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The Marine Geology Of San Miguel Gap Off Point Conception, California

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The Marine Geology Of San Miguel Gap Off Point Conception, California

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Content This dissertation has been microfilmed exactly as received 6 7 - 8039 WRIGHT, Frederick Fenning, 1934- THE MARINE GEOLOGY OF SAN MIGUEL GAP OFF POINT CONCEPTION, CALIFORNIA. University of Southern California, Ph.D., 1967 Geology University Microfilms, Inc., Ann Arbor, M ichigan THE MARINE GEOLOGY OP SAN MIGUEL GAP OPP POINT CONCEPTION, CALIFORNIA by F red erick Penning Wright A D i s s e r t a t io n P resen ted to the FACULTY OP THE GRADUATE SCHOOL UNIVERSITY OP SOUTHERN CALIFORNIA In P a r t i a l F u lf illm e n t o f the Requirements fo r the Degree DOCTOR OP PHILOSOPHY' — . (Geology) January 1967 UNIVERSITY O F S O U T H E R N CALIFORNIA T H E GRA DUATE SC H O O L U N IV ER SIT Y PARK LO S A N G ELES, C A L IFO R N IA 9 0 0 0 7 This dissertation, written by ................... under the direction of his 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 IL O S O P H Y ................. Dean Date J a n u a r y.,... 1.9 6 7................................. DISSERTATION COM M ITTEE Chairman v !m u u (. /Ofto-uJL— PLEASE NOTE: Figure pages are not original copy. They tend to "curl". Filmed in the best possible way. - University Microfilms. CONTENTS | Page: ABSTRACT................................................................................................................. 1! INTRODUCTION....................................................................................................... 3; D e f in i t io n and lo c a t io n o f a r e a ............................................... 3 ^ O b je c tiv e s .................................................................................................. & Sources o f d a t a ....................................................................................... 7; A c k n o w led g m en ts......................................................................................... ■ 8j P reviou s work . . . ...................., .............................................. 9j Shipboard o p e r a t i o n s ........................................................................ 13j j i General . . . ............................................................................. 13! B athym etric and a c o u s t i c r e f l e c t i o n su rveys . . l 6j Bottom sampling p r o g r a m ......................................................... 21j Study and a n a l y s is p r o c e d u r e s ......................................... 27! ! B athym etric d a t a ............................................................................. 27: A c o u stic r e f l e c t i o n data ......................................................... 281 ! S e d i m e n t s ............................................................................................ 32 i Rocks . . . . .................................................................................. 35; I GEOLOGIC ENVIRONMENT....................................... ■ .................................. . 36 G e n e r a l .............................. 36; Transverse ra n g es and Channel I s la n d s ............................... 39! C o n tin en ta l borderland ................................................................... 42 C o n tin en ta l s l o p e ..................................................• ............................ 461 N o rth east P a c i f i c B asin and Murray F racture Zone. . 48: i i OCEANOGRAPHIC ENVIRONMENT . . . . .............................................. General ......................................... ............................................................. Topographic and "bathymetric I n f lu e n c e s .......................... Winds ................................................................................................................ W a v e s ................................................................................................................ Water c h a r a c t e r i s t i c s ........................................................................ C urrents ........................................................................ .......................... U pw elling ...................................................................................................... Sum m ary.............................................................................................. . . . GEOLOGY OF THE SAN MIGUEL GAP REGION ......................................... General .................................................................................. ..................... Physiography and s tr u c tu r e ........................................................ L i t h o l o g y ........................................................................................ . . . G eologic su b reg io n s ............................................................................. I n s u la r and Santa R osa-C ortes R id ges . . . . . . P atton Ridge and Escarpment ................................... . . C en tra l b a sin .................................................................................. A rg u ello P lateau and Escarpment .................................... The g e o lo g i c h i s t o r y o f San Miguel Gap .......................... SEDIMENTS OF THE SAN MIGUEL GAP REGION .................................... General ........................................................................................................... Sediment c o n s t i t u e n t s ........................................................................ D e t r i t a l m a t e r ia ls ........................................................................ A u th ig en ic sedim ents .................................................................. B i o l o g i c sedim ents ........................................................................ i i i Pagei Sedim entary s u b r e g i o n s .................... ■............................................. 163 | I n s u l a r and Santa R o sa -C o r te s R id g e s ........................... 1 6 3; P a tto n Ridge and Escarpment . . . . . . . . . . l67j C e n tr a l b a s in ..................................................................................... 1 6 7^ A r g u e llo P la te a u and Escarpm ent ..................................... l 6 8 ! S p e c i a l f e a t u r e s o f th e sed im e n ts ........................................... 173: B u r r o w s ..................................................................................................... 173' F a e c a l p e l l e t s ..................................................................................... 1 7 8] Fine s t r a t i f i c a t i o n ..................................................................... 178 T u r b id ite l a y e r s ................................................................................ 179 R a fte d d e t r i t a l m a t e r i a l .......................................................... 180 F o r a m in if e r a l c o i l i n g r a t i o s ................................................ l8lj S e d im e n ta tio n r a t e s ................................................................................ 1 8 s I t The sed im en ta ry regim e o f San M iguel G a p ....................... l89j CONCLUSIONS.......................................................................................................... 198 REFERENCES CITED ............................................................................................... 205 APPENDICES............................................................................................................... 216 I . Sample s t a t i o n s in th e San M iguel Gap a rea . 2l8j 1 I I . H ydrographic s t a t i o n s u sed to i l l u s t r a t e ! o c ea n o g ra p h ic c o n d i t i o n s i n th e v i c i n i t y o f San M iguel G a p .............................................................. 226 I I I . Core l o g s ............................................................................... . 228| IV. Rock sam ples from San M iguel G a p ........................ 23ej V. a . Sedim ent c h a r a c t e r i s t i c s * USC d a ta . . . 236 b. Sedim ent c h a r a c t e r ! s t i e s * NCEL d a ta . . . 244 i v Page V I. a . F o r a m in if e r s from San M iguel Gap s e d i m e n t s ........................................................................... 250 b. C o l l i n g r a t i o in fo r m a tio n * G lo b ig e r in a pachyderma ........................................... 252 V I I . Sand f r a c t i o n a n a ly s e s * San M igu el Gap r e g i o n ..................................................................................... 255 LIST OP FIGURES i I ! F igu re Pagp i 1. Map o f p a r t o f th e c e n t r a l and sou th ern ; C a lif o r n ia c o a s t , showing lo c a t i o n o f , San M iguel G a p ......................................................................... 5 2. Ship t r a c k s f o r b a th ym etric su rv e y s, : San M iguel G a p ......................................................................... 18. 3. Ship tr a c k s fo r a c o u s t i c r e f l e c t i o n su r v e y s, j San M iguel G a p ......................................................................... 20 4 . L o c a tio n s o f bottom sample s t a t i o n s , I San M iguel G a p ......................................................................... 24; 5. A c o u s tic r e f l e c t i o n r e c o r d from San M iguel G a p ......................................................................... 30 6 . G e n e r a liz e d t e c t o n i c framework, ! San M iguel Gap a r e a ......................................................... 38 7 . Su rface w ater c i r c u l a t i o n , j N o r th e a st P a c i f i c area .................................................... 53 8 . Hydrographic s t a t i o n s and bathym etry, San M iguel Gap a r e a ......................................................... 56 9. T e m p e r a t u r e -s a lin it y o f w aters o f f P o in t C o n c e p t i o n .................................................................... 65 i 1 0 . Standard w ater p r o p e r t i e s , j San M iguel Gap area . ............................................... 68’ 1 1 . N u tr ie n ts in th e w a ters o f f j P o in t C o n c e p t i o n .................................................................... 74 1 1 2 . Oceanic c u r r e n ts o f f th e C a lif o r n ia j c o a s t ( s u m m e r ) ......................................................................... 73 i 1 3 . Oceanic c u r r e n ts o f f th e C a lif o r n ia i c o a s t ( w i n t e r ) ......................................................................... 77 i 1 14. C urrents o f f P o in t C on ception, j January, 1964 79 i 15. Bottom c u r re n t measurements on j A r g u e llo P la te a u .................................................................... 83 vi F igu re 1 6. 17. 1 8. 19- 2 0 . 21. 2 2 . 23. 24. 25. 2 6. 27. 2 8 . 29. 30. 31. 32. 33. 34. Pagej I P h y sio g ra p h ic r e g io n s w it h in j San M iguel Gap a r e a .......................................................... 94j Bathym etry o f th e San M iguel Gap a r e a ..................... 96' , i Tracing o f a c o u s t i c r e f l e c t i o n j p r o f i l e s 16 and 1 8 ............................................................... lOOj T racing o f a c o u s t i c r e f l e c t i o n I p r o f i l e s 20 and 2 1 ............................................................... 1 0 2! I n t e r p r e t a t i o n o f a c o u s t i c r e f l e c t i o n i p r o f i l e s 16 and 18 . ..................................................... 1051 I n t e r p r e t a t i o n o f a c o u s t i c r e f l e c t i o n i p r o f i l e s 20 and 2 1 ............................................................... 107 Sedim entary and ig n e o u s r o c k s dredged in San M iguel G a p .......................................................................... HOj i Ign eou s ro ck s from the c o n t i n e n t a l s l o p e , j San M iguel Gap a r e a .......................................................... 112! T e x tu ra l c l a s s i f i c a t i o n o f se d im e n ts, San M iguel Gap a r e a .......................................................... 128 D i s t r i b u t i o n o f s a n d - s iz e d m a t e r ia l i n ! su r fa c e s e d i m e n t s .................................................... 130! ] D i s t r i b u t i o n o f g e n e r a l sedim ent t y p e s . . . . 134 D i s t r i b u t i o n o f t e r r e s t r i a l s a n d ................................ 137j D i s t r i b u t i o n o f t o t a l t e r r e s t r i a l m a t e r i a l. . . l 4 l D i s t r i b u t i o n o f g l a u c o n i t e ............................................... l 4 s Coarse f r a c t i o n s o f g l a u c o n i t e - r i c h j su r fa c e sed im en ts ............................................................... 148 1 Sediment c h a r a c t e r i s t i c s , Core AHF 10106 . . . 1 5 ! Sand f r a c t i o n , Core 1 0 1 0 8 ..................................................... 1 5^ i Sand f r a c t i o n s o f some s u r fa c e sed im en ts . . . 157 1 i D i s t r i b u t i o n o f fo r a m in ife r a in sed im en ts . . . 160 v i i F igu re 35. S u rface sedim ent c h a r a c t e r i s t i c s on c r o s s - s e c t i o n a c r o s s th e Gap . . . . 3 6 . S u rface sedim ent c h a r a c t e r i s t i c s on c r o s s - s e c t i o n a c r o s s A r g u e llo P la tea u 37. S p e c ia l f e a t u r e s o f sed im en ts ..................... 3 8 . Cores from San M iguel Gap ................................ 39. Sediment c h a r a c t e r i s t i c s in c o r e s . . . v i i i LIST OP TABLES | Table Page; 1. S e l e c t e d h yd rogra p h ic c r u i s e s i n th e ! v i c i n i t y o f San M iguel G a p ........................................... 55 2. Water ty p e s i n th e sh a llo w c i r c u l a t i o n ; o f f so u th ern C a l i f o r n i a ................................................ 6 3 ! 3 . Bottom w a ter c h a r a c t e r i s t i c s in th e San M iguel Gap a r ea (June., 1 9 6 5 ) . . . . . . 6 9! i 4 . Ig n eo u s ro ck s c o l l e c t e d i n San M iguel f Gap a r e a .......................................................................................... 108j i 5 . Sedim entary r o c k s c o l l e c t e d in j San M iguel Gap a r e a ........................................................... Il4| 6 . Summary o f c h a r a c t e r i s t i c s i n ' sed im en tary s u b r e g io n s o f th e Gap . . . . . 132 7. V a r i e t i e s o f g l a u c o n i t e .......................................................... 152; 1 j 8 . S e d im e n ta tio n r a t e s i n th e v i c i n i t y o f i San M iguel G a p .......................................................................... l84j | 9. R a te s o f a c cu m u la tio n o f th e major sed im en t c o n s t i t u e n t s ., San M iguel Gap a r e a ........................................................... l 88| [ 10. R e l a t i v e c o n t r i b u t i o n s o f p r i n c i p a l ; sed im en t c o n s t i t u e n t s , 1 San M iguel Gap a r e a ........................................................... 190 ix ABSTRACT San M iguel Gap i s a subm arine b a s in which I n t e r s e c t s th e continen-bal s l o p e so u th w est o f P o in t C o n cep tio n . I t l i e s a t the n o r th w e st l i m i t o f th e C a l i f o r n i a c o n t i n e n t a l b o r d e r la n d . The b a s in I s bounded by s t r a i g h t , s t e e p s l o p e s which se p a r a te i t from A r g u e llo P la te a u to th e n o r th and th e Channel I s l a n d s and Santa R o sa -C o r te s R idge to th e e a s t . A g e n t l e r , l e s s r e g u la r s lo p e to th e so u th l e a d s to th e P a t ton R id g e . The b a s in i s 30 x 35 km a t a depth o f 1500 m; i t s l o p e s g e n t l y seaward to b rea ch the c o n t i n e n t a l s lo p e to a depth o f 2500 m. Sub-bottom a c o u s t i c r e f l e c t i o n p r o f i l e s a c r o s s th e Gap, show p r e - and p o s t o r o g e n ic g e n e r a t i o n s o f se d im e n ta ry f i l l , d i s t i n g u i s h e d by m ild p e r ip h e r a l f o l d i n g in th e o l d e r s e c t i o n . Assuming a sed im en t v e l o c i t y o f 2 k m /se c , th e b a s in c o n t a in s a maximum t h i c k n e s s o f 270 m o f p o s t o r o g e n ic and 400 m o f p r e o r o g e n ic f i l l . B en eath th e b a s i n , form ing the c o n t i n e n t a l s l o p e , and o u tc o p p in g on th e r id g e s th e r e i s a u n i t term ed " a c o u s t ic b e d r o c k ." Where sam pled, t h i s i s Miocene (?) b a s a l t or se d im en ta ry ro ck . A c o u s t ic bedrock c o r r e l a t e s w ith th e Channel I s l a n d s s e c t i o n o f C r eta ceo u s to Miocene se d im e n ts and v o l c a n i c s . P o s s i b l e boundary f a u l t s l i e to th e e a s t and n o r th , w h ile to th e so u th th e r e i s a p o s s i b l e dow nfold to form th e Gap b a s i n . The Gap r e g io n i s an e lo n g a t e c o n t i n e n t a l s lo p e s e d i m entary en v iro n m en t, under t e r r e s t r i a l i n f l u e n c e to th e e a s t and o c e a n ic i n f l u e n c e to th e w e s t . T e r r e s t r i a l san d s, nea r th e i s l a n d s , grade i n t o g l a u c o n i t i c sands on th e deeper s l o p e s and h e m ip e la g ic c l a y e y s i l t in th e b a s i n . B oth sed im en t p r o d u c tio n and d i s t r i b u t i o n are c o n t r o l l e d by o c ea n o g ra p h ic a g e n c i e s . In p a r t i c u l a r , str o n g c u r r e n ts i n f l u e n c e th e e n t i r e w ater column. S u rfa c e flo w s o f t e n e x c eed 200 cm /sec , and v e l o c i t i e s a v e r a g in g 5 c m /s e c , p ea k in g o v e r 20 c m /s e c , were measured a t 727 m. T e r r e s t r i a l sands come from th e i s l a n d s ; th e y are c o n t r o l l e d by wave a c t i o n . S i l t s and c l a y s , l a r g e l y d e r iv e d from th e main la n d , are d i s t r i b u t e d by w in d s, s u r f a c e and bottom c u r r e n ts, and are c o n c e n tr a t e d in th e b a s i n . F o r a m in ife r s are e x tr e m e ly common i n th e sed im en t; t h e i r abundance i s a fu n c t i o n o f su r fa c e o r g a n ic p r o d u c t i v i t y and b ottom c u r r e n t w innow ing. G la u c o n ite i s u b iq u it o u s and contem porary; i t c o n s t i t u t e s o v e r o n e - h a l f th e sed im en t where o t h e r d e p o s i t i o n i s i n h i b i t e d . A p ro b ab le a u t h i g e n ic sequ en ce from p r e c i p i t a t i o n i n sm a ll s h e l l s to t y p i c a l g l a u c o n i t e p e l l e t s can be i d e n t i f i e d in Gap se d im e n ts. 1 2 R e l a t i v e c o n t r i b u t i o n s o f th e m ajor se d im e n t c o n s t i t u e n t s were d e ter m in e d f o r e a ch s e c t i o n o f th e Gap a r ea : C o n c e n tr a tio n T e r r e s t r i a l O rganic ( * ) A u t h ig e n ic S a n ta R o s a -C o r te s R idge 50 42 7 C e n t r a l B a s in 76 22 . 2 Deep s l o p e s and t e r r a c e s 30 27 42 S e d im e n ta tio n r a t e s ran ge from 1 3 -1 5 mm/10^ y e a r s on th e deep s l o p e s to 31 mm/lO^ y e a r s a t th e head o f th e b a s i n and 5 4 mm/lo3 y e a r s i n th e c e n t r a l b a s i n . Assuming c o n s t a n t r a te s ., th e o b s e r v e d f i l l t h i c k n e s s i n th e b a s in c o u ld have a c cu m u la ted i n 1 3 .4 x 10^ y e a r s , s i n c e E a r ly P l i o c e n e . A l l d a t e s u s e d i n th e e s t i m a t e s a re b a se d upon th e s i n i s t r a l - t o - d e x t r a l c o i l i n g d i r e c t i o n s h i f t i n th e f o r a m i n i f e r , G lo b ig e r in a pachyderm a, a t th e end o f th e P l e i s t o c e n e . S tu dy o f c o r e s i n t h e Gap r e g io n i n d i c a t e s no s i g n i f i c a n t change in th e se d im e n ta r y o r o c e a n o g r a p h ic r e g im e s s i n c e L ate P l e i s t o c e n e , Two pronounced e a s t - w e s t s t r u c t u r e s , th e Murray F r a c t u r e Zone o f th e P a c i f i c b a s i n and th e T r a n sv e r se Ranges o f C a l i f o r n i a , a r e a l i g n e d w it h th e Gap. I t h a s b een s u g g e s t e d t h a t t h i s b r e a k i n th e c o n t i n e n t a l s l o p e r e p r e s e n t s an i n t e r a c t i o n o f o c e a n ic and c o n t i n e n t a l ' s t r u c t u r e s . A l l e v id e n c e , h ow ever, i n d i c a t e s t h a t San M iguel Gap i s a b o r d e r la n d s t r u c t u r e formed d u rin g Late M iocen e, w hich h a s s u b s e q u e n t ly un dergon e l i t t l e d i s t u r b a n c e . No r e l a t i o n w it h th e e a s t - w e s t s t r u c t u r e s i s c l e a r . INTRODUCTION D e f i n i t i o n and L ocation o f Area San Miguel Gap i s a b a sin a t the extreme northw estern l i m i t o f the C a lif o r n ia c o n t in e n t a l b ord erlan d . I t l i e s app roxim ately 100 km southw est o f P oin t Conception., C a l i f o r n ia . An e n t i r e l y submarine f e a t u r e , whose dim ensions are roughly 40 x 60 km, the b a s in i s e lo n g a te in the e a s t - w est d i r e c t io n and i n t e r s e c t s th e c o n tin e n t a l slo p e j u s t sou th o f R odriguez Seamount (P ig . l ) . The b a s in proper i s d e fin e d by the A rg u ello P lateau to the north, the I n s u la r Ridge and Santa R osa-C ortes Ridge to the e a s t , and the P atton Ridge to the so u th . I t i s open to the P a c i f i c Ocean b a s in to the w e st. The name, San Miguel Gap, was a p p lie d to the b a sin by Uchupi (Uchupi and Emery, 1 9 6 2) because the fe a tu r e i s a d i s t i n c t break in the c o n t in u it y o f the con t i n e n t a l slo p e and i s c lo s e to San Miguel I s la n d . An area 2 o f app roxim ately 4000 km , c e n te r e d about San M iguel Gap, exten d in g from 3 3 ° 4 0 1 to 34°10' North L a titu d e , 1 2 0 °3 0 1 to 1 2 1 ° 0 0 1 West L on gitu de, was s e l e c t e d fo r a d e t a i l e d g e o l o g i c and oceanographic stu d y . The C o n tin en ta l margins are a c t u a l l y among the most g e o l o g i c a l l y im portant r e g io n s o f the w orld, fo r they mark 3 P ig . 1 . — Map o f p a r t o f th e c e n t r a l and sou thern C a li f o r n ia c o a s tj showing l o c a t i o n o f San M iguel Gap. 4 3 5 °- 3 4 ° - 33° - INDEX MAP Bathymetry adapted from Shepard & Emery (1941) U.S. Bureau Commercial Fisheries (I960) Pt. Buchon P t Arguello Pt. C oncep tio n S la. Cruz I. RODRIGJJ SEAM 9 Los A ngeles San Miguel Gap Area S ta B arbara I * S ta. Catalina sland San N icolas [ s a n ' j u a n 1 u SEAMOUNT & em ente K ilom eters N au tical M ifes C o ntours in m otors I \ J 1 th e l i t h o ' l o g i c , s e d i m e n t o lo g ic , and s t r u c t u r a l t r a n s i t i o n from th e c o n t i n e n t s to th e deep ocean b a s i n s . A c o n s i d e r a b le l i t e r a t u r e , e x h a u s t i v e l y r e v ie w e d by T erry (19&5) j e x i s t s , b u t u n f o r t u n a t e ly much o f th e in fo r m a tio n i s l i m i t e d to b a th y m e tr ic d a ta . Samples o f bottom m a t e r i a l e i t h e r on th e s lo p e p rop er o r on the o u t e r c o n t i n e n t a l s h e l f are few and w id e ly sp a c e d . I n h e r e n t l y , th e zone i s more d i f f i c u l t to stu d y than th e in n e r c o n t i n e n t a l s h e l f , where w ater d e p th s are l e s s and n a v i g a t i o n a l c o n t r o l s i m p l i f i e d , o r th e deep ocean b a s i n s where a p p r e c ia b le b ottom s l o p e s a re r a r e and th e v a r i a t i o n in s u b s t r a t a i s l i k e l y to be l e s s r a p id . D e s p it e th e problem s o f w orking on th e c o n t i n e n t a l s l o p e s , t h e s e r e g i o n s d e s e r v e c o n c e n tr a t e d stu d y i f th e r e l a t i o n s h ip betw een th e c o n t i n e n t s and the ocean b a s i n s i s to be c l a r i f i e d . O b j e c t iv e s The San M iguel Gap a rea p r e s e n t s a v a r i e t y o f i n t e r e s t in g p rob lem s. B eca u se o f i t s form and p o s i t i o n , i t r e p r e s e n t s an e x te n d ed c o n t i n e n t a l s lo p e se d im en ta ry en viron m en t, i n f l u e n c e d p r im a r ily by c o a s t a l and sh a llo w w ater p r o c e s s e s to th e e a s t b u t g r a d in g w estward i n t o a more and more o c e a n ic r eg im e. Water d ep th s range from s h o a l w a te r s near th e i s l a n d s to o v e r 3000 m a t th e b a se o f th e P a tto n E s carpm ent, The Gap i s a t a p o i n t where s e v e r a l major t e c t o n i c f e a t u r e s , th e c o n t i n e n t a l s lo p e i t s e l f , th e c o n t in e n - t a l b o r d e r la n d , and th e tren d o f C a l i f o r n i a ' s T ransverse Rangesj appear to j o i n . As w e l l , the Murray F ractu re Zone o f th e P a c i f i c B a sin may I n t e r s e c t th e c o n t in e n t o f North America in t h i s v i c i n i t y . The h i s t o r y o f the Gap i s thus d i r e c t l y r e l a t e d to th e h i s t o r y o f a much broader r e g io n . The s p e c i f i c o b j e c t i v e s o f t h i s stu d y are ( l ) to d e s c r ib e the g e o lo g y o f an anomalous segm ent o f th e c o n t in e n t a l margin and to r e l a t e t h i s to th e r e g io n a l g e o lo g y , and (2) to e x p la in the d i s t r i b u t i o n o f th e contem porary and the s u b -r e c e n t sed im en ts o f the a r ea in terms, o f th e o b serv ed and p o s t u l a t e d p h y s ic o -c h e m ic a l environm ent. S ou rces o f Data T his r e s e a r c h i s based on a t o t a l o f 88 sam ples o f sedim ent and rock from the San M iguel Gap a r e a . The m ajor i t y o f th e s e sam ples were c o l l e c t e d by V e lero IV , th e r e se a rc h v e s s e l o f th e A lla n Hancock F oun dation, U n iv e r s it y o f Southern C a l i f o r n i a . The s t a t i o n s in c lu d e 17 dredge h a u ls ( o f which 9 y i e l d e d r o c k ), 4 l g r a v i t y c o r e s , two p i s t o n c o r e s , and 28 su r fa c e sedim ent sam ples (Appendix I ) . A pproxim ately 1500 km o f co n tin u o u s P r e c is io n Depth R ecorder echograms were made, and a d d i t io n a l b a th y m etr ic in fo rm a t i o n from the U n ited S t a t e s C oast and G eod etic Survey was u t i l i z e d . Continuous a c o u s t i c r e f l e c t i o n p r o f i l e s were made a v a i l a b l e by th e U n ited S t a t e s Naval Ordnance T e st jS tation and by the S crip p s I n s t i t u t i o n o f Oceanography. Ad d i t i o n a l sam ples and o th e r in fo r m a tio n were su p p lie d by the ;United S t a t e s Naval C i v i l E n g in eerin g Laboratory. Acknowledgments This work was made p o s s i b l e by the A llan Hancock Foun d a tio n , U n iv e r s it y o f Southern C a lif o r n ia , which p rovided sh ip tim e on R /y V elero IV under a N a tio n a l S c ie n c e Founda t i o n g r a n t. Much o f the a n a l y s i s and la b o r a to r y work was supported by a Penrose B equest Research Grant from th e Geo l o g i c a l S o c ie t y o f America. Many i n d iv i d u a l s and o r g a n iz a t io n s g e n e r o u sly p rovided 'samples, in fo r m a tio n , and encouragement during the stu dy o f San Miguel Gap. The study would have been im p o s s ib le w ith out th e a c t i v e i n t e r e s t and support o f Capt. Fred Z e is e n - henne and the crew o f V elero IV . I w ish p a r t i c u l a r l y to thank Roland von Huene o f the U n ited S t a t e s Naval Ordnance T est S ta tio n (NOTS), Ronald Jon es, Melvin Hironaka, and 'Kenneth Gray o f the U n ited S t a t e s Naval C i v i l E n gin eering Laboratory (NCEL), and Joseph Curray o f S crip p s I n s t i t u t i o n o f Oceanography. Donald Weaver, David Doerner and the Graduate Geology Seminar at the U n iv e r s it y o f C a lif o r n ia , Santa Barbara, shared t h e i r unique e x p e r ie n c e w ith th e g eo lo g i c problems o f the Northern Channel I s la n d s , The sup p ort and c o n s t r u c t iv e c r i t i c i s m o f P r o fe s s o r s Donn S. Gors- | l i n e j O r v ille L. Bandy, Richard 0. Stone, and John ¥ . R eith I |o f the U n iv e r s it y o f Southern C a lif o r n ia , are g r a t e f u l l y I acknowledged. j I P reviou s Work I i The c o n t in e n t a l margin o f the w est c o a s t o f North -America i s one o f the most thorough ly s tu d ie d such a rea s in the w orld. On the c o n tin e n t , thanks to v a lu a b le m ineral ;d e p o s it s , i n t e n s i v e g e o lo g ic study has been in p r o g r e ss fo r over a cen tu ry. Large q u a n t i t i e s o f petroleum have been ;produced on th e mainland and from the sh a llo w sea f l o o r from Cenozoic marine s t r a t a g e n e r a lly s im ila r to the s e d i ments p r e s e n t l y accum ulating o f f s h o r e . A w ea lth o f g e o lo g ic in fo rm a tio n i s a v a i la b l e on the C a lif o r n ia c o a s t a l r e g io n s , ■summarized and d is c u s s e d in such m assive r ev iew s as S tr u c t u r a l E v o lu tio n o f Southern C a lif o r n ia (Reed and H o l l i s t e r , :1936), The Geology o f Southern C a lif o r n ia (Jahns, 1954) and i many o th e r l e s s comprehensive r e p o r t s . The f i r s t g e o l o g i c a l l y u s e f u l in form a tion from the C a lif o r n ia o f f s h o r e area was provided by the U nited S t a te s iCoast and G eodetic Survey. Their work in th e e a r ly 1 93 0's i i s one o f the f i n e s t , most d e t a i l e d deep-w ater bath ym etric I su rveys ever conducted. These d a ta , in t e r p r e t e d by Shepard and Emery ( l 9 4 l ) , p e rm itted the c le a r d e f i n i t i o n o f the ;v a r ie t y o f submarine topography o f f the C a lif o r n ia c o a st |( P ig . l ) . North o f P o in t C onception, th ere i s a r e l a t i v e l y j '....... ....... 10 iSlmple p a tte r n o f c o n t in e n t a l s h e l f , slo p e and ocean b a s in , jbut to the sou th th e s i t u a t i o n I s a more complex one. Off ;southern C a lif o r n ia and Baja C a l i f o r n ia , a t r a n s i t i o n zone iof r id g e s and b a s in s in t e r v e n e s between a narrow, sh a llo w c o n t in e n t a l s h e l f and the c o n t in e n t a l s lo p e . This i n t e r m ediate zone, termed the c o n t in e n t a l b ord erlan d , may be as : much as 3°0 km w ide. San M iguel Gap l i e s a t th e p o in t ; 1 where the two ty p es o f c o n t in e n t a l margin j o i n . The g e o lo g y o f the o ff s h o r e r e g io n has been stu d ie d 'e x t e n s iv e ly by P. P. Shepard and h i s s tu d e n ts a t S crip p s I n s t i t u t i o n o f Oceanography and by K. 0. Emery's group a t the U n iv e r s it y o f Southern C a l i f o r n ia . Much o f t h i s work on the sed im en ts, rock s and physiography o f the c o n t in e n t a l margin, and e s p e c i a l l y the c o n t in e n t a l b ord erlan d , has been C o l l a t e d by Emery and summarized in h i s u s e f u l book. The Sea o f f Southern C a lif o r n ia ( i 9 6 0 ) . Krause (1964, 1 9 6 5) r ep o rted on th e marine g e o lo g y o f the southern c o n t in e n t a l b ord erlan d , w est o f Baja C a lif o r n ia . U nderstandably enough, a t t e n t io n has been c o n c en tr a ted upon the sh a llo w e r , more a c c e s s i b l e p o r t io n s o f the o f f s h o r e . R e l a t i v e l y few s t u d i e s have been s p e c i f i c a l l y concerned w ith the o u te r c o n t in e n t a l borderland or the c o n t in e n t a l s lo p e . There have been rec o n n a issa n c e s t u d i e s o f the i s l a n d s o f f southern C a lif o r n ia (fo r in s t a n c e , Smith, 1 8 9 8; Bremner, 1 9 3 2, 1 9 3 3) j but u n t i l r e c e n t ly th ere was l i t t l e d e t a i l e d ■ geologic in fo r m a tio n . A comprehensive r e p o r t on San N ico la s | I s la n d (Vedder and Norris., 1 9 63) i s now a v a i l a b l e , and an ;a c t i v e g e o l o g i c mapping program on the Northern Channel ;I s la n d s by D. W. Weaver and h i s s tu d e n ts a t th e U n iv e r s i t y o f C a lifo rn ia ,, Santa Barbara i s in p r o g r e ss (S u lliv a n and 'Weaver., 1965j Weaver and Doerner, 1 9 6 6) . The se d im en to lo g y o f s e v e r a l o f th e o u te r r id g e s and ’b a s in s o f th e b o rd erlan d has been s tu d ie d in d e t a i l . The ■ crest o f th e Santa R osa-C ortes Ridge (Uchupi, 1 9 6 1) , C ortes ;and Tanner Banks (Holzman, 1 9 5 2 ), Tanner B a sin ( G o r s lin e , _ le t a l . , in p r o g r e s s ) , and the s h e l f o f f P o in t C onception j ( D i l l , 1 9 5 2 ), have a l l been i n v e s t i g a t e d . The g e n e r a l 'S t r u c t u r a l framework o f th e margin i s known from the s e is m ic work o f Shorr and R a i t t (1 9 5 8 ). More d e t a i l e d su rveys o f ;th e sh a llo w sub-bottom s t r u c t u r e have been made w ith th e r e c e n t l y d ev elo p ed a c o u s t ic r e f l e c t i o n equipment by Curray n orth o f P o in t C onception ( 1 9 6 5) and Moore sou th o f Concep t i o n ( 1 9 6 6) . G ra v ity su rv e y s o f Santa Barbara Channel are r e p o r te d by von Huene and R idlon ( 1 9 6 6) . The se ism o lo g y and s t r u c t u r e o f much o f the b ord erla n d i s c o n sid e r e d in a r e c e n t r e g io n a l i n v e s t i g a t i o n embracing a l l o f southern C a l i f o r n ia ( A lle n , e t a l . , 1 9 6 5)* The c o n t i n e n t a l s lo p e proper has been the s p e c i f i c s u b j e c t o f very few s t u d i e s . Uchupi and Emery ( 1 9 6 2) r e p o r te d on a r e c o n n a is s a n c e stu d y o f the s lo p e from the l a t i tude o f San F ra n cisco sou th to Cedros I s la n d , o f f Baja C a l i - I f o r n ia . Samples from th e s lo p e and some nearby seamounts ■ were d is c u s s e d by Hanna (1 9 5 2 ). Only two d e t a i l e d s t u d ie s I o f lim it e d s e c t i o n s o f the slo p e e x i s t . Palmer (1964) e x - i lamined Rodriguez Seamount, which i s on the c o n t in e n t a l I slo p e j u s t north o f San Miguel Gap. B u tle r (1964) r ep o rted !on a submarine v a l l e y a t the c r e s t o f the c o n t in e n t a l slo p e iw est o f San D iego. There have been many oceanographic s t u d ie s o f varyin g scope concerned w ith the w aters o f f C a lif o r n ia . P rio r to the Second World War, most o f the work was conducted by ■ships o f S crip p s I n s t i t u t i o n working out o f San D iego. Dur- 'in g the war the m e te o r o lo g ic and an ti-su b m arin e u t i l i t y o f ■oceanographic r e se a r c h was dram atized and e x te n s iv e work by ;S crip p s and v a r io u s U n ited S t a t e s N a v a lla b o r a t o r ie s was :i n i t i a t e d and has been co n tin u ed . The most e x te n s iv e un c l a s s i f i e d su rveys were p erform ed -in co n n ectio n w ith the ;b i o l o g i c a l l y - o r i e n t e d C a lif o r n ia C oop erative Oceanic F is h e r i e s I n v e s t i g a t i o n s (CCOFl). S in ce the l a t e 19 4 0 1s se v e r a l CCOFI c r u is e s each y e a r have been concerned w ith the c h a r a c t e r i s t i c s o f the su rfa c e w ater masses along much o f the C a lif o r n ia c o a s t , and both the data and comprehensive ir e p o r ts have been i s s u e d r e g u la r ly (Marine Research Commit- 't e e , 1950, 1953, 1958, 1 9 6 3) . 13 j Shipboard O p era tio n s j G eneral I The v a l i d i t y o f any s c i e n t i f i c stu d y depends upon th e iq u a lit y o f th e i n i t i a l d a ta . In marine g e o l o g i c work,, th e ‘c r i t i c a l i n i t i a l f a c t o r s are c e r t a i n l y o f g e o g ra p h ic p o s i t i o n and th e c h a r a c t e r i s t i c s o f th e sam pling a p p a ra tu s. I n e v i t a b l y th e r e are economic r a th e r than pure s c i e n t i f i c f a c t o r s which c o n t r o l much o f th e a b s t r a c t e f f i c i e n c y o f the ^op eration s, nam ely, th e h igh c o s t o f sh ip tim e and e q u ip m ent . In a r e g io n such as th e Gap, th e most o b v io u s l i m i t a t i o n upon e f f e c t i v e work i s la c k o f p r e c i s i o n in n a v ig a t i o n . The w eather o f f P o in t C onception i s such t h a t v i s u a l f i x e s are p o s s i b l e o n ly c l o s e to th e i s l a n d s , and th e h o r i zon i s so o f t e n o b scu red th a t c e l e s t i a l n a v ig a t io n i s v i r t u a l l y i m p o s s i b l e . As a co n seq u en ce, most n a v ig a t io n was by radar and dead r e c k o n in g , p a r t i c u l a r l y th e l a t t e r , f o r th e la c k o f good radar t a r g e t s on th e so u th ern s i d e o f th e i s la n d s l i m i t e d e f f e c t i v e radar range to about 15 n a u t i c a l Im iles. Under the b e s t o f c o n d i t i o n s , dead r eck o n in g l e a v e s much to be d e s ir e d ; h e r e , in a r e g io n n o te d f o r s tr o n g , 'v a r ia b le c u r r e n t s , a b s o lu t e r e l i a n c e upon dead reck o n in g can le a d to c h a o s. The o n ly s o l u t i o n was to p la n o p e r a t i o n s to p erm it fr e q u e n t v i s i t s to p o i n t s t h a t co u ld be 'p r e c is e l y l o c a t e d . For s e v e r a l c r u i s e s , a most u s e f u l 14 check point was provided by a buoy anchored a t one o f the NCEL deep sea t e s t s i t e s on Patton Ridge. I t I s d i f f i c u l t to p r e c i s e l y d e fin e the l i m i t s o f n a v i g a t io n a l c o n tr o l in t h i s stu d y . In g e n e r a l, the accuracy during bathym etric surveys was r e l a t i v e l y good. A l l l i n e s were run w ith the sh ip moving a t seven to nine k n o ts, and the l i n e s were d esign ed to perm it freq u en t checks w ith the i s l a n d s or prom inent, i d e n t i f i a b l e bathym etric fe a t u r e s . I f a p p re c ia b le d is c r e p a n c ie s between dead reckoning and a c t u a l p o s i t i o n occu r, i t i s r e l a t i v e l y easy to c o r r e c t back ward along a survey l i n e . Where sounding p r o f i l e s c r o s s , r e l a t i v e p o s i t i o n can be a d ju ste d to g iv e a reason ab le f i t o f the bathym etric d a ta . The n a u t ic a l ch art o f th e r e g io n , U n ited S t a t e s Coast and G eodetic Survey,Chart 5202, was e x trem ely u s e f u l during t h i s phase o f the o p e r a tio n . Con s id e r in g a l l o f the f a c t o r s , n a v ig a tio n a l c o n tr o l during the bathym etric surveys probably v a r ie s from a few ten s o f m eters near the Channel I s la n d s to a maximum o f perhaps a k ilo m ete r (roughly o n e -h a lf n a u t ic a l m ile) in the o u ter Patton Ridge and A rgu ello P lateau s e c t i o n s . Location o f the sampling s t a t i o n s i s much l e s s c l o s e l y c o n t r o lle d . With the gear used fo r bottom sam pling, upwards o f o n e - h a lf hour was req u ired fo r the equipment to reach bottom, and a t l e a s t as long fo r rec o v er y . In the rough w aters o f f P oin t C onception, cu rren ts as g r e a t as two knots are not uncommon. Thus during a s i n g le s t a t i o n , the ship cou ld have moved s e v e r a l k ilo m e t e r s . A rough check upon d r i f t was provided by ob serv in g the depth reco rd er w h ile on s t a t i o n . C le a r ly , i f th ere are a p p r e c ia b le changes in the depth during a sample s t a t i o n , c o n sid e r a b le d r i f t has o c curred. In a s s ig n in g a f i n a l p o s i t i o n to each s t a t i o n , the f o llo w in g f a c t o r s were c o n sid er ed : the b e s t e s tim a te o f p o s i t i o n a t the s t a r t o f the s t a t i o n , the time and depth o f bottom c o n ta c t , the d i r e c t io n and magnitude o f wind and se a s during the s t a t i o n , and any c o n t r o l provided by l a t e r l a n d f a l l s . I t I s b e l ie v e d th a t s t a t i o n l o c a t i o n s are a c cu rate to about 2 km ( l n a u t ic a l m ile ) over most o f the a r ea , but th ere may be even g r e a te r e r r o r s in the p o s i t i o n s o f some o f the more remote s t a t i o n s . F o r tu n a te ly , on the s lo p e s where bottom c o n d it io n s may change r a p id ly and thus p o s i t i o n i s more c r i t i c a l , th e re are enough I d e n t i f i a b l e b ath ym etric f e a t u r e s to a s s i s t m a t e r ia lly in n a v ig a tio n . Samples and su rvey In form ation p rovided by the coope r a t in g n ava l la b o r a t o r ie s are lo c a t e d w ith c o n sid e r a b ly more p r e c is io n than the Y elero IV d a ta . A l l o f the v e s s e l s u t i l i z e d Loran-A or Loran-C, and some o f the s t a t i o n s were p o s i t i o n e d by the commercial R a yd ist system , which i s a c cu rate to a few te n s o f m eters. B a th y m e tric and A c o u s tic R e f l e c t i o n Su rveys In th e c o u r se o f t h i s study., o v e r 800 n a u t i c a l m i le s (a p p r o x im a te ly 1500 km) o f c o n tin u o u s s o n ic bottom p r o f i l e s were made by Y e le r o IV ( P ig . 