e s a volume i n c r e a s e and a c o rr e s p o n d i n g d e n s i t y i n c r e a s e by a f a c t o r of e i g h t . S in c e the p r e s e n t a v e ra g e d e n s i t y of E a r t h i s about 5 - l / 2 , th e av erag e d e n s i t y of E a r t h b e f o r e e x p a n s io n would have been about 44. T h is i s d i f f i c u l t to e x p l a i n . Runcorn has s u g g e s te d t h a t th e l i q u i d c o re may be growing and t h a t th e m an tle p e r i o d i c a l l y r e a c h e s s i z e s a p p r o p r i a t e f o r d i f f e r e n t c i r c u l a t i n g s y s te m s . E a r l y in th e E a r t h ’ s h i s t o r y th e s t a b l e p a t t e r n f o r c o n t i n e n t a l ( l i g h t ) ro c k is b e l i e v e d to have been a l a r g e s i n g l e m ass. L a t e r t h i s s p l i t i n t o s e v e r a l land m asses as the c i r c u l a t i o n p a t t e r n demanded ( G a s k e l l , 1 9 6 2 ). C o n e lu s io n U n f o r t u n a t e l y , to o many i f s and unknowns e x i s t in the t h e o r y of an exp an d in g E a r t h , two o f the most i m p o r t a n t of w hich a r e w heth er an ex p an d in g u n i v e r s e a p p l i e s to E a r t h , and problem s r e l a t e d to th e D oppler s h i f t . I t now a p p e a rs t h a t t h e r e i s l i t t l e e v id e n c e of an exp and ing u n i v e r s e and f o r the h y p o t h e t i c a l d e c r e a s e in th e g r a v i t a t i o n a l co n stan t. 462 Tanner (1964) i n d i c a t e s t h a t the most damaging e v i dence i s g e o l o g i c f o r , a lth o u g h e x p a n s io n may " a c c o u n t f o r the q u e s t i o n a b l e g ra b e n s which a re supposed to mark m id ocean r i d g e s , i t d o e s n ’ t e x p l a i n a n y th in g e l s e v e ry w e l l . ” E rim esco (1963) has a ls o p o i n te d o ut t h a t space on ly i s e x p a n d in g , i n c r e a s i n g d i s t a n c e s betw een gro u p s o f g a l a x i e s , w h i l e i n d i v i d u a l b o d i e s , g a l a x i e s , and c l u s t e r s of g a l a x i e s a re n o t . Furtherm ore., the D o p p le r e f f e c t i s now q u e s t i o n a b l e as a r e s u l t o f E i n s t e i n ’ s work. E rim e sc o h as t h e r e f o r e c o n clu d ed t h a t : A p a rt from th e f a c t t h a t t h e r e i s no e v id e n c e a t a l l f o r an e x p a n s io n of the u n i v e r s e , and c o n s e q u e n t l y a l s o n o t f o r th e h y p o t h e t i c a l d e c r e a s e of the g r a v i t a t i o n a l c o n s t a n t , t h e r e i s a n o th e r argum ent m i t i g a t i n g a g a i n s t th e n o t i o n of an ex p an d in g E a r t h . He s t a t e d t h a t an e x p a n s io n of the E a r t h , due to a d e c r e a s e in the g r a v i t a t i o n a l c o n s t a n t , c o u ld n o t be s e l e c t i v e ; e x p a n s io n would have to be u n if o r m . In o t h e r w o rd s, th e o cean f l o o r co u ld n o t expand a t a f a s t e r r a t e t h a n the r e s t of th e o r o g e n i c s h e l l f o r t h i s would imply t h a t t h e s p r e a d in g e f f e c t p re c e d e d the c a u s e . In c o n c l u s i o n , t h e r e a p p e a rs to be more arg um en ts a g a i n s t an exp an d in g E a r t h than f o r i t . F u r t h e r m o r e , u n l e s s i t can be shown t h a t e x p a n s io n was e q u a l to or g r e a t e r t h a n Carey and Heezen p o s t u l a t e d , i t c a n n o t a cc o u n t f o r the m ajor s u b s id e n c e of ocean b a s i n s and s e a s . 4 6 3 The E a r t h ’ s Geoid D e v i a t i o n s of th e t h e o r e t i c a l g e o id as now w id e ly u s e d , based upon g e n e r a l l y a c c e p te d i n t e r p r e t a t i o n s of i s o - s t a s y , a re o f the o r d e r of tlOO m. The symmetry of th e t h e o r e t i c a l geoid has been d i s r u p t e d . In 1958, the VAN GUARD s a t e l l i t e was l a u n c h e d . I t s o r b i t was c o n t r o l l e d by the g r a v i t a t i o n a l f i e l d of E a r t h and r e v e a l e d th e r e a l shape of th e g e o id . The E a r t h i s p e a r - s h a p e d w ith the s o u t h e r n h e m isp h e re l a r g e r th a n th e n o r t h e r n , and a d i s t i n c t b u lg e o c c u r s in th e m iddle s o u th e r n l a t i t u d e . The b u lg e i s n o t s y m m e tr ic a l about th e a x i s of r o t a t i o n ; i t g iv e s a t r i a x i a l E a r t h . TRANSIT 2A S a t e l l i t e d a t a le d I . J . I z s a k to c o n clu d e t h a t a d i f f e r e n c e of 408 m e x i s t s betw een the two axes o f th e e q u a t o r . VANGUARD a l s o showed t h a t the N orth P o le of r o t a t i o n of E a r t h l i e s a b ou t 1 .5 km above ( o u t s i d e ) and the South P o le a b o u t 1 .5 km below ( i n s i d e ) the s u r f a c e of the t h e o r e t i c a l e l l i p s o i d of g e o d esy . The E a r t h ’ s e q u a t o r i a l b u lg e i s too l a r g e to be in e q u i l i b r i u m w ith the p l a n e t ’s p r e s e n t r a t e o f r o t a t i o n . E a r t h has been slo w in g down, and th e b u lg e c o r r e s p o n d s to the r a t e o f r o t a t i o n about te n m i l l i o n y e a r s ago ( S t u b b s , 1 9 6 4 ). Gordon J . F. MacDonald (1963) c o n c lu d e d t h a t " t h e m an tle must be s t r o n g to be a b le to do t h i s ; so s t r o n g , in f a c t , t h a t c o n v e c ti o n c u r r e n t s would n ev er be a b le to o c cu r i n th e m a n t l e . " R uncorn, on the o t h e r h a n d , exam ined the E a r t h ’ s shape and c o n clu d ed t h a t " h ig h " and "low" a r e a s 464 occur as i n d i c a t e d by the new geoid sh ap e. The h ig h s are a t t r i b u t e d to s u b - c r u s t a l c o n v e c tio n c u r r e n t s . From th e s e d a t a , as w e ll as o th e r i n f o r m a tio n i n v o l v ing geom orphology, p a le o n t o l o g y , p a l e o c l i m a t o l o g y , e t c . , i t i s concluded t h a t E a r th has undergone c o n s i d e r a b l e r e s h a p ing s in c e th e P re ca m b ria n E ra. Erim esco (1961) c o n clu d ed , a f t e r exam ining M. Schw arzbach’ s (1958, r e v i s e d 1963) p a l e - o c l i m a t i c map of th e Devonian p e r i o d , t h a t between e a r l y Precam brian and l a t e M esozoic, the e q u a t o r i a l b ulg e must have s h i f t e d about 30° r e l a t i v e to the E a r t h ’s s u r f a c e . From such i n f o r m a tio n as t h i s i t becomes e v id e n t t h a t the r e s h a p in g of th e geoid through g e o lo g ic tim e as r e s u l t e d in r a t h e r l a r g e doming up and downwarping of ocean b a s i n s and on t e r r e s t r i a l E a r t h . The permanancy of ocean b a s i n s and land may or may n o t be in v o lv e d . Through the use of r a d i o time s i g n a l s around the w o rld , a stu d y of 20 o b s e r v a t o r i e s allow s com parisons of p o s i t i o n s over a 2 0 -y ea r p e r i o d . Stoyko (1942) has co n cluded t h a t two h y p o t h e s is e x p l a i n the o b se rv ed d i s c r e p a n c i e s in o b s e r v a t i o n s : (1) p u l s a t i o n s of the E a r t h ( c o n s i d e r e d an e l a s t i c body), and (2) c o n t r a c t i o n s and d i l a t i o n s of th e E a r t h ’ s s u p e r f i c i a l l a y e r s ( c o n t i n e n t a l d r i f t ) . Stoyko does n o t c o n s id e r the d r i f t th e o r y c ap a b le o f e x p l a i n i n g the observed c o n d i t i o n s whereas the f i r s t hy p o t h e s i s does e x p l a i n v a r i a t i o n s o f 2.6 m or 2.1 m, r e s p e c t i v e l y , of the r a d i u s of the E a rth f o r l a t i t u d e 45° seem 465 to co rresp o n d to the observed v a r i a t i o n s of l o n g i t u d e . Grabau (1934) was one of the p r o p o n e n ts of sea l e v e l p u l s a t io n s w h ile Bucher (1933) b e lie v e d in c r u s t a l p u l s a t i o n s . The o b s e r v a t i o n s of marked movements in w ater l e v e l s in w e lls g r e a t d i s t a n c e s from e a rth q u a k e e p i c e n t e r s g iv e s su p p o r t to the c o n c lu s io n t h a t E arth i s an e l a s t i c body. Enormous l o c a l changes in e l e v a t i o n are n o ted in many p a r t s of the w o rld , p a r t i c u l a r l y i s l a n d s , but most r e s t on e x t r u s i v e rock which p e rh a p s g iv e s a ready e x p l a n a t i o n f o r la r g e changes in e l e v a t i o n . Whether c o n t i n e n t a l masses b e come ocean b a s i n s s t r i t o sensu i s unproved. Much confusion, f o r example, e x i s t s on p r e c i s e l y what c o n s t i t u t e s an "ocean b a s i n . " On the b a s i s of the p r e s e n t p a p e r , i t would seem t h a t c o n s i d e r a b le ev id e n ce e x i s t s showing l a r g e form er land a r e a s are now below sea l e v e l as a r e s u l t of s u b s id e n c e or downwarping. Such a r e a s show t y p i c a l " c o n t i n e n t a l " type rock (based upon se ism ic d a t a ) . No " t y p i c a l o c e a n ic " r e gion i s known to have been u p l i f t e d - -o n ly l o c a l a r e a s or is l a n d s . Erim esco (1963) c o n clud ed: To see in the mid-ocean r i d g e s the r e s u l t s of a g e n e r a l e x p an sio n of the E a rth . . . i s not j u s t i f i e d . As a m a tte r of f a c t , c o n s i d e r i n g the mean l e v e l of th e E a r t h ' s s u r f a c e , i t can be concluded t h a t a l l d e p r e s s io n s more than 4,000 m below th e p r e s e n t se a l e v e l are s u b s id e n c e s . Erim esco (1963) has examined the lo n g - te r m g e o d e tic a f f e c t s c o n c e rn in g the E a r t h ' s shape and c o n clu d ed : 466 1. The shape of the E a rth i s n ot one of e q u i l i brium , and the d i s t r i b u t i o n of ocean b a s i n s and c o n t i n e n t s on i t s s u r f a c e i s in c o m p a tib le w ith any normal and u n d i s t r i b u t e d p l a n e t a r y e v o lu t i o n p r o c e s s . 2. The bulge in the s o u th e r n hem isphere [which i s m o stly an ocean] and updoming in the n o r t h e r n high l a t i t u d e s [where t h e r e i s e v id e n c e of f r a g m e n ta tio n of land] i n d i c a t e s an exp ansio n p r o c e s s in v o lv in g a l a r g e p a r t of th e se a f l o o r . On the o th e r hand, in the so u th e rn hem isphere high l a t i t u d e s , the e v id e n c e s u g g e s t s sub sid ence r e l a t i v e to th e t h e o r e t i c a l e l l i p s o i d of r o t a t i o n . 3. The shape of the geoid i s in c o m p a tib le w ith r e s p e c t to s p h e r i c a l symmetry, h y d r o s t a t i c e q u i l i b r i u m in the E a r t h ’ s i n t e r i o r , and c l a s s i c a l i s o s t a s y [ s i n k - a n d - f 1oat p r o c e s s on the s u r f a c e of the m a n t l e ] . 4. No v a li d re a so n s e x i s t why f u t u r e d e fo r m a tio n s w i l l not occur in th e g e o id , hence, mass d i s p lacem ents in th e m a n tle . 5. In ord er to produce d e fo rm a tio n s of th e g e o id , g r e a t mass d is p la c e m e n ts a s s y m e tr i c r e l a t i v e to the a x is of r o t a t i o n in the E a r t h ’s m antle must be assumed. The g e n e ra l c o n c lu s io n was reached t h a t th e changing shape o f the geoid i s of fu nd am en tal im portance in th e morphology of both m arine and t e r r e s t r i a l f e a t u r e s . C o n t i n e n t a l Growth Many a u th o rs have concluded t h a t the c o n t i n e n t s are growing a t the expense of the o c ea n s. P ure re a s o n in g su g g e s t s t h a t th e lan d s have undergone e r o s i o n s in c e the con t i n e n t s were formed s e v e r a l b i l l i o n y e a r s ago. P r i o r to t h i s no c o n t i n e n t a l c r u s t or c o n t i n e n t a l m asses e x i s t e d . 467 Gussow (1 96 3) e s t i m a t e d the a v e ra g e w a te r d e p th was about 2,00 0 f e e t d u r in g t h i s e a r l y p e r i o d in th e E a r t h ’ s h i s t o r y (b u t no e v id e n c e i s p r e s e n t e d f o r r e a c h i n g t h i s c o n c lu s io n ) . V o lcan ism , s i l i c e o u s d e p o s i t s , and l i m e s t o n e s e v e n t u a l l y formed a g r a n i t i c - t y p e c r u s t . Being l i g h t e r , g r a n i t i c - t y p e c r u s t ( s i a l ) would n o t cause i s o s t a t i c s i n k i n g of i t s own a c c o r d . C l a s t i c s and c a r b o n a t e s a c c u m u late in a s u b s i d i n g r e g i o n , and where s u b s id e n c e d oes n o t o c c u r , a c c u m u la tio n r e a c h e s se a l e v e l and s e d im e n ts e x te n d se a w a rd . In t h i s manner, the c o n t i n e n t s can grow o u tw a rd . T hus, a t some p e r i o d in P re c a m b ria n tim e , a c o n t i n e n t a l - t y p e c r u s t form ed. How l a r g e t h i s c o n t i n e n t or c o n t i n e n t s m ight have b e e n , and p r e c i s e l y how d i f f e r e n t i a t i o n o c c u r r e d , we can o n ly s p e c u l a t e . F o llo w in g th e c o n t i n e n t a l - ty p e c r u s t f o r m a t i o n , t h e r e i s e v id e n c e of w id e s p r e a d o c c u r r e n c e of l a r g e l y s h a l l o w - w a t e r m arine d e p o s i t s . T hus, w h ile th e c o n t i n e n t s o f t e n were in u n d a te d by th e o c e a n , th e y r e t a i n e d t h e i r s i a l i c c h a r a c t e r and buoyancy ( F i g u r e 4 8 ) . A t y p e - s e c t i o n f o r t h i s s o r t o f outward growth of th e c o n t i n e n t s i s a r a r i t y in c o n te m p o ra ry oceans and s e a s . I s l a n d a r c s do n o t a p p e a r to be a r e a s of c o n t i n e n t a l grow th. C l a s s i c a l d e s c r i p t i o n s of th e c o n t i n e n t a l m argin of a w a v e - b u i l t t e r r a c e are shown to be no l o n g e r t e n a b l e . Hence, c o n t i n e n t a l growth by t h i s method can no lo n g e r be a c c e p te d as th e p r i n c i p a l o r i g i n of th e c o n t i n e n t a l t e r r a c e . F i l l i n g of b a s i n s w i t h s e d i m e n ts , such as the B erin g 468 S ea, a p p e a r s to be a l o c a l example of c o n t i n e n t a l grow th. The c l o s e s t exam ples e x i s t i n g to day of " c o n t i n e n t a l grow th" a re the Bahama P l a t f o r m , B lake P l a t e a u , and the G r e a t B a r r i e r R e e f. In each c a s e , h u n d red s to th o u s a n d s of m e te r s of c a r b o n a t e ( r e e f ) d e p o s i t s have a cc u m u la te d on a s u b s id i n g c o n t i n e n t a l - t y p e b l o c k . T his can h a r d l y be c a l l e d c o n t i n e n t a l g ro w th . C e r t a i n l y a fo rm e r c o n t i n e n t a l b lo c k or e p i c o n t i n e n t a l s e a t h a t has r e c e n t l y s u b s id e d (su c h as th e Sea of J a p a n ) c a n n o t be c o n s i d e r e d c o n t i n e n t a l g r o w t h . The l o c a l e x t r u s i o n of b a s a l t i c l a v a fo rm in g i s l a n d s , such as the Haw aiian g ro u p , c o u n t l e s s a t o l l s , and " o c e a n i c - ty p e " i s l a n d s c an n o t be c o n s i d e r e d c o n t i n e n t a l grow th f o r t h e y are n ot c o n t i n e n t a l ( s i a l i c ) s t r u c t u r e s . Many a u t h o r s have arg u e d t h a t a c o n t i n e n t a l - t y p e c r u s t n e v e r f o u n d e r s ( i s e n g u l f e d ) , s i n k s i n t o th e deep s e a , or i s c o n v e r te d i n t o an o c e a n i c - t y p e c r u s t (Gussow, 1963, and o t h e r s ) . Such a c o n c l u s i o n i s b ased upon th e b a s i c t e n e t s of i s o s t a c y . However, g e o l o g i c a l mapping and r e c e n t geo p h y s i c a l work in many a r e a s have s u g g e s te d t h a t f o r m e r t y p i c a l c o n t i n e n t a l - t y p e c r u s t r e g i o n s n o t o n ly have been d e e p l y submerged below se a l e v e l , b u t in some c a s e s have ev en been c o n v e r te d i n t o o c e a n i c - t y p e c r u s t and a l l e v i dence of form er lan d c o m p l e t e l y o b l i t e r a t e d . T h is would im p ly , f i r s t , t h a t c o n t i n e n t s a re becoming s m a l l e r , n o t l a r g e r , and s e c o n d , a mechanism e x i s t s f o r t r a n s f o r m a t i o n 469 of s i a l i n t o sim a. One o f th e most p l a u s i b l e e x p l a n a t i o n s has been p r e s e n t e d by Hess ( 1 9 5 5 ) . T h is t r a n s f o r m a t i o n p e r h a p s a l s o e x p l a i n s the t h i n l a y e r o f anomalous s e d im e n ts i n the deep s e a . B efore deep s e a s e i s m ic i n v e s t i g a t i o n s were u n d e r t a k e n i t was b e l i e v e d by Kuenen, T w en h o fe l, and o t h e r s t h a t th e t o t a l t h i c k n e s s of deep s e a se d im e n t was o f the o r d e r of 2 km t o 3 km. S e ism ic work, how ever, showed t h a t s e d im e n ts were o f t e n l e s s th a n l / 2 km. The r e a s o n f o r t h i s sm a ll t h i c k n e s s r e p r e s e n t s a l o n g s t a n d i n g m y s te ry and i s d i f f i c u l t to e x p l a i n in view o f a c c e p te d r a t e s of s e d i m e n t a t i o n . I n d e e d , i f t u r b i d i t y c u r r e n t s a r e as w id e s p r e a d and common as a re now g e n e r a l l y b e l i e v e d , the p ro b lem becomes even more p e r p l e x i n g . Kuenen (195 0, p . 386) e s t i m a t e d deep s e a s e d im e n ts were ab o ut 3-km t h i c k , or a b o u t tw ice th e ob se r v e d amount ( F ig u r e 4 8 ) . E i t h e r th e r a t e o f s e d i m e n t a t i o n i s g r o s s l y in e r r o r ; the o c ea n s a re much younger th a n b e l i e v e d ; or th e s e d im e n ts have undergone a change in L ayer 2 or r e m e lt e d from below . The t h i n l a y e r of sed im en t in th e deep s e a can p e r h a p s be e x p l a i n e d by m etam orphism . For exam ple, L ayer 2 i s known t o c o n s i s t of v o l c a n i c r o c k s in some a r e a s b u t e l s e where e v id e n c e does not s u p p o r t a c o n c l u s i o n t h a t t h e l a y e r i s m etam orphised se d im e n t b e c a u se i t s s u r f a c e i s much too r o u g h . Ewing and o t h e r s , t h e r e f o r e , have c o n c lu d e d t h a t L ayer 2 i s of ig n e o u s o r i g i n , and s i n c e o v e r l y i n g s e d im e n ts 470 a re n o t d eform ed, the la y e r p r e d a t e s s e d i m e n t a t i o n . H am il ton ( 1 9 5 9 ) , on th e o t h e r hand, b e l i e v e s p a r t of L ayer 2 c o n s i s t s of cemented lim e s to n e and p r o b a b ly was formed as a r e s u l t of d i a g e n e s i s . Mason (1958) showed t h a t the m agn etic a n o m a lie s in Layer 2 o f f the w est c o a s t of the U. S. can o n ly be e x p l a i n e d by the p r e s e n c e of h i g h l y m agnetic r o c k s which b e l i e s s e d im e n ta ry f o r m a t io n s . Hence, he has concluded (Mason, 1962) t h a t l a r g e ano m alies in Layer 2 are due to b a s a l t i c la v a f l o w s . Wide s c a t t e r of s e is m ic v e l o c i t i e s l e a d s him to b e l i e v e t h a t both e x p l a n a t i o n s a re in p a r t c o r r e c t , v i z . the la y e r c o m p rise s v a ry in g q u a n t i t i e s of e x t r u s i v e v o l c a n i c s , u n c o n s o l id a te d s e d im e n ts , and sometimes m etam orphised s e d im e n ts . Economic C o n s i d e r a t i o n s I f major p a r t s of the s e a f l o o r o n ly r e c e n t l y su b sid e d th e n many o f the e p i c o n t i n e n t a l s e a s , l a r g e se a s of geosyn c l i n a l h i s t o r y (su ch as the Sea of J a p a n ) , b o r d e r l a n d s , and s u b m a r in e - f o ld e d m ountain ran g e s ( i n c l u d i n g , p e r h a p s , the Lomonosov Range) r e p r e s e n t p o t e n t i a l m in e r a l p r o v i n c e s com p a r a b l e to th o s e on l a n d . O il and g a s , of c o u r s e , a re p ro b a b ly the two most im p o rta n t r e s o u r c e s . The age of the r o c k s , as w e ll as t h e i r r e l a t i v e l y r e c e n t s u b s id e n c e and p o s s i b l e f o l d i n g , a re f a c t o r s t h a t g r e a t l y i n c r e a s e the p o s s i b i l i t y of f i n d i n g p e tr o le u m . 471 I t is assu red t h a t a l l such p o t e n t i a l s i t e s are u n d e r l a i n by c o n t i n e n t a l - t y p e c r u s t e x c lu d in g , t h e r e f o r e , v i r t u a l l y a l l of the P a c i f i c Ocean seaward of the a n d e s i t e (o r M a rsh a ll) l i n e . But even ex clu d in g t h i s v a s t a r e a , te n s of m i l l i o n s of square k i lo m e te r s of p o t e n t i a l l y p e t r o l i f e r o u s a re a s may la y submerged in deep w a te r. Seism ic p r o f i l i n g w i l l become im p o rta n t in i d e n t i f y i n g p o s s i b l e o i l s t r u c t u r e s . O ther F a c to r s A number of o th e r a re a s which a f f e c t or touch upon the g e n e ra l t o p ic of c o n t i n e n t a l s lo p e s and ocean b a s in s have not been d is c u s s e d b u t, n e v e r t h e l e s s , are of major impor ta n c e . The o r i g i n of g l a c i a l p e r i o d s , the more or l e s s sudden d isa p p e a ra n c e of d i n o s a u r s , the age of a b y s s a l fa u n a , moun t a i n b u i l d i n g , and submarine canyons are exam ples. The su b sid e n c e of ocean b a s i n s may be connected w ith each of t h e s e . F lo r a and fauna p ro b ab ly a re i n t i m a t e l y a f f e c t e d b u t cannot y e t be a s s e s s e d . What e f f e c t do th e s e c o n c lu s io n s have upon w idespread e x p la n a t i o n s of t u r b i d i t y c u r r e n t s , of deep sea r i p p l e marks, d e e p -se a c o n g lo m era tes, and s i m i l a r f e a t u r e s ? These may be more y o u th f u l than g e n e r a l su b s id e n c e , hence, have l i t t l e or no b e a r in g on g e n e r a l su b s id e n c e . Submarine canyons, f o r example, may be i n t i m a t e l y 472 i n v o lv e d or o r i g i n a t e d u r i n g th e p e r i o d o f s u b s id e n c e th ro u g h th e f a u l t i n g and f l e x u r e of th e c o n t i n e n t a l m a rg in . For exam ple, some canyons may be th e d i r e c t r e s u l t of f a u l t i n g . In th e M e d i te r r a n e a n Sea where canyons o c c u r w i t h o u t landw ard h eads a t s i t e s of form er s t r e a m s , the c a n yons may sim p ly r e p r e s e n t the s c a r s a lo ng a f a u l t s c a r p formed d u r i n g s u b s id e n c e of th e M e d i te r r a n e a n Sea. C e r t a i n l y t u r b i d i t y c u r r e n t s or any o t h e r s u g g e s te d t h e o r y f a c e s g r e a t d i f f i c u l t y in e x p l a i n i n g su bm arine canyons whose w a l l s are composed of g r a n i t e and f o r which t h e r e i s no p o s s i b l e so u rc e for t u r b i d i t y c u r r e n t s , or even s e d i m ents f o r e r o s i o n by " sa n d g l a c i e r s . " A no ther p o s s i b l e e x p l a n a t i o n f o r some canyons m ight be th e t h e o r y p r e s e n t e d by du T o i t , B o u r c a r t , and o t h e r s . B a s i c a l l y , t h i s in v o lv e d c u t t i n g of can yo ns as the c o n t i n e n t a l m arg in was s u b j e c t e d t o s u b s id e n c e or f l e x u r e . Can yon c u t t i n g m ight o c c u r by headward e r o s i o n as s u b s i d e n c e , f l e x u r i n g , or f a u l t i n g o c c u r r e d . GENERAL CONCLUSIONS C o n t in e n t a l s lo p e s have few c h a r a c t e r i s t i c s which might be c o n sid ere d u n i v e r s a l or ’’t y p i c a l . " They show g r a d a ti o n s between v a rio u s c h a r a c t e r i s t i c s - - s h a p e s , g r a d i e n t s , p resen c e or absence of submarine canyons, c o m p o sitio n , e t c . While w e ll-d e v e lo p e d c o n t i n e n t a l r i s e s e x i s t in the A t l a n t i c Ocean, th ese f e a t u r e s are by no means t y p i c a l c o n t i n e n t a l slope f e a t u r e s . More commonly, the lower p a r t of the c o n t i n e n t a l slope g rad e s g r a d u a l ly i n t o the a b y s s a l sea f l o o r w ith a small f a n , or apron, a t i t s b a se. Less common are convex-shaped c o n t i n e n t a l s lo p e s having g e n tle upper and s t e e p e r lower s l o p e s . This c h a r a c t e r i s t i c i s f r e q u e n t ly observed on tr e n c h s l o p e s . Many c o n t i n e n t a l s lo p e s t e r minate a b r u p t l y on the a b y s s a l sea f l o o r or in b a s i n s w i t h out a c o n t i n e n t a l r i s e or apron. T h is s u g g e s ts t h a t n e i ther s e d im e n ta tio n nor t u r b i d i t y c u r r e n t s have been a c t i v e . I t a ls o may mean t h a t the re g io n only r e c e n t l y s u f f e r e d t e c t o n i c a c t i v i t y . A few c o n t i n e n t a l s lo p e s te r m in a te in b o r d e r l a n d - l i k e p l a t e a u s having i r r e g u l a r s u r f a c e s , a k i l o meter or more above the a b y ssa l sea f l o o r . The p l a t e a u s may be tens or hundreds of k ilo m e te r s wide. These p l a t e a u s are t e n t a t i v e l y c o n sid ere d foundered c o n t i n e n t a l blocks.