2 ) . O r ie n t a t io n o f th e p r i mary l i n e s was d eterm in ed by th e d e s i r e to c r o s s normal to th e p r i n c i p a l s l o p e s and to o b ta in th e maximum number o f n a v i g a t i o n a l c h e c k p o in t s . A d d it io n a l l i n e s made w h ile ru n n in g to or from sample s t a t i o n s were u s e d when th e n a v ig a t i o n c o n t r o l seemed a d e q u a te. In th e im m ediate v i c i n i t y o f R od riguez Seamount, th e b a th y m e tr ic c o n to u r s were adapted from th e d e t a i l e d work o f Palmer (1 9 6 4 ) . Y e le r o IV i s equip ped w it h a Times F a c s im ile Company Mark IV P r e c i s i o n Depth R ecorder (PDR), co u p le d to an Edo UQN-1 Echo Sounder. The Y e l e r o ' s PDR h as been m o d ifie d f o r d e t a i l e d b a th y m e tr ic su r v e y s by th e e x p a n sio n o f th e v e r t i c a l s c a l e ; fathogram s p r e s e n t 200 I n s t e a d o f th e custom ary 400 fathom s on th e 1 9 - in c h w id th o f th e r e c o r d in g p ap er. Hence, d ep th s are read w ith some c o n fid e n c e to th e n e a r e s t m eter. Dr. Roland von Huene, o f th e N0TS, China Lake, f u r n is h e d a p p r o x im a te ly 140 n a u t i c a l m i le s (2 5 0 km) o f c o n t i n uous a c o u s t i c r e f l e c t i o n r e c o r d s o f su b -b ottom se d im e n ts and s t r u c t u r e c o l l e c t e d i n th e Gap r e g io n (Fig.. 3 ) . A nother 40 m ile s o f r e c o r d from th e a rea was f u r n is h e d by J . Curray o f S I0 . U n f o r t u n a t e ly , t h i s was o b ta in e d on an e a r l y c r u is e Pig. 2 . — Ship tracks for bathymetric surveys, San Miguel Gap. IT BATHYMETRIC SURVEYS-SHIP TRACKS SAN MIGUEL GAP AREA K itom itara Contour* in m atars I SANTA ROSA ISLAND I2f*00* 120*40* P ig . 3 - - - S h ip tr a c k s fo r a c o u s t i c r e f l e c t i o n s u r v e y Sj San M iguel Gap. 19 ACOUSTIC REFLECTION PROFILE LINES SAN MIGUEL GAP AREA K ilO f f ie ttr t iSAN MIGUEL ISLAND1 |SANTA ROSA ISLAND •3000' 1 2 1 '0 0 ' ,0 0 » fr£ .OfroEE when the equipment was s t i l l in the exp erim en ta l sta g e and ; v ery l i t t l e o f the reco rd i s u s e f u l . The d e v ic e u sed in th e se s t u d i e s , th e R a yflex E xp lo ra t io n Company E le c t r o - S o n ic P r o f i l e r (ESP), i s an a r c -so u r c e apparatus which o p e r a te s much l i k e the PDR. The ESP g e n e r a t e s a h ig h v o lt a g e e l e c t r i c a l arc in the w ater, producing a r e l a t i v e l y low freq u en cy, h igh i n t e n s i t y s i g n a l which r e a d i l y p e n e t r a t e s the bottom sed im en ts. During t h i s su r v ey , the in p u t power was approxim ately 1 2 ,0 0 0 j o u l e s and th e retu rn was f i l t e r e d to about 60-120 cps bandpass. Aver age survey speed was 5 kn ots and the arc was t r ig g e r e d a t e i t h e r a 2 or 4 second i q t e r v a l . A number o f hydrophones, arranged in p a r a l l e l , com pleted the system . In appearance, the p r o f i l e s are s im ila r to th o se o f the PDR, ex cep t th a t th e re i s some r ec o rd o f r e f l e c t i o n s from s u r fa c e s beneath the sed im en t-w ater i n t e r f a c e . Bottom Sampling Program Three d i f f e r e n t tec h n iq u es o f bottom sampling were employed in the Gap area: grab samples o f the su rfa c e s e d i ment, sedim ent c o r e s , and rock dred ges. As the study was o r i g i n a l l y planned, emphasis was to be p la c ed upon rock sam pling, fo r the r e l a t i v e l y s te e p s lo p e s surrounding the Gap were assumed to have no more than a very th in veneer o f sedim ent. I t soon became ob viou s however, th a t whatever the th ic k n e s s o f sedim ent, dredges were u s u a l l y unable to p e n e t r a t e the cover to bedrock. L i t t l e more than o n e - h a lf o f the dredges attem pted (9 o f 1 7) y i e l d e d rocks* and o fte n th e re was the p o s s i b i l i t y th a t the rock s c o l l e c t e d were not in p l a c e . Since sedim ent sampling i s more c e r t a in and r e q u ir e s l e s s time* emphasis was s h i f t e d to t h i s a s p e c t o f the p r o j e c t . The stu d y o f San Miguel Gap thu s e v o lv e d in t o a p r im a r ily se d im e n to lo g ic problem. Surface sedim ents were sampled w ith p a r t i c u la r care* fo r th ey r e f l e c t the contempo rary sedim entary environm ent. S t a t io n s were co n c en tr a ted on the s lo p e s surrounding the Gap proper* fo r the s lo p e s tend to be th e a reas o f most marked v a r ia t i o n in sedim ent ch a r a c t e r . Numerous sedim ent c o re s were c o l l e c t e d to perm it some i n t e r p r e t a t i o n o f the more r e c e n t g e o lo g i c h i s t o r y o f the r e g io n . A l l s t a t i o n s from which samples were c o l l e c t e d f o r t h i s stu dy are shown in Figure 4. Most o f the s u r fa c e sediment sam pling was conducted w ith a Hydro P roducts Shipek Sampler fu r n ish ed by George Sch aeffer* then o f NOTS* Pasadena. The Shipek Sampler i s a s p r in g -lo a d e d d e v ic e d e sig n ed to s e t t l e f l a t on the ocean flo o r * then scoop a sample o f the su r fa c e m a te r ia l by the r a p id r o t a t io n o f a h a l f - c y l i n d r i c a l b u ck et. Id e a lly * i t c o l l e c t s a sample w ith a su r fa c e area o f 1 /2 5 m * to a maxi mum depth o f about 10 cm. The Shipek i s one o f the few sam pling d e v ic e s which c o n s i s t e n t l y n o t o n ly r e c o v e r s the sands and o th er co a rse m a te r ia l but a ls o p r o t e c t s the f in e r f r a c t i o n from winnowing during r e t r i e v a l . T w en ty -fiv e P ig . 4 . - “L o c a tio n s o f bottom sample s t a t i o n s j San M iguel Gap. 23 10098 LEGEND O Gravity Coras • Piston Coras S urface S am p les X D redges 0 K ilo m n tan 10 0 N autical M ills 5 Contour* in m ftars SAMPLE LOCATIONS SAN MIGUEL GAP AREA ozO MH5 0349 10350 10351 10348 10347 10097 MH3 di Hz 10353 0095 SANTA 1 0 1 1 9 10354 V SLAND 10367 10356 0368 10099 0369 10370 2 5 0 0 1 0 1 2 2 10357 010107 o 10362 0358 10372 10360 •m 10343 — 3 0 0 0344 / b /D 6 - 1 0 1 1 2 JDl o 0^08 ,500— ^ ( ■ y jtfs J 10346 10339 10366 10364 0365 0363 0342 10340 10345 21*00 120*40 1 2 0 * 2 0 ' 25 Shipek s t a t i o n s were o ccu p ied ; from o n ly fo u r o f t h e s e ( a l l a t dep th s g r e a t e r than 1000 m) was th e re i n s u f f i c i e n t sam p le fo r a n a l y s i s . A few a d d i t io n a l su r fa c e sam ples f u r n is h e d by NCEL were u sed in the stu d y . These were c o l l e c t e d in a 'sand sam pler' o f t h e i r d e sig n which a l s o p r o t e c t s th e sample from w ashing. T h i r t y - e i g h t c o r e s were c o l l e c t e d by V e lero IV and v e s s e l s a tta c h e d to NCEL w ith a g r a v i t y c o r e r o f the E m ery-D ietz p a t t e r n (Emery and D i e t s , 1 9 4 l ) . The core b a r r e l , i n the v a r i a t i o n u sed f o r a l l the Gap sam p lin g, i s f i t t e d w ith a 5 - 5 i n s i d e d iam eter co re l i n e r o f p o l y v i n y l c h lo r id e p l a s t i c which can be removed and capped on sh ipb oard f o r tr a n s p o r t to the la b o r a t o r y . Most o f the sed im en ts i n the Gap were q u it e dense and r e l a t i v e l y c o a r s e g r a in e d , hence th e average le n g t h o f core r e c o v e r e d was about 125 cm, r e g a r d l e s s o f b a r r e l le n g th or amount o f d r iv in g w e ig h t . Depth o f p e n e t r a t io n , as i n d i c a t e d by sedim ent smeared on th e o u t s id e o f the co re tu b e, was c u s to m a r ily w it h in a few p e r c e n t o f the le n g th o f core r e co v er ed . A f t e r i n i t i a l e x p e r ie n c e i n d ic a t e d th a t long c o r e s were u n l i k e l y , a r e l a t i v e l y sh o r t b a r r e l (3 m) was u se d to s i m p l i f y deck p r o c ed u r es. Two p i s t o n c o r e s were c o l l e c t e d i n th e f i n e - g r a i n e d m a t e r ia l a t th e c e n te r o f the Gap. The app aratu s u sed i s a m o d if ic a t io n o f the E m ery-D ietz g r a v i t y c o r in g g ea r w ith a p is t o n p rov id ed to e lim in a t e f r i c t i o n a l com paction o f the sample ( D ie t z , 1952; 2 6 : K u llen b erg, 19^-7) • The t r i g g e r w e ig h t fo r th e p i s t o n c o r e r was equipped w ith a sm a ll g r a v i t y c o r e r ( 3 -5 cm i n s i d e d i am eter) ^ fo r the p i s t o n ten d s to d is r u p t th e su r fa c e la y e r s o f sed im en t. Three sh o r t c o r e s c o l l e c t e d w ith a s i m i la r sm a ll c o re r (P h le g e r , 1951) were s u p p lie d by NCEL. A rugged, in e x p e n s iv e v a r i e t y o f rock dredge, th e type commonly c a l l e d a "pipe d red ge," was u sed in a l l th e rock sam pling a tte m p ts. These p ip e d r e d g es, b u i l t by H. D. P a l mer o f USC, are sim p le c y li n d e r s o f c a s t ir o n , a p p ro xim ately 1 .5 m lo n g , cu t from scrap ped o i l w e l l c a s in g about 50 cm in d iam eter. A p a ir o f h o l e s fo r th e tow ing b r i d l e are cu t a t one end; a t the o th e r a c o a r se g r i l l o f ir o n rod i s welded to r e t a i n th e sam ple. These dred ges o f t e n w eigh over 100 kg, and were som etim es u se d two a t a tim e w ith e x tr a scrap ir o n w e ig h ts a tta c h e d to speed lo w e r in g . W ithin the p ip e , s e v e r a l segm ents o f sm a ll p ip e are s e c u r e ly w elded, arranged so th a t th e y may be p lu gged to r e t a i n sedim ent from the dredge s i t e . B ecause o f t h i s f e a t u r e , many o f the dredges which f a i l e d to y i e l d rock a t l e a s t p ro vid ed a su r fa c e sedim ent sam ple. Only 9 o f th e 17 dredge h a u ls r e covered ro ck , b u t 12 sampled the se d im e n ts, I n e v i t a b l y , the depth l i m i t s a s s ig n e d dredge h a u ls are s u b j e c t i v e . They are an e s tim a te based on the w ater depth a t s t a r t and f i n i s h and r e c o r d s o f th e tim e the g e a r was in c o n t a c t w ith th e bottom . 27 Study and A n a ly s is Procedures B athym etric Data The P r e c is io n Depth Recorder (PDR) produces a time graph (Luskin., e t a l . , 195^)* The o r d in a te r ec o rd s v ery p r e c i s e l y the time o f the o r i g i n a l sonar ping and the tim e o f the echo; the a b s c i s s a i s c o n t r o l l e d by the c o n sta n t speed paper fe e d in g mechanism and th u s, i f th e sh ip i s underway., i n d i c a t e s d is t a n c e . The v e r t i c a l e x a g g e r a tio n o f the bottom p r o f i l e produced by the apparatus i s d i r e c t l y p r o p o r tio n a l to th e s h i p ’ s tru e speed. Since th e depth s c a le on Y e l e r o 1s PDR i s a d ju ste d to show 200 fathoms on 1 9-in c h wide paper, 1 m o f depth i s ap p roxim ately 0 .0 5 i n . and can e a s i l y be rea d . This s c a le assumes a c o n sta n t sound v e l o c i t y o f 4800 f t / s e c , somewhat slow er than t h e _ true v e l o c i t y o f sound in sea w ater, th e r e fo r e a l l depths record ed are s l i g h t l y s h o a l. C o r r e c tio n s were made fo r the 3 .6 m k e e l depth o f Y e l e r o ’s tran sd u cer and fo r sound v e l o c i t y v a r ia t i o n s in the w ater column (Uchupi and Emery, 1963) . Sound v e l o c i t y c o r r e c t io n s are sm all; v a lu e s on the order o f 20 m in 1000 m must be added to y i e l d true depth. Slope c o r r e c t io n s were not made. Soundings were read from the PDR tra ce a t each i n t e r v a l , roughly every 7 0 0 -8 0 0 m, depending upon the su r vey sp eed. The average sounding d e n s ity over the e n t i r e 2 area, th en , was on the order o f 1 .5 soundings p er km . Soundings were a ls o n oted a t p o in t s where th ere was i n t e r e s t i n g b ath ym etric d e t a i l : the to p s o f k n o l l s , the axes o f ch a n n els, the edges o f terra ces,, and th e l i k e . A smooth sh e e t was prepared to a s c a le o f 1 : 25.,000 (very rou gh ly 1 " = 1 /3 n a u t ic a l m ile) from the a d ju ste d s h i p ' s tracks., and the soundings were p l o t t e d and contoured. Contours were drawn a t 100 m around the i s l a n d s and a t a 200 m i n t e r v a l in deeper w ater. C on siderin g v a r i a b i l i t y o f the bathym etry and the n a v ig a t io n a l u n c e r ta in t y over much o f the a rea , t h i s i n t e r v a l was judged adequate. There are few major changes in bath ym etric i n t e r p r e t a t i o n . Older c h a r ts o f the r e g io n (U nited S t a t e s Coast and G eodetic Survey Chart 5202; Shepard and Emery, 19^1) were based on s i n g l e sou nd ings, n ot con tin u ou s p r o f i l e s , thus the r e s o l u t io n was n e c e s s a r i l y co a rse and i n t e r p r e t a t i o n somewhat s u b j e c t i v e . P r o f i l e s , o f c o u r se, show the sm a ller f e a t u r e s such as t e r - . r a c e s , g u l l i e s , and deep water ch an n els in t h e i r proper con t e x t , hence i n t e r p r e t a t i o n can be made w ith more c o n fid e n c e . A c o u stic R e f le c t i o n Data A c o u stic r e f l e c t i o n r eco rd s have a stron g s u p e r f i c i a l resem blance to standard g e o lo g ic c r o s s - s e c t i o n (P ig . 5 ) , but must be in t e r p r e t e d w ith g r e a t c a u tio n . Sound ten d s to be r e f l e c t e d from any zone where th ere i s a marked change in a c o u s t ic impedance. The a c o u s t ic p r o p e r tie s o f sedim entary rock s may be due to v a r ia t i o n s in m ineralogy or g r a in s i z e , F ig . 5 . — A c o u stic r e f l e c t i o n record from San M iguel Gap. 29 ACOUSTIC REFLECTION PROFILE N? 2 0 INSULAR RIDGE PATTON RIDGE A C O U STIC BEDROCK 4 J O _ . A l \ k r ^ v r ' 1 - 4 IA(UCL * n i i i v ^ - j A \ l l \ / ; 2 0 \ 0 ^ n r ^ i '" 'O O fi. n W W ' A ^ ■ : s \ ACOUSTIC BEDROCK O LD ER SE D IM E N T S '--S' jf'A i A -V l V \; 1 2 0 * 4 0 - 120*2 0 ' VERTICAL EXAGGERATION *10 1 O u .2 « i u 2 ■■3 33«40* U) o o r th e y may he r e l a t e d sim ply to d egree o f com paction or w ater c o n te n t (Shumway, i 9 6 0 ) . Thus I t I s r e a l l y im p o s s ib le to know I f a g iv e n echo i s caused by a v a l i d l i t h o l o g i c b reak . S in ce the c o n t r a s t o f sound v e l o c i t i e s i s so c r u c i a l , g r a d a t io n a l c o n t a c t s between even very d i f f e r e n t mate r i a l s are ob scu red . In a d d it io n , v e r y sudden changes in th e a c o u s t i c p r o p e r t i e s may produce such str o n g r e v e r b e r a t i o n s th a t the r e c o r d i s im p o s s ib le to i n t e r p r e t . Sound v e l o c i t i e s in rock or sedim ent are known in o n ly a g e n e r a l way so e s t im a t e s o f depth or t h ic k n e s s are n e v er more than ed u ca ted g u e s s e s (Moore, 1 9 6 6) . Commonly, a la r g e p a r t o f the "s t r a t i g r a p h i c c o r r e la t io n " accom p lish ed w ith a c o u s t i c r e c o r d s i s b ased upon such s u b j e c t i v e c r i t e r i a as the ch a r a c t e r i s t i c d e n s i t y and c o n t i n u it y o f r e f l e c t i n g h o r iz o n s , or even the "texture" o f the r e tu r n . D e s p ite th e o b v io u s l i m i t a t i o n s on p r e c i s e work w ith a c o u s t i c r e f l e c t i o n p r o f i l e s , th ey can be e x tr em e ly u s e f u l . Such r e c o r d s perm it some i n t e r p r e t a t i o n o f the t h i r d dim ension in th e s tr u c tu r e and sedim ent c h a r a c te r in c o m p a r a tiv e ly sh a llo w w ater r e g i o n s . In t h i s stu d y , r e f l e c t i o n r e c o r d s were f i r s t p r o c e ss e d by red u cin g them to a workable s i z e . The o r i g i n a l o f each p r o f i l e a c r o s s th e Gap was s e v e r a l m eters lo n g , fa r too awkward fo r e a sy stu d y and u s e f u l d e t a i l was c l u t t e r e d w ith ex tr a n e o u s n o i s e . A l l r ec o rd s were photographed u s in g a h ig h c o n t r a s t 4 x 5 in c h f i lm (P o la r o id 55 P/N) . The n eg a 32 t i v e was then f i t t e d in the enlarger., p r o je c te d a t a con v e n ie n t working s c a l e , and a l l "real" r e f l e c t i o n s w ith in the s u b s tr a te were tr a c e d . T racin gs were very c a r e f u l l y compared w ith the o r i g i n a l r e c o r d s, and much a d d it io n a l d e t a i l was in c lu d e d . F i n a l l y , a f t e r in k in g , the tr a c e s were reduced to an a p p ro p ria te s i z e fo r in c o r p o r a tio n in the stu d y . Although the i d e n t i f i c a t i o n s o f s p e c i f i c s t r a t i - g rap h ic u n i t s in the f i n a l f i g u r e s may be open to q u e s tio n , a l l the d e t a i l shown i s v a l i d , and must be c o n sid er ed in any r e c o n s t r u c t io n o f the h i s t o r y o f the Gap a rea . Sedim ents Sediment sam ples from the Gap were c a r r ie d to the la b o r a to r y e i t h e r in c a rto n s (s u r fa c e sam ples) or in the s e a le d p l a s t i c c o r e l i n e r s in which the c o re s had been c o l l e c t e d . The c o r e s were extruded in t o h a lv ed s e c t i o n s o f c o r e l i n e r , cut to con ven ien t le n g t h s , s p l i t , and logg ed . One o f the h a lv e s was covered and put a s id e fo r s e v e r a l days to dry, then photographed. A c e r t a in amount o f dehy d r a tio n i n c r e a s e s the c o n t r a s t o f the d i f f e r e n t typ es o f sedim ent, and hence b e t t e r photographs can be made. The o th e r h a l f o f the core was sampled fo r a n a l y s i s . Samples were taken from the top , the bottom , a t each n o t ic e a b le l i t h o l o g i c break, and a t 50 cm i n t e r v a l s in homogenous s e d im ent. At each sam pling p o in t , a 5 cm-long segment was r e moved from the h a l f c o re , any smeared m a te r ia l on the o u t - s id e was trimmed o f f , and th e segment was s p lit ., about o n e - t h i r d (30-40 g , dry w eig h t) fo r a n a l y s i s , the rem ainder fo r s to r a g e as a r e f e r e n c e . An e q u iv a le n t q u a n tity o f sedim ent was taken fo r a n a l y s i s from the s u r fa c e sam p les. In th e e a r l y s t a g e s o f the i n v e s t i g a t i o n , a s e r i e s o f t r i a l s was conducted to determ ine the most p r a c t i c a l a n a l y s i s te c h n iq u e s . I t was soon apparent th a t i t would be p o i n t l e s s to conduct f u l l g r a in s i z e a n a ly s e s on th e Gap sam p les. Such a n a ly s e s are r e a l l y s i g n i f i c a n t in th e i n t e r p r e t a t i o n o f sed im en ts o n ly where m echan ical p r o c e s s e s dom inate. Most o f the Gap sed im en ts are sands (m a te r ia l g r e a t e r than 6 2 n in median d ia m e te r ), b u t they are sands o f an o r g a n ic or a u t h ig e n ic o r ig i n ; o n ly in a few l o c a l i t i e s n ear the i s l a n d s was th e r e an im portant p e r c e n ta g e o f me c h a n i c a l l y in f lu e n c e d t e r r e s t r i a l sand or s h e l l fragm en tal sand. Though s i z e may have l i t t l e g e n e t i c s i g n i f i c a n c e in t h i s s i t u a t i o n , i t rem ains a u s e f u l param eter in the c l a s s i f i c a t i o n o f se d im e n ts. Shepard (1954) proposed a c l a s s i f i c a t i o n b a sed upon the th ree major siz e-c o m p o n e n ts o f most marine se d im e n ts, sand (c o a r s e r than 62 ja), s i l t (6 2 -4 |i), and c la y ( f i n e r than 4 n ) . These v a lu e s , p l o t t e d as p e r c e n ta g e s on a t r ia n g u la r co m p o sitio n diagram, are u s e f u l in the g r o s s c l a s s i f i c a t i o n o f sed im en ts and in th e d i s c r im in a tio n o f sedim entary environm ents (Emery, i 9 6 0 ) . A s i m p l i f i e d v e r s io n o f S h ep ard 's o r i g i n a l scheme was adopted. 3^ D is a g g r e g a t io n was th e f i r s t s t e p in th e a n a l y s i s . T h is was a c co m p lish ed by tre a tm en t o f th e sam ples w ith 50 ml o f 15 p e r c e n t H^O^. Though a sm a ll w e ig h t p e r c e n ta g e o f o r g a n ic m a t e r ia l i s d e s tr o y e d by t h i s p r o c e s s , the sample i s e f f i c i e n t l y d is a g g r e g a t e d and th e m i c r o f o s s i l s are th o r o u g h ly c le a n e d . A f t e r th e r e a c t i o n w ith H^Og was com p le te ,, th e sample was d e s a l t e d by a l t e r n a t e d i s t i l l e d w ater washing and c e n t r i f u g a t i o n u n t i l th e c l a y s rem ained i n s u s p e n s io n , i n d i c a t i n g rem oval o f a l l s a l t s . The sam ples were th en w et s i e v e d on a 6 2 n sc re en to se p a r a te th e sand f r a c t i o n , w hich was d r ie d and w eig h ed . The w a sh in g s, c o n t a i n in g th e f i n e r f r a c t i o n , were g iv e n an a b b r e v ia t e d p i p e t t e a n a l y s i s . A com m ercial d i s p e r s i n g a g e n t , M arasperse, was u se d to p r e v e n t f l o c c u l a t i o n . P i p e t t e s were drawn a t zero tim e ( f o r the s i l t and c la y ) and a t a p p r o x im a te ly 2 hou rs ( f o r c l a y ) . W eight p e r c e n ta g e s o f each c l a s s were then c a l c u l a t e d . The c o a r se f r a c t i o n , u s u a l l y th e major p a r t o f the o r i g i n a l sam ple, was examined under th e b in o c u la r m ic r o s c o p e . In th e p roced u re t h a t became sta n d a rd , a s p l i t o f th e m a t e r i a l was sp rea d a g r a in t h i c k a c r o s s a 4 x 8 cm tr a y r u le d w ith a m i l l i m e t e r g r i d . Under low m a g n if ic a t io n (lOx or 1 5 x ), th e sample was scanned to d eterm in e th e major c o n s t i t u e n t s . Then, under h ig h e r power ( u s u a l l y 3 0 x ), a l l g r a in s in a " ty p ic a l" s e c t i o n o f the sample which la y under th e m icro sco p e c r o s s - h a i r s were i d e n t i f i e d and co u n ted . 35; Commonly t h i s was anywhere from 150 to 250 i n d iv id u a l g r a in s . P ercen ta g es o f the minor components and p o s s i b l e o m issio n s were checked by another scan o f the e n t i r e sample. This m o d ified p o in t countin g techn iqu e i s d i f f i c u l t to r a t i o n a l i z e s t a t i s t i c a l l y (Dennison and Shea., 1966); i t does, however, produce p e r c e n ta g e s which are r ep ro d u c ib le fo r a l l major components o f th e sedim ent (m a te r ia l p r e se n t in con c e n t r a t io n s g r e a t e r than 10 p e r c e n t ) . The very minor con s t i t u e n t s were sim ply noted as " tr a c e ." A fte r co u n tin g , a few r e p r e s e n t a t iv e s o f the dominant c o n s t i t u e n t s , p a r t i c u l a r l y f o r a m in if e r s , and any i n t e r e s t i n g e x o t i c s were p ick ed from th e sample and mounted fo r fu r th e r stu d y . Rocks R e l a t i v e l y few rock s were s u c c e s s f u l l y dredged in the Gap. Many o f th e rock s reco v ered cou ld n ot p o s i t i v e l y be determ ined to have been in p la c e when sampled. F in e g r a in ed ig n e o u s r o c k s, o f t e n rounded to some d egree, were the common sam ple. Because o f th e sp a r se n e ss o f m a t e r ia l, no g r e a t e f f o r t was made to i d e n t i f y the rock s beyond the s u p e r f i c i a l l e v e l . Thin s e c t i o n s were cu t from r e p r e s e n t a t i v e r o c k s, both ig n e o u s and sedim entary, from each dredge h a u l, and th e se were examined w ith the p e t r o l o g i c m icro scop e. T e n ta tiv e i d e n t i f i c a t i o n s o f the rocks were made on the b a s i s o f te x tu r e and the more obvious m ineral con s t i t u e n t s . GEOLOGIC ENVIRONMENT General San Miguel Gap l i e s a t a p o in t where s e v e r a l la r g e - s c a l e p h y sio g ra p h ic and t e c t o n i c r e g io n s meet (F ig . 6 ) . I t a c t u a l l y c o n s t i t u t e s a break in one o f the most continu ous f e a t u r e s on th e fa c e o f the earth., the c o n t in e n t a l slo p e o f w estern North America. O ffsh o re, the Murray F racture Zone o f the North P a c i f i c B asin i s c l o s e l y a lig n e d w ith the Gap. In terms o f the c o n t in e n t a l g e o lo g y , th e Gap i s a t th e e x treme n orthw estern boundary o f th e C a lif o r n ia c o n t in e n t a l b ord erlan d , a r e g io n o f submerged b a s in s and r id g e s p o s s i b l y analogous to the B asin and Range P h ysiograp h ic Prov in c e o f in la n d sou thw estern U n ited S t a t e s . The northern boundary o f the Gap, A rgu ello P lateau and the Channel I s la n d s, are p a rt o f the T ransverse Ranges, an e a s t - w e s t tr e n d in g b lo c k which s t r i k e s a c r o s s th e g e n e r a l n o rth w est- s o u th e a s t topographic g r a in o f the West Coast o f North America. Menard (1955 , 19^0) su g g ested th a t the c o n t in e n t a l s lo p e i s o f f s e t by the i n f lu e n c e o f the Murray F racture Zone a t th e Gap a rea . This i s a d m itte d ly s p e c u l a t i v e , p a r t i c u l a r l y s in c e the sen se o f movement o f the slo p e ( l e f t - 36 F ig . 6 . — G en eralized t e c t o n i c framework* San Miguel Gap area. 37 GENERALIZED TECTONIC FRAMEWORK SAN MIGUEL GAP AREA - MENmcMQ»FMcwnZr.zoNE ^ Boundaries of Physiographic Provinces | ^ Continental Slope Oceanic Fracture Zone Prominent Seamounts ' ■ L Major Deep Sea Fan \ ( / B A S IN RANGES MURRAY FRA I s H l San Miguel Gap v». r x ! % \ K < ' % * ' < S > \ V ' t- Q. \ V G > % \ V . < P ' V CLARION FRACT l a t e r a l ) I s opposed to th a t p o s t u la t e d fo r the Murray F rac tu re Zone (V acquier, e t a l .j 1961; R a ff, 1 9 6 2) . There I s even some p o s s i b i l i t y th a t the in f lu e n c e o f the fr a c tu r e zone can be tra c ed much f a r t h e r e a s t , to the middle o f the North American c o n tin e n t ( A lb r it to n and Smith, 1957; Means, 19 53). Whatever the true s i t u a t i o n , th ere can be no q u es t io n th a t San M iguel Gap l i e s a t a f o c a l p o in t , where many c o n t r a s t in g t e c t o n i c i n f l u e n c e s may have r e a c te d w ith one a n o th er. The g e n e r a l str u c tu r e and h i s t o r y o f each o f the r e g io n s surrounding th e Gap w i l l be b r i e f l y d is c u s s e d . T ransverse Ranges and Channel I s la n d s Im m ediately to the north o f San Miguel Gap l i e s the T ransverse Range P rovince o f C a lif o r n ia . This ph ysio grap h ic r eg io n can be tr a c e d s u b a e r i a l ly from P oin t A rgu ello and San Miguel I s la n d to about 500 km in la n d (B a ile y and Jahns, 195^ ) . The p r o v in ce c o n s i s t s o f a s e r i e s o f ranges and b a s in s very c o n sp ic u o u sly o r ie n t e d in an e a s t - w e s t s e n s e , con tra ry to the g e n e r a l n o r th w e s t-s o u th e a s t o r i e n t a t i o n o f the P en in su la r and Coast Ranges o f C a lif o r n ia . S tr u c tu r a lly the p r o v in ce i s a s e r i e s o f s t e e p - s id e d f o l d s , p a r a l l e l to the tren d o f the m ountains, many o f them broken along t h e i r axes by com p ressio n al f a u l t s or t h r u s t s , and some la rg e b lo c k s which are probably i s o l a t e d by s t r i k e - s l i p f a u l t s (B a ile y and Jahns, 195^)• The San Andreas F au lt System c r o s s e s the trend o f the T ransverse Ranges o b liq u e ly , fo r a time alm ost p a r a l l e l i n g t h e i r s t r i k e (C row ell, 1962 ). In the c e n tr a l p o r tio n o f the p r o v in c e, the Santa Monica F ault System marks the southern boundary. The Santa Monica S y s tem i s la r g e ly composed o f high angle n orth -d ip p in g r e v e r se f a u l t s w ith displacem en t on the order o f 2500 m (Yerkes, e t a l ., 1965). A probable c o n tin u a tio n , the Malibu C oastal F a u lt, extends j u s t south o f the Santa Monica Mountains and the Channel I s la n d s , perhaps as fa r west as Santa Cruz I s land. This segment i s a lso a th r u s t f a u l t w ith c o n s id e r able d isp la cem en t. Most o f the movement on the Malibu S y s tem f a l l s in the Late M iocene-Late P le is to c e n e time i n t e r v a l (R. F. Y erkes, p erson al com m unication). The rocks o f the Transverse Range Province are domi n a n tly sedim ents o f Upper Cretaceous to P le is t o c e n e age. Some metamorphic and ign eou s rocks o f pre-L ate Cretaceous age occur in the Santa Monica-Channel Is la n d segment. These rocks are d i f f e r e n t from the Franciscan basement rocks found both to the north and south, so the area i s d i s tin g u is h e d as an independent b lo c k , the "Anacapia" o f Reed and H o l l i s t e r ( 1 9 3 6). Since i t i s t h i s Channel Isla n d s e c t io n o f the province th at borders the Gap, i t s g e o lo g ic h is t o r y w i l l be d is c u sse d In d e t a i l . A cid ic pre-C retaceous rock s, la r g e ly d a c it e , are p r e s ent on Santa Cruz Isla n d and p o s s ib ly at Richardson Rock, w est o f San Miguel Isla n d (Redwine, 1952; Palmer, 1965b ) . These are unconformably o v e r la in by P aleocene sedim ents on Santa Cruz b u t e lse w h e r e In th e i s l a n d s se d im e n ta tio n s t a r t e d in th e Upper C retaceou s and was v i r t u a l l y c o n tin u ous through m id-Eocene (Weaver and Doerner* 1 9 6 6) . There are in te r m e d ia te to b a s i c v o l c a n i c s in te r b e d d e d w ith s e d i ments o f Upper C retaceou s age exposed on San M iguel and S an ta Rosa Island., p rob ab ly c o r r e l a t i v e w ith th e Jalama V o lc a n ic s o f th e m ainland (D ibb lee* 1950)• The e a r l y Ceno- z o i c sed im en ts appear to be l a r g e l y o f sh a llo w w ater o r ig in * and th e Eocene s e c t i o n o f San M iguel c o n ta in s many w e l l - d e v e lo p ed l i n e a t i o n s and c u r re n t marks p a r a l l e l i n g the co n t i n e n t a l margin and d ip p in g n o r th w est (D. P. D oerner, p e r s o n a l com m u n ication ). During th e Late Eocene and O ligocen e th e area was predom inan tly p o s i t i v e * but th e r e are few s ig n s o f o r o g e n ic a c t i v i t y . By th e E a r ly Miocene th e r e was a g e n e r a l t r a n s g r e s s io n o f th e sea* as in much o f c o a s t a l C a lifo r n ia * and rock s o f the t y p i c a l Monterey-Modelo group o f c a lc a r e o u s and s i l i c e o u s s h a l e s were d e p o s it e d . There was f a i r l y e x t e n s iv e v o lc a n ism in th e w estern p a r t o f the r e g i o n ; both San M iguel and Santa Rosa I s la n d s h ave~con s i d e r a b le ex p o su res o f rock s a n a lo gou s to the T ra n q u illo n V o lc a n ic s o f th e Santa Ynez M ountains. In Late Miocene time* the e n t i r e Channel I s la n d area was f o ld e d and up- - l i f t e d . Most o f the str u c tu r e * f o l d s and f a u l t s * d a te s from t h i s e p is o d e . Only fragm entary P l e i s t o c e n e t e r r a c e d e p o s i t s r eco rd more r e c e n t g e o l o g i c h i s t o r y . T erraces are n o t as prom inent here as th e y are f a r t h e r so u th In the b o r 42 derlan d (Smithy 1 8 9 8; Emery, i 9 6 0 ); presumably the area was c o n sid e r a b ly more s t a b le than the b ord erlan d . C o n tin en ta l Borderland The c o n t in e n t a l borderlan d I s t h e ' l a r g e l y submerged r e g io n o f r id g e s and b a s in s o f f th e southern C a lif o r n ia and Baj.a C a lifo r n ia c o a s t which e xten d s ap p roxim ately 800-900km sou th from th e T ransverse ra n g e s, seaward o f the P en in su la r Ranges (Emery, i 9 6 0 ; Uchupi and Emery, 1 9 6 3; Krause, 196 4). E le v a t io n s w ith in the r e g io n range from over 500 m above sea l e v e l on the s c a t t e r e d i s l a n d s to s e v e r a l thousand me t e r s depth in a few o f the b a s in s . As a g e o lo g i c p r o v in c e , the b orderlan d has a t tim es been combined w ith e i t h e r the T ransverse Ranges or w ith the P en in su la r Ranges. This i s not p r a c t i c a l , fo r th ere are s i g n i f i c a n t d i f f e r e n c e s which make the borderland un iqu e. In marked c o n t r a s t to the g r a n i t i c i n t r u s i v e s o f the Chan n e l I s la n d s and th e b a t h o l i t h i c core o f the P en in su lar Ranges, F r a n c isc a n -ty p e metamorphic rock s have been c o l l e c t e d a t v a r io u s p o in t s in the n orthern borderland (Emery, I960; B u t le r , 1 9 6 4 ). No known in s i t u basement rocks have been dredged in th e southern b orderlan d (Krause, 196 4). The b a s in and range topography o f the e n t i r e b orderlan d i s d i f f e r e n t from the more g r o s s t e c t o n i c s t y l e o f c o a s t a l mountain r a n g es. In terms o f th e deep s t r u c t u r e , th e b ord erla n d I s a very complex t r a n s i t i o n between th e P a c i f i c Ocean b a s in and th e c o n t in e n t o f North America (Shorr and R a i t t , 1 9 5 8 ) . Typ i c a l o c e a n ic c r u s t , i d e n t i f i e d by a s e is m ic v e l o c i t y o f 6 . 7 km /sec, i s p r e s e n t a c r o s s th e e n t i r e b o r d erla n d , but undoubted c o n t i n e n t a l c r u s t has been i d e n t i f i e d under a t l e a s t some o f th e r id g e s and b a s i n s . The M ohorovicic D i s c o n t i n u i t y s y s t e m a t i c a l l y i n c r e a s e s in depth shoreward a c r o s s the b o r d erla n d , from t y p i c a l l y o c e a n ic to t y p i c a l l y c o n t i n e n t a l c o n d i t i o n s . The f a u l t p a tte r n o f the b o rd erla n d has been d e fin e d l a r g e l y on p h y sio g r a p h ic e v id e n c e . I t i s assumed th a t i f th e r e i s l i t t l e e r o s io n or d e p o s i t i o n , then the ob served topography must be t e c t o n i c . T his i s r e a s o n a b le , but i t - i s o f t e n im p o s s ib le to d i s t i n g u i s h f a u l t sc a rp s from the s t e e p l y d ip p in g lim b s o f f o l d s . There appears to be two dominant d i r e c t i o n s o f f a u l t i n g or f o l d i n g in the b o r d e r la n d , a v e ry pronounced n o r t h w e s t-s o u t h e a s t s e t p a r a l l e l to th e C o n tin e n ta l Margin and a more w id e ly spaced, l e s s d i s t i n c t e a s t - w e s t s e t (Shepard and Emery, 19^1; Emery, i 9 6 0 ) . The i n t e r s e c t i o n o f th e se s e t s produ ces th e c h a r a c t e r i s t i c b a s in -r a n g e topography o f the b o r d e r la n d . By a n a l ogy w ith th e b a s in and range p r o v in c e in la n d , the b o rd er la n d has been i n t e r p r e t e d as a r e g io n o f b lo c k f a u l t i n g w ith r e l a t i v e l y in d ep en d en t movement o f th e v a r io u s b lo c k s (Emery, 195^-) . T his g e n e r a l i z a t i o n appears to be tru e fo r 44 th e in n e r and o u te r p a r t s o f the borderland., b u t th e r e i s a c e n t r a l zone o f g e n t l e f o l d i n g running ro u g h ly alon g the tren d o f the Santa R osa-C ortes Ridge (Moore, 196 6 ) . The v a s t m a jo r ity o f th e in s i t u d a te a b le ro ck s c o l l e c t e d w ith in the bo rd erlan d are o f Miocene age (Emery and Shepard., 1945; Emery, i 9 6 0 ) . These in c lu d e a wide v a r i e t y o f normal se d im e n ts, most commonly mudstone and s i l t s t o n e , the common a u t h ig e n ic rock , p h o s p h o r ite , and many sam ples o f a n d e s i t i c and b a s a l t i c v o l c a n i c s . The sedim entary ro ck s have been d a ted p r im a r ily by t h e i r in c lu d e d m i c r o f o s s i l s j the v o l c a n ic s are determ ined l a r g e l y by a n a lo g y w ith the w id esp read Miocene v o l c a n i c s o f th e m ainland (S h e lto n , 1 9 5 4 ). The b a s in s a l l c o n ta in u n c o n s o lid a t e d se d im e n ts, and p etro leu m e x p lo r a t io n has r e v e a le d g r e a t t h ic k n e s s e s o f Late C enozoic m a te r ia l in th e in s h o r e b a s i n s . The t h ic k n e s s o f sedim ent in th e b a s in s i s i n v e r s e l y proportional to d is t a n c e from th e p r e s e n t s h o r e l i n e , and th u s presum ably, from t e r r e s t r i a l so u r c e s o f sedim ent (G o r slin e and Emery, 1959; Moore, 1 9 6 6) . A lthough the g e n e r a l t e c t o n i c p a tte r n may be o ld e r , most o f the o b v io u s s t r u c t u r e o f the b ord erla n d probab ly d a t e s from th e Late Miocene (Shepard and Emery, 1 9 4 l ) . The absen ce o f p ost-M iocen e rock s on the r i d g e s , the p r e v a le n c e o f probab le Miocene v o l c a n i c s , and th e w ell-d ocu m en ted a c c e l e r a t i o n o f se d im e n ta tio n in the in s h o r e b a s in s a l l su g g e s t th a t th e r e was c o n s id e r a b le t e c t o n i c a c t i v i t y in th e ...................................................................^ 5 ■borderland in Late M iocene tim e . I t h as been s u g g e s te d t h a t th e r e h a s been c o n tin u o u s d ia s tr o p h is m in th e e n t i r e C a l i f o r n i a c o a s t a l a rea s i n c e th e m id d le C enozoic ( G i l l u l y , 1949) * C e r t a i n l y t h e r e are many emerged and submerged ma r i n e t e r r a c e s to prove P l e i s t o c e n e a c t i v i t y , and r e l a t i v e movements o f se a and lan d l e v e l o f s e v e r a l thousand m eters have been p o s t u l a t e d (C lem en ts, 1955)* "but most p o s t-M io cen e a c t i v i t y app ears to have been o f f a i r l y sm a ll s c a l e and l i m i t e d to l i n e s e s t a b l i s h e d during the M iocene. To day, t h e r e i s c o n s id e r a b le t e c t o n i c a c t i v i t y on sh ore a lo n g th e C a l i f o r n i a c o a s t , b u t th e b o r d e r la n d app ears to be r e l a t i v e l y q u i e s c e n t (C lem ents and Emery, 19^9; A l l e n , ejb a l ., 1 9 6 5 ). The g e o l o g i c h i s t o r y o f th e b o r d e r la n d i s n o t known i n g r e a t d e t a i l , b u t th e g e n e r a l p a t t e r n I s c l e a r (Emery, i 9 6 0 ) . The a rea a p p a r e n t ly was p a r t o f th e M esozoic Fran c i s c a n g e o s y n c l i n e , reg a rd ed by some a s a e u g e o s y n c l in a l c o n t i n e n t a l r i s e (Drake, e t a l ., 1959; D i e t z , 1 9 6 3 ) . Con s o l i d a t i o n and metamorphism was com p lete by th e Late Meso z o i c , and f a i r l y w id e sp re a d Upper C reta c eo u s sands were d e p o s i t e d in c o a s t a l C a l i f o r n i a (Popenoe, 1954)• The e a r l y C enozoic was r e l a t i v e l y q u i e t , and q u i t e p o s s i b l y much o f th e a r ea was c l o s e to o r above se a l e v e l , r e c e i v i n g l i t t l e se d im e n t, u n t i l th e M iocene, when th e r e was a g e n e r a l t r a n s g r e s s i o n . Through most o f th e M iocene, th e r e was v e r y a c t i v e s e d im e n t a tio n , and toward th e end o f th e epoch, t h e r e 46 was c o n sid e r a b le v olcan ism . In the Late Miocene th e re was an e p iso d e o f major d ia str o p h ism which b lock ed out the s t r u c t u r a l and sedim entary p a t t e r n s which p e r s i s t today. C o n tin en ta l Slope I The c o n t in e n t a l slo p e i s the r e l a t i v e l y ste e p segment o f the c o n t in e n t a l margin, u s u a l l y ex ten d in g from th e con t i n e n t a l s h e l f to a more g e n t l y s lo p in g c o n t in e n t a l r i s e or to a m arginal trough (Heezen, e t a l ., 1959)* Off C a l i f o r n ia , the slo p e i s d iv id e d a t San Miguel Gap in t o two d i f f e r ent s e c t i o n s , the Santa Lucia Escarpment to the n o rth , the P atton Escarpment to the south (Shepard and Emery, 1 9 4 l ) . There i s a rea so n a b ly w e ll- d e v e lo p e d s h e l f o f f northern and c e n tr a l C a lif o r n ia , but o f f southern C a lif o r n ia , the c o n t in e n t a l borderland in t e r v e n e s between the slo p e and a very narrow c o n t in e n t a l s h e l f . The c e n tr a l C a lifo r n ia c o n t in e n t a l margin i s p r im a r ily a d e p o s i t i o n a l f e a t u r e . Curray ( 1965a) found th ic k s e c t io n s o f sedim ent which accum ulated behind and over a w e l l - d e fin e d basement r id g e , probably g r a n i t i c , which ou tcro p s a t the F a ra llo n I s la n d s near San F ran cisco and in the w a lls o f Monterey Submarine Canyon (Hanna, 1952, M artin, 196 4). G eostrop hic contour c u r r e n ts may w e ll have in f lu e n c e d the form o f t h i s slo p e (Heezen, e t a l ., 19 6 6). This s tr u c tu r e i s fundam entally s im ila r to th a t o f th e margin o f the e a s t c o a s t o f North America (Drake, e t a l ., 19 5 9 ). In c o n t r a s t , the P atton Escarpment seaward o f the c o n t in e n t a l borderland appears q u ite d e f i n i t e l y to be a t e c t o n i c f e a tu r e (Uchupi and Emery., 1 9 6 3) • The southern C a lif o r n ia slo p e i s ste e p e r (12° as opposed to 8°) and la c k s submarine canyons., a c h a r a c t e r i s t i c fe a t u r e o f the c e n t r a l and northern C a l i f o r n ia s lo p e . There are a s e r i e s o f Sea v a l l e y s which cu t the P atton Escarpment., and th ere i s some apparent o f f s e t o f the c o n t in e n t a l slo p e in a l e f t - l a t e r a l se n se a t each o f th e se (Uchupi and Emery, 1 9 6 3) . B u tle r (1964) s tu d ie d one such sea v a l l e y w est o f th e Mexican bord er. San M iguel Gap i s the l a r g e s t o f th e s e b reak s, b oth in dim ensions and in ap p arent o f f s e t o f the c o n t in e n t a l s lo p e . Most rock s from the Patton Escarpment proper are e x tr u s i v e ig n e o u s r o ck s, a n d e s ite and b a s a l t (Uchupi and Emery, 1 9 6 3)• From th e P atton R idge, a t the c r e s t o f the c o n t i n e n ta l s lo p e , s i m i la r v o lc a n ic r o c k s, p h o sp h o r ite , and Fran c is c a n - t y p e sedim entary rocks have been r eco v ered (Emery and Shepard, 1945; B u t le r , 1 9 6 4 ). Many o f th e se rock s occur as la r g e , f a i r l y w ell-r o u n d e d c o b b le s or b o u ld e r s , s u g g e s tin g th a t a t one time the r id g e must have been in w ater sh a llo w enough fo r waves to accom plish the rounding. Along the Santa Lucia Escarpment, Miocene sedim entary rock s have been r e c o v er ed a t s e v e r a l dredging s t a t i o n s (Emery and Shepard, 1945; Hanna, 1952; M artin, 19 6 4 ). Quartz d i o r i t e from the F a r a llo n I s la n d s has been dated a s C retaceous by the p o t a s - sium-argon method (C u r tis , e t .a l ., 1958)* Im m ediately to 48 th e north o f San M iguel Gap, a s e a k n o ll on th e A rg u ello P la tea u c o n s i s t s o f p rob ab le Late Miocene b a s a l t and p a la g o - n i t i c t u f f , s i m i la r to th e m a t e r ia l o f nearby Rodriguez S ea mount (Palm er, 1964, 1965a ) . The h i s t o r i e s o f th e two segm ents o f c o n t in e n t a l s lo p e se p a r a te d by San M iguel Gap are a p p a r e n tly d i f f e r e n t . The Santa Lucia Escarpment d ev elo p ed as a d e p o s i t i o n a l f e a t u r e , c e r t a i n l y in much i t s p r e s e n t form s in c e the Late M esozoic. The P atton Escarpment i s p r im a r ily a t e c t o n i c fe a tu r e which shared the h i s t o r y o f the a d ja c e n t b ord erlan d and p robab ly assumed i t s p r e s e n t form during th e Late Miocene p e r io d o f d ia s tr o p h ism . N o r th e a st P a c i f i c B asin and Murray F ractu re Zone The most prom inent f e a tu r e o f the P a c i f i c b a sin in the v i c i n i t y o f San M iguel Gap i s th e Murray F ractu re Zone. T his zone s e p a r a t e s two o f the major d e e p -s e a p h y sio g r a p h ic p r o v in c e s , th e B aja C a lif o r n ia Seamount P rovince to the so u th , and a broad area o f a b y s s a l h i l l s , masked near th e c o n t in e n t by c o a le s c e d d e e p -se a f a n s , to th e n orth (Menard, 1955)• There i s a very th in v e n e er o f sedim ent over t h i s e n t i r e p o r tio n o f the P a c i f i c b a s in , and a v ery gradual s lo p e toward the w e s t. I t has been proposed t h a t t h i s r e g io n r e p r e s e n t s th e w est f la n k o f th e E a st P a c i f i c Oceanic R is e , which may p e n e tr a t e North America a t the G ulf o f C a l i f o r n i a (Menard, 1 9 6 1) . The Murray F ractu re Zone i s n i c e l y a lig n e d w ith a v a r i e t y o f anomalous f e a t u r e s a t the c o n t i n e n t a l margin and on the c o n t in e n t prop er, in c lu d in g San M iguel Gap and th e T ran sverse R anges. This alig n m en t has encouraged c o n s id e r a b le s p e c u la t io n as to p o s s i b l e i n t e r a c t i o n s o f o c e a n ic and c o n t i n e n t a l s t r u c t u r e s ( f o r exam ple, A lb r it t o n and Sm ith, 1957; Menard, 1 9 6 4 ). U n fo r tu n a te ly , e v id e n c e s o f the Murray Zone cannot y e t be tr a c e d to the c o n t i n e n t a l s lo p e (R. von Huene, p e r s o n a l com m unication), so the p o s s i b l e r e l a t i o n s h i p s must s t i l l be regarded as h y p o t h e t i c a l . The Murray F ra ctu re Zone i s a rem arkably s t r a i g h t f e a tu r e which f o l lo w s a g r e a t c i r c l e path perhaps 3000 km a c r o s s the P a c i f i c b a s in toward H aw aii. I t was o r i g i n a l l y i d e n t i f i e d by a narrow zone o f r i f t i n g and th e c h a r a c t e r i s t i c to p o g ra p h ic d i f f e r e n c e s o f th e p r o v in c e s on e i t h e r s id e (Menard, 1955)- Very soon, i t was d is c o v e r e d th a t th e r e was a v e ry str o n g l i n e a r i t y to th e m agnetic anomaly p a t t e r n s in the e a s t e r n P a c i f i c , and th a t t h e s e p a t t e r n s co u ld be matched a c r o s s f r a c t u r e zones i f c o n s id e r a b le s t r i k e - s l i p d isp la c e m e n t was assumed (Mason, 1958; V a c q u ier, 1959; V a cq u ier, e t a l ., 1 9 6 1). A r i g h t - l a t e r a l movement o f 640 km i s proposed fo r p a r t o f th e Murray Zone (R a ff, 1 9 6 2 ) . Q uite r e c e n t l y , th e r e a l i t y o f tremendous d is p la c e m e n ts on the fr a c t u r e zones has been c h a lle n g e d , fo r i f th e e n t i r e n o r t h e a s t P a c i f i c b a s in i s th e fla n k o f an o c e a n ic r i s e , 50 th e m agnetic anomaly p a t t e r n s may sim ply be a f u n c t io n o f d is ta n c e from th e r i s e a x i s and thus are n ot d i r e c t l y c o r r e l a t i v e (T aiw an!, e t a l ., 1 9 6 5). OCEANOGRAPHIC ENVIRONMENT G eneral Atm ospheric and h y d ro sp h er ic c i r c u l a t i o n i s th e r e s u l t o f the uneven s o l a r h e a tin g o f th e e a r t h ’ s s u r f a c e . Winds and o c e a n ic c u r r e n ts are th e mechanisms o f the h e a t t r a n s f e r system which s e r v e s to m ain tain the g l o b a l therm al e q u ilib r iu m . Superim posed on t h i s sim ple "heat engine" model are the d e f l e c t i o n s o f c i r c u l a t i o n due to th e r o t a t i o n o f the e a r th and c o m p lic a tio n s o f d i s s o l v e d or suspended m a t e r ia l in the medium. Oceanic c i r c u l a t i o n p a t t e r n s are o f c o n s id e r a b le s e d im e n to lo g ic in t e r e s t ., f o r w ater m asses are th e p h y s i c a l and ch em ica l environm ent which c o n t r o l s th e tr a n s p o r t , d e p o s i t i o n , and ( in many c a s e s ) the form ation o f the bottom se d im e n ts. In the North P a c i f i c r e g io n , a g r e a t c lo c k w is e gyre c e n te r s about th e Sub-T ropic High, an alogou s to th e G ulf Stream System o f th e A t l a n t i c (s e e P ig . 7 ) . The North Pa c i f i c and A le u tia n C urrents move eastw ard a c r o s s th e ocean under th e i n f l u e n c e o f ' t h e w est wind d r i f t , then, c l o s e to North America, th e y s p l i t . Some o f the w a te rs move n o r th ward and are in c o r p o r a te d in the s u b s id ia r y Alaskan G yral, but most flo w southward alon g th e c o a s t ( T u lly and Barber, 51 F ig . 7 - — S u rface w ater c i r c u l a t i o n . N o r th e a st P a c i f i c a r ea . 52 SUMMER r a w s * • 5 sm a piS I f ALASKAN 1 GYRAL A L E M A N CURRENT ALEUTIAN CURRENT NORTH PACIFIC CURRENT NORTH EQUATORIAL CURRENT NORTH EQUATORIAL CURRENT EQUATORIAL GOUNTFRCURRENT SOUTH EQUATORIAL CURRENT EQUATORIAL COUNTERCURRENT ^_L 13k m m 0° SURFACE WATER CIRCULATION, NORTHEASTERN PACIFIC OCEAN (Adapted from Charts 120 8 122, Office of Climatology, 1961) v _ n U J 1 9 6 1) . This branch, the C a lif o r n ia Current, moves toward, th e Equator, e v e n t u a lly jo in in g the North P a c i f i c Current, com p leting th e g y r a l. T his r o t a t in g system o f winds and su r fa c e c u r r e n ts ten d s to b alan ce the thermal budget o f the Northern Hemisphere by the tr a n sp o r t o f warm w ater n o r th ward to th e w est o f the b a s in and c o o l w aters south on the e a s te r n s i d e . The c o o l e a ste r n c u r r e n t, c o n t r o lle d l a r g e l y by wind s t r e s s r e l a t e d to the m id -o cean ic h ig h , i s r e l a t i v e l y slow and broad, in c o n t r a s t to the narrow, s w if t w estern boundary c u r r e n ts (Munk, 1950; Wooster and R eid, 1963) . There are im portant se a so n a l v a r ia t i o n s in th e North P a c i f i c c i r c u l a t i o n p a t t e r n . In the sp rin g and summer, when the atm ospheric h igh in the c e n t r a l North P a c i f i c i s most pronounced, b r is k n orth and n orthw est winds are the r u le along the w est c o a s t o f the U n ited S t a t e s . These winds serv e to d r iv e th e C a lif o r n ia Current c lo s e in sh o r e and are a p o te n t fa c t o r in the sm all s c a l e u p w e llin g th a t occu rs a t many p o in t s along th e c o a s t (Marine R esearch Com m i t t e e , 1953)• During the w in te r , a major atm ospheric low d e v e lo p s in th e v i c i n i t y o f the A le u tia n I s la n d s , dom inat in g North P a c i f i c c i r c u l a t i o n . The Sub-Tropic High i s g r e a t l y reduced and m ig ra tes to the s o u th e a s t, becoming c e n te r e d o f f the C a lif o r n ia c o a s t (Flem ing, 1955; Mintz and Dean, 195 2 ). A n o r t h - d ir e c t e d su rfa ce c u r r e n t, the D avid son Current or C a lif o r n ia C ou ntercurrent, then d ev elo p s 55 in sh o r e o f f southern and Baja C a lifo r n ia during the f a l l and w in ter and may extend to 45°N (Wooster and Reid,, 1 9 6 3) . C ir c u la tio n in the Gap reg ion i s such th a t the su rface w aters over the e a ste r n tw o -th ir d s shows a marked se a so n a l change] o n ly r a r e ly does t h i s in flu e n c e extend over the e n t ir e r e g io n . Scrip ps I n s t i t u t i o n o f Oceanography has conducted e x te n s iv e hydrographic and b i o l o g i c surveys o f f the C a lifo r n ia c o a s t . As part o f the C a lifo r n ia Cooperative Oceanic F is h e r i e s I n v e s t ig a t io n s (CCOFI), s e v e r a l comprehensive c r u is e s , coverin g the c o a s t a l w aters from San F rancisco south to the end o f Baja C a lifo r n ia , are conducted each y e a r. Hydro- graphic data from th ree o f th e se surveys are used to i l l u s t r a t e oceanographic c o n d itio n s in the v i c i n i t y o f San Miguel Gap (Table l ) . TABLE 1 SELECTED H Y D R O G R A PH IC CRUISES IN T H E VICINITY O F SAN M IGUEL G A P C ruise Name I n s t it u t io n D ates M ission R eference N O R P A C Scripps Summer Part o f an in t e r - N O R PA C n a tio n a l study o f Com m , th e e n tir e north i 9 6 0 P a c ific 1955 CCOFI 6304 Scripps 9 A p r il- Routine hydro and Data 24 May 1 9 6 3 b io lo g ic survey, R eport, San F ran cisco to SIO Ref Baja C a lifo r n ia 64-13 CCOFI 6401 Scripps 9 January- As C ruise 6304, Data 4 March 1964 but w ith d e- R eport, t a i l e d study SIO R ef. o f f P t. Conception 6 3 - 7 The s t a t i o n s s e l e c t e d are d i s t r i b u t e d g e n e r a l ly along the 34th p a r a l l e l , e x ten d in g from in sh o r e o f the Gap on the Santa R osa-C ortes Ridge out to the deep P a c i f i c (F ig . 8 ; Appendix I I ) . Topographic and B athym etric I n flu e n c e s The C a lif o r n ia c o a s t i s an area where o c e a n ic c i r c u l a t io n i s a f f e c t e d by both s u b a e r ia l and submarine r e l i e f . The Coast Ranges c l o s e l y p a r a l l e l the e n t i r e w est c o a s t o f North America and s e v e r e ly r e s t r i c t i n t e r a c t i o n between the c o n t in e n t a l and o c e a n ic c lim a t ic regim es. Even th e custom ary l o c a l c o a s t a l la n d -se a r e l a t i o n s h i p s are c u r t a i l e d by the la c k o f communicating land a r e a s. Only in th e l a t i t u d e o f the T ransverse Ranges does th e topographic s t r i k e o f the mountains perm it c o n t in e n t a l in f lu e n c e to extend o f f s h o r e . At P o in t C onception, about 100 km n o r th e a s t o f the Gap, th e c o a s t l i n e bends sh arp ly eastward along the tren d o f the Transverse Ranges. S in ce the major o ff s h o r e wind and cu rren t s tr e a m lin e s trend s o u th e a s t, p a r a l l e l to the shore o f f northern and c e n tr a l C a lif o r n ia , a d i s t i n c t l e e i s formed south o f P o in t C onception. W ithin th e area s h e l te r e d by the T ransverse Ranges, th e Santa R osa-C ortes Ridge e x ten d s perhaps 300 km southeastw ard from the Channel I s lan d s (s e e F ig . l ) . In e f f e c t , the Santa R osa-C ortes Ridge r e p r e s e n ts a s l i g h t l y submerged p e n in s u la , o f t e n l e s s than 200 m deep, p r o t e c t in g southern C a lif o r n ia in sh o r e F ig . 8 .--H y d r o g r a p h ic s t a t i o n s and bathymetry* San M iguel Gap a r e a . 57 HYDROGRAPHIC STATIONS a BATHYMETRY VICINITY OF SAN MIGUEL GAP O Sept. 1955 • Jan. 1964 POINT CONCEPTION * 2 0 0 ' rNORPAC 6 9 80,55 NORPAC J O ^ 80.60 ■ Z O O - 34° 8 2 5 ? 200 83.5IB, NORPAC 71 &80J0 82.64 83.558 8 3 .6 0 b CONTOURS IN METERS 120° 12 1 ° 122° 59 w aters from the main in f lu e n c e o f the C a lif o r n ia Current (Sverdrup and Fleming, 194-1; Emery, i 9 6 0 ) . In t h i s sub merged embayment, th e in n er c o n t in e n t a l b orderlan d in bath ym etric term in o lo g y , e d d ie s commonly d evelop which con t r i b u t e s t r o n g ly to the s e a s o n a lly n o r th -flo w in g Davidson Current. Winds The wind regime o f f the C a lif o r n ia c o a s t i s c o n t r o lle d by the r e l a t i v e s tr e n g th and p o s i t i o n o f the North P a c i f i c (or Sub-Tropic) atm ospheric High. Storms are r a th e r ra re along the coast., but a p p r e c ia b le winds are common. In the summer, when the High dom inates the e n t i r e North P a c i f i c , i t s w estern rim ex ten d s to the v i c i n i t y o f P o in t C onception. Almost con tin u ou s northw est winds o f Force 4 ( 6 - 8 m /se c, 11- 16 k n ots) or g r e a te r occur in th e Gap r e g io n during t h i s seaso n . The High i s much reduced during Northern Hemis phere winter,, and the a s s o c i a t e d p r e v a ilin g winds,, though s t i l l commonly from the n o rth w est, are l e s s p e r s i s t e n t . In g e n e r a l, the g r e a t e s t wind in f lu e n c e i s found toward the North and West. San Miguel I s la n d , the w esternm ost o f the Channel I s la n d s , i s v ery r a r e ly calm ( l e s s than ,1 p e r ce n t o f the tim e) and winds roughly from th e n orthw est (W N W to NNW ) blow alm ost 70 p e r ce n t o f the time a t an average v e l o c i t y o f 8 m /sec (16 k n o t s ) . In c o n t r a s t , on S a n ta .C a ta lin a I s la n d , fa r th e r south and e a s t , winds average l e s s than 6 0 4 m /sec (7 kn ots) and i t i s calm about 10 p e r ce n t o f the time (G oodridge, i 9 6 0 ) . The im p lic a t io n s o f the wind d i s t r i b u t i o n p a tte r n o f f the southern C a lif o r n ia c o a s t are c l e a r . The sou th flo w in g C a lif o r n ia Current i s a c t i v e l y a s s i s t e d during the season o f str o n g , reg u lar' northw est winds., and then i s a b le to dominate su r fa c e c i r c u l a t i o n b oth o f f s h o r e and in s h o r e . In the f a l l and winter., when the winds are l e s s constant., the e d d ie s which are alw ays p r e s e n t in the deeper w aters over the southern C a lif o r n ia borderland in f lu e n c e the e n t ir e water column and the northward Davidson Current d ev elop s in s h o r e . In Santa Barbara Channel., between the mainland and the Northern Channel Islan ds., the s t r i k e o f the Trans v e r se Ranges encourages e a s t w inds. There, su r fa c e d r i f t to the w est i s o f t e n found throughout the year and i s s t r o n g ly r e in fo r c e d when the in sh o r e e f f e c t o f the C a l i f o r n ia Current d im in is h e s . The Santa Ana winds are i n t e r e s t i n g l o c a l phenomena. These are hot., dry foehn winds which blow o f f s h o r e spasmod i c a l l y from th e in la n d d e s e r t s when th e North P a c i f i c High i s weakened during f a l l and w in te r (Clem ents, e t a l ., 1 9 6 3)- The Santa Ana winds are always r e s t r i c t e d in scop e, but th ey may be q u ite pow erful; v e l o c i t i e s over 30 m /sec (60 k n ots) have been measured in th e se winds (Bowditch, 1958). A p preciable q u a n t i t i e s o f f i n e sedim ent may be s tr ip p e d from 6 l the d e s e r t and c a r r ie d to sea in Santa Anas (Babcock., 1957; Emery, i 9 6 0) . Waves Seas o f f P o in t Conception are t r a d i t i o n a l l y among the most rough to be fo u n d .a lo n g the w est c o a s t o f the U n ited S t a t e s . The n orthw est winds o f sp rin g and summer c o n s t a n t ly g en e ra te s h o r t, s te e p waves in the v i c i n i t y . These waves are o f primary im portance as a l in k in the energy t r a n s f e r system which m a in ta in s the in sh o r e flow o f the C a lif o r n ia C urrent. E d dies r e l a t e d to the Santa Barbara Channel d r i f t c om p lica te t h i s p i c t u r e . A lso , in a l l se a so n s, waves o f a p p re c ia b le magnitude e n te r the area as s w e ll from storms as fa r away as the G ulf o f Alaska and the southw est P a c i f i c (Emery, i 9 6 0 ; Snodgrass, e t a l ., 1 9 6 1). S w ell w ith a wave le n g th as g r e a t as 460 m, propagated from the southw est or w e st, has been observed in the area (Wright, 1 9 6 5) . Such long waves are b e l ie v e d to in f lu e n c e water p a r t i c l e m otions a p p r e c ia b ly to a depth o f o n e - h a lf t h e i r wave le n g th (S v e r drup, e t a l , 19^2 ) , hence th ey are probably a fa c t o r in mix in g th e su r fa c e w ater la y e r s . I t i s p o s s i b l e , to o , th a t i n t e r n a l waves on th e therm oclin e su r fa c e and even deeper may be g en e ra ted by th e se g r e a t waves. I n t e r n a l waves o f sem id iu rn al t i d a l p e r io d , p o s s i b l y g e n era ted a t the c o n t i n e n ta l s lo p e , have been observed o f f southern C a lif o r n ia by Summers and Emery ( 1 9 6 3) . These waves are r ep o rted to have 6 2 an am plitude o f a t l e a s t 20 m and a wave le n g th on the order o f 180 km. O c c a sio n a lly tsunam is have been record ed in southern C a lif o r n ia w aters (Munk, 1 9 6 2); presumably t h e i r in f lu e n c e i s s im ila r to th a t o f the long wave le n g th s w e l l . In terms o f the e n t i r e oceanographic environment o f th e Gap, waves are o f im portance in a v a r ie t y o f ways. Cer t a i n l y th ey h e lp to m aintain the pronounced p yn cn o clin e b e tween the mixed su r fa c e and deeper la y e r s . In sh allow wa ter., near the isla n d s,, wave a c tio n i s c e r t a i n l y a p o te n t agency o f e r o s io n and sedim ent transport., but the g r e a t e s t p a r t o f the area i s fa r too deep fo r t h i s to be a major i n flu e n c e upon the environm ent. The im portance o f t i d a l and i n t e r n a l waves i s d i f f i c u l t to a s s e s s . I t i s p o s s i b l e th a t th ey have an a p p r e c ia b le e f f e c t upon bottom c u r r e n ts over th e Santa R osa-C ortes Ridge and p o s s i b l y over the A rgu ello P la te a u , as w e l l. Water C h a r a c t e r is t ic s Two d i s t i n c t i v e w ater ty p es are p r e s e n t in the sh a llow ( l e s s than 500 m) c i r c u l a t i o n o f f southern C a lif o r n ia . These ty p e s, o r i g i n a l l y d is t in g u is h e d by Sverdrup and Flem in g (1 9 ^ 1 )j were named "Northern” and "Southern" water from t h e i r ’ presumed so u r c e s . Northern w aters are c h a r a c te r iz e d by r e l a t i v e l y low tem perature and low, r a th e r v a r ia b le s a l i n i t y ; Southern w ater ten d s to be warmer and more s a l i n e (Table 2 ). 63 TA BLE 2 W A TER TYPES IN TH E SH A L L O W CIRCULATION OFF SOUTHERN CALIFORNIA (AFTER SVERDRUP AND FLEMING, 1942) Water Type Presumed Source Tem perature °C S a l i n i t y 0 / 0 0 N orthern C a lifo r n ia Current (S u b a r c tic S u rface W ater) 5 .2 - 8 . 5 5 5 .8 0 -3 4 .2 0 Southern Southern C a lifo r n ia E d d ies and D avidson Current 6 .0 - 1 0 .5 3 4 .3 0 -3 4 .4 0 So c l e a r l y d e f in e d are t h e s e w ater t y p e s t h a t v i r t u a l l y a l l w a te r s o v er th e c o n t i n e n t a l b o r d e r la n d can be t r e a t e d as m ix tu r e s o f th e two. At d e p th s g r e a t e r than 200 m, o v er 50 p e r c e n t o f the w ater volume c o n s i s t s o f Southern Water (F lem in g, 194-1), hence I t I s Southern w ater t h a t f i l l s th e o f f s h o r e b a s i n s o f th e b o r d e r la n d . A sta n d ard t e m p e r a t u r e - s a l i n i t y p l o t o f h y d rograp h ic s t a t i o n s from th e g e n e r a l v i c i n i t y o f the Gap ( F ig . 9) c l e a r l y shows th e c h a r a c t e r i s t i c s o f th e p r i n c i p a l w ater ty p e s in th e r e g i o n . With th e e x c e p t io n o f th e NORPAC s t a t i o n s , a l l d a ta i s from a s i n g l e CCOFI c r u i s e in January o f 1964, when th e D avidson Current was a c t i v e . The NORPAC s t a t i o n s were o c c u p ie d in Septem ber o f 1955; when th e r e g io n was dom inated by the C a l i f o r n i a Current r eg im e. The l i m i t s o f N orthern and Southern w ater are shown on th e d i a gram; most o f th e w a te r s o f th e Gap f a l l w it h in th e s e bounds. The s t a t i o n f a r t h e s t o f f s h o r e , NORPAC 71; shows F ig . 9 . — T e m p e r a t u r e - s a lin ity o f w a ters o f f P o in t C onception. 64 SALINITY { % < .) 33.80 34.00 34.20 34.40 83.SSB 83.513 82.64 82.5? NORPAC 70 NORTHERN WATER SOUTHERN WATER NORPAC 71 TEMPERATURE-SAL1NITY CHARACTERISTICS OFF POINT CONCEPTION, CALIFORNIA CCOFI S ta tio n s (Jan u ary ) — NORPAC S ta tio n s (Septem ber) 66 t h e e x p e c t e d N o r th e rn w a te r a t s h a llo w d e p t h s , t h e n , a t a d e p th o f a b o u t 400 m, some I n f l u e n c e o f N orth P a c i f i c I n t e r m e d ia t e w a te r i s a p p a r e n t . T h is I n t e r m e d ia t e w a te r i s p a r t i c u l a r l y c h a r a c t e r i z e d by low s a l i n i t y , due to i t s s o u r c e i n t h e i c e - f e d G u lf o f A la sk a (F le m in g , 1 9 5 5 )- S t a t i o n NORPAC 70 shows th e c o n d i t i o n s t h a t p r e v a i l d u rin g th e p e r io d o f a c t i v e u p w e l l i n g . At d e p th s g r e a t e r than 6 0 0 - 7 0 0 m, a l l w a t e r s i n th e a r e a ap p ea r to be a t r a n s i t i o n i n t o t y p i c a l N orth P a c i f i c Deep w a te r . D epth d i s t r i b u t i o n o f sta n d a r d w a te r p r o p e r t i e s ( s a l i n i t y , t e m p e r a t u r e , and d i s s o l v e d o x y g e n ) show c e r t a i n i n t e r e s t i n g f e a t u r e s (Fig. 10). At th e s u r f a c e , v a l u e s o f a l l th e p r o p e r t i e s a r e h i g h l y v a r i a b l e , r e f l e c t i n g th e f l u c t u a t i n g i n f l u e n c e o f c u r r e n t s , w in d s , and w a v e s. A p ron ou n ced p y n c n o c l i n e s e p a r a t e s th e s u p e r f i c i a l and deep w a t e r s . T h is s u r f a c e c l e a r l y s l o p e s upward to th e w e s t and i s s h a l l o w e s t i n t h e S a n ta R o s a - C o r te s R id ge a r e a . A l l o f th e d e e p e r s t a t i o n s show a marked o xyg en minimum l a y e r , w i t h c o n c e n t r a t i o n s commonly l e s s th an 1 m l/L , a t d e p th s from a b o u t 400 to 800 m. T h is minimum i s p a r t i c u l a r l y w e l l - d e v e l o p e d i n th e w a t e r s i n th e im m ed iate v i c i n i t y o f th e Gap. P r e sum ably i t i s a t l e a s t i n p a r t r e l a t e d to th e h ig h p r o d u c t i v i t y o f th e o v e r l y i n g w a t e r s and th e o x i d a t i v e m e ta b o lis m o f b a c t e r i a d e e p e r i n th e w a te r colum n. B e c a u se o f th e o b v io u s sa m p lin g d i f f i c u l t i e s , t h e r e i s l i t t l e in f o r m a t i o n a v a i l a b l e a b ou t t h e c h a r a c t e r i s t i c s o f F ig . 1 0 . — Standard w ater p r o p e r t ie s , San Miguel Gap area. 67 T*C 2 OXYGEN m l/L NORPAC 71 8 2 .6 4 8 2 .5 7 4 0 0 . S A L IN IT Y X 800 O XYG EN 1400 1600 8 3.5IB T E M P E R A T U R E 2000 ■ 4 0 0 STANDARD WATER CHARACTERISTICS IN THE VICINITY OF SAN M IGUEL GAP o SALINITY (% d • TEMPERATURE (*C) 0 DISSOLVED OXYGEN (ml/L) C T \ 00 69 o c e a n ic bottom w a te r s . F o r t u n a t e ly , the Naval C i v i l E n g i n e e r in g L aboratory has been con d u ctin g i n s i t u s t u d i e s o f deep marine c o r r o s io n and f o u lin g in th e v i c i n i t y o f the Gap (Jones., 1 9 6 5) • In c o n n e c tio n w ith t h e s e stu d ies., the c h a r a c t e r i s t i c s o f th e bottom w a te rs have been determ ined r e p e a t e d ly (Kenneth Gray,, in p r e p a r a tio n ) . Average bottom c o n d it io n s are shown in Table 3* Of p a r t i c u l a r i n t e r e s t are the r e c o r d s from Study I I - l , Table 3, where th e t e s t u n i t ( r e s t i n g on the su r fa c e o f A r g u e llo P la te a u ) i s in the oxygen minimum zone. TABLE 3 BO T T O M W A TER CHARACTERISTICS IN TH E SAN M IGUEL G AP AREA (JUNE, 1 9 6 5 ) NCEL SITE L a t. N Long. W Water Depth (m) Temp. °C S a li n it y (S o /o o ) O 2 (m l/L ) STU 1-1 33°46' 120°37' 1722 2.52 34.59 1.22 STU 1-2,3 33°44' 120 °45' I83O 2.40 34.59 1.54 STU I I - l 34°o6 ' 120°42’ 790 k .69 34. 4i o.4o The major n u t r i e n t s , p h osp h a te, n i t r i t e , and s i l i c a , show very c l e a r l y th e i n f l u e n c e o f organism s in th e w a ter column ( F ig . l l ) . The c h a r a c t e r i s t i c p a t t e r n o f consumption a t th e s u r fa c e and r e g e n e r a tio n w ith depth i s seen in th e ph osp hate and s i l i c a d a ta . N i t r i t e , th e o n ly form o f n i t r o gen which has been r o u t i n e l y determ ined in th e a rea , ten d s to be r e l a t i v e l y h ig h in th e mixed zone, but i s r a p id ly r e - F ig . 1 1 . - - N u t r i e n t s in th e w a te r s o f f P o in t C o n cep tio n . TO 71 NITRITE a PHOSPHATE 9 SILICA 25 10 0 125 50 75 150 1 . 0 200 N IT fflT E P H O S P H A T E 4 00 600 S IL IC A 82.57 800 1000 1200 CL 200 400 83.55B 600 D ISSO LV ED N U T R IE N T S SAN M IG U E L GAP AREA 200 83.5IB 72 moved by b a c t e r i a l a c t i v i t y w ith d ep th . I t i s i n t e r e s t i n g to n o te t h a t o v e r the b o r d e r la n d , th e t h i c k n e s s o f th e mixed l a y e r above th e th e r m o c lin e ( f o r i n s t a n c e , COOFI 6401) i s commonly 4 0 -6 0 m, r o u g h ly the t h i c k n e s s o f th e e u p h o tic l a y e r e x t r a p o l a t e d from s e o c h i d i s c o b s e r v a t i o n s ( S t r i c k land., 1 9 6 5 )• T h is a c c o u n ts i n p a r t f o r th e agreem ent o f depth d i s t r i b u t i o n o f n u t r i e n t c o n c e n t r a t io n s w ith th e p o s i t i o n o f th e t h e r m o c lin e . A b so lu te v a l u e s o f th e n u t r i e n t s are comparable to c o n c e n t r a t io n s a t s i m i l a r d e p th s e l s e where i n th e N orth P a c i f i c , b u t t h e r e are im p o rta n t anoma l i e s r e l a t e d to u p w e llin g w hich have a c o n s id e r a b le i n f lu e n c e upon th e p r o d u c t i v i t y o f the r e g io n . C u rren ts The fundam ental c u r r e n t p a t t e r n i n th e s u r f a c e c i r c u l a t i o n o f f th e C a l i f o r n i a c o a s t i s r e l a t e d to wind s t r e s s . W ell o f f s h o r e , where n o r th w est winds a r e v i r t u a l l y a perman e n t f e a t u r e , th e s l u g g i s h , s o u t h e a s t f lo w in g C a l i f o r n i a Current can alw ays be i d e n t i f i e d . In s h o r e , as n o te d in th e d i s c u s s i o n o f w in d s, th e r e may be an a b s o lu t e r e v e r s a l o f s u r fa c e flo w to form th e D avidson Current (som etim es termed th e C a l i f o r n i a C o u n tercu rren t) when the n o r th w est winds d im in ish in the f a l l and w in t e r . From lo n g -te r m sh ip d r i f t c o m p i la t i o n s , th e average s u r fa c e c u r r e n t v e l o c i t i e s o f f P o in t C on ception are in e i t h e r a n o r t h e r ly or s o u t h e r ly d i r e c t i o n depending upon the s e a so n . They range from 10-25 73 cm /sec (0.2-0.4 knot). Much h ig h er cu rren t v e l o c i t i e s are n ot uncommon., however; v e l o c i t i e s as g r e a t as 100 cm /sec (2 k n o ts) have "been e x p e rien ce d a t sea in th e area by V elero IV (John H a rr is, p e r so n a l com m unication). P o s s ib ly the h ig h v e l o c i t i e s were a s s o c ia t e d w ith l o c a l e d d ie s which are common o f f P o in t C onception. J u s t south o f the Channel I s la n d s , c u r r e n ts over 200 cm /sec (4 k n ots) have been r e corded (D. P. Doerner, p e r so n a l com m unication). Although dynamic h e ig h t anomaly c h a r ts can r e f l e c t on ly the more g r o s s f e a t u r e s o f the c i r c u l a t i o n p a tte r n , the g e o s tr o p h ic c u r r e n ts , th e se a so n a l c o n tr a s t i s obviou s in Figure 12 (Summer) and F igure 13 (W in te r ). The most d e t a i l e d hydrographic study conducted o f f P oin t C onception, p a r t o f CC0FI C ruise 6401 in January o f 1964, i s shown in Figure l 4 . The Davidson Current was pronounced a t the time o f the d e t a i l e d stu d y. Both the t o t a l cu rren t above the 500 d e c ib a r (rou ghly 500 m eters) s u r fa c e and the deeper c u r r e n ts between 200 and 500 d e c ib a r s are shown in a l l the dynamic topography maps. Current d i r e c t io n on th e se c h a r ts i s in d ic a t e d by the arrows on the con tou rs; cu rren t v e l o c i t y i s p r o p o r tio n a l to the sp acin g o f th e con tou rs o f equal dy namic h e ig h t anomaly. Of p a r t i c u la r i n t e r e s t a t a l l se a so n s i s the p r esen ce o f a c o n s id e r a b le system o f e d d ie s ov er the c o n t in e n t a l bord erlan d . This predom inantly c o u n te r c lo c k w ise eddy s y s tem, though ex trem ely v a r ia b le in dim ensions, i s a permanent Fig. 1 2 .--Oceanic currents o f f the C alifornia Coast (Summer). T4 75 CURRENTS OFF THE CALIFORNIA COAST FROM DYNAMIC TOPOGRAPHY : . CCOFI CRUISE 6 3 0 4 , APRIL-MAY 1963 DEEP CIRCULATION 2 0 0 o v er 5 0 0 d ecib ar* <40 <45 <45 0 2 4 8 8 10 0 0 1 dyn.tn c m / w c * ■ «- - « ■ 0 10 2 0 3 0 4 0 5 0 0 .0 5 dyn.m A p p ro x im a te c u r r e n t s p e e d a t 3 0 ° N TOTAL CIRCULATION 0 o ver 5 0 0 d e c lb a re ,6 0 . . 9 0 35* 1.05/ 1 . 0 O 1 -85 .0 5 C o n to u r In te rv a l 0 .0 1 D y n am ic M e te rs cu rren t direction .9 0 1.00 115° 120° 125 * 130 135* Fig. 13---Oceanic currents o f f the C alifornia Coast (W inter). 76 77 CURRENTS OFF THE CALIFORNIA COAST FROM DYNAMIC TOPOGRAPHY DEEP CIRCULATION 2 0 0 o v a r 8 0 0 d acib ara .3 9 CCOFI CRUISE 6 4 0 1 , JAN.-MAR. 1 9 6 4 45 sea Figure 14 4 2 , 4 0 4 5 4 6 30* 4 8 Contour Interval 4 7 4 9 20 ° *2 4 2 |'o 30 4o i o 0 .0 5 dyn.m Approximate current speed at 30°N 4 4 4 3 TOTAL CIRCULATION 0 over 5 0 0 decibars £ 5 1.001 1.05 1.09. 1.05 '.9 0 C ontour interval 0 .0 1 Dynamic Meters 4 -r-C u rr e n t D irection— < I .O I i.ocP 120° 130* 1 3 6 * F ig . 1 4 . --C u rr en ts o f f P o in t C onception, January, 1964. 78 79 C U R R E N T S O F F PT. CONCEPTION FROM DYNAMIC TOPOGRAPHY CCOFI CRUISE 6 4 0 1 , JAN. 1 9 6 4 D EEP CIRCULATION 2 0 0 o v er 5 0 0 d e c ib a rs 6 8 10 1 2 1 4 1 6 IS 25 cm/sac Approximate currant *p*ed at 34.5°N TOTAL CIRCULATION 0 over 5 0 0 d e c ib a rs Contour interval 0.01 Dynamic Meter* > — Current direction------ ► _ L _ 1 2 2 0 J __ 121 ° J ___ 120° 3 3° fe a tu r e o f the deeper c ir c u la t io n and in f lu e n c e s the su rfa ce throughout much o f the year (S ch w artzlose, 1 9 6 3) I t i s p o s s i b l e th a t much o f the s o - c a l l e d Southern water d ev elop s in th e se e d d ie s over the borderland. The d e t a i l e d survey (F ig . 14) shows how complex the c ir c u la t i o n may be o f f P oin t Conception. Presumably, t h i s i s the r e s u l t o f the to p o g r a p h ic a lly determ ined d e f l e c t io n o f the in sh o re and deep n o r th -flo w in g cu r re n ts out in to the stream o f the C a li f o r n ia Current. I t i s l i k e l y th a t e d d ie s i n i t i a t e d in the confused w aters o f f Conception are c a r r ie d southeastward w ith the main d r i f t o f the C a lifo r n ia Current and c o n tr ib u te to the major eddy system over the c e n tr a l borderland (S ver drup, e t a l .j 1942). O ff the c e n tr a l C a lif o r n ia c o a s t , a n o r th -flo w in g cou n tercu rren t a t depths g r e a te r than 200 m beneath the I n shore p o r tio n o f the C a lif o r n ia Current appears to be a permanent f i x t u r e , though the d r iv in g mechanism o f such a current i s u n cle a r (Reid and S ch w artzlose, 1 9 6 2) . Off Monterey Bay, Reid ( 1 9 6 2) made a s e r i e s o f parachute drogue measurements a t a depth o f 250 m in t h i s co u n tercu rren t. He dem onstrated the e x is t e n c e o f a north cu rren t w ith v e l o c i t i e s as g r e a t as 23 cm /sec In the zone from the 1000 fathom (1 8 3 2 m) contour seaward fo r 40 n a u t ic a l m ile s . S t i l l fa r th e r o ffs h o r e (40-100 naut. m i .) , he found th a t the flow a t 250 m was to the s o u th e a st, in accord w ith the su rfa ce c i r c u l a t i o n . A s im ila r s i t u a t i o n , co n sid er a b ly 81' c o n fu s e d by th e many e d d i e s , seem s to o c cu r o f f P o in t Con c e p tio n . Bottom c u r r e n t s are i n e v i t a b l y o f p a r t i c u l a r i n t e r e s t in a stu d y o f th e sed im en ta ry regim e o f an a r e a . B eca u se o f th e tim e r e q u ir e d to ta k e m easurem ents and th e p o s s i b i l i t y o f damage to g e a r , most s t u d i e s must deduce a l l b ottom c u r r e n t in fo r m a tio n from p h o to grap h s and o t h e r i n d i r e c t e v i dence (Heezen and H o l l i s t e r ., 1964; W ild e, 1 9 6 5 ) . F o r tu n a t e l y , in c o n n e c tio n w it h t h e i r deep ocean c o r r o s io n t e s t s , th e N aval C i v i l E n g in e e r in g L a b o ra to ry a t t a c h e d a s a v o n iu s r o t o r typ e c u r r e n t m eter to a t e s t p la tfo r m (STH I I ) . The m eter was moored a l i t t l e more than 1 m o f f th e bottom a t a depth o f 727 m on A r g u e llo P la t e a u . H ourly c u r r e n t m eas urem ents were made o v e r a 6 month p e r io d , p r o v id in g a v i r t u a l l y unique lo n g -te r m r e c o r d o f deep w a ter bottom c u r r e n t s ( F ig . 1 5 )- .The mean c u r r e n t v e l o c i t y on A r g u e llo P la te a u was low, 4 .6 cm /sec ( 0 . 1 k n o t ) , b u t an a p p r e c ia b le number o f r e a d in g s were o f c u r r e n t s g r e a t e r than 20 c m /s e c . A s i n g l e r e a d in g , p o s s i b l y a m a lf u n c t io n , r e g i s t e r e d 1 .9 k n o t s , a l most 100 c m /s e c . Comparable b u t s h o r t - t e r m measurem ents have been made o f b ottom c u r r e n t s on th e B lake P la t e a u , o f f the e a s t c o a s t o f F lo r id a . (R, M. P r a t t , 1 9 6 3 ) . T here, i n a r e g io n swept by th e G ulf Stream , a v e ra g e c u r r e n t s were about 25 cm /sec ( 0 . 