* A 473 474 few c o n t i n e n t a l s l o p e s grade from th e c o a s t to the deep se a w i t h l i t t l e or no i n d i c a t i o n of a d i s t i n c t s h e l f b r e a k . Such s l o p e s commonly have e x c e p t i o n a l l y low g r a d i e n t s . The seaward fa c e of c a r b o n a t e - b u i l t p l a t f o r m s (su ch as the Blake P l a t e a u or th e G re a t B a r r i e r R eef) g e n e r a l l y have very s t e e p g r a d i e n t s and e i t h e r c a r b o n a te or bed rock f r e q u e n tl y i s exposed on i t s f a c e . C o n t i n e n t a l s l o p e s show a com plete g r a d a t i o n betw een a b s o l u t e l y smooth s lo p e s d evo id of any r e l i e f to extrem e i r r e g u l a r i t y both along the s t r i k e and d o w n -slo p e . G e n e r a l l y s p e a k in g , c o n t i n e n t a l s l o p e s of t r e n c h e s are most i r r e g u l a r . No r e l a t i o n s h i p between t y p e s of s l o p e s and the p r e s e n c e or absence of subm arine canyons have been n o te d . T his i s not s u r p r i s i n g c o n s i d e r i n g the sm all number of p r o f i l e s , the t o t a l le n g t h of c o n t i n e n t a l s l o p e s in th e w o rld , and t h e d e a r t h of d a t a on bo tto m sa m p le s. One i n t e r e s t i n g o b s e r v a t i o n was the canyons s u r r o u n d in g J a p a n . Along the P a c i f i c C oast of Japan subm arine canyons commonly t e r m i n a t e on a w e l l- d e v e l o p e d t e r r a c e a t 800 m to 1,000 m. On the Japan Sea s id e o f the J a p a n e s e I s l a n d s , subm arine canyons t e r m i n a t e on a wide t e r r a c e a t 800 m to 1,500 m. T h is t e r ra c e i s c o n s i d e r a b l y s h a l lo w e r th a n the f l o o r of th e Sea of Ja p a n which l i e s a t d e p th s of 3,200 m to 3,500 m. The b r e a k between the c o n t i n e n t a l s h e l f and th e c o n t i n e n t a l s lo p e i s g e n e r a l l y h i g h l y s in u o u s i n d i c a t i n g t h a t some agency ( s e d i m e n t a t i o n , e r o s i o n , or w a rp in g ) has 475 f r e q u e n t l y a l t e r e d the c o n t i n e n t a l s h e l f s in c e i t s form a t i o n d u rin g th e Q u a te rn a ry epoch. In some r e g io n s the s h e l f break may v a ry te n s of m eters in d e p th in a r e l a t i v e ly s h o r t h o r i z o n t a l d i s t a n c e . Deep s h e l f b re a k s are n ot c o r r e l a t e d w ith g l a c i a t e d a re a s or w ith l a t i t u d e . Some deep s h e l v e s occur in non g l a c i a t e d r e g i o n s , such as so u th w e st A f r i c a and n o rth w e s t A u s t r a l i a . Both of th e s e r e g io n s are g e n e r a l l y c o n s id e re d to be h i g h ly s t a b l e P recam brian s h i e l d r e g i o n s . The A n t a r c t i c and A u s t r a l i a n s h e l f b re a k s are not as deep as p r e v i o u s l y r e p o r t e d . They are about 450 m and 300 m to 400 m, r e s p e c t i v e l y . Some h ig h l a t i t u d e s h e lv e s which have s u f f e r e d r e c e n t g l a c i a t i o n show one or more " m o a ts," or deep l o n g i t u d i n a l d e p r e s s io n s p a r a l l e l t o the c o a s t . These d e p r e s s i o n s are a t t r i b u t e d to f a u l t i n g as a r e s u l t of g l a c i a l l o a d in g . C o n t in e n t a l s h e lv e s which a re t i l t e d tow ards shore a re an o th e r f e a t u r e in th e s e r e g i o n s , s u g g e s tin g a r e l a t i v e s u b s id e n c e of the land a r e a . The l e s s loaded o f f s h o r e a re a was l e s s a f f e c t e d and rem ained h ig h . S h e lf -e d g e p ro m o n to rie s o f te n are the r e s u l t of b i o l o g i c a l grow th. These u s u a l l y appear as mounds or h ig h ly i r r e g u l a r masses near th e s h e l f edge. In some i n s t a n c e s the bottom p r o f i l e of the c o n t i n e n t a l t e r r a c e has been s i g n i f i c a n t l y a l t e r e d by th e s e g ro w th s. A s e r i e s of a t o l l s and r e e f s has long been known to 4 7 6 e x i s t (b u t l i t t l e s t u d i e d ) along the n o rth w e st c o a s t of A u s t r a l i a . I t was g e n e r a l l y b e lie v e d t h a t th e s e were n o r mal a t o l l s or perhaps a d is c o n tin u o u s b a r r i e r r e e f ; how e v e r, w id ely spaced echosounding p r o f i l e s i n d i c a t e t h a t these r e e f s are n e a r l y c o n tin u o u s and t h a t o c c a s i o n a l l y the s h e l f edge r e e f s r i s e as c o r a l i s l a n d s or a t o l l s . These r e e f s r i s e from near the edge of a deep s h e l f (300 m to 500 m ), and are re m in is c e n t in many r e s p e c t s w ith the s h e l f edge a t o l l s and r e e f s o c c u rrin g in the Red Sea where a t o l l s and r e e f s r i s e p r e c i p i t o u s l y along the edges of w ide, deep (ab o u t 550 m) fa u lt- f o rm e d p a ir e d p la tf o r m s in the Red Sea g r a b e n . T e r r a c e s , benches, and p l a t e a u s (and o th e r f e a t u r e s with s i m i l a r names and c o n n o ta tio n s ) are w idespread at a l l d e p th s , in a l l oceans and la rg e s e a s , on c o n t i n e n t a l and i n s u l a r s lo p e s , on th e s id e s of g u y o ts, seam ounts, mid ocean r i d g e s , and o th e r e le v a t e d p a r t s of the sea f l o o r . Some tre n c h e s have t e r r a c e s as wide as 700 km, and b e tween the P h i l i p p i n e Trench and the A le u tia n Trench a n e a r ly co n tin u o u s t e r r a c e occurs a t d epth s ran g in g from 1 km to 5 km. In the P h i l i p p i n e Trench a re a t h i s t e r r a c e has a minimum width of 37 km, 20 km to 100 km on the Japan Trench s l o p e , a t l e a s t 93 km on the K urile-K am chatka T rench, and 40 km on th e slo p e s of the A le u tia n T rench. Hence, th ese are major to p o g ra p h ic f e a t u r e s f o r th ey no t on ly a t t a i n g r e a t h o r i z o n t a l d i s t a n c e but a ls o have c o n s i d e r a b le w idth 477 as w e l l . I t i s p o s s i b l e t h a t t h i s same f e a t u r e may a l s o be t r a c e d along the A la sk a n -C a n a d ia n c o a s t . I f so, i t p r o b a b l y l i e s a t a s h a llo w e r d e p th , or a t a b ou t 1,000 m; th e same i s t r u e fo r the W ashington and Oregon c o a s t s . I f i t c o n t i n u e s o f f C a l i f o r n i a i t l i e s at an av erag e d ep th of 500 m, b u t r e a c h e s over 1,000 m or more o f f the s o u t h e r n C a l i f o r n i a B o r d e rla n d . Off C e n t r a l Am erica, a n o t a b l e f e a t u r e o c c u rs a t a d ep th o f a bo ut 3,600 m, and along th e South Amer ic a n c o a s t t e r r a c e s occur a t 1,500 m to 2,500 m. In A n t a r c t i c a , and the A r c t i c O cean, th e c o n t i n e n t a l s lo p e s have a c o r r e l a t i v e f e a t u r e of between 1,000 m to 2,000 m. In the A r c t i c Ocean the t e r r a c e i s v e ry w ide. A c u r s o r y e x a m in a tio n of o t h e r oceans shows no s i m i l a r c o r r e l a t i v e f e a t u r e w ith such p e r s i s t a n c e ; however, d e t a i l e d s t u d i e s may r e v e a l the p r e s e n c e of o t h e r t e r r a c e s . The o r i g i n of the major to p o g r a p h ic f e a t u r e s t r e t c h i n g a c r o s s th e n o r th P a c i f i c is unknown b u t i t i s s u g g e s te d t h a t i t r e p r e s e n t s a m ajor t h r u s t zone ly in g above th e a p p a r e n t l y much d e e p e r d i p - s l i p , h i g h ly s e is m ic f a u l t zone which i s a s s o c i a t e d w ith d e e p - f o c u s e a r t h q u a k e s l y i n g a t the bottom of the t r e n c h . Bottom sam ples c o l l e c t e d from th e wide t e r r a c e on the Ja p an Trench s lo p e are c o n s id e r e d to be t y p i c a l f l u v i a l d e p o s i t s . Ja p a n e s e g e o l o g i s t s have co n clu d ed t h a t t h i s wide t e r r a c e a t d e p th s of 1 km to 3 km i s a w a v e-c u t t e r r a c e 478 t h a t has been submerged as a r e s u l t of c r u s t a l down- w a rp in g . T e r ra c e c u t t i n g i s presumed to have o c c u rre d in post-M iocene tim e . O th e r g e o l o g i s t s d a te c u t t i n g of v a r i ous deep t e r r a c e s as p o s t - E a r l y P lio c e n e * to E a r l y P l i e s t o - cene . The o r i g i n of t e r r a c e s t r a c e d e ls e w h e re over g r e a t d i s t a n c e s l i k e w i s e i s n o t known. P r o b a b ly t h e s e f e a t u r e s do not have a s i n g l e o r i g i n . Some a re s u b a e r i a l l y c u t as i n d i c a t e d by the p re s e n c e of sh a llo w w a te r f o s s i l s , p ho lad b o r i n g s , and s i m i l a r l i t t o r a l c h a r a c t e r i s t i c s . O th e rs are the r e s u l t of t e c to n i s m , s e d i m e n t a t i o n , or v a s t la v a f lo w s , and p o s s i b l y formed by o t h e r c au se s n o t f a m i l i a r to u s . The maximum d e p th to which sea l e v e l h a s been lowered ( o t h e r than g l a c i a l l y - c o n t r o l l e d e u s t a t i c se a l e v e l changes) has never been s e r i o u s l y c o n s id e r e d b ecause i t has been a s sumed th a t no o th e r form of e u s ta s iu m e x i s t s . N e v e r t h e l e s s , c o n s i d e r a b l e e v id e n c e p o i n t s to th e c o n c l u s i o n t h a t many f e a t u r e s were s u b a e r i a l l y eroded a t d e p th s f a r below P l e i s t o c e n e , g l a c i a l l y - c o n t r o l l e d e u s t a t i c c h a n g e s. No sim ple method i s known to a s c e r t a i n e u s t a t i c changes below se a l e v e l b e ca u se d i f f e r e n t i a l su b s id e n c e h a s been w i d e sp re a d in ocean b a s i n s and s e a s . R e l a t i v e l y sh a llo w t e r r a c e s ( l e s s th an 1 km to 2 km) are common in a l l oceans and some t e r r a c e s a p p a r e n t l y can be t r a c e d more or l e s s c o n ti n u o u s l y f o r th o u sa n d s of k i l o m e te r s . Most t e r r a c e s show s i g n s of h aving been w arped. 479 O ften warping c l o s e l y fo llo w s the s i n u o s i t i e s o f the s h e l f edge. T h is s u g g e s ts the fo llo w in g r e l a t i o n s h i p s : (1) the s h e l f b reak and t e r r a c e warps are g e n e t i c a l l y r e l a t e d and t h a t w arping o c curred a f t e r t h e i r f o r m a tio n ; (2) s h e l f edge i r r e g u l a r i t i e s are n ot sim ply a m a tte r of e r o s i o n a l / d e p o s i - t i o n a l p r o c e s s e s of r e l a t i v e l y r e c e n t o r i g i n ; (3) de ep e r t e r r a c e s were formed d u r in g a r e l a t i v e l y s h o r t p e rio d of time s h o r t l y a f t e r , or p o s s i b l y b e f o r e , th e s h e l f was form ed; and (4) warped t e r r a c e s a re t e c t o n i c f e a t u r e s formed when th e s h e l f was warped. A ll oceans and se as c o n ta in r e l a t i v e l y f l a t a r e a s b e yond c o n t i n e n t a l and i n s u l a r s l o p e s which may cover an a re a of hundreds to te n s of th o u san d s of sq u a re k i l o m e t e r s . Some e v id e n c e p o i n t s to a s u b a e r i a l o r i g i n and su b se q u e n t submergence of th e s e l a r g e p l a t e a u s , r i s e s , and ban k s, such as the Blake, Campbell, and Lord Howe P l a t e a u s and R o c k a ll Bank . Few i n s u l a r s lo p e s were s t u d i e d because t h e i r g r a d i e n ts u s u a l l y are so s t e e p t h a t no f e a t u r e s , such as t e r r a c e s , are rec o rd e d on echogram s. T a h i t i , C l i p p e r t o n , Rapa, and s e v e r a l i s l a n d s in the In d ia n Ocean show ev id ence of t e r r a c e s . The Hawaiian I s l a n d s r e c e iv e d s p e c i a l stu d y because w id esp read t e r r a c e s were observed a t s e v e r a l d e p th s around the a r c h i p e l a g o , S h a llo w -w ate r r e e f - b u i l d i n g c a l c a r e o u s m a t e r i a l was re c o v e re d from the d e e p e s t t e r r a c e a t about 900 m. I t was given a p ro b a b le Miocene age. 480 The o c curren ce of th ic k accum ulations o f sh a llo w -w a te r r e e f - b u i l d i n g d e p o s i t s on many i s l a n d s , the G reat B a r r i e r Reef, Bahama P la tf o r m , and o t h e r s su p p o rts the c o n c lu sio n t h a t su b sid en ce has been an im p o rtan t f a c t o r in t h e i r d e velopm ent. That p o r t i o n of the su b sid e n c e which was due to l o c a l i s o s t a t i c ad ju stm en t and to g e n e r a l se a f l o o r s u b s i d ence is p r o b le m a tic . Convergent l i n e s of e v id e n c e , based upon c o u n tle s s f i e l d o b s e r v a t i o n s from a l l oceans and se as and t h e o r e t i c a l s t u d i e s , s t r o n g l y su p p o rts the c o n c lu sio n t h a t most of the w o r l d 's d e p re ssed a re as have undergone s u b s t a n t i a l s u b s i d ence in r e l a t i v e l y r e c e n t g e o lo g ic tim e. F u r t h e r , some former t e r r e s t r i a l r e g io n s not only su b sid e d but have l o s t t h e i r i d e n t i t y of a c o n t i n e n t a l - t y p e x r u s t . O cean ic-ty p e c r u s t o c cu p ies i t s p l a c e . Not a l l t e r r e s t r i a l ( c o n t i n e n t a l - ty p e) c r u s t has l o s t i t s i d e n t i t y . I t i s b e lie v e d t h a t a P recam brian age m assif s t i l l e x i s t s on the f l o o r of the A r c t i c Ocean, and c r u s t s in te r m e d i a t e between o cean ic and t e r r e s t r i a l have been observed. The im portance of t h i s c o n c lu s io n cannot be f u l l y determ ined but i t c e r t a i n l y w i l l r e q u i r e a r e a p p r a i s a l of the fu nd am en tals of t e r r e s t r i a l and marine geology. The o r i g i n of sub sidence must be a w orld-w ide phenom ena, b u t beyond t h a t sim ple s t a te m e n t, a l l a tte m p ts to e x p l a i n s u b s id e n c e , as w e ll as the major E a rth f e a t u r e s , have f a i l e d . While many problem s are a s s o c i a t e d with the o r i g i n 481 of c o n t i n e n t a l s lo p e s , o th e r sea f l o o r f e a t u r e s ( i n f a c t , the o r i g i n of ocean b a s in s and c o n t i n e n t s th e m se lv e s) can be e x p la in e d by c o n t i n e n t a l d r i f t , an expanding E a r th , changes in the shape of the geoid, and c o n v e c tio n c u r r e n t s ; but each of these p o s t u l a t e s involve c o n t r a d i c t o r y e v i dence. Hence, no d e f i n i t e c o n c lu s io n s can be reached con c e rn in g t h e i r t o t a l impact on c o n t i n e n t a l slo p e fo rm a tio n . Much a d d i t i o n a l work must be u n d e rta k e n in a l l phases of marine geology, g e o p h y sics, g e o c h e m istry , and p a le o n to lo g y b e fo re the c o n t r a d i c t i o n s can be r e c o n c i l e d . The o r i g i n of c o n t i n e n t a l s lo p e s i s i n t i m a t e l y r e l a t e d to th e o r i g i n of ocean b a s i n s and c o n t i n e n t s , i n c lu d in g su b s id e n c e . Four b a s ic typ es o f c o n t i n e n t a l t e r r a c e ( s h e l f and s lo p e ) o r i g i n s are pro po sed: (1) f a u l t , (2) f l e x u r e (o r downwarp), (3) com bination of f a u l t and f l e x u r e , and (4) f a u l t ( p o s s i b l y a lso f l e x u r e ) , combined w ith u p b u ild in g of c a rb o n a te r e e f m a t e r i a l on a s u b s id in g f o u n d a tio n . I n cluded under numbers two and t h r e e are such re g io n s as the Gulf Coast G eosyncline where s e d im e n ta tio n in a re g io n of sub sid ence r e s u l t s in a marked f l e x u r e a s s o c i a t e d with su b s u r f a c e f a u l t i n g . The re g io n o f f e a s t e r n G reenlan d, where b a s a l t flow s show a marked f l e x u r e , i s an e x c e p t i o n a l e x ample of type two. B o u rc a rt, J e s s e n , and Novak have been stro n g a d v o ca te s of c o n t i n e n t a l m argins f l e x u r e and have given many exam ples. C o u n tle s s examples of f a u l t - c o n t r o l l e d c o a s t s occur 482 throughout the w orld and t h i s would appear to be the domi nant type of c o n t i n e n t a l margin o r i g i n . The f o u r t h type is e x e m p lifie d by such re g io n s as the G reat B a r r i e r Reef, Blake P l a t e a u , Bahama P la tf o r m , West F l o r i d a Escarpm ent, and Campeche Bank. O b v io u sly , some form of f a u l t i n g or f l e x u r e i s a p r e r e q u i s i t e to upward c o n s t r u c t i o n of c arb o n a te m a t e r i a l f o r the block must su b sid e b e fo r e any a p p r e c i able th ic k n e s s of r e e f m a t e r i a l can accum ulate. These fo u r b a sic ty pes take in to account the s u b s u r f a c e s t r u c t u r e which i s fundam ental to the o r i g i n of c o n t i n e n t a l t e r r a c e s , not j u s t the p r o f i l e observed on an e ch o gram . C o n tin e n ta l s lo p e s in the P a c i f i c Ocean and s lo p e s of i s l a n d a r c s , p a r t of the M e d ite rran e an Sea, and the e a s t e r n p a r t of the Indian Ocean show a d i p - s l i p p lan e which is s e i s m i c a l l y a c t i v e . I t has been p o s t u l a t e d t h a t c o n t i n e n t a l s lo p e s in th ese re g io n s a re the r e s u l t of t h r u s t i n g in which the land i s pushin g over the sea f l o o r (or the con v e r s e ) . C o n tin e n ta l s lo p e s in such r e g io n s may r e p r e s e n t f a u l t s u r f a c e s or have a long h i s t o r y of f l e x u r e . In the l a t t e r c a s e , sedim en ts composing th e c o n t i n e n t a l t e r r a c e s may show u n m ista k ab le s ig n s of being b u i l t upward and o u t ward, b u t t h i s i s a t t r i b u t e d to su b sid e n c e of the c o n t i n e n t a l margin (the o f f s h o r e ocean b a s i n ) s im u lta n e o u s ly w ith s e d im e n ta tio n . Such c o n t i n e n t a l t e r r a c e s would p ro b ab ly show a n ic e p r o g r e s s i o n between o c e a n ic - ty p e to c o n t i n e n t a l - 4 83 typ e c r u s t s . T h is type of c o n t i n e n t a l t e r r a c e h a s a g e n e r a l t r e n d p a r a l l e l to the main o n sh o re s t r u c t u r a l f e a t u r e s such as m o untain r a n g e s . C o n t i n e n t a l s l o p e s of th e A t l a n t i c Ocean and most of the I n d i a n Ocean a re a s e i s m i c and do n o t p o s s e s s d i p - s l i p f a u l t p l a n e s . The c o n t i n e n t a l s l o p e s i n v a r i a b l y c u t o f f c o n t i n e n t a l - t y p e s t r u c t u r e s r a t h e r a b r u p t l y . For exam ple, m ou ntain r a n g e s l i k e the A t l a s t e r m i n a t e a t th e c o a s t l i n e . These t e r r e s t r i a l s t r u c t u r e s may or may n o t c o n ti n u e below se a l e v e l o f f s h o r e . D e t a i l e d s t u d i e s of th e c o n t i n e n t a l m argins commonly show t h a t f a u l t i n g and f l e x u r i n g was r e s p o n s i b l e f o r th e a b r u p t t e r m i n a t i o n of t e r r e s t r i a l f e a t u r e s . R i f t i n g ( i . e . , d r i f t i n g of c o n t i n e n t s ) and s u b s i d ence a re p r i m a r i l y r e s p o n s i b l e f o r t h e s e c o n t i n e n t a l slo p es. Bedrock o u t c r o p s sh o u ld be common on th e s e c o n t i n e n t a l s l o p e s . I f c o n t i n e n t a l d r i f t o c c u r r e d , th e s h o a l i n g of th e M oh orovi^ic d i s c o n t i n u i t y alo n g th e c o n t i n e n t a l m argin i s e x p l a i n e d by a mass t r a n s p o r t of sim a from the oc ea n s t o w ards and under the c o n t i n e n t s . Some b a s a l t i c m a t e r i a l i s e x t r u d e d , fo rm in g the m id-ocean r i d g e s , v o l c a n i c c h a in s l i k e H a w a ii, and v a s t l a v a p l a t e a u s such a s th e Darwin R i s e . In a d d i t i o n , th e r o o t s o f m o u ntain s may grow by a c c r e t i o n of sima below as th e y a re u p l i f t e d . A tte m p ts to c o r r e l a t e s e i s m ic a c t i v i t y w i t h t e c t o n i s m , such as f a u l t i n g , i s n o t e n t i r e l y w a r r a n t e d . Movements may tak e p l a c e s lo w ly by c r e e p w ith l i t t l e or no m a n i f e s t a t i o n 484 in the form o f m easureable e a r t h q u a k e s . While a c o r r e l a t i o n of l a r g e shocks w ith t e c t o n i c a c t i v i t y , such as f a u l t i n g , i s v a l i d , the c o n v e r s e - - t h e absence of e a r t h q u a k e s - - cannot be used to r u l e out l a t e n t , d o rm an t, or slow c re e p . L i t t l e ev id e n ce e x i s t s f o r c o n t i n e n t a l growth; in f a c t , i t ap p ea rs t h a t la r g e c o n t i n e n t a l masses have fo u n d e re d and, in some i n s t a n c e s , have been c o m p le te ly o b l i t e r a t e d . In such a re a s o c e a n ic - ty p e c r u s t o c c u p ie s th e form er p o s i t i o n of c o n t i n e n t a l - t y p e c r u s t . The mechanism f o r the c o n v e r s io n from c o n t i n e n t a l - to o c e a n i c - t y p e c r u s t i s s t i l l p ro b le m a ti c . F i n a l l y , s e v e r a l o th e r f a c t o r s might be im p o rta n t in th e p r e s e n t stu d y but were not i n v e s t i g a t e d . In clud ed are the p o s s i b i l i t i e s t h a t s u b s id e n c e of v a s t a r e a s may, in some i n s t a n c e s , r e p r e s e n t f u t u r e s i t e s of c o n s i d e r a b l e economic im p o rta n c e , e s p e c i a l l y o i l and g a s. O r ig in of g l a c i a l p e r i o d s and submarine canyons a re two enigmas which might f in d a s o l u t i o n in w id e sp rea d su b s id e n c e . A P P E N D I X APPENDIX I n t r o d u c t i o n T h is Appendix l i s t s (1 ) th e n a t u r e of the c o a s t l i n e , or th e b re a k between lan d and s e a , (2 ) e v id e n c e of l a r g e a r e a s of sea f l o o r changes ( s u b s i d e n c e , u p l i f t , f a u l t i n g , f l e x u r i n g , e t c . ) , and (3 ) e v id e n c e of form er land m asses where oceans or s e a s now e x i s t . Of s p e c i a l i n t e r e s t i s the p h y s i c a l r e a s o n s why land i s e l e v a t e d and the s e a f l o o r i s d e p r e s s e d . No c la im i s made f o r c o m p le te n e s s . In f a c t , two m ajor a r e a s were a lm o st c o m p le te ly l e f t out of the Ap pend ix f o r l a c k of s p a c e : p a l e o n t o l o g i c a l and land g e o lo g i c a l e v id e n c e . In th e case of p a l e o n t o l o g y , c o n s i d e r a b l e c o n j e c t u r e e x i s t s on the v a l i d i t y of many i n t e r p r e t a t i o n s , much more so t h a n in th e c ase f o r p h y s i c a l g e o lo g y . Thus, land b r i d g e s have b een prop osed s o l e l y on th e d i s t r i b u t i o n of f l o r a and fa u n a . Since modern b i o l o g i s t s a re o f t e n a t a l o s s to e x p l a i n th e p a t t e r n s of d i s t r i b u t i o n of l i v i n g p l a n t s and an im als i t i s o b v io u s t h a t p a l e o n t o l o g i s t s are a t an even g r e a t e r d i s a d v a n t a g e . The o th e r m ajor group l a r g e l y l e f t out of the Appendix i s e v id e n c e of m ajor changes on l a n d , e . g . , u p l i f t e d m arine 486 487 c u t t e r r a c e s , r e j u v e n a t i o n of s t r e a m s , t h i c k se q u en c e of f a u l t e d and warped P l i o - P l e i s t o c e n e age d e p o s i t s e l e v a t e d th o u sa n d s of m e te r s above s e a l e v e l , r e c e n t e l e v a t i o n of r e e f d e p o s i t s , e t c . Exam ples of b i o l o g i c a l " m is s in g l i n k s " a re th e v e ry d i s t i n c t d i s t r i b u t i o n o f d e e p - s e a f i s h . For exam ple, c e r t a i n d e e p - s e a f i s h c o l l e c t e d by the C h a l l e n g e r E x p e d i t i o n were n e v e r found anywhere i n the ocean a g a in u n t i l th e G a l e t h e a E x p e d i t i o n r e o c c u p i e d i d e n t i c a l C h a ll e n g e r s t a t i o n s and a g a in o b ta in e d the same s p e c i e s . T h us, c e r t a i n s p e c i e s o ccu r in l o c a l r e g i o n s w i t h o u t any known p h y s i c a l , c h e m ic a l, or e c o l o g i c a l b o u n d a r i e s t h a t would l i m i t t h e i r movement t o o t h e r a r e a s . Two s p e c i e s o f f i s h o c c u r n e a r the C a l i f o r n i a - M e x i c o b ou nd ary i n which one s p e c i e s s t o p s a b r u p t l y , n e v e r going f u r t h e r n o r t h , w h ile the o t h e