5 k n o t ) . F ig . 1 5 . --B o tto m c u r r e n t m easurem ents on A r g u e llo P la te a u . 82 0.5 0. 6 CU RREN T V E L O C IT Y D IST R IB U T IO N NUMBER OF OBSERVATIONS 300 Q 0 . 2 M EAN CURRENT VELOCITY a 4.6 CM/SEC S in g le r i a d i n g i a l i o r te o r d « d q | 0 .6 4 , 0 .7 2 , 0 .8 5 , 0 .9 6 , 1.0 1, 1 .2 8 , 1 .5 4 , 1 .6 2 , 8 1 J .9 2 k n o ti. 20 •25 1-30 AZIMUTH AND FREQUENCY OF BOTTOM CURREN TS z o 1 5 I o - J Id > — 2 7 0 ' Id D C a c 3 o Notes- Based upon 4320 hourly observations collected June-December, 1964. The instrument was a Geodyne A-IOO Current Meter, installed approximately one meter off the bottom at a depth of 727 meters. Data furnished by U.S. Naval Civil Engineering Laboratory, courtesy of R.E. Jones. 180* NUMBER OF O BS. O 5 10 BOTTOM CURRENT MEASUREMENTS ARGUELLO PLATEAU oo (JO 84 On A r g u ello P lateau * th e d i r e c t io n o f the cu rren t was predom inantly from the n orthw est or the s o u t h e a s t . This i s p a r a l l e l to the c o n t in e n t a l s lo p e in the area and in the d i r e c t io n o f most m easureable g e o s tr o p h ic flow . Currents from th e northwest., in accord w ith the su r fa c e flow o f the C a lif o r n ia C urrent, are s l i g h t l y more freq u en t than th o se from th e s o u th e a s t . An a p p r e c ia b le number o f measurements i n d i c a t e bottom c u r r e n ts from the n o r th e a s t or sou th w est, p o s s i b l y r e l a t e d to t i d a l flo w or j u s t c o n c e iv a b ly to i n t e r n a l wave m otion s. U pw elling During sp rin g and summer, b r is k northw est winds a s s o c ia t e d w ith the North P a c i f i c High are alm ost co n tin u o u s over the su r fa c e o f the C a lif o r n ia Current. The h igh r e s u l ta n t wind s t r e s s p a r a l l e l to the shore l i n e r e s u l t s in Ek- man Transport o f c o n s id e r a b le volumes o f su rfa c e w ater d i r e c t l y o f f s h o r e . This i s compensated by l a r g e - s c a l e up- w e llin g o f deeper w aters in sh o r e (Sverdrup, e t a l ., 1942). N u tr ie n t elem en ts e s s e n t i a l to p h ytoplan kton growth which tend to be r a p id ly d e p le te d in th e e u p h o tic zone are thus retu rn ed to the su r fa c e w a te r s. This f e r t i l i z a t i o n p r o c e s s , e s s e n t i a l to the o rg a n ic p r o d u c t iv it y req u ire d fo r c o a s t a l f i s h e r i e s , o p e r a te s v i r t u a l l y c o n tin u o u s ly a t v a r io u s p o in t s during the season o f northw est winds along the w est c o a s t o f North America (Sm ith, e t a l . , 1 9 6 6). 85 L a r g e - s c a le u p w e llin g has been I d e n t i f i e d a t one tim e o r an o th er alon g th e e n t i r e cou rse o f th e G a li f o r n i a Cur r e n t . C h a r a c t e r i s t i c a l l y , I t i s a boundary e f f e c t , l i m i t e d to about 50 km seaward o f a n o r th -s o u th c i r c u l a t i o n b a r r ie r (Y oshida, 1955)■ U p w ellin g has been p a r t i c u l a r l y w e l l s t u d ie d on the c e n t r a l C a l i f o r n ia c o a s t , in the v i c i n i t y o f Monterey Bay (Sverdrup, e t a l ., 19^2; Marine R esearch Com m i t t e e , 1 953 )• An annual c y c le i n s u r fa c e w ater tem pera t u r e s and p h ytop la n k ton c o n c e n tr a tio n s e r v e s to d i s t i n g u i s h th r e e p h a ses: the O ceanic P erio d during th e F a l l (September and O ctober) c h a r a c t e r iz e d by c o o l w aters and m oderate o r g a n ic p r o d u c t i v i t y ; the Davidson Current P erio d (November to F e b r u a r y ), when w ater tem p era tu res are f a i r l y h ig h and p r o d u c t i v i t y i s e x tr e m e ly low; and th e U p w ellin g P er io d (March to A u g u st), when th e w a te rs are c o ld and th e r e are alw ays e x t e n s i v e p h ytop la n k ton bloom s in the a r e a . Topographic i n f l u e n c e upon th e u p w e llin g p a tte r n has been c l e a r l y demon s t r a t e d . The lo w e s t w ater tem p era tu res are alw ays reco rd ed o v e r th e head o f Monterey Submarine Canyon, where w a ters from a c o n s id e r a b le depth can be drawn in s h o r e and upward (Marine R esearch Committee, 1953)* The v e r t i c a l c i r c u l a t i o n system i s p a r t i c u l a r l y complex o f f P o in t C onception and in the Gap r e g io n . The b a s i c up w e l li n g mechanism i s s i m i la r to t h a t o f f M onterey, b u t i n ste a d o f a land mass to th e e a s t o f the main stream o f the C a l i f o r n ia C urrent, th e r e i s open w a ter, the Santa Barbara Channel and the c o n t in e n t a l b ord erlan d . Emery ( i 9 6 0 ) su g g e s t e d th a t in s t e a d o f the c l a s s i c concept o f v e r t i c a l mo t io n o f w ater to r e p la c e th a t tra n sp o rte d offsh ore,, th ere may in s t e a d in the b orderlan d be e x t e n s iv e entrainm ent o f s u r fa c e w aters from the Southern C a lif o r n ia Eddy System. He p ic t u r e d e x te n s iv e movements o f w ater seaward a c r o s s and through the deeper gaps in the Santa R osa-C ortes R idge. Un d o u b te d ly , such entrainm ent must occur to some e x t e n t . I f the concep t o f Northern and Southern w ater m asses i s valid., as much as 50 p e r c e n t o f the w aters between 200-400 m over the area between the Santa R osa-C ortes Ridge and the Patton Escarpment may w e l l be o f Southern o r ig i n (Fleming,, 194l) . However., w aters from the Eddy System could be e x p e cted to be d e p le te d in n u t r i e n t s , y e t in t e n s e plankton blooms are commonly en countered along the Santa R osa-C ortes Ridge dur in g the presumed season o f u p w e llin g (Marine R esearch Com m i t t e e , 1 9 5 8 ). As w e l l , the se a s o n a l r i s i n g o f iso th e r m s , the most obviou s p h y s ic a l ev id en ce o f v e r t i c a l m ixin g, i s as pronounced in th e Gap area as i t i s o f f Monterey. I t i s .concluded th a t u p w e llin g in the c l a s s i c sen se must be the p r i n c i p a l m ixing mechanism in the v i c i n i t y o f San Miguel Gap. At the northern margin o f the Gap r e g io n , the mixing s i t u a t i o n i s co m p licated by the c i r c u l a t i o n o f th e Santa Barbara B a sin . At alm ost a l l se a so n s th e re i s a p p r e c ia b le su r fa c e flow to the w e st, presumably due to the topography 87 o f th e T ransverse Ranges. Santa Barbara Channel I s pro t e c t e d from n o rth w est winds, and y e t i s exposed to winds from the e a s t . T his e f f e c t , q u it e p o s s i b l y a s s o c i a t e d w ith the i n f l u e n c e o f th e c o u n te r c lo c k w ise Southern C a l i f o r n i a Eddy, r e s u l t s in a permanent s u r fa c e d r i f t to th e w e s t. Un d o u b te d ly , th e n , s u r fa c e w a te r s from th e channel can e a s i l y become mixed w ith C a l i f o r n ia Current w a te r s d i r e c t l y o f f P o in t C onception and probably cause th e l o c a l e d d ie s found in th e v i c i n i t y . Entrainm ent must be a f a c t o r i n a t l e a s t t h i s l im it e d r e g io n , as opposed to u p w e llin g in th e s t r i c t s e n s e . Records o f sea su r fa c e tem perature and the o t h e r o c e a n o g r a p h ic param eters are not a s com plete f o r th e Gap area as fo r M onterey, but an annual c y c l e i s r e c o g n iz e d . U sing th e d ata o f the r e p e a te d CCOPI c r u i s e s alon g the c o a s t , two p e r i o d s can be d i s t i n g u i s h e d , a n alogou s to th o se f a r t h e r n o r t h , a Davidson Current P e r io d (O ctober to February) and a C a l i f o r n i a C u rren t-U p w ellin g P eriod (March to S e p te m b e r ). There seem to be no ph ases o f the c y c l e c l o s e l y an alogou s to t h e Monterey "Oceanic P e r i o d , " though c o n d it io n s fo r a few weeks in the e a r l y f a l l ( u s u a l l y around the m iddle o f September) seem to i n d i c a t e a s im ila r tim e o f t r a n s i t i o n . Hidaka ( 1 9 6 1) d e r iv e d an a p p a r e n tly v a l id model fo r u p w e llin g which r e q u ir e s v e r t i c a l movement a t a l l l e v e l s in th e w ater column, in c o n t r a s t to the r e l a t i v e l y s u p e r f i c i a l o v e rtu r n assumed by Sverdrup and Fleming ( l 9 4 l ) . Thus th e r e 88- i s a d i s t i n c t p o s s i b i l i t y th a t the Gap i t s e l f , a s a b a th y m e t r ic break i n th e c o n t i n e n t a l s lo p e which e x te n d s to o v e r 2 000 m, may ca u se p a r t i c u l a r l y com prehensive v e r t i c a l m ix in g in i t s v i c i n i t y . I t has o f t e n been o b se r v e d ( f o r e x am ple, Marine R esearch Com m ittee, 1953) th a t p h y to p la n k to n p r o d u c t i v i t y i n the b o r d e r la n d i s e s p e c i a l l y h ig h toward th e n orth ern end o f th e Santa R o sa -C o r te s R idge which i s th e e a s t e r n f l a n k o f th e San M iguel Gap r e g io n . Summary Many complex o cea n o g ra p h ic f a c t o r s i n f l u e n c e the San M iguel Gap a r e a . Though th e b a s i c c i r c u l a t i o n p a t t e r n I s o n ly a m inute segm ent o f the N orth P a c i f i c C urrent System , th e Gap I s a t a p o i n t o f maximum v a r i a t i o n w i t h i n the s y s tem. The C a l i f o r n i a C urrent, th e s o u t h - f lo w in g e a ste r n boundary c u r r e n t o f th e n o rth P a c i f i c , dom in ates the a rea in S p rin g and Summer (M a rch -S ep tem b er). At t h i s tim e, w id e sp re a d u p w e ll i n g , c o n c e n tr a te d a lo n g the S an ta R osa- C o r tes R id g e, r e s u l t s in h ig h p h y to p la n k to n p r o d u c t i v i t y . In f a l l and w in t e r (O ctober to F e b r u a r y ), a n o r t h - f lo w in g s u r fa c e c u r r e n t, th e D avid son , d e v e lo p s in s h o r e and f o r c e s th e main stream o f th e C a l i f o r n i a C urrent w e s t , to the edge o f th e c o n t i n e n t a l m argin. C o u n te r c lo c k w ise e d d i e s , o f t e n o f c o n s id e r a b le m agnitud e, a re a permanent f e a t u r e o f th e c i r c u l a t i o n o f the c o n t i n e n t a l b o r d e r la n d . They d ev elo p i n th e r e g io n s h e l t e r e d by the T r a n sv e r se Ranges and the su b 89 marine p e n in su la o f the Santa R osa-C ortes R idge. These e d d i e s may he an im portant f a c t o r in th e annual appearance o f the Davidson C urrent. At depths g r e a t e r than a few hundred m e te r s, g e o s tr o p h ic c o n s id e r a t io n s i n d ic a t e a dominant flow to th e n o r th w est. In con trast,, measurements a t 700 m on A r g u e llo P la tea u show the bottom c u r r e n ts are from both the n o rth w est and s o u th e a s t . With the e x c e p tio n o f the su r fa c e l a y e r s , w ater c h a r a c t e r i s t i c s throughout the column are r e l a t i v e l y c o n sta n t and t y p i c a l o f the north P a c i f i c . The se a so n a l s h i f t in su r fa c e c u r re n ts in the Gap r e g io n has an im portant consequence: two s i g n i f i c a n t l y d i f f e r e n t w ater m asses a l t e r n a t e l y occupy the eu p h o tic zone each y e a r . In summer the c o ld , f e r t i l e , low s a l i n i t y C a lif o r n ia Current w ith i t s a s s o c i a t e d u p w e llin g dom inates; in w in te r i t s p la c e i s taken by the warmer, more s a l i n e , n u t r ie n t de p l e t e d w aters o f th e Davidson Current. The c lim a te i s such t h a t p r e c i p i t a t i o n , r u n - o f f , and e v a p o ra tio n have l i t t l e e f f e c t upon ocean ograp hic c o n d it io n s . In the w estern o n e- t h ir d o f th e a r ea , c o n d it io n s are r e l a t i v e l y "oceanic" throughout the y e a r , though the c i r c u l a t i o n p a tte r n i s o f t e n con fu sed by e d d ie s r e l a t e d to the Santa Barbara Chan n e l D r i f t . To the e a s t , w ith in the Gap r e g io n , th e r e i s p r o g r e s s i v e l y g r e a t e r in f lu e n c e from u p w e llin g and from sh a llo w w ater e f f e c t s a s s o c i a t e d w ith the I n s u la r and Santa R osa-C ortes R id g es. As a r e s u l t , a d e f i n i t e g r a d ie n t o f 90 o c e a n ic in flu e n c e e x i s t s from e a s t to west a c ro ss the San Miguel Gap Region. GEOLOGY OP THE SAN MIGUEL GAP REGION G eneral San M iguel Gap i s an anomalous g e o l o g i c f e a t u r e . I t i s a trou gh or b a s in about 30 km wide which i n t e r s e c t s th e con t i n e n t a l s lo p e so u th w est o f P o in t C o n ce p tio n , C a l i f o r n i a . As a g e n e r a l r u l e , c o n t i n e n t a l s l o p e s are c o n tin u o u s s t r u c t u r e s , perhaps th e most c o n tin u o u s l i n e a r f e a t u r e s on th e f a c e o f th e e a r t h . Thus San M iguel Gap,, which very c l e a r l y b r e a c h e s th e s lo p e to a' depth o f o v er 25O O m, i s alm ost u n iq u e . As w ell,, the Gap i s a l ig n e d w ith two prom inent t e c t o n i c f e a t u r e s , the Murray F ractu re Zone o f th e P a c i f i c b a s in and the T ran sv erse Ranges o f C a l i f o r n i a . The p o s s i b i l i t y e x i s t s , th e n , t h a t San M iguel Gap r e p r e s e n t s an i n t e r a c t i o n o f some s o r t between o c e a n ic and c o n t i n e n t a l s t r u c t u r e s . I t i s v i r t u a l l y im p o s s ib le to do stan dard g e o l o g i c map p in g and i n t e r p r e t a t i o n in a deep w ater r e g io n l i k e th e Gap. Not o n ly i s th e r e o b v io u s ly complex g e o l o g i c s t r u c t u r e , t h e r e i s a l s o an alm o st u b iq u it o u s b la n k e t o f s e d i m ents which f r u s t r a t e s m ost e f f o r t s to sample th e bedrock. B ecau se o f time and e x p e n se , and th e l i m i t a t i o n s o f sam pling g e a r , few sam ples can be c o l l e c t e d and much o f th e i n t e r - 91 92 p r e t a t io n must be based on i n d i r e c t e v id e n c e . A c o u stic su r v e y in g , both o f the sea f l o o r and o f the sub-bottom , i s r e l a t i v e l y ea sy and r a p id . In t h i s stu dy, a la rg e p a r t o f the i n t e r p r e t a t i o n i s b a sed upon bathym etry and a c o u s t ic r e f l e c t i o n p r o f i l e s o f th e sub-bottom m a t e r ia ls , c o r r e la t e d w herever p o s s i b l e w ith bedrock sam p les. I t must be under stoo d th a t such i n t e r p r e t a t i o n i s s u b j e c t i v e , and o n ly gen e r a l g e o lo g i c c o n c lu s io n s can be drawn w ith the a v a i la b l e d a t a . In an e a r ly sta g e o f the stu d y o f the Gap, i t was c le a r th a t the r e g io n cou ld be d iv id e d n a t u r a l l y i n t o fou r s e c t io n s : the I n s u la r and Santa R osa-C ortes Ridge e a s t o f the b a s in , the P atton Ridge area to the sou th, the A rgu ello P la tea u to the n o r th , and the b a s in proper (F ig . l 6 ) . These s u b d iv is io n s are n a tu r a l p r o v in c e s w ith in the Gap a rea , w ith d i s t i n c t i v e p h y sio g r a p h ic , l i t h o l o g i c , and se d im e n to lo g ic c h a r a c t e r i s t i c s . A fte r a d i s c u s s io n o f the a v a i la b l e g e o l o g i c d a ta , each o f the su b reg io n s w i l l be d is c u s s e d , and an attem pt w i l l be made to tr a c e th e g e o lo g i c h i s t o r y o f the San Miguel Gap area. Physiography and S tr u c tu r e Bottom topography in the Gap r eg io n i s sim ple (F ig . 1 7 ). The b a s in , as d e fin e d by th e 1500 m b ath ym etric con to u r , has the approxim ate shape o f a p a r a lle lo g r a m , about 30 x 35 km. I t i s s l i g h t l y e lo n g a te In a n o r th w e s t-s o u th - F ig . l 6 . --P h y sio g r a p h ic r e g io n s w ith in San Miguel Gap area . 93 PHYSIOGRAPHIC REGIONS SAN MIGUEL GAP AREA l H PROBABLE ROCK ISANTA ROSA ISLAND 2 5 0 0 ' 120*40’ 1 2 1 * 00 ’ Fig. 1 7 .—Bathymetry of the San Miguel Gap area. 95 a r g u e l l o p l a t e a u o1 fo e * j R O D R I G U E Z f ^ ( l ^ eam6 6 ^ v SANTA ROSA iSLAND C o n t o u r s i n M e t e r s 12 0 ° 4 0 ' 97 e a s t d ir e c t io n ; and i t i s the n orth w est an gle o f the p a r a l lelogram th a t i n t e r s e c t s the c o n t in e n t a l slo p e and i s m is s in g . R e l a t i v e l y steep., s t r a i g h t s lo p e s bound the Gap t o ward the n orth , e a s t and w est; a g e n t l e r , l e s s c l e a r l y d e f in e d slo p e i s to the sou th . The f l o o r o f the b a sin has a g e n t le seaward s lo p e . There i s s u r p r i s i n g ly l i t t l e minor r e l i e f in the Gap a rea. S lo p es are o f t e n s te e p , but th ere are few co m p lica t i o n s . No s p e c ta c u la r submarine canyons or f e s t o o n s o f t e r r a c e s mark the s lo p e s around the Gap. There are some ch an n els on the fla n k o f the Santa R osa-C ortes Ridge and on th e f l o o r o f the b a s in , but th e se are minor. With im agin a t i o n , the ch an n els can be i n t e g r a t e d i n t o a rudim entary drainage system , but i t seems probable th a t they r e p r e se n t a minor order o f s t r u c t u r a l c o n t r o l, o n ly c o i n c i d e n t i a l l y se r v in g f o r drainage or sedim ent d i s t r i b u t i o n . One very pronounced te r r a c e i s in the r e g io n , d evelop ed a t 7 0 0 -8 0 0 m on both the Santa R osa-C ortes Ridge and A rgu ello P la te a u . At the base o f the I n s u la r Ridge there i s a lim it e d area o f hummocky topography, w ith r e l i e f on the order o f 10 m. The r e g u l a r i t y o f the bottom topography and g e n e r a l lack o f minor r e l i e f throughout the reg io n r e i n f o r c e s a c o n c lu sio n based upon se d im e n to lo g ic in fo rm a tio n : th a t the e n t i r e area has been the s i t e o f con tin u o u s d e p o s itio n fo r a c o n s id e r a b le tim e. Accumulated sedim ent would tend to obscure minor i r r e g u l a r i t i e s o f the bottom topography. A c o u stic r e f l e c t i o n p r o f i l e s show th ree q u ite d i s t i n c t typ es o f m a te r ia l in the Gap area ( F ig s . 18 and 19)- These are d is t in g u is h e d .p r im a rily on the b a s i s o f the c h a r a c te r i s t i c q u a lit y o f the r e tu r n s (F ig . 5) . W ithin the basin., on p r o f i l e s 1 8 , 2 0, and 2 1, two g e n e r a tio n s o f obviou s s e d i mentary f i l l i n g can be d e te c t e d . These sedim ents are s im i la r to th o se found by Moore ( 1 9 6 6), elsew h ere in the c o n t i n e n ta l b o rd erlan d . F o llo w in g h i s p r a c t i c e , th e se are termed p reo ro g e n ic and p o s to r o g e n ic sed im en ts, fo r the deeper, o ld e r sequence shows s l i g h t but c o n s i s t e n t s ig n s o f minor f o l d i n g . Beneath the sedim ents o f the b a s in , and appar e n t l y cropping out on the s lo p e s o f the Gap, i s a d i f f e r e n t m a te r ia l. A c o u stic p e n e tr a tio n o f t h i s m a te r ia l i s n ot as good as i t u s u a l l y i s in the b a sin sed im en ts, but th ere are d e f i n i t e s ig n s o f g e o lo g i c s t r u c t u r e . The retu rn i s o f te n con fu sed , but i t i s u n q u e stio n a b ly from s t r a t i f i e d rocks o f some s o r t . On the south s id e o f the Gap, t h i s m a te r ia l can be tr a c e d in sh o r e to the i s l a n d s , and probably c o r r e l a t e s w ith the p re-L a te Miocene sedim ents and v o lc a n ic s o f the Channel I s la n d s e c t i o n . In s u c c e s s f u l dredges in the Gap, the m a te r ia l r eco v ered has always been v o lc a n ic rock . This "basement complex," fo r la c k o f a d e f i n i t i v e i d e n t i f i c a tio n throughout the area, and to avoid the c o n n o ta tio n s o f "basement" i s termed " a c o u stic bedrock." The q u a l it y o f th e a c o u s t ic r e f l e c t i o n p r o f i l e s i s such th a t i t I s im p o ss ib le to u n e q u iv o c a lly i d e n t i f y any Fig. 1 8 .--Tracing o f acou stic r e fle c t io n p r o f ile s 1 6 and 1 8 . 99 S E C O N D S INSULAR RIDGE Second Return' 2 0 Kilometers 10 Nautical Miles ' \ v < VERTICAL EXAGGERATION xIO 100 LINE 18 PATTON RIDGE 121 *00" M IG U E L IS L A N D Pig. 1 9 . —Tracing o f acoustic r e fle c tio n p r o file s 20 and 21. 101 ARGUELLO PLATEAU to D z o o W C O 2- 0- I- * o c o o ® C O x: i.o g - Q f 0 20 Kilometers 10 Nautical Miles VERTICAL EXAGGERATION xlO 2 + 102 PATTON RIDGE LINE 21 '20 LINE 20 f a u l t s in the region (R. von Huene, p erso n a l com m unication). There i s , however,, a reaso n ab le p o s s i b i l i t y th a t there are f a u l t s along the tren d o f the In su la r Ridge and at the mar g in o f the A rguello P la te a u . This evid en ce agrees w ith a p h ysio grap h ic in t e r p r e t a t io n o f th ese s t r a i g h t , steep s lo p e s . The apparent disp lacem en t on th e f a u l t s i s n ot g r e a t , perhaps 2 0 0 -3 0 0 m in a v e r t i c a l se n se, d is tr ib u t e d over s e v e r a l p a r a l l e l f a u l t s . The c l e a r e s t example o f t h i s i s seen toward the n o rth end o f p r o f i l e 21. To the south o f the Gap, the str u c tu r e i s l e s s c le a r . The low angle c o n ta ct between the sedim ent f i l l i n g th e b asin and a c o u s tic bedrock su g g e sts th a t t h i s i s a sedim entary, not a t e c t o n i c , c o n ta c t. Shorrand R a i t t (1958) ob ta in ed a r ev ersed se ism ic r e f r a c t io n l in e on Patton Ridge im m ediately to the south o f the Gap and observed th a t th ere was a pronounced north dip to the deep c ru st and mantle in the area. P o s s ib ly t h i s dip I s r e f l e c t e d by th e b eh avior o f the a c o u s tic bedrock. Minor fo ld in g can be seen in th e bedrock, p a r t i c u la r ly In shallow w ater on the In su la r s h e l f . C le a r ly , the s h e l f tr u n c a te s a s e c tio n o f c o n to r te d , s t r a t i f i e d rock. The f o ld s th a t appear in deeper w ater ( fo r example, lin e 1 6 , near 33 °50'N ), are probably a ls o r e a lj t h i s i s the west end o f the w e ll-d e v e lo p e d te r r a c e on th e fla n k o f the Santa R osa-C ortes Ridge. Fig. 2 0 .- - I n t e r p r e t a t i o n of acoustic r e f l e c t i o n p r o f i l e s 16 and 1 8. 104 INTERPRETATION |~ 1 POST-OROGENIC SEDIMENTS ^ PRE-OROGENIC SEDIMENTS m ACOUSTIC BASEMENT Line 18 N - INSULAR RIDGE T T 7 T 7 7 7 7 Sec. Km. OTTO Line 16 2 0 Kilometers 1 0 Noutieot Miles l.0 * H 5 VERTICAL EXAGGERATION xIO Pig. 2 1 .- - I n t e r p r e t a t i o n of a co u stic r e f l e c t i o n p r o f i l e s 20 and 21. 1 0 6 £ i" * D re r'i le s :ation o f a c o u stic ?C and 21. r e f l e c t i o n 106 TIME ( S e c o n d s ) N-Arguello Plateau Line 20 2 0 K il o m e t e r * 10 N a u tic a l M ile* V E R T IC A L E X A G G E R A T IO N x IO INTERPRETATION Q POST-OROGENIC SEDIMENTS | PRE-OROGENIC SEDIMENTS ^ ACOUSTIC BASEMENT 108 L lth o lo g y W ith o n ly two e x c e p tio n s., a l l th e Ig n e o u s r o ck s c o l l e c t e d In th e Gap area are I d e n t i f i a b l e a s b a s i c e x t r u s i v e r o c k s (T able k, F i g s . 22 and 2 3 ) . The e x c e p t i o n s are a TABLE 4 IGNEOUS ROCKS COLLECTED IN SITU, SAN MIGUEL G AP AREA S t a tio n D epth (m) L o ca tio n Rock Type Remarks 10118 10121 10123 10124 10346 10348 D12 780- 715 175- 95 5 5 0 - 5 1 ^ 4o4- 348 Santa R osa-C ortes Ridge Santa R osa-C ortes ■ Ridge Santa R o sa-C ortes Ridge Santa R o sa-C ortes Ridge 10341 2 3 8 6 - I 8 7 2 P a tto n Escarpm ent 1468-1211 1651-1138 844- 798 P a tto n Ridge C o n tin e n ta l slo p e e a s t o f R odriguez Seamount D avid S e a k n o ll, on A r g u e llo P la te a u B a sa lt B a sa lt or a n d e s ite Andes i t e B a sa lt O liv in e b a s a lt and p a la g o n ite B ou ld er o f pum ice V e s ic u la r o l i v i n e b a s a lt W eathered p a la g o n ite S im ila r t o Mio cene v o lc a n ic s on I sla n d s S im ila r to Mio cene v o lc a n ic s on Isla n d s S im ila r t o Mio cene v o lc a n ic s on I sla n d s S im ila r t o Mio cene v o lc a n ic s on I sla n d s Q uite p ro b a b ly r a fte d or f lo a t e d S im ila r to m a te r ia l o f R odriguez Sea mount P ig . 2 2 . --Sedim en tary and ign eou s ro ck s. (a) P o lish e d s e c t io n o f specimen shown in b. (b) Phosphate nodule (probably Miocene) from AHP 10097* Note e x te n s iv e boring and en c r u s t a t io n . Background: 10 cm g r id . (c) Pumice boulder dredged a t AHP 103^ -6 . Specimen i s approxim ately 25x27x30 cm. Background: 10 cm g r id . (d) P o lish ed s e c t io n o f a u th ig e n ic p h osp horite from AHP 10123. Note t y p i c a l b r e c c i a - l i k e appearance. A l l o f t h i s sample, m atrix and cement, i s p h o sp h o r ite . 109 P ig . 2 3 . — Rocks from the c o n t in e n t a l s lo p e . (a) Fresh su r fa c e o f one o f th e b ou ld ers from AHP 103^8. Specimen i s a h ig h ly v e s i c u l a r o l i v i n e b a s a l t . The prom inent ph en ocryst i s p l a g i o c l a s e f e ld s p a r , probably b y to w n ite , and th e r e are a ls o i n c l u s i o n s o f pumice. (b) S e c tio n o f p a la g o n it e w ith manganese c r u st. T his i s from the f l a t t e n e d , t r ia n g u la r specimen j u s t above and to the l e f t o f l a b e l . Note t y p i c a l ir r e g u la r manganese c r u s t and p y r o l u s i t e d e n d r it e s d evelop in g on f r a c t u r e s w ith in the r o c k . (c) Dredge h au l AHP 103^8 from c o n t in e n t a l s lo p e (Santa Lucia Escarpm ent). A l l s p e c i mens are angular b a s a l t , many v e s i c u l a r , w ith m oderately w e ll- d e v e lo p e d manganese c r u s t . Background: 10 cm g r id . (d) A n d e s!te , b a s a l t , and p a la g o n ite b o u ld ers dredged from P atton Escarpment (AHP 103^1). A l l o f t h e s e specim ens have a w e ll-d e v e lo p e d manganese c r u s t . Note cra c k s in c r u s t of b ou ld er in lower r i g h t c o r n e r . Background: 10 cm g r id . I l l METRIC 1 112 q u i t e p o s s i b l y e r r a t i c pumice b o u ld e r from s t a t i o n AHP 10346 on th e P a tto n R idge a r ea ( P ig . 22c) and some a n d e s i t e dredged near Santa Rosa I s l a n d . A l l o f th e o t h e r r o c k s were e i t h e r d e e p ly w ea th ered p a l a g o n i t i z e d b a s a l t or good, "hand specim en" b a s a l t . One o f th e sam p les from th e c o n t i n e n t a l s lo p e (AHP 10348) i s an o l i v i n e b a s a l t , and c o n t a i n e d a l a r g e p h e n o c r y st o f c a l c i c p l a g i o c l a s e f e l d s p a r , p r o b a b ly b y to w n ite ( P ig . 2 3a ) . E n gel and E n gel ( 1 9 6 3 ) su g g e s t t h a t th e boundary betw een o c e a n ic and c o n t i n e n t a l p e - tr o g r a p h ic p r o v i n c e s , th e A n d e s ite L in e , may l i e shoreward o f th e o u t e r escarpm ent in th e b o r d e r la n d j th e appearance o f th e Gap sp ecim en s c e r t a i n l y te n d s to c o r r o b o r a te t h i s h y p o t h e s i s . The r o c k s dredged from th e escarpm ent have an o b v io u s o c e a n ic c h a r a c t e r . Palmer (1964) c o n c lu d e d t h a t th e r o c k s o f R od rigu ez Seamount, j u s t n o r th o f th e Gap on th e c o n t i n e n t a l s l o p e , b e lo n g e d to th e H a w a iite s u i t e o f a l k a l i c b a s a l t s , an undoubted o c e a n ic a s s o c i a t i o n . A l l o f th e se d im e n ta ry r o c k s c o l l e c t e d came from th e s h a llo w e r p a r t s o f th e Santa R o sa -C o r te s and I n s u la r Ridge com p lex, c l o s e to th e Channel I s la n d s (T able P ig s . 22 and 3 6 ) . None o f th e sp ecim en s was s u f f i c i e n t l y f o s s i l i - f e r o u s to p e r m it u n e q u iv o c a l d a t in g , b u t a l l a r e o f ty p e s a n a lo g o u s to th e p r e -L a te M iocene sequ en ce o f th e Channel I s l a n d s and c e n t r a l C a l i f o r n i a C oast Ranges (D. ¥ . Weaver and J . C. C lark , p e r s o n a l co m m u n ication ). T h is in fo r m a tio n p e r m its th e c e r t a i n i d e n t i f i c a t i o n o f a t l e a s t p a r t o f th e 114 a c o u s t i c bedrock o f the Gap r e g io n w ith the T e r tia r y s e c t i o n on the i s l a n d s . TABLE 5 SEDIM ENTARY R O CK S C O LLEC TED IN SITU, SAN M IGUEL G A P AREA S ta tio n Depth (m) L ocation Rock Type Remarks 10097 1 1 0 - 8 3 In su la r Ridge Dark brown phos p h ate nodule Probably from Sisquoc Em. (M iocene) 1 0 1 0 7 550 Santa R osa- C ortes Ridge Y ellow s ilic e o u s sh a le Probably Late Miocene age 1 0 1 1 8 7 8 0 -7 1 5 Santa Rosa- C ortes Ridge Grey sandstone Fresh fragm ents but u n f o s s i l i - fe r o u s 1 0 1 2 7 175- 92 Santa Rosa" C ortes Ridge Yellow-brown s ilic e o u s sh a le S im ila r to S ls - quoc Em. (M iocene) 1 0 1 2 3 550-51^ Santa R osa- C ortes Ridge P h osp h orite and un f0 s s i l i f e r o u s sandstone Undated, but p o s s ib ly p o s t- Miocene .G eologic Subregions .In su lar and Santa Rosa C ortes R idges The s h e l f and slo p e area Im m ediately south o f th e i s la n d s c o n s t i t u t e s a s i n g l e p h y sio g r a p h ic u n i t . There I s no c le a r d i v i s i o n w ith in the Gap area between the n om in ally s o u t h - s lo p in g I n s u la r Ridge and the westward slo p in g fla n k o f the Santa R osa-C ortes R idge. The s h e l f around the i s la n d s i s smooth e x c e p t fo r a l im it e d reg io n between the 115 w e st end o f San Miguel I s la n d and Richardson Rock. Many : sm a ll bottom i r r e g u l a r i t i e s on the order o f 1-4 m in h e ig h t : show on the s h e l f su r fa c e ; th e se are probably p a rt o f a tr u n c a te d d a c i t i c dike swarm (Palmer., 1965b ) . Emery (1958) d i s t i n g u i s h e d as many as four submerged marine t e r r a c e s on the s h e l f sou th o f San Miguel and Santa Rosa I s la n d s . L i t t l e a t t e n t i o n was devoted during t h i s stu d y to the sh a llow s h e l f ; th e se t e r r a c e s were not obviou s in the p r o f i l e s th a t were s tu d ie d . At a depth o f I 3O -I 5O m near the i s l a n d s th e r e i s a w e l l - d e f i n e d s h e l f break. This probably c o r r e l a t e s w ith th e edge o f Emery's fo u rth t e r r a c e . The depth o f th e s h e l f break a g r e e s q u ite w e l l w ith p r e sen t e s tim a te s o f th e maximum e u s t a t i c low ering o f the sea l e v e l during the l a s t major g l a c i a l e p iso d e , the W isconsin (Curray, 1965b ) . This s u g g e s ts th a t a t l e a s t fo r the p a s t few ten s o f thousands o f y e a r s , the area has been r e l a t i v e l y s t a b le . The s lo p e le a d in g from th e i s l a n d s down to th e c e n tr a l b a s in has a range o f from 30 to rJ ° , averaging c l o s e to 4 °. These g r a d ie n t s are comparable to c o n t in e n t a l s lo p e s e l s e where in the world ( n ot o f f southern C a l i f o r n i a ) , and the s l o p e s surrounding the o th er b a s in s o f th e c o n t in e n ta l bord erla n d . There are a few ch an n els develop ed on the s lo p e , p a r t i c u l a r l y in the sh a llo w er p o r t io n s . About 10 km sou th w est o f South P o in t on Santa Rosa Is la n d th e re i s a sm a ll k n o ll on the s lo p e which i s v o lc a n ic (AHP 10124). I t i s not c l e a r whether t h i s r e p r e s e n ts an outcrop (fo r the 116 r o c k s are s i m i l a r to th o s e nearby on Santa Rosa) or a sub m arine v o lc a n ic e v e n t. A s i n g l e pronounced deep t e r r a c e I s p r e s e n t on th e f la n k o f th e Santa R osa-C ortes R id g e . T his fe a tu r e i s ap p r o x im a te ly 15 km wide and s lo p e s from about 600 to s l i g h t l y o v e r 800 m d ep th , w ith an average g r a d ie n t o f l e s s than 1 / 2 ° . On th e s u r fa c e o f the t e r r a c e , r e l i e f i s no more than a m eter or two. Where the R idge j o i n s th e c e n t r a l b a s in and P a tto n Ridge r e g io n s , t h e r e are two q u ite o b v io u s f la t -b o t t o m e d c h a n n els w ith a r e l i e f o f 20-30 m. These f e a t u r e s are p r im a r ily t e c t o n i c , n o t sedim entary, and p o s s i b l y r e p r e s e n t the boundary f a u l t o f the Santa R osa -C ortes R id g e . One anomalous sample was c o l l e c t e d a t a depth o f ' 550 m in th e Santa R o sa -C o rtes Ridge, AHF 10107^ a g r a v it y core w hich c o l l e c t e d o n ly 12 cm o f f a i r l y w e l l - c o n s o l i d a t e d c a lc a r e o u s s i l t s t o n e and mudstone. Only a few f o r a m in ife r s were i s o l a t e d from th e sam ple, b u t th e se in c lu d e d a p r e dom inantly l e f t - c o i l e d group o f G lo b ig e r in a pachyderma ( s u g g e s t in g c o ld e r w ater c o n d it io n s than th e p r e se n t) and a s i n g l e specim en o f M elon is p o m p ilio d e s (J . C, I n g l e , p e r s o n a l com m u n ication ). M elonis i s a deep b a th y a l b e n t h ic fo r a m in ife r a c h a r a c t e r i s t i c today o f water d epth s on th e ord er o f 300 m (Bandy and Kolpack, 1 9 6 3 )• The sample co u ld be P l e i s t o c e n e but i t i s more l i k e l y th a t th e y came from a c o ld w ater phase o f the m id -T e r tia r y "perhaps"Miocene. There I s th e p o s s i b i l i t y , then, o f perhaps 2500 m v e r t i c a l d isp la ce m en t o f th e Santa R osa-C ortes Ridge e i t h e r s in c e P l e i s t o c e n e or perhaps Miocene tim e. The l a t t e r h y p o th e s is seems more r e a so n a b le , s i n c e th ere are no o th e r s ig n s o f a p p r e c ia b le d ia str o p h ism i n the r e c e n t g e o lo g i c h i s t o r y o f the a rea . P atton R idge and Escarpment J u s t south o f the c e n t r a l b a s in o f the Gap, th e re i s a r e g io n o f r a th e r subdued topography, termed the Patton R idge. The r id g e i s an i r r e g u la r bank which e x ten d s as a d i s c r e t e fe a tu r e a t the c r e s t o f the deep c o n t in e n t a l slop e along v i r t u a l l y th e e n t i r e le n g th o f th e C a lif o r n ia c o n t i n e n ta l b ord erla n d . Large rounded v o lc a n ic c o b b le s f r e q u en tly have been c o l l e c t e d from th e su r fa c e o f the P atton R idge, t h e r e fo r e i t was concluded t h a t th e r id g e must at one time have been exposed to wave a c tio n (Uchupi and Emery, 1 9 6 3 ) . Most o f th e samples c o l l e c t e d from the r id g e during t h i s study were r i c h in g l a u c o n i t e , s u g g e s tin g a low r a te o f s e d im e n ta tio n . On th e a c o u s t i c r e f l e c t i o n p r o f i l e s , the m antling sedim ents are so th in a la y e r as to be i n d i s t in g u is h a b le ; the Patton Ridge c o n s i s t s o f a c o u s t ic bedrock e f f e c t i v e l y the same as t h a t o f the I n s u la r and Santa Rosa- C ortes R id g e s. Where the rock o f the r id g e was sampled, i t proved to be the t y p i c a l Miocene (?) v o lc a n ic m a te r ia l o f the c o n t in e n t a l b ord erla n d . The Patton Escarpment in the study area i s extrem ely s t e e p . I t averages about 10°, hut there are s e c t io n s s te e p e r than 30°• At the base o f the escarpm ent, there i s a s l i g h t d e p r e ssio n which c o n ta in s a p o orly d e fin e d channel. This d ep ression se p a r a te s the slo p e here from the fla n k o f A rgu ello d ee p -se a fan., which e f f e c t i v e l y c o n s t i t u t e s the c o n t in e n t a l r i s e o f f P oin t C onception. Both the slo p e and the m arginal trough appear to be la r g e ly bare rock, perhaps w ith sedim ent o ccu rrin g between b o u ld e r s. A dredge haul from the slo p e (AHP 103^1* Pig- 23a) y ie ld e d large., ir r e g u la r fragm ents o f b a s a l t as w e ll as g la u c o n i t ic sand. This rock was n ot broken d i r e c t l y o f f an outcrop when sampled, but a ls o had probably not been tra n sp o rted any d is ta n c e . P o s s ib ly the slo p e i s su rfaced w ith the lo o se v o lc a n ic de b r i s t y p i c a l o f submarine volcan ism . C entral B asin The two c y c le s o f sedim entary f i l l th a t can be d i s t in g u is h e d in the c e n t r a l b a sin are s im ila r . As i s shown in the a c o u s t ic r e f l e c t i o n r e c o r d s, both p r e - and p o s t - o ro g en ic m a te r ia ls are found in a l l p r o f i l e s o f the b a sin . The area o f th ic k sedim ents s lo p e s seaward s l i g h t l y , but in the su bsurface i t has the t y p i c a l form o f a true b a sin . To th e e a s t , on l i n e 16, th ere i s on ly a sm all pocket o f sed im en ts, perhaps 10 km wide and no more than 100 m th ic k . Along p r o f i l e 20, however, in the cen te r o f the b a s in , the A ch a n n el system o f s o r t s i s d e v e lo p ed on th e f l o o r o f th e b a s i n , ru n n in g r o u g h ly n o r th w e st toward th e b reach ed segm ent o f th e c o n t i n e n t a l s l o p e . I t i s l i k e l y t h a t t h i s sy stem f u n c t i o n s to d i s t r i b u t e t u r b i d i t y c u r r e n t o r tu r b id l a y e r f lo w s i n th e b a s i n . A p i s t o n core c o l l e c t e d in the main p o r t io n o f t h i s c h a n n e l, AHF 1 0 3 6 1, c o n ta in e d no p a r t i c u l a r l y anom alous s e d im e n ts . A r g u e llo P la te a u and Escarpm ent North o f th e Gap, t h e A r g u e llo Escarpm ent c o n s i s t s o f a s i n g l e , e x tr e m e ly w e l l - d e v e l o p e d t e r r a c e a t a depth o f 70 0 -8 0 0 m. The t e r r a c e i s e f f e c t i v e l y h o r i z o n t a l f o r a w id th o f o v er 30 km, and th e f e a t u r e can be tr a c e d north o f th e Gap s e v e r a l hundred k il o m e t e r s alo n g th e c e n t r a l C a l i f o r n i a c o a s t (Uchupi and Emery, 1 9 6 3 ) . The t e r r a c e su r fa c e i s so smooth t h a t th e r e may be l e s s than a m eter r e l i e f on a 5 o r 10 km p r o f i l e . A c o u s tic r e f l e c t i o n r e c o r d s (Palm er, 1 9 6 5a) s u g g e s t t h a t A r g u e llo P la te a u i s u n d e r la in by f o ld e d , s t r a t i f i e d r o c k s , and t h a t th e r e are some minor f i l l e d b a s i n s on i t s s u r f a c e . F o ld s in th e su b s u r fa c e ro ck s are v e r y c l e a r l y t r u n c a t e d by th e t e r r a c e s u r f a c e , i n d i c a t i n g t h a t t h i s i s u n q u e s t io n a b ly an e r o s i o n a l f e a t u r e . Rocks b e n e a th th e P la te a u are s i m i l a r i n t h e i r a c o u s t i c c h a r a c t e r i s t i c s to th e a c o u s t i c b ed ro ck o f th e Gap r e g io n . In s e v e r a l o f th e subbottom p r o f i l e s t h e r e are sudden changes in th e d e p th o f p e n e t r a t i o n s u g g e s t in g th a t th e s lo p e s e p a r a t 121 in g the Gap from A r g u ello P la tea u i s a f a u l t scarp . Bottom m a t e r ia ls sampled on the te r r a c e su rfa c e were a l l u n c o n s o li dated sedim ent, probably o f very slow accu m u lation . Pos s i b l e P lio c e n e fo r a m in ife r s were i d e n t i f i e d in th e lower p a r t s o f s e v e r a l sh o rt c o res from the P la te a u . (C. M. Carson,, p e r so n a l com m unication), and a r e l i c t C a s sid u lin a fauna o f P le is t o c e n e age i s found a t the su r fa c e a t s t a t i o n D1 (J. C. Ingle., p e r s o n a l communication) . The one sample o b ta in ed from the c o n t in e n t a l slo p e near the A rg u ello P lateau (AHP 103^-8) was a la r g e haul o f d i s t i n c t i v e v e s i c u l a r o l i v i n e b a s a l t . S u p e r f i c i a l l y , t h i s ma t e r i a l i s s im ila r to v e s i c u la r b a s a l t s dredged in deep w ater near th e Hawaiian I s la n d s (Moore, 1 9 6 5). The g e n e r a l appearance o f the la r g e b lo c k s o f b a s a l t i s t y p i c a l o f rub b l e on the s u r f a c e s o f submarine e x t r u s io n s . I t seems r e a son able to c r e d i t the form ation o f t h i s s lo p e to the same p r o c e s s e s th a t c r e a te d the P atton Escarpment to th e sou th, b u t i t sh ould be n oted th a t the l i t h o l o g y in the two areas i s d i f f e r e n t , and the h i s t o r i e s o f the two segments o f con t i n e n t a l s lo p e need not be s i m i la r . The G eologic H isto ry o f San Miguel. Gap D e sp ite i t s anomalous form, San M iguel Gap has not had a p a r t i c u l a r l y complex h i s t o r y . A ll o f the a v a i la b l e i n form ation s u g g e s t s th a t the Gap behaved sim ply as a p art o f th e C a lif o r n ia c o n t in e n t a l b ord erlan d . None o f the rock or 122 sedim ent ty p e s sampled i s u n u su a l. The form o f the b a sin and i t s sedim ent f i l l i n g are i d e n t i c a l to th o s e o f the o th e r borderlan d b a s i n s . The o n ly unique fe a tu r e o f San M iguel Gap i s th a t i t breach es the c o n t in e n t a l s lo p e . There i s no ev id en ce i n the a r e a , however, th a t the Gap h a s ever behaved in a fa sh io n a t y p i c a l o f the b ord erlan d . As fa r as can be determ ined, San Miguel Gap i s the o u t e r most b a sin o f the c o n t in e n t a l b o rd erla n d , which c o i n c i d e n t a l l y i n t e r s e c t s th e c o n t in e n t a l s lo p e . There i s no p o s i t i v e r ec o rd o f the Gap's h i s t o r y p r io r to the M iocene. Judging from the u n ifo r m ity o f the retu rn from a c o u s t ic bedrock and i t s apparent c o r r e l a t io n w ith th e rocks o f the Channel I s la n d s , "basement" in the area probab ly c o n s i s t s o f in te r b e d d e d sedim ents and v o lc a n ic r o ck s which may be as a n c ie n t as Late C reta ceo u s. Away from the immediate v i c i n i t y o f the i s l a n d s , a l l the bedrock sampled c o n s i s t e d o f Miocene (?) v o lc a n ic r o c k s, q u ite p o s s i b l y produced by submarine e x t r u s i o n s . In Late Miocene tim e, the f a u l t s which d e fin e th e Gap d ev elo p ed , and the b a s in assumed i t s modern form. Since then th e r e has been v i r t u a l l y co n tin u o u s b u t slow sed im e n ta tio n in the a r e a , ■ w ith one minor d istu rb a n ce which produced the s l i g h t f o l d in g which d i s t i n g u i s h e s p r e - and p o s to r o g e n ic sedim entary f i l l in the Gap b a s in . There i s no e v id en ce fo r any im por t a n t Late Quaternary or Recent d ia str o p h ism . At p r e se n t p a t e s o f s e d im e n ta tio n j th e Gap co u ld have "been f i l l e d i t s p r e s e n t l e v e l by c o n tin u o u s s e d im e n ta tio n s i n c e th e E a r ly P l i o c e n e . SEDIMENTS OF THE SAN MIGUEL GAP REGION General To p r o p e r ly c h a r a c t e r iz e the sedim ents o f any r e g io n , i t i s n e c e ss a r y n ot m erely to determ ine the p h y s ic a l p ro p e r t i e s , s i z e param eters and m in eralo gy, b u t a ls o to c o n sid e r the provenance, the p o s s i b l e so u rc es and " p red e p o sitio n a l" h i s t o r y o f the su r fa c e and su b su rface sedim ent. A r a t i o n a l e v a lu a tio n o f a l l the p h y s i c a l, c h em ica l, and b i o l o g i c a g e n c ie s which se r v e to c r e a te and d i s t r i b u t e th e sedim ents i s a r e q u i s i t e to th e u n derstand in g o f a sedim entary en vironm ent. I t i s p a r t i c u l a r l y im portant to a s s e s s the r e l a t i v e r a t e s o f th e a g e n c ie s under the g iv en c o n d it io n s . The u lt im a t e aim o f a sedim ent stu d y i s to so.- e f f e c t i v e l y d e f in e a sedim entary regime th a t the s i g n i f i c a n c e o f a n a lo gous s u i t e s o f a n c ie n t sedim ents becomes com prehensible, and v a l i d r e c o n s t r u c t io n s o f th e a n c ie n t regime may be made. I d e a l l y , i t should be p o s s i b l e to e x p r ess m athem atic a l l y the c o n c e n tr a tio n o f each c o n s t i t u e n t o f a sedim ent, as a fu n c tio n o f supply and rem oval from the system . The ob served sedim ent a t a g iv en p o in t , th en , i s the r e s u l t a n t produced by a s e r i e s o f a d d it io n s o f v e c to r q u a n t i t i e s . 124 125 V e c t o r s , f o r a sed im en tary tren d r e p r e s e n t s both a volume (or mass) and a d i r e c t i o n term. The c o n c e n tr a tio n o f s h e l l s o f p la n k to n ic f o r a m in if e r s in the sedim ent a t a g iv e n p o in t may be taken as an example. The p e r c e n ta g e o f s h e l l s in a volume o f sedim ent i s some fu n c tio n o f th e i n i t i a l p r o d u c t i v i t y o f the o v e r ly in g waters., the r a t e o f de s t r u c t i o n by s o l u t i o n in th e w ater column or by i n g e s t i o n by organisms., the r a t e o f rem oval by winnowing c u r r e n t s , and f i n a l l y o f th e masking e f f e c t s o f th e o th er c o n s t i t u e n t s o f th e sed im en t. In t h i s study,, an attem pt w i l l be made to d e f i n e the v a r io u s f a c t o r s and to a s s ig n them at l e a s t o r d e r -o f-m a g n itu d e q u a n t i t a t i v e l i m i t s . As a sed im en tary sy stem , the Gap area r e p r e s e n t s a model o f th e c o n t i n e n t a l s l o p e . In term s o f depth, i t r a n g es from the low er b a th y a l zone (over 3000 m a t th e b a se o f th e l o c a l s lo p e ) in s h o r e to the narrow s h e l f su r rounding th e Channel I s la n d s . The submarine s lo p e s around th e Gap, o f t e n as s t e e p as 1 0 °, but a v era g in g about 5°j are comparable to th o se o f c o n t in e n t a l s l o p e s e lsew h ere in the w o rld . There are no major submarine canyon system s to b y -p a s s sed im en t. D e s p ite th e p r o p in q u ity o f th e i s la n d s and the la c k o f a broad c o n t i n e n t a l s h e l f , th e c o n t i n e n t a l so u rce area i s so r e s t r i c t e d th a t th ere i s no e x c e s s i v e d i r e c t i n f l u e n c e o f t e r r e s t r i a l d e b r i s . I n s t e a d , the p r i n c i p a l f a c t o r s i n th e environm ent are ocean ograp h ic or c l i m a t o l o g i c , as on th e more t y p i c a l c o n t in e n t a l s l o p e s , 1 2 6 se p a r a te d from the land by broader s h e l v e s . Though the r e l a t i v e I n t e n s i t y may vary considerably,, the a g e n c ie s which r e g u la te the sedim entary regime o f the Gap area can be presumed to c o n tr o l c o n t in e n t a l slo p e se d im en ta tio n e ls e w h e r e . In order to d e fin e a d e q u a tely the contemporary s e d i mentary s i t u a t i o n in the San Miguel Gap a r ea , sampling was a d ju ste d to the t e r r a i n . In the c e n t r a l b a s in , where s e d i m en tation i s r e l a t i v e l y uniform and ra p id , few sam ples were c o l l e c t e d . Two long p is t o n c o r e s in th e c e n te r and a s e r i e s o f sh o r te r g r a v it y c o r e s a t th e b a s e s o f the s u r rounding s lo p e s y i e l d e d g e n e r a l ly homogenous sed im en ts. The p r i n c i p a l e f f o r t was d ir e c t e d to the s lo p e s and r id g e s around the Gap, where c o n d itio n s are more v a r ie d and s e d i m en tation l e s s r a p id . Sample d e n s ity , p a r t i c u l a r l y in the deeper a r e a s, i s not as g r e a t as m ight be d e s ir e d , b u t a r e p r e s e n t a t iv e s u i t e o f sedim ents was c o l l e c t e d . By te x tu r e a lo n e , most o f the samples from the Gap re g io n would be c l a s s i f i e d as sands ( F ig s . 24 and 2 5 ). Only in the deep c e n t r a l p a r t o f the b a sin are th ere appre c ia b le p e r c e n ta g e s o f s i l t and c la y . The sand f r a c t i o n s are dominated by th ree ty p e s o f m a t e r ia l, t e r r e s t r i a l sand, f o r a m in if e r a l s h e l l s , and g la u c o n it e g r a in s . L o c a lly , th ere are a p p r e c ia b le q u a n t i t i e s o f o th e r s a n d -s iz e d mate r i a l , p a r t i c u l a r l y o th er o rg a n ic d e b r is such as sponge s p i c u l e s , diatom f r u s t u l e s , and r a d io la r ia n t e s t s . In a a c o u s t i c s i g n a l co u ld n o t p e n e t r a t e the sed im en tary f i l l . There i s a t l e a s t 500 m t h ic k n e s s o f sedim ent h e r e , and the b a s in i s o v e r 40 km w id e . Toward the mouth o f th e Gap ( l i n e 2 1 ), the f i l l t h in s and a c o u s t i c bedrock i s i d e n t i f i e d b e n e a th th e p r e o r o g e n ic se d im e n ts. Another a c o u s t i c r e f l e c t io n p r o f i l e , not a v a i l a b l e when t h i s stu d y was in p r o g r e s s , was made a lo n g the approxim ate a x i s o f the Gap (R. von Huene, p e r s o n a l com m unication). I t shows an a c o u s t i c b ed rock su r fa c e which appears i n the zone between l i n e 20 and 21, and which s lo p e s upward to th e w e s t . I t appears to e x ten d to th e se a f l o o r a t the p o in t where th e p r o j e c t e d t r a c e o f the escarpm ents p a s s th e mouth o f San M iguel Gap. U n f o r t u n a t e ly , t h i s f e a t u r e was n ot known w h ile sam pling o p e r a t io n s were condu cted. There i s a s l i g h t s lo p e seaward and o f t e n to the south ov er much o f the s u r fa c e o f th e b a s in f l o o r . G ra d ien ts are g e n t l e (c o n s id e r a b ly l e s s than 1/ 2° ) , and o n ly a t one p o in t i s th e r e any c l e a r l y anomalous topography on the b a sin f l o o r . A zone a t th e base o f the I n s u la r R id ge, a p p r o x i m a tely the area o f s t a t i o n s 1 0 0 9 9 and 1 0 1 0 3, has a hummocky appearance on the depth r e c o r d e r p r o f i l e s , w ith r e l i e f com monly on th e order o f 10 m. The a c o u s t i c r e f l e c t i o n rec o rd s i n d i c a t e t h a t th e re i s a p o s s i b i l i t y t h a t t h i s might be a su r fa c e on slumped m a t e r i a l. The sed im en ts sampled h e r e , how ever, are t y p i c a l o f b a s in c o n d i t i o n s . F ig . 2 4 . — T ex tu ra l c l a s s i f i c a t i o n o f sed im en ts, San Miguel Gap area. 127 TEX TU RA L C L A SSIFIC A T IO N O F SE D IM E N T S SAN MIGUEL GAP AREA AREA E. PATTON RIDGE AREA I. INSULAR RIDGE 8 SANTA ROSA-CORTES * RIDGE / 8 ESCARPMENT CLAY AREA EE. ARGUELLO AREA El. SAN MIGUEL GAP PLATEAU (BASIN) CLAYEY SAND / clayey' \ SILT SILTY SAND Collar S h .p a rd , 1954) 128 P ig. 2 5 . - - D i s t r ib u t i o n o f sa n d -siz e d m a te r ia l in su rfa ce sedim ents. 129 CONCENTRATION SAND-SIZED MATERIAL IN SURFACE SE D IM E N T S m OVER 75% \ \ v 75-50% 50-25% ' / / / LESS THAN 25% 0 K tlo m alflft 10 0 Nautical M i l n 5 Contour* fn m tttra SAN MIGUEL ISLAND SANTA ROSA ISLAND ' ^W .VA v a VAV*VAv I*/tW A W j- a \ v » m \v a v a v a v 121*00 20*40 2 0 *20 ’ | .O fr » £ £ 1301 131 very few areas., th ere are c o n c e n tr a tio n s o f p h o sp h o r ite , v o lc a n ic ru b b le, and g l a s s sh ard s. There i s a f a i r l y clear, zo n a tio n o f the Gap r e g io n in t o fou r d i s t i n c t sedim entary su b reg ion s or p r o v in c e s (Table 6 ) . These zones, d e fin e d in terms o f the p r in c ip a l c o n s t i t u e n t s o f the sedim ent, c o r respond c l o s e l y to the major p h y sio g r a p h ic s u b d iv is io n s o f the Gap reg io n (F ig . 1 6 ) . Both the stu dy o f c o re s and sub bottom a c o u s t ic record s su g g e st th a t sedim entary c o n d it io n s have been r e l a t i v e l y c o n sta n t s in c e c e r t a i n l y th e Late P l e i s t o c e n e . Thus an in t e g r a t e d sedim entary system d e fin e d fo r th e contemporary s i t u a t i o n in the Gap area may be e x tended to c h a r a c t e r iz e an a p p re c ia b le tim e span. D e s c r ip t iv e sedim ent names based upon te x tu r e and s i m p l i f i e d m ineralogy are a p p lie d to the sedim ents o f the Gap (F ig . 26 ) . T e r r e s t r i a l q u a r t z - f e ld s p a r sand i s the dominant m a te r ia l on th e In su la r Ridge and in a zone e x ten d in g westward a c r o ss the A rg u ello P la te a u . G la u c o n itic sand occu rs on most o f th e s lo p e s and deep r id g e s . Though th ere i s c o n sid e r a b le v a r ia t i o n in p r o p e r t ie s , th e sedim ent in th e b a sin i s a "green mud." At -a few s t a t i o n s near Santa Rosa I s la n d , th e dominant sedim ent c o n s i s t s o f f a i r l y la r g e fragm ents o f m ollu sk s and o th e r r e l a t i v e l y la rg e shallow w ater organism s. This sedim ent i s termed " s h e ll d eb r is sand." F oram in ifers are so common in s e v e r a l sam ples th a t the d e e p -se a s t r a t ig r a p h i c terms " fo r a m in ife r a l ooze" or " g lo b ig e r in a ooze" might be a p p lic a b le . This p r a c t i c e was T A B L E 6 SUMMARY OF CHAEACTERISTICS IN SEDIMENTARY SUBREGIONS OF TRE GAP ° ] o Total Sample Sediment Size ($) Major Constituents Foraminifera Subregion Dimension Clay Silt Sand Organic Authigenic Terrestrial Plankton!c Benthonic Insular and Santa Rosa- Cortes Ridges Surface sediment 14 - . 96 1 0 .1 2 84.9 0 4 2 .8 8 7.85 3 4 .1 9 1 8 .7 3 12.95 Total 6 .2 2 1 2 .6 3 8 0 .6 1 4 1 .8 9 7 .4 1 31.4 7 2 0 .0 2 1 1 .6 6 Patton Ridge and e scarpment Surface sediment 5 - 0 1 7 .9 2 8 7 .0 6 2 9 .8 2 5 1 .1 6 5 .3 8 1 1 .6 1 1 6 .6 3 Total 7 .8 4 1 7 .6 6 74.50 2 6 .8 9 4 1 .2 7 5 .8 6 1 1 .5 2 13-99 Basin of San Miguel Gap Surface sediment 2 1 .6 0 3 6 .3 1 4 2 .0 8 2 6 .6 2 4 .0 8 1 1 .3 8 1 1 .3 6 1 1 .1 4 Total 2 5 .5 1 45-37 3 2 .1 8 2 1 .9 4 2 .7 9 7.-42 1 0 .9 0 7 .3 6 Arguello Plateau and escarpment All surf sediment 5 .0 8 1 2 .7 8 8 2 .1 2 2 0 .4 2 2 6 .5 2 34.94 6 . 9 1 1 0 .5 4 U ) ro P ig . 2 6 . - - D i s t r i b u t i o n o f g e n e r a l sed im en t t y p e s . 133 SEDIMENT TYPES-SAN MIGUEL GAP AREA m TERRESTRIAL SAND W i GLAUCONITE SAND GREEN M UD SHELL DEBRIS SAND f / t PROBABLE ROCK 0 Kilometer* 10 0 Noutical Mile* 5 Contours in m eters SAN MIGUEL ISLAND SANTA ROSA ISLAND 7. -‘V C - ~ ' £ ' . r . ■ > ' 1 2 1 ° 0 0' I20-40' \20‘20' . 135 not fo llo w ed because the g e n e tic circu m stances o f th ese slo p e sedim ents are ra th er d i f f e r e n t from those o f the deep- sea fo r a m in ife r a l sedim ents. The major c o n s t it u e n t s o f the sedim ents o f the Gap and the c h a r a c t e r i s t i c s o f each o f the sedim entary su bregion s w i l l be d is c u sse d in some d e t a i l . The smoothed data i s shown in F igures 27-29 and the a c tu a l measurements are ta b u la ted in Appendices V-VII. Sediment C o n stitu e n ts P e t r i t a l M a terials Sediments composed o f m in erals which formed elsew h ere and were tra n sp o rted to the s i t e o f d e p o s itio n by p h y s ic a l a g e n c ie s are termed d e t r i t a l . By fa r the most obvious such m a te r ia l in the Gap region i s t e r r e s t r i a l sand (F ig . 27). Here^ most o f the a v a ila b le coarse t e r r e s t r i a l m a ter ia l i s d eriv ed lo c a lly ,, by the marine e r o sio n o f the sedim entary and igneous rocks o f San Miguel and Santa Rosa I s la n d s . T e r r e s t r i a l d eb ris from the mainland i s in te r c e p t e d by the Santa Barbara Channel, whereas Santa Cruz submarine canyon between Santa Rosa and Santa Cruz I s la n d s p rev en ts the en tr y o f m a te r ia l from the e a ster n In su la r Ridge. The source rock s on the is la n d s are predom inantly Late Cretaceous to Miocene sands and s i l t s t o n e s and u n co n so lid a te d P le is t o c e n e to Recent te r r a c e and c o a s t a l dune d e p o s it s . There are a ls o minor exposures o f igneous v o lc a n ic and i n t r u s iv e rock s ranging in com position from b a s a lt to d a c it e . P ig . 2 7 . — D is t r ib u t io n o f t e r r e s t r i a l sand. 136 TERRESTRIAL SAND CONCENTRATION IN SURFACE SEDIMENTS OVER 50% \\\Y 50-25% 11111 25-5% ' / / / / . LESS THAN 5% Kilometer* 0 Nautical Miles 5 Contours in m eters ISAN MIGUEL ISLAND' ISANTA ROSA ISLAND, ■ 3000' I20°40’ l20o2<r 138 The dominant d e t r i t a l m in e r a ls a r e q u a rtz and th e f e l d spars,, and th e a v era g e g r a in s i z e i s r e l a t i v e l y f i n e . As m ig h t be e x p e c te d o f reworked s e d im e n ts, th e c o a r s e r sands 'are f a i r l y w e ll-r o u n d e d , o f m o d e r a te ly h ig h s p h e r i c i t y , w h il e th e f i n e r sands show l e s s s ig n o f a b r a s io n . Q u a n tita t i v e l y im p o rta n t o c c u r r e n c e s o f v o l c a n ic r u b b le and g l a s s sh a r d s are p r e s e n t in s e v e r a l s u r f a c e sam ples from P a tto n R id ge and th e P a tto n Escarpm ent. B ecau se o f t h e i r l i m i t e d d i s t r i b u t i o n , l o c a l d e r i v a t i o n i s assumed. Heavy m in e r a ls , e x c lu d in g m ica, are s c a r c e and i n c o n sp ic u o u s i n t e r r e s t r i a l sands from th e Gap r e g i o n . Magne t i t e , h o r n b len d e , g a r n e t, z ir c o n , and o l i v i n e were r e c o g n i z e d , b u t th e c o n c e n t r a t io n o f h e a v i e s was n e v e r s u f f i c i e n t to en cou rage d e t a i l e d s t u d i e s o f th e p r o v e n a n c e . Mica f l a k e s were i n v i r t u a l l y a l l th e sam p les; th e y o f t e n c o n s t i t u t e s e v e r a l p e r c e n t o f th e sand f r a c t i o n . U n f o r t u n a t e ly , t h e p h y s i c a l form o f th e m ica s i s such th a t th e y a re t r a n s p o r t e d so e a s i l y by winds and c u r r e n t s th a t th e y are n ot p a r t i c u l a r l y d i a g n o s t i c in any n e a r sh o r e se d im en ta ry e n viro n m en t. Mica i s by f a r th e commonest m in e r a l in th e su sp en ded m a t e r ia l in th e w a te r s o f f P o in t C on ception (R o d o lfo , 1 9 6 4 ). C o n c e n tr a tio n s o f s i l t and c la y g r e a t e r than 25 p e r c e n t a r e alm o st e n t i r e l y r e s t r i c t e d to th e c e n t r a l b a s in o f the Gap. E xam ination o f th e c h a r t ( P ig . 2 7 ) w hich shows d i s t r i b u t i o n o f s a n d - s iz e d m a t e r i a l v e ry c l e a r l y i l l u s t r a t e s 139 t h i s . Comparison sh ou ld he made w ith a p l o t o f t o t a l t e r r e s t r i a l m a t e r ia l (F ig . 2 8 ) , where the s i l t and c la y f r a c t i o n s are lumped w ith th e t e r r e s t r i a l sand. As m ight he a n t i c i p a t e d on th e c o n t i n e n t a l slope., th e sed im en ts are dom inated hy t e r r e s t r i a l d e h r is . No c la y a n a ly s e s were a t tem pted during t h i s s t u d y , h u t th e s i l t f r a c t i o n from the c e n t r a l b a s in was examined under o il-im m e r s io n m icroscope (x 8 0 ) . The s i l t c o n s i s t e d alm ost e x c l u s i v e l y o f f i n e , a n g u la r q u artz g r a in s . In view o f th e ex tr em e ly h ig h p h y to p la n k to n p r o d u c t i v i t y in the a r e a , th e r e i s a s u r p r i s i n g l y low c o n c e n tr a t io n o f diatom f r u s t u l e s or o th e r f i n e b i t s o f o r g a n ic d e h r i s — l e s s than 5 p e r c e n t o f th e s i l t f r a c t i o n o f s u r f a c e sedim ent from th e c e n t r a l b a s in o f the Gap. A u th ig e n ic Sedim ents A u th ig e n ic m a t e r ia ls e s s e n t i a l l y form in s i t u a t the se d im e n t-w a te r i n t e r f a c e , e i t h e r by p r e c i p i t a t i o n from sea w a ter or by some h a l m y r o l i t i c r e a c t i o n w ith sea w a te r. Three m a t e r i a ls o f t h i s s o r t are in th e sed im en ts o f the Gap: g l a u c o n i t e , p h o s p h o r ite , and "manganese n o d u le s." None o f t h e s e can be very c l e a r l y d e fin e d as m in e r a ls , though th e y are d i s t i n c t i v e c o n s t i t u e n t s o f the sed im en t. P h o sp h o r ite which i s w id esp read in o th e r p a r t s o f the b o r d e r la n d was found i n q u a n t it y a t o n ly a s i n g l e s t a t i o n in th e Gap (AHF 1 0 1 2 3 ). There, a dredge hau l a c r o s s a minor r i s e a t a depth o f about 500 m on the f la n k o f th e F ig . 2 8 . - - D i s t r i b u t i o n o f t o t a l t e r r e s t r i a l m a t e r ia l. 140 TOTAL TERRESTRIAL MATERIAL IN SURFACE SEDIMENTS OVER 50% \ \ \ \ \ 50-25% 25-5% ' / / / / LESS THAN 5"/! M a ^Va ViVa VAVAVAVa VAV 0 K llom atati 10 0 Nautical M ilts 5 Contours in m tta rs SAN MIGUEL ISLAND SANTA ROSA ISLAND M>AL*M>Y4 AMA>A\*.O.v * :♦ ♦.♦A V .> .M.MA*Av A*A*A* M»>WAVAVA\W 2 5 0 0 yo>>>.0>>AM A»:O Aw>>>A*>ACA<0> > A M A » .. *A V A V A V A4 AVA’ AAVA4 A * A *A V A V A V A V A A V A *A *A A *A *A *A *a 21*00 120*40 120*20 1 1 7 L 33*40' ^ ^ 3 4 * 0 ? Santa R o sa-C o rtes Ridge y i e l d e d c o n s id e r a b le q u a n t i t i e s o f p h o sp h o r ite both a s b lo c k s ( F ig . 21d) and as g r a in s in th e sed im en t. T h is a u t h ig e n ic m a te r ia l i s a complex m ixture o f hydrous c a lc iu m phosphate w ith some carbonate* oxide* and flu o r id e * probab ly the m in era l c o ll o p h a n i t e (Emery and D ietz* 1950)• I t seems l i k e l y t h a t p h o sp h o r ite may form by d i r e c t p r e c i p i t a t i o n as a c o l l o i d from seaw ater in a r ea s o f u p w ellin g * where cool* deep w a te rs su p e r s a tu r a te d w ith phosphate io n are brought to the s u r fa c e under r a p id ly changing p ressu re* tem perature* and pH c o n d it io n s (Emery* i 9 6 0 ) . A v a r i e t y o f e v id en ce i n d i c a t e s t h a t most o f th e p h o sp h o r ite o f the b ord erla n d i s probably o f Miocene age* p o s s i b l y w ith a l e s s e r c y c le o f d e p o s it io n during the P l e i s to c e n e (Emery and D ietz* 1950)- P h o sp h o rite i s common on the c r e s t o f th e Santa R o sa -C o rtes Ridge* where i t o ccu rs on a s u b s t r a t e o f Eocene to Late Miocene age (Uchupi* 1 9 6 1 ) . Uchupi conclu ded t h a t i t s age th e re was c e r t a i n l y p o s t-M io c e n e . No d a ta b le f o s s i l s were found a s s o c i a t e d w ith the occu rr en ce a t s t a t i o n AHF 10123; i t seems l i k e l y th a t t h i s s i n g l e p h o sp h o r ite i s r e l i c t * p o s s i b l y as o ld as M iocene. G rains o f an a u t h ig e n ic su b sta n ce s i m i la r to the manganese n o d u les o f th e deep sea were r ec o v e r e d from s e v e r a l s t a t i o n s on the P atton Ridge and Escarpment. This ma t e r i a l o c c u r s as i n d i v i d u a l g r a in s or fla k e s* averagin g perhaps 1 -2 mm in diam eter* in the sediment* or more com monly as c r u s t s on dredged v o lc a n ic r o c k s. I t i s t y p i c a l l y a f r i a b l e dark r u s t y brown to so o ty b la c k g r a n u la r sub s ta n c e , presum ably an in t im a t e m ixture o f h yd rated manganese and ir o n o x i d e s . An attem p t to a n a ly z e the "manganese c ru st" w ith th e X -ray d if f r a c t o m e t e r produced o n ly a str o n g "noise" p a t te r n w ith no i d e n t i f i a b l e peaks (K. S. R o d o lfo , p e r s o n a l co m m u n ica tio n ). P y r o l u s it e and lim o n it e were d i s t in g u is h e d in the m a t e r ia l by hand-specim en te c h n iq u e s; no fu r th e r i d e n t i f i c a t i o n was p r a c t i c a l . Ferromanganese m ate r i a l o f a s i m i la r appearance i s commonly a s s o c i a t e d w ith submarine v o lc a n ism throughout the w orld (B o n a tti and Nay- udUj 1 9 6 5 ) . This m a t e r ia l q u a l i f i e s a s a sedim ent in o n ly a l i m i t e d se n s e ; where i t o c cu rs in th e Gap i t p robab ly i s an i n d i c a t i o n o f e x tr em e ly nearby submarine v o lc a n ic a c t i v i t y . G la u c o n ite i s one o f th e commonest m in e r a ls th a t occu r in the sed im en ts o f th e Gap (F ig . 2 9 -3 3 )- I t o c cu rs as an a ccessory., in t r a c e amounts, throughout th e e n t i r e r e g io n ; on th e deep r id g e s and s l o p e s i t o f t e n dom inates th e s e d i ment. G la u c o n ite i s th e common name f o r a fa m ily o f i r o n - and p o t a s s iu m -r ic h c la y s o f v a r ie d m in e ra lo g y , c h a r a c t e r i z e d by a g r e e n is h c o lo r and i r r e g u l a r form. In th e Gap a r e a , g l a u c o n i t e i s most o f t e n found as rounded, o b la t e p e l l e t s 0 . 1 - 1 . 5 mm in maximum dim en sion , b u t g la u c o n it e i s a l s o common as f i l l i n g s , i n t e r n a l m olds, and rep la cem en ts o f the s h e l l s o f sm a ll b e n th ic and p la n k to n ic organism s, p a r t i c u l a r l y f o r a m i n i f e r s . F ig . 2 9 . — D i s t r i b u t i o n o f g l a u c o n i t e . 144 GLAUCONITE CONCENTRATION IN SURFACE SEDIMENTS m OVER 50% \ \ W 50-25% III ] | 25-5% ' / / / / LESS THAN 5% 0 ABSENT K lb T d ert C ontain jn matara 1 2 1 * 0 0‘ 120*20 ' 120*40' As an a c c e s s o r y m in eral in marine sediments* g la u c o n ite i s w id esp read . In f a i r l y h ig h c o n c en tr a tio n s* i t i s p a r t i c u l a r l y c h a r a c t e r i s t i c o f the contemporary o u te r c o n t i n e n ta l s h e lv e s and slop es* but a ls o has been r e c o g n iz e d in sedim ents from most marine environm ents ranging in age back to the Precambrian. Cloud (1955) summarized th e e x te n s iv e l i t e r a t u r e on g la u c o n ite occu rren ce and concluded th a t i t s form ation r eq u ire d normal marine waters* red u cin g c o n d i t i o n s in the sediment* and s u i t a b l e source m a t e r ia ls . Source m a t e r ia ls su g g e ste d are m icaceous m in e ra ls d eriv ed from the w eathering o f ig n e o u s and metamorphic t e r r a i n s . As w ell* a h igh o rgan ic c o n ten t in th e sedim ent and a low r a t e o f se d im e n ta tio n were s a id to fa v o r g la u c o n it e g e n e s i s . More r e c e n t stu d ie s * p a r t i c u l a r l y o f g la u c o n it e in modern sedim ents* have a l t e r e d many o f the o ld e r i d e a s (Emery* 1960j Ehlmann* e t a l .* 19^3; W. L. Pratt* 19^3; Borchert* 1 9 6 5) . The con sen su s today i s th a t n e it h e r reducing c o n d i t i o n s nor a h igh c o n c e n tr a tio n o f o rg a n ic m atter in the sedim ent are e s s e n t i a l and th a t even a v a i la b l e source m ate r i a l s are n o t c r i t i c a l . The t y p i c a l occu rren ce o f g la u c o n i t e in the Gap r e g io n i s in a rea s o f slow sedim entation* where th e re are a p p r e c ia b le bottom currents* and where sedim ents and w ater are both r e a so n a b ly w e ll-o x g e n a te d . I t has been su g g ested th a t much i f not a l l o f the g lau c o n it e in the b orderlan d i s r e l i c t * a sou v en ir o f former c o n d it io n s (Emery* e t a l ., 195 2). T his c o n c lu sio n i s based F ig . 3 0 . —Coarse f r a c t io n s o f g l a u c o n i t e - r ic h su rface sedim ents from the Gap. Background i n . a l l photos i s 1 m m g r id . (a) From c r e s t o f P atton Ridge (AHF 10345), showing g la u c o n ite weathered v o lc a n ic rubb le, and a few f o r a m in if e r s . (b) From Patton Escarpment (AHF 1034l) showing a very h ig h percentage o f g la u c o n it e . (c) Surface sediment from e a stern part o f Patton Ridge area (AHF 10108). (d) T yp ical g l a u c o n it e - r ic h sedim ent from A rguello Plateau ( D l ) . 147 > X * fc • , ? 5 5 ' a K S3 E S 63 E» S3 r*: ; w s-ss east-a;'-* ss?;ks'k & v m > ~ . ‘ tS u i s -,-< £ ; v . ? - 3 r- T-EC aH B E .-sE * . -i? 3 S . ' .^ £ 3 S i f t i E f f i iii IBB Bffi IBB BB ■as. ' V.JB ' ,;bm i ’■ H -B r a p ^S?3r “ s ■ H I ® * " ' . IPSH? S i V nfl WE35m£** <£:f i i 5*3.J^-~ & 15 if i J? \i ;,* K:: ? : • '•.': i'l A s ? r Y E T I R J W E » 5 5 ® s r ? a ! ® ia B B \%as s i a s K s u & i a i a d B s s s e s s s f f .' p r i y & j y y K ? ? , I B S f l B B C S S f i H K a a ESCiiS"^;-^ IB B I B 8 B S I B B h i R B K E B SSM « « i iB B H H E H B H S E a r o ia H53®»-i:Ki; i'. B i f l ■■■— ■BMW* ' . ^ V | i t ' 1~ f ' I ^ j ' T X T 8tri upon the freq u en t i d e n t i f i c a t i o n o f g la u c o n i t ic i n t e r n a l molds o f fo r a m in ife r s no lon g er common in the r e g io n . In the Gap a rea , the g l a u c o n i t ic sands appear d e f i n i t e l y to be o f contemporaneous o r ig i n , though o f very slow form ation. Both su rfa ce sedim ents and the bottoms o f sh ort c o r e s, a l l c o n ta in in g over 50 p ercen t g la u c o n it e , con tain contemporary assem blages o f fo r a m in ife r s , o fte n w ith an a p p recia b le ad m ixture o f f o s s i l fo r a m in ife r s th a t may be as o ld as P l i o cene. The i n c lu s i o n o f the o ld e r m i c r o f o s s i l s even in su r fa ce sedim ent i s a t t r ib u t e d to the extrem ely low r a te o f sed im en tation and the m ixing a c t i v i t i e s o f burrowing b en th ic in fa u n a . To t e s t the h y p o th e sis th a t g la u c o n ite i s forming con tem poraneously in the Gap area, a 50 cm g l a u c o n i t e - r ic h core from a te r r a c e a t approxim ately 700 m on the fla n k o f the Santa R osa-C ortes Ridge was examined in d e t a i l . The sedim ent o f the core i s an homogenous g la u c o n i t ic fo ra m in i- f e r a l sand w ith never l e s s than 35 p e r ce n t g la u c o n ite by volume (P ig . 3 l ) • Continuous sed im en tation sin c e th e Late P le is t o c e n e was demonstrated by a study o f the c o i l i n g ha b i t s o f G lob ig erin a pachyderma w ith in the c o re. F ive d i f fe r e n t v a r i e t i e s o f g la u c o n ite were d is tin g u is h e d in the sedim ent, forming a g r a d a tio n a l, p o s s i b l y g e n e t i c , sequence (Table 7 ) . F ig . 3 1 • --Sedim en t c h a r a c t e r i s t i c s , Core AHF 10106. 150 SEDIM ENT SIZE ( % SAND) T E o U i tr o o x l- Q . W Q 25 50 CONSTITUENTS OF SAND FRACTION VARIETIES OF GLAUCONITE ( % ) 100 0 COILING DIRECTION Globigerina pachyderm a ( % D EX TRA L) 100 ?,L S ' ‘> S: * a z < 'L V .V - V .i,:, h .**/>.T' ’ A'-mv? ‘ : V I s * • i ♦ V - tv v 't > Vv. * ' * L \ v \ 'V v ’ > » <v £<C y«Jvx>.V )>,$3 SEDIMENT CHARACTERISTICS CORE AHF 10106 V J l J = i 152 TABLE 7 VARIETIES O R GLAUCONITE FR O M SEDIMENTS IN SAN MIGUEL G A P REGION Type Color Form O ccurrence Remarks 1 Y ello w ish S o f t , c la y e y in t e r n a l m olds Only w ith in t e s t s o f F oram in ifera P o s s ib le p recu rso r o f g la u c o n ite 2 Very p a le green As f i l l i n g s and in t e r n a l molds W ith in s h e lls o f foram s and o th er sm a ll organism s 3 Medium. green Homogenous, f a i r l y dense a s m olds or replacem ent s O bvious organ ic hut no lo n g er con ta in e d • in s h e l l s 4 Medium to dark green Homogenous, o ft e n w ith d e s s ic a t io n crack s Ovoid t o o b la te p e l l e t s S im ila r to f a e c a l p e l l e t s ; commonest form o f g la u c o n ite 5 Dark green t o "black O ften sh in y Ir r e g u la r or o o l i t i c appearance P o s s ib le f i n a l form, much lik e many a n c ie n t g la u c o n ite s At a l l l e v e l s In th e c o r e , the commonest form o f g l a u c o n i t e was th e t y p i c a l p e l l e t (Type # 4 ) , b u t th e r e was a s y s te m a tic d e c r e a se in the " l e s s mature" forms and an in c r e a s e in the d e n s e , alm ost b la c k form. A s i m i l a r sequence,, a ls o i n t e r p r e te d as e v o lu t io n a r y , was o b served in g l a u c o n i t i c s e d i ments from the c o n t i n e n t a l slo p e o f f the s o u th e a s te r n U n ited S t a t e s (Ehlmann, e t a l , , 1 9 6 3). G la u c o n ite ty p e s ob served in the Gap a rea can be recon c i l e d to form an e v o lu t io n a r y seq u en ce. I n i t i a l l y . , c o l l o i d a l c l a y s are p r e c i p i t a t e d w ith in th e m icroenvironm ent o f P ig . 3 2 . --S a n d f r a c t i o n o f sed im en ts from core 10108 i n th e P atton Ridge a r e a . A l l sed im en ts are h ig h in g l a u c o n i t e and f o r a m in if e r s , and in a l l sam ples hut th e s u r f a c e , th e r e i s an a p p r e c ia b le p e r c e n ta g e o f l i g h t brown w eathered v o lc a n ic r u b b le . S c a le s i m i la r in a l l p h o to s: mm g r id back ground. (a) 0 - 5 cm (b) 1 5 -2 0 cm (c) 95-100 cm (d) 1 1 7 -1 2 2 cm 153 sm all s h e l l s , p a r t i c u l a r l y f o r a m in ife r a l t e s t s . I d e n t i f i ab le g la u c o n it e "matures" w ith in the s h e l l s by the e n r ic h ment o f iro n and p otassiu m and the grad u al e x p u lsio n o f some o f the a tta c h e d w ater m o le c u le s . C la s s ic g la u c o n it e p e l l e t s appear to be formed by the passage o f the sedim ent, l a r g e ly organ ic s h e l l d e b r is and g la u c o n it e , through th e i n t e s t i n e s o f mud e a tin g organism s. Much o f the s h e l l mate r i a l i s d i s s o l v e d and th e p e l l e t s are en rich ed in g la u c o n i t e . Ir o n -b e a r in g o o l i t e s d e r iv e d from f a e c a l p e l l e t s , p o s s i b l y o f g la u c o n it e , have r e c e n t l y been r e c o g n iz e d in sedim ents o f f the c o a s t o f Gabon (P. G ir e s s e , quoted in Dangeard and R io u lt , 1 9 6 5)• The p o ly c h a e te H eterom astus filo b r a n c h u s and s e v e r a l s p e c i e s o f e c h in o id s l i v e in t h i s environm ent and produce f a e c a l p e l l e t s o f the proper form and dim ensions (Hartman, 1 9 6 3)• Beyond t h i s s ta g e , the f i n a l form o f g la u c o n it e may be produced by fu r th e r e x p u l sio n o f w ater and the a c c r e t io n o f more g la u c o n ite and p o s s i b l y p h o sp h o r ite on the su rfa c e o f the p e l l e t . I f t h i s phenomenon proceeds a t the r a te su g g ested in core 10106 (B ig. 3 1 ), i t would take l i t t l e more than o n e - h a lf m illio n y e a r s to produce a f u l l y mature g la u c o n it e sedim ent. B i o lo g i c Sediments Organisms are o f t e n im portant as a source o f sed im en ts. The s h e l l s and s k e le t o n s o f many c r e a tu r e s are found in the sedim ent, and th e se remains are t r u l y sedim ent components, Pig* 33*— Sand f r a c t io n s o f sedim ents from the San Miguel Gap. Background i s m m g r id . (a) Very r ic h fo r a m in ife r a l sand la y er from upper part o f core 10115 (45-50 cm ). Note the d i v e r s i t y o f h e n th ic forms. (h) T yp ical su rfa ce sediment on Patton Ridge (AHF 10364), note high c o n c e n tr a tio n s o f g la u c o n ite , fo r a m in ife r s , and one la r g e r fragment o f v o lc a n i c ruhh le. (c) Surface sediment from s h e l f near Santa Rosa Is la n d (AHF 10370) showing high c o n cen tra tio n o f m ollusk d eb ris and t e r r e s t r i a l sand and g r a v e l. (d) Enlargement o f some o f the sedim ents from AHF 10370. 1 5 6 157 W O #5»W i^ fo r as soon as any marine c re a tu re d ie s i t s hard p a r t s are su b je c t to p r e c i s e l y the same i n f l u e n c e s as any o th e r s o l i d m a te r ia l in the se a . Of p a r t i c u la r im portance in th e s e d i ments o f the Gap area are the t e s t s o f p la n k to n ic and ben- th o n ic f o r a m i n if e r s . As w e l l , th e re are a p p re c ia b le quan t i t i e s o f r a d io la r ia n s * diatoms* sponge s p ic u le s* and e c h i- noid s p in e s . More rare are lumps o f tar* u n i d e n t i f i a b l e woody and c h it in o u s fragments* and b i t s o f f i s h s k e le to n . Without qu estion * the most common and v a r ia b le o f the b i o l o g i c c o n tr ib u t io n s i s th a t o f the fo r a m in ife r s ; o th e r ty p e s o f o rg a n ic m a te r ia l are e i t h e r u b iq u ito u s in sm all q u a n t i t i e s or r e s t r i c t e d in d i s t r i b u t i o n . C alcareous s h e l l s o f both ben th on ic and p la n k to n ic f o r a m in ife r s are p r e se n t in a l l the sedim ents o f th e Gap r e g io n (F ig . 3 4 ). In some l o c a l i t i e s th ey c o n s t i t u t e as much as 50 p e r ce n t o f the su rfa ce sedim ent. Often the c o a r s e s t sedim ent a t a deep w ater s t a t i o n w i l l be the t e s t s o f b en th on ic fo r a m in if e r s . The g r e a te r p a rt o f the area i s in the b a th y a l fa u n a l zone ( 2 0 0 -3 0 0 0 m)* hence the dominant s p e c i e s are th o se c h a r a c t e r i s t i c o f th a t depth range. Prominent b en th o n ic genera in c lu d e A s t a c o lu s * B o l i v i n a * B u lim in a , C a s s id u lin a * C i b i c i d e s * D e n t a lin a , N odosaria, R obulus* and U v ig e r in a . Most o f the p la n k to n ic forms are from the fa m ily G lo b ig e r in id a e * and the u s e f u l c li m a t ic i n d icator* G lo b ig er in a pachyderma, i s p r e se n t in a l l sam ples. A ll s p e c ie s i d e n t i f i e d are l i s t e d in Appendix VI. Arena- F ig . 3 4 . — D is t r ib u t io n o f fo r a m in ife r a in sed im en ts. 159 BENTHIC AND PLANKTONIC FORAMINIFERA IN SURFACE SEDIMENTS OVER 5 0 % \\\Y 5 0 -2 5 7 . Mill 25-5% / / / / / LESS THAN 5 7 . ■ 2 5 0 0 - 1 2 1 * 0 0' 1 2 0 * 2 0' 161 ceou s f o r a m in ife r s are rare; a few specim ens o f B a th y sip h on , Cyclammina, G o e s e lla , Hormosina and M a r tin o ttie 1 1 a were found in deep w ater a t the base o f the In s u la r R idge. There i s no c le a r trend in th e p la n k to n ic to b en th on ic ratio., but h ig h er r e l a t i v e c o n c e n tr a tio n s o f th e sm all p la n k to n ic s occur in the c e n t r a l b a s in . Sponge s p i c u l e s are the most common s i l i c e o u s organic d e b r is . There are a few p e r c e n t o f th e se q u it e d i s t i n c t i v e g l a s s y fragm ents in v i r t u a l l y every sample. The common s p ic u le ty p e s were monaxons, t r ia x o n s , and t e tr a x o n s . They u s u a l l y range from 1 -3 m m in maximum dim ension, and the ma j o r i t y o f the s p i c u l e s are undamaged, but th ere are sm aller broken fragm ents. U n fo r tu n a te ly , very l i t t l e can be d e t e r mined about the sponges th a t s e c r e t e d th e s e s p i c u l e s . Sponge i d e n t i f i c a t i o n depends upon g r o ss t i s s u e morphology and s p ic u le type a s s o c i a t i o n s ; i s o l a t e d s p i c u l e s u s u a l l y cannot be i d e n t i f i e d . Presumably, the s p i c u le s came from sm a ll, l o c a l , s o f t - s u b s t r a t e s i l i c o - s p o n g e s . There was l i t t l e tr a n sp o r t or the d e l i c a t e s p i c u l e s would have s u f fe r e d more damage than i s u s u a l l y seen . By i n f e r e n c e , th ere must be s u f f i c i e n t c i r c u l a t i o n o f org an ic d e b r is in the b o t tom w aters to support th e se f i l t e r - f e e d i n g anim als. R a d io la r ia n s and diatom s c o n s t i t u t e the remainder o f the s i l i c e o u s o rg a n ic rem ains. They are w idesp read, but alm ost never a s i g n i f i c a n t f r a c t i o n o f the sedim ent. In an 162 a r ea o f such h ig h known o r g a n ic p ro d u ctio n * i t i s s u r p r i s i n g to f i n d so low a c o n c e n tr a t io n o f diatom f r u s t u l e s . Appar e n t l y th e e n t i r e c y c l e o f diatom bloom and r e g e n e r a t io n i s a c co m p lish ed in th e s u p e r f i c i a l w a t e r s . C alca reo u s fragm en ts o f m o llu sk s h e l l s * s o l i t a r y corals* and bryozoan c o l o n i e s are found in the s h a llo w w a te r s e d i ment n ea r th e i s l a n d s . Some sam p les are v i r t u a l l y a coquina o f worn* broken s h e l l s * e s p e c i a l l y s h e l l s o f p e le c y p o d s and g a s tr o p o d s ( F ig . 