r n e v e r i s found s o u th o f the b o r d e r . No known r e a s o n s e x i s t f o r th e a b r u p t t e r m i n a t i o n o f s p e c i e s (A. B. R e c h n i t z e r , p e r s o n a l c o m m u n ica tio n ). D ata in t a b u l a r form was c o l l e c t e d o v e r a p e r i o d of s e v e r a l y e a r s . No a tt e m p t h a s been made to e d i t , e l u c i d a t e or r e f u t e what may be c o n f l i c t i n g views or e r r o r s ( o r ch an ges in th e view s by i n d i v i d u a l i n v e s t i g a t o r s ) based upon more d e t a i l e d work, p a r t i c u l a r l y by r e c e n t i n v e s t i g a t o r s u s i n g modern g e o p h y s i c a l and g e o ch e m ica l t e c h n i q u e s . N e v e r t h e l e s s some, and p r o b a b ly m ost, of th e o l d e r r e f e r e n c e s in v o lv e b a s i c f i e l d o b s e r v a t i o n s t h a t a re s t i l l 488 v a l i d . T h is c o n c l u s i o n seems j u s t i f i e d b e c a u s e the c o n c l u s i o n s of i n v e s t i g a t o r s , w h i l e s u f f e r i n g from i n a c c u r a c i e s in d e t a i l , a p p e a r f u n d a m e n t a l l y c o r r e c t . A n o te of c a u t i o n sh o u ld be i n t e r j e c t e d h e r e . U n t i l v e r y r e c e n t l y ( i n the l a s t d e c a d e ) , i t was a lm o st i m p o s s i b l e to c o r r e c t l y d e c i p h e r o f f - s h o r e s e a f l o o r s t r u c t u r e s . A quantum jump in know ledge o c c u r r e d w i t h the use of c o n t i n u o u s s e i s m i c p r o f i l i n g e q u ip m e n t w hich g i v e s a su b - s e a f l o o r " p i c t u r e " o f g e o l o g i c s t r u c t u r e . A d m i t t e d l y , e x i s t i n g equipm ent h a s much to be d e s i r e d b u t i n d i s p u t a b l e p r o o f shows t h a t c o n t i n u o u s s e i s m i c p r o f i l i n g e q u ip m en t can and o f t e n d o e s r e v e a l s u b s u r f a c e f a u l t s , w a r p i n g , f l e x u r e s , e t c . P r i o r to th e use o f t h i s eq u ip m en t su c h f e a t u r e s l o c a t e d o f f s h o r e were b a se d l a r g e l y upon (1 ) p r o j e c t i o n of o n s h o re s t r u c t u r e s , ( 2 ) i n f e r r e d s t r u c t u r e s b a se d upon lan d g e o lo g y , and ( 3 ) e c h o s o u n d i n g , o f t e n combined w i t h t h e c o l l e c t i o n of b o tto m sa m p le s and b o tto m p h o t o g r a p h s . Some o f th e c r i t e r i a u sed to r e c o g n i z e subm erged g e o l o g i c f e a t u r e s , s p e c i f i c a l l y f a u l t i n g , w a r p in g , and s u b s i d e n c e , a re sum m arized below . I t sh o u ld be o b v io u s t h a t q u a n t i t a t i v e and q u a l i t a t i v e i n f o r m a t i o n w i l l grow as s t a t e - o f - t h e - a r t i n m arin e t e c h n o lo g y a d v a n c e s . W hile d i v i n g (SCUBA and d eep s u b m e r s i b l e s ) u l t i m a t e l y may be u s e f u l , i t h a s c o n t r i b u t e d l i t t l e to d a t e i n m arine g e o lo g y ( T e r r y , 1 9 6 4 ). F r a c t u r e zo n es a r e e n o rm o u s ly l o n g , t h i n b an ds w hich 489 are c o n s p i c u o u s ly more m ou ntaino us th a n the s e a f l o o r around them and which o r d i n a r i l y s e p a r a t e r e g i o n s w ith d i f f e r e n t d e p t h s . L ess s p e c t a c u l a r f a u l t s a l s o occur on the se a f l o o r . Menard (1963) has d e s c r i b e d the m ajor f r a c t u r e zones in the P a c i f i c Ocean and A lle n (1962) has d e s c r i b e d s i m i l a r f r a c t u r e zones on land i n the w e s t e r n P a c i f i c . The San Andreas f a u l t i s a t y p i c a l m ajor f r a c t u r e zone on la n d . Heezen, Bunce, H e rse y , and Tharp (1964) r e c e n t l y d e s c r i b e d f r a c t u r e zones in the A t l a n t i c Ocean and d i s c u s s e d some of the problem s a s s o c i a t e d w i t h i d e n t i f i c a t i o n o f f r a c t u r e zones in r e g i o n s of i r r e g u l a r b o tto m to p o g ra p h y . C u r i o u s l y , i n s t a n c e s e x i s t where se a f l o o r f a u l t i n g has been used to l o c a t e f a u l t s and m ajor f r a c t u r e zones on lan d ( A l l e n , 1962; I r v i n g , 1951 and 19 5 3 ). T able 26 l i s t s some of the e v id e n c e used f o r r e c o g n i z i n g f a u l t i n g , and o t h e r f e a t u r e s , as w e ll as the t e c h n iq u e employed f o r o b t a i n i n g i n f o r m a t i o n . Warping i s more d i f f i c u l t to r e c o g n i z e below s e a l e v e l b u t many of the c r i t e r i a used to d e te r m in e f a u l t i n g a ls o a p p l i e s to w a rp in g . Most im p o r ta n t a re obvio us e x t e n s i o n s of land f e a t u r e s o f f s h o r e . The use o f c o n tin u o u s s e is m ic p r o f i l i n g equipm ent has been p a r t i c u l a r l y f r u i t f u l h e r e . V a r i a t i o n of known t r e n d s may s u g g e s t w a rp in g , a s , f o r e x ample, v a r i a t i o n s i n s h e l f b r e a k s . 490 Table 26 EVIDENCE USED FOR RECOG NITION OF FAULTING AND OTHER FEATURES Topography F a u l t s a re lo n g , r e l a t i v e l y narrow , s t r a i g h t or g e n t l y curved s t e e p s lo p e s w ith or w i t h o u t l i n e a r d e p r e s s i o n s . C l o s e ly - s p a c e d l i n e a r c o n t o u r s , more or l e s s in a r e g i o n of o th e r w i s e low r e l i e f . METHODS FOR RECOGNIZING FEATURES E c h o s o u n d in g , c o n tin u o u s s e i s m ic p r o f i l i n g (ESP), r e f r a c t i o n and r e f l e c t i o n s e is m o lo g y , p r o j e c t i o n of land f a u l t s . I n d i v i d u a l a c o u s t i c p r o f i l e s may r e v e a l a m ajor change in r e l i e f , or long l i n e a r f e a t u r e s w ith low r e l i e f may be c o n sp ic u o u s o n ly by con s t r u c t i n g b a th y m e t r i c c h a r t s . More m ountainous th a n se a f l o o r n e a rb y (p e rh a p s i n c l u d e s r i d g e s and d e p r e s s i o n s ) . S e p a r a t i o n of m ajor r e g i o n s of d i f f e r e n t d e p th s ( e . g . , Mendocino E s c a r p m e n t) . O f f s e t to p o g ra p h y , en e c h e lo n p a t t e r n s , sag ponds, s a d d l e s , e t c . Alignm ent o f v o lc a n o e s , seam o u n ts, g u y o ts , e t c . Major to p o g r a p h ic changes f o l lo w in g e a r t h q u a k e s ( e . g . , A la s k a , Sagami Bay, J a p a n , and L i s b o n ) . Narrow a n d /o r s t r a i g h t c o n t i n e n t a l or i n s u l a r s h e l f . Moats ( o r g r a b e n s ) commonly found p a r a l l e l to sh o re in hig h l a t i t u d e s . 491 T able 26 (C on tin u ed ) EVIDENCE USED FOR RECOG NITION OF FAULTING AND OTHER FEATURES Graben a n d /o r h o r s t f e a t u r e s . S t e p - l i k e ( o r s t a i r c a s e ) s t r u e tu r e s . R e c o g n itio n of seco n d ary f a u l t . f e a t u r e s : a lig n m e n t of o t h e r t o p o g r a p h i c , g e o p h y s i c a l d a t a , e t c . S e p a r a t i o n of m ag netic a n o m a l i e s . D i f f e r e n c e in g r a v i t y a n o m a l i e s . D i f f e r e n c e s in c r u s t a l l a y e r s , sed im en t t h i c k n e s s e s . S e ism ic a c t i v i t y ( r e q u i r e s use o f o t h e r d a t a ) . D i s t i n c t change from c o n t i n e n t a l to o c e a n i c - t y p e s t r u c t u r e . Heat flo w (? ) METHODS FOR RECOGNIZING FEATURES Sea and a i r b o r n e m agneto m eter m easurem ents ( v i a c o n s t r u c t i o n of c h a r t s or m atching p r o f i l e s ) . G r a v it y p r o f i l e s or c h a r t s of g r a v i t y a n o m a lie s . R e f l e c t i o n and r e f r a c t i o n se ism o lo g y ( g r a v i t y and m agn etic d a t a g ive s u b o r d i n a te d a t a ) . R eco rd in g e p i c e n t e r s and p l o t t i n g t h e i r d i s t r i b u t i o n on c h a r t s ( e s p e c i a l l y co n t a i n i n g b a th y m e try and o t h e r parame t e r s ) . G r a v i t y , m a g n e tic , s e i s m i c , p e t r o g r a p h y , ( p a l e o n t o l o g y ? ), d r e d g i n g , photography. Heat flow m easurem ents ( i n s u f f i c i e n t d a t a to show ma j o r d i f f e r e n c e s ) . 492 T a b le 26 (C o n tin u e d ) EVIDENCE USED FOR RECOG NITION OF FAULTING AND OTHER FEATURES METHODS FOR RECOGNIZING FEATURES S t r a t i g r a p h y O f f s e t s t r u c t u r e s ( v e r t i c a l or h o r i z o n t a l ) . B a th y m e tr y , g r a v i t y , mag n e t i c d r e d g i n g , c o r i n g , u n d e r w a t e r p h o t o g r a p h y , p a l e o n t o l o g i c a l s t u d i e s , s e i s mic (ESP, e t c . ) . R e p e t i t i o n or o m is s io n of s t r a t a . F a u l t b r e c c i a . Sudden change in f a c i e s . P e t r o g r a p h y O f f s e t or m ajor b r e a k s in ro c k t y p e s . Sou rce a r e a ( i n d i c a t i o n o f m ajor la n d a r e a n e a r b y to s u p p l y d e t r i t u s ; la n d a r e a now o c c u p ie d by d e ep w a t e r ) C o r in g , d r e d g i n g , m a g n e tic g r a v i t y , and s e i s m i c i n v e s t i g a t i o n s . Rock a n a l y s e s . D e t a i l e d mapping of ro c k s u i t e s . O ceanography D i f f e r e n c e s in te m p e r a t u r e , ort, and o t h e r p h y s i c a l / c h e m i c a l or b i o l o g i c a l d i f f e r e n c e s i n f e r a r i d g e , s i l l s , o r b a s i n s . C o l l e c t i o n o f w a te r sam p l e s , t e m p e r a t u r e m e a s u r e m e n ts , c a l c u l a t i o n o f crt, a n a l y s i s o f f a u n a l d i s t r i b u t i o n ( g e o g r a p h i c a l l y and v e r t i c a l l y ) . O th er D r i l l i n g ( e . g . , o i l w e l l s ) 493 Table 26 (C ontinued) EVIDENCE USED FOR RECOG- METHODS FOR RECOGNIZING NITION OF FAULTING AND FEATURES OTHER FEATURES ______________________ Land Geology P r o j e c t i o n of f a u l t s or s t r u c t u r e s o f f s h o r e . Abrupt te r m in a t io n of s t r u c t u r e or tre n d l i n e s ( i n c l u d in g m ountain ra n g e s) a t th e s h o r e l i n e . Major d i f f e r e n c e s in g e o l ogy of land a re a s s e p a r a te d by b o d ie s of w a ter ( s t r a i t s , e t c .). Evidence of la r g e r e c e n t u p l i f t s of land ne ar the c o a s t l i n e . D e t a ile d g e o lo g ic mapping, in c lu d in g p a le o n to lo g y , s t r a t i g r a p h y , s t r u c t u r e , and g e o p h y sic a l i n v e s t i g a t i o n s . Subsidence is more s u b t l e , u s u a l l y in v o lv in g the em ployment of c o n v ergen t l i n e s of ev id ence i n c l u d i n g : 1. Recovery or o b s e r v a t i o n of o b v io u s ly sh a llo w -w a te r f e a t u r e s such a s: a. L i t t o r a l sedim en tary d e p o s i t s b. R ock -bo rers ( e . g . , pholad h o l e s ) c. Drumlins and s h o r e - i c e f e a t u r e s d. O ffsh o re b a r s and l a r g e sand waves 494 e. P re se n c e of o y s t e r s and o t h e r sJiallow -w ater anim als f . M a rin e -c u t p l a t f o r m s ( t e r r a c e s , g u y o ts) a t d e p th s c o n s i d e r a b l y below wave b a s e . 2. F e a t u r e s or d e p o s i t s formed only on lan d ; e . g . , pahoehoe la v a 3. R e su rv ey s, e . g . , Sagami Bay a f t e r 1923 Tokyo e a rth q u a k e 4. D eep-sea low a r e a w ith l i t t l e or no se d im e n ta ry th ic k n e ss 5. Cores showing major l i t h o l o g i c or f a u n a l changes. In clu d e d h e re are changes from f i n e - g r a i n e d to l a r g e l y c l a s t i c d e p o s i t s ; n o n - t u r b i d i t y c u r r e n t d e p o s i t s , or p y r o c l a s t i c s , s u g g e s tin g r e l a t i v e u p l i f t of source a re a n earb y (o r s u b s id e n c e ) . 6. Former land a r e a s , now d i s a p p e a r e d , are u s u a l l y i n d i c a t e d by s t u d i e s of se d im e n ta ry sequ ences and by ev id e n ce of ic e movements ( s t r i a t i o n s , e t c . ) . I t i s n o tew o rth y t h a t e v id e n ce of su b s id e n c e beyond the l i t t o r a l zone, or very sh a llo w w a t e r , i s te n u o u s . Hence, i t would be e x tre m e ly d i f f i c u l t , i f n o t im p o s s i b l e , to prove a t our p r e s e n t s t a t e of knowledge t h a t an a re a s u b s id e d , say from 1,000 m to 5,000 m. One of th e u s e f u l t o o l s h ere might be the f o r m a t io n of c e r t a i n a u t h i g e n i c m i n e r a l s , or s u r f i c i a l la v a f e a t u r e s under v a ry in g p r e s s u r e . Some s t r i k i n g ev id e n ce of su b sid e n c e has o c c u rre d in 495 h i s t o r i c tim e . As the bottom i s su rvey ed in more d e t a i l t h i s form of ev id e n ce w i l l become more u s e f u l . I t does not h e lp when c o n s id e r in g more a n c i e n t movements. General After noting the contrast between the outlines of the ocean basins and the structures of continents, Suess stated: "these ocean basins are areas of subsidence. . . as soon as we recognize the ocean basins as sunken areas, the continents assume the character of horsts. . . . The crust of the Earth gives way and falls in: the sea follows i t . . . but while the subsidences of the crust are local events, the subsidence of the sea extends over the whole submerged surface of the planet. It brings about a general negative movement." (All changes affecting the height of the sea at one time over the whole globe he designated as "eustatic move ments. ") "The formation of the sea basin produces spasmodic eustatic negative movements. A sinking of the sea floor at any place lets the ocean down from its shores all over the Earth, while sedimentation raises sea level. ” Suess, 1906 Taylor, 1910 Subsidence has left its traces everywhere. Suess, 1904 Continents have sunk and been rebuilt up. Suess, 1888 Haug, 1900 Termier, 1924 Umbgrove, 1947 Existence of atolls, guyots, and drowned ancient volcanoes, islands or shallow banks indicate subsidence. Drowning amounts to 170-1300 m; weight of coral alone on a shallow bank is not sufficient to cause subsidence. Menard, 1964 "... there are many geological pointers that this great ocean being a foundered area of ordinary continental character, perhaps traversed by fold systems and certainly subject to undulations of the ocean bottom on a large scale. . . The history of the Rockies geosyncline throughout the Paleozoic and Mesozoic indicates the former existence of a western continent and continental massif in Mexico Lees, 1950 v O O' Margins of present continents do not show any structural design at all suggestive that they have always been margins. It is the exception rather than the rule for a coast to be determined in its alignment by the grain of a fold or compression system. West coasts of North and South America due to Rockies and Andean Mountain system, but Central American coast is not. Rockies-Andean geosyncline is intra-continental and not a marginal feature, and a source area of land must have existed in the Pacific to provide clastic rocks. Vertical movements of the ocean floors on a large scale have taken place during the Tertiary and since early Cretaceous down-warpings of continental margins have been so vast that it is no longer possible to speculate on the size or even the position of pre-Cretaceous Oceans. The margins of the continents also provide abundant testimony of large-scale downwarping during the Cretaceous, Tertiary, and even Recent times on a scale comparable with vertical movements within the continents themselves. Individual downwarps amount to 35,000 to more than 50,000 ft. Some reason must exist for great downwarps of oceans; perhaps great lava outpourings associated. Mediterranean-type seas were formed recently, still further increasing the oceanic area. Displacement of faults on land are equal or exceed the depth of ocean basins. Examples; Worchester fault in Cape Colony, Africa, has a downthrow of 12, 000 ft. Similar magnitudes reported in Columbia and in Aegean region. "Near the shelf the surface is often undulating because of the pressure of the sediment sliding down the continental slope." Horsts and graben have been detected on the bottom. Abyssal hill topography is the result of stretching of the under-lying layers. Downwarping which sinks continental surfaces to oceanic depths has been known to occur. Concept of permanence of oceans is so firmly thrust Lees, 1953 Beloussov, 1951; Muratov, 1957; Tikhomirov, 1958; Beloussov and Rudich, 1960 Suess, 1906 du Toit, 1926 Rastall, 1911 Gregory, 1930 Koczy, 1953 Lees (in Hill, 1953) \0 --3 upon geologists that their interpretations are arranged to fit and have rejected any hypothesis which allows the extension of geological struc tures into the deep sea. An example of earth movements extending into deep sea is the San Andreas fault. In addition to glacial lowering of sea level of about 100 m, a simul taneous or subsequent downward movement of the bottom (continental terrace) has also taken place. Umbgrove, 1947 Thickenings at continental margin classified: (1) warping accompanied by faults, (2) updoming accompanied by faults and slight folding, (3) folding and over-thrusting, accompanied by underthrust of the ocean floor, giving origin to a deep-sea trough. Jessen, 1943 (in Umbgrove, 1947) Bevelled tops of guyots or flat-topped seamounts cut at sea level, evidence points to slow subsidence estimated at 20 m/million yrs. Hess, 1946 Woollard, 1954 Kuenen, 1954, 1955 Atolls and seamounts point to relative subsidence and under favorable climatic conditions reef growth can keep up with subsidence. Estimated rated of subsidence of 0.5 cm/century. Appears both are volcanic and sink after formation. Kuenen, 1950 The present continental terraces are young — Mesozoic and Cenozoic. Postulates that Paleozoic terraces have all foundered, so they now lie beneath the deep sea waters. Ibid A minimum of 13 major fracture zones have been discovered in the Pacific. They are wrench faults and have a vertical difference up to 3,000 m. They indicate a marked difference or change in the relative relief of the sea floor. Menard, 1964 Mendocino Ridge is composed of basalt and was at one time at sea level, probably existing then as a chain of islands. Krause, Menard, and Smith, 1964 ^ 00 Oceans extending their area at the continent’s expense and have and are becoming considerably deeper as pointed out by many geologists. Authors summarized evidence as follows: 1. Generally "superimposed" character of the Atlantic and Indian Oceans in relation to structure of continents. 2. Existence of high dry land in the lower Paleozoic to the northwest of present Scandinavian peninsula (as indicated by direction of drift or source of clastic sediments of Cambrian and Silurian sediments). 3. Better land connections between South America, Africa, India, Australia and Antarctica in the Paleozoic (Gondwanaland continent). 4 . The former and definite development of continental deposits of the Karoo basin beyond the present-day continents of Africa, i. e . , beyond coastline. 5. A land connection across the North Atlantic from Europe to North America. 6. A land connection between islands of Indonesia and the continent, and between the islands of Japan and the continent, as well as between New Zealand and Australia, persisting into the Neogene. 7. Traces of U. Paleozoic glacial invasion from direction of Indian Ocean as shown by presence of granite boulders. 8. Evidence of high dry land east of Appalachians during Paleozoic - now occupied by Atlantic Ocean. 9. Existence in L. Mesozoic of dry land west of Congo Basin off African Coast. 10. Internal seas of Indonesian archipelago, south of South China, East China, Japan, Okhotsk and Bering Seas formed as a result of crustal subsidence only recently, not earlier than middle Tertiary, in place of then existing land units. 11. Evidence pointing to youth of Caribbean Sea which subsided during post-Cretaceous time. Beloussov, 1955, 1960, 1962 Beloussov and Rudich, 1960 Khayin, 1957 Panov, 1950 499 12. Formation during the Teritary and Quaternary of the northern part of the Atlantic Ocean. 13. Youth of western Mediterranean. Uplifted dry land still existed during Paleogene. Now oceanic-type crust. 14. Recent formation of the Black and Southern Caspian Seas. Now oceanic-type crust. 15. Evidence of recent deepening of oceanic depressions in post- Cretaceous time. a. Truncated seamounts (guyots) down to 2 .5 km. b. U. Cretaceous fossils on summits of seamounts. c. Subsidence by about 1.3 km of bottom of reefs during the Tertiary (as revealed by drilling information). d. Littoral Monoclinal flexures indicating recent tectonic deflection of oceanic depressions. Although the geological structures of the sea floor are far from complete, "yet it enables us to draw one undisputable conclusion: The contem porary sea basins are new geological features whose existing boundaries probably were established only by the end of the Tertiary period and whose final contours were delineated in the Quaternary period. It is evident that the geological processes that determine the contours and relief of contemporary sea floors have not been interrupted at the present tim e." Guyots are attributed to addition of juvenile water to the oceans; Vening Meinesz disagrees. Paleozoic ice movements: In east South Africa direction of ice is from east and northeast; in Australia and Tasmania it is from south; Falkland Island, it is from north (?S.). South America, from east. (In India ice striations far inland so inconclusive; Antarctica has no evidence). If several ice centers in different oceans, where were glaciers from them collecting large amounts of debris - continental terraces too narrow as source area. Behrmann, 1958 Klenova, 1960 Revelle, 1955 Vening Meinesz, 1964 Ahmad, 1961 U l o O Drowned islands (guyots) suggest a secular deepening of the oceans indicating eventually the existence of a secular earth contraction. The continents are the scars of past orogenic unrest indicating the sites of crustal reductions. The oceans represent the unchanged old crust covered by secular sedimentation in variable thickness (5 - 20 kms) with faulting zones like the Mid-Atlantic Ridge and isolated volcanic cones caused by crustal splittings during major tectonic paroxysms. Vapor from crystallizing magma and the secular surface reduction of the contracting earth caused a secular deepening of the oceans, drowning dead volcanic cones. The deeper the older they are; in younger epochs coral growth could compensate the slow drowning. Due to cyclical nature of tectonic unrest manifested too in preferred ages of radioactive minerals, the top of drowned islands should stand, according to this explanation on preferred levels. Statistics of known top levels seem to confirm this conclusion. "If there is ocean where there was land, then the former sial of that area must now exist somewhere else. . . the only alternative to lateral drift is removal of the sial at the base by magmatic currents in the substratum, but if this be a possible method of sinking land-bridges, then it implies a process capable of transporting continents." "Clearly it is difficult to sink continents as it is to tear them forcibly apart, and in the absence of a clear geophysical lead one must choose between the alternatives of vertical or lateral displacement on their individual merits in relation to other problems. Here continental drift has more than one decided advantage “Currently, because of the inherent difficulty of getting rid of large land masses without leaving any trace, the tendency has been to believe that chains of islands existed beyond the coasts. This hypothesis of 'island arcs', however, appears to be applicable only to the orthogeosynclinal basin, whereas the [[innumerable examples of sea source areasj do not seem to have been restricted to those earth features. Moreover, it seems Sonder, 1948, 1952 Holmes, 1929 Ahmad, 1961 501 hard to believe that every major continent in the past has chains of islands all around it, nor is the feature restricted to Gondwanaland, for Schuchert had to presume the former existence of Appalachia and other hypothetical land masses to explain the sources of sediments on the coasts of North America. . . . On the other hand, in any reconstruction of the land-form on the Drift Hypothesis, Australia had extensive land areas on both sides. South America had it on the east, and Africa had land areas to the south, as well as to the east and the west. Does it suggest that these sediments came from these lands now across the sea?" "... the oceanic crust has undergone fracturing and deformation and has been mountain-built just as much as the continental crust, and has also suffered displacements in geographic positions." "... There are no areas of foundered continental crust. . . The fact remains that a land source must be found beyond the margins of the Noith American continent. . . Where is the source of the thick Devonian delta deposits of the eastern United States, which were derived from the east, from a land mass beyond the margins of the continent? Similarly, where is the land mass that supplied the sediments of the Arctic slope of Alaska and Canada, which were derived from a land mass lying to the north during Devonian, Mississippian, Permian, and Triassic time? Or where is the land mass that supplied the Mesozoic and Tertiary deposits of Spitsbergen, which were derived from the west? If large borderlands of continental crust have not moved vertically and subsided in the ocean basins, the only alternative is that they must have moved horizontally across them. Gussow, 1963 "Very obviously, the continents are growing at the expense of the oceans, and geological evidence indicates that the oceans have been getting deeper. Guyots rising 9,000 to 12,000 ft. from the ocean floor and their flat eroded summits at 3,000 to 6,000 ft. and more below sea level (Hess, 1946) are a permanent record of the deepening of the ocean basins. 