33c and 3 3 d ). Few e n t i r e • s h e l l s occur* but fragm en ts up to 5 cm i n maximum d im en sion were n o t uncommon. B i t s o f e c h in o id sp in e were commonly e n c o u n te re d i n b o th sh a llo w and deep w a te r . Most o f t h e s e fragm en ts a r e s p in e s o f th e burrow ing h e a r t u r c h in s* B r i s a s t e r tow n send i and B r i s s o p s i s p a c i f i c a , mud e a t e r s t h a t c o n t r ib u t e to th e m ix in g and o x y g e n a tio n o f th e sed im en t (F. C. Z iesenhenne* p e r s o n a l co m m u n ic a tio n ). A few m a ssiv e frag m en ts o f p in k ish * l o n g i t u d i n a l l y furrow ed s p i n e s o f A l l o c e n t r o t u s f r a g i l - i s were found. A l l o c e n t r o t u s i s a common e p i f a u n a l b e n th ic echinoderm in th e b a th y a l zone o f f so u th ern C a l i f o r n i a . A l though l i v i n g sp ecim en s o f o p h iu r io d s and p o ly c h a e t e worms were c o l l e c t e d w it h s e v e r a l samples* no d ir e c t ' c o n t r i b u t i o n to th e sed im e n ts by t h e s e o rgan ism s c o u ld be i d e n t i f i e d . The o n ly v e r t e b r a t e rem ains e n c o u n te r e d were from th e c e n t r a l b a s i n . There* in s e v e r a l samples* fragm en ts o f f i s h sc a le * v e r te b r a e * and broken t e e t h were r e c o v e r e d . Sm all lumps o f t a r are o f t e n se en in th e sam ples from the 163 I n s u la r and Santa R osa-C ortes R id g e s, and q u ite rarely,, elsew h ere in the r e g io n . The ta r i s probably d e r iv e d from s e v e r a l a c t i v e o i l se ep s in the sh allow w ater j u s t northw est o f San M iguel I s la n d . Sedim entary Subregions In su la r and Santa R osa-C ortes Ridges The e a s t e r n margin o f the San M iguel Gap area i s a con tin u ou s s lo p e p a r a l l e l to and about 50 km in s id e the tru e c o n t in e n t a l s lo p e . This slope., e f f e c t i v e l y the w estern fla n k o f th e Santa R osa-C ortes Ridge but le a d in g a ls o to the w estern Channel I s la n d s , c o n s t i t u t e s a s in g le t r a n s i t i o n a l sedim entary u n i t . The subregion grades down from c o n t in e n t a l s h e l f c o n d it io n s In sh a llow w ater to a p p ro x i m ately o n e - h a l f the depth o f the true c o n t in e n t a l s lo p e . In terms o f the g r a d ie n t, t h i s slo p e i s more t y p i c a l o f c o n t in e n t a l s lo p e s than th e P atton Escarpment to the w e st. S lo p es range from 3°~7°j a veragin g about 4 ° , and are compar ab le to th e l i m i t s o f 3 0 -6 0 e s t a b l i s h e d i n the g e n e r a lly a c cep ted d e f i n i t i o n o f the c o n t in e n t a l s lo p e {Heezen, e t a l ., 19 59). In c o n t r a s t , the P atton Escarpment i s much more abrupt; s l o p e s th ere average about 10° and may be as high as 15° . The t r a n s i t i o n o f sedim ent ty p es on the e a s t slo p e o f the Gap I s d i s t i n c t i v e (F ig . 35)• On th e s h e l f , th e re i s F ig . 35*- - S u r f a c e sedim ent c h a r a c t e r i s t i c s on c r o s s - s e c t i o n a c r o s s the Gap. 164 SAMPLE STATIONS 10346 10341 10361 10362 10103 10118 10357 10336 10367 S a n to R o ta J j l o n d SEA L E V E L / v r ' PA T TON RID G E j f c " I N S U L A R R I D G E 8 0 0 M. TERRACE SAN MIGUEL GAP (BASIN) PATTON ESCARPMENT 1 8 0 * 4 0 * Kilomaior* VERTICAL EXAGGERATION xIO 0 No til fed M EEai 5 3 0 0 0 S 3 N 0 * 166 l i t t l e f i n e m a te r ia l ( s i l t and c la y ) and a r e l a t i v e l y h igh c o n c e n tr a tio n o f th e la r g e r b en th on ic f o r a m in if e r s . T e r r e s t r i a l sand c o n s t i t u t e s the major p o r tio n o f the sediment* and th ere i s an a p p r e c ia b le p ercen tag e o f coarse o rg a n ic d e b r is . At the s h e l f break* broken m ollu sk s h e l l s and f r a g ments o f bryozoans are common. There are s e v e r a l sedimentary tre n d s a s s o c i a t e d w ith in c r e a s in g depth and/or d is ta n c e from the i s l a n d s . A sy s te m a tic d ecrea se in the p rop ortio n o f t e r r e s t r i a l sand and co a rse o rg a n ic d e b r is i s c l o s e l y compen- s a te d -b y an in c r e a s e in the f i n e d e t r i t u s . The r a t i o o f p la n k to n ic to b en th o n ic fo r a m in ife r s i n c r e a s e s as soon as th e most sh allo w w aters o f the s h e l f are passed* then r e mains r e l a t i v e l y c o n s ta n t. There i s one obviou s break in the pattern* an alm ost h o r iz o n t a l te r r a c e 4-5 km wide a t about 800 m depth. A d i s t i n c t i v e g l a u c o n i t e - r i c h sand* very s i m i la r to th a t f a r t h e r o ffsh o re * has develop ed on the t e r r a c e . I t i s p o s s i b l e th a t t h i s r e p r e s e n t s a r e l i c t d ep osit* but the p o p u la tio n o f G lo b ig er in a pachyderma in the su r fa c e sedim ents o f the t e r r a c e i s 80-90 p e r c e n t d extra l* a Recent fa u n a . On th e s h e l f j u s t south o f San M iguel I s la n d th e re i s a sm all p e r cen ta g e o f f a i r l y w ell-r o u n d e d medium qu artz sand w ith a d i s t i n c t i v e l i g h t brown ir o n o x id e su rfa c e s t a i n . Such sands were d e sc r ib e d by Emery ( i 9 6 0 ) as r e l i c t m a teria l. This i s a p o s s i b i l i t y ; th e se b ro w n -stain ed sands might be r e l i c t and then l a t e r d i l u t e d w ith o th e r t e r r e s t r i a l sand 167 by the mixing a c t i v i t y o f burrowing organism s. I t i s more lik e ly ., however., th a t the g r a in s are p r e s e n t ly being d eriv ed by a e o lia n a c tio n from San M iguel I s la n d . There i s an e x ten siv e., probable P le is t o c e n e dune f i e l d on the i s l a n d which was r eju v e n a te d in h i s t o r i c tim es by o v e r -g r a z in g (Bremner, 1933 j W right, 1 9 6 3)• Patton Ridge and Escarpment The most c h a r a c t e r i s t i c fe a tu r e o f the sedim ents o f the P atton Ridge and Escarpment i s th e extrem ely h ig h con c e n tr a tio n o f g l a u c o n i t e . Some o f th e h ig h e s t p er ce n ta g es o f g la u c o n it e ever r e p o r te d in marine sedim ents are in t h i s a rea. Throughout the e n t i r e su b regio n , the average p e r c e n t age i s over 40 p e r ce n t and s e v e r a l sam ples have g la u c o n ite c o n c e n tr a tio n s as h ig h as 70 p ercen t o f the sedim ent. Un d e r sta n d a b ly , the p r o p o r tio n s o f c la y , s i l t , and t e r r e s t r i a l sand are q u ite low, and the numbers o f fo r a m in ife r a d ecrease seaward in a sy s te m a tic fa s h io n . The m a jo r ity o f the s e d i ment sampling attem p ts on th e o u te r r id g e and escarpment were u n s u c c e s s f u l. A la r g e p a r t o f the area i s probably bare o f sedim ent. C en tral Basin The c e n tr a l b a s in o f San Miguel Gap i s c h a r a c te r iz e d by g e n t l e s lo p e s , averagin g perhaps l o 3 0 ', but a l l bathyme t r i c ev id en ce i n d i c a t e s th a t the e n t i r e b a sin has a seaward 1 6 8 d ip . As noted , th e r e are chann els on the f l o o r o f the b a sin which can perhaps be r e c o n c ile d in t o a drainage system . T y p ic a l sedim ents o f the area are homogenous f i n e grey s i l t s and clays., w ith moderate numbers o f fo r a m in ife r s . Traces o f g la u c o n it e are found, u s u a l l y c l e a r l y a s s o c ia t e d w ith f o r a m in if e r a l t e s t s . A p p reciab le c o n c e n tr a tio n s o f diatom f r u s t u l e s o c cu r in a l l the b a s in sed im en ts, and o th e r f i n e s i l i c e o u s d e b r is , r a d io la r ia n s and sponge s p ic u l e s , are somewhat more common here than in th e remainder o f th e Gap a r ea . A few probable t u r b i d it e sands are found in th e b a s in and th e re i s a s i n g l e p u z z lin g occu rren ce o f f i n e l y lam inated m a t e r ia l. A rg u e llo P lateau and Escarpment There are two s t r i k i n g l y d i f f e r e n t sedim ent ty p es on th e A r g u ello P la te a u , the m arginal p la tfo r m to the north o f th e b a s in . Both on the s e c t i o n (P ig . 3 6 ) and on the c h a r ts o f sedim ent p r o p e r t ie s ( P ig s . 27 and 2 9 ), the c o n tr a s t i s o b v io u s. To the sou th and e a s t on the l e v e l p la t e a u , th ere are g l a u c o n i t e - r i c h sedim ents s im ila r to the m a te r ia l on th e P atton Ridge. To the sou th and w e s t, th ere i s a sudden t r a n s i t i o n in t o sedim ent h igh in t e r r e s t r i a l sand. Higher p e r c e n ta g e s o f t e r r e s t r i a l sand are p r e se n t in t h i s area than on the In su la r S h e lf , About 20 km fa r th e r to the n o r th , a l i n e o f c o r e s ex ten d in g from P oin t A rg u ello to the Escarpment again sampled g l a u c o n i t e - r i c h sedim ent in s im ila r F ig . 3 ^ •--S u r fa c e sedim ent c h a r a c t e r i s t i c s on c r o s s - s e c t i o n a c r o ss A rg u ello P la te a u . 1 6 9 1 0 3 4 7 1 0 3 4 8 1 0 3 4 9 SAMPLE STATIONS 1 0 3 5 0 D 4 ____________D 5 1 0 3 5 2 UJ o a: llJ CL UJ > f- < _i = > 5 3 O 2 5 - 5 0 7 5 100 N 1 (0 0> iT » E s a . - . 0 1 HER GL&OC0NJT£ ERRESTRIAL SAND - - ' Q. UJ O 'Hi 5 o o h k _ 0 ) 1000 1500 ■SEA LEVEL- R 0 D R IG U E Z SEAM OUNT A’ R ichardson R ock A R G U E L L O PL A T E A U PATTON ESCARPM ENT Nautical Miles VERTICAL EXAGGERATION xIO ^ 2 0 0 0 1 0 p ■ n o r 5 INSULAR RIDGE 120*40 3 2 1 0 0 I2 0 °2 0 ' SAN MIGUEL ISLAND 171 depths ( D i l l , 1 9 5 2 ). E v id e n tly , th e re i s a zone o f t e r r e s t r i a l sand ex ten d in g along the trend o f the Santa Barbara B asin westward to the c o n t in e n t a l s lo p e . The t e r r e s t r i a l sand on A rg u ello P latea u i s a c le a n , very f i n e quartz sand w ith minor amounts o f fe ld s p a r and heavy m in e r a ls. A fte r e lim in a t io n o f th e tr a c e o f g la u c o n i t e by e le c tr o m a g n e tic se p a r a tio n and treatm ent w ith hydro c h lo r ic a c id to remove th e c a lc a r e o u s f o r a m in ife r a l t e s t s , a f u l l s i z e a n a l y s is was performed on the t e r r e s t r i a l sand f r a c t i o n o f one o f th e se samples (AHF 10348). Over 90 p e r cen t o f the sample f e l l i n t o the 6 2 -1 2 5 micron s i z e c l a s s . The m a te r ia l i s extrem ely w e l l - s o r t e d , very f in e sand. There are th r ee p o s s i b l e e x p la n a tio n s fo r the p e c u lia r t e r r e s t r i a l sand d i s t r i b u t i o n p a tte r n on A rg u ello P lateau : ( l ) The d i s t r i b u t i o n i s the r e s u l t o f submarine w eathering o f o u tcrop s o f a n c ie n t sed im en ts, co m p lete ly u n r e la te d to the contemporary environment; (2) The m a te r ia l i s r e l i c t , and was d e p o s ite d under a sedim entary regime somewhat d i f f e r e n t from the p r e se n t s i t u a t i o n ; and ( 3 ) The t e r r e s t r i a l sedim ent i s contemporary, but due to some agency o f e x trem ely lim it e d scop e. F o ra m in ifers from both the g la u c o n i t e and t e r r e s t r i a l sand a reas on A rgu ello P lateau were examined to determ ine the age o f the su rfa c e sed im en ts. U n fo r tu n a te ly , th e faunas p o s s e s s r e l a t i v e l y few o f the c h r o n o lo g ic a lly u s e f u l p la n k to n ic fo r a m in ife r s , and the b e n th ic ty p es are m ostly u n d ia g n o stic b a th y a l s p e c i e s , common to the C a l i f o r n ia c o a s t s in c e th e Middle T e r tia r y ( j . C. Ingle., J r . , and 0. L. Bandy., p e r s o n a l com m unication). At one s t a t i o n a d e f i n i t e l y r e l i c t p o p u la tio n , a C a s s id u lin a fauna o f p robab ly P l e i s t o c e n e age was found., but no very d e f i n i t e age co u ld be a s s ig n e d to th e o th e r su r fa c e sam p les. F o r a m in ife r s from the bottom s o f s e v e r a l c o r e s in both the g la u c o n it e and t e r r e s t r i a l sand a r e a s y i e l d e d a fauna i n c lu d in g B ulim ina subacum inata, a p o s s i b l e i n d i c a t o r o f P l i o cene age (C. M. Carson., p e r s o n a l com m unication). Because o f the v e r y sm a ll p er ce n ta g e o f p la n k to n ic f o r a m i n if e r s , i t was d i f f i c u l t to determ ine c o i l i n g r a t i o s o f G lo b ig e r in a pachyderma w ith c o n fid e n c e , but i f a llo w a n ce i s made fo r slow se d im e n ta tio n and c o n s id e r a b le m ixing by burrow ers, the r a t i o s u g g e s t s a p o s t - P l e i s t o c e n e age ( 5 8 -8 6 p e r c e n t d e x t r a l ) , There are no i n d i c a t i o n s in t h e s e c o r e s or e l s e where in the Gap area o f any very s t r i k i n g change in the sedim entary environm ent through the Late P l e is t o c e n e to R ecent I n t e r v a l sampled. On th e b a s i s o f the ex tr em e ly f i n e g r a in s i z e o f the t e r r e s t r i a l sands and t h e i r r e s t r i c t e d d i s t r i b u t i o n on A r g u e llo P la te a u , i t i s r e a so n a b le to a s c r ib e them to westward wind and cu r re n t tr a n s p o r t from th e in la n d d e s e r t s o f C a l i f o r n i a , c o n c e n tr a te d by th e Santa Barbara Channel. P o s s ib ly t h i s m a te r ia l was In trod u ced in t o th e e a s t end o f Santa Barbara Channel by the Santa C lara R iv e r , tr a n sp o r te d alon g the m ainland s h e l f to P o in t C onception and from th e re g r a d u a lly moved seaward by g r a v it y 173 and the westward channel d r i f t . S p e c ia l F e a tu r e s o f th e Sedim ents Burrows C le a r ly r e c o g n iz a b le anim al burrows occur in c o r e s from a l l p a r t s o f th e Gap r e g io n e x c e p t th e c e n t r a l b a sin ( F ig s . 37 and 3 8 ) . Quite commonly* th e sedim ent f i l l i n g the burrows d i f f e r e d m arkedly from the surrounding m a t e r ia l g iv in g many o f the c o r e s a very s t r i k i n g m o ttle d appearance. C lose exam in ation o f th e more n e a r ly homogenous c o r e s o f the b a s in was n e c e s s a r y to i d e n t i f y burrows* but even there* s l i g h t v a r i a t i o n s in th e t e x t u r e o f th e sedim ent demon s t r a t e d t h e i r p r e s e n c e . Burrows ran gin g from a few m i l l i m eters up to 10 cm in d iam eter were o b ser v ed . In many o f th e la r g e r burrows ( t y p i c a l l y 3 -5 cm in diam eter)* th e re were r e l a t i v e l y h ig h c o n c e n tr a tio n s o f the s p in e s o f B r i s a s - t e r and B r i s s o p s i s * the p rob ab le r e s p o n s ib l e o rgan ism s. P o ly c h a e te worms are common burrowing organism s in the b a th y a l environm ent (Hartman and Barnard* 1958 ) ; i t i s probab le th a t th ey made many o f th e sm a lle r burrows. Throughout the area th e re i s c o n s ta n t m ixing and oxygena t i o n o f the sedim ent by th e s e organ ism s. Fig. 3 7 ---S p e c ia l fea tu res on San Miguel Gap Sediments. (a) Top: f i n e s t r a t i f i c a t i o n in s e c t i o n 100-118 cm i n core AHF 10115; bottom: burrows showing an enrichm ent in g l a u c o n i t e , s e c t i o n 40 -6 0 cm., AHF 10109. (b) Both specim ens are s e c t i o n s o f AHF 10109 showing t y p i c a l m o ttle d appearance due to burrowing o rg a n ism s. L igh t m a t e r ia l c o n s i s t s l a r g e l y o f fo.ra- m i n i f e r a l t e s t s ., dark m a t e r ia l i s g l a u c o n i t e . (c) Coarse f r a c t i o n from th e f i n e l y s t r a t i f i e d p o r t i o n o f core AHF 10115* i n t e r v a l 95-100 cm. Note moderate s i z e fo r a m in if e r a , one dark, i r r e g u la r lump o f t a r , and f i n e d e b r is c o n s i s t i n g o f diatom s and sponge s p i c u l e s . Background i s mm sq u a r es. (d) G la u c o n it e - r ic h burrow f i l l i n g ( i n t e r v a l 21 -2 2 cm in core AHF 10111) showing a few g r a in s o f t e r r e s t r i a l q u a rtz and a h ig h c o n c e n tr a tio n o f g l a u c o n i t e . 174 175 Fig, 3 8 . --Cores from San Miguel Gap area. (a) Two p is to n co res from the c e n tr a l basin., d e p i c t in g g e n e ra l homogenity o f the sediment and the few sand l a y e r s . Meter s t i c k for s c a l e . (b) G ravity core from Patton Ridge (AHF 10108) and a deep te r r a c e on the Santa R osa-C ortes Ridge (AHF 10106). Note dark c o lo r ( i n d i c a t in g high c o n c en tr a tio n o f g la u c o n i t e ) , the m o ttlin g due to burrowing organism s, and the r a f t e d p eb b les and ro ck s. S cale i s meter s t i c k . (c) G ravity core AHF 10115 from e a ste r n end o f c e n tr a l b a s in . Core segments approxim ately 1 /2 m each, top o f core to the upper l e f t . Note r a f t e d p eb b les and burrows in upper l a y e r s , and s ig n s o f s t r a t i f i c a t i o n in lower s e c t i o n s . (d) E n tire sample from g r a v it y core 10107. M oderately c o n s o lid a te d s i l i c e o u s sh a le and mudstone, probably Miocene. Background: m m graph paper. 176 A HF 10 ll S t7 4 *«. B A H F 1010*7 177 3 178 F a ecal P e l l e t s G la u co n ite o f the t y p i c a l p e l l e t form was commonly found c o n c e n tr a te d in the la r g e r burrows. U s u a lly th e bur row f i l l i n g c o n ta in s ap p ro x im a tely the normal p e r cen ta g e o f t e r r e s t r i a l sand, but o n ly t r a c e s o f the sm a ll c a lc a r e o u s and s i l i c e o u s s h e l l s which are p l e n t i f u l in the surrounding sed im en ts. A s i m i la r enrichm ent in g la u c o n it e was noted in some o f the sm a lle r burrows. As has been noted, c e r t a in o f the p o ly c h a e te worms are known to c a s t f a e c a l p e l l e t s o f the s i z e .and shape o f the g la u c o n it e p e l l e t s . I t i s not known what s o r t o f excrem ent th e echinoderm s produce. I t i s r e a so n a b le to s u g g e s t th a t p assage through the d i g e s t i v e t r a c t s o f m ud-eating organism s may a c c e le r a t e g l a u c o n i t i z a - tio n or a t l e a s t c o n c e n tr a te g la u c o n it e which has formed w ith in th e t e s t s o f sm a lle r organism s. F in e S t r a t i f i c a t i o n There i s an en ig m atic occu rren ce o f v e ry f i n e l y s t r a t i f ie d sedim ent in the low er p a r t (72-174 cm) o f core AHF 10115 from the e a s te r n end o f the c e n tr a l b a s in (F ig . 3 7a). Almost w h ite lam inae, o f t e n l e s s than a m illim e t e r in t h i c k n e ss , are in a ground mass o f g r e y s i l t and c la y . As many as seven laminae were counted in a c e n tim e te r o f c o r e . The l i g h t la y e r s c o n s i s t l a r g e l y o f diatom f r u s t u l e s and f in e sponge s p i c u l e s , w ith a very few fo r a m in if e r s . These l a y 179 e r s are a t t r ib u t e d to se a so n a l phytoplankton blooms. Con c eiv a b ly * so g r e a t was the prod u ction th a t a t tim es more diatom s were produced than co u ld be consumed in the su r fa c e w ater l a y e r s . A sudden in c r e a s e in the a v a i la b l e orga n ic d e t r i t u s in the bottom w aters might t r i g g e r a p o p u la tio n e x p lo s io n among the f i l t e r - f e e d i n g sponges. C ertainly* th e se a so n a l v a r ia t io n in u p w e llin g and w ater c h a r a c t e r i s t i c s a t the su r fa c e i s now s u f f i c i e n t l y g r e a t th a t the bottom sedim ents might be exp ected to show se a so n a l laminae were i t not fo r the a c t i v i t y o f m ud-eating organism s. The p rob lem i s to e x p la in the i n h i b i t i o n o f the b en th on ic in fa u n a . The lam inae in the Gap are s im ila r to th o se d e sc r ib e d by HiHlsemann and Emery ( 1 9 6 1) from Santa Barbara Basin* but there* deep water c i r c u l a t i o n i s r e s t r i c t e d by a s i l l . Low c o n c e n tr a tio n s o f oxygen and a p p re c ia b le q u a n t i t i e s o f h y drogen s u l f i d e se rv e to l i m i t the b en th ic p o p u la tio n and thus p r e se r v e lam inae. San Miguel Gap* a t l e a s t in i t s p r e se n t form* could never m aintain stagn a n t c o n d it io n s . T u rb id ite Layers No sand la y e r s showing the c l a s s i c graded te x tu r e o f a t u r b i d i t e were observed in c o r e s from the Gap r e g io n . In the c e n tr a l basin* however* a few ungraded sands were encountered in a predom inantly f in e - g r a in e d m a trix . Some o f th e se layers* such as the i n t e r v a l s 1 5 -1 6 cm and 6 0 -6 4 cm i n core AHF IO3 6 1* are much h ig h er in t e r r e s t r i a l sand than 180 th e surrounding sedim ent (F ig. 3 8 a ) . Other la y e r s , i n c l u d in g th e i n t e r v a l 1 5 ^ -1 5 8 cm in th e same c o r e , c o n ta in the rem ains o f bryozoans and m ollu sk s which a re common in s h a l lower w a te rs. B enthic fo r a m in ife r s were examined to see i f th e re were any c l e a r l y d is p la c e d forms; u n f o r t u n a t e ly , a l l s p e c i e s i d e n t i f i e d were eu ryb ath yal in ra n g e. Sand la y e r s a c t u a l l y c o n s t i t u t e about 5 p ercen t o f the t h ic k n e s s o f b oth o f th e c e n tr a l b a sin p i s t o n cores (AHF IO3 6I and IO3 6 2 ) . S im ila r la y e r s are not p r e sen t e lsew h ere in th e r e g io n . I t i s probable t h a t th e se sands are t u r b i d i - t e s , but c l e a r l y they are not o f g r ea t im portance i n the sedim entary economy o f th e Gap. This i s n o t a s u r p r is in g c o n c lu s io n , c o n s id e r in g the ab sen ce o f an e x te n s iv e source area o r o f submarine canyons to c o n c e n tr a te p o t e n t i a l l y un s t a b le m a t e r ia l. Furthermore, th e dem onstrated a c t i v i t y o f the burrowing b e n th ic fauna would obscure such la y e r s u n le s s se d im e n ta tio n was very ra p id . R afted D e t r i t a l M aterial Quite fr e q u e n tly e r r a t i c fragm ents o f rock were c o l l e c t e d throughout the a r ea (F ig . 38b ) . These were. In most i n s t a n c e s , w e ll-r o u n d e d p e b b le s, some as la r g e as th e core l i n e r (5 cm). Their com p osition was g e n e r a l ly th a t o f the more r e s i s t a n t rocks o f the Channel I s la n d s , b a sic and i n ter m ed ia te v o lc a n ic p e b b le s , and a few fragm ents o f s i l i ceous s h a le . D i s t r i b u t i o n o f t h e s e rocks was random; p r e 181 sumably th e y were e i t h e r r a f t e d i n t o th e a r e a by k e lp h o l d f a s t s u p r o o te d from th e I n s u la r s h e l f or th e y may r e p r e s e n t stom ach s t o n e s o f m arine mammals (Emery, 1 9 6 3 )• F o r a m in if e r a l C o ilin g R a t io s One o f th e common p la n k t o n ic f o r a m i n if e r s in a l l o f th e Gap se d im e n ts i s G lo b ig e r in a pachyderma (E h r e n b e r g ). T h is I s a s m a ll, s p i r a l l y - c o i l e d z o o p la n k to n ic c r e a tu r e w hich h as been d em o n stra ted to e x h i b i t a p r e f e r e n t i a l c o i l in g d i r e c t i o n r e l a t e d to w a ter tem p eratu re (Bandy, I960; E r ic s o n , e t a l . , 1 9 6 4 ). In tem p erate and t r o p i c w a t e r s , G. pachyderma p o p u la t io n s ten d to c o i l in a d e x t r a l f a s h i o n . In the A r c t i c , m ost r e p r e s e n t a t i v e s o f th e s p e c i e s e x h i b i t s i n i s t r a l c o i l i n g . Inasmuch a s th e s p e c i e s e x i s t e d th ro u g h o u t th e Late C e n o z o ic , i t i s a c o n v e n ie n t i n d i c a t o r o f b o th w ater te m p er a tu r es and c l i m a t i c c h a n g e s. P r e s e n t p o p u la t io n s o f G. pachyderma o f f th e so u th e rn C a l i f o r n i a c o a s t are p r e d o m in a n tly d e x t r a l in c o i l i n g , b u t p r i o r to 1 1 ,0 0 0 y e a r s ago (d a te d by Carbon 1 4 ) , m ost pachyderm as were s i n i s t r a l . T h is d a te c o r r e l a t e s w ith t h a t o f changes i n many o t h e r c l i m a t i c i n d i c a t o r s , and i s t e n t a t i v e l y a c c e p te d by d e e p - s e a s t r a t i g r a p h e r s as th e P le i s t o c e n e - R e c e n t boundary (B r o ec k e r, e t a l . , I960 ; Kulp, 1 9 6 1 ) . A s t a n d a r d iz e d te c h n iq u e was d e v is e d f o r th e u s e o f G. pachyderma c o i l i n g r a t i o s In s t u d i e s o f L ate C en ozoic m arine se d im e n ts ( j . C. I n g l e , J r . , p e r s o n a l com m u n ication ). 182 A r b it r a r ily ., th e c o i l i n g d i r e c t i o n o f th e f i r s t one hundred o f t h e s e f o r a m in if e r s en co u n tered in a sample i s d eterm ined. T his fig u re,, s t a t e d a s a p e r c e n ta g e , i s e f f e c t i v e as a d e v i c e f o r s t r a t i g r a p h i c c o r r e l a t i o n and z o n a tio n . C o ilin g r a t i o s were determ ined by t h i s system f o r s i x c o r e s from th e Gap area (Appendix V lb , P ig s . 31 and 3 9 ). Three o f t h e s e c o r e s were examined s p e c i f i c a l l y f o r t h i s study,, th e o th e r th r e e by o t h e r s in c o n n e c tio n w ith graduate course work ( P r e r ic h s , 1964; H a ck ett, 1 9 6 5)• Because o f the h ig h deg ree o f m ixing i n the c o r e s and in c o n v e n ie n t sam pling i n t e r v a l s in s e v e r a l o f th e c o r e s , the 1 1 ,0 0 0 y e a r s h i f t i n c o i l i n g d i r e c t i o n i s n ot as c l e a r l y d e f in e d as m ight be d e s i r e d . The change in c o i l i n g i s found, however, in each o f th e c o r e s , and th u s a t l e a s t one o b j e c t i v e d a te can be a s s ig n e d i n the c o r e s . As w e l l , a d e x t r a l c o i l i n g h a b it o f G. pachyderma i n th e s u r fa c e sedim ent i s a most u s e f u l t e s t o f p rob ab le co n tem p o ra n eity . S e d im en ta tio n r a t e s d e r iv e d from t h e s e d a ta w i l l be d is c u s s e d in a l a t e r s e c t i o n . S e d im e n ta tio n R ates There are many problem s in h e r e n t i n any a ttem p t to e s tim a te th e r a te a t which sedim ent accu m u lates i n an e n v ir o n ment. P a r t i c u l a r l y c r i t i c a l i s th e n e c e s s a r y assum ption o f c o n tin u o u s s e d im e n ta tio n in th e c o r e s s tu d ie d . U n le ss th e r e are d i s c r e t e " d is c o n fo r m itie s " shown b y , perhaps, a marked .change in the m ic r o fa u n a l p o p u la tio n or by a l a y e r o f a u t h ig e n ic m a t e r i a l, i t i s o f t e n im p o s s ib le to be c o m p le te ly c e r t a i n th a t a g iv e n core has an unbroken seq u en ce. Mixing by b e n t h ic burrowers te n d s to r a p i d l y d e s t r o y w h atever e v i dence t h e r e m ight be o f an h i a t u s . The p i c t u r e i s f u r th e r co m p lic a te d by d i f f e r e n t i a l com paction and d ew aterin g o f the se d im e n ts and by random e le m e n ts such as t u r b i d i t e l a y e r s , r a f t e d d e b r i s , and th e p o s s i b l e a d d it io n or s u b t r a c tio n o f m a te r ia l by slum ping. In th e Gap a rea , t h e o n ly p o s s i b l e c r i t e r i a fo r th e s e l e c t i o n o f c o r e s fo r se d im e n ta tio n r a t e s t u d i e s are: ( l ) The sample must come from a p h y sio g r a p h ic a r e a where d is tu r b a n c e i s u n l i k e l y — n o t from a s te e p s lo p e , o r the f o o t o f a s l o p e , or th e a x i s o f a submarine ch a n n el, and (2) The sed im en t c h a r a c t e r i s t i c s w ith in t h e core sh ould in g e n e r a l be f a i r l y u n iform . No sudden, i n e x p l i c a b l e v a r i a t i o n s can be a c c e p te d . Cores from th e b a s in , th e deeper p art o f the Santa R osa -C ortes R idge, and the P a tto n R idge were s t u d ie d to determ ine at l e a s t r e l a t i v e r a t e s o f se d im e n ta tio n (T able 8 , P ig . 3 9 ). U n fo r tu n a te ly , no c o res from the r e g io n o f l a r g e - s c a l e t e r r e s t r i a l sand i n f l u e n c e n ea r the i s l a n d s were judged s u i t a b le f o r r a te d e t e r m in a tio n s . A l l c a l c u l a t i o n s a r e based on the assum ption th a t th e p o in t where th e c o i l i n g r a t i o o f the G lo b ig e r in a pachyderma p o p u la tio n dropped below 50 p e r c en t d e x t r a l was 11,000 y e a r s ago. Por com parison, the ta b le a l s o i n c lu d e s se d im e n ta tio n r a t e s determ ined e l s e - 184 T A B L E 8 SEDIMENTATION RATES IN TH E VICINITY OF SAN MIGUEL G AP S ed im en tation Depth Rate (m) D atin g Method y rs/cm mm/lO3 y rs R eferen ce S ta . No. L o c a lity 10106 San M iguel Gap., Santa R osa- C ortes Ridge 10116 San M iguel Gap, e a s t end o f B asin IO5 6 I San M iguel Gap, C en tra l B asin JD2 San M iguel Gap, Santa R osa- C ortes Ridge JD3 San M iguel Gap, P a tto n Ridge 4700 Santa Cruz B asin 4701 Santa Barbara B asin 4696 Tanner B asin 4697 C o n tin en ta l Slope 4698 "Deep Sea" o f f Southern C a li fo r n ia 660 C o ilin g r a t io s 7 8 6 13 o f G. pachy derma 1532 C o ilin g r a t io s 3 2 3 31 o f G. pachy derma 2120 C o ilin g r a t io s 186 54 o f G. pachy derma 719 C o ilin g r a t io s 733 14 o f G. pachy derma 1 7 8 9 C o ilin g r a t io s 646 15 o f G. pachy derma 1 9 6 6 C o ilin g r a t io s 30 333 o f G. pachy derma 6 2 7 C o ilin g r a t io s 5 2000 o f G. pachy derma 1551 C o ilin g r a t io s 49 204 o f G. pachy derma 1674 C o ilin g r a t io s 180 55 o f G. pachy derma 3752 C o ilin g r a t io s 2 8 9 34 o f G. pachy- derma T h is stu d y T h is study T h is study H ackett 1965 H ackett 1965 Bandy i 9 6 0 Bandy i 9 6 0 Bandy i 9 6 0 Bandy i 9 6 0 Bandy i 9 6 0 Fig. 39•--Sediment c h a r a c te r is tic s in cores. 185 JD 3 COMPOSITION (%) % D EXTRA L 121*0 0 ' (20 *4 0 ' 120*20 ' 34*00 361 10116, 10361 COMPOSITION {%) %DEXTRAL 100 10116 JD 2 COMPOSITION (%) %DEXTRAL COMPOSITION (%) "ADEXTRAL 100 LEGEND E M I T errestrial S an d m Glauconite □ O rganic Sand H sin |;S f:| Clay %DEXTRAL = ■ P e rce n ta g e right-coiled (temperate) G lo b ig a r in a p a c h y d e rm a I — 1 00 CT\ DEPTH IN CORE (CM) 187 where in the b ord erla n d and f a r t h e r o f f the sou th ern C a l i f o r n ia c o a s t (Bandy, i 9 6 0 ). The most ra p id se d im e n ta tio n in the Gap area o c c u r s in the c e n t r a l b a s in . I f a l l the n e c e s s a r y assum p tion s have been s a t i s f i e d , se d im e n ta tio n i s a c t u a l l y fo u r tim es f a s t e r in th e b a s in than on th e surrounding slo p e and r i d g e s . The se d im e n ta tio n r a t e s determ ined in San M iguel Gap are more c l o s e l y comparable to the v a lu e s ob served on the c o n t i n e n t a l s lo p e and in th e deep sea than to th o s e o f th e in s h o r e b a s i n s . V a r ia tio n in se d im e n ta tio n r a t e s w ith in the Gap area i s n ot s u r p r is in g , c o n s id e r in g the a p p r e c ia b le v a r i a t i o n s known in the sedim entary a g e n c ie s o f the a r ea . The data may be f u r t h e r a b s t r a c te d to y i e l d e s t im a t e s o f th e accum ulation r a t e s o f th e p r i n c i p a l sedim ent c o n s t i t u e n t s (Table 9 )- These c a l c u l a t i o n s are made by f i r s t e lim in a t in g a l l the random sedim ent i n the core above the e s t a b l i s h e d datum, t o t a l i n g th e r e l a t i v e freq u en cy o f each c o n s t i t u e n t in the core segm ent, and f i n a l l y d i v i s i o n by th e tim e span. This p r o c e s s y i e l d s a r a th e r s p e c u l a t i v e accu m u lation r a t e , b u t i s a f ig u r e which s e r v e s as a meas ure o f the r e l a t i v e p o te n c y o f a sedim entary agency i n the d i f f e r e n t s u b r e g io n s. Accum ulation r a t e s were computed fo r the two most c o n s i s t e n t and r e l i a b l e c o r e s s tu d ie d , one from th e "green mud" area o f th e c e n t r a l b a s i n , . the o th e r in th e g l a u c o n i t e - r i c h sedim ent o f the t e r r a c e on the fla n k o f th e Santa R o sa -C o rtes R idge. There i s l i t t l e s i m i l a r i t y 188 T A B L E 9 BATES O F ACCUM ULATION O F TH E M A JO R SEDIM ENT CONSTITUENTS, SAN MIGUEL GAP AREA A ccum ulation (mm/lO3 y e a r s ) Sand F o ram in ifera Core L o c a lity Sedim ent Type Clay A uthi- S i l t O rganic g e n ic -T erres t r i a l P lan k - to n ic Ben- th o n ic 10361 C en tral B asin Green mud 1 2 2 2 . 5 1 1 . 0 1-5 3 .5 6 . 0 3-5 1 0 1 0 6 Santa R osa- C ortes Ridge G la u co n itic sand 1 . 1 2 .5 3 .8 5 .6 0 . 8 1 . 