502 "The mature topography of the continental slopes is so fresh that it is either actively forming now or has been fashioned by 'yesterday'. ” Slope is formed by erosion and deposition. Tsunamis are important in origin." Some people believe that sediments push down land (such as Colorado Plateau, Grand Canyon section). Sediments laid down must push aside heavier rocks at bottom of crust. This would require accumulation of a greater thickness of lighter material in order to push aside an equal weight of heavier material at depth. A land surface that lies near sea level can therefore, never disappear below water merely by piling up sediments. The crust must be forced down by other independent forces. The earth's surface can and do bend down and thick sediments exist because there was a depression, not that a depression exists because there were sediments. . . . If some sinking were to take place, where no large amount of sediment is available, as the site of land bridge, the sinking would not be compensated by deposits, the land bridge would vanish. This may have happened but not on scale as "Gondwanaland, " because sialic rocks are missing. Large vertical displacement of parts of continental surfaces is contrary to Wegener's basic assumption as the corresponding behavior of the ocean floor. Kurt Wegener (Alfred's brother) said (1939): "The results of pure geophysics. . . have furnished clear proof, that only horizontal move ments (of crustal units), if any, are possible. . . and that the emergence and submergence of continents must be relegated to the realm of fantasy." Favors Earth contraction theory. Reduction in earth’s volume has resulted in sporadic but continual sinking of crustal segments. All of these move ments are vertical downward, horizontal movements have been secondary. Besides sinking, fragmentation occurred, as well as some rotation. The downwarp of the Atlantic basin dragged the surface of the basement rocks of the continental platform down to great depths in places. Bucher, 1940 Bucher, 1952 Landes, 1952 503 Fault-bounded Pacific does not show similar downward drag of the edges of the continental platform; however, foundering of the continental margins about the Pacific may have been encouraged by subsidence of Pacific Basin. Subsidence is widely evident on continents: Michigan (14,000 ft), Illinois and Permian (West Texas) Basins, the geosynclines, marginal embayments, and grabens. Appalachian geosyncline subsided 30,000 ft. north flank of Gulf geosyncline 30,000 to 70,000 ft. Most continental slopes "represent a zone of recurrent faulting at the juncture between the light continental and the heavy oceanic segment of the earths crust." Principal evidence for the youthfulness of oceanic depressions: (1) Paleo- geographic data indicating the existence of drift sources within the limits of the present oceans (e. g. "Appalachia, ” and dry land in the Okhotsk Sea); traces of glacier advance from the sea onto the continents of South America and South Africa in the U. Paleozoic, and of "continental bridges" between certain continents (e.g . South America and Africa and elsewhere); (2) Existence of underwater valleys (canyons) extending to great depths, with at least part of the formation having a subaerial origin; (3) guyots with summits sometimes deeper than 2 km; (4) the con siderable thickness of reef formation; (5) the continuation of continental structural elements into oceanic depressions; (6) the existence of sub- oceanic ridges (Mid-Atlantic Ridge, the Lomonosov Ridge etc.) that are regarded as analogous to the young fold-systems on the continents; and (7) the fault character of many parts of the ocean coastlines and the association of major youthful volcanic manifestations with the rims of the oceanic depressions. . . All these facts undoubtedly point to a recent extensive deepening and expansion of the oceans, but they cannot yet be counted as proof of the recent formation of the oceans as a whole — The division of terrestrial crust into continents and oceans is relatively ancient, and profound differences exist between them. But this does not mean "permanency” of these forms of crustal relief and structure. Moore, 1936 Cohee, 1948 Landes, 1952 Shepard, 1948 Khayin, 1957 U l o ■ P * Most marine geologists today think that the sea floor has subsided, but there is a small minority who think that perhaps the ocean volume increased enough to explain most of the relatively sinking of seamounts. If the latter idea is correct, something on the order of a 30% increase in the volume of the oceans must have occurred during the last 100 million years. "With oceanic segments taking the lead in downward crowding [lateral stress ~ \ , the greatest intensity of thrusting in the average case should be expected in the critical border tracts between oceanic and continental segm ents. Ordinarily, less intensity of compressive stress should prevail in the interior of the segments. . . Other things being equal, the general result should be greatest deformation in the broder tracts. With each recurring period of diastrophism, the denser ocean segments, furthered by sediment from the land areas, should sink, and the eroded and lightened continental masses should rise. . . . " Layer 2 (in seismic refraction work) is a mystery. Believes it is mostly a few hundred ft. of limestone, resting on a lower velocity layer (not determined). Most probable age is (if it exists) is Cretaceous. It could be the result of enormous animal activity in seas. Seamounts originated in Cretaceous time also. Many continental connections until Cretaceous, from here on rocks are dissimilar, The Cretaceous is thus a truly catastrophic time of widespread sedimentation and of continental drift. The Pacific Ocean has sunk an average 700 fms as indicated by average depth of guyots in 100 million years, or an average of 1 cm/1000 years. An overall rise in sea level will not account for thousands of ft. of move ment since cretaceous. There is a large body of evidence pointing to continental drift. There is no doubt that continents have moved up and down; the oceans do not appear to have moved upwards to become land. Much evidence on permancy of ocean floors exists. Hamilton, 1957 Chamberlin, T.C. Gaskell, 1960 , 1924 505 Major evidence of continental drift: (1) Otogenic activity in southern continents is localized in a belt that can be followed through Goodwanaland as the Samfrau geosyncline. (2) Glaciation in the Carboniferous and Permian eras seem to radiate from a point now occupied by South Pole, but appears to cover parts of the southern continents in such a fashion as to suggest that the latter were closer together at that time. (3) Paleobiological evidence seem to indicate that die southern continents had, even in relatively recent times, some land connections between each other, e.g . Marsupials in South America and Australia, and the distribution of scorpionidae. It is thus assumed continents have drifted about 14,000 km since Carboniferous. du Toit, 1937 Lotze, 1938 Maach, 1953 "From the general absence of abyssal types of deposits from among the stratified rocks many persons have concluded that the oceans were dominantly shallow, during the Paleozoic at least, and that only sub sequently did deepening take place . . . It is generally accepted that the dominant features of the present oceans were determined by the world-wide diastrophism of the Tertiary Ocean depressions are down-folds forming geosynclines and foredeeps. Pratje, 1928 Sea floor depressions are hollows left when the lands drifted apart; the banks and rises being continental fragments that have become detached during the westward drift. Taylor, 1910 Wegener, 1924 Glacial fluctuations of sea level were superimposed on a gradual lowering of sea level due to some cause, such as sinking of the bottom of the sea. Zeuner, 1945 Subsidence of vast areas in the Pacific and Indian Oceans is still con tinuing, to which the formation of the groups of atolls bear testimony. Hobbs, 1923 Excessive shrinkage of Earth took place during Pleistocene, resulting in subsidence of the ocean basins of 20,000 - 30,000 ft. Landes, 1952 U\ O O' Ancient land masses Lauiasia Baltic and Canadian shields are large domelike upwarps surrounded by marginal zones of subsidence. "The application of the turbidity current concept to ancient sediments may lessen the need for wide oscillations of sea level, large and rapid vertical movements, and huge hypothetical continental sources of sediment, such as Appalacia.” "When mountain chains after a course of 2,000 mi. end suddenly at a coast, it is obvious that the land has been cut short as when the grain of a piece of wood ends abruptly on the edge." He points as an example the Armorican Mtns. in France, and the corresponding structures in Devon and southwestern Ireland. "Appalachia" "Cascadia" "Llanoria" "Pearyyis” "Scandic" At present the Laurasian block (Paleozoic land mass) is divided into two parts by the Arctic and north Atlantic Oceans. Arguments that these oceans had not yet opened during early Mesozoic are from stratigraphical and facies resemblances between Dev. formations (many fresh water deposits) in Greenland, Norway, Scotland, and eastern United States. Carboniferous coal belts run through North America and Europe; they were together near the equator then. Identical hot climates in both continents are also suggested by late Paleozoic and Triassic evaporites. Caledonian and Hercynian fold belts are continuous from North America to Europe when Atlantic closed. Today belts end abruptly at both sides of ocean. Also Great Glen Fault of Scotland may be a continuation of Cabot Fault in America. Paleomagnetic data very definitely support thesis. Paleomagnetic data show blocks remained together until Cretaceous. Stille, 1955 Ewing, Ericson, and Heezen, 1958 Gregory, 1930 Barrell, 1914 Schuchert, 1917, 1924 DeGeer, 1919 du Toit, 1937 Carey, 1958 Wilson, 1962 Van Hilten, 1964 Bullard, 1964 507 Gondwanaland "Tasm antis" (Also called Melanesian plateau, and Australasia) Gondwanaland was a major Paleozoic land mass (South America, Africa, Madagascar, Antarctica, Australia and India). Late Paleozoic glaciation left traces (tilliies, striated pavements) on several continents; indicate movement of glaciers were from the present oceans land in-ward. Remarkable similarity of flora and fauna; in development of formations in different blocks; structural similarities; and "fir" of Africa and South America. Continents started breaking up in Mesozoic. Big problem is bow blocks fit together, i .e ., reassembled. Paleomagnetic data seem to confirm former continent, but need more data. Clarke, in 1878, suggested extension of east Australia had been lost by subsidence in to the Pacific. Schuchert pictured it as "the eastern half of the Australasian continent, a land about 1800 miles east and west, and 2200 miles north and south," and included New Zealand, Fiji, and Tonga. Sussmilch and David also thought of it as of considerable size and referred to it as "a separate land area . . . which existed to the east of Australian continent at least as far back as the beginning of the Devonian period and probably as far back as the beginning of the Palaeozoic era." They called it "Tasmantis" and thought it included part of Queensland and New South Wales - the New England plateau - originally belonged to this "lost land. ” Bryan stated that there is little direct evidence for or against such a land mass before the Mesozoic era, and "Quite clearly the minor topographic features of the land surface can be traced beneath the Pacific . . . But many major geographical features also appear to be truncated at the coastline and something far more important than a relatively small change in sea-level is indicated . . . Geologically the incompleteness of Australia is even more marked." New Caledonia is a remnant of a once continuous continent, the Melanesian plateau, which extended westward to east Australia and New Guinea and perhaps to New Zealand. Bryan concluded that (1) in Mesozoic era an east extension of Australian continent reached far into Pacific, (2) at end of era, various parts of Australasia ceased to exist. "A great Australasian continent existed immediately to the west of this Line [the Andesire or Marshall LineJ from as early as pre-Cambrian times and persisted throughout the du Toil, 1937 Carey, 195'8 Maack, 1960 Ahmad, 1960, 1961 Pflug, 1963 Bullard, 1964 Van Hilten, 1964 Sussmilch and David, 1919 Bryan, 1944 Ewing, 1952 Ahman, 1961 508 Paleozoic and Mesozoic eras.” All authorities (Bryan, Sussmilch, David, Walhom, Sdnicheit, d aik e, A ndrew *) believe that land man was down-faulted, but A fam an believes Antarctica is this "lost land" of Bryan and others. That is, the region drifted away and did not subside. Major land bridge existed in North Pacific "During the Quaternary Period, the face of the continents was changed. The area of the present-day continents is greater than it was in Tertiary times. Along with die increase in dry land area there was at certain points a submergence of land, which is still continuing today on the eastern rim of Asia. B ut in general the oceanic waters have today been concentrated into a smaller area than previously. Since the volume of water in the oceans can scarcely have diminished, we can only suppose that die depth of the oceanic depressions has somewhat increased....” Zeuner (1945) pointed out that it is otherwise simply impossible to explain the decrease in the height of the younger marine terraces of the Mediterranean. "Consequently there was, throughout the Quaternary, a general lowering of the world ocean level due to subsidence of the ocean floor." At the present time the mean height of the continents is estimated at 875 m; believe at beginning of the Quaternary height not more than 500 m. Some mountains rose 2 km during the Quaternary (Pamir and Tien Shan). In addition, subsidence occurred throughout die Neogene and Quaternary; locally amounting to 10 km. Thus, relief of Earth increased during Quaternary - the land rose and ocean floor subsided. "These changes constituted one of the chief processes of development of the Earth's surface - processes of irreversible development." The East African Rift Valleys ate associated with a huge elevation (East African Arch), which developed in a thickening of the terrestrial crust, its contraction in the direction of the slope of the Moho surface Dodson, 1952 Seward, 1931 Markov. 1962 Rybin, 1964 U l O vO (ie. perpendicular to the shore of the Indian Ocean), has brought about a westward expansion of the Indian Ocean. Collapse of the arch along fractures parallel the Indian Ocean. Other areas are believed to show such a collapse. (See discussion by Hope in translation for applications elsewhere.) Oceanic ridges generally have the following characteristics: associated with basaltic volcanism; peridotite xenoliths are the only foreign rocks; almost all are devoid of linear small-scale ridges parallel to their main axes, hence probably they are not folded rocks; fault scarps are common; high seismicity; usually there is some evidence that they stood higher with respect to sea level at some time in the past (e.g . apparent erosion surfaces on their tops, benches on their slopes or guyots); most rocks are dated as Quaternary but rarely Tertiary (none older than Tertiary); gravity profiles over ridges show no well-defined pattern. (Interpertation of isostatic gravity anomalies, except for huge anomalies in island arcs, has been uniquely unsuccessful.) It seems possible that the oceans were shallower and the crust thinner than now. If so, some features of the oldest rocks of Canada and Southern Rhodesia can be explained. If it is assumed that the continental and ocean sectors have always been in isostatic equilibrium as they appear to be today, then it follows that the depth to the Mohorovicic under continents has been directly related to sea-level. If the volume of water rose relatively, then it is likely that the subsequent deformation, erosion and isostatic adjustment would thicken the continental crust by just the right amount to bring it back to equilibrium with the water level. No conclusion can be drawn regarding the rate of increase of the volume of sea water by this criterion. If some other means of estimating the rate of transfer of water from the interior of the earth to the oceans in the past, then one could also estimate the thickness of continents (or vice versa). Certainly the oceans have grown. If they were shallower in the Archean, then the continents were much thinner. Hess, 1954 Hess, 1954 at M O Many areas show relative shifts - mainland of North Am. moves southward (eg. right lateral fault along San Andreas fault); Bartlett fault zone; western side of Japan moves southward relative to Pacific; Philippines move along major faults (continental side moves southward relative to Pacific side). General rotation of Pacific Basin. If we accept the drift hypothesis, the tectonic origin of submarine canyons cannot be directly rejected. If, however, we assume that a warping of the mainland has taken place simultaneously with the subsidence of the ocean basins, their genesis should be explained in quite a different way. The valleys previously cut into a gently sloping coastline may subside between the continents and the deeper basins, assuming an oblique position of the hinge-zone. General shifting of climatic zones between Paleozoic and the Tertiary had been assumed on Paleo -clim atic evidence 20 yrs before Paleo magnetic data became available. Paleomagnetic data corroborates this shift. Twenty years ago geophysicists apparently "killed" polar wandering and continental drift; today few geophysicists ignore the possibility of these. The melting of existing ice caps would add 20.2 million krr?of water to the sea and raise its level about 55-56 m. The bottom of the sea would sink isostatically under greater load of the water, as likewise the continents must rise when liberated from ice loads. When isostatic equilibrium was reached, the depression of the ocean parts of the earth's crust would have forced as much subcrustal "magma" out of its place as flowed under the lifted continents. The effect would be to d i m i n i s h by about 30" J o of the increased depth of the sea — the raising of sea level caused by the melting away of the continental ices (the density of the ice being 0 .9 vs. 3.0 for the "magma"). If Wegmann, 1948 Tanner, 1964 Wegmann, 1948 Lotze, 1938 Martin, 1961 Martin, 1961 Ramsay, 1930 Nansen, 1922 511 isostatic balance of Greenland and Antarctica are considered volume of adjusted would equal 30° ! o increase in depth: result sea level would rise 50-56 m. - Capacity of ocean basins was enlarged by diastrophism in connection with Alpine Orogeny and the sinking of the sea; the continents came to stand higher over the sea-level than before. Lowering of sea level allowed cutting of canyons. At the start of the Pleistocene, Fennoscandia, Precambrian areas etc. where glaciation occurred, were over-elevated on the continental shelves. Just such conditions caused Quaternary glaciation. Ramsay, 1330 The floor of the Atlantic shows the character of a subsiding land. Krenkel, 1325 Islands investigated in the main ocean basins have subsided at rates varying from 4 to over 50 m/10® yrs. Many islands have been uplifted but the amount of uplift is in general much less than the amount of subsidence. It is therefore easy to believe that uplift may be only a temporary and unusual state for islands. Tectonic disturbance seems to be the most likely cause of uplift. "The general conclusion that ocean islands sink except where recently uplifted by tectonic forces supports the view that the earth is not infinitely rigid, but capable of creep or flow. The pattern in the Pacific is like that of a thin plate with a tear in it which rests upon a viscous fluid. The plate represents the Pacific Ocean floor. Its extreme edges have been forced down and flow has caused the plate from 200 to 700 km inside those edges to rise...." Wilson, 1362 Atolls of Pacific Basin are grouped, concluded the entire SW Pacific sea floor had sunk. Menard agrees: area was first elevated then sunk. Darwin, 1896 Menard, 1358, 1964 Clastic sedimentation has depressed sea floor and this accounts for sinking of Guyots. (He thought they were Precambrian volcanoes.) Hess, 1964 L n M C O Volume of oceans increased by about 28fr during past 10& years; most of the water came from the mantle under ocean basins, and if sea level is taken as constant in order to maintain the freeboard of the continents, the sea floor would have sunk. Revelle, 1955 All dated horizons below sea level in the Pacific plot on a straight line when depth is plotted against age. Suggests eustatic change in sea level. Menard, 1964 Little of the terrestrial topography is older than Tertiary and most of it is no older than Pleistocene. (No rocks older than Cretaceous in ocean basins except where older rocks downfaulted or folded.) Ashley, 1931 Thombury, 1954 ( 5 1 3 Pacific Ocean Islands New Zealand Northeast of Aukland (Whangarea Harbor area) Submerged coast. Mukamuka Point (near Wellington) Results of earthquake of 23 Jan. 1855 — Uplifted nine feet while uplift in the town was only two feet. On the opposite side of Cook Strait submergence took place. Cook and Foveaux Straits Formed after the Glacial Period. Post Glacial elevation of approximately 5,000 feet during which time above straits were not laid bare. Proves that the depression was much more considerable than the elevation that followed. Same is shown by numerous fiords on the southwest coast of South Island. Lyttelton (Banks Peninsula) On east coast of South Island uplift of land in the last twenty years equals three feet. Auckland Harbor Reefs and banks formerly unnoticed have become more dangerous to shipping through uplift. North Island west coast Submerged forests north of New Plymouth. Both North and South Islands East coasts of islands undergoing slow upheaval whereas west coasts of islands undergoing slow subsidence. Near Wellington Shoreline fault scarp so recent that no wave-cut platform has been eroded at base of cliffs. Near Wellington Earthquake of 1855 Movement in the nature of a tilt with maximum uplift of nine feet. Thombuiy, 1954 Hocksterter, 1864 (txans. by F lem ing, 1959) Ibid Ibid Ibid Ibid Ibid Hinds. 1943 Cotton, 1955 514 North Island, Southwest Coast Port Nicholson East Coast of Marlborough Tasman Basin Port Nicholson Depression Marianas Arc "Melanesian Continent" "Melanesia”, East "Melanesian Subcontinent” At Tongue Point an emergence of 240 feet gentle seaward slope covered with layer of gravel and flattened shingle. Similar to materials composing existing beach. Another similar series of platforms. Faulted, uplifted coast— rejuvenation of topography, presence of an uplifted delta, residuals of a slightly elevated wave-cut platform, a long strip of strand plainly of recera origin. Subsided to a depth of about 2,650 fms. since Tertiary time and as a unified geomorphological feature il is of late or post-Tertiary origin. Northwest side of port formed by Wellington fault. Southeast side caused by subsidence; tilting and warping. Islands of arc have an essential uniform westward, northwestward tilting. Various angles of tilt recorded. Thought to be submerged continent. Submergence thought to be at close of Tertiary or at time of Laramide Revolution. Fault zone, on top of which formed the series of islands extending from New Zealand to Samoa; implies that a block must have foundered east of this area. Ever-increasing evidence of paleogeographic nature that these basins, at least in part, represent former semi-continental areas that have been recently fragmented and have suffered differential subsidence. Ibid Ibid Ibid Glaessner, 1952 Standard, 1961 Ibid Hobbs, 1944 Hess, 1948 Tayama, 1939, 1952 Chubb, 1934 Ladd, 1934 Umbgrove, 1947 Umbgrove, 1947 Fairbridge, 1961 515 Australia East Coast Cape Howe to Brisbane Seward directed monocline. King, 1962 New South Wales Heavy mineral assemblage indicate that in Permian-Triassic times sediments were derived from the east. Culey, 1938 Great Barrier Reef Downfaulting (block?) Steers, 1929 Seaward of Great Barrier Reef probably consists of downfaulted blocks. Steep seaward face probably a fault scarp. Jessen, 1943 From Cape Howe to Cooktown Fault-line coast. Strong downfaulting, Tertiary age. du Toit, 1937 Entire east coast Entire east coast of Australia shows physiographic evidence for relatively recent subsidence. Various drowned river valleys show subsidence of about 200 feet. (May be eustatic, ed.) Sussmilch, 1922 Coral Sea Floor known to have subsided in Recent geological time. King. 1962 Sunken fragment of Australia. Bryan, 1944 Breaksea Spit Breaksea Spit, north of Sandy Cape, has been referred to as a region of seafloor change, and being near the Queensland Coast, may bear upon evloution of Great Barrier Reef. Early navigators (including Cook) reported water of moderate depth. It was resurveyed in 1869 by the British Admiralty. In 1904, area 5-10 miles from Breaksea Spit had greatly altered in 34 years; from 20-30 fms to 200-300 fms. This change was attributed to scouring by currents because no earthquakes were noted in area. Change extended over more than a hundred sq.mi. In 1918, a strong earthquake was recorded nearby. In 1927, area resurveyed, and the conclusion was that the 100 fm isobath had been altered appreciably Bryan, 1936 or (-» O' between 1898 and 1904, and position was also noted between 1879 and 1898. In 1934, head of the Hydrographic Office seriously questioned navigational accuracy of surveys, hence validity of any real change in area. Biyan concludes alleged changes "not proven." East Australia South end of Great Barrier Reef has subsided 200 ft since post-glacial rise in sea level as determined by borings. Richards and Hill, 1942 Standard, 1961 Marginal Seas Hast Indies Submergence of shallow seas in East Indies are "either as a result of the post-glacial rise of sea-level or as a consequence of a real down- warp movement of the bottom, or a combination of both phenomena." There seems no doubt that in the deeper basins and troughs, submergence is the result of actual subsidence of the bottom, initiated in the not very distant past. Thick sequences of Tertiary nonvolcanic clastic sediments on most of the islands indicate that a land area must have "occupied the site of the present deep sea at the time when the sediments were deposited." Further evidence is furnished by atolls and barrier reefs. Umbgrove, 1947, 1949 Dry land extended considerably farther to sea off Indonesia. Many islands, seas, and straits formed in historic time. Beloussov, 1955 Hebrides Shelf Drowned plains of subaerial erosion. Panzer, 1928 Sunda Shelf Submerged, Pleistocene. Umbgrove, 1947 South China Sea Celebes Sea Bandu Sea Java Sea All are sunken blocks bounded by flexures or fractures. Formed in Tertiary. Kuenen, 1929-30 Yellow Sea Drowned plains of subaerial erosion. Lantensach, 1932 ^ M East China Sea Submerged. King, 1962 Shelf area between Gulf of Siam and Straits of Macassar Submerged recently. King, 1962 Internal seas of Indonesian Archipelago South China Sea East China Sea Sea of Japan Okhotsk Sea Bering Sea All formed as a result of crustal subsidence recently — no earlier than mid-Tertiary. Beloussov and Rudich, 1960 Sea of Japan Formed in Miocene. Beloussov, 1962 East China Sea Subsided in Pliocene or before. Lindberg, 1955 Hong Kong Pleistocene — submergence of possibly 500-600 ft greater than present. Characteristics: fiords and archipelagos. Recent— Uplift in stages. Characteristics: rock terraces and hanging valleys. Very Recent— Estimated relative rise of coastline is one foot in 200 years. (May be eustatic, ed.) Davis (undated) Celebes Sea In central depression numerous faults and local downwarpings at about 2,600 fms. Downdrop is approximately 73 fms. Krause, 1964e Sulu Sea Sulu Sea floor (2,700 fms) shows evidence of faults and monoclinal warps. Ibid l-» 00 Philippean Islands Hueh Cum inc found three living specimens of mollusk Conus gloriamaris in 1838 on a reef. Several weeks later, all traces of the reef vanished in an earthquake and tsunamis. No specimens of this mollusk have been found; a total of 25 specimens exist in world. An, 1965 Philippean Trench Thrust and cross faults. Marova, 1963 Kawio Strait Bottom photographs from 500-672 fms revealed well-rounded conglomerate. Strait sunk at least 600 fms in Recent or late Pleistocene time. Krause, 1964e Mindanao Faults and downwarps are common. Ibid Japan Enoshima Island Coast of emergence— uplifted at time of 1933 earthquake. Three distinct disturbances 1. Formation of sedimentary basins in earliest Miocene 2. Geanticlinal uplift in Latest Miocene 3. General uplift in late Pliocene. Shepard, 1963 Sato, Unpubl. (See text) Sea of Japan Sagami Bay is a fault trough 800 fms deep. Shepard, 1963 Modem geosyncline. Klenova and Gershanovich, 1951 During the Cretaceous as well as Jurassic time there was dry land in place of Sea of Japan (a major source area of clastic sediments). Intense subsidence began to take place only at the beginning of the Neogene. Subsidence accompanied by intense vulcanism. Since old land of Sea of Japan had continental (granitic) crust until relatively recently, and now has oceanic type crust; terrestrial crust must have been transformed. Andreyeva and Udintsev, 1958 Sysoyev et al, 1958 Kuno, 1959 Beloussov and Rndich, 1960 Mean shelf break is 146 m, minimum 97 m, max. 248 m. Warping and subsidence indicated. Kanayev, 1963 K v O Sakhalin Island Sea of Okhotsk ________________ I ----------------------------------------------------------------------- Downwarp; part of the Sea of Japan geosyncline as shown by south Sakhalin; west coast. Shelf break is 149 m on west and 164 m on east. Tilting and sub sidence of bordering Deriugin Depression in Okhotsk Sea. Within boundaries of Sea of Okhotsk the borders of the continent of Asia are platform-like structure. This is a fragment of the Mesozoic plate, fractured by movements during the Tertiary into separate blocks. One of these blocks, surrounded by Tertiary mountain structure of Sakhalin and Kamchatka, is found to have been depressed to about 1,200 m in the central part of the Sea of Okhotsk. Two large elevations occur on its surface, with peaks at 893 and 932 m. Tops are flat and dissected by submarine valleys — considered to be subaerially cut then submerged. Sakhalin and Hokkaido Islands and Kamchatka Peninsula were elevated in connection with Tertiary folding. Between these elevations is region not touched by folding; it was a platform, but was fractured and under went oscillatory movements. This was the central platform of Okhotsk Sea. Southern part is a Quaternary geosyncline. Formation of con temporary geosynclineal zone of Okhotsk Sea evidently belongs to the Tertiary period or earlier. Much of bottom relief is inherited (relic), e .g ., "submarine rolls, terraces on the slopes of the submarine base of Sakhalin and Kamchatka. Lindberg postulated that certain areas in the past were connected by direct contact of rivers of the basin of the Okhotsk Sea in the period when there was land now occuplied by Okhotsk Sea. A similar conclusion was reached by Vasiliev on endemic types of plants. Both believe that dislocation of the areas took place as a result of sinking of ancient land. During the Paleozoic and Mesozoic either a dry land or shallow sea. During the Upper Cretaceous outskirts of the platform were covered by an epicontinental sea. Region was undergoing erosion during Paleogene. Klenova and Gershanovich, 1951 Lavrov, 1960 Kanayev, 1963 Chemekov, 1957 Zatonsky, Kanaev, and Uditsev, 1961 Vasiliev, 1939 Lindberg, 1946, 1952 Udintsev, 1955 Ushakov, 1950 Udintsev, 1957a, 1957b Beloussov and Rudich, 1960 Q c£ Udintsev dates the appearance of the Sea of Okhotsk as Quaternary. Ushakov found convincing signs of extreme youth of deep troughs of Sea of Okhotsk. Sea basin was formed during the Quaternary; its formation began in late Pliocene or in early Quaternary. Major fault between Okhotsk and Kurile Arc; sea in central part next to arch is subsiding rapidly. Ushakov, 1950 Udintsev, 1955 Lindberg, 1956 Goryachev, 1960 Mean shelf break is 149 m; min. 95 m; max. 349 m. Great mean depth in northern part of Okhotsk Sea is connected with subsidence here of extensive part of sea floor. Many depressed underseas surfaces of abrasional-accumulation planation. Udintsev, 1957 Kanayev, 1963 A typical geosyncline in its southern part; platform in northern part. Klenova, 1960 Russia East Coast Great Kurile Range 3 major zones: (1) Southern zone — from Hokkaido to Urup Island, most rapidly rising zone; (2) Central zone— from Urup Island to Severigin Peak most rapidly subsiding zone; (3) Northern zone — from Severigin Peak to Kamchatka, most rapidly rising zone. Beloussov and Rudich, 1960 Gorychev, 1962 Kurile Island Ridge Mean depth of shelf break of entire ridge is 143 m; for Greater Kurile Ridge mean shelf break is 143 m, for Lesser Kurile Ridge 164 m. Difference in depth of northwest and southwest shelf breaks for Greater Kurile arc is 20 m; for Lesser Kurile Arc 87 m. Along inner side (Okhotsk Sea) of Greater Kurile Arc, shelf break is about same depth, while oceanic (trench) side shelf break decrease in the central sector compared with north and south islands (suggests that opposite the gap in the outer — "Vitiaz" — ridge, the shelf on the inner ridge is less tilted, because not as much loading on the sea floor by the outer volcanic ridge). Most depressed on shelf edges of islands which share a common founda tion with the outer ridge. Kanayev, 1963 to r to M - Formed in Quaternary. Okhotsk Sea and Pacific Ocean contain identical deep water fauna. Ocean water recently invaded Okhotsk Sea from Pacific through Kurile St. Large faults bound the Kurile Range forming a large horst of Kurile Arc. Arc is subsiding in central part. Ushakov, 1950 Udintsev, 1955 Shelf break is 133 m on northwest side and 153 m on southeast side, reflecting a subsidence and tilting of shelf, due to deepening of the Kurile-Kamchatka Trench. Kanayev, 1963 Kurile-Kamchatka Arc Entire Kurile-Kamchatka Trench represents geosynclinal downbowing. Middle part of Vityaz Ridge is considerably depressed; consists of a series of steps; it is assumed that deformation of these surfaces was due to differential vertical movements. Zatonsky, Kanaev, and Udintsev, 1961 Vityaz Ridge Outer Ridge (Vityaz Ridge) shows a marked increase in depth on the sea ward side compared to inner edge. In southern sector of the outer ridge a considerable subsidence of the planed off surface is noted, viz. 1,220 m. The sunken parts of the planed off surface are separated from one another by scarps, evidence of differential block movements in part of the ridge. Kanayev, 1963 Kamchatka Peninsula Shelf break is 133 m on west and 145 m on east. Tilting and subsidence due to deepening of Kurile-Kamchatka Trench. Evidence of subsidence at south tip of Kamchatka. On east Kamchatka also uplift and stable shelf. Kanayev and Larina, 1959 Kanayev, 1963 Kamchatka (S) and Paramushir Is. Shelf edge shows considerable downwarping and deepening; result of tectonic deformation. Kanaev and Larina, 1959 Kron^ki and Kamchatka Gulfs Evidence of subsidence in middle parts of the gulfs; shelf edge fluctuates as much as 87 m in Karaginski Gulf. Kanayev, 1959 Boichenko, 1961 Il'vin, 1961 Kanayev, 1963 0J w North America United States South Coast of Alaska Aleutian Arc area Sunken or depressed foreland, apparently due to the stupendous weight and pressure of the adjacent ranges. This, and other arcs, are overthrust upon the ocean floor, and the troughs are probably due in part to plastic yielding and perhaps in part also to plastic flow. Taylor, 1910 Near Rat Islands - - Early to mid-Tertiary time, uplift, erosion, much faulting, some folding. Gates and Gibson, 1956 Bearing Sea General Region of recent intensive subsidence. Berzukiv and Udintsev, 1953 - 1955 Mean shelf break is 167 m; min. 97 m; max. 379 m. Differential movements. Kanayev, 1963 Depression in west Bering Sea formed relatively recently. Beloussov and Rudich, 1960 Late Tertiary volcanic activity. Normal faulting to present. Bower’s Bank and Basin -- Major reverse fault block formed in Late Cretaceous or early Tertiary time. Nichols, Perry and Kofoed, 1964 Bogoslof Island Submergence since Pleistocene. Smith, 1937 South Alaska Yakutat Bay to Cross Sound -- Regional upwarping in Plio-Pleistocene. Recent submergence. Peacock, 1935 Prince William Sound Area -- Subsidence and emergence in historical time (1964 earthquake). USC & GS Prelim Rept. 1964 J* C O C O Prince Henry Sound - - Subsidence. Tan and Martin, 1906 Pamplona Rock -- Subsidence in historical time of 120 m. Jordan, 1958 Valdez Area -- Subsidence of harbor from 10 to 40 meters after 1964 Prince William Sound earthquake. USC & GS Prelim Rept. 1964 Several parts of west and northwest coasts are believed to be of fault origin. West, 1951 Offshore tectonics from 1964 Alaskan earthquake were of greater magni tude offshore than onshore. An area southwest of Montague Island uplifted S O ft. Malloy, 1964 In 1899, vertical movement along fault near Lituya Bay was 47 ft; in 1958 it was 5 ft. vertically (on seaward side) and 20 ft. right lateral. Jordan, 1959 West Coast British Columbia Fiord land, fractured and uplifted before Glacial Epoch, regional subsidence, glaciation. Peacock, 1935 British Columbia and Alaska Submergence. I Lees. 1953 Oregon, Washington, British Columbia Land mass existed to west of coast at die beginning of the Tertiary and only recently disappeared. Snavely and Wagner, 1963; Taliaffero, 1943 Washington - Oregon Early Eocene — Eugeogyncline. Middle Eocene — Major uplift south of the geosyncline. Late Eocene — Local uplift divided basin into separate basins. Oligocene — Regional uplift south part of geosyncline. Regional subsidence north part of geosyncline. Early Miocene— Deposition. Middle Miocene— Folding and faulting along northeast structural trends. Late Miocene— Sedimentation and downwarping were equal. Source area was mountainous region now west of coastline. Snavely and Wagner, 1963 L a to Oregon Central-fault and fold structures exist on both continental shelf and slope. South of Coos Bay -- Escarpment from Coos Bay to Mendocino Escarpment. Byme, 1962 Oregon and California "The Francescan-Knoxville sequence accumulated in a geosyncline that came into existence as a result of the Nevadian orogeny. . . As the ancestral Siena Nevada emerged, along broad trough was formed at the site of the present Coast Ranges was flooded for the first time in the Mesozoic. At the same time a high rugged land mass came into being, or an already existent land mass was greatly uplifted west of the present coast lin e." Sedimentological and seismic evidence lend support to this assumed land mass. Taliaffero, 1943 California From San Francisco to Cedros Island, Baja California continental slope is major fracture zone of earth's crust. This transition from sialic continental plateau to the more mafic ocean basin is abrupt. Structural discontinuity near base of continental slope is shown by geophysical measurements. Faulting. Instability of this coast. Udhupi and Emery, 1963 Southern California Continental borderland, ridge and basin (horst and graben), faulting, broad downwarp of submerged margin in pre-Pleistocene time. Emery, 1954 Faulting in basins. Shepard and Emery, 1941 Emery, 1960 Emergent coast in Ventura area. Putnam, 1937 Entire northeast coast of San Clemente Island is fault scarp. Shepard, 1963 Rodriquez Seamount - - Subsidence of cone essentially complete by Pleistocene time. Palmer, 1964 Ul D O Ul West coast of Santa Cruz Island is fault controlled. Guilcher, 1958 Correlation of Davis Seaknoll with nearby Rodriquez Seamount suggests that the outer Arguello Plateau was a bank prior to subsidence which began in pre-late Miocene time; may be as recent as pre-late Pleistocene. Plamer (unpubl.) Cores and dredges off southern California borderland suggest landmass to the west of many of the basins during Eocene time. Unpubl. data (RDT) Depths of shelf breaks indicate warping to southwest. Emery, 1958 Mexico Baja California Borderland Faulting is widespread in borderland including along the seaward margin of the borderland. The province consists of basins and ridges consists of (1) a fault zone trending from Islas Los Coronados to Bahia Todos Santos, (2) SE - NS faulting, especially a trend toward San Clemente Island., (3) the Santo Tomas fault zone - trending W SW across the borderland from Bahia Soledad, (4) several E-W fault zones, (5) faulting along the seaward margin of the borderland, (6) very large magnetic anomalies associated with present coast line, (7) N-S geomagnetic anomalies in the deep-sea crust, (8) much* minor faulting, and (9) broad folding of the borderland. Seismicity associated only with numbers 1 to 3. Krause, 1964a East and west coasts of Gulf of California Origin by faulting. Peninsular side, steep scarps. Initiation of Gulf trough in Mesozoic. Related to San Andreas fault. Intrusion of peninsular batholith during mid-Cretaceous. Peninsula elevated in mid- Miocene. Subsidence of the Gulf and uplift of peninsula. Formation of fault blocks. Region still in formative stage. Byrne and Emery, 1960 Both coasts fault controlled. Guilcher, 1958 Fault trough coast. Shepard, 1963 C S J O' 526 Continental rift scar (the slope left after the rifting apart of the continental block). Dietz, 1964 Theories proposed for origin of Gulf: (1) Down-faulting of an elongate block which once joined Baja California directly with the Mexican mainland; (2) Emergence of the peninsula of Baja California at some distance from what was at one time the continental margin, leaving the Gulf as an oceanic area in between; (3) Strike-slip movement of great magnitude along one or more fault systems, such as the San Andreas to produce a sliver of land almost completely separated from the mainland; (4) Cross-strike movement of Baja California from the Mexican main land and flooding of the resulting gap. Allison, 1964 Hamilton, 1961 Phillips, 1964 Harrison and Mathur, 1964 Byrne and Emery, 1960 Shepard, 1950 Graben or half-graben shown not true on basis of geophysical evidence. Allison, 1964; Phillips, 1964; Harrison and Mathur, 1964 Hypothesis No. 2 (above) lacks geological evidence; No. 3 not supported if strike-slip movement occurred later than the earliest Mesozoic. Allison, 1964 Gulf formed by Baja California moving by right-lateral movement on several en echelon strike-slip faults. Concurrently, entire lower half of the Peninsula swung gradually westward. Gulf formed by open break in crust. Rusnak et al, 1964 Gulf formed in late Miocene time. Wilson, 1949 Pattern of submarine canyons indicate that the valleys are old, deeply submerged stream valleys (to 500-600 fms) modified by marine processes, especially as they sank below sea level. Recovered shallow water shells indicates submergence. Shepard, 1964 In the central, east section, faults appear paralleled to the coast. Harrison and Mathur, 1964 to Mid-Atlantic Ridge enters Indian Ocean and Pacific Ocean. One branch goes into Red Sea and another ends near the Gulf of California. In both areas tensional cracks allowed denser material to well up. Bullard, 1962 Rusnak and Fisher, 1964 West Cbast Mainland from Mazatlan to southern border Coasts of Jalisco, Colima, Michoacan, Guerro and Oaxaco -- Miocene to Recent volcanics. Folded and faulted Paleozoic, Mesozoic, and Cenozoic sedimentary and metamorphic rocks and granites largely of Cretaceous age. Schudiert, 1935 Ishthmus of Tehuantepec Downfaulted during late Pliocene and Pleistocene to its present low elevation. Webber and Ojeda, 1956 Southeast of Chiapas to southern Mexican border Late Cenozoic to recent andesitic volcanoes have buried the west ends of east-trending mountain ranges of folded and faulted upper Paleozoic age rocks. Schucheit, 1935 Guatamala - El Salvador - Nicaragua West Coast From southern Mexican border to Lake Nicaragua - - same as immediately above. Ibid Central America Tres Marias Islas to Panama A marginal reverse fault complex dips eastward beneath the continent. Benioff, 1954 Gulf of Tehuantepec Deep shelf breaks and terraces on the continental slope suggest down- warped or downfaulted shelf. Faulting of probable Late Miocene age on land; may be related to offshore area. Fisher, 1961 Webber and Ojeda, 1956 General Shear faults resulting from horizontal compression would be localized at continental margins and that with continuing compression the higher Gunn, 1941 Ul C O 00 continental mass would overthrust the ocean basin and simultaneously form a linear deep at the toe of the overriding block and a line of volcanoes, parallel to the deep, 50-90 km inland from the continental margin. During the Mesozoic large land masses existed in the Pacific Ocean, west of Cordilleras and the Andes and in the present-day Caribbean. Eardley, 1951 South America A large land mass of unknown dimensions has undoubtedly sunk into the Pacific Ocean. Gerth reported that a long stretch of mountain-chains foundered near Payta. Umbgrove, 1947 Gerth, 1939 Columbia West Coast Panama to Ecuador Columbian Andes -- Late Triassic to end of Jurassic uplift and erosion. Beginning of Cretaceous to end of Cretaceous, subsidence. After Cretaceous uplift and folding. Beloussov, 1962 Peru * West Coast Northwest coast Faulting. Iddings and Olsson, 1928 Peru - Northern Chile Subsidence and deposition in late Triassic to end of Jurassic. Beginning of Cretaceous, uplift eastward overturning of folding. Beloussov, 1962 West Coast Peru - Chile Andrean batholith emplaced in late Cretaceous - early Cretaceous time; uplift and block faulting throughout region in early to mid-Tertiary time. Extensive vulcanism started in Miocene and continued with associated faulting, over most of region until present. Present day tectonic activity indicated by visible coastal fault scarps, trench, recent vulcanism and frequent strong earthquakes. Munoz Cristi, 1956 Oppenheim, 1947 Jenks, 1956 Fisher and Raitt, 1962 South of 26° S, the upper slopes may be related to recent faulting and uplift in the area near Valparaiso and Central Chile, rough trench topo graphy may be due to more intense tectonic activity seaward of the axis. Fisher and Raitt, 1962 Ul D O Southern Chile Same as Panama to Ecuador Beloussov, 1962 Peru-Chile (Trench area) History of area: (1) Emplacement of Andean batholith in late Cretaceous - early Tertiary time. (2) Uplift and block faulting through out region in early to mid-Tertiary time. (3) Extensive vulcanism began in Miocene and continued with associated faulting over most of the region until the present time. Fisher and Raitt, 1962 General Primary (structural) coast. Flank of an accretionary folded belt or orogen (usually a collapsed continental rise prism.) Steep declivity. Dietz, 1964 From Lima, Peru to tip of South America Coasts have been continuously, recently and synchronously upraised for a length of 2480 miles. Evidence, paleontological, 1300 ft elevation at Valparaiso. All this took place within period of existing mollusca and cirripedes. Elevation at Valparaiso partly attributed to earthquake of 1822. At Chiloe elevation is gradual and equals approximately four ft in four yrs. Many correlative terraces along coast. Darwin, 1846 Island Hawaii General Crustal depression caused by a great load of volcanics. Dominant move ment is submergence, emergence due in part to eustatic changes. Dietz and Menard, 1953 Dietz (in Hamilton, 1957) Ul U > o Atlantic Ocean General Gregory presented a lengthy summary on the history of the Atlamic Ocean using paleogeography and paleontology. He indicated that major land bridges existed. Main subsidence of the Atlantic began