7 2 .0 In a ccu m lation r a t e s o f any o f the major c o n s t i t u e n t s b e tween th e two a r e a s . This i s a c le a r r e f l e c t i o n o f the d i f f e r e n t a g e n c ie s th a t c o n t r o l se d im e n ta tio n in d i f f e r e n t . p a r t s o f the Gap r e g io n . I f the c a lc u l a t e d se d im e n ta tio n r a te fo r the c e n t r a l b a s in i s a c c e p te d as v a l i d o v e r a c o n s id e r a b le span o f g e o l o g i c tim e, a n oth er i n t e r e s t i n g c a l c u l a t i o n may be made. From th e a c o u s t i c r e f l e c t i o n s t u d i e s , u s in g a sedim ent v e l o c i t y o f 2 km /sec, the maximum t h ic k n e s s o f " p o st-o r o g e n ic " sed im en ts i s a p p ro x im a tely 270 m, th e maximum o f " p re -o ro - g en ic" i s som ething in e x c e s s o f 400 m. Taking th e c a l c u l a t e d se d im e n ta tio n r a te o f 50 mm/lO^ y e a r s , t e n t a t i v e e s t i m ates may be made o f the time r e q u ir e d to f i l l the b a s in w ith sedim ent to i t s p r e s e n t l e v e l . Assuming a c o n sta n t sed im en tary regim e through th e Late C en ozoic, i t may have 189 taken 5 «^ x 10^ y e a r s to d e p o s i t th e p o s t - o r o g e n i c sed im en t and an a d d i t i o n a l 8 x 10^ y e a r s to a ccu m u late th e p r e - o r o - g e n ic m a t e r i a l . There i s , o f c o u r s e , no way to a s s e s s th e tim e span r e p r e s e n t e d by th e s l i g h t u n c o n fo r m ity betw een th e two c y c l e s o f s e d im e n ts . The tim e e s t i m a t e s th u s p la c e th e m inor o r og en y a p p r o x im a te ly i n th e Late P lio c e n e ., and th e i n i t i a t i o n o f s e d im e n t a t io n ( i f th e o r o g en y was o f s h o r t d u r a tio n ) m ight have o c c u r r e d a t ab ou t th e M io c e n e - P lio c e n e boundary. The Sed im en tary Regime o f San M iguel Gap The se d im e n ta r y regim e o f an a r ea i s th e complex p h y s i c o - c h e m i c a l b u d g e t o f th e t o t a l m a t e r i a l and e n e rg y i n v o l v e d in th e e n v ir o n m e n t. I f a l l p o s s i b l e components, o f ' such a s y s te m were to be c o n s id e r e d , th e r e s u l t would be to o com plex f o r r a t i o n a l a n a ly s is ., b u t in m ost s i t u a t i o n s o n ly a l i m i t e d number o f p r o c e s s e s have m easu ra b le i n f l u e n c e . These p r o c e s s e s can be d i v i d e d i n t o two c a t e g o r i e s , p r o c e s s e s t h a t c o n t r o l th e p r o d u c tio n o f se d im e n ts and p r o c e s s e s w hich c o n t r o l th e d i s t r i b u t i o n o f s e d im e n t s . There are t h r e e p r i n c i p a l ways in w hich sed im e n t i s g e n e r a t e d i n th e Gap a r ea : ( l ) By th e e r o s i o n o f p r e e x i s t i n g r o c k s , p r i m a r i l y around th e w e ste r n Channel I s la n d s , b u t a l s o on th e m ainland; (2) By th e o r g a n ic p r o d u c t i o n o f s m a ll s h e l l e d o r g a n ism s, e i t h e r among th e p la n k to n or on the bottom; o r , ( 3 ) By a u t h i g e n e s i s o f th e m in era l g l a u c o n i t e , a p p a re n tly by the rem oval and r e c r y s t a l l i z a t i o n o f suspended or c o l l o i d a l c la y s from th e w ater column. The , r e l a t i v e magnitude o f th e s e s e d im e n t- c o n tr ib u to r s in each s e c t i o n o f th e Gap has been determ ined, and can be e x p r e sse d as a p e r c e n ta g e o f the t o t a l accu m u latin g sedim ent (Table 1 0 ). Each p r o c e s s must be r e l a t e d to i t s own s e t o f con t r o l l i n g c ir c u m sta n c e s . TABLE 10 RELATIVE CONTRIBUTIONS OP PRINCIPAL SEDIMENT CONSTITUENTS, SAN MIGUEL GAP AREA R egion C o n trib u tio n T e r r e s t r i a l Organic W A u thigen ic; Santa R o sa -C o rtes Ridge 50 42 7 C en tra l B a sin 76 22 2 Deep s l o p e s and t e r r a c e s 30 27 42 Both e r o s io n and d i s t r i b u t i o n o f th e c o a rse t e r r e s t r i a l m a t e r ia l in th e Gap, p r im a r ily d e r iv e d from the i s l a n d s , are a ccom p lish ed m ainly by wave a c t i o n . The waves a t t a c k the shore l i n e , and, to g e th e r w ith g r a v i t y , th ey c o n t r o l s e d i ment movements on th e s h e l f . As n oted e a r l i e r , th e waves th e m se lv e s are l a r g e l y l o c a l l y g e n e r a te d by the b r i s k p r e v a i l i n g n orth w est w ind s. A lthough f i n e t e r r e s t r i a l d e t r i t u s , s i l t and c l a y , occu r in q u a n tity o n ly in th e b a s in o f th e Gap, th e volume o f such m a t e r ia l i s c o n s id e r a b ly g r e a t e r j 191: than th a t o f th e o th e r se d im e n ts. I t i s l i k e l y th a t t h i s f i n e m a te r ia l r e p r e s e n t s p r im a r ily w in d -tra n sp o rted d e b r is from the m ainland. The I s la n d s , ex cep t where th ere has been very r e c e n t o v e r g r a z in g , have a t h ic k v e g e t a t io n c o v e r ;’ many p a r ts o f mainland C a lif o r n ia , however, are s e m i-d e s e r t, w ith sc a n ty cover and l i t t l e su r fa c e r u n - o f f to carry s e d i ment to the se a . Such an area i s p a r t i c u l a r l y v u ln er a b le to a e o lia n e r o s io n and d u st and sand storms are f a i r l y com mon. C on siderab le q u a n t i t i e s o f f i n e sedim ent are c a r r ie d to sea during the p e r io d ic Santa Ana w inds. Most o f the o rga n ic f r a c t i o n o f th e Gap sedim ents o c cu rs as the c a lc a r e o u s s h e l l s o f fo r a m in if e r s , both plan k- t o n ic and b e n th o n ic . F o ra m in ifer s, and the o th e r q u a n t it a t i v e l y im portant o rga n ic sedim ent c o n tr ib u to r s , the sponges, r a d i o la r i a n s , m o llu sk s, and echinoderm s, are a l l d i r e c t l y or i n d i r e c t l y dependent upon produ ction among the phytoplankton o f the su rfa ce w a te r s. These t i n y p la n t s are th em selv es very d i r e c t l y c o n t r o l l e d by the a v a i l a b i l i t y o f s o la r energy f o r p h o to s y n th e s is and o f the f e r t i l i t y o f th e w a ters, the c o n c e n tr a tio n s o f a v a ila b le ph osp hate, n it r o g e n , and s i l i c a . The c h a r a c te r o f the w aters and n o ta b ly t h e i r pronounced se a so n a l v a r i a b i l i t y are a fu n c tio n o f the l o c a l ocean o g ra p h ic environm ent. C o n trols upon the p rod u ction o f g la u c o n it e are more d i f f i c u l t to d e f in e . The ev id en ce i n d i c a t e s th a t i f th ere i s a supply o f suspended c la y s , a s u i t a b le s u b s t r a t e , and p a r t i c u l a r l y a v ery low r a te o f su p p ly o f o th e r sedim ents., g l a u c o n i t e w i l l form. A u t h ig e n e s is o f g l a u c o n i t e as o b served in the Gap area appears to fo llo w th e se ' s t e p s : (1) C o l l o i d a l c la y p a r t i c l e s e n t e r , e i t h e r through the a p e r tu r e or through p o r e s , th e s h e l l s o f sm a ll dead orga n ism s, (2) W ithin the m icro-en vironm ent o f the s h e l l s , r e c o g n iz a b le g l a u c o n i t e d e v e lo p s by r e a c t io n w ith sea w ater or i n t e r s t i t i a l w a ters and by r e c r y s t a l l i z a t i o n , and ( 3 ) The most t y p i c a l g l a u c o n i t e p e l l e t s seem to have been c o n s o lid a t e d as the f a e c a l p e l l e t s o f burrowing o rg a n ism s. The u lt im a t e sou rce or m in era logy o f th e c la y s does n ot appear to be c r i t i c a l , nor do c o n d it io n s in the w ater column, e x c e p t as th e y may in f l u e n c e the a v a i l a b i l i t y o f th e r e q u ir e d sub s t r a t e and th e a c t i v i t i e s o f b e n th ic org an ism s. C le a r ly , to su pp ort the b e n th ic c r e a t u r e s , the bottom w a te r s must have a r e a so n a b le c o n c e n tr a tio n o f d i s s o l v e d oxygen. P er haps th e most im portant f a c t o r in the developm ent o f g la u c o n i t e - r i c h sed im en ts i s n e g a t iv e : accu m u lation o f o th e r sorts! o f sedim ent must be a t a v ery low r a t e . Even more than su p p ly, d i s t r i b u t i o n o f sed im en ts in the Gap area i s under the c o n t r o l o f ocean ograp h ic a g e n c ie s . This i n f l u e n c e may be d i r e c t and o b v io u s, the wind, wave, o r: cu r re n t tr a n s p o r t o f d i s c r e t e sedim ent p a r t i c l e s . On th e o th e r hand, perhaps o f eq u a l im portance, are some more su b t l e ocean ograp h ic i n f l u e n c e s upon the sed im en t, th e movement; o f d i s s o l v e d and suspended m a t e r ia ls which may r e a c t or 193 p r e c i p i t a t e to produce sedim ent or which may serve l o c a l l y to enhance o rg a n ic p r o d u c t iv it y . D ir e c t wind and wave a c t io n s i g n i f i c a n t l y in f lu e n c e the c o a r se r sedim ents o n ly in a r e s t r i c t e d p o r tio n o f the Gap r e g io n . On the I n s u la r S h e lf , undoubtedly the waves both produce and d i s t r i b u t e the sedim ent. Small q u a n t i t i e s | o f a e o lia n sand are c a r r ie d in t o the Gap d i r e c t l y from the dune f i e l d s o f San Miguel I s la n d . Less ob viou s b u t prob a b ly more im portant in the sedim entary regim e i s th e i n t r o d u ctio n o f f i n e t e r r e s t r i a l debris., s i l t and c la y , in t o the s u r fa c e w a ters o f th e borderland from the C a lif o r n ia d e s e r t s by Santa Ana w inds. I t i s im p o ss ib le to d is c r im in a te the source o f v e ry f i n e sedim ents w ith any p re cisio n ,, but by i n f e r e n c e , a e o lia n tr a n sp o r t must be im portant. Because o f the l o c a l c lim a te and physiography, r e l a t i v e l y l i t t l e s e d i ment i s In trod uced i n t o the sea o f f southern C a lif o r n ia by r u n o f f. As noted e a r l i e r , "dust" from the Santa Ana winds i s d e p o s ite d from the atmosphere a l l over the b orderlan d, and thus e n te r s the su r fa c e water c i r c u l a t i o n . Rodolfo (1964) has dem onstrated th a t la rg e q u a n t i t i e s o f suspended sedim ent may occur in the su r fa c e w aters o f f C a lif o r n ia , but the data are n ot s u f fic ie n tly ^ com plete to perm it r a t i o n a l e s tim a tio n o f the volumes involv<3% \ A eo lian m a te r ia l i s too \\s- V ; ’ v\- f i n e to accumulate on the c u r re n t-sw ep t r id g e s and thus must p r im a r ily be d e p o s ite d in t h e c e n tr a l b a s in . ± 9 ^ Perhaps the most s t r i k i n g ocean ograp h ic agency which i n f l u e n c e s th e sed im en ts o f th e Gap are su r fa c e c u r r e n ts . There i s a str o n g c o n t r a s t "between se a so n s in the r e g io n . In sp rin g and summer, the area i s dominated by th e so u th - flo w in g C a l i f o r n ia C u rren t, which i s very low in suspended sed im en ts b u t c u sto m a r ily a s s o c i a t e d w ith e x t e n s i v e u p w e ll- in g , which f e r t i l i z e s th e e u p h o tic zone. For fou r o r f i v e months in th e f a l l and w i n t e r * th e Davidson Current a p p ears. T his n o r th -flo w in g c u r re n t i s r e l a t i v e l y i n f e r t i l e . , but has : had an o p p o r tu n ity to r e c e iv e q u a n t i t i e s o f wind-blown s e d i ment over th e b o r d erla n d . Thus th e su r fa c e c u r r e n ts tend to expose the Gap area a l t e r n a t e l y to both o c e a n ic and co n t i n e n t a l i n f l u e n c e s . Bottom c u r r e n ts are a ls o im portant in th e sedim entary regim e o f the Gap. C urrents which average ap p ro xim ately 5 cm /sec and which o f t e n reach 20 cm /sec have been measured ■ on A r g u e llo P la te a u . Judging from the s i m i l a r i t y o f the sediments., e q u iv a le n t c u r r e n ts probab ly occu r on the o th e r r i s e s surrounding th e c e n t r a l b a s in . Such c u r r e n ts are cap a b le o f markedly in f l u e n c in g the bottom sedim ent d i s t r i b u t i o n . In theory., a flow o f 5 cm /sec can tr a n s p o r t qu artz g r a in s as c o a r se as 500 g In median diam eter; a cu r re n t o f 20 cm /sec i s capable o f ero d in g such g r a in s (H julstrom , 1939; Sundborg, 1 9 5 6 ). T his s i z e i s c o n s id e r a b ly c o a r se r than most o f the sands o f the Gap a r e a . Presumably, s e d i ment can accum ulate in the c u r r e n t-sw e p t a rea s b eca u se o f | 195 the roughness o f th e-b ottom and v a r i a b i l i t y o f the c u r r e n ts . Fine sedim ents are sca rc e in the a rea s o f a p p r e c ia b le c u r r e n ts ; i t i s obviou s th a t th e re must be c o n sid e r a b le winnow in g . The t e r r e s t r i a l sands d i s t r i b u t e d a c r o ss A rg u ello P la teau can probably a ls o be a t t r ib u t e d to bottom c u r r e n ts. A deep cu rren t s e t t i n g toward the w est i s a permanent fe a tu r e o f c i r c u l a t i o n in Santa Barbara Channel. This cu rren t i s i n t e n s i f i e d during th e season o f Davidson Current i n f l u e n c e . G eostrop hic com putations s u g g e s t th a t the deep cu r re n ts have; a v e l o c i t y o f a t l e a s t 20 cm /sec. Such cu r re n ts are p e r f e c t l y capable o f tr a n sp o r tin g medium and f i n e sand. I t i s su g g ested th a t f i n e sands o f th e mainland Santa Barbara s h e l f are moved westward p a s t P o in t C onception, and, under the in f lu e n c e o f the c u r r e n ts and g r a v it y , form a sh a rp ly d e fin e d f a l l - o u t zone which exten d s to the c o n t in e n t a l s lo p e . Undoubtedly, th e e d d ie s develop ed by the i n t e r a c t i o n o f the c u r r e n ts o f f P o in t Conception con'cribute to the l o s s in competence cau sin g d e p o s itio n o f th ese sed im en ts. The bulk o f f i n e d e t r i t u s in the Gap r eg io n o ccu rs in the c e n t r a l b a s in . This m a te r ia l undoubtedly i n c lu d e s the s i l t and c la y which was not ab le to s e t t l e ou t on the r i s e s . I t i s l i k e l y th a t th e mechanism o f tra n sp o rt in v o lv e d i s the "turbid layer" cu rren t proposed by Moore ( 1 9 6 5^1 9 6 6) and Vernon ( 1 9 6 5) . On a normal s h e l f , the m ixture o f sand and f i n e r m a te r ia l in tro d u ced by a r i v e r i s f r a c t io n e d in q u ite sh a llo w w ater. The sand i s in c o rp o ra te d i n t o the l i t t o r a l tr a n sp o r t system and thus rea c h e s deep w a ter on ly by submarine canyons and g u l l i e s . The f i n e r m a te r ia l forms a su sp en sion which flo w s g r a d u a lly dow nslope, s lo w ly lo s in g sedim ent u n t i l i t i s f i n a l l y ponded by a l o c a l h ig h or d i s s ip a te d in the deep se a . In the Gap a rea , p a r t i c u l a r l y during the tim es o f Davidson Current a c t i v i t y , a c o n s id e r a b le amount o f f i n e sedim ent s e t t l e s ou t o f the su rfa c e w ater la y e r s and f in d s i t s way to the bottom . Prom the r id g e s and s l o p e s , th e f i n e s are co n c en tr a ted i n t o the s h e l t e r e d b a s in , where, though th ere i s no tru e s i l l , most o f th e d e b r is probably f a l l s o u t. R ecent experim en ts by Kuenen ( 1 9 6 5 ) i n d ic a t e th a t in c la y su sp en sion flow s o f 10 cm /sec or l e s s , d e s p it e th e t h e o r e t i c a l c a p a c it y o f th e c u r r e n t, a l l o f the m a te r ia l e v e n t u a lly comes to the bottom . Turbid l a y e r tr a n sp o r t o f f i n e i n i t i a l l y a e o lia n sedim ents probably a ccou n ts f o r a la r g e p r o p o rtio n o f the contemporary s e d i m entation in the o u te r b ord erlan d . As has been observed (G o rslin e and Emery, 1959; Emery, i 9 6 0 ) , the b orderlan d b a s in s are f i l l i n g a t a r a t e p r o p o r tio n a l to t h e i r d is ta n c e from the sh o re. The extrem ely low r a te o f se d im en ta tio n on the c o n t in e n t a l slo p e and in th e Gap i s c l e a r l y r e l a t e d to d is ta n c e from sh ore, and more p a r t i c u l a r l y , to th e amount o f l o c a l in f lu e n c e from the sed im en t-la d en southern C a lif o r n ia su r fa c e w aters o f the Davidson Current. The d i s t r i b u t i o n o f t e r r e s t r i a l sed im en t i n th e Gap i s c o n t r o l l e d by o c e a n o g r a p h ic f a c t o r s , e s p e c i a l l y th e s u r f a c e and deep c u r r e n t p a t t e r n s . B i o l o g i c se d im e n ts are r e l a t e d a l s o to th e c u r r e n t s and p a r t i c u l a r l y to th e c o n c u r r e n t phenomenon o f u p -w ellin g . The s p e c t a c u l a r d evelop m en t o f th e a u t h i g e n i c m in e r a l, g l a u c o n i t e , i s made p o s s i b l e by th e e l i m i n a t i o n o f o t h e r s e d im e n t s . There i s no q u e s t io n t h a t th e se d im e n ta r y regim e o f th e San M igu el Gap a r e a i s c o n t r o l l e d by th e l o c a l o cea n o g ra p h y . When s i m i l a r s u i t e s o f s e d im e n ts are d i s c o v e r e d in con tem p orary o r a n c i e n t o c c u r r e n c e s , th e c o n d i t i o n s w hich p r e v a i l a t th e Gap can be a s sumed to have c o n t r o l l e d th e l o c a l se d im e n ta r y r e g im e . CONCLUSIONS 1. San Miguel Gap i s a submarine b asin o f f P oint Conception a t the extreme northw estern corner o f the C a lif o r n ia c o n tin e n ta l borderland. 2. The Gap i s unique in th a t i t i n t e r s e c t s and breaches the c o n tin e n ta l slo p e to a depth o f over 2500 m, 3 . To the north and e a s t , the Gap i s bounded by ste e p s lo p e s , probably f a u l t s ; to the south the str u c tu r e i s u n cle a r but more l i k e l y i t i s a downfold r a th e r than a f a u l t . 4. Bedrock sampled in the Gap c o n s i s t s o f igneous and sedim entary rocks analogous to the Lower T e r tia r y sequence o f the Channel I s la n d s . The igneous rocks are predom inantly b a s a l t s and appear to have r e s u lt e d from submarine e x tr u s io n . 5. There are two g e n e r a tio n s o f sediment in the b a s in , as determined by a c o u s tic r e f l e c t i o n p r o f i l i n g . The o ld e r sequence, termed p reorogen ic sediment, has been g e n t ly fo ld e d , e s p e c i a l l y around the margins o f the Gap; the younger p o sto ro g e n ic sedim ents are un distu rb ed . 198 6 . Assuming an average sound v e l o c i t y in th e s e d i ments o f 2 k m /sec } the maximum th ic k n e s s o f p o s t - o r o g en ic sedim ent i s 270 m and the maximum t h i c k n e ss o f p reo ro g en ic sedim ent i s g r e a te r than 400 m. 7. The g e o lo g ic h i s t o r y o f the r e g io n i s s i m i la r to th a t o f the c o n t in e n t a l b ord erlan d . San M iguel Gap was formed in the Late Miocene and h as been r e l a t i v e l y q u ie s c e n t s in c e . 8 . As a contemporary sedim entary environm ent, the Gap i s an e lo n g a te c o n t in e n t a l slo p e j open to the deep sea on the w e st. 9. Sedim ents on the s h e l f and slo p e o f the I n s u la r and Santa R osa-G ortes Ridge su bregion are t e r r e s t r i a l sands grading in t o c la y e y s i l t and s i l t y c la y in the Gap b a s in . 10. On the deeper r id g e s and s lo p e s o f the Gap area, th e c h a r a c t e r i s t i c sedim ent i s a fo r a m in ife r a l g l a u c o n i t i c sand. The c o n c e n tr a tio n o f g la u c o n i t e i s i n v e r s e l y p r o p o r tio n a l to the r a te o f se d im e n ta tio n . 11. I t i s l i k e l y th a t contemporary a u th ig e n ic g la u c o n i t e i s forming in the r e g io n . A p o s s i b l e e v o lu t io n a r y sequence o f g la u c o n it e ty p e s has been r ec o g n ize d : a) Y e llo w ish brown c la y s found w ith in sm all s h e l l s ( e s p e c i a l l y fo r a m in if e r a l t e s t s ) ; ; a p p a r e n tly a p r e cu rso r o f tru e g l a u c o n i t e . b) Very p a le g r e e n is h m a t e r i a l found as f i l l i n g s and i n t e r n a l molds o f sm a ll s h e l l s . c) Medium green t y p i c a l g l a u c o n i t e o f o b v io u s o r g a n ic a f f i n i t i e s , found as i n t e r n a l m olds or a s f i l l i n g s o f broken t e s t s . d) Medium to dark green o v o id or i r r e g u l a r p e l l e t s o f g l a u c o n i t e , o f t e n w ith pronounced d e s - s i c a t i o n c r a c k s . T his form i s th e c l a s s i c " g la u c o n ite p e l l e t " and may r e p r e s e n t f a e c a l p e l l e t s . e) Dark green to b la c k , o f t e n p o l i s h e d , i r r e g u l a r p e l l e t s , a l s o showing d e s s i c a t i o n c r a c k s. 12. I f the sequence o f g l a u c o n i t e ty p e s i s t r u l y g e n e t i c , i t i s p rop osed th a t g l a u c o n i t e in t h i s e n vironm ent d e v e lo p s as f o l lo w s : a) I n i t i a l p r e c i p i t a t i o n ( a u t h i g e n e s i s ) o f c l a y s from sea w ater w ith in th e t e s t s o f sm all orga n ism s. b) Gradual developm ent to t y p i c a l g l a u c o n i t e w it h in the m icroen vironm ents o f f e r e d by th e s h e l l s . Presumably b a c t e r i a l decay o f p r o t o plasm w i l l r e s u l t in r ed u cin g c o n d it io n s w ith in the s h e l l s . 2 0 1 g) As d ia g e n e s is p r o c ee d s, the e n c lo s in g s h e l l s become weakened and tend to crumble. This p r o c e s s i s a c c e le r a t e d by passage through the gu ts o f m ud-eating organism s. d) The commonest form o f g la u c o n it e in the s e d i ments (typ e "d"), probab ly r e p r e s e n t s f a e c a l p e l l e t s , e n r ich ed in g la u c o n it e by the d i s s o l u t i o n o f CaCO^ and SiOg w ith in the g u ts o f m ud-eating organism s such as echinoderm s and p o ly c h a e te worms. e) A d d itio n a l c la y s may p r e c i p i t a t e on the su r fa c e s o f formed g r a in s , to produce the p o lis h e d e f f e c t sometimes seen . 1 3 . The Gap a r ea can be d iv id e d in t o th r ee p r i n c ip a l sedim entary subareas; w ith in th e s e , r e l a t i v e con t r i b u t i o n s o f the major sedim ent c o n s t i t u e n t s were determ ined: a) Santa R osa-C ortes R idge-~50 p e r c e n t T e r r e s t r i a l , 42 p e r c e n t O rganic, 7 p e r c e n t A u th i- g e n ic . b) C entral B a s in --7 6 p e r ce n t T e r r e s t r i a l , 22 p e r cent O rganic, 2 p e r ce n t A u th ig en ic. c) Deep s lo p e s and t e r r a c e s - - 3 0 p e r ce n t T e r r e s t r i a l , 27 p e r ce n t O rganic, 42 p e r ce n t A u th i gen ic . 2 0 2 14. S ed im en tation r a t e s range from 13-15 mm/10^ y e a r s on the deep s lo p e s to 31 mm/10^ y e a r s a t the head o f the b a s in and 54 mm/10^ y e a r s in the c e n t r a l b a s in . A l l d a te s u sed in t h i s stu d y are based upon the s i n i s t r a l to d e x t r a l c o i l i n g d i r e c t i o n s h i f t in the s h e l l s o f th e fo r a m in ife r s G lo b ig er in a pachyderma, a t the end o f th e P l e i s t o c e n e . 15. Both sedim ent p r o d u ctio n and d i s t r i b u t i o n in the San Miguel Gap area can be r e l a t e d to o cea n o graphic a g e n c ie s : a) The c o a r s e r t e r r e s t r i a l d e b r is (62 m- median diam eter) i s d e r iv e d p r im a r ily from the Channel I s la n d s ; i t i s eroded and tr a n sp o r te d m ainly by wave a c t i o n . "b) S i l t s and c la y s j l a r g e l y d e r iv e d from the mainlands are c o n t r o l l e d by winds., su rfa c e and bottom c u r r e n ts . They are c o n c e n tr a te d by tu r b id la y e r flow in the c e n tr a l b a s in . c) F o r a m in ife r a l abundance in th e sedim ents i s a fu n c tio n o f s u r fa c e o rg a n ic p r o d u c t iv it y and bottom c u r re n t winnowing. d) G la u co n ite i s u b iq u ito u s in the r eg io n s but i s a major c o n s t i t u e n t o f the sedim ent o n ly where o th e r d e p o s it io n I s i n h i b i t e d . ..................203 16. The oceanography o f the Gap reg io n i s d i s t i n c t i v e ; t h i s i s a p o in t o f maximum v a r ia tio n in th e North P a c i f ic c i r c u l a t i o n p a tte r n , where there i s an a b so lu te se a so n a l r e v e r s a l in o cea n ic cu rren t d i r e c tio n and e x te n s iv e r e l a t e d u p w e llin g . 17. Gores which have p e n e tra te d to sedim ent o f Late W isconsin Age show r e l a t i v e l y l i t t l e v a r ia tio n in sedim ent c h a r a c t e r i s t i c s . 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F lem in g, 1942, The Oceans: t h e i r p h y s i c s , c h e m istr y and g e n e r a l b io lo g y ' ( P r e n t i c e - H a l l , New Y o rk ), 1097 p. T alw ani, M., X. Le P ich o n , J . R, H e i n t z l e r , 1965* E a st Pa c i f i c R i s e - - t h e m a gn etic p a t t e r n and th e f r a c t u r e zon es: S c ie n c e , v. 150, p. 1 1 0 9 -1 1 1 5 . T erry, R. D ., 1 9 6 5 * C o n tin e n ta l s l o p e s o f th e w orld : Unpubl. D o c to r a l d i s s e r t a t i o n . D ept. G eology , U n iv. So. C a l i f . , 648 p. T u lly , J . P. and F. G. B ark er, 1961, An e s t u a r i n e model o f th e s u b - A r c tic P a c i f i c Ocean, p. 4 2 5 -4 5 4 i n M. S e a r s, e d . , Oceanography (Am. A sso c , f o r Adv. S c ie n c e , W ashing to n , D.C .), 654 p. U chupi, E . , 1961, Submarine g e o lo g y o f the Santa R o sa -C o rtes R idge: Jour. Sed. P e t r o lo g y , v . 31, p. 5 3 4 -5 4 5 . U chupi, E. and K. 0. Emery, 1 9 6 3* The c o n t i n e n t a l s lo p e b e tween San F r a n c is c o , C a l i f o r n i a and Cedros I s l a n d , Mexico: D eep -Sea R e sea rch , v. 10, p. 3 9 7 -4 4 7 . V a c q u ie r , V ., 1959* Measurement o f h o r i z o n t a l d is p la c e m e n t a lo n g f a u l t s in th e ocean f l o o r : N atu re, v . 1 8 3 , p. 4 5 2 - 45 3. ■ - V a c q u ie r , V ., A. D. R a f f , and R. E. Warren, 1 9 6 1, H o r iz o n ta l d is p la c e m e n ts i n th e f l o o r o f th e n o r t h e a s t P a c i f i c Ocean: G eo l. Soc. America B u l l . , v. 72, p. 1 2 5 1 -1 2 5 8 . Vedder, J . G. and R. M. N o r r is , 1 9 6 3* G eology o f San N ic o la s I s la n d , C a l i f o r n ia : U.S. G eo l. Survey P r o f. Paper 3 6 9 * 65 p. Vernon, J . W., 1 9 6 5 * S h e l f sedim ent t r a n s p o r t system : Unpub. d i s s e r t a t i o n , Dept, o f G eo logy , U n iv. So. C a l i f . , 135 P. von Huene, R. and J. B. R id lo n , 1966, O ffsh o re g r a v i t y a n o m a lies in th e Santa Barbara Channel: J o u r . Geophys. R es., v. 71, P- 4 5 7 -4 6 3 . Weaver, D. W. and D. P. D oern er, 1 9 6 6, W estern A nacapia~~a summary o f th e C enozoic h i s t o r y o f th e n orth ern Channel I s la n d s : U npubl. m a n u sc rip t. D ept, o f G eology, U n iv . o f C a l i f . , Santa B arbara, 9 p. 215 Wilde., P ., 1965j E stim a tes o f bottom cu rren t v e l o c i t i e s from g ra in s i z e measurements fo r sedim ents from the Monterey D eep -sea fan* p. 718-727 in Ocean S c ie n c e and Ocean E n g in e e r in g - 1 9 6 5 : Trans. Marine Technology Soc. and Am. Soc. Limnology and Oceanography Conf., Washing to n , D.C. Wooster., W. S. and J. L. R eid, Jr.., 1963j E astern boundary c u r r e n ts , p. 253-280, in. M. N. H i l l , e d ., The Sea, v. 2 (J. W iley and Sons, N.Y.), 554 p. W right, E. P ., 1 9 6 3^ C o a sta l dunes o f southern C a lif o r n ia , P oin t Conception to Santa Monica: Unpubl. r e p o r t, Seminar in D e se rt G eology, D ept, o f G eology, U niv. So. C a l i f . , 15 p. _________ , 1 9 6 5^ Wave o b s e r v a tio n by shipboard radar, ~ pi 5 0 b -5 l4 in. Ocean S c ie n c e and Ocean E ngineering~1965j Trans. Marine Technology Soc. and Am. Soc. Limnology and Oceanography Conf., Washington, D.C., 14-17 June, 1965. Y erk es, R. P ., T. H. McCulloh, J. E. Schoellham er, and J . G. Tedder, 1 9 6 5^ Geology o f the Los A ngeles B a sin , C a lifo r n ia -~ a n in tr o d u c tio n : U.S. G eol. Survey P rof. Paper 4 2 0 -A, 57 P* Y oshida, Kozo, 1955 j C oa stal u p w e llin g o f f the C a lif o r n ia c o a s t and i t s e f f e c t s on p r o d u c t iv it y o f the -waters, p. 104-106 in. UNESCO Symposium on P h y s ic a l Oceanography: UNESCO and Japan Soc. fo r the Promotion o f S c ie n c e , Tokyo, 19-22 October, 1955 j 292 p. A P P E N D I C E S 2 1 6 » APPENDIX I 217 2 1 8 S A M P L E ST A T IO N S IN T H E S A N M IG U E L G A P R E G IO N S ta tio n 3 , Numbers L ocation L a t. N. Long. W . Depth (m) A rea* 3 Gear° Remarks IOO95 AHF 3 4 o0 0 'l8 " 1 2 0 °3 7 ' 2 0 " 1155- 9 1 0 I A S u rface sed im en t, no rock 1 0 0 9 6 AHF — 0 2 ' 3 0 " — 3 4 ' 1 8 " 3 1 8 - 2 1 1 I A S u rface sed im en t, no rock 10097 AHF — 0 3 ' 4 2 " — 3 1 145" H O - 8 3 I A Large phosphate nodule 1 0 0 9 8 AHF — 0 8 ' 1 0 " — 3 5 ’0 0 " 92- ? I A L ost dredge 1 0 0 9 9 AHF 3 3 °5 5 '28" — 33'30" i4 8 6 I I I C ( 7 0 0 ) C ore, 121 cm 1 0 1 0 0 AHF — 5 6 ' 0 5 " — 32'33" 1114 I C ( 7 0 0 ) Core, 142 cm 1 0 1 0 1 AHF — 5 6 '5 5 ” — 3 1 * 2 5 " 733 I C . ( 7 0 0 ) Core, l l 8 cm 1 0 1 0 2 AHF — 5 6 ' 5 0 " — 3 0 ’0 0 " 3 6 7 I c ( 7 0 0 ) Core, 5 cm el The l e t t e r d e s ig n a tio n w ith each sample number in d ic a t e s so u rce: AHF, A lla n Hancock F oundation (USC); D, sam ples c o lle c t e d fo r t h i s stud y from USNS D avis Ly USNOTS p e r so n n e l; JD and M H, sam ples fu r n ish e d by USNCEL. ^Area c o d e : I - In su la r Ridge and Santa R osa-C ortes Ridge I I - P a tto n R idge and Escarpment I I I - San M iguel Gap (B a sin ) IV - A rg u ello P la tea u and Escarpment Sam pling Gear: A ~ S in g le p ip e dredge B - Double p ip e dredge C - G ravity core (w eigh t em ployed, l b s . ) 5*5 cm I .D . D - P is to n co re (w eight em ployed, l b s . ) 5 . 5 cm I.D . E - Shipek Sampler F - NOEL Su rface Sedim ent Grab G - P h leg er C ore, 3-5 cm I.D . 2 1 9 SAMPLE STATIONS IN THE SAN MIGUEL GAP REGION— c o n tin u e d S ta tio n ' a L ocation Depth Numbers L at. N. Long. W . (m) Area Gear Remarks 1 0 1 0 5 AHF 10104 AHF 10105 AHF 1 0 1 0 6 AHF 1 0 1 0 7 AHF 1 0 1 0 8 AHF 10109 AHF 1 0 1 1 0 AH F 1 0 1 1 1 AHF 10112 AHF 1 0 1 1 5 AH F 10114 AH F 1 0 1 1 5 AHF 1 0 1 1 6 AHF 1 0 1 1 7 AHF 5 5 °4 9 ' 2 8 ” 1 2 0 o2 9 ’2 6 " 1 7 0 6 i l l — 4 9 ’59" — 2 6 ’49" 1 5 0 5 I I I 5 0 ' 0 0 " — 2 5 ' 0 0 ” 9 1 8 — 5 0 ' 5 0 " — 2 0 ' 5 0 " 6 ’ 6o 5 1 ' 0 0 ” 4 l'5 0 " 4 5 1 4 5 " 45'56” 4i'2 8” 45'58” 45'45" 4 7 ' 5 0 " 47' 54" 4 7'10” — 1 6 T 1 2 " 5 5 0 1 — 5 9 ’48” 1 0 1 5 1 1 — 5 1 ' 45 " 1284 11 — 5 2 ' 5 8 " 1 6 6 9 1 1 — 5 7 ' 5 6 " 1404 I I — 5 5 ’15" 1211 II — 2 7 '5 4 ” 1 5 6 5 III — 2 8 ' 5 6 " 1 7 2 1 I I I — 2 9 ’i4" 1 6 8 8 i n — 2 6 ' 5 0 " 1 5 5 2 III C (TOO) C ( 7 0 0 ) c (7 0 0 ) c ( 7 0 0 ) c (TOO) c (5 0 0 ) c ( 5 0 0 ) c (5 0 0 ) c (5 0 0 ) 5 1 * 5 0 " — 2 5 ’ 0 0 " 9 1 8 I I I c ( 5 0 0 ) c (5 0 0 ) c (5 0 0 ) c (5 0 0 ) c (5 0 0 ) Core, 155 cm Core, 1 8 5 cm Core, 122 cm Core, 50 cm Core, 12 cm (con s o lid a te d s e d 't ) Core, 122 cm Core, 114 cm Core, 118 cm Core, 124 cm Su rface sed im en t, no rock Core, 9 2 cm Core, 5 cm Core, 174 cm Core, 191 cm Core, 5 cm 2 2 0 SAM PLE STATIONS IN THE SAN MIGUEL GAP REGION-—c o n tin u ed Location Depth Station Numbers Lat. N. Long. W. (m) Area Gear Remarks 1 0 1 1 8 A H F 10119 A H F 10120 AH F 10121 A H F 10122 AHF 10123 AH F 33°51'26" 12 0 o23'50" 7 8 0 - I 715 10124 AHF 10339 A H F 10340 A H F 10341 A H F 10342 A H F 56'30" 54'56" 56'00" 53'08" — 50'02" — 4 2 ’45" — 4 l , 09" — 4o '30" 23'06" 16'57" 16' 30" 330- 2 9 3 2 5 7 - 1 9 3 1 7 5 - 92 1 7 1 4 5 " 5 8 5 . 330 50!o6" — 15'20" 550- 1 51^ 11'15" 4o4- 1 348 — 58'09" 3417 IV 53’50" 2644 iv 53'06" 2386- IV 1872 4l ' 45" — 51'30" 1284 iv A Plentiful rock- che rt, pho sphor- ite, volcanics, surface sediment A No rock — surface sediment A No rock - surface sediment A Plentiful rock - ? basalt. Surface sediment and sedi mentary rock A Plentiful rock - surface sediment A Plentiful rock, volcanics and pho sphorit e, surf. sediment and sedi mentary rock A Plentiful rock - volcanics and phosphorite gabbro. no sed1t. G Manganese crust (700) fragment s C Fragments of (700) volcanic rubble B Plentiful rock ~ basalt surface sediment C Few fragments of (700) weathered volcanic debris, tar, sponge fragment s 2 2 1 SAM PLE STATIONS IN THE SAN MIGUEL G A P REGION— co n tin u ed S ta tio n L ocation Depth. ^ Numbers L at. N. Long. W . (m) Area Gear Remarks 103^5 33°45*55" 1 20°53*12" 1321 IV E No sample A H F I 0 3 I& — 45*29" — 48*13" 1 3 7 6 IV E No sample AH F 1 03^ 5 — 40'30" — 4 1 ’ 15" 1211 I I E Surface sedim ent AH F 10346 — 41'20" — 43'40" l4 6 8 - I I A S in g le la rg e pum- AH F 1211 ic e b ou ld er, sur fa c e sediment 1 0 3 4 7 3 4 °o 4 ’30" 121o0 6 ’00" 1 9 2 7 - IV B S a f t ie s broken but AHF 17^3 empty dredge r e covered 10348 — 01'30" 120°59'00" 1 6 5 1 - IV B P le n t if u l rock - AHF I I 3 8 v e s ic u la r b a s a lt su rfa ce sedim ent 10 349 — 06'30" — 53'30" 95b V E Surface sediment A H F 10350 — 05'53" — 47'16" 743 ■ V E Surface sedim ent A H F 10351 — 06'11" — 4 l'30" 716 V E Surface sedim ent AH F 1 0 3 5 2 — 0 6 115" — 3 5 ’33" 1 5 8 I E Surface sedim ent AH F 10353 — 01*26" — 3 2 '15" 312 I E Surface sedim ent A H F 1035^ — 5 6 * 1 2 " — 24*30" 239 I E Surface sedim ent A H F 10355 — 5 6 -0 0 " — 25*03" 275 I E Surface sedim ent A H F 10356 — 55'00" — 19*75" 220 I E Surface sedim ent A H F 2 2 2 SAM PLE STATIONS IN TEE SAN MIGUEL GAP REGION— co n tin u ed S ta tio n 8 , Numbers L ocation L at. N. Long. W . Depth (m) A k Area Gear0 Remarks 10357 A H F 3 4 °5 2 ‘06" 1 2 0 °2 1 ’0 0 " 697 I E Surface sedim ent 10358 AH F — 4 9 1 05" —■ 1 9 ' 1 2 " 6 6 1 I E Surface sedim ent 10359 A H F — 4 5 ' 3 2 " — 1 9 >32" 8 2 5 I E Surface sedim ent IO3 6O A H F — 4 5 148" — 1 9 '2 5 " 1055 I E Surface sediment IO3 6 I AH F 33°49'26" — ■ 4 3 '4o" 2 1 2 0 I I I D ( 5 0 0 ) Core, 195 cm 1 0 3 6 2 A H F — 4 9 ' 3 0 " — 3 3 ’1 2 " 1927 I I I D ( 5 0 0 ) Core, 125 cm - 10363 A H F — 42'00" — 3 3 ' 0 0 " 1138 II E Surface sedim ent 10364 AH F — 4 2 ’48" — 2 8 ’5 8 " 1 1 8 1 I I E Surface sedim ent IO365 AH F — 4 2 ’1 2 " — 2 3 ' 2 0 " 1 0 0 9 ■ I E No sample recovered IO3 6 6 AHF — 4 2 ’46" — 1 7 ' 2 8 " 972 I E No sample recovered 10367 AH F — 5 6 ' 3 2 " .— 1 7 ' 0 0 " 95 I E Surface sedim ent IO3 6 8 AH F — 5 5 '0 0 " — 1 6 ’0 0 " 184 I E Surface sedim ent IO3 6 9 A H F — 5 4 '3 6 " — 1 3 ’0 0 " 92 I E Surface sedim ent 1 0 3 7 0 — 53'24" — 0 8 ’0 0 " 83 I E Surface sedim ent A H F 223 SAMPLE STATIONS IN THE SAN MIGUEL GAP REGION— c o n tin u e d S t a t io n 3 Numbers L o ca tio n L a t. N. Long. W . Depth (m) A rea*3 Gear Remarks 1 0 3 7 1 AHF 3 3 ° 5 0 rU3" 1 2 0 °o 6 ' 1 1 9 I E S u rfa ce sed im ent 10372 AHF — 4 6 ' 5 0 " — 0 7 ' 0 4 " 459 I E S u rfa ce sed im ent D1 3 4 ° 0 3 , oo" — 4 2 .6 ' V F S u rfa ce sed im ent D2 — 0 7 . 1 ' — 4 2 .8 ' V G S u rfa ce sed im ent d4 — 05' — 4 5 ’ V F S u rfa ce sed im ent D5 — 0 4 . 3 ' — 4 o . 5 ' ¥ G S u rfa ce sed im ent D 6 33'° 1 * 4 . 3 5 ' — 3 5 .4 ' 1 3 6 3 II F S u rfa ce sed im en t DIO — 4 7 ’ — 1 7 .5 ' 7 7 9 I G S u rfa ce sed im ent D12 3 ^ °0 7 ’ — 55 ’ 8 4 4 - 7 9 8 V A P l e n t i f u l rock P a la g o n itiz e d b a s a lt JD1 3 3 ° 4 4 .2 1 ' — 3 7 -5 ' 1735 III 0 O L T \ K ' l C ore, 100 cm JD2 — 5 4 .5 ' — 2 8 .7 ' 7 1 9 I c ( 3 5 0 ) C ore, 9 8 cm JT >3 — 4 4 .2 ' — 4 4 .5 1 1 7 8 9 III c ( 3 5 0 ) C ore, 82 cm JD4 — 4 5 .5 ' — 4 5 .7 ’ 2 0 5 5 I I I c (3 5 0 ) C ore, 142 cm JD5 — 4 3 -3 ' — 4 3 . 8 ’ 1 8 0 0 III c ( 3 5 0 ) C ore, 7 2 cm JD6 — 4 3 . 3 ’ — 4 3 . 5 ’ 1 7 7 0 I I * — > C ore, 93 cm JD7 — 4 5 .5 ' — 4 3 . 3 * 1 8 7 5 I I c ( 3 5 0 ) C ore, 1 3 6 cm 224 SAM PLE STATIONS IN TH E SAN MIGUEL G AP REGION— c o n tin u ed S ta tio n 8 , Numbers L ocation L at. N. Long. W . Depth (m) Area3 0 Gear Remarks JD8 120 o 4 3 .2 ' 1 8 1 9 II C (350) Core, 9 1 cm JL9 — 4 5. 5 ’ — 4 4 .6 ' 1 8 0 9 III C (350) Core, 6 0 cm MH-1 3 4 °0 5 . 0 ' — 4l.8 ' 730 IV c ( 3 5 0 ) Core, 6 9 cm MH-2 — o4 .o' — 4 1. 8 ' 76 8 IV c (3 5 0 ) Core, 13 cm Pebble la y e r a t 5 " MH-3 — o4 . 8 ' — 4 2 . 7 ' 738 IV c ( 3 5 0 ) Core, 66 cm mh- 4 — 0 4 .3 ' — 4 3 . 2 ' 751 IV c ( 3 5 0 ) Core, 28 cm Pebble la y e r a t 11" MH-5 — 0 6 .2 ' — 4 1 .8 ' 723 IV c (3 5 0 ) Core, 6 9 cm MH-6 — 0 6 .2 ' — 4 3 .3 ' 736 IV c ( 3 3 0 ) Core, 84 cm MH-7 — 0 6 . O ' — 4 4 .2 ' 752 IV c (3 5 0 ) Core, 38 cm MH-8 — 0 4 . 9 ' — 4 4 .1 ' 7 6 1 IV c (3 5 0 ) Core, 66 cm APPENDIX I I 2 2 6 H YDRO G RAPH IC STATIONS USED T O ILLUSTRATE OCEANOG RAPH IC CONDITIONS IN TH E VICINITY O F SAN M IGUEL G A P C ruise S ta tio n Number L a t. N. Long. W . Date Maximum Sample Depth (m) N O R PA C 69 34°19' 1 2 0 °48' 7 Sep 55 562 N O R PA C 70 34°09' 121°09' 6 Sep 55 1 3 6 1 N O R PA C 71 3 3 = 4 9 . 1 2 1 °5 1 ’ 6 Sep 55 2 5 2 9 CCOFI 6401 8 0 .5 5 3 4 ° l8 .5 1 120°48' 16 Jan 6k 612 CCOFI 6401 8 0 . 6 0 34°09' 121°09' 1 6 Jan 6k 1 1 5 8 CCOFI 6401 8 0 .7 0 33°48' 1 2 1 05 1 ’ 16 Jan 6k 1044 CCOFI 6401 8 2 .5 2 3 3 °5 6 .5 ' 1 2 0 °4 5 ’ 13 Jan 6k 1264 CCOFI 6401 8 2 .6 4 33°44' 1 2 1 °12' 13 Jan 6k 1 1 6 7 CCOFI 6401 8 5 . 5 IB 33°52' 1 2 0 °0 8 . 5 r 11 Jan 6k 1 93 CCOFI 6401 85.55B 33°44' 12Q°2b.5' 11 Jan 6k 6 1 1 CCOFI 6km 8 3 . 6ob 33°34' 1 2 0 °45' 11 Jan 6k 6 26 APPENDIX I I I 228 L O G S O F C O R E S C O L L E C T E D IN S A N M IG U E L G A P R E G IO N AHF IOO9 9 - T o ta l le n g th , 121 cm. E n tir e core ex trem ely homogeneous o liv e -g r e e n c la y ; no s t r a t i f i c a t i o n , burrow s, e t c . to be see n . Strong sm e ll o f S2 S a t bottom o f c o r e . AHF 10100 - T o ta l le n g th , 14-2 cm. Su rface s e c tio n (0 -8 cm) g r ey -g re en s i l t y m a te r ia l "with la r g e fo r a m in ife r a sh ovin g; rem ainder o f core f e a t u r e le s s , fin e r -g r a in e d m a te r ia l s im ila r to 10099. AHF 10101 - T o ta l le n g th 118 cm. F a ir ly homogeneous s i l t y C layey sand, o liv e -g r e e n but w ith dark la y e r 6 3 - 7 6 cm and m o ttlin g (prob. burrow s) in bottom p a rt o f core (7 6 - I I 8 cm ). AHF 10102 - T o ta l le n g th , 5 cm. Core f a i l e d t o p e n e tr a te beyond a la y e r o f f in e dark o liv e - g r e e n s i l t y sand. AHF 10103 ~ T o ta l le n g th , 155 cnn E n tir e core c o n s is t s o f homogeneous green c la y ey s i l t w ith v e r y f a i n t tr a c e s o f s t r a t i f i c a t i o n th ro u g h o u t. AHF 10104- - T o ta l le n g th , 18 5 cm. S im ila r to 10103 but th e r e are fo r a m in ife r a l sand la y e r s a t 3 1 - 3 3 cm and 1 2 0 - 1 2 1 cm and a s in g le burrow (p o s s ib ly e c h in o id ) a t IO3-IO 6 cm. AHF 10105 - T o ta l le n g th , 122 cm. E n tir e core m o ttle d dark o liv e green s i l t y c la y in appearance. A rock ap p roxim ately th e s iz e o f th e co re tu be o ccu rs a t 7 1 - 7^ cm, a c la y b a l l a t 1 0 0 - 1 0 3 cm. AHF 10106 - T o ta l le n g th , 50 cm. Compact, homogenous, v e ry dark green sandy s i l t , no sig n s o f s t r a t i f i c a t i o n . E n tir e core v e ry h igh in g la u c o n ite . AHF 10107 ~ T o ta l le n g th , 12 cm. Upper 5 cm b u f f , c o n s o lid a te d s i l t - sto n e c o n ta in in g a v ery few fo r a m in ife r a . Lower 7 cm un- f o s s i l i f e r o u s v e r y dark gray to b la c k s h a le . T h is sample was e f f e c t i v e l y rock, n o t "sedim ent"; th e co rin g equipm ent was damaged and 70 0 l b s . o f w e ig h ts were l o s t c o lle c t i n g t h i s . AHF 10108 - T o ta l le n g th , 122 cm. Coarse g la u c o n ite -r ic h fo r a m in ife r a l sand a t su rfa ce (0 - 1 1 cm ), dense dark brow n-green "clay" (p o s s ib le burrow) 11-25 cm. Remainder o f core dark grey c la y w ith some (r a fte d ? ) p eb b les 1 6 - 1 8 , 2 2 - 2 3 , 4-5-46, 8 5 - 8 6 cm. Bottom (1 1 9 -1 2 2 ) darker gray s i l t . AHF 10109 - T o ta l le n g th I lk cm. .E n tir e core m o ttled l i g h t and dark green s i l t y c la y , h igh in g la u c o n ite . 229 L O G S O F C O B E S C O L L E C T E D IN S A N M IG U E L G A P R E G IO N — eontlaued AHF 10110 - T o ta l le n g th , 118 cm. 0 -4 0 cm homogeneous o liv e - g r e e n s i l t y c la y , rem ainder ( 4 0 - l l 8 cm) ir r e g u la r ly m o ttle d w ith l i g h t and dark green m a t e r ia l. A prom inent dark zone ("bur row?) a t 7^ -79 cm, lump o f t a r a t 52 cm. AHF 10111 - T o ta l le n g th , 124 cm. E n tir e core s tr o n g ly m o ttle d w ith Ir r e g u la r la y e r s o f l i g h t g r e y -g r e e n fo r a m in ife r a l sand in dark green s i l t y sand. Prom inent s t r a t a o f l i g h t m a te r ia l 3 8 -4 6 and 53“57 cm, app arent f i l l e d "burrows (r ic h in g la u c o n it e ) a t 2 1 -2 2 , 2 8 -3 1 , 6 9 -7 1 j 8 2 - 8 3 , 9 2 -9 6 cm. Bottom in v e r y dark (a lm o st b la c k ) green sand (1 2 1 -1 2 4 cm). AHF 10113 - T o ta l le n g t h , 92 cm. 0 -7 3 cm homogeneous l i g h t o liv e - g r e e n g la u c o n it ic s i l t y c la y , w ith s l i g h t m o ttlin g b e g in n in g a t 40 cm. The segm ent'"73-87 shows more m o t tlin g . Core b o t tom s in l i g h t g rey fo r a m in if e r a l sand. AHF 10114 - T o ta l le n g th , 5 cm. Core tu b e p e n e tr a te d o n ly 5 cm in to l i g h t g rey fo r a m in ife r a l sand. AHF 10115 - T o ta l le n g th , 174 cm. Top (0 -3 0 cm) c o n s is t s o f l i g h t o liv e - g r e e n s i l t y sand w ith " s e v e r a l (r a fte d ? ) p e b b le s a t 2 3 cm. Segment from 3 0 -7 2 cm i s dark g r ee n , but w ith bur rows in 3 0 -4 0 cm f i l l e d w ith m a te r ia l l i k e to p 30 cm. Re m ainder o f core (7 2 - 1 7 ^-) shows v e r y r e g u la r , alm ost v a r v e - l i k e s t r a t i f i c a t i o n o f p a le g r ey s t o grey-brow n s i l t ; v e ry t h in l i g h t la m in a e . AHF 10116 - T o ta l le n g t h , 191 cm. Homogeneous l i g h t o liv e - g r e e n s i l t y c la y w ith f a i n t s t r a t i f i c a t i o n th rou gh ou t c o r e . Prom inent l i g h t la y e r s a t 9^ ~ 96 and 1 0 7 - 1 2 0 cm, darker zone 4 5 - 5 8 cm. AHF 10117 - T o ta l le n g t h , 5 cm. L ig h t green homogeneous s i l t . T h is sam ple f i l l e d th e co re b a r r e l perhaps 15 cm above th e core c a tc h e r , s u g g e s tin g th a t a sand la y e r b elow washed ou t o f th e tu b e and was l o s t d u rin g r e t r i e v a l . AHF 10359 - A few fragm en ts o f m an gan ese-iron c r u s t , s im ila r t o th a t found in v o lc a n ic ro ck s in th e a rea were caught in g r ea se on th e core c u t t e r . The c o r e - c u t t e r was s e v e r e ly b e n t. AHF 10304 — Fragm ents o f v o lc a n ic ru b b le and manganese c r u s t w ere tra p p ed in co re tu b e above th e c a tc h e r . AHF 10342 - A few fragm en ts o f p a la g o n itiz e d v o lc a n ic d e b r is , a lump o f t a r , and broken p ie c e s o f a s i l i c i o u s sponge caught above core c a tc h e r . LOGS AHF IO36I ■ AHF 10 3 6 2 • M H - 1 • M H - 2 ■ MH - 3 ■ M H - 4 ■ M H - 5 ■ M H - 6 ■ M H - 7 ■ M H - 8 ■ 230 O F G O E E S C O L L E C T E D IN S A W M IG U E L G A P R E G IO N —continued ■ T o ta l len gth y 195 cm- E n tir e core green s i l t y c la y , w ith minor d is c r e t e sand la y e r s (? t u r b id it e s ) a t 1 5 - 1 6 ; 78- J 9 > 154-158 cm and an apparent "burrow a t 5 5 -6 4 cm. • T o ta l le n g th ; 125 cm. S im ila r to IO3 6 I ; w ith sand la y e r s a t 4 9 -5 5 cm and 113-118 cm. • T o ta l le n g th ; 69 cm. O liv e gray sand; m o ttle d w ith o l i v e - hrown m a te r ia l. G lau con ite v ery common th rou gh ou t. • T o ta l le n g th ; 13 cm. V ery sh ort g la u c o n it ic sand core which te r m in a tes in a p eb b ly la y e r in c lu d in g manganese fragm ents 2 -3 cm in d iam eter and a lump o f a sp h a lt. • T o ta l le n g th ; 66 cm. O liv e brown g la u c o n it ic sand w ith lig h t e r c o lo re d m o ttle s ; p o s s ib le t r a c e s o f s t r a t i f i c a t i o n . ■ T o ta l le n g th ; 28 cm. S t r a t if ie d green-brown to dark green g la u c o n it ic q u a r tz ite sand. Bottom s in la y e r o f (r a fte d ? ) p e b b les; in c lu d in g q u a r tz ite ; s i l t sto n e (w ith pholad b o r in g s ) ; p h o sp h ite . T o ta l le n g th ; 69 cm. S li g h t ly s t r a t i f i e d green-brown g la u c o n it ic sand. Some m o ttlin g . T o ta l le n g th ; 84 cm. O liv e brown sand; q u artzose homogenous near to p ; but showing h o r iz o n ta l s t r a t i f i c a t i o n toward b o t tom. • T o ta l le n g th ; 3 8 cm. Homogenous o l i v e brown sand; becom ing l ig h t e r and more d i s t i n c t l y s t r a t i f i e d toward base o f c o r e . ■ T o ta l le n g th ; 66 cm. M o ttled g la u c o n itic q u artzose sand; brow n-green t o dark green in c o lo r ; w ith much m o ttlin g . T races o f h o r iz o n ta l s t r a t i f i c a t i o n toward b a se . APPENDIX IV 2 3 2 R O C K S A M P L E S F R O M S A U M IG U E L G A P AHF 10097 31 J-°02, 3 0 % 120°31, ^5"‘ W 1 1 0 -8 3 m depth At slop e-b reak on In su la r R idge, due w est o f San M iguel Isla n d . One la rg e b ou ld er, e x te n s iv e ly "bored by pholads and worms and h e a v ily en cru sted w ith bryozoans, worms,, and s o lit a r y c o r a l. Phosphate, but u n lik e borderland "phosp horite." P o s s ib ly a nodule from Miocene Sisquoc Form ation. A H F 10098 3ij-°08’1 0 % 120°35,00"W 92-? m depth At slop e-b rea k , extreme w estern end o f In su la r Ridge. Hung dredge on hard rock and l o s t a l l gear. AHF 10107 33°51,0 0 % 120°l6'12"W 550 m depth On w est fla n k , Santa R osa-C ortes R idge, 15 km w est o f South P o in t, Santa Rosa Isla n d . G ravity core recovered about 12 cm o f s ilic e o u s sh ale con tain in g few fo ra m in ifera . P o s s ib ly P le is to c e n e , but more probably M iocene. AHF 10112 33043'38"H, 120°33,15"W approx. 