in the Cretaceous and was completed in the Miocene. Subsidence corresponded to upbuilding of the mountains of the Alpine system and Western America. Lt. A. Sainthill, on 3 Aug. 1832, at 42° 37' N, 41° 45' W found rocky bottom at 100 fms and reported discolored water, probably from a sub marine volcano. In 1858, no bottom was found at 3000 fms 30 mi away at 42° V N, 41° 28' W. In 1864, A. Milne reported a bank at 81-92 fms between 42° to 45° N, and 35° to 42° W. In 1868, HMS GANNET found no bottom at 4,300 fms at Sainthill's position, or at 2,280 fms on Milne’s Bank. Soundings to 3,000 and 4,300 fms were made without reaching bottom. This only proves the unreliability of the soundings, it does not disprove of Sainthill and Milne Banks. Milne Bank appears to be confirmed and in 1921, was reentered on Admiralty chart No. 2127, at 43° 47' N, 38° 42' W, after USS INNACO found bottom at 63 and 73 fms. Distribution of depressions corresponds to sunken lands and uplands of the adjacent continents. The plan of the ridges is that of a lattice, with intervening depressions. "Main role in the formation of the bottom topography of the Atlantic Ocean belongs to the earth’s internal forces. . . The complex relief of the ocean floor has, evidently, been formed over very prolonged geo logical time. Many of the topographical forms were rejuvenated in Cainozoic time. The process of rejuvenation of the submarine relief is continuing at present too. A less significant role in the formation of the bottom relief belongs to exogenic factors: sedimentation, bottom currents, mud flows, and slides." Floor of Atlantic Ocean has been dry land in the past. Gregory, 1929 Krenkel, 1925 Grabovskii, Greku, and Metalnikov, 1961 Wills, 1951 cn co "... between the end of the Paleozoic and late Triassic time the possible forerunner of the present North American Basin of the Atlantic deepened and widened very greatly. " Daly, 1951 Seismic investigation along a line extending 170 mi. W SW from Lizard. Presence of submerged block probably consisting of igneous rock covered by Triassic strata. Bullard and Gaskell, 1938 Umbgrove, 1947 Appalachia Land mass extended at least 200 mi. beyond the east coast of North America and now lies submerged to a depth of at least 3000 to 4000 m. Began to founder in Triassic and continued until at least Tertiary. Barrell, 1914 Schuchert, 1935 Umbgrove, 1947 Gilluly, 1964 Ewing, Crary, Rutherford, and Miller, 1937 South America General During Devonian dry land existed to east of coast of South America in present-day Atlantic. Symposium . . . on Gondwana, 1952 Argentina East Ooast Rio Plata River to tip of South America Slow gradual elevation of the 1180 mi coast. Have been at least eight periods of denudation. Land up to a height of from 950 to 1200 ft has been worked by the sea. Evidence -- Correlative terraces and paleontologic evidence all along coast. Darwin, 1846 Brazil East Coast Rio Grande del Sul Coast Basic rock is Precambrian shield plus sediments to Quanternary age. Gondwana sediments deposited on ancient crystalline rocks unconformably. Gondwana sediments are capped by basalt flows believed to be largest in world (Baker) totalling 3300 ft (Triassic or Jurassic). Between Jurassic Baker, 1923 Delaney, 1962 Ul U > D O and Cretaceous enormous faulting occurred, at which time assumed Gondwana of South America and South Africa supposedly separated. Present day scarp in coastal plain is 1000 m higher than coastal plain. Faulting has continued into Recent. Recent faults parallel the coastline, and all are down-to-the-coast variety, tilted slightly landward. Recent epeirogenic uplift of the coastal plain. Leinz, 1948 Garvalho, 1933 Argentina - Brazil East Coast Rio Plata to Amazon River Fault-line coast. du Toit, 1937 Surinam - British Guiana Fault-line coast. du Toit, 1937 Panama East Coast Ishthmus area Emergence at end of Oligocene. King, 1962 Campeche Bank North and west sides are bounded by faults up to 8000 ft long. Gealy, 1955 Campeche Bay Fault controlled. Cr eager, 1953 Price, 1951 Weaver, 1950 Tamayo, 1949 Yucatan Peninsula Fault controlled. Tamayo, 1949 Creager, 1953 Weaver, 1950 Csema et al, 1961 Hoskin, 1963 Price, 1951 Eardley, 1954 o j L ynch. 1954 00 Mexico - British Honduras Boundary Yucatan area Bartlett Trough Evidence inconclusive as to whether Campeche Bank is bounded by scarps and of tectonic origin, or is the product of calcareous deposition on buried volcanoes. If gulf is stationary and >10,000 ft of calcareous sediment has accumulated, platform must have undergone subsidence of this order, and marginal depressions would be expected. None found. Lower continental slope is less steep than upper slope. Faulting and sedimentation have controlled the continental slope features. Possible faulting of continental margin. Carbonate upbuilt coast (atoll-like). Marked offshore orientation of surface and subsurface features. Offshore lineations are superficial expression of major submarine topographic features on a greater scale than on adjacent coastlands. Three platforms: shelf, "upper platform" (400 fms), and "lower platform" (1000 fms). Escarpments form part of tectonic system. Atolls and crest of barrier reef are associated with scarps and platforms. Steep scarps attributed to faulting; unlikely that escarpments are con structional reef forms (Stoddart, 1962). Faulting may have occurred in Pliocene, continuing into Pleistocene. Only evidence of faults is existence of reefs themselves. Fault controlled. Trench extends for > 1000 miles. Maximum depth of trough is about 7000 m. Northern rim of trough can be traced in the faulted Sierra Maestra of southern Cuba, through Cayman and Misteriosa Gealy, 1955 Lyons, 1957 Moody, 1950 Stetson, 1951 Creager, 1958 Alvarez, 1954 Dietz, 1964 Stoddart, 1960, 1962 Ower, 1928 Edwards, 1957 Vermeer, 1959 Stoddart, 1962 Taber. 1922, 1931, 1934 Matley, 1926 534 Banks, and probably into Maya Mountains of southern British Honduras. Southern rim of trough is formed by island of Jamaica, the Pedro, Rosalind and Nicaraguan Banks, and the mountains of the Republic of Honduras. Walper, 1960 Dixon, 1956 Schuchert, 1935 Agassiz, 1894 Appears to pass westward into Lake Izabal - Rio Dulce lowlands of Guatamala, and Walper says fracture zone followed into the Alta Verapaz. Movement was initiated along Bartlett axis in pre-Cretaceous times, but maximum dislocation occurred in late Tertiary, probably reading maxi mum in Pliocene (Dixon and Schuchert). Extensive uplifted terraces of Plio-Pleistocene age indicate great movement. Major zone of wrench - or trans-current-faulting, along which con siderable lateral movement has occurred. Moody and Hill, 1956 Hess and Maxwell, 1953 West Indies (Antilles) Tuiks Island (west side) Complete absence of sloping shelf; faulting suggested. Several contour lines were mn and showed perpendicular to overhanging coast. Peake (in Gardiner, 1914) Cuba South Coast Entire south coast Faulting. King, 1962 Strike-slip faulting. Hess and Maxwell, 1963 Haiti - Dominican Republic South Coast Entire south coast Strike-slip faulting. Ibid i Netherlands Antilles Islands of Aruba, Bonaire, Curacao Uplift - wave-cut marine terraces - Pleistocene. Simultaneous change in sea level and rise of the land. Ibid oj Ul Jamaica AH coasts Quaternary to Recent uplift where beaches have been reported at various levels up to 600 m. du Toit, 1937 Port Royal Submergence as effect of earthquake in 1692. Deacon, 1962 Puerto Rico North Coast Puerto Rican Trench area Sinking of the crust. Belussov and Rudich, 1960 Virgin Is. Platform Edge of platform shows very high amplitude magnetic anomalies on both sides. Anomaly on southern side is attributed to a fault of late Cenozoic age (Schuchert, p. 474). Anomaly on northern side is related to fault described by Butterlin. Schuchert, 1935 Butterlin, 1956 Bracey and Avery, 1963 Gulf of Mexico General Faulting accounts for major surface and subsurface features. Gealy, 1955; Kidd, 1939; Pool, 1940; Storm, 1945; Sheets, 1947; Treadwell, 1949; Fisk, 1944; Shepard, 1948; Pressler, 1947; Jordan and Stewart, 1959, 1961; Weaver, Carsey, Stetson (in Jordan, 1951); Stetson, 1953; Kofoed and Jordan, 1964 Flexure coast. Continental margin warping, subsidence since Cretaceous. Hill, 1963 Ul G O O ' A subsiding geosyncline. Barton et al, 1933: Russell, 1936; Lawson, 1942; Storm, 1945; Glaessner and Teichert, 1947; Beloussov, 1962 "The areal distribution of Citronelle fm. yields suggestive evidence that an extensive and perhaps profound subsidence of the northern portion of the Gulf of Mexico occurred in latest Pliocene or earliest Pleistocene tim e." Moody, 1950 Texas, Louisiana coast is a continental embankment (uplapped continental rise in turn covered by pro-delta beds). Deitz, 1964 Tectonically quiescent. King,' 1962 Flexure and faulting. Dietz, 1952 Flexures. lessen, 1943 Subsidence since Cretaceous. Beloussov, 1960 Crustal instability. King, 1962 The Gulf of Mexico is not a permanent oceanic feature, but it has been downfaulted to its present site by peripheral faults, such as West Florida Escarpment and escarpment off Yucatan. Moody, 1950 Weaver, 1950 Stetson, 1951 Eardley, 1954 Suggested vertical faulting of 5,000 to 10,000 ft on major scarps during the last 10,000 to 20,000 yrs. (Ewing et al, 1958, do not agree). Greenman and LeBlanc, 1956; Ewing, Ericson and Heezen, 1958 Ul O J Gulf is typical oceanic structure, modified by the accumulation of 7 km of sediments. Downfaulting did not occur. Ewing, Worzel, Erickson and Heezen, 1955 Faulting and downthrown towards Sigsbee Deep. Gealy, 1955 Sigsbee Escarpment appears to be surface expression of a fault or a sharp flexure. Ewing, 1960 Scarps coincide with buried volcanoes around which calcareous material accumulated (West Florida and Campeche Banks). No linear anomalies could be found which might be associated with a large normal fault in basement rock. Miller and Ewing, 1956 "In the northwestern Gulf of Mexico, reflection records show conclusively that, at least as far back as the Late Tertiary, the structure is formed by simple sedimentary upbuilding and outbuilding with accompanying subsidence." Moore and Curray, 1963a, 1964 Magnetic contour interval of Miller and Ewing (1956) was 100 gammas, yet instrument error was about 350 gammas. Hence, contouring and conclusions of Miller and Ewing suspect. Creager, 1958 "The Gulf is well out of isostatic equilibrium and that additional loading of sediments in the future will cause it to founder more Lyons, 1957 Subsidence has been going on since the Cretaceous, and the aggregate thickness of post-Oligocene deposits is about 62, 000 ft in southern Louisiana. Crouch, 1959 Evidence of subsidence is widespread in the coastal region. Fisk, 1939 Welder, 1959 Gulf was formed by the collapse of the foreland of the Antillean Cordillera and that outline has not been influenced by mountain folds. Suess, 1888 (ji CO 00 In Paleozoic large land (Llanoria) mass existed in Gulf of Mexico area. Eardley, 1951 Land mass existed during Jurassic and Cretaceous furnished clastic sedi ments. Land mass low-lying, partially submerged in the NW during Jurassic and regionally submerged during the Cretaceous. Volcanism centers in Cretaceous were east of Puerto Rico. Meyerhoff, 1954 , * Eastern Carribbean Basin believed due to middle and late Tertiary sub sidence. Western Caribbean Basin believed due to Cretaceous and early Tertiary subsidence. Gulf of Mexico postulated to have started subsiding in Permian time. Eardley, 1954 Major structure in Greater Antilles result of fragmentation by a series of E-W trending strike-slip faults of great displacement. Hess and Maxwell, 1963 United States Florida West Coast Steep escarpments due to reef growth (includes Bahamas area etc.) Newell and Rigby, 1957; Newell, 1959 Carbonate up-building (atoll-like). Dietz, 1964 Western Straits of Florida Escarpments interpreted as fault origin. Area of undulating bottom interpreted as a set of step-faults related to the larger Pourtales Escarpment. Jordan and Stewart, 1961 An extension of the Gulf of Mexico Basin formed the South Florida Embayment as early as the Jurassic. This embayment trends NW between Cuba and the Bahamas, Cuba and Florida. Pressler, 1947 This embayment is more localized but the axis of this basin does trend E-W. Jordan, Malloy, and Kofoed, 1964 L n w v O Narrow shelf east of Floridian Peninsular Arch and gradually descent to the 100 fm isobath to the west was interpreted as due to a western tilting of the continental shelf, but evidence is inconclusive. Leverett, 1931; Cooke, 1945; Jordan, Malloy and Kofoed, 1964 Clear evidence of such a fault zone is lacking. The only suggestion of such a fault may be a depression at the base of the slope off Miami and this feature is discontinuous. . . "There is no surviving evidence of a fault trace on the Bahama side of the Straits of Florida." Authors evidently prefer Newell's (1955) theory of subsidence, and the Straits are regions of less active deposition. Hurley et al, 1962 Hurley, 1964 Sink holes; karst topography considerably below sea level indicates sub sidence in Straits of Florida. Jordan, 1954; Jordan and Stewart, 1961; Jordan, Malloy and Kofoed, 1964 Pourtales Terrace is a downwarped segment of the continental shelf, partly faulted. Jordan, Malloy and Kofoed, 1964 Fault control for Pourtales Terrace. Pressler, 1947 Graben area; probably pre-Cretaceous, Florida Keys to Cuba. Siegler, 1959, 1961 Bahama Platform Bahamas composed of horizontal strata as fragments of Mexico-Florida plate. Suess, 1885 (1904-5) The Bahamas are all of dune origin. Agassiz, 1894 (in Lee, 1S51) The Bahamas may be the remnants fold volcanic piles. Hill (in Lee, 1951) dear example of reefs growing on a platform built up of foreign material. Grabau, 1912 (in Lee, 1951) Ul A o Bahama Ridge is composed of series of West Indian Cretaceous folds. . . worn down. . . covered with a veneer of calcareous sand. Woodring, 1928 (in Lee, 1951) Bahamas Negative isostatic anomalies are supposed to indicate that Bahamas are not underlain by igneous rocks; the large majority of the islands stations of this type in the world give positive anomalies, most are formed by igneous rocks. He considers "there seems to be good evidence that the Bahama Bank and the surrounding area are in isostatic equilibrium to a marked degree and that the anomalies at several stations are probably due to abnormally light material close to the stations." Field, 1931 Agrees with Field, region not immediately underlain by igneous rocks, but rather that there is a great thickness of light sediments. Hess, 1936 Bahamas are a great thickness of light sediments. . . features interpreted as river valleys. Hess, 1933 (see 1959) The older, the northern part of the Bahamas, belongs to the Cuban fore land . The younger southeastern part of the archipelago grew up as a slightly crescentric Bahamian volcanic arc. Essentially unfolded. Schuchert, 1934 Tongue of the Ocean (TOTO) Andros Island once faced the open Atlantic, and later the suspected volcanic eastern portion of the Great Bahama Bank grew up in front of Andros leaving TOTO (Tongue of the Ocean) between. Schuchert, 1935 Hess theory must be reconsidered. The shape of "dry" valleys in lim e stone country is one of cliffs on either side with a scree forming a V at the bottom — no such V recorded which could be interpreted as old sub merged water course. Also, little drainage, or watershed; thus hard to visualize as 5000 ft deep gorge and 30-35 mi across. No sign of tapering toward the headwaters. Lee, 1951 Many terraces can be correlated, especially at 3, 600 to 4,200 ft, but others occur sporatically. 541 Slight folding is indicated. Sedimentation.was originally greater in the south of Exuma than the north; the south was quite recently tilted upwards relative to the north and for this reason increasingly greater land areas are to be seen towards the south of Exumas Cays (this also applies to Ragged Is. gr. and to many of the First Line Islands. Gentle settlement and warping took place as the most recent of all structural events. Differences in gradient may be explained either as relatively more rapid deposition and contemporaneous subsidence as the gradient increased, or as the different natural angles of repose of sediments of different composition. Quiet and relatively uniform sedimentation. No serious faulting is apparent. Details of geophysical work seem to confirm views of Suess and Schuchert (unfolded, but differential compaction on banks and instability in marginal areas has caused slight folding, warping and faulting.) The entire volcanic arc extends at least as far as Abaco. This has been called the "First Line." Formation of troughs like TOTO and Exuma Sound has fundamentally different characteristics from the formation of the "First Line" of Islands. Exuma Cays and their extension to Ragged Is. have been called the "Second Line. ” At least from "Second Line” W , sedn. has been proceeding quietly at least since the Cretaceous. Dif ferential compaction and isostatic adjustment have given rise to slight folding, warping, and tilting. Gravity anomalies in "First Line" are governed by original volcanic arc; and by the slight folding, warping, and tilting, and by submerged indurated reefs in the Second Line. Major troughs are simply areas where relatively little sedn. has taken place, but which, like rest of Banks have been subjected to isostatic settlement. Formation of subsidiary lines of reefs, cays, and islands seem to have been the result of regional alterations in sea level which might be related to glaciation. Most of the gravity anomalies can be explained by simple erosion of the Worzel, Ewing and deep-water portions without compensation, or alternatively, construction Drake, 1953 of the shallow-water portions without regional compensation. Newell combined above: the deep channels ate mainly the results of constructional processes through differential deposition and bypassing. Newell, 1955 Goedicke found several deep reflecting horizons but no basement. Goedicke, 1960 Turbidity current erosion may be largely responsible for excavation of TOTO and Providence Channels. Ericson, Ewing and Heezen, 1952 Lack of source of large quantities of sediment negates the possibility of turbidity current erosion creating TOTO; suggested that the channel originated through some type of block faulting. Miami University report, 1958 Flanks of TOTO are steep (15-20°). have bare rock walls to 100-200 fms; below here the bottom of the channel slope is gentle, and has sediment banket. Turbidity currents originate in upper channel, flow down the slope and distribute sediment on channel floor. Photographs at 1000 fm in center of channel show rock outcrop, indicating subaerial erosion of the exposure at some earlier geologic time. Busby, 1962b Low negative gravity anomalies can be explained by assuming 1 to 4 km of light material. While small thickness may be result of sedimentation, tenuous explanation for thick deposits. Alternative view is downfaulting (graben) with the faults assumed to correspond with outline of depres sions. Down-faulting lowers lighter material in the down-faulted block to the same level as heavier material on the sides, thus causing the anomaly. Talwani, Worzel, and Ewing, 1959 Sedimentation in topographic low caused down-faulting by low-density material would accentuate this anomaly. Neither erosion of the channel nor upbuilding of banks explain anomalies. Disagrees with above explanation. Terrain of gently folded sedimentary rocks >14,000 ft, upon which a trellis drainage pattern developed when it was above sea level. A brief rapid submergence drowned the river Hess, 1933, 1959 L n & C a J valleys, followed by slow submergence. Reefs grew upwards from valley sides forming banks thus preserving drainage features. With continuing subsidence most sedimentation was confined behind reefs, preserving valleys. Turbidity currents intermittenly spread out sediments in valleys and kept "river" channels open and draining them from the shallower areas to 2,500 fms. Where they debouched into the open ocean. Detrital sediment filling valleys was less than detrital and chemical sediment on bank would account for present gravity field. To form parallel graben separated by horsts of approximately equal widths seems mechanically unlikely. Also difficult to form such struc tures and preserve horizontal attitudes of the layers both under banks and in down-dropped blocks; it would be necessary to assume faults are young- cut Tertiary rocks on the banks. Aseismicity argues against young faults. Possibly old graben and more recent subsidence of the foundation and upgrowth of banks. Concluded marine erosion not likely to produce a valley with an inner gorge or channel running down the middle and a continuous slope in one direction. Photographs near northern part of TOTO revealed cavities in indurated limestone surface at 1000 fms. Also smooth vertical scarp, pebbles and cobbles, and oscillation ripple marks. Excludes solution, of burrowing organisms, turbidity currents, slumping or formation of features at present depth. Concludes some of the features can only be explained by subaerial theory. Tentatively concludes "gradual subsidence, brought about by deposition of material on the prominences bounding the channel, or downdropping of the channel floor by faulting can be applied." Subaerial erosion and subsidence of 6000 ft is implied. Major breaks in slope in Exuma Sound are noted at a depth of about 400 fms. Change may mark hiatus in sedimentation or a period of less sedimentation. Believe area is downfaulted; probably pre-Cretaceous. Break in slope support postulation of graben; the trough also has a flat bottom with steep sides which are marked by a step-like descent. Busby, 1962a Siegler, 1959, 1961, Miami University, 1958 L n ■ P > Flatness is believed to reflect underlying deeply buried pre-Cretaceous structural pattern. (Either subaerial erosion or turbidity currents result in V-shaped profile.) Area between 70-74° W , 21° 30' N - 24° N was magnetically surveyed. Linearity, extent, and abrupt changes in both magnitude and direction of magnetic anomalies suggest they are the result of at least three major faults and appear to intersect at common point 35 n. miles north of Caicos Bank (22° 35’ N, 72° W). Several other smaller faults also suggested, dividing area into five crustal blocks. Bracey, 1963 Bracy and Avery, 1963 Florida-Bahama platform has been subsiding since at least early Cretaceous time. Well on Andros Island to 4,446 m went through thick section of Tertiary and Cretaceous shallow water carbonates; bottom in L. Cretaceous without reaching basement. Subsidence appears inter rupted, but average subsidence rate~ 4 cm/1000 yrs. Crust decreases from about 30 km at E edge, and oceanic thicknesses reported for adjacent Blake-Bahama abyssal plain. Implied that outer slope is built by calcareous deposits, except lower slope (scree). Emiliani, 1965 Blake Plateau Blake Plateau is a continuation of the Bahama Plateau carbonate province and includes part of Florida Peninsula. Blake Plateau is not significant from Bahama Platform. Has at least 4000 m carbonate rock. Features characteristic of carbonate banks or reefs, rather than terrigenous shelves. Pratt and Heezen, 1964 East Coast From Florida to Massachussetts Sinking at rate of 0.02 ft/yr. Deacon, 1962 Between Cape Hat eras and Cape May Structural benches on continental slope. Heezen et al, 1959 New York Constructional coast, subsidence. Hill. 1963 £ L a General Subsiding and constructional coast. General subsidence, downwarped Appalachian basement. Ibid Shelf widens from 95 km east of Cape Henry to 150 km near the Hudson Channel, and is 125-135 km wide from Long Island to Georges Bank. Outer edge shows a downward tilt to NE. Shelf edge changes from 60 to 80 fms and Franklin shore from 40 to 60 fm . Veatch and Smith, 1939 Flexure. Bourcart, 1938 Face of prograded shore zone or paralic beds. Moderate declivity. Dietz, 1964 Observed seismic profiles are interpreted as the result of faulting, and involves differential vertical movements. Region is basically a graben structure under continental margins formed during Miocene. Engelen, 1963 Large wrench faulting is assumed near 40° N. Drake and Woodward, 1963 Thick sediments on shelf, slope and continental rise require regional subsidence of terrace during deposition (East Coast and Gulf of Mexico). Moore and Curray, 1963a, 1963b Several troughs located along east coast offshore. Continental shelf was formed in part by isostatic sinking of offshore crust beneath the sedi mentary load supplied by rivers, but sinking was also by a mechanism other than isostatic depression. Appalachia disappeared in area. Sub- crustal erosion by currents beneath the M discontinuity caused thinning. Relationships do not seem to require either a drastic change in the volume of the sea in Cretaceous time (to explain Pacific guyots), or a late date for the birth of the Atlantic. Drake, Ewing and Sutton, 1959; Gilluly, 1964; Barrell, 1914 Maine Bay of Fundy Conspicuous coastal escarpments occur below sea level and submarine scarps occur along the coast of New Brunswick and northeast Maine and Koons, 1941 Johnson, 1925 ^ O' others traced to Casco Bay. Bay of Fundy is submerged Triassic low land produced by subaerial agencies and bounded by fault scarps. Canada East Coast Nova Scotia Fault-line coast. du Toit, 1937 Newfoundland Fault-line coast. Ibid Hudson Bay and Newfoundland Real uplift exceeds magnitude of Fennoscandia. Rate equals over I n / century and in some places even 2 to 3 m/century. Kaarainen, 1953 Labrador Fault-line coast. du Toit, 1937 Fractured coast. King, 1962 Greenland - Canada Rift zones between Grant Land/Grinnell Land, Ellesmere Land/N. Greenland, Baffin Land /Greenland, Greenland/Labrador, Barrow St. and Lancaster S t., Banks St. and McClintock Channel. Rifting no older than Tertiary. Taylor, 1910 Baffin Island North, West and South Coasts Fault-line coast. duToit, 1937 Arctic Islands of Canada and Hudson Bay Shallow submergence. King, 1962 Greenland - Scotland "It is clear that the Caledonian otogenic belt must pass out to sea south of Scoresby Sound and north of Kangerdlugssuag. If we accept the relative positions of Greenland and Europe before the formation of the Atlantic, which have recently been obtained by Bullard (1964) from Wager and Hamilton, 1964 Ul - P » -q estimates of the best fit of the 100 fm line off the east Greenland and European coasts, it is seen that east Greenland Caledonian orogenic belt passes, without change in direction, into the British- Caledonian belt". These are the Lewisian rocks of the Scottish Caledonian belt. West Coast Tectonic faults occur at the edge of the land, and also bound offshore troughs. Made more complex by isostatic uplift. "The increase in vulcanism and tectonic activity in the Tertiary is connected with the faults and vertical movements of individual masses which complicate the ancient structures of the land and basically determine the modem features of the coast and shelf morphology." Rvachev, 1963 Deep channels parallel to shore like Norway. Fracture zone. Stdrmer (in Holtedahl, 1935) Southwest Greenland Dredge sample from Banan Banke (off Godthaab) (45 - 350 m ), angular rounded gravel to 20 cm diameter. Rxs are Precambrian age; include early Paleocene fresh water deposits, and L. Cretaceous age pollen and spores. Rocks are in situ, deposited as moraine, partly altered by wave action during lower stand of sea level. Bank is separated from mainland by a depression (150 - 500 m deep). Faulting must have caused depression isolating bank. Faulting post-Holocene. Dibner et al, 1963 West Coast Entire west coast Fault-line coast. du Toit, 1937 East Coast Entire west coast Fault-line coast. Ibid Flexure. Wagner and Deer, 1938 Cloos, 1939 Rocks of Cretaceous age are dislocated on coast. Beloussov, 1955 00 Northeast coast Upwarping of the coast by deglaciation and also a eustatic rise of sea level. Emergence has been greater than sea level rise. Highest ex waterline is 213 to 246 ft above present sea level. Evidence - - marine fossils and strandlines. Boyd, 1948 Europe Scandinavian - Spitsbergen Large Tertiary land mass existed west of Spitsbergen. Frebold, 1935 West coast of Spitsbergen (offshore) controlled by faulting. Holtedahl, 1936 Wegmann, 1948 Orvin, 1940 Scandinavian - Scottish “continent." A large land area existed off Scandinavia and the British Isles during the Paleozoic. ; Stamp, 1947 Eardley, 1948 L. Paleozoic facies in Scandinavian mountains show that in Cambrian and in Ord. detritus was carried into the sea which then occupied the place of these mountains from some elevated land-masses situated northwest of Norway, that is beyond the present-day Atlantic Ocean. Holtedahl, 1920 "Scandia" or “Scandic" Land mass lay above sea-level until the Lower Tertiary. Its former extent is hypothetical. Driftists (Wegener et al) consider Greenland was the source area of elastics in Spitsbergen etc. and has drifted away. De Geer, 1919 Bailey and Holtedahl, 1938 Holtedahl, 1920 Frebold, 1935 Umbgrove, 1947 Wegmann, 1948 Baltic Sea Alandskaya and Landsort Trenches are of tectonic origin (depth 495 m). Larionova, 1959 Barents Sea Central flexure most important structural element. Klenova, 1960 Norway West Ooast Entire West Ooast Submerged river system. i Uparching, Quaternary and present. Umbgrove, 1947 Beloussov, 1962 Rifting during late Tertiary uplift. Holtedahl, 1920, 1940, £ 1951, 1955 0 Block faulting. Hill, 1963 Norwegian Shelf Drowned plains of subaerial erosion. Ahlmann, 1919 Evers, 1937 Norwegian Sea (Skandik) Flexure. de Geer, 1910 General Faulting. Holtedahl, 1940 Emery, 1950 Wave-built embankment. Stetson, 1949, 1953 Upbuilding and outbuilding on subsiding foundation. Daly, 1952 Umbgrove, 1947 Kuenen, 1950 Nansen, 1904 Rode, 1930 Erosional. Jessen, 1943 Ziemendorff, 1910 West and North coasts Fault-line coasts. du Toit, 1937 Sweden East Coast General Uparching, Quaternary and present. Beloussov, 1962 Finland West Coast General Uparching, Quaternary and present. Real uplift of F.enno-scandia since end of Glacial Period. Beloussov, 1962 Kaarainen, 1953 Ul in o North Sea British Isles Rockall Bank Uplift and faulting. The lines which are parallel with the east and west coasts of the North Sea are traces of displacements. In each of these displacements the W block is reported to have drifted southwards in relation to the eastern block. Hela, 1953 Bubnoff, 1942 Subsiding basin. Downward movement is still going on in southeast England, but some areas show no such movement. Author finds evidence of post-Raman flooding — lower Thames, Ingoldmells, the Fens, Somerset, Dungeness, Southampton, Bristol Channel, Wirral coasts, Lancashire, the Solway, the Tyne, the Hebrides and other locations. Amount of subsidence is ~ 4.50 m for the Thames,^- 2.40 m for Romney Marsh, and 1.5 m in Ireland. Assumes a value of 2 to 3 m. While local tectonic movement has occurred, most rise is due to recent (post-Roman) eustatic rise in sea level. (Note Valentin, Geogr. J ., V 119, 1953, p. 299, is in direct opposition to this view). During Ice Ages a land mass to northwest (instead of northeast) was the site of a continental ice sheet entered British Isles. Suggested that continental slope and submarine canyons can only be explained by supposing the sea floor once stood at a level several thousand feet above present sea level. Views in agreement with J.W. Spencer, W. Upham, but A. Geikie and Hudlesonwere skeptical. Hill. 1963 Hafeman, 1954 Forrest, 1933 Hapgood, 1958 Hull, 1899 " ... it can hardly be explained without subsidence." Davis, 1928 "Rockall Bank is essentially a submerged basalt plateau.. . 9 5 * 7 0 consists Robinson, 1952 of this type of rock." (Actually Rockall itslf is a granite porphyry). U l Ui Scotland West Coast Entire west coast Fault-line coast. du Toit, 1937 Submarine features of W. Scotland are those of a submerged land sur face with well-developed drainage systems. River systems can be traced on charts. Extend to depths of about 70 fms, with deeps to 130 fms. Deeps probably formed by glaciers. Much evidence of offshore faulting; breaking up of bottom must have been accomplished during Tertiary times. Outer Hebrides is a huge block dipping down to the W. Ting, 1937 Ireland (north coast) Fault-line coast. du Toit, 1937 Ireland (southwest) Hercynian ranges downwarped under Atlantic. Lees, 1953 Netherlands West Ooast Entire west coast Submergence - Recent, at rate of 1 ft/century. Lees, 1953 Subsidence of 3 mm/yr is 50 x greater than average value for past 200 million years. Umbgrove, 1951 Kuenen, 1955 English Channel Since Amorican orogeny the Channel has been an area with a tendency to iotermittant downwarps while surrounding land areas of Devon and Cornwall (England) have been areas of intermittant uplift. King, W.B.R., 1954 English Channel Deeper parts of the English Channel indicates submergence. Gardiner, 1914 Irish Sea Deeper parts of the Irish Sea indicates submergence. Ibid' Portugal West Ooast Entire west coast Flexure coast. Lautensach, 1932 Ul L n bJ Bay of Biscay Spain to Brittany English Channel Irish Sea South slope of Bay of Biscay has a very steep and straight continental slope and is aligned with the continental slope of the British Isles. This rift is associated with folding in Pyrenees. Major section of coast and offshore area was submerged during Lisbon earthquake (1755). Author shows a major rift (Lisbon scarp) extending from southwest tip of Spain, curved inland slightly in Spain, crosses the coast and parallels the shore off Portugal, curving into English Channel until it reaches France at Brittany. Deeper parts of the English Channel indicates submergence. Deeper parts of the Irish Sea indicates submergence. Carey, 1958 (RDT) Carey, 1958 Gardiner, 1914 Ibid 553 Africa Morocco West Ooast Entire west coast Northwest Africa Spanish Sahara West Coast Entire west coast French Equatorial Africa Continental flexure. Beds have distinct seaward tilt or flexure. Atlas Mountains south of Agadir strike out into Atlantic Ocean at right angles to continental margin. Other areas have similar cut-off of mountain ranges and zones of compression. Thus, oceans must conceal a comparable complex of compression zones continuous with those of the continents. Cretaceous rocks of Grand Canary, near Las Palmas Island and in Hierro, belong to a continuation of the Atlas Mountains. Base of Madeira is the corresponding continuation of the Moroccan Meseta. The Azores is a continuation of the Spanish Meseta. Cape Verde Islands are continuous with the old rocks of Mauretania. Atlas Mountains extended westwards into the Atlantic, and were cut off by subsidence along the Moroccan coast in recent times. The Atlas sinks toward the Atlantic to rise again in the Canaries, and its western end (joining the Americas) foundered in Pleistocene times. Gregory rejects land beyond the Canaries. Rift along the shoreline. Downwarping. Bourcart, 1938 Umbgrove, 1947 Lees, 1953 Gentil (in Gregory, 1930) Gentil and Lecointre (in Gregcry, 1930) Gentil, 1912, 1914 Gregory, 1929 Mazarovic, 1952 Lees, 1953 554 Senegal West Ooast From Spanish Sahara to Barthurst, Senegal Guinea West Ooast Entire west coast Sierra Leone West Coast Coastal plain Rio de Oro West Coast Entire west coast Liberia West Coast Entire west coast Ivory Coast South Coast Entire south coast Dahomey South Coast Entire south coast Rift along the shoreline. Flexure. Fault-line coast. Uplift probably in Pleistocene. Fault-line coast. Flexure. Fault-line coast. Marginal flexure and faulting. Pleistocene? Marginal flexure. Downwarping. Mazarovic, 1952 Jaranoff, 1943 du Toit, 1937 Dixey, 1928 du Toit, 1937 Jaranoff, 1943 du Toit, 1937 Slansky, 1958 Le Bourdiec, 1958 Slansky, 1958 Le Bourdiec, 1958 Lees, 1953 Source of the Gold Coast Blanket deposits lay to the southwest, in the region that is now sea. "Thus where the Atlantic now lies there must formerly have been a great river, possibly transporting gold from a continent that has since subsided far beneath the waves, or drifted away to the west where, perhaps, part of it is still recognized in the auriferous tract of Guiana and Brazil." Bray (in Holmes, 1929) Togo South Coast Entire south coast Marginal flexure of great age. Slansky, 1958 Nigeria South Coast Niger River delta area Downwarp at continental margin. Allen, 1964 Allen and Wells, 1962 Nigeria Downwarping. Lees, 1953 Congo West Coast Congo River delta , area Tertiary and Cretaceous beds of coastal plain are more than 1000 m thick and rest on a Cretaceous peneplaned surface sloping seaward. Mid- to Late-Miocene peneplan was uplifted and warped by Mid- to Late- Miocene disturbances. Included downwarping seaward. Veatdi, 1935 Veatch and Smith, 1939 "A consideration of the source of the sediments forming the Lubilash of of the western Congo, likewise, points to a more elevated, though not necessarily mountainous, land mass occupying the present depressed coastal plain region and extending into what is now the Atlantic Ocean. Veatch, 1939 During the U. Paleozoic, Triassic, and Jurassic dry land (a source area) existed in place of the Atlantic Ocean to the west of Congo Basin. Umbgrove, 1947 Ul Ul O ' Gardiner, 1914 Entire west coast Real subsidence of the whole coast, not by faulting. Angola West Coast Entire west coast Flexure coast. Repeated warpings along a hinge line. Jessen, 1936 Downwarping. Lees, 1953 Southwest Africa West Coast Entire west coast Intermittant emergence occurred between late Tertiary and late Pleistocene. Krige, 1929 Diamonds won from west coast of Africa are said to be identical with those of Brazil and are not akin to those of Africa. Ahmad, 1961 From Cape Lopez to Cape of Good Hope Fault-line coast. i du Toit, 1937 General West Coast Periodic tension from Mesozoic on. One or more coastal faults accompanied by downwarping along the continental edges. du Toit, 1940 During U. Paleozoic thick sediments of continental origin were laid down in Karroo Basin. The east-west belt of Karroo are cut on east and west by the oceanic coasts, and continued far into Indian and Atlantic Oceans. In U. Paleozoic and beginning of Mesozoic dry land existed south of Cape Mtns., as is proved by the drift of material from the south. Umbgrove, 1947 Symposium. . . on Gondwana, 1952 South African Variscides Southern part of south African Variscides and the probable connection with the Cedar Mtns. disappeared into the sea. Nothing is known of the original extent of this land mass. Umbgrove, 1947 U » Ul -4 Islands Canary Azores Cape Verde Is Azores "Traces of recent subsidences are to be seen on all shores of the Atlantic Ocean. There is a continental block of considerable size submerged below the level of the sea in the region of the Canary, Azores and Cape Verde Islands. People see in it that the Island of Atlantis, the catastrophic submergence of which is known to us from the ancient historians.” In 1898, at 47° N, 29° 40' W an Atlantic cable broke at a depth of 3100 m. Retrieved rugged lava, fragments of tachylite - a glassy lava, (generally recognized that crystal structure is different under atmospheric and submarine conditions under great pressures). Tachylite normally forms under atmospheric conditions, hence this glassy rock from 3100 m did not originate at that depth £see discussion by Menard, 1964^. Furthermore, crystals break down when they have been in sea water for > 15,000 yrs, hence lava was submerged < 15,000 yrs ago. Concludes that region lying 900 km north of Azores, perhaps including Azores, subsided relatively recently. According to Plato’s account this would have taken place 11,515 yeajs ago, or about same time glaciers retreated from Europe. In addition, Soviet Scientists date Arctic water at about 12,000 yrs. This relationship is used to argue that submergence of Atlantis caused the beginning of the Ice Ages (by blocking flow of warm water into Arctic Ocean). In 1811, a small island appeared near Azores. In 1867, another island emerged in the same region - both "suddenly disappeared". Not characterized by typical Mid-Atlantic Ridge type structure; owes its present character to combined effect of at least two major structural events, and therefore does not constitute a typical outcrop of the Mid-Atlantic Ridge. Klenova, 1948 Termier, 1924 Hagemeister, 1955 Hagemeister, 1955 Tolstoy, 1951 558 Azores Plateau St. Paul Rocks Mid-Atlantic Ridge Azores uplift has relatively height of 3,100 m is start of rise. Youthful form. Wide occurrence of steep ledges indicate presence of fractures and faults on the ridge slopes. On north and south of Azores rise is an intermediate "terraced zone" bounded by steep ledges of a faulted character with bottom slopes up to 15°. Elongated ridges and long narrow, closed depressions alternate, bordered by abrupt slopes. Similar abrupt slopes on the islands are due to faulting. Two major periods of activity in Iceland and Azores: late Tertiary to Recent, and middle or early Tertiary. Might be associated with Alpine orogenies. "In 1932, near St. Paul Rocks, two small islets arose to the surface but were soon swallowed up again in the watery depths. . . There is nothing improbable in the idea that at such a time a great land-mass might have disappeared in the middle of the Atlantic Ocean, a land-mass for which the accepted name is Atlantis". Kolbe found fresh water diatoms in several cores of the equatorial region of the Atlantic Ocean (located 810-1160 km from Africa). Kolbe said they gave the distinct impression of a lake sediment, and discussed how the diatoms might have reached the area including wind or by rivers from Africa. He rejected each as well as turbidity currents since the diatoms in core 234 are on a rise and separated from Africa by a depression at least 1000 m lower than where the core was obtained. Malaise rejects a river and wind origin because these would transport the diatoms away from the region of the cores. Malaise concludes that this part of the ocean (Mid-Atlantic Ridge) formerly was above sea level and that core 234 happened to hit the bottom of a former lake, now submerged by the sea. His general theory contained in a book published in 1951, revives Plato's story of "Atlantis” (see Malaise). Grabovskii, Greku, and Metal'nikov, 1961 Cloos, 1939 Bucher, 1952 Hagemeister, 1955 Kolbe, 1953, 1955, 1957 Malaise, 1951, 1956 Ui U l V 0 Submerged mountain range. "It is apparently a sort of borst-ridge — a residual ridge along a line of parting or rifting of the Earth-crust having moved away from it on both sides." Most probably the two continents moved away from the ridge; the ridge marks the place of original separation of continents. Mid-Atlantic Ridge is an anticline between two geosynclines. Mid-Atlantic Ridge is a horst left between two rift-valleys due to east ward movement of Eur-Africa and the westward movement of America. Large escarpments in mid-Atlantic Ridge are apparently of fault origin. A graben cuts ridge transversely at about 30° N, is about 5.5 km deep. Wide terraces on either side of ridge, up to 50 km wide, heights vary up to hundreds of meters; believe of fault origin. Mid-Atlantic Ridge "is the former floor of the rift-valley which was in existence during the period when the Atlantic Ocean was composed of relatively narrow fracture, which was subsequently filled with sunken margins, shore deposits, and also partly with molten sia l." Considerable evidence of fracturing on the ridge. Main east-west trough cutting through the main range at 30° N is almost certainly a fault. Topography could be produced by folding (sedimentary rocks have been recovered). Origin— folding, or faulting, or combination of both — cannot be answered yet. Evidence of fracturing. Much outpouring of lava; sedimentary rocks dreged up. Tentatively suggested ridge may be a belt of Tertiary folds, the high degree of seismicity of which would be due to block faulting following a distribution of tectonic forces. Taylor, 1910 Gregory, 1930 Taylor, 1910 Beloussov, 1955 Wegener, 1924 Tolstoy, 1951 Gutenberg and Richter, 1949 560 Rocks dredged big angular blocks of basalt and related rocks with fresh surfaces, such as would accumulate at the foot of a fault scarp on land. Showed slickensides; fault breccia. Some basalt had glassy surface, indicating rapid chilling. Rocks and topography suggest trough (in ridge) is graben. In seismically actively region. Believe trough region is a fairly recent feature. Bucher, 1952 Shand, 1949 Tolstoy and Ewing, 1949 Differential torsion of the hemispheres. Prinz, 1891 Median anticline (of what he termed the Mid-Atlantic "geosyncline"). Haug, 1900 Ridge built up by lateral pressure, as indicated by crushed rocks and metamorphism. Also Prinz's theory of differential torsion of the two hemispheres might explain the trend of the ridge, especially the equatorial flexure. Washington, 1930 Believes in essential similarity between pattern of continental and oceanic structures in the North Atlantic and surrounding areas. The ocean floor seems to be comparable to that of the basins and swells of the continental areas outside the orogenic belts, although the scale is both larger horizontally and vertically on the oceanic structures. Similar to fault-controlled mountain ranges on land. Bucher, 1940 (in Tolstoy, 1951) Mid-Atlantic Ridge and African Rift Valleys are of basically the same structure. Rift Valley is clearly faulted resulting from extension of crust. Therefore Mid-Atlantic Ridge is the result of normal faulting. Not known if forces were horizontal extension or vertical uplift. Heezen and Ewing (in Heezen, Tharp and Ewing, 1959) Proposed a mechanism relating suboceanic uplift to expansion due to serpentinezation of the upper mantle. Hess, 1954 Atlantis Seamount Flat-topped bedrock at 180 fms, cobbles, current ripples, sands; slopes covered with sand and cobbles to 400 fms; slump features at 570 fms, volcanic agglomerate recovered from 400 fms, and a ton of pteropod Heezen, Ewing, Erickson and Bentley, 1954 o Cruiser and Great Meteor Seamouas Hudson Canyon Is. cobbles from summit; one cobble dated at 12,000 yrs plus or minus 900. State of lithification suggested lithified under subaerial conditions, and seamount may have been an island within past 12,000 yrs. Depth of deposition was less than today's depth. Summits at 150 and 165 fins; sandy without ripples or cobbles. Symmetrical ripples photographed on slopes to 1200-1400 fms. Atlantis, Cruiser and Great Meteor all appear youthful "guyots" may have originated as volcanoes which were later capped by Is. and more recently have sunk. Hudson Canyon sinks far below maximum glacial lowering of sea level. But its connection with the Hudson River valleys seems so obvious that one rejects unwillingly the interpretation that it is a submarine river channel formed during an Ice Age. A possible explanation may perhaps be found in facts connected with the situation of the region. Just outside the great No. Am. glaciation, the depression of which drove up a high and large swell along the ice bonier, so high that the slope where the Hudson Canyon appears was lifted over the sea level of that tim e. The channel could be eroded away in this way, and when the swell was leveled again by the vanishing ice sheet, the river channel sank to its present position below the limit for the sea's reduction by max. glaciation. There are some indications of such swelling of the earth's crust in these zones. The depths of submarine canyons in prolongation of the rivers on die Atlantic Coast show decreasing depths from the Hudson Canyon southward, corresponding with die decreasing height of the "swell”. Elsewhere he considers canyons cut before the Ice Age; they are drowned valleys. Heezen, Ewing, Erickson and Bentley, 1954 Ramsay, 1930 U \ O ' C s J Arctic Ocean General Land existed in the Arctic Basin and the land subsided during Precambrian or perhaps early Paleozoic time. Alaskan geosynclinal deposits point to an Arctic source where water is deep today. Eardley, 1948, 1961; West, 1951; Saks et al, 1955 Arctic Ocean has existed since the Mesozoic. Since its formation it has undergone many changes and during the Quaternary it was completely formed. Belov and Lapina, 1959 "The Polar basin represents a depression existing from the most ancient tim e, which was expanded in the direction of the Atlantic Ocean by subsidence, separated by elevations that are the left-overs of a North Atlantic continent." Haug (in Panov, 1957) Central Polar Basin is a present-day geosyncline; objected to by Nansen. Huddleston, 1884 Mesozoic folds continue below sea level into Arctic Basin. Panov, 1943, 1957 Suess, 1921-24 Polar Basin represents "an isolated segment of the simatic zone of the globe." Mazarovich, 1952 Arctic Ocean is Pacific Ocean structure. Gutenberg and Richter, Believe in permanence of the polar ocean depressions; might be similar to other permanent oceanic depressions. Stille, 1948 Polar Basin was formed by continental drift as early as Paleozoic; later it gradually expanded by further movement of the continents. Wegener, 1924 Polar Basin formed by displacements of the continental masses from north to south; southward movement of Asiatic continent. Taylor, 1928 (in Panov, 1957) Polar Basin formed by southward displacement of the continents during die Tertiary, du Toit and Taylor indicated the basic cause for a deep ocean basin's formation was a profound subsidence of terrestrial crust in the Central part of the Arctic. du Toit, 1939 Taylor (in Panov, 1957) Ul O' w An ancient stable structure occurs in the central part of the Arctic. This is an archaic (probably Precambrian) stable structure. Includes the "Hyperborean Platform." Arkhangelski, 1938, 1947 Ancient platform structure surrounded by young folded zones. Panov, 1957 An ancient land mass, the "Arctic bridge" occurred in the central Arctic, which during the Quaternary was an accumulation region for great masses of continental ice. In the second half of Quaternary subsidence of the Arctic Bridge lead to formation of the central Arctic Basin. Hills, 1939 Formation of the polar oceanic depression was due to subsidence of stable structures. "The Oceanic depressions of the Arctic represent the deep basins of recent tectonic subsidence. Geologically they mark the sub sidence of stable structures was already in evidence at the end of the Mesozoic and it continued into the Tertiary and Quaternary." Panov, 1948 Atlantic and Arctic Oceans similar geologically, and between latter and Tarim depression in Central Asia. Concluded that Polar Basin was formed by a vertical displacement of the terrestrial crust within the lines of the surrounding fold-structures. 0 . Holtedahl, 1929, 1930 Oceanic depressions in Arctic are typical geosynclinal depressions; part of a geosynclinal region existed from the Paleozoic. Subsidence of folded structures of Alpine age. Kobler, 1928 1935 Fold systems of North Siberia might continue across to Arctic Coast of America. Suess, 1921-24 Stille, 1928 Shatski, 1935 Central Arctic was a region of fold structures of different ages; a region where structures of various ages subsided. But he renounced this, and began to defend great antiquity and permancy of Arctic Ocean regions. Stille, 1928 Ul O' 4* In the Mesozoic there existed north of Alaska, a stable structure or craton (Panov considers this part of the "Hyperborean Massif"). Possibly occurs folded structures of various ages, remaining as direct continuations of continental fold structures and occupying great areas in the Central Arctic. Eardley, 1948 Panov, 1957 Author sums up evidence: majority of recent workers agree that subsided fold structures of various ages exist in this region and are a direct con tinuation of fold structures of the surrounding continents. Some authors suggest that in the Central Arctic there are structures of platform type, like the ancient stable block called by N. S. Shatski the "Hyperborean Massif." Panov, 1957 Shatski (in Hope, 1959) Land masses north of Alaska and New Siberian Islands suggested by direction of drift. Eardley, 1948 Hope, 1959, 1964 Atlasov, et al 1964 A line can be drawn northward from Vesteraalen, Norway, following the continental slope off Bear Is. and Spitsbergen, cut across Nansen threshold between Spitsbergen and Greenland, following continental slope N and W of Arctic archipelago to Amundsen Sound. First part (Norway to Spitsbergen), high land to right, Scandic sea basin to left. Beyond Nansen threshold, high area is to left, and deep sea to right. Relief may reach 7000 m. This is called De Geer's line. Taylor and du Toit regard this as possible path of displacement, along which the land masses may have drifted. Holtedahl and Frebold stated that East Greenland was not the source area for clastic material in Spitsbergen. De Geer, 1926 Wegmann, 1948 Taylor, 1910 du Toit, 1937 Polar Sea either formed by subsidence or it is the opening formed be tween two land masses that have moved away from each other. Wegmann, 1948 Siberia Several large segments of east and northeast coasts are believed to have a fault origin. West, 1951 m O ' U l Between Yenisei and Lena Rivers, L. and M. Paleozoic rocks was "Beringia”, a land mass now occupied by present-day Bering and Okhotsk Seas. Leptev Sea probably was also a source area (i.e . topographic high, now submerged) during Permian and Triassic periods. Popov, 1945 Kalinko, 1956 Kara Sea (Novozemel'skaya Trench) Tectonic origin (depth 545 m). Larionova, 1959 White Sea Trench in western part is of tectonic origin. Ibid Barents Sea Barents Sea shelf formation coincided with lowering of North Atlantic and Arctic Ocean, but subsidence was not everywhere equal. Klenova, 1960 Novaya Zemlya Trench to east of island started to subside; it has subsided since then and is active today. Ibid i 5 6 6 Antarctica East Antarctica General South Orkney Islands South Victoria Land From Lister Peak to Terra Nova Parts of Antarctica Falkland Is. Rifting, blockfaulting. Shelf bottom is irregular, as though sinking of the center of the continent under the ice cap had been isostatically compensated by a rise of the mountain rim with strong outward tilting of the marginal regions. Intensely folded and faulted. Fault-line coast. Uplapped continental rise. Gentle declivity. In Paleozoic ice moved from direction of the oceans (from the south). Hill, 1963 King, 1962 King, 1962 Priestley and David (in du Toit, 1937) Dietz, 1964 King, 1953 567 Mediterranean Sea General Foundered continental segment. Suess, 1904 Continental-type crust, based upon small evidence available. Mediterranean has about same sediment thickness as Pacific and Atlantic. Not constructed like typical ocean; nor is it intermediate (like around Japan). The original ocean was narrow eventually filled up altogether; only a small vertical movement was required to transform the basin into the center of a continent stretching from England to the Sahara. Reasons for these vertical movements not known. The center of the area again became a sea (in Middle Triassic times), as a result of movement of relative displacement of European and African coasts. Submergence shown by signs of faulting along both coasts, which suggests whole central block sank about two miles, tearing the European and African coasts as it did so. GaskeU, 1960 Europe France South Coast Entire south coast Flexure coast. Large flexure in Tertiary time. Probably still in progress in Nice area. Bourcart, 1938 St. Tropez area Ancient stonemason's yard 650 feet from shore and in 20 ft of water. Dated to 149 AD. Ibid Fos-sur-Mer area Old Roman villa in water 15 ft deep. Ibid Italy A.E. Gunther (Nature, V. 201, p. 909, 1964) suggested presence of Lithodomus borings on columns in temples of Paestum, erosional surfaces at about 20 mi. in Italy and Sicily indicate extensive rise and fall of relative sea level between 500 and 1500 AD. No sea level change of more than 2 m in 2000 yrs. and probably not more than 1 m. Possibly local earth movements lower and raise archaeological remains, aligning them with Pleistocene terraces. No evidence of widespread submersion and uplift. Flemming, 1964 Ul O ' 0 0 Gunther's estimated rate of uplift following temple construction is 3 - 4 cm/century. Burton found slower rate in Calabria. Terraces to 1,000 m above present sea level. Uplift began Calabrian Stage of Pleistocene. This would average 1 mm/century. More than half the Quaternary uplift occurred during Calabrian Stage, and in post-Calabrian times movement slowed down. Omori estimated average uplift for Calabro- Sicilian area for 1900-1908, was 2 - 4 mm/yr. Modem movements of uplift and subsidence is southern Italy and most uniform over whole region, therefore correlation cannot be relied upon except over short distances. A 18-m historical level cannot be sustained. Burton, 1964 West Ooast Naples, Sonentine From Roman time to 12th century, submergence from 16 to 30 ft. From 16th century to present it has risen to the present level, 16 ft below sea level. Deacon, 1962 Capri Blue Grotto -- Roman land level 20 ft higher than at present. Deacon, 1962 Tyrrhenian Sea At the beginning of the Miocene, high dry land existed in place of the Tyrrhenaian Sea, from which granite boulders were eroded. Gravity data indicates oceanic structure of crust under sea. Behrmann, 1958 Gagelyants et al, 1958 Kroptkin et al, 1958 Tyrrhenic land-mass is assumed by many geologists to lie between Italy, Sardinia, and Sicily. Wegmann, 1948 Greece Seven miles offshore from town of Zante earthquake in 1873 formed submarine fault scarp 600 ft high. Grabau, 1960 Gulf of Corinth Ancient city of Helike destroyed 373 BC by submergence. Now lies beneath 20 ft of water. Deacon, 1962 Crete Coast near Iraklion Village of Matala Rose 20 - 30 cm. during Levante earthquake of 1926. Tombs in cliffs lie submerged nearly two meters below sea level implying a total submergence since Christian era of at least four meters. Boekschoten, 1963 Ibid Ct O ' v O Asia Africa Bay of Ay. Nikolaos Shows typical features of submergence. Creutzberg, 1960 Limani Chersonisos Roman settlement originally built inland. Foundations now exposed on beach. Boekschoten, 1962b Israel West Coast Entire west coast Phase a. — Folding was prominent during upper Cretaceous. Ceased after Oligocene. Phase b. -- Regional epeircgenic movement (uplift) towards end of Oligocene. Phase c. -- Gradual and regional subsidence-Neogene transgression of the sea. Phase d. -- Differential uplift and subsidence since end of Neogene. Neev, 1960 Libya North Coast Cyrenaican Coast At Appolonia - - Roman fish raising tanks 6-1/2 ft below sea level. Deacon, 1962 Phycus Tunnels, caves, passages and tanks 3 to 6 ft below sea level. Ibid Tunisia North Coast Entire north coast Flexure coast. Folding, faulting. Castany (in Bourcart, 1959) Folded coast. Guilcher, 1954 Algeria North Coast Entire north coast Flexure coast. General marginal flexure with folding. Rosfelder, 1955 Glaneeaud, 1954 ui S' Folded coast. Guilcher, 1954 At Cherchel Sunken Roman harbor. Deacon, 1962 Morocco North Coast Entire north coast Flexed coast. Bourcart and Glangeaud, 1954 Flexure and seaward dipping beds. Bourcart and Lecompte (in Umbgrove, 1941) Southern Europe and North Africa General These areas studied in detail and extended worldwide, indicate subsidence of the bottom subsequent to glacial cutting. Bourcart, 1938 Considerable land areas existed during die Mesozoic and the Paleocene Anderson, 1936 to north of Algeria and Tunis. Merla, 1954 Migliorini, 1948 ■ > 3 t-* Indian Ocean General Coasts fronting the western Indian Ocean are the fractured or monoclinal edges of plateaus. King, 1962 Site of present Indian Ocean was occupied by Gondwanaland in Permo- Carboniferous times. East coast of South Africa, Madagascar and India took shape towards end of Jurassic or early Cretaceous. After Miocene transgression and an uplift, the west coast of India was faulted down in Plio-Pleistocene times, the fault extending into the Persian Gulf region. Dismemberment of Gondwanaland was complete by early Cretaceous when different units drifted apart. The final shape was attained during the Tertiary, at the time of the great Deccan lava flows, and the formation of the Himalayan Mountain system with their extension west ward into Persia and Syria, and eastward into Indonesia. Krishnan, 1959 Ahmad, 1961 Believes tectonic features of Africa are vertically controlled rather than horizontally controlled. Brock, 1955 Continental slope is a secondary structural feature. Continental rift scar (the slope left after the rifting apart of a continental block). Steep declivity. Dietz, 1964 Vast parts of southern Indian Ocean have been uplifted due to tension. Great lava outpourings occurred. Three separate "volcanic upheavals” have been identified. "With the abrupt variation of depth the entire expanse of the upheaval, the presence of sharp peaks, and the newness of the formations give credence to the conjecture that this area in the recent geological past was compressed to pieces and then submerged.” Deposition of CaC03 is just beginning. Bears witness of connection in Cenozoic time of Antarctica with other southern hemisphere continents. These expanses were former dry lands; now "sunken islands." Maltsev, 1959 In U. Paleozoic the southern continents were ice-capped. Ice moved from direction of Indian Ocean; also carried boulders of Archean crystalline rocks. Umbgrove, 1947 Ahmad, 1961 ^ to Africa, Arabia, India and around Arabian Sea are areas faulted in Wiseman and Sewell, probable Pliocene or post-Pleistocene age, and included Oman - Indus arc to break down into Arabian Sea, 1937 Arabian Sea Downfaulting during late Cretaceous time. Burrard, 1916 Extensive studies indicate a major submarine fault zone closely parallel Guha, 1959 to the west coast of India. This is of recent origin, belonging to the Wiseman and Seymour, Deccan trap period. 1937 Africa Cape Region Karro beds had a source area to the east. du Toit, 1939 Entire African east coast Fault-line coast. du Toit, 1937 Southeast Africa East Coast General Seward dipping. Cloos, 1937, 1939; Penck, 1908 Flexure. Penck, 1908 Republic of South Africa East Coast Agulhas Bank Area Bevelled folds of Paleozoic age. Wellington, 1955 Encompassed by two monoclinal warps which define the east and west coasts respectively. King, 1964 Natal East Coast Entire east coast Step-faulted, tilted blocks induced by tension at right angles to present coastline - end of Jurassic. Maud, 1961 u> C O Flexure. Penck, 1908 Primary monoclinal coast with secondary faulting. King. 1962 Fault-line coast. Kent, 1938 Flexure coast, monoclinal - surface sediments and basement flexured. King. 1940 Port Elizabeth to Durban Flexure? Downfaulting? Pepper and Everhart, 1963 Durban to 31° 31' S Monoclinal flexure? Pepper and Everhart, 1963 Suggests faulting? Wellington, 1955 Durban to Cape St. Lucia Faulting? Pepper and Everhart, 1963 Mozambique East Coast Lorenco Marques Bay to Beira Folding? Faulting? Ibid 15° 30* S to Ruvuma River Faulting? During Cretaceous time. Wellington, 1955 Madagascar-Mozambique Mozambique Channel Intermittant down-flexuring. Block faulting during early Jurassic and Cretaceous. Baker and Miller, 1963 Dixey, 1956 L n -0 - T Madagascar East Coast Entire east coast Downfaulting, fault scarp coast. Besaire, 1954 Straight upraised and fractured eastern coast. Land tilted slightly to west or northwest. du Toit, 1937 Madagascar West Coast Entire west coast Downfaulting, horst and graben structure. Hinds, 1943 Tanganyika East Coast Ruvuma River to 8° 42’ S Downfaulting. Pepper and Everhart, 1963 Tanganyika-Kenya East Coast Mombasa to Dares Salaam Possible downfaulted blocks. Ibid Kenya - Somali Republic East Coast Mombasa to Cape Guaidafui Normal faulting. Ibid Kenya-Tanganyika . Broad bay between 3° and 8° S, and the deep channels separating Latham and Pemba Islands were formed by subsidence. Farguharson, 1936 Entire East coasts Faulted coastline. du Toit, 1937 Faults are assumed to parallel the coast offshore. Carey, 1958 Somali Republic North Coast Gulf of Aden Coast Step faulting, rift bordered by fault zone. Pepper and Everhart, 1963 Downfaulted in late Pliocene time. Girdler, 1958 Faulted synclinal trough rather than rift. Hensen (in Quennell, 1958) Red Sea Coasts are fault controlled. Carey, 1958 Formed by pulling apart of Arabia and Egypt. Gaskell, 1960 The physical features of the Red Sea imply that the region represents an incipient ocean that is actually being created. The Gulf of California may also represent another such region. Rirdler (in Stubbs, 1964) Egypt - Saudi Arabia Farson Bank Downfaulted coast. Guilcher and Nesteroff, 1955 Gulf of Aqaba Faulting. Uplift of Midian Islands. Schick, 1958 General Rift. King, 1962 Fault-line coast. du Toit, 1937 Believe Red Sea is a paar and not a graben. (Paar is a depression caused by moving apart of two crustal blocks - a tensional feature.) Swartz and Arden, 1960 Fault trough coast. Shepard, 1963 U l <1 O ' Arabia South Coast Entire south coast Fault-line coast. du Toit, 1937 Aden Protectorate - Oman South Coast Sa'id to Ras al Hadd Step faulting, rift bordered by fault zone. Pepper and Everhart, 1963 Downfaulted in late Pliocene time. Girdler, 1958 Faulted synclinal trough rather than rift. Hensen (in Quennell, 1958) Oman - Iran Gulf of Oman Fault trough? Downwarped in Miocene? Probably bounded by faults. Pepper and Everhart, 1963 Iran - Pakistan South Coast Me^an Coast Downfaulting, Pliocene or later. Wadia, 1944 Pakistan - India West Coast Karachi to Gulf of Cutch Folding Tertiary beds. Ghosh, 1959 India West Coast Gulf of Cutch to Gulf of Bombay Downfaulted in Pliocene or post-Pliocene. Weisman and Seymour, 1937 Tear fault? Schroeder, 1961 L n Kathiawar Coast and Gulf of Cutch Uplift. Burrard, 1916 Bombay Coast Unmistakeable signs of emergence. Burrard, 1916 Gulf of Cambay to Cape Cormorin Crack in sub-crust. Ibid Malabar Coast Unmistakeable signs of submergence. Ibid Bombay to tip of India Deccan Traps area. Geology of offshore area not well known. Down- faulting in the west possibly during early or middle Miocene. Crookshank, 1952 Krishnan, 1956 Bhavnager to tip Fault-line coast. du Toit, 1937 Bombay Coast Downfaulting of Arabian Sea floor (late Cretaceous) has counterpart in recent elevation of Deccan Plateau. Krishnaswamy, 1954 Suggests that a crack in the sub-crust extends from Cape Cormorin to Cambay and as crack occurred the Western Ghats been elevated. Ghats elevation took place during Tertiary Age. Burrard, 1916 Malabar Coast Same geological history as Bombay Coast. Krishnaswamy, 1954 South Coast Uttatur beds, Cretaceous age of south India had a sea source. Krishnan (in Ahmad, 1961) Tip of India to Ceylon Submerged barrier reefs. Krishnaswamy, 1954 Western Ceylon Possible fault scarp. Pepper and Everhart, 1963 00 East Coast Madras Coast Coconada Bay to False Point False Point to Ganges River Ganges and Brahmaputra Rivers area Ganges trough Burma West Coast Arakan Coast Burma - Malaya West Coast Andaman Sea Indonesia General Sumatra West Coast Entire west coast Reefless coast of emergence. Faulting? Downwarping and faulting. Deltas built out in spite of possible submergence. Fault warp. Folding, faulting, warping. Submergence, not older than Miocene, or in part Pliocene. Wave-like outward spread of uplifts from certain centers. Uplifts during Tertiary. Sumatra and Java composed of uplifted foredeep deposits. Folding is intermediate and discontinuous. Normal faulting. Upwarp of island arc in Tertiary. Downwarp of area between islands and Sumatra into deep inner trough. South of islands deepened to form outer trough. Krishnaswamy, 1954 Pepper and Everhart, 1963 Ibid Krishnaswamy, 1954 Daly, 1951 Cbhibber, 1934 King, 1962 van Bemmelen, 1949 Pepper and Everhart, 1963 5 7 9 1 Java South Coast Entire south coast Typical trench (island arc). Timor Folding in late Tertiary, simple folding in Pliocene. Major uplifts on Timor and nearby islands. Suggests uplift still con tinuing. Both coasts bordered by large faults. Timor Trough — Uplift and subsidence has been active since the Miocene Period. Gageonnet and Lemoine, 1957 Molengraaff, 1913 Australia General Much volcanic activity to east of Australia during Triassic - Jurassic time. David and Browne, 1950 North Coast Bonaparte Gulf Basin Slow subsidence. Teichert and Fairbridge, 1948 Sahul Shelf Area Broad warping, stable area, no folding. Fairbridge, 1953 Northwest Coast Rowley Shelf Area Narrow shelf off Northwest Cape may be fault controlled. Possible down warping of continental shelf opposite Canning Basin. Carrigy and Fairbridge, 1954 West Coast Source rocks of western Australia was to west. Ahmad, 1961 Dirk Hertog Shelf May be related to faulting. Ibid Rottnest Shelf Sedimentary feature moulded by downwarping and faulting. Jutson, 1934 Cape Inscription to Cape Leeuin Fault-line coast. du Toit, 1937 Cl 00 O Rodriquez Island Uplift within Recent about 500 ft with some submergence. Reed, 1944; Wilson, 1963 Aldebra Island Uplift. Ibid Chagos Archipelago Uplift. Reed, 1944 Tilted, submergence. Wilson, 1963 Maldive Islands Group Intermittant uplift, tilting. Reed, 1944 Negative gravity anomalies, interpreted as downwarp correlative with downwarp present over south end of Indian Peninsula. If so, faulting occurred between the Laccadive and Maldive Archipelago along the line of the Eight Degree Channel. Glennie, 1936 Wiseman and Seymour, 1937 Cosmoledo Group Uplift, Recent. Reed, 1944; Wilson, 1963 Providence Reef & Islets Suggested 700 fms submergence. Fryer, 1910 Gardiner, 1907-09 Wiseman, 1926-36 Fryer and Gardiner, 1910-12 St. Pierre Atoll Elevated atoll. Gardiner, 1907-09 Farquhar Atoll Elevated atoll. Fryer, 1910-12 Gardiner, 1907-09 Astove Atoll Elevated atoll. Wilson, 1963 Assumption Island Elevated reef. Ibid Christmas Island Uplift, post-Miocene. Andrews, 1900 ^ 00 South Coast Recherche Shelf Down faulting? Pepper and Everhart, 1963 Eucla Shelf No faulting along coast or continental shelf. Edge of shelf may be fault scarp. Ibid Eucla Shelf to Otway Cape Normal faulting. Ibid Bass Strait Downwarped block or graben in late Tertiary. Boutakoff, 1955 Tasmania (western) Normal faulting, folding. Ibid During Paleozoic, ice sheet moved from a land mass lying to the south - west of Tasmania. King, 1953 Longwell, 1958 Ice did not move across Tasmania into Australia; Tasmania was glaciated from a local center in the NW, and ice moved eastward and partly southward. Darlington, 1964 Banks, 1962 Tasmania All coasts are fault-line coasts. du Toit, 1937 Indian Ocean Islands Mauritius Unequal uplift in Recent. Reed, 1944 Surrounding bank Seychelles Rapidly submerged. Seychelles were left behind when ocean spread apart. Two possible con nections: if Carlsberg Ridge divides the Indian Ocean, Seychelles could be part of Africa, or it could be connected via Madagascar. Possible Seychelles move northward (strike-slip fault) and was once connected to Madagascar on east side (where great fault has been identified). West side of Seychelles has highly magnetic ridge which is in line with Mada gascar fault. Recent discovery of Amirantes Trench (7° to 9°S; 52o - 540 E ) indicating tectonic activity. Upward of 200 ft in Recent. Davis, 1928 Davis and Francis, 1964 Loncarevic, 1964 (A 00 Reed, 1944 w Heard Island Macquarie Island 380 miles south of Crozet Island Indian Ocean Ridges Carlesberg P o s s i b l e h o r s t . Recent isostatic rise of plus 40 ft. "Underwater upheaval that bears witness to the existence in Cenozoic times of a continental connection of Antarctica to the rest of the continent of the southern hemisphere. These formations were once dry land.” Evidence is paleogecgraphic. Where ridges approaches Horn of Africa (Cape GuardafuQ, it has been fractured and western section moved 300 km to N. Loncarevic suggests may be enormous fault stretching from southern tip of Madagascar to N. shore of Gulf of Aden and beyond. Lambeth, 1952 Mawson, 1943 Meal'tsev, 1959 Matthews, 1963 Loncarevic, 1964 U l 00 Black and Caspian Seas Russia, Turkey, Bulgaria, Rumania Black Sea Quaternary downwarping. Beloussov, 1964 S. Crimean Coast Fault coast. Larionova, 1959 Paleogeography up to very latest stages, only shallow-water basins existed in place of the Black Sea. An oceanic structure lies below Black Sea. Shallow-water deposits found at 1800 m. No basin even at end of Pliocene's formed in Quaternary. Arkhangelsk! and Strakhov, 1938 Gagel'gants et al, 1958 Neprochnov, 1958, 1959a, 1959b Beloussov, 1960 Beloussov and Rudich, 1960 Russia - Iran Caspian Sea Ibid (for southern part of Caspian Sea) Ibid Kroptkin et al, 1958 Quaternary downwarping. Beloussov, 1962 Ul 00 4* R E F E R E N C E S C I T E D REFERENCES CITED An., 1954, New S o v ie t r e s e a r c h e s , e x p l o r a t i o n and d i s c o v e r ie s in the C e n t r a l A r c t i c : I z v . A kad. Nauk SSSR, no. 5. (T ra n s. Canada DRB T 165 S, p. 5; a l s o DRB t r a n s . T 196 R, p . 4 f o o t n o t e ) . An., 1965, S h e l l s from cones to n a u t i l i : The S c ie n c e s ( P u b l. by N. Y. Acad. S c i . ) , v. 4, no. 8, p . 13-16. Adams, F. 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Creator Terry, Richard Dean (author)

Core Title Continental Slopes Of The World

Degree Doctor of Philosophy

Degree Program Geology

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag Geology,OAI-PMH Harvest

Language English

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Advisor Gorsline, Donn S. (committee chair), Bandy, Orville L. (committee member), Merriam, Richard (committee member)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c18-899246

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