1211 m depth On slop e south o f c e n tr a l b a sin , k6 km southw est o f South P o in t, Santa Rosa Isla n d . Ho a c tu a l rock , but fla k e s o f manganese cru st (probably from v o lc a n ic rock) recovered from sedim ent tu b e. AHF 10118 33°51'26"H, 120°23'50"W 7 8 0 -7 1 5 m depth Santa R osa-C ortes R idge, 18 km south o f San M iguel Isla n d S ev era l g o o d -sized ta b u la r b lock s o f (?) b a s a lt , one o f th e se w ith pholad b o rin g s, a lso one w ith fragm ents o f (dead) en cru stin g bryozoan, th e se two most probably r a fte d . A few angular fragm ents o f u n fo s s ilife r o u s grey sandston e. AHF 10121 3 3 °5 6 '0 0 % 120°l6'30"W 175-192 m depth At sh e lf-b re a k , 8 km south o f w est end o f Santa Rosa Isla n d . Assortm ent o f ro ck s, in clu d in g m o stly b a sic v o lc a n lc s , rounded pholad bored and en cru sted , one la r g e , angu lar, fr e sh fragment o f yellow -brow n s ilic e o u s s h a le , co n ta in in g p ie c e s o f r a d io la r ia and s i l i c i f i e d fo ra m in ifera . Probably from Sisquoc Formation (M iocene). 233 R O C K S A M P L E S F R O M SA N M IG U E L G A P —continued ABF 10123 3 3 ° 5 0 to6"N, 1 2 0 °1 5 '2 0 " W 5 5 0 -5 1 4 m depth A cro ss a d iv id e "between two c h a n n e ls, 16 km so u th w est of* S ou th P o in t, S an ta Rosa I s la n d . A la r g e h a u l of* r o c k s, m o stly p h o s p h o r ite , p lu s a few fra g m en ts o f sa n d sto n e and v o lc a n ic r o c k . The v o lc a n ic ro ck s are a n d e s it e s s im ila r t o th e Upper Santa Cruz V o lc a n - i c s (M io cen e). One w e ll-r o u n d e d v o lc a n ic b o u ld e r , prob a b ly r a f t e d . AHF 10124 3 3 05O '0 2 "N, 120°11'15"W 4 0 4 -3 4 8 m d ep th A c ro ss a l o c a l h ig h on s lo p e o f S an ta R o sa -C o rtes R id g e, 10 km s o u th e a s t o f South P o in t , S an ta Rosa I s la n d . A n gu lar t o subrounded b o u ld e r s o f v o lc a n ic ro ck (? b a s a l t ) , one fragm ent o f p h o sp h o r ite , one f r e s h , a n g u la r co b b le o f g a b b ro . ABF 10339 3 3 ° 4 2 , 45"N, 1 2 0 o 58'09"W 3417 m d ep th In a x i s o f s l i g h t tr o u g h , seaw ard o f P a tto n E scarpm ent. G ra v ity co re r e c o v e r e d no sed im en t, b u t a few fragm en ts m anganese c r u s t w ere caught in g r e a se on co re c u t t e r . Core c u t t e r b e n t. P ro b a b le o u tcro p o f v o lc a n ic ro ck . AHF 1 0 3 4 0 3 3 °4 l'0 9 " N , 1 2 0 ° 5 3 , 5 0 m W 2644 m d ep th On P a tto n Escarpm ent G r a v ity c o r e . Couple o f c h ip s o f v e r y w ea th ered ig n e o u s ro ck and m anganese c r u s t cau gh t in co re c a tc h e r . C u tter and c a tc h e r damaged. AHF 10341 33°40'30" N , 1 2 0 o53'06"W 2 3 8 6 - I 8 7 2 m d ep th On P a tto n Escarpm ent A good dredge h a u l, a l l v o lc a n ic r o c k s , m ost w ith w e l l - d ev elo p ed m anganese c r u s t . L arger fra g m en ts b a s a lt or o l i v i n e b a s a lt , s e v e r a l p ie c e s w ith o b v io u s flo w s t r u c t u r e s . One fragm en t o f p a la g o n it e , s im ila r t o m a t e r ia l dredged from R od rigu ez Seamount and D a v is S e a k n o ll. AHF 10342 3 3 ° 4 l , 45"N, 1 2 0 ° 5 1 '3 0 ”W 1284 m depth On P a tto n R idge S e v e r a l broken fra g m en ts o f d ark , f in e - g r a in e d w ea th ered ig n e o u s rock and b i t s o f (d ead ) s i l i c e o u s sponge caught above co re c a tc h e r in g r a v it y co re t u b e . AHF 10343 AHF 10344 AHF 10345 AHF 10346 AHF 10347 AHF 10348 D 12 2 3 4 H O C K S A M P L E S F H O M S A W M IG U E L G A P —continued 3 3 ° 4 5 '5 5 % 120°53'12"W 1 3 2 1 m depth 3 3 °4 5 '2 9 ’% 120°48'13" ¥ 1 3 7 6 m depth On P atton Ridge Two attem p ts to sample w ith sh ipek ; no recovery on e ith e r s ta tio n and sc r a tc h e s were found on equipment each tim e. Probable rock bottom . 3 3 °4 o , 30'% 120°4i'15"W 1 2 1 1 m depth On P atton Ridge Sample in sh ip ek c o n s is te d o f a sm a ll q u a n tity foram in i f e r a l g la u c o n ite sand and a sm a ll, fr e s h chip o f dark, w eathered v o lc a n ic ro ck . Probable rock and sedim ent bottom . 3 3 ° 4 l'2 0 ,% 1 2 0 °4 3 '4 o" W 1468-1211 m depth On P a tto n Eidge One la r g e r e l a t i v e l y fr e s h pumice b o u ld er. 3 4 o 0 4 ’30"N, 1 2 1 °0 6 ' 00"W 1927-1743 m depth On n orth w est fla n k o f R odriguez Seamount Dredge fo u le d on rock r e p e a te d ly , f i n a l l y s a f t i e s gave and dredge was recovered empty. Obvious rock bottom . 3 4 o0 1 '3 0 i% 1 2 0 °5 9 , 0 0 ,tW 1 6 5 1 - 1 1 3 8 m depth On escarpm ent due e a s t o f Rodriguez Seamount Many la r g e , angular r o ck s, m o stly v e s ic u la r o liv in e b a s a lt , w ith moderate manganese c r u s t. 34°07'00"N , 1 2 0 °5 5 ' 0 0 " W 844-798 m depth D avis s e a k n o ll, oh A rg u ello P la tea u Weathered p a la g m ltic b a s a lt (Palm er, 1 9 6 5 a ) . APPENDIX Va S E D IM E N T C H A R A C T E R IS T IC S , S A IT -M IG U E L G A P R E G IO N (U S C D A T A ) Station Interval Texture ($)a Sand Fraction ( j S ) " * 3 Foraminifera in Sand Fraction i^ o)0 N um ber (cm) Clay S ilt Sand Organic Authigenie Allogenic Plankton I c Benthonic P/B Ratio 10095 1 1 .7 0 2 3 .6 1 64.6 8 2 8 .6 0 1 .9 5 34.45 6 .5 0 1 3 .0 0 0 .5 0 1 0 0 9 6 3 .0 8 6 .0 0 9 0 .9 0 5 1 .8 7 0 39.13 2 7 .3 0 1 8 .2 0 1 .5 0 10 0 9 9 0 - 5 2 3 .5 3 6 3 .0 1 13.46 1 1 .0 5 0 1.95 ^.55 3.25 i .4 o 60 - 65 2 6 .4 9 6 2 .2 7 11.24 1 0 .7 8 0 0.22 6 .0 5 1 .6 5 3 . 6 7 116 - 1 2 1 3 5 .6 5 5 6 .3 0 8 .0 5 7 .8 4 0 . 0 8 0 .0 8 5 .2 0 1 .2 0 4 .3 3 10100 0 - 5 8 . 7 1 1 2 .1 1 79-18 64.78 0 . 7 9 13.43 4 3 .4 5 7.90 5-50 95 -100 1 6 . 4o 34.54 49.0 6 40 .6 7 0 . 4 9 6.8 6 2 4 .5 0 9 .8 0 2 .5 0 135 -lk-2 3 2 .1 0 43.62 2 4 .2 7 2 2 .3 2 0 .2 4 1 .4 4 1 8 .0 0 2 .4 0 7.50 10101 0 - 5 1 3 .2 8 2 0 .8 3 6 5 .8 9 3 9 .6 0 1 .3 2 2 5 .0 8 9 .9 0 2 3 .1 0 2 . 3 3 50 - 55 3 .5 8 19.85 7 6 .5 6 42.35 1 .5 4 3 3 .1 1 3 0 .8 0 3 .8 5 8 . 0 0 70 - 75 8 .6 2 16 .5 4 74.84 2 9 .2 5 0 45.75 18.75 3 .7 5 5 .0 0 113 -118 9 .0 0 12.75 7 8 .2 5 28.86 tr 49.1 4 1 1 .7 0 1 1 ,7 0 1 . 0 0 10102 0 - 5 1 .3 6 3 .1 3 95.49 3 8 .0 0 0.95 5 6 .0 5 0 .9 5 1 .9 0 0 . 5 0 10105 0 - 5 26.4 2 2 8 .1 2 4 5 .4 5 3 6 .0 0 0 9 .0 0 2 2 .5 0 1 1 .2 5 2 . 0 0 95 - 1 0 0 36.43 43.6 9 1 9 .8 7 15.4 0 0 .2 0 4 .4 o 1 1 .0 0 3 .0 0 3 . 6 7 150 -155 34.72 40.4 3 2 4 .8 4 21.75 0.25 3 .0 0 17.5 0 2 . 5 0 7 .0 0 aTexture i s p resen ted as p ercen t By w eigh t: Clay, l e s s than 4 m icrons; S i l t , 4-62 m icrons; Sand, g r ea ter th an 62 m icrons. ■ u Sand fraction figures represent percent by volume of the entire sample, summarizing the data contained in Appendix VII. jo C T \ S E D IM E N T C H A R A C T E R IS T IC S , S A N M IG U E L G A P R E G IO N (U S C DATA)--continued Station Interval Texture ($)a Sand Fraction {^ o)° Foraminifera in Sand Fraction { < jo )° Num ber (cm) Clay S ilt Sand Organic Authigenie Allogenic Planktonic Benthonic p/ b Ratio 10104 0 - - 5 22.88 4 0 .2 6 36.85 2 4 .4 2 t r 12.58 11.10 7. 4o 1.50 95 - -100 1 1 .0 5 5 7 -6 4 31.30 24.80 0.62 5 .5 8 21.70 1 .5 5 , i4 .oo 180 - -185 l4 . 8o 2 9 .3 1 5 5 -8 8 42.32 O.56 15.12 30.80 2.80 ( 11.00 10105 0 - - 5 1 4 .0 2 22.01 6 3 .9 5 47.36 2.56 l4 .0 8 32.00 9.60 3 -3 3 60 - - 65 7.62 12.15 8 0 .5 7 6 4 .8 0 4 .0 5 12.15 4 8 .6 0 12.15 4 .oo 117 • -122 3*11 17.61 7 9 .2 7 52.14 6 .3 2 2 0 .5 4 39.50 7.90 5.00 10106 0 - - 1 77.05 30.80 3 4 .6 5 1 1 .5 5 1 5 .4 0 1 1 .5 5 1 .3 3 4.5- - 5 .5 88.67 31.03 48.77 8.87 15.07 13.30 1.13 9 . 5- - 1 0 .5 88.52 30.98 4 8 .6 8 8.85 17.70 13.28 1 .3 3 1 4. 5- - 1 5 .5 83.19 29.05 41.50 12.45 16.60 12.45 1 .3 3 1 9. 5- - 20.5 88.17 39.60 35.20 4 .4o 22.00 17.60 1.25 2 4. 5- - 2 5 .5 81.91 3 9 .3 6 30.34 12.30 20.50 16.4o 1.25 2 9 . 5- - 3 0 .5 82.09 24.60 49.20 8.20 12.30 12.30 1.00 3 4. 5- - 3 5 .5 9 1 .4 6 18.30 68.63 4.58 10.98 7 .3 2 1.50 3 9- 5- - 4o .5 81.83 4i.oo 32.80 8.20 20.50 1 3 .9 4 1.47 4 4. 5- - 4 5 .5 8 4 .9 1 32.30 42.50 10.20 17.00 12.75 1 .3 3 49.5- - 50.5 85.49 25.50 51.00 8.50 1 5 .3 0 10.20 1.50 10108 0 • - 5 5.22 7 .0 9 87.67 39.60 4 4 .0 0 4 . 4o 8.80 30.80 0.28 15 - - 20 4 .4 5 1 0 .9 5 8 4 .5 8 8.50 61.20 1 4 .4 5 t r 8.50 — 95 ■ -100 16.93 6 6 .2 4 16.82 12.75 1.36 2 .5 5 5.10 7 .6 5 0.67 117 - -122 24.07 6 0 .4 5 1 5.4 6. 9 .7 5 0.45 4 .8 0 5 .2 5 4.50 1.16 10109 0 - - 5 6.56 12.07 81.36 12.96 6 4 .8 0 3 .2 4 2 .4 3 9 .7 2 0.25 50 ■ - 55 6.16 l4 .l8 7 9 .6 5 2 4 .0 0 52.00 4 .0 0 16.00 8.00 2.00 110 ■ -1 1 4 5 .2 4 11.52 8 3 .2 3 29.05 49.80 4.15 8.30 20.75 o.4o 237 S E D IM E N T C H A R A C T E R IS T IC S , S A N M IG U E L G A P R E G IO N (U S C D A T A )—continued Station Interval Texture ($)a Sand Traction Foraminifera in Sand Fraction N um ber (cm) Clay S ilt Sand Organic Authigenie Allogenic Planktonlc Benthonic P/B Ratio 10110 0 - 5 16.92 1 9 .7 9 63.27 3 9 .6 9 10.71 12.60 22.05 1 5 .7 5 i.4o 50 - 55 10.87 12.86 76.26 3 5 .7 2 13.68 26.60 26.60 7.60 3 .5 0 70 - 75 12.75 21.06 66.18 10.56 4 8 .8 4 6.60 3 .3 0 6.60 0.50 113 -118 16.08 59.98 23.92 10.56 9.60 3 .8 4 3.60 4 . 8o 0 .7 5 10111 0 - 5 12.13 13.63 74.24 3 4 .7 8 29.60 9.62 l4 . 8o 1 4 .8 0 1.00 21 - 22 0.71 0.12 9 9 .1 5 t r 9 4 .0 5 4 .9 5 0 — — 38 - 43 10.63 i4 .oi 7 5 .3 5 6 3 .7 5 11.25 t r 3 3 .7 5 30.00 1.12 95 -100 4.97 13.54 8 1 .4 8 12.15 6 4 .8 0 4 .0 5 1.62 4 .0 5 o.4o 121 -1 2 4 6.68 13.26 80. o4 12.00 60.00 8.00 2 .4 0 9.60 0.25 10112 O.89 3.69 9 5 .4 0 3 4 .2 0 5 9 .8 5 0 .9 5 9 .5 0 2 3 .7 5 o.4o 10113 0 - 5 19.68 22.15 58.16 30.16 1 4 .5 0 1 3 .3 4 11.60 14.50 0.80 45 - 50 13.16 18.87 6 7 .9 5 23.80 23.80 20.4o 3 . 4o 17.00 0.20 87 - 92 20.50 40.94 3 8 .5 5 2 5 .7 4 9*75 3.12 7.80 9 .7 5 0.80 1 0 1 1 4 0 - 5 8.26 13.10 78.63 3 7 .1 3 3.16 3 8 ,7 1 7 .9 0 1 9 .7 5 o.4o 10115 0 - 5 IO.25 17.04 72.70 2 8 .4 7 18.25 2 5 .5 5 1 0 .9 5 l4 . 6o 0 .7 5 30 - 35 1 3 -3 4 22.78 63.87 21.12 2 2 .4 0 2 0 .4 8 9.60 9.60 1.00 45 - 50 2 2 .4 5 54.56 22.97 1 8 .4 0 1 .1 5 3 -4 5 9.20 8.05 i.i4 95 -100 3 8 .1 3 54.44 13.38 1 2 .4 8 0.52 t r 3.25 3 .2 5 1.00 169 -1 7 4 5 8 .3 9 51.54 10.06 9.80 0.10 0.10 0.20 0.50 o.4o ro L O CD S E D IM E N T C H A R A C 1E R IST IC S , SM M IG U E L G A P R E G IO N (U S C D A T A )—continued Station Interval Texture ( 0 jc )& Sand Fraction Foraminifera in Sand Fraction {'jo )° N um ber (cm) Clay S ilt Sand Organic Authigenie Allogenic Planktonic Benthonic p/ b Ratio 10116 0 “ 5 17.12 31.75 5 1 .1 1 4 1 .8 2 3 -5 7 5.61 1 7 .8 5 20.4o 0 .8 8 50 - 55 4.74 1 0 .8 6 8 4 .3 9 3 7 .8 0 2 1 .0 0 25.20 12.60 16.80 0 -7 5 95 -100 1 5 -5 2 26.65 60.02 27.60 7.20 25.20 6.00 18.00 0 .3 3 115 -120 16.30 3 4 .2 4 49.45 2 4 .0 1 7 -3 5 1 7 .6 4 9.80 9.80 1.00 170 -176 1 0 .9 4 28.10 6 0 .9 4 32.23 7 .3 2 2 1 .3 5 12.20 18.30 0.67 186 -191 5 -0 3 5 1 .5 9 45.38 44.55 0 .4 5 t r 18.00 !3..50 ■ 1.33 10117 0 - 5 27.72 63.32 8.96 8.28 0.27 0 .4 5 1.80 9.00 2.00 10118 5 -7 2 5.83 9 0 .4 3 1 7 -1 0 3 8 .7 0 3 4 .2 0 4 .5 0 9.00 10119 1.76 3 -7 9 9 4 .4 4 16.92 7 .5 2 6 9 .5 6 4 .7 0 4.70 1.00 10120 2.19 4 -5 3 9 3 .2 6 22.32 0 .9 3 6 9 .7 5 9 .3 0 4.65 2.00 10121 1.62 9.56 88.80 62.30 0 26.70 1.78 6.23 0.28 10122 1,18 1.65 97.15 4 1 .7 1 t r 5 5 .2 9 1 9 .4 0 1 4 .5 5 1 .3 3 10123 7.83 21.61 70.55 23.43 3 6 .9 2 IO.65 3 -5 5 1 4 .2 0 0.25 1 0 3 4 1 3 -3 9 9.70 86.89 12.18 69.6O 5.22 1 .7 4 6.96 0.25 1 0 3 ^ 5 0 2.50 9 7 .5 0 11.76 7 9 .3 8 6.86 1 .9 6 9.80 0.20 1 0 3 4 6 ---- 3.65 5 .8 5 90.49 15.30 72.00 2.70 6.30 9.00 0.70 2 3 9 S E D IM E H T C H A R A C T E R IS T IC S , S A N M IG U E L G A P R E G IO N (U S C R A T A )—continued Station Interval Texture ($)a Sand Fraction { io ) ° Foraminifera in Sand Fraction (jjo)0 N um ber (cm) Clay S ilt Sand Organic Authigenie Allogenic Planhtonic Benthonic P/B Ratio 10^48 — 1 .3 4 5 .1 8 9 3 .4 7 1 0 .2 3 0 .9 3 81.8 4 1 ,8 6 2 .7 9 0 . 6 7 1034g — 6 . 2 3 7 .6 8 8 6 .0 7 2 0.6 4 4 .3 0 61.06 1 2 .9 0 4 .3 0 3 .0 0 10350 — 6 . 8 7 7 .6 6 8 5 .4 5 2 2 .9 5 12.75 49.30 1 0 .2 0 8 .5 0 1 .2 0 10351 — 1 6 .0 8 5 0 .6 9 3 3 .2 1 2 0 .1 3 0 .6 6 1 2 .2 1 8 .2 5 4 .9 5 1 . 6 7 10352 — 2 .6 9 1 5 .1 2 8 2 .1 8 4 9 .2 0 1 .6 4 3 1 .1 6 2 0 .5 0 9 .8 4 2 . 0 8 10353 1 .0 0 0 .7 5 9 8 .2 4 5 8 .8 0 tr 39.20 1 9 .6 0 2 4 .5 0 0 .8 0 10354 — 3 .1 6 5 . 7 9 9 1 . o4 4 5 .5 0 1 .8 2 4 3.6 8 1 5 .6 5 18.20 0.75 10355 — 2 .1 6 4 .9 8 92 .8 4 4 9 .2 9 tr 43.7 1 2 7 .9 0 15.95 2 .0 0 10356 — 2 .2 6 2 . 0 9 9 5 .6 3 4 5 .1 2 O.9 6 4 9.92 1 9 .2 0 i 4.4o 1 .5 5 10357 — 8 .7 5 1 8 .9 7 7 2 .2 6 3 8 .8 8 2 .8 8 30.2 4 2 1 .6 0 1 0 .8 0 2 . 0 0 1 0358 — 5 .0 2 2 6 .0 2 68.9 4 44.85 1 7 .2 5 6 .9 0 2 4 .1 5 10.55 2 .3 5 10359 — 5 . 9 5 4 .2 3 8 9 .8 3 5 2 .2 0 2 7 .0 0 10.80 51.50 1 2 .6 0 2 .5 0 1 0360 — 2 4 .3 2 3 4 .9 2 4 0 .7 4 3 1 .9 8 4 .9 2 4 .1 0 1 8 .4 5 8 . 2 0 2 .2 5 2 4 0 SEDIM EHT CHARACTERISTICS, SM MIGUEL G AP REGION (USC DATA)— co n tin u ed S ta tio n I n te r v a l T exture ($ )a Sand F r a c tio n ($)^ F o ra m in ifera in Sand F r a c tio n Humber (cm) C lay S i l t Sand O rganic A u th ig e n ie A llo g e n ic P la n k to n ic B en th on ic P/B R a tio 1 0 3 6 1 0 - 5 32.53 4 0 .5 8 2 6 .8 9 2 2 .1 4 0 .5 4 4 .3 2 1 0 .8 0 4.05 2 . 6 7 15 - 16 l 4 . 4 i 1 7 .9 7 6 7 .6 2 36.04 3 .4 o 2 8 .5 6 2 3 .8 0 6 . 8 0 3 .5 0 25 - 30 32.74 4 4 .5 4 2 2 .7 2 17.48 0 .2 3 5 .2 9 1 2 .6 5 3 .4 5 3 . 6 7 50 - 55 3 8 .9 1 42.82 1 8 .2 8 1 6 .7 4 t r 1 .2 6 13.50 1 . 8 0 7 .5 0 60 - 64 1 .9 1 3 .8 2 9 4 .2 8 45.12 t r 48.88 1 4 .1 0 18.80 0 .7 5 100 - 1 0 5 40.82 5 4 .5 7 4 .6 0 4.10 0 0 .9 0 1 .5 0 1 .0 0 1 .5 0 145 -1 5 0 36.33 4 5 .7 8 1 7 .8 8 15.30 t r 2 .7 0 9 .0 0 3 .6 0 2 . 5 0 154 - 1 5 8 3.76 5 .2 6 9 0 .9 8 55.5 1 t r 3 1 .8 5 1 3 .6 5 2 2 .7 5 0 .6 0 175 - 1 8 0 1 1 .6 0 5 4 .1 1 3 4 .2 9 24.82 t r 9 .1 8 1 0 .2 0 8 .5 0 1 .2 0 190 -195 33.12 4 9 .6 1 1 7 .2 7 11.3 9 t r 5 . 6 1 5-95 3-57 1-75 10362 0 - 5 2 7 .6 0 4 3 .7 2 2 8 .6 8 2 6 .6 8 t r 2 .3 2 1 4 .5 0 7 .2 5 2 .0 0 35 - 4o 29.9 3 4 9 .3 7 2 0 .7 0 19.5 3 t r 1 .4 7 1 2 .6 0 4 .2 0 3 .0 0 49 - 53 1 6 .8 0 3 3 .7 9 4 9 .4 1 4 5 .5 7 t r 3.43 2 9 .4 0 1 2 .2 5 2 .4 0 60 - 65 8 . 4 l 8 5 .2 5 6 .3 4 5-88 t r 0.12 5 .4 o 0 . 3 0 18.00 95 -1 0 0 7 . 1 1 8 3 .2 0 9 .6 8 9 .3 0 t r 0 .7 0 8 .0 0 0 . 8 0 10.00 113 - 1 1 8 2 .7 9 4 .5 2 9 2 .6 9 88.35 t r 4.65 46.50 2 7 .9 0 1 . 6 7 120 -1 2 5 7 . 6 1 7 5 .7 5 16.64 1 3 .9 4 t r 3 .0 6 8 .5 0 ' 3 .4 0 2 . 5 0 10363 — 2 .4 o 3 .8 6 93.73 37.60 51.70 4 .7 0 14.10 1 8 .8 0 0 .7 5 1 0 3 6 4 — 0 .6 2 0 .7 5 9 8 .6 2 45.50 45.50 t r 1 4 .8 5 34.65 0 .4 3 1 0 3 6 7 — 1 .1 6 3 . 1 1 9 5.71 51 .8 4 O.9 6 43.20 7 .6 8 24.0 0 0 .3 2 2 4 1 SEDIMENT CHARACTERISTICS, SAN MIGUEL G A P REGION (USC DATA)— con tin u ed S ta tio n Number In te r v a l (cm) Texture ($ )a Sand F ra ctio n ($>) Organic A uthigenie A llo g en ic Foram inifera P lankton ic in Sand F ra ctio n ($)k Benthonic P/B R atio 10368 1 -9 7 2 .3 7 9 5 .6 5 5 4 .7 2 t r 4 1.2 8 . 9 .5 6 2 4 .0 0 0.4o IO369 1 .3 7 3 .4 8 9 5 -1 4 3 1 .3 5 0 63.65 1 4 .2 5 9 .5 1 1.50 10370 ------ 3 .9 6 1 1 .4 2 8 4 .6 1 5 6 .9 5 0.85 27.20 8.50 17.00 0.50 1 0 3 7 1 ------ 0 0.51 9 9 .4 8 6 4 .3 5 0 34.65 1 .9 8 2 .9 7 0.67 1 0 3 7 2 ----- 0 .5 9 1.21 98.18 5 5 .8 6 1 4 .7 0 , 27.44 3 4 .3 0 1 4 .7 0 2.33 D1 ----- 0.88 3.68 9 5 .4 3 3 3 .2 5 5 7 .0 0 4.75 t r 3 3 .2 5 — D2 ------ 4 .1 8 1 4 .8 2 80.99 16.20 0 6 4 .8 0 4 .0 5 12.15 0.33 d4 1.82 4 .8 5 9 3 .3 1 18.60 69.75 4 .6 5 4 .6 5 1 3 .9 5 0 .3 3 D5 ------ 3.22 7 .7 0 89.07 21.36 66.75 0.89 1 3 .3 5 4 .4 5 3.00 D6 3 .3 1 8.16 88.52 4 4 .5 0 35.60 8.90 3 1 .1 5 8 .9 0 3.50 DIO 0 - 5 4.78 12.37 82.83 29.05 29.05 24.90 1 2 .4 5 16.60 0 .7 5 25 - 50 8.18 4l.4l 5 0 .3 9 3 2 .5 0 0 17.50 1 2 .5 0 2.50 5.00 2 4 2 APPENDIX Vb SEDIMENT CHARACTERISTICS; SAM MIGUEL GAP REGION (USNCEL DATA) (Conventions as in Appendix Va) S ta tio n Number In te r v a l (cm) Texture Clay S i l t W Sand Med. D ia. 0 0 Bulk Wet D en sity Color (GSA N o.) Sand F ra ctio n Organ- A u th i- T erres- i c g en ic t r i a l JD-1 0 - 7.5 4 3 . 8 4 0 .9 15-3 7 -7 1 .4 4 1 10Y4/2 Tr 6 . 1 9-2 1 5 - 2 2 .5 3 9 .0 4 3 .7 1 7 .3 9 -4 I .5 2 9 10Y4/2 Tr 8 .6 8 .6 3 0 - 37-5 4 0 .0 33.5 2 6 .5 9 -7 1.5 6 8 10Y4/2 Tr 1 5 .9 1 0 .6 1*5- 5 2 .5 3 4 . 4 3 8 . 7 2 6 .4 1 6 , 0 I .6 5 1 10Y4/2 Tr 1 3 .2 1 3 .2 6 0 - 6 7 .5 3 6 .5 31.5 3 2 .0 1 8 . 0 1 .6 4 9 10Y4/2 Tr 1 6 .0 1 6 .0 7 5 - 8 2 .5 314-. 0 3 7 .0 2 9 . 0 1 9 . 0 1 .6 7 9 10Y4/2 Tr 1 1 .6 1 7 . 4 9 0 - 97-5 3 0 .0 4 2 .0 2 8 . 0 2 5 . 0 1 .6 6 7 10Y4/2 Tr 1 1 .2 1 6 .8 JD-2 0 - 7-5 1 2 .5 6 6 .0 21.5 4 6 .0 1 . 6 8 7 10Y4/2 7.5 l . l 1 2 . 9 1 5- 2 2 .5 2 0 .5 4 5 .5 3 4 .0 4 9 . 0 1.659 5Y4/4 6 .8 1 .7 2 5 .5 3 0 - 37-5 1 9 . 6 4 4 .4 3 6 .0 5 1 . 0 1 .6 6 9 5Y4/4 7 .2 1 .8 2 7 . 0 4 5 - 5 2 .5 2 6 .5 3 2 .5 4i.o 4 8 .0 1.6 7 3 5Y4/4 1 6 .4 — 2 4 .6 6 0 - 6 7 .5 2 9 .5 48.5 2 2 . 0 2 8 . 0 1 .6 4 0 5Y4/4 4 .4 Tr 1 7 . 6 7 5- 8 2 .5 2 9 .7 4 5 . 3 2 5 . 0 2 9 . 0 1 .6 5 0 5Y4/4 1 0 .0 — 1 5 . 0 9 0 - 97-5 33-2 4 3 .0 2 3 . 8 2 3 . 0 1.6 2 2 5^ 4/4 8 . 3 Tr 1 5 .5 JD-3 0 - 7-5 4 1 .7 31.5 2 6 . 8 7 . 6 1.295 10YR4/2 1 . 3 2 2 .8 2 .7 1 5 - 2 2 .5 3 7 .3 6 0 . 6 2 , 1 7 . 8 1 .2 8 7 10YR4/2 2 .1 Tr — 3 0 - 37.5 4 8 .0 4 7 .5 4.5' 4 . 3 1 .2 7 5 5Y 4/4 4 .5 Tr — 4 5 - 52.5 49-9 4 5 . 1 4 .0 3 -9 1 .2 7 4 5Y4/4 4 .0 Tr — 6 0 - 6 7 .5 5 1 . 3 4 5 .2 3 .5 3 . 8 1.266 5Y4/4 3-5 Tr — 7 5- 8 2 .5 5 6 . 0 4 1.5 2-5 3 .4 1-377 5Y4/4 2 . 5 Tr — + 717S SEDIMENT CHARACTERISTICS, SAN MIGUEL G A P REGION (USNCEL DATA)— co n tin u ed S ta tio n Number In te r v a l (cm) Texture ($) Clay S i l t Sand Med. D ia. (n) Bulk Wet D en sity Color (GSA No.) Sand F ra ctio n Organ- A u th i- T erres- ic g en ic t r i a l JD- 4 0- 7 -5 2 5 .5 24.5 50.0 61 I.638 5Y 4 / 4 Tr 3 5 -0 15-0 15- 22.5 29.0 27.0 4 4 .0 42 1 .7 0 3 10Y4 /2 Tr 3 5 -2 8.8 30- 3 7 -5 3 1 .4 30.3 38.3 28 1 .6 5 4 10Y4 /2 Tr 3 4 .5 3 .8 4 5- 5 2 .5 2 3 .5 24.5 52.0 69 1 .7 4 4 10Y 4 /2 Tr 4 9 .4 2.6 60- 67.5 2 3 .4 2 4 .8 51.8 68 1 .7 5 4 10Y4 /2 Tr 3 6 .3 1 5 .5 75- 82.5 22.2 30.1 47.7 55 1 .7 2 4 5Y 4 / 4 Tr 3 3 .4 1 4 .3 90- 9 7 -5 20.0 25.7 5 4 .3 76 1 .7 7 9 5Y 4 / 4 Tr 32.6 21.7 105-112.5 1 9 .5 26.0 5 4 .5 76 1 .6 6 4 10Y4 /2 Tr 2 7 .3 27.2 120-127.5 19.2 27.5 5 4 .3 74 1 .7 4 6 10Y4 /2 Tr 32.6 21.7 1 3 5-1 4 2 .5 2 4 .8 28.0 47.2 56 1 .7 5 2 10Y 4 /2 Tr 3 7 -8 9 .4 JD-5 0- 7 .5 21.0 19.1 5 9 -9 130 1.681 5Y4 / 4 Tr 5 9 -9 Tr 15- 22.5 50.0 38.0 12.0 44 1.386 5Y3 /2 Tr 12.0 Tr 30- 3 7 .5 4 5 .7 50.3 4.0 5.1 1 .4 6 4 573/2 4 .0 Tr Tr 45- 5 2 .5 4 6 .7 4 6 .8 6.5 3 .9 1 .4 6 2 5Y3 /2 3 - 9 Tr 2.6 6o~ 67.5 4 8 .2 4 8 .3 3 -5 4 .4 1 .5 0 3 5Y 3 /2 1.2 Tr 2.3 jd-6 0- 7.5 16.8 2 2 .4 60.8 91 1 .6 5 4 5Y4 / 4 3 .0 5 7 -8 Tr 15- 22.5 16.7 1 7 .3 66.0 127 1 .6 6 4 5Y4 / 4 3 - 3 5 9 .4 3 - 3 3 0- 3 7 .5 19.0 19.6 61.4 100 1.711 5Y4 / 4 3 - 1 5 8 .3 3 .1 4 5- 5 2 .5 i4 .o 19.0 67.0 110 1 .7 7 7 5Y4 / 4 6.7 4 6 .9 1 3 .4 60- 67.5 17.5 22.8 5 9 - 7 85 1 .7 1 9 5Y 4 / 4 Tr 5 6 .7 3 .0 7 5- 82.5 i4 .o 1 7 .4 68.6 120 1 .8 4 5 5Y 4 / 4 3 .4 65.2 Tr ro -t= r ] ui SEDIMENT CHARACTERISTICS, SAN MIGUEL G A P REGION (USNCEL DATA)— con tin u ed Station Number Sand Fraction Interval (cm) Texture (<$>) Clay Silt Sand Med. Dia. 6-0 Bulk Wet Density Color (GSA No .) Organ ic Authi- genic Terre; trial o - 7 -5 1 9 .3 2 9 . 7 5 1 .0 65 1.6 4 8 5Y4/4 Tr 3 0 .6 2 0 .4 1 5 - 2 2 .5 24. 9 2 9 . 1 4 6 .0 56 1.649 5Y4/4 Tr ■41.4 4 .6 30- 37-5 2 1 .6 5 2 .2 4 6 .2 56 1.719 5Y4/4 2 -3 39-3 4 .6 4 5 - 52.3 2 4 .1 2 6 .5 4 9 .4 60 I .7 0 9 5Y4/4 Tr 44.5 ^ .9 6 0 - 6 7 .5 1 7 .9 2 4 .5 57-8 83 .1.785 5Y4/4 Tr 5 2 .0 5 -8 75- 8 2 .5 2 2 .6 2 9 . 4 4 8 .0 56 1 ,6 9 1 5Y4/4 4 .8 2 4 .0 1 9 .2 9 0- 97-5 1 8 .3 2 7 . 1 5 4 .6 75 1.770 5Y4/4 Tr 4 3 . 7 1 0 .9 1 05- 1 1 2 .5 2 0 .0 2 6 . 3 53-7 72 1 .7 8 3 5Y4/4 Tr 4 8 .3 5 A 120-127.5 2 2 .3 2 7 . 7 5 0 .0 61 1.801 5T5/6 Tr 4 5 .0 5 .0 0 - 7-5 1 8 .6 1 9 .6 6 1 .8 96 1 .7 0 4 5Y4/4 Tr 6 1 .8 Tr 1 5 - 2 2 .5 2 1 .9 1 9 .4 5 8 .7 97 1 .6 5 7 5Y4/4 Tr 5 8 .7 Tr 3 0- 37.5 2 2 .2 2 1 .5 5 6 .3 80 1.725 5Y4/4 Tr 5 6 .3 Tr 45- 52.5 2 1 .0 2 1 .0 5 8 .0 . 8 7 1.715 5Y4/4 Tr 5 5 .1 2 .9 6 0 - 6 7 .5 1 9 .7 1 9 .8 5 8 .5 95 1.771 5Y4/4 Tr 58.5 Tr 75- 8 2 .5 1 7 .9 2 1 .6 6 0 .5 95 1 .8 1 3 5Y4/4 Tr 5^-5 6 . 0 0 - 7-5 2 0 .8 2 7 . 1 5 2 .1 75 1.534 10YB2/2 Tr 4 9 .5 2 . 6 1 5 - 2 2 .5 3 5 .5 5 8 .0 6-5 9-5 1 .3 6 7 10YR2/2 6 .5 — — 30- 37.5 3 ^ .5 5 8 .7 6 .8 11.0 1.357 10YR2/2 6 .8 — — 4 5 - 52.5 3 7 .3 5 6 .2 6 .5 8 .3 1.344 10YE2/2 6 .5 Tr — 60- 6 7 .5 3 7 .5 5 1 .8 1 0 . 7 7-9 I .3 2 7 10YR2/2 1 0 .7 — Tr JD-7 jd-8 JD-9 9trs SEDIMENT CHARACTERISTICS, SAN MIGUEL G A P REGION (USNCEL DATA)— con tin u ed Station Interval Texture w Med. Dia. Bulk Wet Color Sand Fraction Forams ($>) Number (cm) Clay Silt Sand (n) Density (GSA No.) Org. Authi. Terres. Plank. Benth. p / b MH-l 0 - 7-5 12 .4 1 1 .6 7 6 .0 115 I .6 6 9 5Y4/4 3-8 45.6 2 6 .6 tr 2 .3 _ 1 5 -2 2 .5 1 6 .8 15.2 6 8 .0 100 1.746 5 1 5 /2 3 .4 4 0.8 2 5 . 8 0 .7 1 .4 0 .5 0 50-57-5 1 5 .5 1 1 .9 7 2 .8 105 1.805 5Y5 / 2 2 .9 4 3 .7 2 6 .2 tr 1 .5 — 4 5 - 5 2 .5 1 5 .7 1 1 .8 7 4 .5 96 1 .8 1 6 5Y3/2 2 .7 4 4 .7 2 6 . 1 1 .5 1 .5 1 .0 0 6 0 - 6 7 .5 1 2 .8 1 2 .4 7 4 .8 85 1 .8 2 9 5Y3/2 3-7 5 2 .4 1 8 .7 1 .5 1.5 1 .0 0 MS-2 0 - 7-5 9-9 1 0 .5 79-8 214 I .7 6 6 5Y4/4 3-9 5 5 .9 2 0 .0 0 . 8 2 .4 0 . 3 3 MH-3 0 - 7 .5 1 2.2 1 1 .5 7 6 .5 121 1.699 5Y4/4 1 .5 5 7.2 17.5 — 1 .5 — 15- 2 2 .5 1 5 .9 1 4 .5 6 9 .8 100 I . 76I 5Y4/4 2 .8 4 8 .9 1 8 .1 0 .7 2 .1 0 .3 3 50- 5 7 .5 1 5 .2 1 4 .4 7 2 .4 102 1.847 5Y4/4 3 .6 5 0 .7 1 8 . 1 — 2 .2 — 4 5 - 5 2 .5 l 4 .6 1 2 .5 7 5 .1 85 1 .8 5 5 5Y4/4 6 .6 3 6 .6 2 9 .9 2 . 9 3 -7 0 .8 0 6 0 - 6 7 .5 1 2 .9 1 2 .9 7 4 .2 85 1 .8 8 1 5Y4/4 3-7 2 9 .7 4 o .8 1 .5 2 .2 0 .6 6 mh-4 0 - 7 .5 9-9 1 1 .5 7 8 .7 189 1.779 5Y4/4 6 . 3 39.^ 33-0 1 . 6 3-9 o .4 o 15- 2 2 .5 1 5 .0 9-8 7 5 .2 i4 o 1 .8 0 5 5Y3/2 tr 4 5 .1 3 0 .1 tr tr _ M H-5 0 - 7 .5 15.2 15-7 6 9 . 1 68 1 .5 5 0 5Y4/4 1 3 . 8 6 .9 4 8.4 1 .4 2 .1 0 .6 6 1 1 1 5 - 2 2 .5 1 5 .7 1 6 .6 6 7 . 1 68 1.646 5Y4/4 2 4 .8 0 . 7 3 5 .6 1 3 .4 6 . 7 2 .0 0 1 50-57-5 1 6 .0 1 5 .8 68.2 74 1.7 5 1 5Y4/4 2 3 .9 6 .8 37-5 6 .8 1 0 .2 0 .6 6 4 5 -5 2 .5 1 4 .9 1 2 .5 7 2 .6 75 1 .7 5 1 5Y4/4 1 7 . 4 1 0 .9 4 4 .3 3 . 6 1 0 .9 0 . 3 3 6 0 - 6 7 .5 1 4 .9 1 2 .8 7 2 .5 74 . 1 .7 6 1 5Y4/4 2 5 .3 7 .2 3 9.8 1 0 .8 1 0 .8 1 .0 0 SEDIMENT CHARACTERISTICS^ SAN MIGUEL G A P REGION (USNCEL DATA)— con tin u ed S ta tio n In te r v a l Texture W Med. D ia. B u ll Wet Color Sand F raction Forams (io) Number (cm) Clay S i l t Sand (n) D en sity (GSA N o.) Org. A u th i. T erres. Plank. B enth. p / b mh- 6 0 - 7-5 1 7 .7 1 2 .6 6 9 .7 74 1 .5 8 2 5Y4/4 2 0 . 9 7 .0 4 1 .8 3-5 3-5 1.00 1 5 -2 2 .5 1 8 .2 1 6 .3 65.5 72 1 .6 1 3 5Y4/4 2 6 .2 3-3 3 6 .O 1 3 .1 3-3 4.00 3 0 -3 7 .5 17.5 1 6 .5 6 6 .0 72 1.703 5Y4/4 1 9 .8 3-3 4 2 .9 1 3 .2 t r — 4 5 -5 2 .5 1 5 .6 1 6 .4 6 8 .0 78 I . 76I 5Y4/4 . 1 3 .6 3-4 5 1 .0 6 . 8 3-4 2.00 6 0 - 6 7 .5 1 4 .1 1 3 .5 7 2 .4 77 I .7 6 6 5Y4/4 1 8 .1 7 .2 4 7 .1 1 0 .9 3 .6 3 .0 0 7 5-82.5 1 3 .6 1 7 .0 6 9 . 4 76 1 .6 9 7 5Y4/4 2 0 . 8 6 . 9 4 1 .7 1 3 .9 3.5 4 .0 0 MH-7 0 - 7 -5 1 1 .6 1 0 .0 7 8 .4 94 1.653 5Y4/4 3-9 3 1 . 4 4 3 . 1 t r 3-9 — 1 5 - 2 2 .5 1 7 .7 1 7 . 9 6 4 .4 73 1 .7 2 1 5Y4/4 5-2 1 9 .3 39-9 1-3 3 .2 o. 4o 3 0 -3 7 .5 1 4 . 9 1 4 .4 7 0 . 7 88 1.745 5Y3/2 5-7 2 1 .2 4 2 .8 1 .4 3-5 o. 4o mh-8 0 - 7-5 1 0 .0 8 .7 8 1 .2 128 1 .7 4 9 5Y4/4 1 0 .6 32.5 3 8 .1 1 .6 8 .1 0 .2 0 1 5 -2 2 .5 1 6 . 7 1 4 .8 6 8 .5 98 1.732 5Y3/2 6 .8 34.3 2 7 .4 0 .7 5-5 0 .1 2 3 0 -3 7 .5 1 4 .3 1 2 .3 73-4 92 1.819 5Y3/2 7-3 3 6 .7 2 9 .4 2 . 9 3 -7 0 .8 0 4 5 -5 2 .5 15.5 1 2 .3 7 2 .2 8 7 1 .8 4 3 5Y3/2 1 0 .1 32.5 2 9 .6 2 .9 7-2 o. 4o 6 0 -6 7 .5 1 2 .8 12.6 74.6 101 1 .8 9 5 5Y3/2 6 .0 2 9 .8 3 8 .8 1-5 3-7 o. 4o -t= - oo APPENDIX VI 250 FORAMINIFERA FROM SAN MIGUEL GAP a. L i s t o f F o ra m in ifer a I d e n t i f i e d i n Sedim ents from San M iguel Gap Region^ P la n k to n ic S p e c ie s G lo b ig e r in a b u l l o i d e s G. e g g e r i G. pachyderma G. quinqueloba G. su b c r e ta c e a G lo b i g e r in it a g l u t i n a t a G lo b o r o ta lia hexagona G. s c i t u l a O rbulina u n iv e r s a S p h a e ro id in a b u l l o i d e s . B en th on ic S p e c ie s A n gu lo gerin a sp. A s ta c o lu s sp. A s tr o r h iz a l i n e a r i s B athysiph on d i s c r e t a B o l iv i n a advena B. a r g en te a B. p a c i f i c a B. p s e u d o p lic a t a B. su b sp in e sc e n s B u lim ina a f f i n i s B. barbata B. r o s t r a t a B. s t r i a t a B. subacuminata C an cris sp. C a s s i d e l l a complanata C a s s id u lin a c a l i f o r n i c a C. cushman1 C. quadrata C. su b glob osa C. tr a n s lu c e n s C a s s id u lin o id e s t e n u is 1 I d e n t i f i c a t i o n s by J. C. I n g l e , Jr., R. J. E c h o ls , W. E. F r e r ic h s , and 0. L. Bandy, a l l o f A lla n Hancock F ou n d ation , U n iv e r s i t y o f Southern C a l i f o r n ia , and C. M. Carson o f V entura, C a l i f o r n i a . 251 a. L i s t o f F o ra m in ifer a I d e n t i f i e d in Sedim ents from San M iguel Gap R e g i o n - - c o n tin u e d C i b i c i d e s lo b a tu s G. mckannai C r ib r o sto m o id es sp. Cyclammina sp. D e n ta lin a sp. E g g e r e lla advena E ilo h e d r a l e v i c u l a F is s u r i n a m argin ata F. orb ign yan a Gaudryina a r e n a r ia G o e s e lla f l i n t i i G lob obu lim ina p a c i f i c a G yroid in a gemma Hormosina g l o b u l i f e r a Lagena h i s p id a L. s u l c a t a M argin u lin a s p . M a r t i n o t t i e l l a bradyana M elon is b a r le e a n u s M. p o m p ilio id e s N o d osaria s p . P la n u lin a sp. P l e c t o f r o n d i c u l a r i a s p . Psammosphaera sp. P u l l e n i a b u l l o i d e s P. S a lis b u r y ! Pyrgo c u l t r a t u s S t i l o s t o m e l l a advena S. l e p id u l a T r i l o c u l i n a o b lo n g a ta T. t r i c a r i n a t a U v ig e r in a au b eria n a U. h i s p i d a U. jun cea J. p e r e g r in a U. s e n t i c o s t a b . C o ilin g in R a tio s o f G lo b ig e r in a Cores from San M iguel pachyderma Gap Region 252 (Ehrenberg) S t a t io n I n t e r v a l (cm) % D e x tr a l R eferen ce 10106 0 - 1 82 FFW 4. .5- 5 .5 54 FFW 9..5- 1 0 .5 48 FFW 14. .5- 1 5 .5 38 FFW 19.,5- 2 0 .5 24 FFW 24. 5- 2 5 .5 10 FFW 29.■ 5- 3 0 .5 38 FFW 34..5“ 3 5 .5 20 FFW 39.,5- 4 0 .5 24 FFW 44. 5- 4 5 .5 28 FFW 49.■5- 5 0 .5 4o FFW 10116 0 - 5 94 FFW 50 - 55 28 FFW 95 -1 0 0 21 FFW 115 -1 2 0 36 FFW 170 -1 7 6 10 FFW 10107 0 - 5 1 7b FFW 10358 0 - 5 92 FFW 10361 0 - 5 84 FFW 15 - 16 78 FFW 25 - 30 90 FFW 50 - 55 92 FFW 60 - 64 44 FFW 100 -105 38 FFW 145 -1 5 0 76 FFW 154 -1 5 8 66 FFW 175 -1 8 0 28 FFW 190 -195 78 FFW JD 2 7-.5 - 15 80 BEH 2 2 . ■ 5 - 30 15 BEH 37..5 - 45 10 BEH 52.. 5 - 60 85 BEH 67..5 - 75 20 BEH 8 2 . .5 - 90 5 BEH 97.,5 - 1 0 .5 15 BEH b . C o ilin g R a tio s o f G lo b ig e r in a pachyderma (Ehrenberg) in Cores from San M iguel Gap R e g io n - - co n tin u ed S t a t io n I n t e r v a l (cm) $ D e x tra l 0 R eferen ce JD 3 7 . 5 - 15 60 BEH 2 2 . 5 - 30 35 BEH 3 7 .5 - 45 40 BEH 5 2 . 5 - 60 95 BEH- 6 7 . 5 - 75 0 BEH JD 4 7 - 5 - 15 30 WEF 2 2 . 5 - 30 60 WEF 3 7 - 5 - 45 - - 20 WEF 5 2 . 5 - 60 30 WEF 6 7 . 5 - 75 10 WEF 8 2 . 5 - 90 15 WEF 9 7 .5 -1 0 5 30 WEF 1 1 2 . 5 -1 2 0 20 WEF 1 2 7 .5 -1 3 5 75 WEF R efer en ce s: W EHj F r e r ic h s (1 9 6 4 ); BEH, H ackett ( 1 9 6 5 ); FFW, t h i s s t u d y . 1 3 Only s i x G. pachyderma were i s o l a t e d ; one o f th e se was d e x t r a l . APPENDIX V I I e F F H F ro n o vi ro H ^C O H O I I I I I F F ro o -pro ro ro v 4= - i ro V J ro v i o h - f F to b o o 4 o i $ i 1 1 - 3 I 4 1 I 1 F J J 4 1 - 3 4 1 - 3 4 F 4 O o n F H ■ V I I 1 1 I F F I I ( - 3 4 4 1 1 4 ! I ( F 1114 F F 4 C D 4 I F v v v j v - j - f h vo ro o v n o u i v n ■rS I I o F F O 0 1 I F H -O V i CD V I V l V l F VIVI \J1 VI VI VI rotH h ro o' o o v I I F 1 I 4 i i vi -j h ro vi i i I i I F 1 4 * i { { 4 3 1 - 3 I 1 4 I 3 f f ro 4 •cR 'cR < < <J < o o o o F F F F o o o o ( f t ( f t ( f t ( f t F F F F p p p p W W W M 01 W CO CD- H O O V O I I I F Vi 4r-vi V I F fO O O V i ro H H v o ro 1 - 3 4 1 - 3 1 - 3 4 4 I 1 1 I 1 1 I — 1 vi o vj r o VI CM -1 H \_ n 4rvji vi F 1 - 3 1 H 4 4 1 H H vi ro v o v o 1 - 3 1 1 - 3 4 I 4 ! i i 1 - 3 F 1 - 3 4 4 4 F o v V l V O N — o o v 1 F I 4 F S F O CO F N O F -V V I Vi O I I I 1 to o r o r o o o v V J V I F F v o 4 O vi - f f vi o VI o VI I 1 1 I I I 1 - 3 I 1 - 3 4 1 4 I I I 1 1 - 3 111-3 4 1 1 4 H U 1 - 3 1 - 3 1 - 3 4 4 4 4 1 1 - 3 1 4 F 4 F O F O O N - f F'Vi vi ro ro f f N O - f = - N Q 4^N O -F N O 4 = “N O -F O v v v v v v v v v v I 1 I 1 1 I I 1 1 1 1 vi - f - fvj vi ro ro f f O V I O V I O V I O V I O V I F N n ui vn vn ui vi vji vn \ji vn F t o r o F F r o r o r o r o F r o co o v ro vi vi vi o o — i o F F F r o r O F F F F viFi c d vi o o vi vi vn vn 1111 I I I I I 1 I I 1 1 F I F 1 - 3 1 - 3 1 I 4 1 4 4 4 1 I I ] I I j I I j 1 1 I 1 1 I 1 I ! I I 1 - 3 I 4 I 4 3 a 4 O F O vn F F O N F] O O 1 1 1 to O N ro v v V G \ V | o o o F F F o v V i i 1 - 3 4 I 1 1 I F O F O •F C O N O O V O 1 1 1 F F C O O V I o V vn fj vi V O O ro vn vi o 1 I I l l l F i -3 4 4 V i- 3 4 r o F o 5 V V V O O v o ! I 1 F F v o V o v F] V V O V O f f r o O v V 1 I 1 1 t I 4 3 ro F 4 1 - 3 1 - 3 1 - 3 4 4 4 O r o F F — 3 V O V J O O O 1 ! I I F FF] o n C D V V V F ro FVI v v o v ro v v v v F F F F F O O O O O F F O O o O O N O N O N O F O N O O N V liii i i i i f - 3 4 F 1 - 3 F 4 F 4 V J 1 - 3 1 - 3 F 1 - 3 1 - 3 11-3 4 rovi 4 4 ro 4 4 1 4 1 l-3>-3l-3 1 4 4 4 1 1 - 3 4 1 1 1 1 - 3 1 1 1 4 i ro i I I I I 1111 1 1 - 3 I 4 I I I I I I I 1 I I 1 - 3 I 1 I 1 4 I I I I 1 1 1 - 3 I I I I 4 1-3 1 1-3 4 I 4 1 1 - 3 1 4 I i- 3 F I 4 4 F 4 F 1 -3 4 4 ro V 1 - 3 1 - 3 F 1 - 3 1 - 3 i- 3 4 4 4 4 4 4 1 - 3 1 - 3 4 4 1 - 3 F F 4 4 1-3 4 1 - 3 1 I 4 1 1 F F F 4 4 4 F F F F F F 4 4 ro 4 4 _ F F 4 4 ro F I 4 4 F F F F F F F f v vi v o v o v - ^ o o o v o f ro r o G\ -F F FVJ O N FVJ V I F F FVJ r o fi w v o v v v o o o v o v o dvj r o F F 4 4 F F ro 4 I F I I FFFF i i F Fl F F F K 1411 4444 1 1 44 144 F 4 I O F F 4 F F 1 4 4 1 ro ro v F 4 5 5 5 V F F O O V < < < o o o F F F o o o F F F n > < t > o C 3 * O ' O ' 4 4 4 F F F c d t n c n r e v r o |_ ip p i^ ro f ro fofvj f f f r o v r o v o r o o v o v v v o o v v v o v v i o o v v ro V C D < 1 O O S F P v ro < < o o o o ( f t C f a F F P P F V N O v v o 1 1 I F F F O ro o v -vi V V V o v F ro F o o o 11 F VI v I n | n | _ ^ j_ 3 ^_ q 4F|-J4 4t— ‘4 4 4VJVJ V V FJ V V — J VlVIO fO VVVllO VitOV F F 4 F 4 F I F 4 ro F I fO 4 F I F F F F 4 14 4 4 4 F 1 I F F 4 to F I 14 4 ro E f r o 4 rovj r o F I F F I 4 1 4 4 I F F I I 1 i ro jo ~ vj f vj vi ro f ro O N O N FVJ F F O O O V F O V ro r o w I p 4 ^ B o * sir ( D 4 P F W F F O N O N O O ro o n F V v O NV V V V V F F ro V V V I I F \ 1 4 0 1 V V o ro vj v v v v F F 4 O V F co v o F ro v 4 I 1 F I I 4 F F I 4 4 1 FFF 4 4 4 F 4 VJ V F 4 F 4 1 F i ro v w o S 3 C D H > 4 P f l > 3- O [ v r o ro I F r o fi F 4 1 F 1 4 F 4 I V F V r o r o S ta tio n Number I n te r v a l (cm) P la n k to n ic B enthonic A renaceous RacLiolarians Diatoms Sponge S p icu les E chinoid Fragm ents M o H u sk Fragment s C hitinous Fragments Carbonaceous Fragm ents Tar G lauconite (Foram C a sts) G lauconite (Other) Mica T e r r e s t r i a l Sand O th er C o n s titu e n ts o h i P = 1 3 ~ b n > 4 p S A N D FR A C TIO N ANALYSES, S A N M IG U E L G A P REGION F F F O O O V N V N V N O N vn vn O vo 00 0 1 o , i O 1 vn i vn vn ro h o f 43 4 ro F F F F £ O O C O O V N V N V N V N V N vn vn vn vn vn — J o\ vn f V N o o 0 1 0 1 O j I vn I vn i vn vn vn V N ro V N F ro o o O vn o F F F IO ro vn vn vn o vn 1 43 43 43 l F 4 4 4 o vn Vn ro o j F F F F F K F O O O O C O O V N V N V N V N V N V N V N vn vn f F F f F" F O V O C O O N vn F O O 0 1 0 1 0 1 0 1 O j 1 vn I vn 1 vn i vn i vn i vn vn ro ro ro vn vn 43 43 1 to F O F O V N 1 s 1 - 3 4 F O F ro v n vn ro -f ro ro vn 1 - 3 4 F F F O F C F O F fo ro ro F IO o o j o ■ 0 1 i vn i Vn 1 vn ro F o IO O F vn vn - a 1 43 ! 1 4 1 1 -3 43 V N 4 4 H 3 4 V N 1 -3 4 4 3 4 43 4 1 - 3 4 4 3 4 1 - 3 4 4 3 4 F O F vn ro vn r o v n o vn vn V N 4 3 4 V N V N H ro 43 4 4 3 4 1 3 1 4 4 3 4 4 3 4 43 4 43 4 43 4 vn Co vn 43 4 ro Co vn 1 43 4 43 4 F 1 43 4 4 3 4 4 3 4 43 4 43 4 vn o 43 4 43 4 H O F 43 4 43 4 ro ro vn ro V N o V N o K ro o F o F O V N 43 4 vn O -V I o vn o 43 4 43 4 VN F I V N F V N 1 43 4 43 4 43 4 f o F F IO VN VN Vn 0 \ C 0 O vn vn vn V n 1 -3 4 h rl (D 4 c+ 9 ^ 3 F ro vn vn 43 F 4 vn 'cR u 1 Q 4 0 P D O <1 o ( D p F S C D r o V N vn V N <1 o o F F 0 0 H 4 c pi u 1 o' & o' F F n > (D F O F o CD •d f c y * 0 4 H- c+ ( t> Vn vn V N O vn w 4 0 — J vn F F F F F F F O O O O o O o F F F F F F F F F F F F F F V O Co -F On vn F V N F F F F C o-^ f V0 vn O N VO FVN CO F O O O O N O vn vn o O V O Vn Vn O O O - J vn o I ! I 1 I 1 1 I 1 F F F F I ! I I I F F 1 1 I 1 V O - 3 IO O vn -0 o vn vn V O Vn vn vn vn F O N O o vn vn P O O vn vn vn IO vn vn ro F IO ro F F V N IO F F F F to ro vn vn o O O O O Vn vn ro vn o vn vn O O vn c F F Vn V N fO V N IO F io v n f ro ro ro ro ro vn O O o o o o o o • vn vn vn vn o vn vn vn vn 43 4 43 4 I I -1 I vn V N 1 0 vn 43 ! 4 1 43 4 ro F vn vn IO V N vn to V N -0 F o vn ro IO o P 4 Q P 4 < 1 V ( D < J F 0 F 1 43 h3 I 1 4 4 1 V N 4 F F IO V N I I 43 43 1 I 4 F 4 I I 1 ] F F I 43 43 I 4 4 Vn vn vn vn V N F 43 43 4 43 4 43 4 43 4 43 I 43 4 i 4 ro F I I I I 43 43 43 4 4 4 F 43 43 43 43 1 4 4 4 4 I ! i 43 43 1 43 43 43 4 4 I 4 4 4 p vn vn vn vn vn I J 43 1 114 1 i I 43 1 4 F 1 I I F F 1 ro I o o 43 4 43 43 43 43 4 4 F 4 4 F 43 V N V N F V n F 4 vn vn O O O 43 t F 4 -I 43 F V N V N 4 vn ro vn 43 vn 4 tx j lx | F F » C O P * F o * c4 o o tr 4 n > n > CD CD 43 V N 4 IO 43 43 [0 4 4 IO vn V N Co vn vn IO vn o 4 ro F on ro vn vn I I I 43 43 43 I 43 1 1 1 4 4 IO 4 1 4 1*3 4 1 ] ro 1 j 43 I I 4 1 I 4 3 4 F F ro F ro VN IO O - N O I O F ro Vn vn vn VN O O O I I 43 1 1 4 F O F £ 0 1 vn F O 43 4 43 4 ro ro covn o F vn v n VN <i < g 0 0 B F F 0 O H > 4 T O T O P F F T O P P — CD CD c+ CD CD CD S ta tio n Number Interval (cm) P lanktonic Benthonic Arenaceous R adiolarians Diatoms Sponge Spicules Echinoid Fragments M o H usk Fragments C hitinous Fragment s Carbonaceous Fragment s Tar Glauconite (Foram C asts) Glauconite (Other) Mica T e r r e s tr ia l Sand O ther C o n stitu e n ts h a 0 4 1 S ' R (D 4 P Q 43 8 t e i Hi i C O E P H 2 Q 8 f h o 4 c+ H- B a > F « I ■ tj i f c * i 1 a o o \ i v n - F " I V ) r o v n o 0 1 O O t o t i l V N O v n 1 V n I v n 1 v n 1 v n r o a v n v n V N V n a v n v n v n r o v n o 10 v n a v n a v n V N a O 4 V N I V N a 4 a 4 ro i o i ro 1 v n H 3 V N 4 V n V n fO o a I 0 1 v n a 4 V N a a a o o o V N V N V N - V ] > 4 1 ro a O o ! v n V N v n 0 1 v n ro V N 0 1 v n H O ro o a a a a a o o o o o V N V N V N V N V N o \ O N C F \ O V v o C D • 4 ] - f r - V N o 0 1 o O t 0 1 1 v n 1 v n 1 v n I v n 1 v n o V N ro 1 — 1a i — ’ a a o v - a v N V O ~ 4 ] v n - a o own ro a O v o v n o o v n - F = ” v n o O O v n v n o l I 1 I I a I a 1 a I a i a 1 I I I 1 O N v n v o C D v n v n o O W n V N a ■ v n V N O v n V n o C O o v n 4 = - v n O o v v n B 6 ro vn 00 ro v n V N v n H1 v n I O O B P- 0 V N 1 1 I B B v n v n c o V O O N O v v n o o o o o o o ro v n ro ro ro O O c o v n v n o v n ro H o V N o M o a 4 O N O H a 4 a 4 — - 3 v n a 4 ZSs a 4 a 4 a 4 v n v n to o " W < o a C D c r1 4 H * 03 a 4 a O a 4 V N o ro ro V N V N V N H v n a 4 a 4 a 4 o v o a 4 I a i l a i i 1 4 i 1 4 i I I i a 1 i a 1 I i 4 I 4 I I 2 1 1 a 1 I I J 1 i 4 a a 1 a a ro o 4 I 4 a o v n 1 i i a VN v n a I i i o O a a a VN 4 ro ro VN 4 4 ro r o VN ro o v a a a o v n v n v n o v n 4 VN v n v n ro a a W o v 4 4 trf Q bd £? < i 4 4 4 4 o V! P < < J a O < o < J o N C D N C D • O a O a P P a 2 P C D 03 C Q a H o V N o\ H 4 H - C O H I-* H O V n vn vn C D ro V n a a i a a ro o 4 i 4 4 ro a a i i a i i 4 4 I I 4 1 i a a i a i a a 4 4 1 4 1 4 4 i i i a a a a I I 1 4 4 4 4 a i a i a a a 4 I 4 I 4 4 4 a a a i a a a 4 4 4 1 4 4 4 I I 1 I I I I I I 1 I I I I v n ro ro ro ro ro v n j i v n v n v n 4 v n v n v n a 4 a H * 03 P ... c + C D C D c + & V N V N l— 1 v n v n I— 1 — J v n v n Jpr v n o v n o o v n v n v n v n o iDrororororoHaaa O v n v n o O O O V n o v n [ ) a i i j i a i a 1 I t i a a I a 1 I 4 1 i i i to a 4 i 4 1 I 1 i 4 4 I 4 a i i a i a 1 i a a a a a a a a a I 4 I ro i 4 I 4 1 i 4 4 4 4 4 4 4 a 4 v n 4 1 i i i i a i 1 I 1 I a l i i i 1 i i i i i 4 1 I I i I 1 1 4 1 i i i I i h a i a 1 4 i —1 a i —'a i —1 1 0 0 4 O v n v n v n v n v n O vn vn vn to vn hf a POtO i a i 1 V N vn I 1 V N a a a i a i 4 4 4 1 4 1 i a a a i I 4 4 4 I i t i a a i 1 l I 4 4 I a 4 a a i 4 4 I i i a i 1 4 i a 1 4 a i a 4 I 4 a 4 a to ro i r a I I 4 i a i a a 1 4 1 4 V N 4 h 3 h 3 v n ro 4 4 v n ro ro v n ro a vn ro vn a a vn ro - a a o v n v n v j i v n o v n o O vn a a 4 4 a a 4 4 C < J o o N I N O O P P P P C O C O 4 J O C O C O 5 B c + d h i o’ S tatio n Number In te rv a l (cm ) Planktonic Benthonic Arenaceous R adiolarians Diatoms Sponge S picules Echinoid Fragments M o H u sk Fragments C h itin o u s Fragments Carbonaceous Fragments Tar Glauconite (Foram Casts) Glauconite (Other) Mica T e rre s tria l Sand Other Constituents H > n > p S A N D F R A C T IO N A N A L Y S E S , S A N M IG U E L G A P R E G IO N —continued

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Geology In The Junior College

Asset Metadata

Creator Wright, Frederick Fenning (author)

Core Title The Marine Geology Of San Miguel Gap Off Point Conception, California

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

Contributor Digitized by ProQuest (provenance)

Advisor Gorsline, Donn S. (committee chair), Reith, John W. (committee member), Stone, Richard O. (committee member)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c18-131044

Unique identifier UC11360252

Identifier 6708039.pdf (filename),usctheses-c18-131044 (legacy record id)

Legacy Identifier 6708039.pdf

Dmrecord 131044

Document Type Dissertation

Rights Wright, Frederick Fenning

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA