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Paleoenvironmental analysis of late Cretaceous continental slope deposits (Holz Shale Member, Ladd Formation), Black Star Canyon (Santa Ana Mountains), Southern California

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Paleoenvironmental analysis of late Cretaceous continental slope deposits (Holz Shale Member, Ladd Formation), Black Star Canyon (Santa Ana Mountains), Southern California

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Content PALEOENVIRONMENTAL ANALYSIS OF LATE CRETACEOUS CONTINENTAL SLOPE DEPOSITS (HOLZ SHALE MEMBER, LADD FORMATION), BLACK STAR CANYON (SANTA ANA MOUNTAINS), SOUTHERN CALIFORNIA by Steven Paul Buck A Thesis P resen ted to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In P a r t i a l F u lf illm e n t of the Requirements fo r the Degree MASTER OF SCIENCE (Geological Sciences) December 1983 UMI Number: EP58715 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI EP58715 Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 UNIVERSITY O F S O U T H E R N CALIFO RNIA TH E GRADUATE SC H O O L U N IV ERSITY PARK LO S A N G ELE S. C A LIFO R N IA 9 0 0 0 7 This thesis, written by Steven Paul Buck under the direction of hxs....Thesis Committee, and approved by all its members, has been pre sented to and accepted by the Dean of The Graduate School, in partial fulfillment of the requirements for the degree of ...........Master, of„.Science................ df D ean DatesJ. T H E SIS c o m m i t t : C h a i tan ABSTRACT Sedim entologic, ic h n o lo g ic , and p a le o n to lo g ic a n a ly se s of :he Holz Shale Member (Ladd Formation) in Black S ta r Canyon, Santa Ana Mountains, southern C a lif o r n ia , support a c o n t i n e n ta l slope and upper submarine fan paleoenvironm ental i n t e r p r e t a t i o n . This dominantly sh ale and mudstone member is d is s e c te d by numerous c o a rse -g ra in e d c h a n n e l - f i l l depo s i t s t h a t are i n t e r p r e t e d as a n c ie n t submarine channels and g u l l i e s . Sediment g ra v ity flows of d e b ris flow, high-den- s it y t u r b i d i t y c u r r e n t, and low -d en sity t u r b i d i t y c u rre n t o r ig in , are the dominant modes of d e p o s itio n which f i l l e d th ese channels. Evidence of penecontemporaneous slumping, t r a c t i o n c u rre n t a c t i v i t y , and pebbly mudstone d e p o s itio n su g g ests th ese sed im en tatio n mechanisms were a lso l o c a l l y im portant in the form ation of the c o a rse -g ra in e d s t r a t a . I n t e r c a l a t e d f i n e - g r a i n e d sandstones, s h a le s, and mudstones dominated d e p o s itio n in the in te rc h a n n e l region. These s t r a t a r e p re s e n t sediments d ep o sited by d i l u t e t u r b i d i t y c u r r e n ts , c o n to u r-fo llo w in g bottom c u r r e n ts ( c o n t o u r i t e s ) , and hem ipelagic se d im en tatio n . Dependent upon sedim entation r a t e s , the d e n sity of in fa u n a l organisms, i i and d iss o lv e d oxygen l e v e l s , th ese rocks d isp la y a complete range of b i o l o g i c a l l y - to p h y sic a lly -d o m in a te d sedimento- lo g ic t e x t u r e s . D iagenetic carbonate c o n c re tio n s abound in th e se f in e - g r a i n e d s t r a t a and provided a means fo r d e t a i l e d exam ination of these d e p o s its through p r e s e r v a tio n of the i n i t i a l sediment f a b r i c . Carbonate nodules are formed through b a c t e r i a l decomposition of abundant organic m atter in very porous, w a te r-la d e n sedim ents. Benthic paleocommunities in th e f in e - g r a i n e d rocks are dominated by the e p ifa u n a l b iv a lv e Inoceramus and in fa u n a l, d e p o s it- f e e d in g Chondrites t r a c e s . C h a n n e l- f i ll d e p o s its were in h a b ite d by t h a l a s s i n i d shrimp which produced l o c a l l y abundant Qphiomorpha and T h a la ss in o id e s tra c e f o s s i l s . The u b iq u ito u s presence of t e r r e s t r i a l p la n t and wood fragm ents i s c h a r a c t e r i s t i c of s t r a t a throughout t h i s member. Micro f o s s i l analyses provide a Coniacian to Santonian age fo r th ese outcrops and a paleo b ath y m etric i n t e r p r e t a t i o n of bathyal depths. The p ro fu sio n of t e r r e s t r i a l organic m a t e r ia ls , the paucity of d isp la c e d s h e l f a l faunas, and the very c o a rse g rained t e x t u r e of the c h a n n e l - f i l l d e p o s its , suggest t h a t th ese sediments were funneled d i r e c t l y o ff the shore and in t o the Cretaceous submarine channel system. The focus of t h i s sediment i n f lu x was lo c a te d in th e Black S ta r Canyon i i i region where most of the Holz Shale c h a n n e l - f i l l d e p o s its are s i t u a t e d . P a l i n s p a s t i c r e c o n s t r u c t i o n s of a s s o c ia te d Cretaceous sequences i n d i c a t e t h a t a submarine fan complex, fed by Holz Shale submarine channels, may p r e s e n tly be lo c a te d to the North in the Santa Monica Mountains of the Transverse Ranges. ACKNOWLEDGMENTS I am deeply indebted to the many in d i v i d u a l s who provided a s s i s ta n c e during the course of t h i s re se a rc h p r o je c t. To my t h e s i s ad v iso r, Dr. David J. B o t t j e r , I extend my most sincere g rad itu d e for in tro d u c in g me to the Holz Shale controversy, for continuous guidance throughout the study, and for making my stay in southern C a lif o r n ia both a fun and rewarding ex p erien ce. I am g r a t e f u l to Drs. Donn S. Gors- Line and Robert G. Douglas fo r c r i t i c a l l y reviewing t h i s m anuscript and fo r providing a w ealth of h e lp fu l su g g estio n s along the way. Dr. Robert H. Osborne i s thanked for h elp in g to r e f i n e my f i e l d tech n iq u es and for answering a barrage of q u estio n s. A.A. Almgren and M.V. Filewicz (Union Oil Company of C a lif o rn ia ) provided generous a s s i s ta n c e in performing n i c r o f o s s i l a n a ly se s. I am also indebted to LouElla Saul for a id in g in macrofaunal i d e n t i f i c a t i o n s and V icto r Santos for performing LECO gasom etric d e te rm in a tio n s . To my fellow stu d e n ts James Browning, Mike Edelman, Gene Enzweiler, Rick l a z l e t t , Dave Hicks, Paul S criv n e r, and Chuck Savrda, I give Tiany thanks fo r im portant d is c u s s io n s and e d u c a tio n a l e n te rta in m e n t throughout t h i s study. E n lig h ten in g conversa- v t i o n s w ith I .P . Colburn, M.H. Link, B.P. Luyendyk, T.L. Ku, W.V. S l i t e r , R.H. Tschudy, and J. Wolfe are a lso acknow ledged. To my loving p a r e n ts , Paul and M arguerite Buck, I am fo re v e r g r a t e f u l for p roviding encouragement and support during the d u ra tio n of my c o lle g e ed u catio n . F in a n c ia l support fo r t h i s p r o je c t was provided by Mobil Oil Corpora t io n , U n iv ersity of Southern C a lif o r n ia Department of G eological Sciences, Sigma Xi Research S o ciety , and N ational Science Foundation (NSF Grant EAR82-13202). In a d d itio n , acknowledgment i s made to the Donors of the Petroleum Research Fund, ad m in istered by the American Chemical S o ciety , for support of t h i s re se a rc h through a grant awarded to Dr. David J. B o t t j e r . CONTENTS ABSTRACT.........................................................................................................................i i ACKNOWLEDGMENTS ...................................................................................................... v Chapter page I. INTRODUCTION ............................................................................................. 1 I I . METHODS...........................................................................................................10 I I I . SUBMARINE CANYONS AND CHANNELS ................................................ 19 General I n tr o d u c tio n ............................................................. 19 C h a n n e l-F ill D e p o s i ts : I n tr o d u c tio n .......................... 23 Submarine Canyon D eposits ................................................... 27 Submarine Chute and Gully D eposits .......................... 63 Submarine C h a n n e l-F ill D e p o s its : Conclusions . . 72 IV. INTERCHANNEL DEPOSITS .................................................................... 77 I n tr o d u c tio n .................................................................................. 77 Sedim entologic T e x tu r e s :B io lo g ic a l versus Physical Mechanisms ................................................... 81 Fine-G rained Sandstone In te rb e d s ............................... 87 Fine-G rained Sandstone Outerops:Bottom Current E v i d e n c e ................................................................................91 C o n c l u s i o n s .......................................................................................... 96 V. CARBONATE CONCRETIONS .................................................................... 97 I n tr o d u c tio n .................................................................................. 97 Concretion Morphologies ................................................... 100 Concretion Compositions ................................................... 106 Organic A s so c ia tio n s ........................................................ 107 B a c te r i a l A sso c ia tio n s ................................................... 115 Timing Of Concretion Formation ............................... 116 A dditional F ie ld O bservations .................................... 129 C o n c l u s i o n s ........................................................................................135 v i i VI.MICROPALEONTOLOGY ............................... 13F I n tr o d u c tio n ............................................................................ 136 Black S ta r Canyon A n a l y s e s ................................................137 VII. MACROPALEONTOLOGY ......................................................................... 140 V III. ICHNOLOGY....................................................................................................151 Traces of C h an n e l-F ill D eposits ............................... 151 Traces of In te rc h a n n e l D eposits ............................... 161 IX. STRATIGRAPHY...............................................................................................168 X. PALEOENVIRONMENTAL SUMMARY ..................................................... 171 XI. PALEOGEOGRAPHY..........................................................................................178 XII. CONCLUSIONS...............................................................................................185 X III. REFERENCES................................................................................... 187 Appendix page A. STRATIGRAPHIC SECTIONS ............................................................... 207 B. CONCRETION COMPOSITION ANALYSIS RESULTS . . . . 229 C. MICROFOSSIL IDENTIFICATION TABLE ...................................... 231 D. MACROFOSSIL IDENTIFICATION TABLE 234 vii:. LIST OF FIGURES Figure page 1. Location map showing area of f i e l d study and o u t l i n e of Upper Cretaceous s t r a t a t h a t crop out in Santa Ana Mountains, southern C a l i f o r n i a ..........................................2 2. G eneralized s t r a t i g r a p h i c column fo r Upper Cretaceous s t r a t a in Santa Ana Mountains . . . . 5 3. Regional s t r a t i g r a p h i c c r o s s - s e c t i o n fo r Upper Cretaceous s t r a t a of the Santa Ana Mountains. . . 7 4. Location map of exposures measured along Black S ta r Channel Road, Black S ta r Channel, southern C a l i f o r n i a ...............................................................................................11 5. Location map of m ic ro f o s s il sample s i t e s along Black S ta r Channel Road and I r v i n e Company F ire ro a d . . 14 6. T u rb id ite Facies A s so c ia tio n s of Mutti and Ricci Lucchi ( 1978)..................................................................................... 25 7. A c r o s s - s e c t i o n a l view of channel 1. This outcrop i s f a u l t e d and i s surrounded by sh ale s t r a t a . . . . 28 8. Truncation su rfa c e a t base of conglom eratic d e b ris flow d e p o s it (F acies A) in channel 1 ............................ 31 9. Igneous cobble and s c a t t e r e d sh a le rip - u p c l a s t s lo c a te d in c e n tr a l zone of h ig h -d e n sity t u r b i d i t e (F acies A) in channel 1 ............................................................. 34 10. Abundant sh ale rip -u p c l a s t s d isp e rs e d in a massive, very c o a rse -g ra in e d sandstone stratum (F a c ie s A) in channel 1 .........................................................................................36 11. Deformed rip - u p c l a s t s in c e n tr a l zone of high- d e n sity t u r b i d i t e (F acies A) in channel 1. . . . 3£ 12. A s e r i e s of th re e en echelon sh ale r ip - u p c l a s t s a t the top of a h ig h -d e n s ity t u r b i d i t e (F acies A) in channel 1 .................................................................................................40 ia 13. Igneous cobble and pebble c l a s t s found a t the top of a h ig h -d e n s ity t u r b i d i t e d e p o s it (F acies A) in channel 1 .......................................................................................................42 14. Cross-bedded sandstone le n s o v e rly in g a massive, very c o a rs e -g ra in e d sandstone stratum (F a c ie s B) in channel 1 ............................................................................................... 45 15. Bedding plane of c o n c e n tra te d organic fragm ents from a p la n a r-la m in a te d , f in e - g r a i n e d sandstone in te rb e d (F acies C) in channel 1 ................................................47 16. Amalgamated, crudely im b ricated , conglomerate stratum c o n ta in in g very c o a rse -g ra in e d sandstone le n s (F acies A) in channel 1 ....................................................... 49 17. Sandstone lev ee f a c i e s (F acies E) a d ja c e n t to channel 2 .......................................................................................................53 18. L e n tic u la r t u r b i d i t e sandstone s t r a t a (F acies B) se p a ra te d by th in sh ale in te rb e d s in channel 2. . 55 19. Slump d e p o site d s t r a t a in channel 2 c o n s is t i n g of a conglomerate pod surrounded by deformed sandstone s t r a t a (F acies F ) ...................................................................................57 20. Pebbly mudstone u n it immediately o v e rly in g channel 2 t h a t d is p la y s s c a t t e r e d igneous pebbles and cobbles in a s i l t y m atrix (F acies F ) ............................... 61 21. Sandstone gully d e p o s it (F acies B) with lower e ro sio n a l c o n ta c t observed along I rv in e Company F i r e r o a d ..........................................................................................................65 22. Sandstone gully d e p o s it (F acies B) on I rv in e Company F ire ro a d showing a f i n i n g - and thinning-upw ards sequence..........................................................................................................67 23. Sandstone chute d e p o s it (F acies B) t h a t was cut and f i l l e d by a s in g le d e p o s itio n a l u n i t .....................................70 24. Bouma T a-b sequence d is p la y in g graded bedding and p la n a r -la m in a tio n s a c c e n tu a te d by m ica-g rain c o n c e n tra tio n s (F acies B ) ..............................................................74 25. Thin, f in e - g r a i n e d sandstone beds in te rb e d d e d with sh ale s t r a t a and s c a t t e r e d carbonate c o n c re tio n s (Facies G) .................................................................................................... 89 x 26. Thin, f in e - g r a i n e d , cross-bedded sandstone le n s e s se p a ra te d by p la n a r-la m in a te d bed s........................................94 27. D iscontinuous carbonate bed formed by the c o a le sc in g of 3 to 4 in d iv id u a l c o n c r e t i o n s ...........................................101 28. H ighly-fragm ented, rudimentary c o n c re tio n s in shale o u tc ro p ..........................................................................................................104 2 9. Inoceramus valve preserved in a carbonate c o n c r e t i o n .................................................................................................. 108 BO. Ammonite preserved w ith in a carbonate c o n c re tio n . 110 31. V e r t i c a l , c y l i n d r i c a l carbonate c o n c re tio n in a shale outcrop a t BS-9 along Black S ta r Canyon Road................................................................................. 113 32. Bending of sh a le s t r a t a around a carbonate c o n c re tio n along I rv in e Company F ire ro a d . . . . 119 33. Deformation of a sandstone bed o v e rly in g a c o n c re tio n le n s a t BS-120 along Black S ta r Canyon Road..................................................................................................................121 34. In c o rp o ra tio n of a sandstone bed i n t o th e top of the und erly in g c o n c re tio n a t BS-120 along Black S tar Canyon Road................................................................................................123 35. Fragmented carbonate c o n c re tio n t h a t formed p r io r to slumping of surrounding sh a le s t r a t a ................................ 127 36. Five, v e r t i c a l l y stacked carbonate c o n c re tio n s se p a ra te d by th in sh ale i n t e r b e d s ........................................131 37. Carbonate co n c re tio n with w e ll-p re s e rv e d Chondrites t r a c e s on e x t e r i o r s u r f a c e ..........................................................133 38. Leaf im pressions found w ith in carbonate c o n c r e t i o n s ................................................................................................145 39. Seed im pressions found w ith in carbonate c o n c r e t i o n s ................................................................................................147 40. Small carbonized log preserved w ith in a carbonate co n c re tio n from BS-9 along Black S ta r Canyon Road..................................................................................................................149 41. Ophiomorpha t r a c e s on sandstone bedding s u rfa c e in c h a n n e l - f i l l d e p o s it of channel 2 ........................................152 xi 42. T h a la ss in o id e s burrow in sandstone t u r b i d i t e d e p o s it from channel 2 ........................................................................................155 4 3 . 44. 4 5 . 4 6 . Escape s t r u c t u r e a t the base of a h ig h -d e n s ity t u r b i d i t e d e p o sit (F acies A) in a submarine chute d e p o s it along I rv in e Company F i r e r o a d ................................. 157 Chondrites t r a c e s in c o n c re tio n slab s e c t io n from BS-24 (50x m a g n i f i c a t i o n ) ............................................................162 Zoophycus leb en ssp u ren d is p la y in g meniscus back f i l l i n g in c o n c re tio n sla b s e c tio n from BS-24 (50x m a g n i f i c a t i o n ) ........................................................................... 166 Map showing p re se n t p o s it i o n s of Santa Ana Mountains, Santa Monica Mountains, and Simi H i l l s , and major f a u l t systems t h a t s e p a ra te the P en in su lar and Transverse Ranges .................................. 179 Chapter I INTRODUCTION This study focused on the Upper Cretaceous (Turonian-Cam- panian) Holz Shale Member (Ladd Formation) in Black S ta r Canyon, southern C a l i f o r n i a (see Figure 1). I n i t i a l s tu d ie s on th e se s t r a t a were performed by E.L. Packard in 1916, but i t was not u n t i l 1937 t h a t W.P. Poponoe used m egafossil date to e s t a b l i s h the s t r a t i g r a p h i c d i v i s i o n s used today. The Upper Cretaceous s t r a t i g r a p h i c sequence in the Santa Ana Mountains i s grouped i n t o th re e fo rm atio n al u n i t s (see Figure 2 ): the b asal Trabuco Formation; the in te rm e d ia te Ladd Formation (Baker Canyon and Holz Shale Members); and the uppermost W illiams Formation (Shulz and P le a s a n ts Members). The Trabuco Formation i s a red, d iso rg a n iz e d p eb b le -c o b b le -b o u ld e r conglomerate with in terb e d d ed c o a rse - sand l e n s e s . The Ladd Formation i s composed of a lower sandstone-conglom erate member (Baker Canyon Member) t h a t grades v e r t i c a l l y in to the Holz Shale Member which i s dominated by f i s s i l e s h a le s and mudstones, but a lso in c lu d e s in te rb e d d e d sandstones and la r g e l e n t i c u l a r conglomerate and sandstone d e p o s its . The W illiams Formation i s comprised of a lower u n it (Shulz Member) of in terb e d d ed f i s s i l e 1 Figure 1 Location map showing area of f i e l d study and o u t l i n e of Upper Cretaceous s t r a t a t h a t crop out in Santa Ana Mountains, southern C a lif o r n ia . Numbered s t a t i o n s correspond to l o c a t i o n s of s t r a t i g r a p h i c s e c t io n s shown in Figure 3 (m odified a f t e r Sundberg and Cooper,1978). 2 Block Stor Canyon .-W f Mio m i Cjrn -•H «r«irQ Cyn , - S c n tic p e Cjrn Son C m . \U CTr.. 3 mudstones, cross-bedded sandstones, and le n s e s of d iso rg a n iz e d cobble-conglom erates, and an upper u n it (P le a s a n ts Member) of poorly-bedded, medium- to c o a rse grained sandstones. Paleoenvironm ental i n t e r p r e t a t i o n s of these s t r a t i g r a p h i c u n i t s have g e n e ra lly agreed upon an o v e r a ll t r a n s g r e s s i v e - r e g r e s s i v e - t r a n s g r e s s i v e sequence (Almgren,1973,1982; Sundberg and Cooper,1978,1982; S a u l , 1982). S p e c if ic e n v i ronments of d e p o s itio n p o s tu la te d fo r these Cretaceous rocks in clu d e a l l u v i a l fan d e p o s its (Trabuco Formation) and h ig h-energy, shallow marine environments (Baker Channel Member, Shulz Member, and P le a s a n ts Member) (Sundberg and Cooper,1978,1982; Cooper e t a l ., 1 9 8 2 ; Saul ,1982). In c o n t r a s t to the general agreement of i n t e r p r e t a t i o n s mentioned above, paleoenvironm ental s tu d ie s of the Holz Shale Member have produced some sharply c o n f l i c t i n g i n t e r p r e t a t i o n s (Almgren,1973,1982; L an g ,1976,1978; Sundberg and Cooper,1978,1982; S u ndberg,1980; Link and B o t t j e r ,1982, Lee, 1982). Paleoenvironm ental i n t e r p r e t a t i o n s of the Holz Shale follow two b asic schools of thought: 1. a shallow marine, r e s t r i c t e d - c i r c u l a t i o n , paleoenvironment (Wheeler,1952; Orr,1964; L ang,1976,1978; Sundberg and Cooper,1978,1982; Sundberg, 1980); and 2. a deep marine, slope to bathyal 4 Figure 2 G en eralized s t r a t i g r a p h i c column for Upper Cretaceous s t r a t a in Santa Ana Mountains (modified from Sundberg and Cooper,1978). 5 o to to UPPER CRETACEOUS S c n t o n l o n - C o n i o c i a n Companion U J U J lu Q. U J 5 2 o n 5 < u. to 2 2: < o 5o X I Q J r o t i O X ) c •o •O ( J o jQ * tc < i o L U ll_ a. a U l o aj < < 0 U-OO (O ^ (A O U J a O Figure 3 • Regional s t r a t i g r a p h i c c r o s s - s e c t i o n fo r Upper Cretaceous s t r a t a of the Santa Ana Mountains. S t r a t i g r a p h i c sequence in c lu d e s the basalmost Trabuco Formation (D cg.), the o v e rly in g Baker Channel Member (O cg.), the mudstone s t r a t a and conglomerate l e s e s of the Holz Shale Member (M dstn.), and the uppermost W illiams Formation ( S s c g l . ) . Refer to Figure 1 for exact l o c a t i o n s of numbered s t r a t i g r a p h i c s e c tio n s (modified a f t e r Sundberg and Cooper,1978). 7 C O FAULT CONTACT Black Star Canyon UNCONFORMITY NW © © L 1 T M 0 F A C E S E l Sscgl 800 1 1 1 Mdstn i n 600 a > A 00 E l Ocgl 2 200 E l Dcg. 0 y t *>. ^ .^ .1 K i I o m e 1 e r c 0 I 2 3 A ) C i ^ I Z Z : .W f f l L y C I Z D r i y v ^ o>. paleoenvironment (Almgren,1973,1982; Blake and C o lb u rn ,1982; Lee, 1982; Link and B o t t j e r , 1982). Although a number of s tu d i e s have examined v ario u s a s p e c ts of the Holz Shale Member in c lu d in g m ic r o f o s s il data (Wheeler,1952; Orr,1964; Almgren,1973,1982; T r o t t e n , 1974; L an g ,1976,1978; L e e ,1982), megafauna c o l l e c t i o n s ( Poponoe,1937,1942; Sundberg and C ooper,1978; S u ndberg,1980,1982; S a u l , 1982), tra c e f o s s i l info rm atio n ( B o t t j e r e t a l . , 1 9 8 2 ) , and sedimentology of c o a rse -g ra in e d d e p o s its (Blake and C o lb u rn ,1982; Colburn and B l a k e , 1982; Link and B o t t j e r ,1982), most s tu d ie s have been lim i t e d in scope and t h e i r r e s u l t s have y e t to s e t f o r t h a more d e f i n i t i v e i n t e r p r e t a t i o n . In a d d itio n , d e t a i l e d s tu d i e s of the f in e - g r a i n e d rocks are la c k in g . I t i s the opinion of t h i s author t h a t the key to a c c u ra te p aleo en v i ronmental i n t e r p r e t a t i o n s i s not to focus on any s in g le body of geologic data, but to re se a rc h and s y n th e s is in fo rm atio n from a number of r e l a t e d d i s c i p l i n e s to form ulate a reaso n able model which in c o r p o ra te s a l l the a v a i l a b l e data. This r e se a rc h p r o je c t was designed to examine the p rev io u sly u nstudied geology of the Holz Shale ( e . g . , f in e - g r a in e d sedimentology, carbonate c o n c re tio n a n a l y s is , e t c . ) , and to u t i l i z e data from the d i s c i p l i n e s of paleontology, ichnology, and sedimentology in hopes of la y in g to r e s t the controversy which has surrounded geologic s tu d i e s of the Holz Shale fo r the p ast decade. 9 Chapter I I METHODS Analysis of the Holz Shale Member in Black S ta r Channel was completed by in c o r p o ra tin g both f i e l d and la b o r a to ry tech n iq u es i n t o the study. The s t r a t i g r a p h i c columns p resen ted in Appendix A r e p re s e n t summary d e s c r i p t i o n s of d e t a i l e d s t r a t i g r a p h i c data c o l l e c t e d from the discontinuous exposures of t h i s member along Black S ta r Channel Road, Black S ta r Channel Quadrangle, C a lif o r n ia (see Figure 4 ). Due to the d isc o n tin u o u s n atu re of outcrops in the f i e l d area, a pace-and-compass t r a v e r s e was i n i t i a l l y sta k e d -o u t so a c c u ra te r e fe r e n c e p o in ts were a v a i l a b l e for r e p o r tin g of sample s i t e l o c a t i o n s . Geometric c a l c u l a t i o n s based on t r a v e r s e measurements were u t i l i z e d to determine tru e s t r a t i g r a p h i c th ic k n e s s e s where d i r e c t measurements were u n a tta in a b le because of covered exposure. C o lle c tio n of s t r a t i g r a p h i c f i e l d data focused on the g a th e rin g of d e t a i l e d p a le o n to lo g ic , sedim entologic, and ic h n o lo g ic in fo rm a tio n . Except fo r the u b iq u ito u s occur rence of t e r r e s t r i a l p la n t and wood fragm ents and abundant Inoceramus v alv es, m a c ro fo s s ils are r e l a t i v e l y r a re in t h i s 10 Figure 4 Location map of exposures measured along Black S ta r Channel Road, Black S ta r Channel, southern C a l i f o r n i a . Stake numbers are a lso l i s t e d on the s t r a t i g r a p h i c columns in Appendix A making c o r r e l a t i o n of outcrop l o c a t i o n s and s t r a t i g r a p h i c s e c t io n s p o s s ib le . 11 33 ° 47 ' 30 " area. T herefore, a l l observed f o s s i l s were c o l l e c t e d for i d e n t i f i c a t i o n and a n a l y s is purposes. For m i c r o f o s s i l an aly ses, one Hubco sample bag (12 x 6.5 inches) was h a l f f i l l e d from 2-3 fo o t-d eep ex c a v a tio n s made a t each exposure along Black S ta r Channel Road and numerous s i t e s along I rv in e Company F ire ro a d (see Figure 5 ). Sedimentologic a n a ly se s in the f i e l d c o n c e n tra te d on documentation of l a t e r a l and v e r t i c a l t e x t u r a l changes, c o l l e c t i o n of numerous 0 7 5 ) sandstone and s h a le hand samples fo r la b o r a tory study, and c o l l e c t i o n of v i r t u a l l y every co n c re tio n w ith in t h i s s t r a t i g r a p h i c s e c t io n (>120). Carbonate concre tio n s are, for the most p a rt, evenly d i s t r i b u t e d throughout the sh ale o u tcrops. On the average, a co n c re tio n sample was s tu d ie d from every 0.5 to 1.0 m i n t e r v a l of sh ale s e c tio n . As a r e s u l t of the highly weathered and fragmented c o n d itio n of a l l f in e - and c o a rs e -g ra in e d s t r a t a in the f i e l d , most a n a ly se s of sedim entologic t e x t u r e s and s t r u c t u r e s were performed in the la b o r a to ry and w i l l be d isc u sse d below. F ie ld o b s e rv a tio n s of b i o tu r b a te s t r u c t u r e s c o n c e n tra te d on l a t e r a l and v e r t i c a l v a r i a t i o n s of tra c e f o s s i l s , b io tu rb a - tio n i n t e n s i t y , e x te rn a l morphologic c h a r a c t e r i s t i c s of t r a c e s , leb en ssp u ren compostion, and i n t e r r e l a t i o n s h i p s between t r a c e s and a s s o c ia te d sedim entologic and p ale o n to - lo g ic c h a r a c t e r i s t i c s . 13 Figure 5: Location map of m ic r o f o s s il sample s i t e s along Black S ta r Channel Road and I r v i n e Company F ire ro a d . These sample l o c a t i o n s a re a lso marked on the corresponding s t r a t i g r a p h i c columns in Appendix A. I rv in e Company F ire ro a d i s not a formal s t r e e t name, but w i l l be used in the t e x t to r e f e r to the road la b e le d as such on t h i s map. 14 __ % ' A 'rv N \ w & l ., ~Jm.W ffj ' w m m 7 /t//A 1 1 7 40 ’ 15 In a d d itio n to s t r a t i g r a p h i c o b s e rv a tio n s and measure ments made from exposures on Black S tar Channel Road, more general s tu d i e s were performed on Holz Shale outcrops of I rv in e Company F ire ro a d , S ilv e ra d o Channel streambanks, and the mountainous t e r r a i n f la n k in g both e a s t and west sid e s of Black S ta r Channel. These s t u d i e s co n ce n tra te d on l a t e r a l sedim entologic v a r i a t i o n s w ith in the s t r a t i g r a p h i c s e c tio n and included numerous o b s e rv a tio n s on l e n t i c u l a r sandstone and conglomerate d e p o s its . The base map used fo r t h i s fie ld w o rk was taken from Schoellhamer e t a l.(1 9 8 2 ) and was f i e l d checked fo r d e t a i l in th e Black S ta r Channel area. Except fo r the absence of a few minor c h a n n e l - f i l l d e p o s its , the map was found to be im p re ssiv e ly accu ra te in d e t a i l . Laboratory study of c o n c re tio n s and o th er hand samples was performed u t i l i z i n g many v a rie d te c h n iq u e s. S e r ia l sla b b in g of rock samples in p e rp e n d ic u la r planes allowed fo r th re e -d im e n sio n a l study of primary and b i o tu r b a te s t r u c tu r e s . F r ia b l e samples were coated in p o ly e s te r boat r e s i n , on the advice of Dr. Robert H. Osborne (U n iv e rsity of Southern C a l i f o r n i a ) , so t h a t clean slab b in g on a rock saw could be performed. This technique worked extrem ely well as i t q uickly soaked in t o a l l cracks and c re v a sse s bonding the sample in to a coherent mass. Following sla b b in g , various te c h n iq u e s were attem pted to a c c e n tu a te both p h y sica l and biogenic s t r u c t u r e s . 16 A ccentuation tech n iq u es used in t h i s study included s t a i n i n g of slabbed samples with the b i o l o g i c a l dye A liz a rin Red in an attem pt to h i g h l i g h t burrow w a lls where clay m in era ls were c o n c e n tra te d ( a f t e r H am blin,1962), the use of f a s t - d r y i n g h ig h -g lo s s lacq u er spray, and e tc h in g techniques with h y d ro c h lo ric acid (c o n c re tio n use o n ly ). Of the th re e tech n iq u es attem pted, only the la c q u e r spray was found to be u sefu l in h i g h l i g h t i n g sedimentary and b i o tu r b a te s t r u c t u r e s beyond what was v i s i b l e with the naked eye. In a d d itio n to the v is u a l a n aly ses of the hand samples, p e tro g ra p h ic s t u d i e s were performed on approxim ately t h i r t y sandstone, c o n c re tio n , and mudstone samples. P etro g rap h ic a n a ly se s proved extremely v alu ab le in a s c e r t a i n i n g t e x t u r a l r e l a t i o n s h i p s w ith in the f i n e - g r a i n e d rocks, and are u t i l i z e d throughout the t e x t in sedim entologic d e s c r i p t i o n s of these d e p o s its . Sample l o c a t i o n s of t h i n - s e c t i o n s made fo r t h i s study are la b e le d on the s t r a t i g r a p h i c columns in Appendix A. To complement the t e x t u r a l s tu d ie s , geochemical analyses using X-ray d i f f r a c t i o n and LECO gasom etric and combustion ap p aratu s (as d e sc rib e d by Kolpack and B e l l , 1968) were made. X-ray d i f f r a c t i o n s tu d i e s c o n c e n tra te d on i d e n t i f i n g the m in era lo g ic c o n s t i t u i e n t s of sampled c o n c re tio n s and a lso a few samples of the surrounding s h a le s . Gasometric d eterm i n a tio n s of organic carbon and calcium carbonate c o n te n ts 17 a lso focused on c o n c re tio n com positions, but s im i l a r l y included a few sh ale samples. The r e s u l t s of th ese an aly ses w i l l be p resen ted and d isc u sse d l a t e r in t h i s paper. 18 Chapter I I I SUBMARINE CANYONS AND CHANNELS 3.1 GENERAL INTRODUCTION One of the most c h a r a c t e r i s t i c f e a t u r e s of submarine slope environments are c h a n n e l - f i l l d e p o s its ( S t a n le y ,1969; Stanley and U nrug,1972; Mutti and Ricci Lucchi,1 9 7 8 ). In the past two decades, the u n d erstanding and re c o g n itio n of submarine channel d e p o s its has expanded ra p id ly and the l i t e r a t u r e now c o n ta in s many examples in both modern (F i s h e r ,1961; B uffington and Moore,1963; S t a n l e y ,1974; Karig e t a l .,1 9 7 8 ; Kulm and S c h eid eg g ar,1979; McGregor and B e n n e tt,1979; P rio r e t a l . , 1 9 8 l ; McGregor e t a l .,1 9 8 2 ; S t u b b l e f i e l d e t a l .,1 9 8 2 ; Twichell and R o b e r t s ,1982) and a n c ie n t environments (W alker,1966,1978; Aalto and D ott,1970; Lowe,1972; Keith and F riedm an,1977; Dott and B i r d , 1979; Picha,1979; Winn and D o t t , 1979; B e r r y h i l l ,1981; Hein and Walker,1982). Commonly a s s o c ia te d with l a r g e submarine channels a re s im ila r , s m a l l e r - s c a l e channels and g u l l i e s t h a t are u su a lly lo c a te d towards th e head of a channel (Coleman e t a l .,1 9 8 1 ; P rio r e t a l .,1981; T w itchell and R o b e r t s ,1982; May e t a l . , 1 9 8 3 ) . These channels u su ally coalesce downslope forming p in n a te drainage p a t t e r n s t h a t 19 c lo se ly resemble modern, f l u v i a l drainage systems (Karig e t a l .,1 9 7 8 ; McGregor e t a l .,1 9 8 2 ; F arre e t a l . , 1983). The o r ig in of submarine channels i s open to some debate. The two most popular hypotheses used to e x p la in the develop ment of these slope f e a t u r e s in clu d e submarine e ro sio n by mass-wasting p ro c e sse s ( S h e p a rd ,1955,1973; Bouma,198l; P rio r et a l . ,1981 ; T w itch e ll and Roberts, 1982), and i n i t i a t i o n by s u b a e ria l f l u v i a l e ro sio n with subsequent m o d ific a tio n by submarine m ass-w asting (B uffington and Moore,1963; In d e r- b itz e n and Simpson,1971; May e t a l . , 1 9 8 3 ) . I t seems l i k e l y t h a t both hypotheses are probably c o r r e c t and t h a t d i f f e r e n t geologic s e t t i n g s would account fo r d i f f e r e n t mechanisms of form ation. The d i s t i n c t i o n between th ese pro cesses i s d i f f i c u l t to e v a lu a te in modern environments and i s exceed ingly arduous in the rock reco rd , e s p e c i a l l y i f p re s e r v a tio n of l a t e r a l l y e q u iv a le n t environments i s not complete ( e . g . , f l u v i a l / d e l t a i c systems d i r e c t l y a s s o c ia te d w ith a submarine c h a n n e l) . D ise c tin g the f i n e - g r a i n e d sedim ents t h a t dominate the slope environment, submarine channels and v a l l e y s serve as co n d u its fo r c o a rs e -g ra in e d sedim ents to bypass the c o n t i n en tal s h e lf (Shepard and D i l l , 1966; Normark,1974,1978; Karig e t a l ., 1 9 7 8 ; McGregor and B e n n e tt,1979; Dott and B i r d , 1979). The small chutes and g u l l i e s t h a t form the channel t r i b u t a r y system also play an im portant r o le in the 20 o v e r a ll d i s t r i b u t i o n of sediment along the c o n tin e n ta l slope (Underwood and K a r i g , 1980). The channel drainage system c a p tu re s sediment g ra v ity flows moving down the slope and r e d i r e c t s them towards the major channel a x is. This complex system of sed im en tatio n accounts fo r the p o ly g e n e tic h is to r y of submarine channels and reco rd s an i n t r i c a t e i n t e r p l a y of both d e p o s itio n a l and e r o s io n a l pro cesses (Chough and H e s s e ,1976; M utti,1977; B e lla ic h e e t a l .,1 9 7 9 ; S h e p a rd ,19 81). Nelson and Kulm (1973) developed a c l a s s i f i c a t i o n scheme fo r deep-sea channels based on the r e l a t i v e importance of e ro s io n a l versus d e p o s itio n a l fo rc e s . They d e sig n a te th re e end members of a g ra d a tio n a l sequence of channels t h a t range from 1. channels cut e n t i r e l y by e ro siv e p ro cesses, to 2. channels c o n s tru c te d by a combination of both d e p o s itio n a l and e r o s io n a l fo rc e s , to 3. channels b u i l t e n t i r e l y by d e p o s itio n a l p ro c e sse s. The source of these f o rc e s i s g e n e ra lly considered to be sediment g ra v ity flows which o r i g i n a t e on the upper slope or ste e p channel-head w a lls as slumps or s l i d e s (G orsline and Emery,1959; D o t t , 1963; Middleton and Hampton,1973; Nardin e t a l ., 1 9 7 9 b ) . A complete continuum of mechanical behavior of sediment g ra v ity flows from e l a s t i c through p l a s t i c through viscous flow has been p o s tu la te d ( D o t t , 1963; Middleton and 21 Hampton,1973,1976; Embley,1976; Nardin e t a l 19 7 9 a ,1979b; Lowe,1979). This continuum i s thought to be the r e s u l t of in c r e a s in g sediment water content downslope by tu r b u le n t mixing a cro ss th e upper i n t e r f a c e of a flow, mixing by flow se p a ra tio n along the head of a flow, or mixing of water trapped beneath the flow (Middleton and Hampton,1973). In a d d itio n to having d i f f e r e n t support mechanisms op erate along t h i s g r a d a tio n a l sequence, i t has a lso been suggested t h a t d i f f e r e n t mechanisms can occur sim ultaneously, e f f e c t i n g d i f f e r e n t g r a i n - s i z e p o p u la tio n s w ith in the same flow (Lowe,1982). Considering the la r g e number of permuta tio n s of support mechanisms t h a t could a r i s e during d i f f e re n t c o n d itio n s of flow, i t seems l i k e l y t h a t a n a l y s is of the f i n a l d e p o s it w i l l recognize only the most re c e n t and most dominant of these p ro c e sse s. For these reasons, the f i e l d and la b o r a to ry analyses of c o a rs e -g ra in e d d e p o s its w ith in the Holz Shale Member t h a t w i l l be d iscu ssed below, are recognized as the end products of a complex s e t of r h e o lo g ic a l p ro cesses, and not d e f i n i t i v e i d e n t i f i c a t i o n s of a n c ie n t sediment g ra v ity flows. 22 3.2 CHANNEL-FILL DEPOSITS: INTRODUCTION The Holz Shale Member in Black S ta r Channel c o n ta in s a number of la r g e , l e n t i c u l a r , cl iff - f o r m in g d e p o s its t h a t are comprised of d isc o n tin u o u s, c o a rs e -g ra in e d sandstones and d iso rg a n iz e d conglom erates. These d e p o s its range in t h i c k ness from 2 to 60 m although a s im ila r d e p o s it 168 m th ic k i s lo c a te d between W illiams and Black S ta r Canyons (Blake and C o lb u rn ,1982). Three, la rg e l e n t i c u l a r d e p o s its crop out along Black S ta r Canyon Road and are d e sc rib e d in d e t a i l in Appendix A (43 to 53, 109, 144 to 184 m). These s t r a t a are i n t e r p r e t e d as submarine channel d e p o s its based on e x te r n a l morphology, i n t e r n a l composition ( i . e . , m a s s -tra n s ported sed im en ts), and bathym etric d e te rm in a tio n s of surrounding s t r a t a from m ic r o f o s s il data. The channel d e p o s its g e n e ra lly e x h i b i t m oderately- to s te e p ly - d ip p in g w a lls and t r u n c a t io n of u n d erly in g sh a le s t r a t a where c o n ta c ts are v i s i b l e . Most channels are exposed in c r o s s - s e c t i o n a l view only and t h e r e f o r e , a n a ly s is of l a t e r a l v a r i a t i o n s w ith in a d e p o sit i s very lim ite d . These l e n t i c u l a r d e p o s its can be s e p a ra te d i n t o two general s iz e c l a s s e s based on width and th ic k n e s s dimensions. The la r g e r channels have th ic k n e s s e s of 40 to 60 m and w idths of 80 to 120 m. These d e p o s its w i l l be r e f e r e d to as a n c ie n t submarine channel d e p o s its . The sm aller channels range in 23 th ic k n e s s from 0.25 to 10 m and range in width from 5 to 20 m, and w i l l be termed submarine chutes and g u l l i e s . The fo llo w in g d e s c r i p t i o n s of the s t r a t a comprising the channel d e p o s its a re based on f a c i e s a s s o c i a t i o n s of Mutti and Ricci Lucchi (1978; see Figure 6) and Middleton and Hampton’ s (1973,1976) c l a s s i f i c a t i o n scheme of sediment g ra v ity flows as m odified by Lowe (1982). D e s c rip tio n s below and in Appendix A of sediment s o r t i n g a re based on Compton (1962, p . 214), terms fo r degree of rounding of g ra in s a re based on Powers (1953), g r a i n - s i z e d e s c r i p t i o n s are based on the Wentworth s c a le , and c o lo r d e s c r i p t i o n s are from the rock- c o lo r c h a r t d i s t r i b u t e d by the N ational Research Council (Goddard e t a l . , 1 9 4 8 ) . 24 Figure 6: T u r b id ite Facies A s so c ia tio n s of Mutti and Ricci Lucchi ( 1978) . £ !l T u r b i d i t e F acies Of Mutti And Ricci Lucchi ( 1 9 7 8 ) : Facies A: Poorly sorted, coarse-grained sandstones and conglom era tes that generally lack sedimentary s tr u c tu r e s . Beds are commonly le n t ic u l a r , are amalgamated, and include graded bedding and abundant rip-up c l a s t s . Facies B: Lenticular, massive, medium- to fine-grained sandstones that are b e tt e r sorted and more l a t e r a l l y continuous than beds of Facies A. Shale c la s ts and erosional features are quite frequent. Dish s tr u c tu re s are occasionally present. Facies C: Medium- to fin e -g ra in e d sandstones with thin shale interbeds. Sandstone s t r a t a are bounded by even and p a ra lle l surfaces that are l a t e r a l l y continuous. Complete Bouma sequences, shale c l a s t s , and broad, low r e l i e f channels occur in this facies. Facies D: Laterally continuous fin e - and v e r y fine-grained sandstones, s i l t s t o n e s , and shales. Thin current laminae and Bouma sequences commonly found. Facies E: Very sim ila r to Facies D but displays higher sand- shale ra tio s , thinner irre g u la r beds, and more discontinuous beds with wedging and lensing. Facies F: Chaotic deposits produced by mass movement of sediments ( i . e . , slumps, mudflows, e t c . ) . Facies G: Fine-grained sediments with in d is t in c t or poorly-developed bedding. The shales and marls are infe rre d to by produced by deposition of d ilu te suspensions including t u rb id ity c u rre n ts, nepheloid layers, etc. 26 3.3 SUBMARINE CANYON DEPOSITS The l a r g e s t c o a rse -g ra in e d d e p o s it in Black S ta r Canyon ( r e f e r e d to as channel 1 ;see Figure 7) is approxim ately 60 rr th ic k and 120 m wide and crops out along the s o u th e a st wall of the canyon forming a fragmented, v e r t i c a l c l i f f face. These s t r a t a are o f f s e t by a number of la r g e normal f a u l t s and form the only lo n g i t u d i n a l view of a channel d e p o s it p re se n t in the f i e l d are a . This d e p o s it shows an e a s t-w e s t e lo n g a tio n and c o n ta in s a l im ite d number of p a le o c u rre n t i n d i c a t o r s (p la n a r c ro s s -la m in a tio n s , conglomerate c l a s t im b ric a tio n , and poorly-developed f l u t e c a s ts ) t h a t demons t r a t e a w e s t e r l y - t r a n s p o r t d i r e c t i o n . Study of channel 1 was l i m i t e d by the v e r t i c a l n atu re of outcrop exposures, but d e t a i l e d exam ination of the lowermost s t r a t a , and more general o b s e rv a tio n s of the o v e rly in g beds w ith b in o c u la rs re v e a le d d isc o n tin u o u s, l e n t i c u l a r d e p o s its t h a t e x h i b i t a s e r i e s of th re e t h in n in g - and fining-upw ards sequences. The d e p o s its of channel 1 are dominated by s t r a t a of f a c i e s A. The th in n in g - and fining-upw ards sequences in channel 1 c o n s is t of lowermost conglomerate beds 0.5 to 4.0 m th ic k t h a t in c lu d e both m a trix -su p p o rte d and c l a s t - s u p ported s t r a t a w ith subangular to w ell-rounded igneous pebbles, cobbles, and b o ulders. Conglomerate beds comprise 27 Figure 7 A c r o s s - s e c t i o n a l view of channel 1. This outcrop i s f a u l t e d and i s surrounded by sh ale s t r a t a . 28 29 approximately 50 to 60% of t h i s outcrop, are g e n e ra lly d iso rg a n iz e d but d isp la y lo c a l i z e d crude im b ric a tio n , c o n tain abundant rip - u p c l a s t s , have a very c o a rse -g ra in e d sand m atrix , and e x h i b i t numerous t r u n c a t io n s u rfa c e s of und erly in g s t r a t a (F igure 8 ). These d e p o s its are i n t e r preted as d e b ris-flo w d e p o s its based on t h e i r poor s o rtin g , abundance of m atrix and la r g e c l a s t s , lack of t r a c t i o n - c u r re n t s t r u c t u r e s , presence of la r g e c l a s t s f l o a t i n g atop the d e p o s it, and random o r i e n t a t i o n of r i p c l a s t s . Conglomerate c l a s t s in clu d e rocks of both i n t r u s i v e and e x t r u s i v e igneous compostion and an o ccasio n al sandstone c l a s t . Igneous c l a s t s in clu d e rocks of p o r p h y r itic in te rm e d ia te ( d i o r i t e - g r a n i t e ) i n t r u s i v e , in te rm e d ia te - f e l s i c p h e n o c ry stic v itro p h y r e , and b a s a l t i c a n d e s ite composition ( i d e n t i f i e d by Rick H a z le tt, U n iv e rsity of Southern C a l i f o r n i a ) . For the sake of b re v ity , the term igneous w i l l be used throughout the remainder of the te x t when d e s c rib in g c l a s t s of s im ila r com position. The reader i s r e f e r e d to Colburn and Blake (1982) for a d e t a i l e d study of c l a s t composition and source provenance of Upper C reta ceous s t r a t a in S ilv e ra d o Canyon. Interbedded w ith the conglomerate beds are c o a rse - to very c o a rse -g ra in e d sandstone s t r a t a t h a t are i n t e r p r e t e d as low- and h ig h -d e n s ity t u r b i d i t y c u r r e n ts ( a f t e r Lowe,1982). Low-density t u r b i d i t y c u r r e n ts are i d e n t i f i e d based on Bouma 30 Figure T runcation su rfa c e a t base d e b ris flow d e p o sit (Facie of conglomerati A) in channel t u r b i d i t e d i v i s i o n s (mostly T a-b and a few T a-b-c sequences), abundant r ip -u p c l a s t s near the base of a stratum , and scoured basal c o n ta c ts with poorly-developed f l u t e and load c a s t s . H igh-density t u r b i d i t y c u r r e n ts c o n s is t of massive or crudely graded beds with s c a t t e r e d cobbles and rip - u p c l a s t s t h a t are c o n c e n tra te d along c e n t r a l shear planes w ith in the d e p o s it (F ig u res 9 & 10) or are buoyed-up towards the upper c o n ta c t. Deformed r ip -u p c l a s t s (see Figure 11) and a s e r i e s of th ru s te d , en echelon rip -u p c l a s t s (see Figure 12) are also observed in th ese d e p o s its . Cobbles and pebbles are commonly found f l o a t i n g atop th ese h ig h -d e n s ity t u r b i d i t e s (Figure 14) and e x h i b i t c u rre n t shadows of pebbles and coarse sand c o n c e n tra te d on the w estern or le e side of the cobbles. Occasional occur rences of T h a la ss in o id e s and Qphiomorpha t r a c e s were a lso observed on upper bedding s u rf a c e s of the sandstone s t r a t a . Overlying the sandstone s t r a t a and s e p a ra tin g in d iv id u a l d e p o s itio n a l u n i t s are f i n e - s c a l e p la n a r- and c r o s s - la m i nated beds of f i n e - to medium-grained sand (Figure 13). P la n a r-la m in a te d u n i t s commonly d isp la y c o n c e n tra tio n s of t e r r e s t r i a l p la n t and wood fragm ents (Figure 15) and are i n t e r p r e t e d with the cross-bedded u n i t s as t r a c t i o n - c u r r e n t d e p o s its t h a t formed from downslope c u r r e n ts flow ing w ith in the channel. D iscontinuous, th in (<6 cm) san d y -sh ale 31 Figure 9 Igneous cobble and s c a t t e r e d sh a le rip - u p c l a s t s lo c a te d in c e n t r a l zone of h ig h -d e n sity t u r b i d i t e (F acies A) in channel 1. 34 35i F ig u re 10 : Abundant sh ale r ip - u p c l a s t s d isp e rse d in a massive, very c o a rse -g ra in e d sandstone stratum (F acies A) in channel 1. 36 F ig u re 11 : Deformed r ip -u p c l a s t s in c e n tr a l zone of high d e n sity t u r b i d i t e (F acies A) in channel 1. 39 Figure 12: A s e r i e s of th re e en echelon sh ale r ip -u p c l a s t s a t the top of a h ig h -d e n s ity t u r b i d i t e (F acies A) in channel 1. 40 Figure 13: Igneous cobble and pebble c l a s t s found a t the top of a h ig h -d e n s ity t u r b i d i t e d e p o s it (F acies A) in channel 1. 42 Lnterbeds are r a r e in t h i s d e p o s it and are commonly t r u n cated by o v e rly in g s t r a t a . At the southwest end of t h i s d e p o s it, a small c r o s s - s e c tio n a l exposure i s v i s i b l e . This outcrop i s dominated by an amalgamated 4 m -thick, pebble-cobble, c la s t- s u p p o r t e d conglomerate. Subrounded to rounded igneous c l a s t s d isp lay a n o rth -so u th im b ric a tio n with a so u th e rly dip. Enclosed w ith in t h i s d e p o s it are two very c o a rs e -g ra in e d sandstone Lenses t h a t e x h i b i t poorly-developed p la n a r -la m in a tio n s (Figure 16). These le n s e s probably r e p re s e n t p o s t-d e p o s i- tio n a l v e r t i c a l movement of the sand m atrix t h a t occurred when the la r g e c l a s t s s e t t l e d , f o rc in g the viscous m atrix upwards (D.S. G o r s l i n e , 1983,pers.comm.). This conglomerate bed i s i n t e r p r e t e d as a d e b ris flow d e p o s it. I t probably o r ig in a te d as a slump or s l i d e o ff the channel w all, or was captured by the drainage system feed in g t h i s channel, hence e x p lain in g the cobble im b ric a tio n normal to the channel axis. S im ilar d e p o s its o r i g i n a t i n g from the sid e s of channels have been recognized in buried submarine channels in the Northwest Gulf of Mexico ( B e r r y h i l l ,1981). L a te ra l changes in t h i s s t r a t i g r a p h i c s e c tio n o u tsid e the c h a n n e l - f i l l d e p o s it are very d i f f i c u l t to analyze due to in te n se v e g e ta tio n cover and modern stream ero sio n . Limited exposures o u tsid e the channel d e p o s it d isp lay p o o rly -d e v e l- 44 Figure 14: Cross-bedded sandstone le n s o v e rly in g a massive, very c o a rs e -g ra in e d sandstone stratum (F a c ie s B) in channel 1. Figure 15 : Bedding plane of co n c e n tra te d o rganic fragm ents from a p la n a r-la m in a te d , f in e - g r a i n e d sandstone in te rb e d (F acies C) in channel 1. 47 48 figure 16 Amalgamated, crudely im bricated, conglomerate stratum c o n ta in in g very c o a rse -g ra in e d sandstone le n s (F acies A) in channel 1. 49 oped sandstone lev ee f a c i e s and dominant, high ly -frag m en ted sh a le s t r a t a of f a c i e s G. The second and only other example of a small submarine channel d e p o s it in Black S ta r Canyon ( r e f e r e d to as channel 2) is d escrib ed in d e t a i l in Appendix A (144 to 184 m). This outcrop along Black S ta r Canyon Road r e p r e s e n t s the most complete and most a c c e s s i b l e v e r t i c a l c h a n n e l - f i l l exposure in the area. Channel 2 i s dominated by f a c i e s A with l o c a l i z e d occu rren c es of f a c i e s F and poorly-developed levee f a c i e s (Figure 17). S t r a t a comprising channel 2 are very s im ila r in t e x t u r e and s t r u c t u r e to the ones d escrib ed above fo r channel 1, with a few n o tab le ex c e p tio n s. The most s t r i k i n g d i f f e r e n c e between channel 1 and channel 2 i s the li m i t e d occurrence of conglomerate s t r a t a in channel 2 (< 10%) and a lso the la c k of abundant boulders contained w ithin them. Channel 2 i s dominated by l e n t i c u l a r , c o a rse grained to pebbly sandstones t h a t are i n t e r p r e t e d as both low -density and h ig h -d e n s ity t u r b i d i t y c u r r e n ts (Figure 18). D i s ti n c t i o n between h ig h -d e n s ity and low -d en sity t u r b i d i t y c u r re n ts i s based on primary s t r u c t u r e s and sediment t e x t u r e s as d escrib ed p r e v io u sly . These sandstone beds commonly e x h i b i t amalgamated bedding, poorly-developed s o le marks, abundant r ip - u p c l a s t s , Bouma T a-b sequences, p la n a r -la m in a tio n s a c c e n tu a te d by m ica-g rain c o n c e n tr a tio n s , i r r e g u l a r sharp b asal c o n ta c ts , abundant T h a la ss in o id e s and 51 Ophiomopha tr a c e s , and l o c a liz e d occurrences of t e r r e s t r i a l organic fragments. Other noteworthy d iff e r e n c e s between channel 1 and channel 2 include in channel 2 in creased occurrence of more l a t e r a l l y p e r s i s t a n t shale in te rb e d s (maximum thickness=1 m; average 1-3 cm), g r e a te r c o n c e n tra tio n s of Ophiomorpha and T h a la ssin o id es tr a c e s on bedding su rfa c e s of sandstone s t r a t a , and the presence of slum p-deposited sandstone and conglomerate beds (see Appendix A ,155 m) . This penecontem- poraneously deformed d e p o sit occurs as a package of sand stone s t r a t a and th in , shale in te rb e d s t h a t d isp la y s wavy and co n to rte d bedding with a pod of diso rg an ized pebble-cob- b le -b o u ld e r conglomerate enclosed w ith in (see Figure 19). S im ilar slump d e p o sits might also occur in channel 1, but none were observed in the lim ite d exposures a v a ila b le . Another i n t e r e s t i n g fe a tu re of channel 2 is the very- coarse grained te x tu r e of the uppermost s t r a t a . A s e r i e s of th re e disorganized, c la s t- s u p p o rte d , pebble-cobble conglom e r a te s con tain in g a few rare igneous boulders, form the top of t h i s d e p o sit. These s t r a t a are l o c a l l y channelized and d i s s e c t underlying s t r a t a , contain two very c o arse-g rain ed sand le n se s, and are o v e rla in conformably by a 1.5 m-thick pebbly mudstone bed t h a t grades v e r t i c a l l y in to f i s s i l e shale s t r a t a . These conglomerate d e p o sits, along with the 52 Figure 17 : Sandstone levee f a c i e s (F acies E) a d ja c e n t channel 2. 54 Figure 18 : L e n tic u la r t u r b i d i t e sandstone s t r a t a (F acies B) s e p a ra te d by th in sh ale in te rb e d s in channel 2. Note rock hammer in lower r ig h t-h a n d coner for s c a le . 55 Figure 19 Slump d ep o sited s t r a t a in channel 2 c o n s is t i n g of a conglomerate pod surrounded by deformed sandstone s t r a t a (F a c ie s F). 57 few other conglomerate beds found in channel 2, are i n t e r p reted as c o a rs e -g ra in e d d e b ris-flo w d e p o s its . These uppermost conglom erates may have plugged channel 2 when dep o sited and prevented f u r t h e r s e d im e n t-g ra v ity flow d e p o s itio n w ith in th e channel. This would e x p la in the sudden f in i n g of the o v erly in g s t r a t a . S im ilar d e p o s itio n a l mechanisms have been recognized in Paleozoic submarine channels in Canada (Hein and W a lk e r,1982) and in modern channels on the North American A t l a n t i c slope (McGregor and B e n n e t t , 1979). The p o o r ly - s o rte d , pebbly mudstone u n it t h a t o v e r l ie s the uppermost conglom erates of channel 2 c o n ta in s rounded to subrounded pebbles and cobbles of igneous composition (Figure 20). The c l a s t s occur in small, d isco n tin u o u s zones w ith in a s a n d y - s i lt y m atrix and a lso as in d iv id u a l c l a s t s s c a t t e r e d throughout the mudstone u n i t . Bedding i s very poorly developed but ranges from i r r e g u l a r p la n a r-la m in a - t io n s to c o n to rte d bedding. An i d e n t i c a l d e p o s it occurs a t the base of Black S ta r Canyon Road (see Appendix A,2 m) and i s a s s o c ia te d w ith a small chute d e p o s it. Pebbly mudstones are c h a r a c t e r i s t i c of slope environments (Stanley and U nrug,1972) and have been observed in modern submarine channels (G orsline and Emery,1959; S t a n l e y ,1974). Emplace ment mechanisms fo r pebbly mudstones in clu d e the downslope slumping of coarse c l a s t s in a w a t e r - s a t u r a t e d mud m atrix . 59 This slumping i s thought to occur as a very viscous flow which j u s t surpassed i t s l i q u i d l i m i t , but reg ain ed cohesion t h i x o t r o p i c a l l y before a tru e t u r b i d i t y c u rre n t developed ( C r o w e ll,1957; D o tt,1 9 6 3 ). P a le o c u rre n t i n d i c a t o r s w ith in channel 2 are very ra re . Sole marks are very poorly developed and in clu d e i r r e g u l a r to lo b a te load c a s t s and a few poorly-developed f l u t e c a s t s . The f l u t e c a s ts i n d i c a t e a p a le o c u rre n t d i r e c t i o n range of s o u th e a st-so u th w e s t. The e lo n g a tio n d i r e c t i o n of channel 2 i s very d i f f i c u l t to determine due to poor exposure and in te n s e v e g e ta tio n cover, but a general south-southw est e lo n g a tio n seems probable from the geologic map of Schoel- hamer e t a l . (1982) and t a l u s boundaries i d e n t i f i e d in the f i e l d . I f these p a le o c u rre n t d i r e c t i o n s are considered re a so n a b le e s tim a te s , then they would i n d i c a t e t h a t channel 1 and channel 2 probably jo in e d somewhere on the slope environment. In f a c t , f i e l d r e l a t i o n s h i p s of channel 2 and the s o u th e r ly - im b r ic a te d conglomerate describ ed from the southwest exposure of channel 1, i n d i c a t e th a t channel 2 might have been the source or channel of t r a n s p o r t fo r t h i s conglomerate d e p o s it. 60 Figure 20: Pebbly mudstone u n i t immediately o v erly in g channel 2 t h a t d is p la y s s c a t t e r e d igneous pebbles and cobbles in a s i l t y m atrix (F acies F). 61 6 2 3.4 SUBMARINE CHUTE AND GULLY DEPOSITS In a d d itio n to the la rg e submarine c h a n n e l - f i l l d e p o s its found in the Holz Shale Member of Black S tar Canyon, th e re are a lso a number of sm aller, l e n t i c u l a r , c o a rse -g ra in e d d e p o s its . These channels have s te e p ly - to m o d e ra te ly -d ip ping w a lls , e ro s io n a l basal c o n ta c ts , and are f i l l e d with d e p o s its i n t e r p r e t e d as m a s s -tra n s p o rte d sedim ents. These c h a n n e l - f i l l d e p o s its d i f f e r from the la r g e r sequences previously d e sc rib e d in t h a t they r a r e l y co n tain sediments g re a te r than pebble siz e , are dominated by medium- to co a rse -g ra in e d sands of f a c i e s B, and the s m a lle st channels appear have been cut and f i l l e d by a s in g le d e p o s itio n a l jni t . These sm aller channels can be d ivided in to two groups based on whether they r e p re s e n t one d e p o s itio n a l u n i t or more than one d e p o s itio n a l p u lse. The channels which r e p re s e n t two or more d e p o s itio n a l u n i t s (F ig u res 21 & 22) cend to be c o a r s e r - g ra in e d , have g r e a te r th ic k n e s s e s , and d isp la y b e tte r -d e v e lo p e d channel morphologies than the s i n g l e - d e p o s i t i o n a l - u n i t channels. Two such d e p o s its occur along Black S ta r Canyon Road and are d escrib ed in Appendix A ;see 109 m and 43 to 53 m). The s t r a t a which comprise these channels are dominantly very c o a rs e -g ra in e d to pebbly 63 sandstones t h a t d isp la y abundant r ip - u p c l a s t s , pebbly c h a n n e l-la g d e p o s its , scoured basal c o n ta c ts , amalgamated massive bedding, graded bedding, Bouma T a-b sequences, poorly developed le v e e f a c i e s , r a r e so le marks, l o c a l l y abundant Qphiomorpha and T h a la ss in o id e s t r a c e s , r a r e escape s tr u c t u e s , and c e n t r a l l y - c o n c e n t r a t e d zones of r ip - u p c l a s t s and s c a t t e r e d cobbles. These sandstone s t r a t a a re i n t e r p reted as h ig h -d e n s ity and lo w -d en sity t u r b i d i t y c u r re n ts based on primary s t r u c t u r e s and sediment t e x t u r e s as d escrib ed p re v io u sly . In te rb e d s of p la n a r- and c r o s s - la m i nated f i n e - to medium-grained sands i n d i c a t e t r a c t i o n - c u r r e n t p ro cesses were im portant between d e p o s itio n of sediment g r a v ity flows. Also, the occurrence of a d isc o n tin u o u s, re v e rse -g ra d e d , p o o r ly - s o r te d pebble-conglom erate with c o a rse -g ra in e d sand m atrix in one channel (see Appendix A,45 m) , suggests t h a t g rain -flo w d e p o s itio n may also have playec. a minor r o le in th e f i l l i n g of these channels. P a le o c u rre n t data from th ese channels i s very lim ite d . Rare c r o s s -la m in a tio n s and th re e c h a n n e l-a x is measurements i n d i c a t e a t e n t a t i v e w est-southw est t r a n s p o r t d i r e c t i o n . Sole marks were not observed on th e s t r a t a comprising th ese d e p o s its . The s i n g l e - d e p o s i t i o n a l - u n i t channels or chutes (Figure 23) occur as d isc o n tin u o u s sandstone beds t h a t la c k a 64 Figure 21 Sandstone gully d e p o s it (F acies B) with lower e ro sio n a l co n ta c t observed along I rv in e Company Fi reroad. 65 66 " 1 Figure 22: Sandstone gully d e p o s it (F acies B) on I rv in e Company F irero ad showing a f i n i n g - and th in n in g - upwards sequence. 67 68 ^ e ll-d e v e lo p e d channel morphology, but in s te a d slowly pinch-out in o p p o site d i r e c t i o n s (see Appendix A ,117 and 1 m). The broad and shallow n atu re of these d e p o s its and the fin e grading commonly observed w ith in beds, in d i c a t e t h a t these channels were cut and f i l l e d by the same d e p o s itio n a l event (M u tti,1977). These s t r a t a are dominantly medium- to c o a rse -g ra in e d sandstones with r a re occurrences of pebble- and c o b b le -siz e d c l a s t s . They a lso commonly e x h i b i t massive bedding, s c a t t e r e d r ip - u p c l a s t s , p la n a r -la m in a tio n s accen tu a te d by mica g r a in s , i r r e g u l a r b asal c o n ta c ts w ith poorly- developed f l u t e and load c a s t s , and r a r e Qphiomorpha and T h a la ssin o id es tra c e f o s s i l s . Therefore, such d e p o s its are i n t e r p r e t e d as lo w -d en sity t u r b i d i t y c u r re n ts t h a t s p i l l e d ever the c o n tin e n ta l s h e lfb re a k and d is s e c te d the s o f t, nuddy slope sedim ents. One chute d e p o s it (see Appendix A ,1 m) c o n ta in s s c a t t e r e d cobbles and pebbles in a co arse-sa n d m atrix w ith a few cobbles f l o a t i n g atop the stratu m . This chute d e p o s it i s in t e r p r e t e d as a d e b ris flow or h ig h -d e n sity t u r b i d i t y c u rre n t based on the evidence of stro n g buoyant f o rc e s ( f l o a t i n g c o b b le s ), but i t i s the only chute d e p o s it t h a t d isp la y s th ese f e a t u r e s . P a le o c u rre n t data from the chute d e p o s its i s a lso very Limited. Poorly-developed to o l and f l u t e s t r u c t u r e s d isp lay 69 Figure 23 : Sandstone chute d e p o s it (F acies B) t h a t was cut and f i l l e d by a s in g le d e p o s itio n a l u n i t . This chute outcrops a t the base of Black S ta r Canyon Road (Appendix A, 1 m) and a lso in th e a d ja c e n t stream bank. 70 71 a g e n e ra lly e a s t-w e s t o r i e n t a t i o n i n d i c a t i n g a southw est- west t r a n s p o r t d i r e c t i o n . 3.5 SUBMARINE CHANNEL-FILL DEPOSITS: CONCLUSIONS The c o a rs e -g ra in e d c h a n n e l - f i l l d e p o s its of the Holz Shale Member in Black S tar Canyon are dominated by f a c i e s A, B, and o c c a s io n a lly F. H igh-density t u r b i d i t y c u r r e n ts , d e b ris flows, and low -d en sity t u r b i d i t y c u r r e n ts appear to be the dominant flow mechanisms r e s p o n s ib le fo r d e p o s itio n of these s t r a t a . Locally, buoyant f o rc e s appear to have been very im portant in d e p o s its c o n ta in in g numerous f l o a t i n g c o b b le -s iz e d c l a s t s . P lan ar- and c ro s s -la m in a te d u n i t s t h a t s e p a ra te more massive, co arser d e p o s its i n d i c a t e t h a t t r a c t i o n c u r r e n ts were also im p o rtan t, and might be a t t r i buted to downslope c u r re n ts or r e s id u a l very low -density t u r b i d i t y c u r r e n ts produced by d e p o s itio n of h ig h -d e n sity t u r b i d i t y c u r r e n ts (Lowe,1982). Grain-flow d e p o s its may account for a li m i t e d number of these s t r a t a , but are considered of minor importance as they re q u ire very stee p slope angles to occur, and r a r e l y d e p o s it beds g r e a te r than 5 cm -thick (Lowe,1976). The la c k of dish s t r u c t u r e s , sandstone dikes, and dew atering tubes i n d i c a t e s t h a t l i q u i f ie d and f l u i d i z e d flow also played a minor or n o n - e x is ta n t r o le in the d e p o s itio n of these s t r a t a . lc Sandstone beds w ith in th ese channels co n ta in an abundance; of mica g ra in s t h a t occurs dissem inated through massive bedded u n i t s and a lso in c o n c e n tra te d zones forming p la n a r - la m in a tio n s. High mica c o n te n ts of sandstone d e p o s its are c h a r a c t e r i s t i c of slope and o th e r deep marine sediments (Southard and S t a n l e y ,1974; Doyle e t a l . , 1 9 7 9 ) . In ad d i tio n , Bouma T a-b and T a -b -c sequences and a s s o c i a t e d s c o u r - a n d - f i l l channels, a l l of which f re q u e n tly occur in Holz Shale s t r a t a , are common f e a t u r e s of submarine channel d e p o s its (Hein and Walker,1982). Planar la m in a tio n s a c c e n tu a te d by mica g ra in s are commonly observed in graded Bouma T a-b sequences (Figure 2 4 ). These p a r a l l e l c o n c e n tr a tio n s of mica g ra in s are thought to be the r e s u l t of h y d ra u lic s o r t i n g along the viscous boundary l a y e r . P e rio d ic c h a o tic v o r t i c e s or ,fb u r s t s ,f develop in the boundary la y e r and allow fin e grains ( e . g . , mica g ra in s) to be d e p o site d during sed im e n ta tio n of c o a rse r m a t e r i a l s . B u rsts a l t e r n a t e with "sweeps” or in ru s h e s of higher v e lo c ity f l u i d s which t r a n s p o r t new in flu x e s of sediment. This b u rst and sweep mechanism produces graded s t r a t a with laminae of f i n e - g r a i n e d s e d i ments. A d e t a i l e d d is c u s s io n of t h i s mechanism i s given by McCave and Sw ift (1976) and Hesse and Chough (1980). , J 3 Figure 24: Bouma T a-b sequence d is p la y in g graded bedding and p la n a r - la m in a tio n s a c c e n tu a te d by m ica-g rain c o n c e n tr a tio n s (F a c ie s B). This stratum i s from channel 2 and i s a good example of the t y p ic a l sandstones t h a t f i l l the channel. 74 lb P a le o c u rre n t i n d i c a t o r s in th e c h a n n e l - f i l l s t r a t a are uncommon, but suggest a w e s te rly t r a n s p o r t d i r e c t i o n for channel 1, a south-southw est d i r e c t i o n fo r channel 2, and a w est-so u th w est d i r e c t i o n fo r the sm aller chutes and g u l l i e s . Although d i r e c t o b s e rv a tio n s are la c k in g , i t seems p la u sib le t h a t the sm aller chutes and g u l l i e s t h a t d isp la y a s i g n i f i cant range in p a le o c u rre n t d i r e c t i o n s may have formed a simple t r i b u t a r y system t h a t fed th e major channels. S im ila rly , i t seems probable from the o r i e n t a t i o n s of channel 1 and channel 2, t h a t these two la r g e channels were probably connected a t one time on th e a n c ie n t c o n tin e n ta l slope. 7d Chapter IV INTERCHANNEL DEPOSITS 4.1 INTRODUCTION In te rc h a n n e l d e p o s its of the c o n tin e n ta l slope en v iro n ment are c h a r a c t e r iz e d by f in e - g r a i n e d sedim ents with planar to wavy, d isc o n tin u o u s bedding and high mica and organic m atter com positions ( C o l l i n s o n , 1969; Cook e t a l . , 1 9 8 2 ) . Interbedded t u r b i d i t e s , c o n to u r ite s , and hem ipelagic s e d i ments are common d e p o s its in deep-sea marine environments (Stow and L o v e ll ,1979). Mud t u r b i d i t e s are commonly a s s o c i ated with submarine channels and are thought to be produced by overbank flow, slope f a i l u r e , and d i l u t e t u r b i d i t y c u r r e n ts t h a t breached the channel co n fin es and were depo s i t e d on the in te rc h a n n e l region (Hesse and Chough,1980). Hemipelagic sed im en tatio n i s produced by the slow s e t t l i n g of suspended p a r t i c l e s in nepheloid la y e r s t h a t o r ig in a te d on the c o n tin e n ta l s h e lf and t r a n s p o r t e d f i n e - g r a i n e d sedim ents downslope to deeper-w ater environments ( T h o rn to n ,1981b ; McGrail and C a r n e s ,1983). Nepheloid l a y e r s have a lso been r e p o rte d in a s s o c i a t i o n with modern submarine: channels (Beer and G o r s l i n e , 1971; Drake and G o r s l i n e , 1973; Stokke e t a l . , 1 9 7 7 ) . C o n to u rite s are sediments d e p o site d by 77 c o n to u r-fo llo w in g , ocean bottom c u r re n ts t h a t a re driven by j therm o -h alin e c i r c u l a t i o n (Bouma and H o l l i s t e r , 1973) . These c i r c u l a t i o n p a t t e r n s a re d riven by g r a v i t a t i o n a l fo rc e s th a t i a c t on density d i f f e r e n c e s of deep water masses (Bouma and H o l l i s t e r ,1973; Stow and L o v e l l , 1979). Bottom photograph evidence from s tu d ie s over the past t h i r t y y ears has shown t h a t bottom c u r r e n ts a re im portant fo rc e s in reworking, t r a n s p o r t in g , and d e p o s itin g sediment in c o n t i n e n t a l slope environments ( J o r d a n , 1951; Northrup and H eezen,1951; Elmen- dork and H eezen,1957; P icard and D i e t z , 1961; Heezen and j H o l l i s t e r , 1964). ] i j D i s ti n c t i o n between t u r b i d i t e s , c o n t o u r it e s , and hemipe- j i l a g ic sedim ents i s very d i f f i c u l t ( S ta n le y , 1 969 ; Hesse, 1975;! K ellin g and S t a n l e y ,1976; P i p e r , 1978). I t has been j ! suggested t h a t th e re e x i s t s a f u l l continuum between d i l u t e j j t u r b i d i t y c u r r e n ts , contour c u r r e n ts , and hem ipelagic j i se d im en tatio n from nepheloid flow, and hence, a complete j i g ra d a tio n between th e r e s u l t a n t d e p o s its (Stow and j L o v e ll ,1979). Even so, many attem pts have been made to j i d e n t i f y c r i t e r i a t h a t w i l l aid in r e c o g n itio n of each of | th e se d e p o s itio n a l mechanisms. Commonly used c h a r a c t e r i s - j t i c s for d i s t i n g u i s h i n g mud t u r b i d i t e s from hem ipelagic | i sediments in clu d e r e l a t i v e amounts of b i o t u r b a t i o n , calcium j carbonate c o n te n t, color comparisons, m icrofaunal co n ten t, 78 g r a i n - s i z e a n a ly se s, sedimentary s t r u c t u r e s , and organic carbon content (Griggs e t a l . ,1969; Rupke and S t a n e l y ,197^; H e s s e ,1975). Although p o s i t i v e i d e n t i f i c a t i o n i s v i r t u a l l y im possible, many s tu d ie s t h a t u t i l i z e d v a rio u s s e t s of these c r i t e r i a have demonstrated t h a t d i s t i n c t i o n a t a high i p r o b a b i li t y le v e l i s f e a s i b l e . In c o n t r a s t to the stro n g case fo r d i s t i n c t i o n of t u r b i d i t e s and hem ipelagic sedim ents, attem p ts to s e p a ra te t u r b i d i t e d e p o s its from c o n to u r ite d e p o s its have proven much more d i f f i c u l t . I t has been suggested t h a t c o n t o u r it e s and j t u r b i d i t e s are d i f f i c u l t to d i s t i n g u i s h because the j h y d ra u lic s o r t i n g and d e p o s itio n a l mechanisms of both j I pro cesses are very s im ila r ( H e s s e ,1975). In f a c t , some j au th o rs have gone as f a r as to s t a t e t h a t no r e a l d i f f e r - j ences e x i s t between c o n t o u r it e s and d i s t a l t u r b i d i t e s (K eith and F riedm an,1977). Nonetheless, a s im ila r s e t of c r i t e r i a j has been developed to aid in the r e c o g n itio n process and in c lu d e s c h a r a c t e r i s t i c s such as the degree of s o r tin g , m in era lo g ic and t e x t u r a l com positions, g ra in f a b r i c s , sedim entary s t r u c t u r e s h i g h lig h te d by heavy m ineral p la c e r ( d e p o s its , f in i n g and s o r t i n g tre n d s , and d i r e c t i o n a l s t r u c - j tu re tre n d s p e rp e n d ic u la r or p a r a l l e l to bathym etric cont- j ! i ours. U n fo rtu n a te ly , t u r b i d i t e s and c o n t o u r it e s commonly j d isp la y very s im ila r i f not i d e n t i c a l c h a r a c t e r i s t i c s . 1 3 T herefore, re c e n t s tu d i e s have suggested t h a t i n t e r p r e t a t i o n of d i r e c t i o n a l s t r u c t u r e s i s the most r e l i a b l e method for d i s t i n c t i o n , e s p e c i a l l y in a n c ie n t sediments (A nketell and L o v e l l , 1976; S tow ,1979). Another im portant d e p o s itio n a l mechanism in deep-sea | marine environments i s the process of m ass-w asting. Studies! j of modern deep-water environments have dem onstrated a j j s i g n i f i c a n t occurrence of f in e - g r a i n e d slumps, d e b ris flows,I I j mud flows, and l i q u e f a c t i o n s t r u c t u r e s (Hein and Gors- j i i l i n e , 1981). The s t a b i l i t y of sediments in a submarine | environment i s determined by sed im en tatio n r a t e s , slope j ! g r a d ie n ts , and the sed im en t1s bulk p r o p e r t i e s (L e w is,1971; j I Haner and G o r s l i n e , 1978; F i e l d , 1981). Of th ese th re e j v a r i a b l e s , the sed im en tatio n r a t e appears to be the primary ! ! c o n t r o l l i n g f a c t o r in determ ining where m ass-w asting occurs j (Moore,1961; M o rg en stern ,1967; Hein and G o r s l i n e , 1981). In r a p id ly d e p o site d f in e - g r a i n e d sedim ents, c o n s o lid a tio n cannot keep pace w ith d e p o s itio n and t h e r e f o r e , excess pore p re s s u re s in c re a se causing u n d e rc o n so lid a tio n and a r e s u l t a n t decrease in shear s tr e n g th ( T e rz a g h i,1956). Therefore, in a re a s of ra p id s e d im e n ta tio n , th e re e x i s t s a c r i t i c a l | sed im en tatio n r a t e where shear s tr e n g th i s reduced enough ! i t h a t g r a v i t a t i o n a l fo rc e s exceed f r i c t i o n a l fo rc e s and ! ! f a i l u r e occurs (G orsline and Prensky,1975). j | | so! The sim ultaneous and s e q u e n tia l occurrence of these d i f f e r e n t d e p o s itio n a l mechanisms w ith in th e c o n tin e n ta l slope environment produces a very complex sedimentary system. Analyses of the f in e - g r a i n e d s t r a t a of the Holz | I Shale Member s im i l a r l y d isp la y a com plicated i n t e r a c t i o n of j | many d i f f e r e n t d e p o s itio n a l p ro c e sse s. The r e s u l t s of thesej an a ly se s w i l l be the focus of the fo llo w in g s e c tio n . j i I 4.2 SEDIMENTQLOGIC TEXTURES:BIQLOGICAL VERSUS PHYSICAL MECHANISMS i The f in e - g r a i n e d rocks fo r which the Holz Shale Member j 1 was named c o n s is t of highly fragmented and weathered shales,j mudstones, and f i n e - g r a i n e d sa n d sto n es. S c a tte r e d i t I i throughout th ese s t r a t a are numerous carbonate c o n c re tio n s ! which were p re v io u sly m i s i n t e r p r e t e d as d isco n tin u o u s | primary carbonate beds ( Sundberg, 1 980) . This m isin te rp re ts -! j tio n i s e a s i l y understood c o n s id e rin g the f a i r l y common ; I occurrence of l a t e r a l l y d isco n tin u o u s c o n c re tio n a ry beds j formed by c o a le s c in g of in d iv id u a l c o n c re tio n s along bedding plan es. As a r e s u l t of poor exposures of these f in e - g r a in e d s t r a t a , d e t a i l e d a n a ly se s focused on the carbonate concre tio n s in hopes of reaching a re a so n a b le understan d in g of what the o r i g i n a l sediment f a b r i c was l i k e . F o rtu n a te ly , I the c o n c re tio n s did provide a window through which t e x t u r a l | tre n d s of these f i n e - g r a i n e d s t r a t a could be examined. In I t h i s c h a p te r, the primary sediments and t h e i r i n t e r p r e t e d j nechanisms of d e p o s itio n from co n c re tio n s tu d i e s w i l l be | j d iscu ssed . Following th ese a n a ly se s, the carbonate concre- j tio n s and t h e i r s ig n i f i c a n c e in t h i s s t r a t i g r a p h i c sequence rfill be examined in d e t a i l . j The sedim entologic t e x t u r e s examined in outcrop and in j the c o n c re tio n s d isp la y a complete range from e n t i r e l y | p h y sic a lly -d o m in a te d t e x t u r e s to e n t i r e l y b io lo g ic a lly -d o m i-j nated t e x t u r e s . The b io lo g ic a lly -d o m in a te d t e x t u r e s consistl of homogeneous sedim ents d is p la y in g i n d i s t i n c t to d i s t i n c t j occurrences of abundant C h o n d rite s T common P l a n o l i t e s T and j j occasio n al Zoophvcus t r a c e s . No evidence of p h y sica l S s t r u c t u r e s was found in th e se rocks. These sediment j i t e x t u r e s were commonly a s s o c ia te d with outcrops of clayey j ! sh a le s t r a t a la c k in g abundant f in e - g r a i n e d t u r b i d i t e sand- j i stone in te r b e d s . Based on th e absence of both primary i i s t r u c t u r e s and any t e x t u r a l tre n d s ( e . g . , graded bedding), j the slow r a t e of d e p o s itio n re q u ire d fo r complete biogenic J I reworking (Howard,1975), and the paucity of a s s o c ia te d | i \ t u r b i d i t i c san d sto n es, th ese d e p o s its are i n t e r p r e t e d as J hem ipelagic sedim ents t h a t were probably derived from nepheloid plumes and p e la g ic p a r t i c l e r a i n . At the other end of the spectrum, the p h y sic a lly -d o m i nated t e x t u r e s occur in two very d i f f e r e n t l i t h o l o g i e s . The 82 f i r s t type was found in the c o a r s e s t sh ale outcrops (sandy j I i s i l t s ) where sandstone in te rb e d s are very common. These j ! rocks commonly d isp la y p la n a r -la m in a tio n s up to 4 cm th ic k , j c o n c e n tr a tio n s of organic fragm ents p a r a l l e l to bedding, | | graded bedding, c u t - a n d - f i l l s t r u c t u r e s , micro-flam e s t r u c - j i tu r e s (<1 cm), and penecontemporaneous deform ation of j I I laminae. These d e p o s its a re i n t e r p r e t e d as f i n e - g r a i n e d , I i I d i l u t e t u r b i d i t e s t h a t were d e p o site d ra p id ly enough to j ! prevent b i o t u r b a t i o n . The r a p id d e p o s itio n of these w ater- s a tu r a t e d muds a lso produced u n s ta b le sedim entologic condi tio n s where s m a ll- s c a le slumping and deform ation of laminae took p la c e . The a s s o c i a t i o n of these rocks w ith numerous j c o a r s e - g r a in e d t u r b i d i t e s in outcrop i n d i c a t e s t h a t tu rb u - j l e n t pro cesses were im portant in d e p o s itio n of these strata,!, and su g g ests the p o s s i b l i t y t h a t these f in e - g r a i n e d deposits! might a c t u a l l y have r e s u l t e d from r e s id u a l flows d erived j j from the c o a r s e r - g r a in e d t u r b i d i t e s (Lowe,1982). j I The second l i t h o l o g y which d is p la y s a p h y sic a lly -d o m i- | | nated t e x t u r e was found in outcrops s im ila r to the b i o l o g i - j | cally -d o m in a te d t e x t u r e s , but c o n ta in s only a very minute amount of b io t u r b a t i o n ( ra r e C hondrites t r a c e s ) . These j i rocks e x h ib ite d very f i n e - s c a l e p la n a r -la m in a tio n s (1 to 2 J mm-thick) of dark, o r g a n i c - r i c h , clayey to s i l t y sediments j t h a t c lo s e ly resemble varves and occur in packages 2 to 4 cm -thick. S e p a ra tin g th ese varved u n i t s are l i g h t e r co lo red , f a i n t l y - l a m i n a t e d beds (0.5 to 4.0 cm -thick) of c la y - s iz e d sedim ents t h a t commonly d isp lay i r r e g u l a r , sharp basal c o n ta c ts and o c c a sio n a l c u t - a n d - f i l l s t r u c t u r e s . Rocks c o n ta in in g th e se sediment t e x t u r e s commonly e x h i b i t ] j penecontemporaneous deform ation in c lu d in g slump-produced [ j overtu rn ed fo ld s , s m a ll- s c a le b a ll- a n d - p illo w s t r u c t u r e s , ] and p in c h in g -o u t of in d iv id u a l d e p o s itio n a l u n i t s . P etro - | i graphic study of these d e p o s its rev e a le d abundant fo ra m in i- ! i f e r a l t e s t s and common s i l t - s i z e d q u artz g ra in s ( <7%) in the varved u n i t s . The unusually good p r e s e r v a tio n of foram J t e s t s i s probably a r e s u l t of the la c k of b i o t u r b a t i o n and | | has been observed in f in e ly - la m in a te d , anaerobic s t r a t a of j l the Monterey Formation (R.G. D o u g las,1983,pers. comm.). j j These p h y sica lly -d o m in ated rocks of the Holz Shale are j | i n t e r p r e t e d as se a so n a lly produced, deep-marine varves t h a t j are se p a ra te d by f in e - g r a i n e d clay d e p o s its of d i l u t e j | t u r b i d i t y c u rre n t o r ig i n . S im ilar varve d e p o s itio n has been observed in modern deep-sea b asins in the C a l i f o r n i a Border land and i s a s s o c ia te d w ith anaerobic bottom w aters (T h o rn to n ,1981 a ) . Considering the general absence of biogenic s t r u c t u r e s , the good p r e s e r v a tio n of foram t e s t s , I and the s i m i l a r i t y to modern anaerobic d e p o s itio n a l systems,| i t seems l i k e l y t h a t these Cretaceous s t r a t a were a lso d ep o sited in a n aero b ic sedim entary environments. 84 Regional or global anoxic ev en ts, e s p e c i a l l y in C reta- j ceous s t r a t a , have been recognized in the rock record j i worldwide (Schlanger and J e n k i n s , 1976; Schlanger and I j C ita, 1982). Theories a tte m p tin g to e x p la in th ese events are! i j based on a combination of c lim a tic , oceanographic, and j t e c t o n i c f a c t o r s (F ish e r and A r t h u r , 1977; R o th ,1978; Schlanger and J e n k i n s , 1976; T h i e r s t e i n and B e rg e r,1978). Laminated s t r a t a of Upper Cretaceous age, p o ssib ly a s s o c i ated with an oceanic anoxic event, have been re p o rte d from | outcrops near San Diego, C a lif o r n ia ( S l i t e r ,1975). These ! d e p o s its are l i t h o l o g i c a l l y very s im ila r to the varved s t r a t a observed in t h i s study. D i s t r i b u t i o n of modern an aero b ic environments i s cont- j j r o ll e d by lo c a l basin geometry, and c lim a tic and oceano- | i graphic f a c t o r s ( Savrda,1983). These marine anoxic environ-| ments can be divided i n t o th re e b asic c a te g o r i e s : anoxic j s i l l e d b a s in s ; anoxic l a y e r s caused by upw elling; and ! open-ocean anoxic l a y e r s (Demaison and Moore,1980). Unfor t u n a te ly , applying t h i s c l a s s i f i c a t i o n scheme to the rock record i s f a i r l y d i f f i c u l t . This i s e s p e c i a l l y tru e of the Holz Shale Member, where li m i t e d outcrop exposures make basin a n a l y s is extrem ely arduous. The lim i t e d occurrence of lam inated s t r a t a in the Holz Shale Member (BS-9 outcrop o n ly ), su g g ests t h a t anoxia was a temporary c o n d itio n and was not p re v a le n t throughout d e p o s itio n of t h i s s e c tio n . ____________________________________________________________________________________ Previous s tu d i e s of the Holz Shale have p o s tu la te d anaerobicj d e p o s itio n fo r most of these s t r a t a (Sundberg and Cooper,1978). These i n t e r p r e t a t i o n s were based on the abundance of p y r it e and organic m a t e r ia ls which suggest reducing environments w ith in the sediments, but not neces- j s a r i l y an anoxic w ater column. From an aly ses performed in j t h i s study, i t appears t h a t d e p o s itio n of most of the Holz \ Shale s t r a t a occurred in a h ighly reducing sediment column J which under s p e c ia l environmental c o n d itio n s, a lso inclu d ed j an anaerobic zone above the sedim ent-w ater i n t e r f a c e . | In te rm e d ia te to the two end member t e x t u r e s are rocks j I t h a t d isp lay both p h y sica l and biogenic s t r u c t u r e s . These j I ! rocks commonly d isp la y massive bedding, f i n e - s c a l e p la n a r- j la m in a tio n s (<1 cm), o c casio n al graded bedding, s m a ll- s c a le j j c u t - a n d - f i l l s t r u c t u r e s , and micro-normal f a u l t s (<1 cm ' | o f f s e t ) , a l l of which were d is r u p te d and p a r t i a l l y destroyedj by the burrowing a c t i v i t y of d e p o s it- f e e d in g organisms. B io tu rb a te s t r u c t u r e s are dominated by C h o n d ritie s t r a c e s , / j i i but a lso in clu d e P l a n o l i t i e s and Zoophvcus leb en ssp u ren . j f This sediment t e x t u r e was the most commonly observed texturej in the s t r a t i graphic s e c tio n stu d ie d , and was a s s o c ia te d w ith outcrops of s i l t y s h a le s t h a t e x h ib ite d a frequency of I sandstone in te rb e d s in te rm e d ia te to outcrops of the two i | end-member t e x t u r e s . This in te rm e d ia te t e x t u r e i s i n t e r - | p reted as a combination of hem ipelagic and d i l u t e t u r b i d i t y c u rre n t d e p o s itio n , where sed im en tatio n r a t e s were f a s t enough to prevent complete biogenic reworking, but a t a l e v e l where in fa u n a l organisms could s t i l l f l o u r i s h . No d i s t i n c t v e r t i c a l tre n d s of these sedim entologic t e x t u r e s are apparent in t h i s s t r a t i g r a p h i c s e c tio n . j I i 4.3 FINE-GRAINED SANDSTONE INTERBEDS Another im portant a sp e c t of the f i n e - g r a i n e d outcrops of the Holz Shale Member i s the l a r g e number of very f in e - to f i n e - g r a i n e d sandstone in te rb e d s t h a t are s l i g h t l y more r e s i s t a n t than the surrounding sh a le s t r a t a (see Figure 25). i > These th in beds range in th ic k n e s s from 1 to 9 cm (average S 2.5 cm), are f a i r l y continuous in outcrop although they j i commonly pinch and swell along s t r i k e , d isp la y sharp I ! j i r r e g u l a r lower c o n ta c ts , and both sharp and g ra d a tio n a l upper c o n ta c ts . Primary s t r u c t u r e s w ith in th e se s t r a t a were i not v i s i b l e in the f i e l d , but l a b o r a to r y slab b in g re v e a le d | Bouma T d-e , T c-e , and r a r e l y T b-e sequences, slump- I ! produced recumbent f o ld in g , small flame s t r u c t u r e s , and | f i n e - s c a l e graded bedding. S im ilar to the sandstone s t r a t a ! of the c h a n n e l - f i l l d e p o s its , these beds a lso co n ta in la r g e j amounts of mica g ra in s . Based on primary s t r u c t u r e s and | i t e x t u r a l tre n d s, these d e p o s its are i n t e r p r e t e d as low-den- s i t y t u r b i d i t y c u r r e n t s ( c l a s s i c t u r b i d i t e s ) t h a t lacked the 87 e ro sio n a l power of the t h ic k e r , channelized t u r b i d i t e s and th e r e f o r e , have g r e a te r l a t e r a l c o n t i n u i t y . Although l a t e r a l sedim entologic tre n d s a re d i f f i c u l t to analyze due to th e d isc o n tin u o u s n a tu re of exposures, f i e l d r e l a t i o n s h i p s i n d i c a t e a t e n t a t i v e a s s o c i a t i o n of channel- f i l l d e p o s its and a g r e a te r frequency of sandstone in te rb e d s in outcrop. For example, the number of sandstone in te rb e d s per u n i t th ic k n e ss of s t r a t i g r a p h i c s e c tio n i n c r e a s e s j i u p sectio n in outcrops u nderlying the submarine channel a t A2| i m in Appendix A. This in c re a se in frequency may be the j i i r e s u l t of g r e a te r se d im en tatio n r a t e s and t u r b i d i t e deposi- ! I tio n necessary for the i n i t i a t i o n of submarine channel | form ation. A g r e a t e r frequency of th in sandstone beds in j j outcrops t h a t are l a t e r a l e q u iv a le n ts to c h a n n e l - f i l l d e p o s its was a lso observed in two o u tcro p s. This frequency in c re a se i s most l i k e l y due to the c o n s tr u c tio n of lev ee d e p o s its as a r e s u l t of s p i l l - o v e r of lo w -d en sity t u r b i d i t y c u r r e n ts from the a s s o c ia te d channels. 88 ! ___j Figure 25: Thin, f in e - g r a i n e d sandstone beds in te rb e d d e d w ith sh a le s t r a t a and s c a t t e r e d carbonate c o n c re tio n s (F acies G). This exposure i s lo c a te d along I r v in e Company F ire ro a d . 89 S M 90 4.4 FINE-GRAINED SANDSTONE OUTCROPS:BOTTOM CURRENT EVIDENCE In a d d itio n to the many f in e - g r a i n e d Holz Shale outcrops t h a t are dominated by sh ale s t r a t a , th e re are a lso two li m i t e d outcrops t h a t are comprised predominantly of very f i n e - to f in e - g r a i n e d san d sto n es. One such exposure occurs on Black S ta r Canyon Road (see Appendix A, 84 to 91 m ) and c o n s i s t s of planar-bedded, 1 to 3 cm -thick, f i n e - to very f in e - g r a i n e d sandstone s t r a t a t h a t e x h i b i t numerous i n t e r bedded, medium-grained sand s t r i n g e r s (1 to 6 m m -thick). These s t r a t a d isp la y poorly-developed p lan ar c ro s s -la m in a t io n s , r a re r i p p l e marks, rip -u p c l a s t s , c u t - a n d - f i l l s t r u c t u r e s , and abundant t e r r e s t r i a l p la n t and wood f r a g ments. Interbedded w ith these s t r a t a are a few c o a rse grained sandstone beds d is p la y in g graded bedding, cu t-a n d - f i l l s t r u c t u r e s , r ip -u p c l a s t s , Bouma T a - b -c - d - a , T b-c-d , and T a-b -c sequences, flame s t r u c t u r e s , and r a r e l y zones of abundant r ip -u p c l a s t s lo c a te d towards the upper bed c o n ta c t. These d e p o s its are i n t e r p r e t e d as lo w -d en sity t u r b i d i t y c u r r e n ts w ith the r a r e occurrence of a high-den- s it y t u r b i d i t y c u r r e n t. The presence of r ip p l e marks, l e n t i c u l a r c ro ss -la m in a te d beds, and medium-grained sand s t r i n g e r s , i n d i c a t e s t h a t reworking of these t u r b i d i t e s by 91 bottom c u r r e n ts was a lso an im portant process in the c o n s tr u c tio n of these d e p o s its . The second outcrop dominated by fin e sands occurs on I rv in e Company F ire ro a d about 100 yards above i t s i n t e r s e c tio n w ith Black S ta r Canyon Road. This outcrop c o n ta in s th in n ly -b ed d ed (0.5 to 3.0 c m - th i c k ) , very f in e - to f i n e grained, l e n t i c u l a r sandstone beds t h a t commonly d isp lay planar c r o s s - la m in a tio n s (Figure 26). These small le n se s e x h i b i t very sharp upper and lower c o n ta c ts , m oderately- to w e l l - s o r t e d t e x t u r e s , and heavy mineral p la c e r d e p o s its a c c e n tu a tin g la m in a tio n s . S e p a ra tin g th ese l e n t i c u l a r u n its are p la n a r-la m in a te d , more l a t e r a l l y continuous u n i t s d isp la y in g s im i l a r sediment t e x t u r e s . The l e n t i c u l a r nature of these th in beds and the u b iq u ito u s presence of c r o s s - l a m inations make t h i s outcrop unique from any o th e rs in Black S ta r Canyon. Although p a le o c u rre n t measurements are d i f f i c u l t in such f i n e - g r a i n e d and f r i a b l e rocks, c ro ss -la m in a tio n s of these s t r a t a i n d i c a t e a s o u th e rly t r a n s p o r t d i r e c ti o n . Assuming a general n o rth -s o u th o r i e n t a t i o n of the Cretaceous C a l i f o r n i a c o n tin e n ta l margin (Blake and Col burn, 1982; D ic k in s o n ,1983), the c u r r e n ts d e p o s itin g these sediments appear to have been flow ing in a d i r e c t i o n normal to the expected downslope t r a n s p o r t d i r e c t i o n . Based on t h i s d i r e c t i o n a l s t r u c t u r e i n t e r p r e t a t i o n , the w e l l - s o r t e d t e x t u r e of these sands, t h e i r unique bedding s t y l e , and the 92 presence of heavy mineral p la c e r d e p o s its , th ese rocks are i n t e r p r e t e d as a n c ie n t c o n t o u r it e s . These s t r a t a may bottom c u r r e n ts or p o ssib ly r e p re s e n t primary deposi on j u s t the reworking of f i n e - g r a i n e d t u r b i d i t e s (Stow and L o v e l l , 1979). Figure 26 : Thin, f in e - g r a in e d , cross-bedded sandstone l e n s e s s e p a ra te d by p la n a r-la m in a te d beds, penny fo r s c a le . This outcrop occurs along I rv in e Company F ire ro a d . Note 94 95 4.5 CONCLUSIONS The f in e - g r a i n e d s t r a t a of the Holz Shale Member r e p r e sent a complex system of d e p o s itio n a l mechanisms. Processes of d e p o s itio n i n t e r p r e t e d for these rocks in clu d e t u r b i d i t y c u r re n ts , hem ipelagic sed im en tatio n , slump d e p o s itio n , and bottom c u rre n t sed im en tatio n . Following d e p o s itio n , b io lo g ic a l fo rc e s , under optimum c o n d itio n s, c re a te d e n t i r e l y new sedim entologic t e x t u r e s . With f u r t h e r b u r ia l and the passing of time, d ia g e n e tic p ro c e sse s began to a l t e r the sedim ents. In the f in e - g r a i n e d s t r a t a of the Holz Shale, form ation of carbonate c o n c re tio n s played a major r o le in the d ia g e n e tic a l t e r a t i o n of these sediments, y e t w ithout th ese c o n c re tio n s, many of the previous a n a ly se s would have been im p o ssib le. The follo w in g ch ap ter w i l l examine these carbonate c o n c re tio n s and t h e i r paleoenvironm ental s i g n i f i cance in t h i s Cretaceous s t r a t i g r a p h i c sequence. Chapter V | CARBONATE CONCRETIONS j 5.1 INTRODUCTION The o r ig i n of carbonate c o n c re tio n s i s an i n t r i g u i n g geologic problem. C oncretions commonly contain w e l l - p r e served f o s s i l m a t e r ia ls , so the a s s o c i a t i o n of organic compounds and th e form ation of c o n c re tio n s i s an old one. The b a sic problem w ith t h i s a s s o c i a t i o n i s t h a t decay of j i organic m a t e r i a l s i s known to produce v ario u s o rganic acid s j i i such as carbonic acid ( B ern er,1968), which should prevent j I I the p r e c i p i t a t i o n of carbonate m in e ra ls, not promote i t . j This problem was l a i d to r e s t by a s e t of experim ental s tu d ie s (B e rn e r,1968,1969) t h a t dem onstrated a s i g n i f i c a n t r i s e in th e pH of w aters immediately surrounding decaying organic m atter during the e a rly s ta g e s of decomposition. This in c re a se d a l k a l i n i t y was shown to be caused by the r e l e a s e of ammonia and other amines from organic decay p ro c e sse s. The l o s s of n itro g e n compounds during the e a r l i e s t sta g e s of decay has a ls o been observed in e x p e r i mental s tu d i e s of phytoplankton decomposition (K ra u s e ,1959) and in modern sediments where c a rb o n -n itro g e n r a t i o s were 97 m u c h higher in marine sediments than in the o r i g i n a l b io lo g ic a l source of organic m atter ( Emery,1960). In a d d itio n , ammonia and a s s o c ia te d amines are well-known products of b a c t e r i a l decay of organic m a t e r i a l s (Thimann,1963). Berner (1968) suggests t h a t the ammonia produced by organic decay r e a c t s with b a c t e r i a l l y generated CC > 2 to form dissoved carbonate and b ic a rb o n a te io n s: c o 2 + n h 3 + h2 o - - n h 4 + h c o 3 C02 + 2NH3 + H20 - - 2NH4 + C03 . Due to the in c re a se d a l k a l i n i t y and form ation of high carbonate ion c o n c e n tr a tio n s , p r e c i p i t a t i o n of carbonate compounds was expected, but never found. In ste a d , the i form ation of n a tu r a l calcium s a l t s of f a t t y a c id s, c a lle d a d ip o cere, was observed (B ern er,1968,1969). Adipocere has been r e p o rte d to form c o n c r e t i o n - l i k e s t r u c t u r e s around decaying organic m a tte r (Sondheimer e t a l . , 1 9 6 6 ) , and i t has been suggested t h a t with in c re a se d d ia g e n e s is, adipocere i s i I a l t e r e d to calcium carbonate through the breakdown of f a t t y / acids (B ern er,1968). This sequence of chemical r e a c tio n s i s thought to be the b a sic s e t of developmental sta g e s t h a t produce most carbonate c o n c re tio n s. Most c o n c re tio n s are thought to be the r e s u l t of ea rly d ia g e n e tic p ro c e sse s (Weeks,1953; P a n t i n , 1958; G a b i n e t , 1974; Hudson,1978; G a u t i e r ,1982), although c o n c re tio n s formed much 98 l a t e r in a sed im en t’ s d ia g e n e tic h i s t o r y have a lso been r e p o rte d ( R a is w e ll,1971). To remove some of the ambiguity a s s o c ia te d with d e s c r i p t i o n s of the timing of c o n c re tio n form ation, Pantin (1958) devised a r e l a t i v e time s c a le t h a t d i s t i n g u i s h e s th re e major periods of co n c re tio n a ry growth. This system in c lu d e s : l .s y n g e n e t i c growth, form ation a t or in c o n ta c t with the sedim ent-w ater i n t e r f a c e ; 2 . d ia g e n e tic growth, form ation soon a f t e r b u r ia l in uncompacted s e d i ments; 3 . e p ig e n e tic growth, l a t e form ation in o ld e r, compacted sedim ents. Evidence su p p o rtin g a p a r t i c u l a r age c l a s s in c lu d e s : carbon and oxygen iso to p e s tu d i e s in d ic a tin g t h a t form ation occurred in c o n ta c t with seawater (syngen- e t i c ; G a u t i e r , 1982); presence of e n c ru s tin g or boring tra c e s on th e e x t e r i o r su rfa c e of a c o n c re tio n (sy n g e n e tic or d i a g e n e t i c ; P a n t i n , 1958); th e bending of s t r a t a around c o n c re tio n s ( d ia g e n e t i c ; Tom kieff,1927; Weeks,1953,1957); non-compacted t r a c e f o s s i l s w ith in c o n c re tio n s (sy n g e n e tic or d ia g e n e tic ; Dickson and B a rb e r,1976); r a d i a l in c re a se of compaction of laminae w ith in a c o n c re tio n (d ia g e n e tic or e p ig e n e tic ; R a is w e ll,1971); and th e presence of s e p ta r i a n s t r u c t u r e s a s s o c i a t e d with uncompacted, w a te r-la d e n s e d i ments (sy n g e n e tic or d ia g e n e tic ; Lippman,1955; Rais- w ell, 1971). Many of these c r i t e r i a apply to more than one of P a n t i n ’ s time d i v i s i o n s and t h e r e f o r e , i t i s u su a lly necessary to u t i l i z e as many c h a r a c t e r i s t i c s as p o s s ib le . In the fo llo w in g s e c tio n s , many d i f f e r e n t c r i t e r i a w i l l be 99 examined to determine the r e l a t i v e time of form ation of carbonate c o n c re tio n s from the Holz Shale Member. 5.2 CONCRETION MORPHOLOGIES The carbonate c o n c re tio n s of the Holz Shale Member in clu d e a wide range of shapes and s iz e s . By f a r the most dominant shape (>85%) i s an e l l i p s o i d a l sphere t h a t i s u su a lly o rie n te d p a r a l l e l to bedding. Other l e s s common shapes include round sp h eres, c y l i n d r i c a l pipes, and i r r e g u la r ly - s h a p e d r e c t a n g l e s . Dimensions of these d ia g e n e tic f e a t u r e s are a lso very v a r i a b l e and range from 5 cm to 1.5 m in diameter (average = 0.5 m) and 5 cm to 1 m in th ic k n e ss (average = 20 cm) for in d iv id u a l e l l i p s o i d s . Concretions commonly occur in groups of 2 to 5 lo c a te d along the same s t r a t i g r a p h i c horizon, and in a number of outcrops coalesce j to form d isco n tin u o u s c o n c re tio n a ry s t r a t a . F a in t remnant boundaries of the in d iv id u a l c o n c re tio n s t h a t form these carbonate beds are o c c a s io n a lly v i s i b l e in outcrop (Figure 27). However, when such c o n ta c ts are no longer apparent, frag m en tatio n of the stratum w ith a hammer u su a lly produces a number of in d iv id u a l e l l i p s o i d a l blocks. S im ilar c o a l escing of c o n c re tio n a ry nodules has been recognized in Holocene carbonate sediments of the P ersian Gulf (Taylor and I l l i n g , 1969). 100 7 ig u re 27 : D iscontinuous carbonate bed formed by the c o a le s c in g of 3 to 4 in d iv id u a l c o n c re tio n s. This stratum occurs a t BS-65 along Black S tar Canyon Road. 101 1C2 In d iv id u a l c o n c re tio n s in the Holz Shale are predomi nantly well-cem ented nodules w ith d i s t i n c t boundaries s e p a ra tin g the c o n c re tio n s from the surrounding s t r a t a . In a d d itio n , the outcrops along Black S ta r Canyon Road a lso co n ta in numerous rudimentary c o n c re tio n s t h a t c o n s is t of small spheres of fragmented sh a le s t r a t a t h a t d isp lay f a i n t c o n c e n tric l a y e r s . These i n c i p i e n t nodules are s l i g h t l y more r e s i s t a n t than the surrounding s t r a t a , but la c k the w ell-cem ented appearance of the s o li d c o n c re tio n s (see Figure 28). These young c o n c re tio n s a lso la c k the w e ll- d e fin e d boundaries c h a r a c t e r i s t i c of the fu lly -d e v e lo p e d nodules. The rudim entary c o n c re tio n s appear to have never reached f u l l d ia g e n e tic m a tu rity , but the cause of t h i s incomplete cem entation i s unknown. 1 03 Figure 28: Highly-fragm ented, rudimentary c o n c re tio n s in shale outcrop. These c o n c re tio n s were observed a t BS-9 along Black S ta r Canyon Road. 105 5.3 CONCRETION COMPOSITIONS Analyses performed in t h i s study to determine the chem i c a l composition of the Holz Shale c o n c re tio n s included X-ray d i f f r a c t i o n , p e tro g ra p h ic , and LECO gasom etric te c h n i ques. P etro g ra p h ic exam ination of the c o n c re tio n s rev ealed a dominantly c la y - s i z e d sediment w ith small amounts of q u artz s i l t g ra in s (<10%) and abundant c a l c i t e cement. D e t r i t a l carbonate g ra in s were ab sen t, or a very minor component (<2%) of the c o n c re tio n s examined in t h i n - s e c t i o n . LECO gasom etric d e te rm in a tio n s co n c e n tra te d on organic carbon and carbonate a n aly ses (see Appendix B ) . Ten concre t i o n samples d isp la y e d o rganic carbon com positions ranging I from 0 to 1.3%. Samples were avoided t h a t contained bedding planes of f o s s i l p la n t d e b ris so t h a t organic carbon j measurements were not i n f l a t e d . Carbonate carbon a n a ly se s ! I i showed a range of 55.1 to 75.0% (average 64.7%) for the same ten co n c re tio n samples. X-ray d i f f r a c t i o n a n a ly s e s, also of the same c o n c re tio n s, showed c a l c i t e to be the p r i n c i p l e component of these c o n c re tio n s, with quartz being a d i s t a n t second. In a d d itio n , small amounts of p la g io c la s e f e ld s p a r and muscovite were a lso found in two samples. The la c k of i ! j c l e a r l y defined clay mineral peaks, in l i g h t of the abun- j dance of c l a y - s i z e d sedim ents, i s thought to be a r e s u l t of j d i a g e n e tic f a c t o r s t h a t produced an amorphous clay te x tu r e . 106 S im ilar c o m p licatio n s in com positional an aly ses have been j noted in other s t u d i e s of carbonate sediments j ( B o t t j e r , 1983,pers.com m .). j 5.4 ORGANIC ASSOCIATIONS j j The carbonate c o n c re tio n s s tu d ie d from the Holz Shale ! commonly contained Inoceramus valves or valve fragm ents (Figure 29), and a number of examples were found where large: Inoceramus s h e l l s formed the e n t i r e e x t e r i o r su rfa c e of the e l l i p s o i d a l nodule. In r a r e in s ta n c e s , w e ll-p re s e rv e d ammonite s h e l l s were a lso found w ith in the c o n c re tio n s (F igure 30). These organic remains ( s h e l l s and p o s s ib le body t i s s u e s ) probably served as n u c le i fo r i n i t i a l carbo nate p r e c i p i t a t i o n during i n c i p i e n t c o n c re tio n form ation. Many of the c o n c re tio n s s tu d ie d la c k a carbonate nucleus, but in s te a d d isp la y high c o n c e n tra tio n s of t e r r e s t r i a l organic fragm ents. Bedding planes of c o n c e n tra te d p la n t anc wood fragm ents were u su a lly observed w ith in samples of c o n c re tio n a ry beds, i n d i c a t i n g t h a t l i n e a r form ation of th ese carbonate nodules was d i r e c t l y a s s o c ia te d w ith dep o si ti o n of th ese o r g a n i c - r i c h l a y e r s . I t was a lso f a i r l y common fo r c o n c re tio n s to la c k an obvious nucleus around which p r e c i p i t a t i o n took p lace. These samples u su a lly d isp la y abundant b io tu r b a te s t r u c t u r e s . I t has been demons t r a t e d t h a t bio g en ic s t r u c t u r e s can a lso a c t as co n c re tio n 107 Figure 29: Inoceramus valve preserved in a carbonate c o n c re tio n . This sample was c o l l e c t e d a t BS-9 along Black S ta r Canyon Road. 102 Figure 30 Ammonite preserved w ith in a carbonate c o n c re tio n . This sample was found a t BS-12 along Black S ta r Canyon Road. n°i 111 nu clei due to high organic content and p e rm e a b ility of a s s o c ia te d sedim ents ( Kennedy,1970,1975; Bromley and E k d a le ,in p r e s s ) . In f a c t , the few c y l i n d r i c a l c o n c re tio n s found in the Holz Shale c lo se ly resemble v e r t i c a l burrow s t r u c t u r e s (Figure 31), but la b o r a to ry and f i e l d an a ly se s f a i l e d to confirm t h i s p o s s ib le o r ig i n . Many of the c o n c re tio n s t h a t d isp la y p h y sica lly -d o m in ated t e x t u r e s la c k an obvious org an ic nucleus and a ls o any evidence of b i o t u r b a t i o n . However, these c o n c re tio n s u su a lly p reserv e sediments t h a t were r ic h in d issem inated o rganic fragm ents. Based on the dominant a s s o c i a t i o n of carbonate c o n c re tio n s and p reserv ed o rganic m a t e r i a l s , i t appears h ig h ly probable t h a t decay p ro cesses played an im portant r o le in form ation of these d ia g e n e tic nodules. N e v e rth e le ss, o b s e rv a tio n s of abundant p la n t and wood fragm ents and o c c a sio n a l body f o s s i l s in s t r a t a la c k in g carbonate c o n c re tio n s in d i c a t e t h a t other f a c t o r s were also i nvol ved. 112 V e r t i c a l , c y l i n d r i c a l carbonate c o n c re tio n in a sh ale outcrop a t BS-9 along Black S ta r Canyon Road. 5.5 BACTERIAL ASSOCIATIONS The f in e - g r a i n e d rocks of the Holz Shale Member contain an abundance of p y r it e , e s p e c i a l l y in the sediments preserved in c o n c re tio n s . The presence of p y r it e in both the c o n c re tio n s and the surrounding s t r a t a su g g ests t h a t p y r it e form ation occurred e i t h e r p rio r to or contemporaneous w ith c o n c re tio n form ation (Dickson and B a rb e r,1976). Fully- and p a r t i a l l y - p y r i t i z e d organic fragm ents, r a d i o l a r i a n s , anc f o r a m in if e r a l t e s t s a re commonly observed in c o n c re tio n s la t s e c tio n s , but only o c c a s io n a lly in the surrounding s t r a t a . P y r ite form ation i s c lo se ly a s s o c ia te d w ith su lfa te -re d u c in g , b a c t e r i a and org an ic m atter decay in highly reducing en v i ronments (Krauskopf,1967; A lts c h u le r e t a l . , 1 9 8 3 ) . There fo re, the abundance of organic m atte r, the phenomenal p re s e r v a tio n of i n t r i c a t e c e l l u l a r s t r u c t u r e of some f o s s i l p la n t m a t e r ia ls , the common occurrence of p y r it e , and the dark color of the Holz Shale Member, suggest t h a t d e p o s itio n of these f in e - g r a i n e d rocks occurred in a h ighly reducing environment t h a t contained s u lf a t e - r e d u c i n g b a c t e r i a . The importance of b a c t e r i a l decomposition in the forma tio n of c o n c re tio n s has been recognized in numerous s tu d i e s (B e rn e r, 1 968,1 969 ,* G abinet, 1 974 ; R a is w e ll, 1 976 ; Hudson,1978). The c o n c e n tra tio n of p y r i t e w ith in the Holz 11E Shale c o n c re tio n s su g g ests t h a t s u l f a t e - r e d u c i n g b a c t e r i a also played a r o le in the form ation of these c o n c re tio n s. I f b a c t e r i a p o p u la tio n s were not e q u ally d i s t r i b u t e d throughout t h i s Cretaceous paleoenvironm ent, then the presence of carbonate c o n c re tio n s may in d ic a te s p e c i f i c | l o c a t i o n s where abundant b a c t e r i a li v e d . The decay of organic m atter through b a c t e r i a l decomposition would release* the necessary ammonia and a s s o c i a t e d amines to c r e a te an a l k a l i n e microenvironment where adipocere p r e c i p i t a t i o n could occur. Subsequent d ia g e n e s is would then a l t e r these i n c i p i e n t nodules to the carbonate co n c re tio n s p r e s e n tly found in the Holz Shale. This patchy d i s t r i b u t i o n of b a c t e r i a p o p u la tio n s might a lso e x p la in why carbonate c o n c re tio n s are not found in a l l o r g a n ic - r ic h rocks. 5.6 TIMING OF CONCRETION FORMATION The h y p o th e sis t h a t b a c t e r i a p o p u la tio n s played an im portant r o le in the form ation of c o n c re tio n s in the Holz Shale Member i s supported by the w ealth of evidence su g g estin g a very e a rly d ia g e n e tic age fo r th ese nodules. One o b se rv a tio n t h a t i n d i c a t e s an e a r ly d ia g e n e tic age i s the la c k of r a d i a l deform ation of laminae w ith in th ese c o n c re tio n s . Raiswell (1971) c l e a r l y demonstrated t h a t c o n c re tio n s which formed over a s u b s t a n t i a l time period 116 d isp la y e d in c re a se d pinching of laminae towards the edges due to g r e a te r compaction with time. The absence of t h i s c h a r a c t e r i s t i c in Holz Shale c o n c re tio n s su g g ests t h a t form ation occurred before any s i g n i f i c a n t sediment compac tio n took place, or a l t e r n a t i v e l y , t h a t nodule growth occurred so r a p id ly t h a t no temporal d if f e r e n c e s in the compaction of th ese sediments i s ap p aren t. The former appears to be the c o r r e c t e x p la n a tio n based on the u b iq u i tous presence of non-compacted t r a c e f o s s i l c r o s s - s e c t i o n s which suggest t h a t no p r io r compaction had o ccurred (Dickson and B a rb e r,1976). These c h a r a c t e r i s t i c s suggest e i t h e r a d ia g e n e tic or sy n g en etic o r ig i n for Holz Shale c o n c re tio n s, but the complete la c k of boring or e n c ru stin g t r a c e s p reclu d es the sy n g en etic p o s s i b i l i t y . Another l i n e of evidence su p p o rtin g the e a rly d ia g e n e tic o r i g i n of these calc a re o u s nodules i s the deform ation or bending of s t r a t a around th ese c o n c re tio n s in outcrop. The bending of s t r a t a around th ese nodules i s most commonly observed in sh ale s t r a t a (Figure 32), but a number of sandstone beds d isp la y s im ila r warping (Figure 33). This deform ation su g g ests t h a t co n c re tio n form ation occurred p r io r to l i t h i f i c a t i o n of the surrounding s t r a t a (Weeks,1 953; R a is w e ll,1971) . This i s supported by the f i e l d o b se rv a tio n of one sandstone stratum t h a t was in c o rp o ra te d ____________ H Z in to the und erly in g c o n c re tio n a ry bed fo llo w in g e a r l i e r bending of the sandstone (see Figure 34). The presence of s e p ta r ia n s t r u c t u r e s in many Holz Shale c o n c re tio n s a lso suggests an e a r ly d ia g e n e tic age. Although the exact mechanism of form ation of these i n t e r n a l s t r u c t u r e s i s s t i l l u n c e rta in , i t has been demonstrated t h a t most, s e p ta r i a n cracks are the r e s u l t of dehydration of highly porous, w a te r-la d e n sediments ( Lippman,1955; R a is w e ll,1971). This d ehydration i s a s s o c ia te d with co n c re tio n a ry growth and i n d i c a t e s an e a r ly d ia g e n e tic o r i g i n of the nodules (Rais- w ell, 1971). Approximately 40% of the c o n c re tio n s sampled fo r t h i s study contained c a l c i t e - f i l l e d s e p ta r i a n s t r u c t u r e s which were always a s s o c ia te d with abundant b iogenic s t r u c t u r e s . As f a r as t h i s author i s aware, no s p e c i f i c a s s o c i a tio n of s e p ta r i a n cracks and abundant b i o t u r b a t i o n has been r e p o rte d p r e v io u sly . I t i s suggested here t h a t t h i s a s s o c i a tio n i s the r e s u l t of in c re a se d p o ro s ity and p e rm e a b ility , and g r e a te r i n t e r g r a n u l a r w ater c o n te n ts caused by in te n siv e mixing by d e p o s it- f e e d in g in fa u n a . The in c re a se d water c o n te n ts of these b io tu rb a te d sedim ents r e s u l t e d in g r e a te r amounts of d ia g e n e tic dehydration and t h e r e f o r e , the forma tio n of these s e p ta r i a n s t r u c t u r e s . A dditional evidence fo r the e a r ly form ation of these c o n c re tio n s i s found in p o ro s ity e s tim a te s o b ta in e d through la b o r a to ry a n a ly se s. The g e n e ra lly accepted model for 116 Figure 32 Bending of sh ale s t r a t a c o n c re tio n along I rv in e around a carbonate Company F ire ro a d . 11 12d Figure 33: Deformation of a sandstone bed o v e rly in g a c o n c re tio n le n s a t BS-120 along Black S tar Canyon Road. Figure 34 : I n c o rp o r a tio n of a sandstone bed i n t o the top of the und erly in g c o n c re tio n a t BS-120 along Black S ta r Canyon Road. 123 124 c o n c re tio n cem entation suggests t h a t p r e c i p i t a t i o n of calcium carbonate f i l l s only open pore spaces w ith in the sediment ( Lippman,1955; R a is w e ll,1971,1976; O e rte l and C u r t i s , 1972; G a u t i e r ,1982). I f t h i s model is a c c u ra te , then the volume of carbonate in a co n c re tio n should r e f l e c t the approximate p o ro sity of the o r i g i n a l sediment. Problems t h a t could com plicate t h i s c o r r e l a t i o n in clu d e enlargement of pore spaces due to carbonate c r y s t a l growth, replacement of carbonate d e t r i t a l g ra in s, or the incomplete f i l l i n g of pore spaces by cement m a te r ia l ( R a is w e ll,1971; G a u t i e r , 1982). In t h i s study th ese co m p licatio n s can be ignored based on the presence of s e p ta r ia n s t r u c t u r e s which suggest pore spaces were not completely f i l l e d , the small volume of s e p ta r i a n s t r u c t u r e s (average < 5%), which i n d i c a te s cementing was almost complete, the t e x t u r a l evidence which suggests l i t t l e compaction took place p r io r to cemen t a t i o n , and the p aucity of d e t r i t a l carbonate g ra in s in the surrounding sedim ents (< 3%). The carbonate a n aly ses run in t h i s study show a range of 55 to 75% (average = 65%) for ten co n c re tio n samples (see Appendix B ) . S im ilar p o ro sity ranges have been measured in o th er d ia g e n e tic c o n c re tio n s tu d i e s and were used to e s tim a te depths of form ation of 2 to 10 m ( Rai s w e l l , 1 971,1 976 ,* Hudson, 1978; G a u t i e r , 1 982) . These depth e s tim a te s are based upon v e r t i c a l p o ro sity g r a d ie n ts measured in modern d e p o s itio n a l environments (Rieke and C h i l i n g a r i a n , 1974; E n g l e h a r d t ,1977). Assuming __________________________________ 1 2 5- the carbonate volume measurements of t h i s study to be approximate e s tim a te s of the o r i g i n a l sediment p o ro s ity , these an a ly se s a lso i n d i c a t e t h a t co n c re tio n form ation in the Holz Shale occurred a t very shallow depths (<10 m) in uncompacted sedim ents. In a d d itio n to the stro n g s u p p o rtin g evidence presen ted above fo r an e a rly d ia g e n e tic age for the Holz Shale Member c o n c re tio n s, i t has been suggested (B ern er,1964) t h a t p y r it e form ation can occur only in open geochemical systems ( i . e . , sediments in f u l l communication w ith s e a w a te r). Hence, the abundant p y r it e observed in th e Holz Shale c o n c re tio n s suggests a very shallow depth of form ation. S im ila rly , a f i e l d o b s e rv a tio n of a la r g e c o n c re tio n which ap p aren tly slumped in the s o f t , muddy sediments and produced a sw irled and c o n to rte d sh a le outcrop, also i n d i c a t e s a p r e - l i t h i f i c a - tio n o r ig i n (Figure 35). T herefore, based on a l l the evidence p resen ted above, i t seems ev id en t t h a t carbonate c o n c re tio n s in the Holz Shale Member formed from ea rly d ia g e n e tic p ro cesses in very porous, w a te r-la d e n sedim ents. 126 Figure 35 Fragmented carbonate co n c re tio n t h a t formed p r io r to slumping of surrounding sh a le s t r a t a . This exposure i s found a t BS-60 on Black S ta r Cayon Road. 127 128 5.7 ADDITIONAL FIELD OBSERVATIONS An i n t e r e s t i n g a sp e c t of the c o n c re tio n s of the Holz Shale Member i s t h a t they a l l occur in the f in e - g r a i n e d s t r a t a . Approximately 95% of a l l the c o n c re tio n s observed were lo c a te d in sh a le outcrops w ith the remainder being found in the f i n e - g r a i n e d sandstone exposures. This predo minance of c o n c re tio n s in f i n e r - g r a i n e d s t r a t a has a lso beer observed in previous c o n c re tio n s tu d ie s ( G a b i n e t ,1974). Muddy sediments u su a lly co n tain more d ia g e n e tic s t r u c t u r e s than c o a rse r sediments because they co n ta in abundant clay m in era ls which are chem ically r e a c t i v e , they have high i n t e r s t i t i a l f l u i d c o n te n ts t h a t m igrate slowly, and oxygen l e v e l s are commonly low ( P o tt e r e t a l . , 1 9 8 0 ) . The concre ti o n s of the Holz Shale a lso show a dominant o r i e n t a t i o n p a r a l l e l to bedding. This o r i e n t a t i o n i s a common tre n d in many c o n c re tio n a ry form ations ( R a isw e ll,1971; G a b i n e t ,1974; O ertel and C u r t i s , 1974; Hudson,1978). I t i s thought to be the r e s u l t of g r e a t e r p e rm e a b ility along bedding planes where the m ig ra tio n of pore w aters removes excess gaseous CO2 allow ing carbonate p r e c i p i t a t i o n to occur (R ais- w ell, 1971). This tre n d su g g ests t h a t even a t the shallow depths p o s tu la te d fo r c o n c re tio n form ation, v e r t i c a l perme a b i l i t y g r a d ie n ts were s u b s t a n t i a l l y lower t h a t g ra d ie n ts p a r a l l e l to bedding. ___________________________________. ________________________________________________________________ 1 2 3 An i n t e r e s t i n g v a r i a t i o n of t h i s tre n d i s a la rg e concre tio n observed in the f i e l d t h a t i s a c t u a l l y composed of f iv e , v e r t i c a l l y stacked c o n c re tio n s s e p a ra te d by th in (<4 cm) sh ale p a r tin g s (see Figure 36). Examination of these th in shale beds o u tsid e the c o n c re tio n was very lim ite d due to poor exposure, but i t seems ev id e n t t h a t these s t r a t a acted as impermeable b a r r i e r s p re v e n tin g the c o a le sc in g of in d iv id u a l c o n c re tio n s in a c a r b o n a te -r ic h environment. The cause of t h i s im perm eability is unknown. Another example i n d i c a t i n g a unique environment of co n c re tio n form ation i s shown in Figure 37. This co n cretio n d is p la y s w e ll- p re s e rv e d , complex Chondrites networks covering the e n t i r e e x t e r i o r su rface of the nodule. I n t e r n a lly , the C hondrites t r a c e s have produced a h e a v ily b i o t u r - bated t e x t u r e la c k in g the c l e a r l y defined burrows v i s i b l e or the e x te rn a l s u rf a c e . No other c o n c re tio n s were found to e x h i b i t such s t r u c t u r e s , and so i t i s concluded t h a t t h i s nodule r e p r e s e n t s a s p e c ia l geochemical paleoenvironm ent. Although the exact cause of t h i s unusual p re s e r v a tio n i s u n c e r ta in , i t seems probable t h a t organic compounds excretec by the burrowing organisms were geochemically a l t e r e d to form r e s i s t a n t sediments t h a t preserved th ese tr a c e f o s s i l s (T.L. Ku,1983 , per s.comm.). 13C Figure 36 Five, v e r t i c a l l y stacked carbonate c o n c re tio n s s e p a ra te d by th in sh a le i n t e r b e d s . This unique c o n c re tio n assemblage i s lo c a te d a t BS-22 along Black S ta r Canyon Road. 131 132 Figure 37 Carbonate c o n c re tio n C hondrites t r a c e s on with w e ll-p re s e rv e d e x t e r i o r s u rfa c e . 133 134 5.8 CONCLUSIONS The f in e - g r a i n e d s t r a t a of the Holz Shale Member in Black S ta r Canyon c o n ta in numerous carbonate c o n c re tio n s . These d ia g e n e tic nodules occur in many d i f f e r e n t shapes and s iz e s , but are u su a lly e l l i p t i c a l spheres t h a t are o r ie n te d p a r a l l e l to bedding. The form ation of these c o n c re tio n s appears to be the r e s u l t of organic m atter decay by b a c t e r i a l decomposition in a h ig h ly -re d u c in g environment. The cem entation of these nodules occurred during e a rly d ia g e n e s is of very porous, w a te r - s a t u r a te d muds. The Holz Shale c o n c re tio n s have provided a w ealth of in fo rm atio n about f i n e - g r a i n e d sediment d e p o s itio n a l mechanisms and a lso about the general d e p o s itio n a l environment in which these rocks were formed. To f u r t h e r understand t h i s Cretaceous paleoenvironm ent, the next chapter w i l l examine p aleo n to - lo g ic an a ly se s performed in t h i s study. 135 Chapter VI MICROPALEONTOLOGY 6.1 INTRODUCTION A number of previous s tu d i e s have analyzed th e microfauna of the Holz Shale Member (W heeler,1952; Orr,1964; Almgren,1973,1982; T r o t t e n , 1974; L an g ,1976,1978; L e e , 1982). A g r e a t deal of the controversy surrounding p ale o e n v iro n - mental i n t e r p r e t a t i o n s of these s t r a t a i s based upon bathy m etric d e te rm in a tio n s of m icrofaunal assemblages (Almgren,1973,1982; L a n g ,1976,1978; L e e ,1982). The funda mental cause of such s i g n i f i c a n t l y d i f f e r e n t i n t e r p r e t a t i o n s ( i . e . , bathyal versus n e r i t i c depths) is ro o te d in the bathym etric models used fo r each a n a ly s is (D o u g la s,1982). The model u t i l i z e d by Lang (1976,1978) is based upon F i s h e r ’ s o< index (W illiams, 1 964) , a measure of taxonomic d i v e r s i t y t h a t can be u t i l i z e d for e s tim a tin g paleobathyme- t r i e s . I t has been dem onstrated t h a t t h i s index i s depen dent upon sample s iz e (Murray,1973), thereby r e s t r i c t i n g i t s u s e fu ln e s s in p a le o e c o lo g ic a n a ly s e s. In a d d itio n , even in modern environments, co m plicating f a c t o r s such as sediment r e d i s t r i b u t i o n , sampling e f f e c t s , and faunal p a tc h in e s s, 136 make c o r r e l a t i o n of sp ecies d i v e r s i t y d if f e r e n c e s and depth z o n a tio n s extrem ely d i f f i c u l t (D o u g la s,1982). The model used by Almgren (1973,1982) and Lee (1982) is one based upon homeomorphic comparisons of Cretaceous and modern b en th ic foram assemblages ( S l i t e r and B a k e r ,1972). The b a sic premise of t h i s theory i s t h a t foram sp e c ie s with s im ila r morphologies w i l l respond to changing environm ental c o n d itio n s in a s im ila r fa sh io n (Bandy,1960). Depth d e t e r m inations based upon Cretaceous foram f a c i e s are li m i t e d by the la c k of a complete u n d erstanding of how Cretaceous environmental g r a d ie n ts d i f f e r e d from modern analogs (D o u g la s,1982). Although exact b athym etric e s tim a te s are very d i f f i c u l t in Cretaceous rocks, the S l i t e r - B a k e r model (1972) provides the best means fo r determ ining r e l a t i v e bath y m etries from Cretaceous foram assemblages (D o u g la s,1982). For these reaso n s, the B a k e r - S l it e r model was employed in foram an aly ses performed in t h i s study. 6.2 BLACK STAR CANYON ANALYSES Samples fo r m i c r o f o s s i l data were c o l l e c t e d from outcrops along Black S ta r Canyon Road and I rv in e Company F irero ad (see Figure 5 ). The purpose of these a n aly ses was to o b ta ir b i o s t r a t i g r a p h i c and p aleo b ath y m etric in fo rm atio n from Holz Shale S t r a t a in Black S ta r Canyon to complement o ther geologic a n a ly se s performed in t h i s study. All i d e n t i f i c a - __________________________________________ . 1 3 1 ti o n s and i n t e r p r e t a t i o n s of f o ra m in if e ra and c a lc a re o u s nannoplankton were performed by A.A. Almgren and M.V. Filew icz (Union Oil Company of C a l i f o r n i a ) , r e s p e c t i v e l y . Taxonomic l i s t s corresponding to these samples are presented in Appendix C. Assemblages of f o ra m in if e ra p re se n t in th e se samples are dominated by a g g u ltin a te d forms and are s im i l a r to those p re se n t in the lower s e c tio n of the Holz Shale Member in S ilv e ra d o Canyon (see Almgren,1982, Figure 3, sample AA164-AA42). This i n t e r v a l i s assig n ed to the G-1 Zone of P.P. Goudkoff’ s (1945) f o r a m in if e r a l zo n a tio n . The presence of Gaudrvina p v ram id a taT a s p e c ie s c h a r a c t e r i s t i c of the G-1 Zone, su p p o rts a s im ila r c o r r e l a t i o n fo r Black S ta r Canyon s t r a t a . A newly recognized genus fo r t h i s are a , Budasheva- e l l a C ?). i s a lso p re se n t in a few samples (see Appendix D). Based on the S l i t e r - B a k e r Model, the assemblage of foram in i f e r a p re se n t in th ese samples i n d i c a t e s a paleobathymetry of bathyal (middle b ath y a l? ) water depths. Calcareous n a n n o f o s s ils a re r a r e and poorly p erserved in f i v e of the samples c o l l e c t e d , and are t o t a l l y absent in the remaining tw elve. B i o s t r a t i g r a p h i c a n a l y s i s of th ese sparse m i c r o f o s s i l s i n d i c a t e s a C oniacian-S antonian age fo r these s t r a t a . This age assignment i s compatible w ith the G-1 Zone i n t e r p r e t a t i o n fo r the fo ra m in if e ra assemblage, and i s also __________________________________________ 1JL8 com patible with age d e te rm in a tio n s of previous Holz Shale s tu d ie s ( Poponoe,1942; Orr,1964; Almgren,1973,1982; L e e ,1982). The lim i t e d occurrence of c a lc a re o u s f o ra m in if e ra and nannoplankton su g g ests t h a t d i s s o l u t i o n pro cesses played an im portant r o le in the s e l e c t i v e p re s e r v a tio n of these faunas. The presence of abundant a g g lu tin a te d forms and p y r i t i z e d c a s t s su p p o rts t h i s id ea. The problem of p r e f e r e n t i a l d i s s o l u t i o n should however, c r e a te fo ra m in if e ra assemblages t h a t appear to be of shallow er w ater o r ig in through the d e s tr u c t i o n of d e l i c a t e bathyal forms and the p re s e r v a tio n of robust s h e l f a l forms (D o u g la s,1982). Therefore, s e l e c t i v e p re s e r v a tio n of microfauna in the Holz Shale suggests t h a t these s t r a t a were d ep o sited in w aters of at l e a s t upper bathyal depth. This bathym etric e stim a te su p p o rts the paleoenvironm ental i n t e r p r e t a t i o n of a c o n t i n en tal slope environment p o s tu la te d p re v io u sly from sedimen- to lo g ic a n a ly se s of these Holz Shale s t r a t a . 1 3 _ 9 J Chapter VII MACROPALEONTOLOGY The macrofauna and m acro flo ra of the Holz Shale Member ir Black S ta r Canyon i s c h a r a c t e r iz e d by abundant Inoceramus v alv es, the u b iq u ito u s presence of t e r r e s t r i a l p la n t and wood fragm ents, and the general paucity of other body f o s s i l s . Inoceramus i s g e n e ra lly a f l a t , broad, th i n - s h e lle d b iv alv e s p e c i f i c a l l y adapted to l i v i n g on s o f t, muddy s u b s t r a t e s (Cox e t a l ., 1 9 6 9 ; Kaufmann,1974). This o p p o r tu n i s t i c genus ( Kauffman,1981) fre q u e n tly provides a firm s u b s t r a te fo r subsequent i n v e r t e b r a t e c o lo n iz a tio n (Cox e t a l ., 1 9 6 9 ; Kaufmann,1974,1981; Ward,in p r e s s ) , but no evidence of t h i s process was observed in t h i s study. Although the Molluscan fam ily Inoceramidae d is p la y s a broad h a b i t a t to le ra n c e in s t r a t a worldwide ( Kaufmann,1965), these Mesozoic b iv a lv e s are the dominant, u n tra n sp o rte d macroin v e r t e b r a t e s in f in e - g r a i n e d , deep-marine, Upper Cretaceous s t r a t a throughout C a l i f o r n i a (Page e t a l .,1 9 5 1 ; R u s t , 1966; Lowe,1972; S u n d b erg ,1979; Yeo,198l; Link and B o t t j e r ,1982; B o t t j e r ,1982). 140 Inoceramus valves in Black S ta r Canyon are most commonly preserved in carbonate c o n c re tio n s, but are a lso found in a\ few t u r b i d i t e sandstone d e p o s its . The presence of many la r g e , t h i n - s h e l l e d valv es t h a t are o c c a s io n a lly a r t i c u l a t e d s u g g e sts t h a t th ese f o s s i l s have undergone l i t t l e or no t r a n s p o r t a t i o n ; fragm ents p reserved in t u r b i d i t e d e p o s its are obvious e x c e p tio n s. The specimens examined in t h i s study a l l e x h i b i t the c h a r a c t e r i s t i c Inoceramus p ris m a tic s h e l l s t r u c t u r e and appear to be composed of o r i g i n a l ca lc a re o u s m a t e r ia l. These Inoceramus f o s s i l s are i n t e r p re te d as deep-water b iv a lv e s (o u te r n e r i t i c to bathyal depths) based on comparisons to shallow -w ater museum s p e c i mens ( L. R. S a u l, 1 983 , per s. comm.) . Inoceramus valves are by f a r the most common body f o s s i l s in the Holz Shale of Black S ta r Canyon, but o ther i n v e r t e b r a te specimens c o l l e c t e d in clu d e the b iv a lv e s Propeamussium s p . and Indoerammatodon s p . . the ammonites B ostrvchoceras eloneatum , B a c u lite s s p . T and Eupachvdiscus harad ai ( ? ) , anc s c a t t e r e d a rth ro p o d appendages (see Appendix D ). These f o s s i l s are a lso thought to have undergone l i t t l e or no t r a n s p o r t a t i o n based on the p re s e r v a tio n of fin e s h e ll s t r u c t u r e , lack of frag m en tatio n , b iv a lv e a r t i c u l a t i o n , and comparisons to modern analogs ( L .R .S a u l,1 9 8 3 ,pers.comm.). 141 In a d d itio n to th e se indigenous specimens, one sample was found to c o n tain a p o s s ib le tra n s p o r te d fauna c o n s is t i n g of more ro b u st, but u n i d e n t i f i a b l e b iv alv e and gastropod fragm ents. This sample was the only observed occurrence of a p o t e n t i a l l y tr a n s p o r te d fauna except fo r a few th in t u r b i d i t e sandstones t h a t contained r a r e , t h i c k - s h e l l e d , b iv a lv e fragm ents. Body f o s s i l s were conspicuously absent from c h a n n e l - f i l l d e p o s its , but t h i s could be a r e s u l t of in c re a se d d i s s o l u t i o n in th e c o a r s e r - g ra in e d rocks. The m a c ro in v e rte b ra te body f o s s i l s examined in t h i s study are not d ia g n o s tic of a s p e c i f i c paleoenvironm ent, but they do suggest a deep-marine d e p o s itio n a l system (o u te r n e r i t i c to bathyal depth) where muddy s u b s t r a t e s were common. This co n clu sio n i s com patible w ith i n t e r p r e t a t i o n s made e a r l i e r in t h i s paper. P lan t f o s s i l s in t h i s s t r a t i g r a p h i c s e c tio n are abundant and in clu d e w e ll- p re s e rv e d l e a f im pressions (Figure 38), seeds (Figure 39), twigs, and small logs (Figure 40). The abundance of p la n t and wood fragm ents in th ese s t r a t a i s one; of the most s t r i k i n g f e a t u r e s of t h i s sequence. These organic remains are p reserved as o x id ized im pressions and carbonized compressions in which i n t r i c a t e s t r u c t u r a l d e ta ii i s o fte n p re s e n t. P r e s e r v a tio n of t h i s c e l l u l a r s t r u c t u r e i s commonly observed w ith in carbonate c o n c re tio n s. Concen 142 t r a t i o n s of p la n t remains occur along bedding p lanes both w ith in and between sediment g ra v ity flows. Such c o n c e n tra tio n s are much more f re q u e n tly observed in outcrops of f i n e - g r a i n e d s t r a t a , but s im ila r zones do occur w ith in the c h a n n e l - f i l l d e p o s its . The abundance of p la n t m a te r ia l preserved in t h i s s e c tio n im p lie s t h a t sedim entation r a t e s were a t l e a s t i n t e r m i t t e n t l y ra p id , and t h a t reducing c o n d itio n s e x i s t e d during d e p o s itio n of these s t r a t a . I t is thought t h a t most of the p la n t and wood fragm ents found in t h i s s t r a t i g r a p h i c sequence are a s s o c ia te d with d i l u t e t u r b i d i t y or downslope c u r r e n ts t h a t o r ig i n a t e d as overbank or oversh elfed g e flows and were d ep o sited in th e i n t e r channel reg io n . A l t e r n a t iv e mechanisms fo r implacement of the organic m atter in c lu d e s th e slow s e t t l i n g of w aterlogged fragm ents in th e water column, and th e in p u t of c o n c e n tra t io n s of p la n t and wood m a t e r i a l s during major storms. The author b e lie v e s t h a t th ese a l t e r n a t i v e mechanisms a lso c o n tr ib u te d o rganic m a t e r i a l s to the Holz Shale s t r a t a , but t h a t d i l u t e sediment flows were the primary source of t e r r e s t r i a l organic fragm ents. U n fo rtu n a te ly , the science of Cretaceous paleobotany has not y e t developed to the point where u sefu l p a le o e c o lo g ic or b i o s t r a t i g r a p h i c in fo rm atio n can be a t t a i n e d from th ese types of remains (J. Wolfe, 1983,per s.comm.). However, the p ro fu sio n of t e r r e s t r i a l organic m a t e r i a l s in s t r a t a i n t e r p r e t e d as sediment 143 g r a v ity flows does i n d i c a t e dominant sediment source close: to th e c o n tin e n ta l margin Th dea w i l l be e la b o r a te d o 1 a te r t h i s paper 144 Figure 38: Leaf im pressions found w ith in carbonate c o n c re tio n s . Both c o n c re tio n samples were found a t BS-33 along Black S ta r Canyon Road. _U 15L 146 Figure 39: Seed im pressions found w ith in carbonate c o n c re tio n s . The top photograph was taken a t 50x m a g n ific a tio n . The upper specimens were found a t BS-24 and the lower specimen was c o l l e c t e d a t BS-33 along Black S ta r Canyon Road. 141 Figure 40: Small carbonized log p reserv ed w ith in a carbonate c o n c re tio n from BS-9 along Black S tar Canyon Road. 149 ___ Chapter V III ICHNOLOGY 8.1 TRACES OF CHANNEL-FILL DEPOSITS The ichnofauna of the c o a rse -g ra in e d s t r a t a in Black S ta r Canyon i s dominated by abundant Qphiomorpha and uncommon T h a la ss in o id e s tr a c e s (Figure 41). These burrows are c i r c u l a r to ovate in c r o s s - s e c t i o n (0.5 to 3.0 cm in diam e t e r ) , but are u s u a lly observed as h o r iz o n ta l e p ic h n ia l rid g e s ( a f t e r M a rtin s s o n ,1970). E pichnial grooves are also r a r e l y found in th ese s t r a t a . Trace morphologies range from s t r a i g h t to sinuous tubes t h a t commonly e x h i b i t t y p i c a l Y-shaped branching. No v e r t i c a l or l a t e r a l tre n d s in tr a c e composition or morphology were e v id e n t. I n d iv id u a l leb en s- spuren can o fte n be tra c e d along bedding s u rf a c e s fo r d is ta n c e s up to 60 cm and are u su a lly f i l l e d w ith sediment from the o v erly in g stra tu m . Qphiomorpha and T h a la ss in o id e s t r a c e s have i d e n t i c a l morphologies except Qphiomorpha burrows have a f e c a l p e l l e t l i n i n g . V e r t i c a l l y - o r i e n t e d s in g le tubes are uncommon in outcrop, but appear to o r i g i n a t e from upper bedding s u rf a c e s (Figure 151 Figure 41 Ophiomorpha tr a c e s on sandstone bedding su rfa c e in c h a n n e l - f i l l d e p o s it of channel 2. 152 42). Occasional escape s t r u c t u r e s evidence ra p id d e p o s itio n of these c o a rs e -g ra in e d d e p o s its (Figure 43). The presence of fe c a l p e l l e t - l i n e d Ophiomorpha and u nlined T h a la ss in o id e s t r a c e s on the same stratum i n d i c a t e s t h a t the o r ig i n a l s u b s t r a te was f a i r l y cohesive, but l o c a l l y v a r i a b l e (Frey and Howard, 1 970) . Qphiomorpha and T h a la ss in o id e s lebensspuren are co n sid ered to be dw elling s t r u c t u r e s produced by suspension- feeding t h a l a s s i n i d shrimp (Frey e t a l . , 1 9 7 8 ) . O rig in a lly considered r e l i a b l e i n d i c a t o r s of shallow water, high-energy marine environments ( S e i l a c h e r ,1967), th ese ichnogenera have also been more r e c e n t l y re p o rte d from a number of h ig h -e n ergy, deep-marine d e p o s itio n a l environments (Kern and Warme,1974; C rim e s,1977; B o t t j e r ,1981). The wide depth range of these biogenic s t r u c t u r e s i s thought to be the r e s u l t of s im i l a r environmental c o n d itio n s produced in both high-energy h a b i t a t s ( e . g . , high c u rre n t a c t i v i t y , r e l a t i v e l y low organic c o n te n ts, sandy s u b s t r a t e s , and i n t e r m i t te n t periods of high oxygenation; C rim es,1977; B o t t j e r , 1981). The presence of these tra c e f o s s i l s in Holz Shale c h a n n e l - f i l l d e p o s its im p lie s t h a t s im ila r environ mental c o n d itio n s were p re se n t during d e p o s itio n of these s t r a t a . 154 [Figure 42: T h a la ss in o id e s burrow in sandstone t u r b i d i t e d e p o s it from channel 2. 155 156 fig u re 43 : Escape s t r u c t u r e a t the base of a h ig h -d e n s ity t u r b i d i t e d e p o s it (F acies A) in a submarine chute d e p o s it along I rv in e Company F ire ro a d . 157 158 The dominance of h o r i z o n t a l l y o r ie n te d t r a c e s in e p ic h n ia l p o s itio n su g g ests t h a t th ese t r a c e s re p re s e n t p o s t- d e p o s it i o n a l c o lo n iz a tio n of these sandy s u b s t r a t e s . The low d i v e r s i t y of bio g en ic s t r u c t u r e s observed in the D h a n n e l-fill d e p o s its i s probably a r e s u l t of low organic contents ( l e s s d e p o s it fe e d e rs ) and the e ro s io n a l removal of tra c e s by ra p id ly d e p o site d sediments ( C rim es,1970,1977) . In a d d itio n , the paucity of b i o tu r b a te s t r u c t u r e s in chan nels c o n ta in in g conglomerate s t r a t a might i n d i c a t e t h a t these h a b i t a t s were in h o s p i t a b l e to t h a l a s s i n i d shrimp because sediments were too c o a rse -g ra in e d , e r o s io n a l fo rces were too extreme, sed im en tatio n r a t e s were too high, or a combination of the above. The abundance of tr a c e f o s s i l s in channels t h a t c o n tain th i c k e r sh a le in te rb e d s s i g n i f i e s t h a t i n t e r m i t t e n t se d im en tatio n of c o a rs e -g ra in e d d e p o s its was an im portant f a c t o r in the c o lo n iz a tio n of these sedim ents. B io tu rb a tio n i s an im portant f a c t o r e f f e c t i n g s t a b i l i t y of sediments in slope environments (M o rg en stern ,1967 ; S t a n l e y ,1971; K e llin g and S t a n l e y ,1976; Nardin e t a l.,1 9 7 9 b ; Bennett and N e ls o n ,1983). Burrowing a c t i v i t y a l t e r s the o r i g i n a l s t r u c t u r e , packing, t e x tu r e , p o r o s ity , and perme a b i l i t y of the sedim ents, and thereby changes t h e i r shear s tr e n g th and load c a p a c ity (M o rg e n ste rn ,1967; S t a n l e y ,1971). In creased i n t r o d u c t i o n of water in t o the sediments through 1 59 b io tu r b a tio n , enhances u n d e rc o n so lid a tio n and promotes slope f a i l u r e and slumping ( R ic h a r d s ,1965; M o rg en stern ,1967). The abundance of b iogenic s t r u c t u r e s in t h i s s t r a t i g r a p h i c s e c tio n i n d i c a t e s t h a t in te n s e burrowing a c t i v i t y occurred during d e p o s itio n of these s t r a t a . Although s p e c i f i c examples of b io lo g ic a lly - in d u c e d f a i l u r e are p r a c t i c a l l y im possible to i d e n t i f y in the rock reco rd , the dominance of b io tu r b a te s t r u c t u r e s in many Holz Shale s t r a t a suggests t h a t in fa u n a l burrowing played a major r o le in a l t e r i n g the o r i g i n a l sediment f a b r i c , and might have also promoted i s o l a t e d o ccu rren c es of slope f a i l u r e . Infaunal burrowing has a lso been shown to have s t a b i l i z i n g e f f e c t s on sediments a t the sedim ent-w ater i n t e r f a c e . P roduction of fe c a l p e l l e t s and f e c a l mounds by b en th ic i n v e r t e b r a t e s r e s u l t s in sediments which have s i g n i f i c a n t l y g r e a te r c r i t i c a l entrainm ent v e l o c i t i e s than " fre e " s e d i ments due to mucous adhesion between f e c a l m a t e r ia ls (Nowell e t a l . , 1 9 8 1 ) . Biogenic sediment a l t e r a t i o n can a lso in c r e a s e the average sediment age ( i . e . , time since d eposi tio n ) of s u r f i c i a l sediments and change boundary roughness c h a r a c t e r i s t i c s (Jumars e t a l .,1 9 8 1 ; Nowell e t a l . , 1 9 8 1 ) . U n fo rtu n ately , sediment-organism i n t e r a c t i o n s such as th ese are d i f f i c u l t to e v a lu a te in the rock reco rd , but co n sid e rin g the evidence fo r e x te n siv e in fa u n a l a c t i v i t y during 160 d e p o s itio n of the Holz Shale, these f a c t o r s may also have played a minor r o le in determ ining the f i n a l c h a r a c t e r i s t i c s of these c l a s t i c s t r a t a . 8.2 TRACES QF INTERCHANNEL DEPOSITS The ichnofauna of the f i n e - g r a i n e d s t r a t a in Black S ta r Canyon i s dominated by abundant C h o n d rite s T common P la n o l- i t e s , and r a r e Zoophvcus t r a c e s . The study of t r a c e f o s s i l s in th ese s t r a t a was l i m i t e d to co n c re tio n samples because of the sev e re ly weathered n a tu re of the corresponding o u tcro p s. C hondrites s t r u c t u r e s occurred as c o n c e n tra te d groups of i r r e g u l a r l y ovate to c i r c u l a r c r o s s - s e c t i o n s (0.5 to 3.0 mm in diam eter) t h a t were ac c e n tu a te d by tonal c o n t r a s t s in c o n c re tio n sla b s e c t io n s (Figure 44). The burrow i n f i l l of th ese t r a c e s was u su a lly darker colored than the surrounding sediment, although in v e rse color schemes were i n f r e q u e n tly observed. This to n a l c o n t r a s t i s probably the r e s u l t of d ia g e n e tic d i f f e r e n t i a t i o n of the o r g a n ic - r ic h burrow i n f i l l ( Simpson,1975). C hondrites lebensspuren e x h ib ite d the t y p i c a l dichotomous branching p a t t e r n when lo n g i t u d i n a l s e c tio n s were v i s i b l e . Meniscus b a c k - f i l l i n g was uncommon in th e se s e c tio n s . Chondrites tr a c e s are considered feed in g s t r u c t u r e s produced by s o ft-b o d ie d , d e p o s it- f e e d in g organisms ( Simpson,1957). P o ss ib le producers of these s t r u c t u r e s 161 Figure 44: Chondrites t r a c e s in c o n c re tio n slab s e c tio n from BS-24 (50x m a g n if ic a tio n ) . include p o ly ch aetes, s ip u n c u lid s , or even d e p o s it- f e e d in g arth ro p o d s (Osgood,1975). Chondrites i s c h a r a c t e r i s t i c of q u ie t w ater, o r g a n i c - r i c h sedimentary environments, but e x h i b i t s a broad h a b i t a t to le ra n c e ( S e i l a c h e r ,1978). I t has been r e p o rte d from numerous deep-marine c l a s t i c sequences ( H e s se ,1972,1975; Kern and Warme,1974; S l i t e r , 1 9 7 5 ; B o t t j e r , 1 981) , and has been used as evidence fo r i n t e r p r e t a ti o n s of slow, hem ipelagic sed im en tatio n (H e ss e ,1972). P l a n o l i t e s leb en ssp u ren occur as e l l i p s o i d a l c r o s s - s e c t i o n s (0.4 to 1.2 cm small a x is diameter range) and s in g le tu n n e ls t h a t show a range between h o r iz o n ta l and v e r t i c a l o r i e n t a t i o n s . These t r a c e s d isp la y a tonal c o n t r a s t s im ila r to Chondrites burrows, which i s a lso thought to be the r e s u l t of d ia g e n e tic d i f f e r e n t i a t i o n . Reburrowing of P l a n o l i t e s by Chondrites is very common in th e c o n c re tio n s s tu d ie d and i n d i c a t e s m u l t i p l e periods of b io t u r b a t i o n . Meniscus b a c k - f i l l i n g and branching of P l a n o l i t e s is absent in th e se s t r a t a . P l a n o l i t e s t r a c e s a re feed in g s t r u c t u r e s produced by d e p o s it- f e e d in g organims. These f o s s i l s a re f a c i e s indepen dent and are found in l i t t o r a l to bathyal paleoenvironm ents ( C ham berlain,1978). The s i g n i f i c a n t l y lower abundance of P l a n o l i t e s burrows, r e l a t i v e to Chondrites t r a c e s , i n d i c a t e s t h a t the P l a n o l i t e s -pro d u cin g organism was a much sc a rc e r i n h a b i t a n t of t h i s muddy, d e p o s itio n a l paleoenvironm ent. 164 Zoophvcus t r a c e f o s s i l s are uncommon in the Holz Shale of 31ack S tar Canyon. These leb en ssp u ren c o n s is t of meniscus b a c k - f i l l e d , s h e e t - l i k e s t r u c t u r e s t h a t are o r ie n te d subpar a l l e l to subnormal to bedding (Figure 45). Zoophvcus t r a c e s are acc e n tu a te d by l i g h t e r colored burrow i n f i l l than the surrounding sedim ent. The few specimens observed are always found in a s s o c i a t i o n w ith dense p o p u la tio n s of Chondrites and s c a t t e r e d P l a n o l i t e s t r a c e s . Zoophvcus t r a c e s are feeding s t r u c t u r e s produced by d e p o s it- f e e d in g , worm-like organisms ( P l i c k a , 1968). This f o s s i l was once considered a c h a r a c t e r i s t i c middle to upper bathyal b iogenic s t r u c t u r e ( S e i l a c h e r ,1967), but i s now recognized to range i n t o shallow n e r i t i c environments (H allam ,1975). The predominace of tra c e f o s s i l s of d e p o s it- f e e d in g organisms in th ese s t r a t a , im plies a paleoenvironment where f in e - g r a in e d , o r g a n i c - r i c h sediments were being d e p o site d . The b io lo g ic a lly -d o m in a te d sediment t e x t u r e s a s s o c i a t e d with abundant occurrences of these t r a c e s a re c h a r a c t e r i s t i c of slow, hem ipelagic se d im en tatio n (Howard,1975). Although none of the leb en ssp u ren observed in th e se s t r a t a are d ia g n o s tic of a s p e c i f i c d e p o s itio n a l environment, t h e i r presence i s com patible w ith a c o n tin e n ta l slope p a leo en v i- ronmental i n t e r p r e t a t i o n . 165 j Figure 45: Zoophycus leb en ssp u ren d isp la y in g meniscus back f i l l i n g in co n c re tio n slab s e c tio n from BS-24 (50x m a g n if ic a tio n ) . | I 166 Chapter IX STRATIGRAPHY The outcrops of the Holz Shale Member along Black S ta r Canyon Road and I r v in e Company F ire ro a d appear to be c o rre - Lative to the lower t h i r d of the S ilv e ra d o Canyon Holz Shale DUtcrop (see Almgren,1982, Figure 3, AA164-AA42) based on inicrofaunal and f i e l d r e l a t i o n s h i p s . The basal c o n ta c t of t h i s member in Black S ta r Canyon i s not exposed due to f a u l t i n g and dense v e g e ta tio n cover. The upper c o n ta c t i s Bxposed in v e r t i c a l c l i f f fa c e s and d is p la y s a sharp, sro s io n a l su rface p a r a l l e l to bedding. The o v e rly in g Williams s t r a t a c o n s is t of pebble and cobble conglomerates th a t produce a sharp l i t h o l o g i c boundary. M icrofaunal samples taken from Holz Shale s t r a t a immediately beneath the Williams-Holz c o n ta c t i n d i c a t e t h a t s t r a t a e q u iv a le n t to the upper h a l f of the S ilv e ra d o Canyon s e c tio n have been removed or were never d e p o site d . The p o s s i b i l i t y of a d isconform ity at t h i s c o n ta c t has been suggested by Poponoe (19^2) and Colburn (1973), although apparent g r a d a tio n a l c o n ta c ts are also exposed to the s o u th e a st on S ilv e ra d o Truck T r a il (see Cooper e t a l . , 1 9 8 2 ) . The sharp l i t h o l o g i c c o n t r a s t acro ss the Holz-W illiams c o n ta c t, the absence of upper Holz micro- 168 f o s s i l s , and the e r o s io n a l su rfa c e p re se n t in Black S ta r Canyon, imply t h a t a disconform ity occurs a t t h i s forma- t i o n a l boundary. The presence of a g ra d a tio n a l c o n ta c t to the so u th e a st suggests t h a t l a t e r a l v a r i a t i o n s occurred in the deposi- t i o n a l and/or t e c t o n i c h i s t o r y of t h i s sequence. A d i s t i n c t la c k of abundant sandstone s t r a t a and a complete absence of c h a n n e l - f i l l d e p o s its in S ilv e ra d o Canyon, also support t h i s id ea. The abundance of c o a rs e -g ra in e d d e p o s its between Black S ta r and Ladd Canyons su g g ests t h a t t h i s p a r t of the Cretaceous basin was the focus of sediment i n f lu x o f f the c o n tin e n t. In W illiams Canyon, the presence of another la r g e c h a n n e l - f i l l d e p o s it i n d i c a t e s t h a t an a d d i t i o n a l fo cal p o in t may have been lo c a te d to the South. The paucity of c o a rs e -g ra in e d s t r a t a in the S ilv e ra d o Canyon region could be the r e s u l t of a more d i s t a l d e p o s itio n a l environ ment, or one lo c a te d in an i n t e r d i s t r i b u t a r y area. Consid e rin g the dominant w e s te rly t r a n s p o r t d i r e c t i o n i n t e r p r e t e d fo r these s t r a t a and the n o rth -s o u th o r i e n t a t i o n of the Cretaceous c o n tin e n ta l margin, the l a t e r e x p la n a tio n seems more re a so n a b le . The th ic k n e s s e s of Holz Shale sequences in Black S ta r and S ilv e ra d o Canyons a re approximately equal (see Figure 3 ). However, as d isc u sse d p re v io u sly , m ic r o f o s s il a n aly ses coupled with o b s e rv a tio n s of a disconform ity a t the top of 169 t h i s s e c tio n su g g ests th e removal of a s i g n i f i c a n t s t r a t i - graphic th ic k n e s s in Black S ta r Canyon. This im p lie s t h a t d e p o s itio n r a t e s in th e Black S ta r Canyon area were much g r e a t e r than those in S ilv e ra d o Canyon. The W illiams Formation i s i n t e r p r e t e d as s h e l f a l d e p o s its t h a t s ig n ify a r e g r e s s i v e sequence (Sundberg and C ooper,1978; Almgren,1982; S a u l , 1982). This r e g r e s s i o n could have been caused by t e c t o n i c u p l i f t of the crato n , subsidence of the b asin , or a e u s t a t i c r i s e in sea l e v e l . The presence of both a disconform able Holz-W illiams c o n ta c t in Black S ta r Canyon and a g r a d a tio n a l boundary near S ilv e ra d o Canyon could have r e s u l t e d from d i f f e r e n t i a l t e c t o n i c u p l i f t ( g r e a t e r to the N orth), or a l t e r n a t i v e l y , i t might s ig n ify t h a t Black S ta r Canyon s t r a t a r e p r e s e n t a more proximal d e p o s itio n a l paleoenvironment where a r e g r e s s io n would have produced g r e a t e r e ro sio n of d e p o site d sedim ents. In e i t h e r case, sea l e v e l f l u c t u a t i o n s on t h i s narrow c o n tin e n ta l margin c re a te d s u b s t a n t i a l changes in th e d e p o s itio n a l and e r o s io n a l pro cesses t h a t produced th ese s t r a t a . 170 Chapter X PALEOENVIRONMENTAL SUMMARY Sedim entologic, ic h n o lo g ic , and p a le o n to lo g ic a n a ly se s of the Holz Shale Member in Black S ta r Canyon stro n g ly support a c o n tin e n ta l slope and upper submarine fan p aleo en v iro n - mental i n t e r p r e t a t i o n . C o arse-g rain ed , c h a n n e l - f i l l depo s i t s , one of the most c h a r a c t e r i s t i c f e a t u r e s of slope and upper fan d e p o s itio n a l systems (S tan ley and U nrug,1972; Mutti and Ricci L u c ch i,1978), are prominent f e a t u r e s of t h i s Upper Cretaceous s t r a t i g r a p h i c sequence. S im ilar to modern examples t h a t have been stu d ie d , th ese channels re c o rd a complex i n t e r p l a y of d e p o s itio n a l and e r o s io n a l f o rc e s t h a t are dominated by the implacement of mass t r a n s p o r t e d s e d i ments. The dominant types of sediment g ra v ity flows respon s i b l e fo r d e p o s itio n of these d e p o s its in clu d e conglom eratic d e b ris flows, h ig h -d e n s ity t u r b i d i t y c u r r e n ts , and c l a s s i c Bouma lo w -d en sity t u r b i d i t e s . In a d d itio n , slum p-deposited s t r a t a and t r a c t i o n - c u r r e n t d e p o s its a lso reco rd im portant d e p o s itio n a l mechanisms. A ssociated d e p o s its of pebbly mudstones and p o o rly-developed le v e e f a c i e s s tre n g th e n t h i s paleoenvironm ental i n t e r p r e t a t i o n . 171 The d i s s e c t i o n of contemporary f in e - g r a i n e d sedim ents by c h a n n e l - f i l l d e p o s its im p lie s t h a t d e p o s itio n of Holz Shale s t r a t a probably occurred on a middle slope paleoenvironment where an apron of f in e sediments was accum ulating. In upper slope and s h e l f a l environments, submarine channels u su a lly la c k le v e e d e p o s its , are deeply in c is e d , and cut older margin sediments or bedrock (D.S. G o r s l i n e , 1983,pers.comm.). T herefore, t h i s s t r a t i g r a p h i c sequence could by s t r i c t d e f i n i t i o n , also be co n sid e red upper submarine fan d e p o s its . Due to the overlap of c o n tin e n ta l slope and upper fan d e p o s itio n a l systems, the d i s t i n c t i o n between th e se paleoen- vironments i s commonly one of sem antics. Although the term c o n tin e n ta l slope i s used throughout the t e x t fo r s p e c i f i c paleoenvironm ental i n t e r p r e t a t i o n s of these rocks, an i n t e r p r e t a t i o n of upper submarine fan i s co n sid e red an eq u ally v a lid one. S e p a ra tin g th e se l e n t i c u l a r d e p o s its a re f in e - g r a i n e d san d sto n es, mudstones, and s h a le s t h a t a lso r e p r e s e n t an i n t r i c a t e system of d e p o s itio n a l mechanisms. Interbedded t u r b i d i t e s , c o n t o u r it e s , and hem ipelagic sedim ents dominate d e p o s itio n on the in te rc h a n n e l region. Abundant p y r i t e and carbonate c o n c re tio n s, common f e a t u r e s of c o n t i n e n t a l slope environments (Cook e t a l . , 1 9 8 2 ) , evidence s i g n i f i c a n t d i a g e n e tic a l t e r a t i o n of th ese sedim ents. Analyses of these 11,2 carbonate nodules suggest an e a rly d ia g e n tic age of forma tio n in muddy, w a t e r - s a t u r a te d sedim ents t h a t were l o c a l l y anaerobic. P a le o n to lo g ic a n a ly se s of the s t r a t a i n d i c a t e t h a t ben th ic organisms were w ell adapted to t h e i r s p e c i f i c h a b i t a t , but t h a t o v e r a ll community sp e c ie s r ic h n e s s was very low. The f in e - g r a i n e d d e p o s its of the Holz Shale are dominated by the e p ifa u n a l su sp e n sio n -fe e d e r b iv a lv e In o cer- arnus, and th e d e p o s it- f e e d in g t r a c e f o s s i l C h o n d rite s . This broad, t h i n - s h e l l e d b iv a lv e was w ell designed fo r f l o a t i n g atop th e soupy in te rc h a n n e l muds. The l o c a l l y abundant infauna produced b i o t u r b a t e sedim entologic t e x t u r e s and may have c o n tr ib u te d to the i n s t a b i l i t y of these sedim ents. These in te rc h a n n e l are a s appear to have shown a complete range of b e n th ic h a b i t a t s from low-energy, b i o l o g i c a l l y - d o minated environments to hig h -e n erg y , p h y sica lly -d o m in ated environments with l o c a l occurrences of anaerobic c o n d itio n s . The c o a rs e -g ra in e d d e p o s its of the Holz Shale Member also d isp la y e d a b e n th ic community with a low sp e c ie s r ic h n e s s . The submarine channel h a b i t a t s were c h a r a c te r iz e d by high r a t e s of d e p o s itio n , s tro n g c u r r e n t s , and a firm s u b s t r a t e , and supported a s u sp e n sio n -fe e d in g fanua of t h a l a s s i n i d shrimp. Areas of very c o a rs e -g ra in e d d e p o s itio n a re devoid of any b e n th ic p a le o n to lo g ic evidence. D isplaced s h e l f a l faunas are uncommon in the c h a n n e l - f i l l d e p o s its . 173 The p ro fu sio n of t e r r e s t r i a l p la n t and wood fragm ents in t h i s s e c tio n , and t h e i r a s s o c i a t i o n w ith sediment g ra v ity flow d e p o s its , suggest t h a t the sediment source fo r these d e p o s its was lo c a te d proximal to the c o n tin e n ta l margin. S im ila rly , the w ell-rounded n a tu re of the la r g e igneous c l a s t s in the c h a n n e l - f i l l d e p o s its im p lies a f l u v i a l or shallow s h e lf a l o r ig i n . Previous s tu d i e s of t h i s sedimen ta ry sequence have p o s tu la te d a narrow Cretaceous c o n t i n e n ta l s h e lf , very s im ila r to the modern C a l i f o r n i a c o a s t l i n e (Blake and C o lb u rn ,1982; Sundberg and Cooper,1982). I t i s not uncommon on such a c tiv e c o n tin e n ta l margins fo r submarine channels to c lo se ly approach the shore. For example, the South Branch of the La J o l l a Submarine Canyon comes to w ith in 60 m of the sea c l i f f s and many channels o ff Baja, C a lif o r n ia extend i n t o the s u rf zone (Shepard and D i l l , 1966). Considering the abundance of t e r r e s t r i a l p la n t m a t e r ia l, the w ell-rounded conglomerate c l a s t s , and the c o a rs e -g ra in e d t e x t u r e of these d e p o s its , i t appears plau s i b l e t h a t one or more of the Cretaceous submarine channels of the Holz Shale Member was r e c e iv in g sediment d i r e c t l y from t e r r e s t r i a l environments. The p aucity of d is p la c e d s h e l f a l faunas in th e Holz Shale s t r a t a su p p o rts t h i s h y p o th e sis . Submarine channel heads lo c a te d c lo s e r to the shelfedge would have cap tu red s e d i ments t h a t had a longer re sid e n c e time on th e c o n tin e n ta l ___________ WL s h e lf , and t h e r e f o r e , would have been more apt to contain abundant s h e l f a l faunas. The la c k of shallow water f o s s i l s in the f i n e - or c o a rs e -g ra in e d Holz s t r a t a su g g ests t h a t the sediment source might have been a f l u v i a l system feeding d i r e c t l y in to th e se submarine channels. The p o s tu la te d f l u v i a l sediment source would a lso help e x p la in the abun dance of t e r r e s t r i a l p la n t f o s s i l s t h a t dominate t h i s s t r a t i g r a p h i c sequence. An a l t e r n a t e e x p la n a tio n fo r t h i s paucity of s h e ll m a t e r ia ls i s t h a t d ia g e n e tic d i s s o l u t i o n destroyed f o s s i l s t h a t were once p re se n t, but t h i s seems h ighly u n lik e ly due to the presence of s c a t t e r e d , t h i n - s h e lle d , b iv alv e fragm ents such as Propeamussium. Unfortu n a te ly , t h i s h y p o th e sis i s v i r t u a l l y u n v e r i f i a b l e due to the d isc o n tin u o u s n a tu re of the outcrops, but the presence of a s s o c ia te d a l l u v i a l fan d e p o s its (Trabuco Formation) su g g e sts t h a t f l u v i a l d e p o s itio n was o c c u rrin g in the Santa Ana Mountains during Cretaceous time. Previous s tu d i e s of both modern and a n c ie n t slope depo s i t s have shown slumping to be an im portant d e p o s itio n a l p ro c e ss. Up to 50% of some slope sequences c o n s is t of mass t r a n s p o r t e d sedim ents in c lu d in g slumps and s l i d e s (Cook,1979). The r e c o g n itio n of slump d e p o s its can be very d i f f i c u l t in the rock reco rd as t e c t o n i c and penecontempora- neous deform ation d isp la y very s im ila r c h a r a c t e r i s t i c s ( H elw ig,1970), I d e n t i f i c a t i o n of slumped s t r a t a in the Holz 175 Shale Member was e s p e c i a l l y c h a lle n g in g due to the highly f a u l te d and fragmented n a tu re of the o u tcrops. Although s m a ll- s c a le slumping was observed in channel 2 and a lso w ith in many t u r b i d i t i c sands of the in te rc h a n n e l region, no l a r g e - s c a l e slump d e p o s its were recognized. This could be a r e s u l t of the d isc o n tin u o u s outcrop exposures in Black S ta r Canyon, which g r e a tly l i m i t the s iz e of slump d e p o s its t h a t can be i d e n t i f i e d in the f i e l d . This la c k of l a r g e - s c a l e slump d e p o s its might a lso i n d i c a t e t h a t th ese rocks r e p r e sent a slope paleoenvironment where major slump d e p o s its o r ig i n a t e d , but subsequently tr a v e le d f a r t h e r downslope before being d e p o site d . Another p erp lex in g q u e s tio n surrounding d e p o s itio n of th ese s t r a t a , i s what happened to the sediments t h a t were t r a n s p o r te d downslope w ith in th e se channels. In most examples of both modern and a n c ie n t submarine channels, debouching of sediments t r a n s p o r t e d downslope r e s u l t s in the development of submarine fa n s. P a le o c u rre n t s tu d i e s of the l a r g e s t Holz Shale c h a n n e l - f i l l d e p o s it, the Mustang-Spring Lens (Blake and Col burn, 1982), and an a ly se s performed in t h i s study, suggest a dominant w est-southw est t r a n s p o r t d i r e c t i o n . T herefore, development of a deep-marine fan f a c i e s would be expected somewhere to the west of Black S ta r Canyon. Based on s t r u c t u r a l tre n d s of th ese Cretaceous 176 s t r a t a (southw est d ip ), these h y p othesized d e p o s its should be lo c a te d in th e su b su rfa c e . However, s p a rs e ly lo c a te d w ell s i t e s in th e reg io n west of Black S ta r Canyon have provided no evidence t h a t such a complex e x i s t s (Schoelhamer e t a l . , 1.981). C onsidering th e a c t i v e t e c t o n i c f o rc e s t h a t have reshaped th e geologic provinces of southern C a lif o rn ia in p o st-C retaceo u s time, the p o s s i b i l i t y of l a t e r a l displacem ent of such a d e p o s it seems very f e a s i b l e , espe c i a l l y in l i g h t of very re c e n t t e c t o n i c i n t e r p r e t a t i o n s (Luyendyk e t a l ., 1 9 8 0 ; D ic k in s o n ,1983), Paleogeographic im p lic a tio n s of th ese id eas w i l l be h ig h l i g h t e d in the fo llo w in g c h a p te r. 177 Chapter XI PALEOGEOGRAPHY The Cretaceous s t r a t a examined in t h i s study are lo c a te d in th e n o rth e rn Santa Ana Mountains a t the n o r th e a s t end of the P en in su lar Ranges. S im ilar Upper Cretaceous sequences are p re se n t to the North in the Santa Monica Mountains and Simi H i l l s of the Transverse Ranges (see Figure 46). C ru sta l blocks of the P e n in su la r and Transverse Ranges c o n ta in numerous l a r g e - s c a l e f a u l t s and are s e p a ra te d by the Malibu Coast F a u lt, a l e f t - l a t e r a l s t r i k e s l i p f a u l t of Paleogene age (Luyendyk e t a l . , 1 9 8 0 ) . This area was te c to n - i c a l l y very a c tiv e in l a t e Cretaceous time, and p a l i n s p a s t i c r e c o n s t r u c t i o n s of these blocks show a complex h i s t o r y of l a t e r a l and r o t a t i o n a l movement (Couch,1979; D ic k in s o n ,1983)• A re c e n t t e c t o n i c model based upon remnant m agnetic data, su g g ests t h a t clockwise r o t a t i o n (70 to 80°) of c r u s t a l panels of the Transverse Ranges took place during middle to l a t e Miocene time (Luyendyk e t a l . , 1 9 8 0 , Figure 3 ) . These e a s t-w e s t c r u s t a l blocks are bounded by s i n i s t r a l f a u l t s anc were i n i t i a l l y o r ie n te d n e a rly n o rth -s o u th . S im ila r r o t a - 17*' Figure 46: Map showing p re se n t p o s it i o n s of Santa Ana Mountains, Santa Monica Mountains, and Simi H i l l s , and major f a u l t systems t h a t s e p a ra te the P e n in su la r and Transverse Ranges (modified from Carey and C o lb u rn ,1978). 179 1801 Transverse Ranges •••.+ Peninsular Ranges tio n a l displacem ents have been p o s tu la te d by Jones and I r v i n (1975), Kamerling and Luyendyk (1979), and Crouch (1979)* P a le o te c to n ic r e c o n s t r u c t i o n of t h i s area would in clu d e r o t a t i n g the Santa Monica Mountains and the Simi H i l l s back a g a in st the f la n k of the P e n in su la r Ranges ( D ic k in s o n ,1983). This r e c o n s t r u c t i o n places th e Cretaceous sequences of the Santa Monica Mountains and th e Simi H i l l s in c lo se proximity to the Santa Ana Mountains, and su g g ests a p o s s ib le a s s o c i a tion of d e p o s itio n a l systems. The Cretaceous s t r a t i graphic sequences of the Santa Monica Mountains and th e Santa Ana Mountains d isp la y s t r i k i n g s i m i l a r i t i e s . From a chronologic view point, the two s e c tio n s r e p r e s e n t s im ila r t i m e - s t r a t i g r a p h i c u n i t s . Both s e c tio n s in c lu d e basal a l l u v i a l fan d e p o s its of the Trabuco Formation t h a t a re o v e r la in by Turonian to Campanian narine s t r a t a ( C o lb u rn ,1973). The marine sequence in th e Santa Monica Mountains c o n s is ts of the Lower Chico Formation, an inner submarine fan d e p o sit, and th e Upper Chico Formation, a middle fan f a c i e s w ith p o s s ib le s h e l f a l sands near the base (Carey and C o lb u rn ,1978). F o ra m in ife ra l c o r r e l a t i o n s suggest t h a t the ,ower Chico Formation i s time e q u iv a le n t to the lower and p o ssib ly the middle Holz Shale s e c tio n s of the Santa Ana Mountains (Almgren,1973). 181 The Upper Cretaceous sequence in the Simi H i l l s i s l i m i t e d to exposures of the Chatsworth Formation (form erly the Chico Formation) t h a t are time c o r r e l a t i v e to th e Upper Chico Formation in th e Santa Monica Mountains (Almgen,1973). The d e p o s itio n a l base of t h i s s t r a t i graphic sequence i s not exposed in th e Simi H i l l s , but i t has been suggested t h a t s t r a t a as old as Turonian age might l i e beneath these Campanian beds (Colburn e t a l . , 1 9 8 1 a ) . The Chatsworth Formation i s i n t e r p r e t e d as middle to o uter submarine fan and minor slope d e p o s its ( L i n k , 1981; S quires e t a l .,1 9 8 1 ) which formed a la r g e submarine fan complex w ith the Upper Chico Formation (S q u ires e t a l . , 1 9 8 1 ) . Provenance s tu d i e s of conglomerate c l a s t s from the Trabuco Formation and th e Holz Shale Member in th e Santa Ana Mountains (Colburn and B l a k e ,1982) have shown t h a t the local basement complex of the P e n in su la r Ranges (Bedford Canyon Formation, Santiago Peak V olcanics, and Southern C a l i f o r n i a B a th o lith ) i s th e most l i k e l y source t e r r a i n fo r these d e p o s its . Provenance s tu d i e s of the Trabuco, Lower Chico, and Upper Chico Formations of the Santa Monica Mountains suggest the p o s s i b i l i t y of m u ltip le source t e r r a i n s , one of which might a lso be the basement complex of the Santa Ana Mountains (Carey and C o lb u rn ,1978; C o lb u rn ,1981). Simi l a r l y , a conglomerate c l a s t study of the Chatsworth Forma 182 tio n a lso suggests a source t e r r a i n in the P e n in su la r Ranges ( C o lb u rn ,1981; Colburn e t a l ., 1 9 8 1 b ) . P a le o c u rre n t i n d i c a t o r s in the Trabuco and Lower Chico Formation in th e Santa Monica Mountains are sc a rc e , but are abundant in th e Upper Chico Formation where they d isp la y an u n ro ta te d n o r th e r ly t r a n s p o r t d i r e c t i o n (Carey and C o lb u rn ,1978). P a le o c u rre n t a n a ly se s of the Chatsworth Formation suggest a dominant n o rth -n o rth w e st t r a n s p o r t d i r e c t i o n fo r th ese deep-marine s t r a t a (S q u ires e t a l . , 1 9 8 1 ) . C o rrectio n fo r 80° of Miocene clockwise r o t a t i o n r e s u l t s in a general w est-so u th w est p a le o c u rre n t d i r e c t i o n for both Cretaceous sequences, matching th e dominant t r a n s p o rt d i r e c t i o n of the major Holz Shale submarine channel d e p o s its (Blake and C o lb u rn ,1982; Sundberg and Cooper,1982; t h i s s t u d y ) . P a le o te c to n ic r e c o n s t r u c t i o n s of the T ransverse Ranges su g g ests t h a t Upper Cretaceous d e p o s itio n a l b a sin s in the Santa Monica Mountains could have been d i r e c t l y a d ja c e n t to those of the Santa Ana Mountains (Luyendyk,198 3, pers.comm.). Provenance s tu d i e s of conglomerate c l a s t com positions and p a le o c u rre n t a n a ly s e s t e n t a t i v e l y imply t h a t sediment t r a n s p o r t d i r e c t i o n s and source t e r r a i n s were s im ila r for the Holz Shale Member and th e Lower Chico Formation. Based on t h i s geologic evidence, i t i s p o s tu la te d here t h a t the Lower Chico Formation in th e Santa Monica Mountains r e p re - 183 se n ts the mid and lower submarine fan d e p o s its c r e a te d by the debouching of sediment from Holz Shale submarine chan n els. Cretaceous s t r a t a of s im ila r age in th e Simi H i l l s are not exposed, but may be p re se n t subsurface beneath the Chatsworth Formation. I f the Chatsworth Formation r e p r e s e n ts a more d i s t a l submarine fan d e p o s itio n a l environment than th e Upper Chico Formation, as suggested by f a c i e s analyses ( C o lb u rn ,1981), than Coniacian to Santonian depo s i t s of middle to o u ter fan f a c i e s might a ls o be lo c a te d beneath the Chatsworth sequence. Geologic evidence which com plicates th e c o r r e l a t i o n of the Holz Shale Member and the Lower Chico Formation in c lu d e s the d i f f e r e n t l i t h o l o g i c c h a r a c te r of v o lc a n ic conglomerate c l a s t s in th e two sequences ( C o lb u rn ,1983,pers,comm.), and t e n t a t i v e , m icroscopic p a le o c u r re n t i n d i c a t o r s ( t u r b i d i t e g rain f a b r i c s ) t h a t suggest a c o r re c te d e a s t e r l y t r a n s p o r t d i r e c t i o n fo r Lower Chico s t r a t a (Carey and C o lb u rn ,1978). However, th ese anamolous p a le o c u r re n ts do not r e f u t e the proposed c o r r e l a t i o n s as p a le o c u r re n t p a t t e r n s of the Lower Chico Formation appear very v a r i a b l e ; d iv e rg e n t and conver gent p a t t e r n s w ith south, west, and northw est t r a n s p o r t d i r e c t i o n have been re p o rte d ( C o lb u rn ,1973; Carey and C o lb u rn ,1978). N e v e rth e le ss, th ese anamolous f i e l d r e l a t i o n s h ip s must be re so lv e d i f the h y p o th e tic a l c o r r e l a t i o n s p re se n te d in t h i s paper are to be s u b s t a n t i a t e d . Chapter XII CONCLUSIONS The f i e l d and la b o r a to ry an a ly se s performed fo r t h i s study s tro n g ly support the paleoenvironm ental i n t e r p r e t a t i o r of slope d e p o s itio n for the Holz Shale Member. C h a n n e l- f ill d e p o s its , pebbly mudstones, s m a ll- s c a le slump d e p o s its , and numerous sediment g ra v ity flow d e p o s its are key i n d i c a t o r s of slope and upper fan d e p o s itio n . The presence of numerous submarine channels and small g u l l i e s t h a t d i s s e c t contempo rary f in e - g r a i n e d sedim ents su g g ests a m id-slope or upper fan paleoenvironm ent. A g r e a t deal of the con tro v ersy surrounding previous paleoenvironm ental i n t e r p r e t a t i o n s of the Holz Shale Member was the r e s u l t of narrowly focused geologic s tu d i e s . In completing a comprehensive a n a l y s is of the sedim entology, ichnology, and paleontology of outcrops in Black S ta r Canyon, the author hopes to have reso lv ed most of t h i s c o n te n tio n . The paleogeographic c o r r e l a t i o n s proposed in t h i s paper r e q u ir e a d d i t i o n a l re se a rc h to be s u b s t a n t i a t e d . 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Appendix A STRATIGRAPHIC SECTIONS S t r a t i g r a p h i c columns of Holz Shale Member outcrops along Black S ta r Canyon Road, Black S ta r Canyon, Santa Ana Moun t a i n s , southern C a l i f o r n i a . 207 KEY ? v .v r • • * SHALE SILTSTONE PEBBLY MUDSTONE VERY FINE- TO FINE-GRAINED SANDSTONE V » MEDIUM- TO VERY COARSE-GRAINED SANDSTONE ; ,V PEBBLE CONGLOMERATE j i # * I t n 1 COBBLE CONGLOMERATE Z Z 'i AMMALGAMATED BED o O O C CARBONATE CONCRETION CONCRETIONARY BED 208 VERTICAL »S C AL E , 2 6 0 “ m = microfossil sample t = thin-section sample B S-2 = stake location O u t c r o p o f h i g h l y - f r a g n e u t e d , i a - t e r b e d d e d s i l t y s h a l e s and f i n e g r a i n e d s a n d s t o n e s d i s p l a y i n g a c o a r - s e n i n g - u p w a r d s s e q u e n c e . S a n d s t o n e b e d s c o s p r i s e 2 0 - 2 5 S o f l o w e r t h i r d o f o u t c r o p and i n c r e a s e i n f r e g a e n c y up- s e c t i o n w h ere e x p o s u r e i s p r e d o m i n a n t l y ( 9 0 - 9 5 S ) t h i n n l y - b e d d e d s a n d s t o n e s . U p p e rm o st 2 a o f o u t c r o p sh o w s i n - ., c r e a s e d o c c u r e n c e o f s h a l e s t r a t a , b a t s a n d s t o n e s s t i l l d o a i n a n t (> 6 0 % ). S a n d s t o n e s t r a t a r a n g e f r o a f i n e - t o c o a r s e - g r a i n e d i n c l u d i n g r a r e (<5 c s - t i i c k ) p e b b l y s a n d s t o n e s n e a r t o p , h a r e t h i c k n e s s ravage o f 0 . 5 - 1 0 ca ( a v g . 1 . 5 c a ) , d i s p l a y s h a r p p l a n a r c o n t a c t s , p l a n a r - l a z i n a t i o n s a c c e n t u a t e d by a i c a - g r a i n c o n c e n t r a t i o n s , and a b u n d a n t o r g a n i c f r a g m e n t s t h a t l o c a l l y d i s p l a y p a r a l l e l o r i e n t a t i o n i n a 52-SB d i r e c t i o n . . S l a b b e d s e c t i o n s o f s a n d s t o n e s d i s p l a y Bouaa T a - b - a , c - d , and b - c s e q u e n c e s , a a s s i v e b e d d i n g , g r a d e d b e d d i n g , c n t - a n d - f i l i s t r u c t u r e s , a b u n d a n t r i p u p c l a s t s , and l o c a l l y a b u n d a n t O ph loB orn'ca and T h a l a s - s . i s o i c e s b u rr o w s d i s p l a y i n g a e a i s c u s b a c k f i l l i n g . S a n d s t o n e s t r a t a h a v e f r e s h c o l o r o f p a l e y e l l o w i s h brown (10 IB 6 / 2 ) and w e a t h e r e d c o l o r o f 209 2 5 0 “) - r S > - 125 * p a l e brown (5 IS 5 / 2 ) . S h a l e s t r a t a v e r y f r a g m e n t e d , c o n t a i n t h i n ( < 0 . 5 cm) f i n e - g r a i n e d s a n d s t r i n g e r s , l o c a l l y a b u n d a n t o r g a n i c f r a g o e n t s com m only a s s o c i a t e d w i t h c a r b o n a t e c o n c r e t i o n s , and d i s p l a y c o m p l e t e r a n g e o f c o n c r e t i o n f o r m a t i o n fr o m r n d a B e n - t a r y c o n c r e t i o n s t h r o u g h l a t e r a l l y c o n t i n u o u s c o n c r e t i o n a r y b e d s * B u d a - a e n t a r y c o n c r e t i o n s p r e d o m i n a n t i n l o w e r h a l f o f o u t c r o p and f u l l y - c e m e n ted c o n c r e t i o n s and c o n c r e t i o n a r y b e d s i n u p p e r h a l f . C o n c r e t i o n a r y b e d s c o n t a i n b e d d i n g p l a n e s o f o r g a n i c —f r a g m e n t c o n c e n t r a t i o n s t h a t f o r a p l a a e s o f w e a k n e s s i n s t r a t a . S l a b b e d c o n c r e t i o n s d i s p l a y l a m i n a e o f s i l t and f i n e - g r a i n e d s a n d l o c a l l y d i s r u p t e d by C h o n d r i t e s b u r r o w s . T h in l e n s o r s t r i n g e r s (<1 c a - t h i c f c ) o f f i n e — t o a e d i u a - g r a i n e d s a n d d i s p l a y c i o s s - i a - a i n a t i o n s and c u t - a n d - f i i l s t r u c t u r e s . C o n c r e t i o n s a l s o c o n t a i n s m a l l f l a m e s t r u c t u r e s and l o c a l i z e d s o f t - s e d i a e n t d e f o r m a t i o n o f p l a n a r - l a m i n a t i o n s . S h a l e s t r a t a d i s p l a y f r e s h and w e a t h e r e d c o l o r o f p a l e brown (5 IB 5 / 2 ) . 210 =s= 2 20 - 215-- D o a i n a n t l y s h a l e o a t c r o p v i t h a b u n d a n t c a r b o n a t e c o n c r e t i o n s a n d s c a t t e r e d v e r y f i n e - t o a e d i n n - g r a i n e d s a n d s t o n e b e d s . S a n d s t o n e b e d s r a n g e i n t h i c k n e s s f r o n 1 - 5 cm , c o n t a i n l o c a l l y a b u n d a n t p l a n t a nd wood f r a g - a e n t s , e x h i b i t s h a r p u p p e r a n d l o w e r c o n t a c t s , a nd h a r e f r e s h c o l o r o f p a l e y e l l o w i s h brow n {10 IB 6 / 2 ) a nd w e a t h e r e d c o l o r o f s o d e r a t e b row n (5 IB 3 4 ) • S l a b b e d s e c t i o n s sh o w s a s s i v e b e d d i n g w i t h h i g h c o n c e n t r a t i o n s o f a i c a g r a i n s and l o c a l l y a b n n d a a t C h on d r i t e s t r a c e s . S h a l e s a r e h i g h l y - f r a g a e n t e d and d i s p l a y f r e s h a n d w e a t h e r e d c o l o r o f d a r k y e l l o w i s h brown {10 TB 4 / 2 ) - S l a b b e d c o n c r e t i o n s sh o w a d o a i n a n t l y b i o t u r b a t e d t e x t u r e w i t h C h o n d r i t e s . F l a n o l i t i e s , and Z o o p h y c o s t r a c e s p r e s o r t e d . Con c r e t i o n s c o n t a i n a b u n d a n t o r g a n i c f r a g a e n t s , b o t h I n o c e r a a u s f r a g a e n t s and e n t i r e w a i v e s o r i e n t e d p a r a l l e l t o b e d d i n g , c a l c i t e - f i l i e d s e p t a r i a n c r a c k s (<5X w o l u a e ) , an d p a r t i a l l y - p y - r i t i z e d p l a n t f r a g m e n t s . 211 210- 2 0 5 ' 212 936473^633609963539050 200* ! 9 5-- 1901 I n t e r b e d d e d s h a l e s and t h i n , f i n e g r a i n e d s a n d s t o n e b e d s . l a t e r a l l y c o n t i n u o u s s a n d s t o n e b e d s r a n g e i n t h i c k f r o n 1 - 5 c i , p i n c h and s w e l l l a t e r a l l y , d i s p l a y s h a r p b a s a l c o n t a c t s l a c k i n g a n y s o l e n a r k s , s h a r p u p p e r c o n t a c t s , an d c o n t a i n l o c a l l y a b u n d a n t p l a n t and I n o c e r a n u s f r a g n e n t s . . . S a n d s t o n e s d i s p l a y f r e s h c o l o r o f p a l e brow n {5 I S 5 / 2 ) a n d w e a t h e r e d c o l o r o f g r a y i s h r e d <10 H U /2 ) . S l a b b e d s a n d s t o n e s e x h i b i t l o c a l l y a b u n d a n t C h o n d r i t e s , B o u a a T d - e s e q u e n c e s , p l a n a r - l a a i n a t i o n s a c c e n t u a t e d by o r i e n t e d a i c a - g r a i n c o n c e n t r a t i o n s , c e n t r a l l y - c o n c e n t r a t e d r i p u p c l a s t s , a nd p e n e c o n t e B p o r a n e o u s s l u a p - p r o d n c e a r e c u a b e n f o l d s . S h a l e s t r a t a a r e h i g h l y w e a t h e r e d , c o n t a i n s p a r s e c a r b o n a t e c o n c r e t i o n s , a nd h a v e f r e s h and w e a t h e r e d c o l o r o f p a l e b row n (5 IB 5 / 2 ) . . S l a b b e d c o n c r e t i o n s d i s p l a y c u t - a n d - f i l l s t r u c t u r e s i n c l a y and s i l t - s i z e d s e d i a e n t s , a i n o r s o f t - s e d i - a e n t d e f o r m a t i o n , a nd a b u n d a n t C h o n d r i t e s t r a c e s * 213 185 ‘ .O* V S ^ o x o T ^ .< ^ C ? .< 3 * . O ’ o : o . p * o.-^vj) . 0 . 0 , 0 0 -W P e b b l y m u d s t o n e z o n e o v e r l i e s c h a n n e l d e p o s i t c o n f o r m a b l y a n d c o n t a i n s s c a t t e r e d t h i n ( 1 - 3 c a - t h i c k ) , d i s c o n t i n u o u s f i n e - t o m e d i u m - g r a in e d s a n d s t o n e l a m i n a e - . P e b b l e s a n d o c c a s i o n a l c o b b l e s a r e l i t h o l o g i c a l l y i d e n t i c a l t o l o w e r c o n g l o a e r a t e c l a s t s a n d o c c u r i n c o n c e n t r a t e d z o n e s s u b p a r a l l e l t o b e d d i n g and a l s o s c a t t e r e d i n d i v i d u a l l y t h r o u g h o u t z o n e - f lu d s t o n e i s h i g h l y - f r a g m e n t e d , c o n s i s t s o f s a n d y s i l t - s i z e d s e d i a e n t s , l a c k s w e l l - d e v e l o p e d b e d d i n g , c o n t a i n s r a r e c a r b o n a t e c o n c r e t i o n s t h a t e x h i b i t p e n e c o n - t e a p e r a n e o u s s l u m p i n g , an d d i s p l a y s f r e s h a n d w e a t h e r e d c o l o r o f d a r k y e l l o w i s h b r o (1 0 12 ft/2 ) - 180 I n t e r b e d d e d l e n t i c u l a r , m e d iu m - t o v e r y c o a r s e - g r a i n e d and p e b b l y s a n d s t o n e s , t h i n d i s c o n t i n u o u s s a n d y —s i l t - s t o n e s t r a t a , and u p p e r m o s t c o b b l e - c o n g l o m e r a t e b e d s - S a n d s t o n e s t r a t a d o m i n a t e o u t c r o p (SOS) a n d r a n g e i n t h i c k n e s s fr o m 1 - 1 1 0 cm { a v g . 20 c m ) . S a n d s t o n e s a r e com m on ly a a a a l g a a a t e d , e x h i b i t a a s s i v e b e d d i n g , g r a d e d b e d d i n g , i r r e g u l a r l o a d an d f l u t e c a s t s , a b u n d a n t r i p u p c l a s t s , s c o u r e d b a s a l c o n t a c t s and s h a r p u p p e r c o n t a c t s , a b u n d a n t Qp h i o a o r p h a t r a c e s , f r e s h c o l o r o f l i g h t brow n (5 IB 5 / 6 ) , and w e a t h e r e d c o l o r o f g r a y i s h o r a n g e {10 IB 7 / « ) . F i n e - g r a i n e d i n t e r b e d s o f s a n d y - s i l t s t o n e a n d f i n e - g r a i n e d s a n d s t o n e c o n t a i n l a m in a e o f c o n c e n t r a t e d o r g a n i c f r a g m e n t s a n d d i s p l a y f i n e - s c a l e p l a n a r - l a m i n a t i o n s 2 - 3 m a - t h i c k . P e b b l y s a n d s t o n e b e d s p r e d o m i n a n t l y d i s o r g a n i z e d b u t l o c a l l y d i s p l a y c r u d e g r a d i n g . C o a r s e - g r a i n e d o u t c r o p c a p ped by d i s o r g a n i z e d p e b b l e - c o b b l e - b o l d e r c o n g l o a e r a t e b e d s c o n t a i n i n g c l a s t - s u p p o r t e d , a n g u l a r t o s u b r o u n d e d 214 175 170 COVERED • % • * * • \ >*.,. <=>..<=> j i g n e o n s c l a s t s i n a v e r y c o a r s e - g r a i n e d s a n d m a t r i x . . C o n g lo m e r a t e b e d s l o c a l l y c h a n n e l i z e d and c u t i n t o l o s e r s a n d s t o n e s t r a t a , c o n t a i n n u m e r o u s r i p n p c l a s t s , a n d c o n t a i n v e r y c o a r s e - g r a i n e d s a n d b e d s ( 6 - 1 3 c a - t h i c k ) • P o o r l y e x p o s e d o u t c r o p o f v e r y f r a g m e n t e d a n d w e a t h e r e d s h a l e s t r a t a c o n t a i n i n g t h i n (<h b b ) , d i s c o n t i n u o u s f i n e - g r a i n e d s a n d s t r i n g e r s . l a t e r - b e d d e d w i t h s h a l e s i s o n e 2 8 - 6 1 c a - t h i c k , v e r y c o a r s e - t o a e d i a s s - g r a i n e d , g r a d e d s a n d s t o n e s t r a t n s d i s p l a y i n g B ouaa T a - b s e q u e n c e * O u t c r o p o f l e n t i c u l a r , a e d i u a - t o v e r y c o a r s e - g r a i n e d and p e b b l y s a n d s t o n e s t r a t a i n t e r c a l a t e d w i t h d i s c o n t i n u o u s s h a l e and s a n d y - s i l t s t o n e b e d s * S a n d s t o n e b e d s h a v e t h i c k n e s s r a n g e o f 2 - 8 2 c a , a r e c o a s o n l y a a a a l- g a a a t e d , d i s p l a y m a s s i v e b e d d i n g , r a r e r e v e r s e g r a d i n g , a b u n d a n t r i p u p c l a s t s , s c o u r e d b a s a l c o n t a c t s and s h a r p u p p e r c o n t a c t s . I r r e g u l a r l o b a t e l o a d c a s t s , p o o r l y - d e v e l o p e d f l u t e c a s t s , a b u n d a n t B ou n a T a - b s e q u e n c e s , f r e s h c o l o r o f v e r y p a l e o r a n g e (1 0 IB 8 / 2 ) a nd w e a t h e r e d c o l o r o f g r a y i s h 215 o r a n g e (1 0 IB 7 / 4 ) . P e b b l y s a n d s t o n e s p r e d o a i n a n t l y d i s o r g a n i z e d w i t h l o c a l i z e d SB i a b r i c a t i o a p r e s e n t . O c c a s i o n a l X n o c e r a a u s f r a g w e n t s a nd a b u n - d a n t Q p h io n o r p h a n e t w o r k t r a c e s f o u n d i n s a n d s t o n e s . D i s c o n t i n u o u s s a a d y - s i l t s t o n e a n d s h a l e b e d s s e p a r a t e s a n d s t o n e s t r a t a a n d a r e c o a n o n l y s c o u r e d b y o v e r l y i n g s t r a t a . T h e s e f i n e r - g r a i n e d b e d s r a n g e i n t h i c k n e s s f r o a 2 t a t o 2 0 c a {1 c > a v g . ) , c o n t a i n l a n i n a e o f ' c o n c e n t r a t e d o r g a n i c f r a g m e n t s , h a v e fe w s n a i l (< 1 5 c a l o n g ) c o n c r e t i o n s l o c a t e d o n l y i n t h i c k e r s h a l e s t r a t a , d i s p l a y f r e s h c o l o r o f o l i v e g r a y (5 IB 4 / 1 ) a nd w e a t h e r e d c o l o r o f p a l e y e l l o w i s h brow n (10 I B 6 / 2 ) . . COVERED ^ 165 216 155- f p s p s $ m s t & 150' s • V . * * J * * s « d « < i • m • • * \ I:,;.:.; / .V7773 C o a r s e - g r a i n e d , l a t e r a l l y d i s c o n t i n u o u s o a t c r o p c o a p r i s e d o f f i n e - t o v e r y c o a r s e - g r a i n e d s a n d s t o n e s t r a t a , t h i n s h a l e i n t e r b e d s , a n d s p a r s e c o n - g l o n e r a t e s t r a t a . S a n d s t o n e b e d s d o - ■ i n a n t l y c o a r s e - t o T e r y c o a r s e g r a i n e d w i t h s h a r p a p p e r a n d l o v e r c o n t a c t s , i r r e g n l a r b a s a l c o n t a c t s w i t h p o o r l y - d e v e l o p e d l o a d c a s t s , and a b u n d a n t r i p u p c l a s t s . S a n d s t o n e s t r a t a r a n g e i n t h i c k n e s s f r o a 7 ^ 8 1 c b , sh o w l a t e r a l p i n c h i n g a nd s w e l l i n g , d i s p l a y d o a i n a n t B o a a n a T a— b s e q u e n c e s , g r a d e d b e d d i n g , a b u n - d a n t p l a n a r - l a a i n a t i o n s a c c e n t u a t e d by n i c a g r a i n c o n c e n t r a t i o n s , o c c a s i o n a l a a a a l g a a a t i o n o f b e d s , a b u n d a n t o r g a n i c f r a g a e n t s a nd o c c a s i o n a l I n o c e r a a u s f r a g a e n t s , a o d e r a t a t o p o o r s o r t i n g , a n d a b u n d a n t T h a l a s s i n o i d e s a nd O p h io - a o r p h a t r a c e s o n b e d d i n g p l a n e s o f t h i c k e r s t r a t a . S a n d s t o n e b e d s h a v e f r e s h c o l o r o f l i g h t b ro w n (5 IB 5 / 6 ) a nd w e a t h e r e d c o l o r o f v e r y p a l e o r a n g e (1 0 I S 3 / 2 ) . A t 153 a 1-5 d i s o r g a n i z e d , c l a s t - s u p p o r t e d , p e b b l e - c o b - b l e - c c n g l o a e r a t e b e d w i t h c o a r s e - g r a i n e d s a n d e a t r i x a nd s u b - r o u n d e d t o s u b a n g u l a r i g n e o u s c l a s t s ( 1 - 1 5 c a d i a a e t e r ) . . C o n g l o a e r a t e b e d s h o w s s c o u r e d b a s a l c o n t a c t w i t h i n j e c t i o n o f c l a s t s i n t o u n d e r l y i n g s a n d s t o n e b e d . At 1 5 4 - 1 5 8 b is a p a c k a g e o f s l u e p e d a n d c o n t o r t e d c o a r s e - t o v e r y c o a r s e - g r a i n e d s a n d s t o n e a n d i n t e r b e d d e d s h a l e s t r a t a l i t h o l o g i c a l - l y s i a i l a x t o u n d e r l y i n g s t r a t a . Up p e r m o s t c o n g l o a e r a t e d e p o s i t (1 5 8 a) i s a l e n t i c u l a r , d i s o r g a n i z e d p e b b l e - c o b b l e - b o l d e r - c o n g l o a e r a t e w i t h ma t r i x - s u p p o r t e d , r o u n d e d t o s u b r o u n d e d i g n e o u s c l a s t s ( 1 - 7 4 c * d i a s e t e r ) and a s c o u r e d b a s a l c o n t a c t . ft % • • _ * / | *#•*[ j * a » • * * » » »\ j 217 145-r % • \ i « • • i • • • • t < » % i» * v • • • • • • % t * • % ♦ 4 • • t • » m . • t t < , * t • * # • * • 15 m COVERED /x ,/x ,/5sAN 1 2 5 COVERED H a l t e d e x p o s u r e o f f r a g a e u t e d s i l t y s h a l e s and tw o f i n e - g r a i n e d s a n d s t o n e b e d s , l a r g e s a n d s t o n e b e d p i n c h e s a n d s w e l l s a l o n g s t r i k e and h a s t h i c k n e s s r a n g e o f 1 5 - 2 8 c a . l e a t h e r e d s u r f a c e o f b e d d i s p l a y s f a i n t s l u a p s t r u c t u r e s / b u t s l a b b e d s e c t i o n s sh o w ^ w e l l - d e v e l o p e d pen-econ- t e a p o r a a e o a s s l u e p i n g , a s n a l g a a a t i o n o f d e p o s i t i o n a l u n i t s , r i p u p c l a s t s , a i n o r l o a d c a s t s , a n d B o u a a T a - b - c s e g u e n c e s w i t h d i s h i n g r i p p l e s . R i - n o r s a n d s t o n e s t r a t u m i s 4 c a - t h i c k , l a t e r a l l y c o n t i n u o u s , and d i s p l a y s p l a n a r - l a a i n a t i o n s . B o th s a n d s t o n e b e d s h a v e s h a r p a p p e r a n d l o w e r c o n t a c t s a nd h a v e f r e s h c o l o r o f l i g h t brow n (5 IB 6 / 1 ) and w e a t h e r e d c o l o r o f a o d e r a t e y e l l o w i s h brow n (1 0 IB 5 / U ) . Bo c o n c r e t i o n s v i s i b l e i a o u t c r o p . I n t e r c a l a t e d s i l t y s h a - le s and c o a r s e - t o v e r y c o a r s e - g r a i n e d s a n d s t o n e b e d s t h a t r a n g e i n t h i c k n e s s fr o m 1 2 - 2 8 c a (18 c a a v g . ) , p i n c h a nd s w e l l a l o n g s t r i k e , and p i n c h o u t i n o p p o s i t e d i r e c t i o n s . S a n d s t o n e s d i s p l a y s h a r p u p p e r and l o w e r c o n t a c t s , c u t - a n d - f i l l s t r u c t u r e s , p o o r l y - d e v e l o p e d f l u t e a n d g r o o v e c a s t s , p l a n a r - 218 120 • • • • • • • A % ♦ * •.•J 3 COVERED I! 5 - COVERED l a a i n a t i o a s a c c e n t a a t e d by a i c a g r a i n s , r i p u p c l a s t s , o c c a s i o n a l l o a d c a s t s , f r e s h c o l o r o f l i g h t b row n (5 IB 5 / 6 ) , w e a t h e r e d c o l o r o f a o d e r a t e y e l l o w i s h brow n (TO IB 5 / h ) . T h i n (<5 c a - t h i c k ) , f i n e - g r a i n e d s a n d s t o n e b e d s s h o v i n g p l a n a r - l a a i n a t i o n s a c c e n t a a t e d by a i c a g r a i n s , a r e v e r y s p a r s e l y d i s t r i b u t e d i n a p p e r h a l f o f o u t c r o p ( 1 - 2 b e d s / 2 a o u t c r o p ) . S h a l e s a r e h i g h l y w e a t h e r e d a nd f r a g m e n t e d , d i s p l a y o n l y r u d i m e n t a r y c o n c r e t i o n s i n l o w e r h a l f o f o u t c r o p a nd r e r y s p a r s e f u l l y - d e v e l o p e d c o n c r e t i o n s i n u p p e r h a l f , h a r e f r e s h c o l o r o f d u sk y brow n (5 IB 2 / 2 ) , a n d w e a t h e r e d c o l o r o f p a l e brow n (5 IB 5 / 2 ) , . S l a b b e d s e c t i o n s o f s a n d s t o n e s e x h i b i t e d B o u a a T a - b a n d d— e s e q u e n c e s , g r a d e d b e d s e n t i r e l y p l a n a r - l a n i n a t e d w i t h c o n c e n t r a t i o n s o f o r i e n t e d a i c a g r a i n s s e p a r a t i n g l a - a i n a e , m a s s i v e b e d d i n g w i t h r i p u p c o n c e n t r a t i o n s i n b o t h c e n t r a l and t o p r e g i o n s o f b e d s , o n e a a u a l g a a a t e d b e d , l o a d c a s t s , f l a n e s t r u c t u r e s , a n d l o c a l i z e d a b u n d a n c e o f T h a l a s s i n o i d e s t r a c e s . S l a b b e d c o n c r e t i o n s a a p l e s d i s p l a y p h y s i c a l l y d o a i n a t e d t e x t u r e s w i t h a l e r n a t i n g s i l t and f i n e - t o a e d - i u a - g r a i n e d s a n d l a a i n a e ( 1 - 3 s e - t h i c k ) » P l a n t f r a g a e n t s , a b u n d a n t i n a l l s a a p l e s , show p a r a l l e l o r i e n t a t i o n t o b e d d i n g and d i s p l a y p a r t i a l p y r i t i - z a t i o n . l o c a l l y a b u n d a n t C h o n d r i t e s an d B l a n o l i t i e s t r a c e s a nd a i c r o f l a a e s t r u c t u r e s (<5 i b ) d i s r u p t l a a i n a e o v e r s a a l l a r e a s . P o o r l y e x p o s e d o u t c r o p d c a i n a t e d by 1 . 5 a - t h i c k , _6.5 * - w i d e , v e r y c o a r s e - t o a e d i u a - g r a i n e d l e n t i c u l a r s a n d s t o n e . l a a a l g a s a t i o n e v i d e n c e d by tw o d i s c o n t i n u o u s , 0 . 5 - 1 c a - t h i c k s i l t b e d s t h a t s e p a r a t e t h r e e s a n d d e p o s i t i o n a l u n i t s . S a n d s t o n e i s p o o r l y s o r t e d , d i s p l a y s s a s s i v e and g r a d e d b e d d i n g , s h a r p u n d u l a t i n g l o w e r __________ 212. 110- 15 m COVERED 90- c o n t a c t l a c k i n g any s e l l d e v e l o p e d s o l e n a r k s , a nd a b r u p t u p p e r c o n t a c t . 16 c a - t h i c k , c o a r s e — t o n e d i u m - g r a i n e d s a n d s t o n e a s s o c i a t e d w i t h l e n t i c u l a r s a n d s t o n e and p i n c h e s o u t a w ay f r o a a x i s . S u r r o u n d i n g l e n t i c u l a r s a n d s t o n e a r e h i g h l y - f r a g a e n t e d , g r i t t y ( c o a r s e - s i l t ) s h a l e s t h a t a p p e a r t o b e c u t b y s a n d s t o n e b e d . I t b a s e o f o u t c r o p h a v e d i s c o n t i n u o u s e x p o s u r e o f t h r e e a e d i u a - t o c o a r s e - g r a i n e d , 5 - 1 2 c a - t h i c k s a n d s t o n e b e d s . S e a t h e r e d s u r f a c e s o f t h e s e s a n d s t o n e s d i s p l a y no p r i a a r y s t r u c t u r e s , b u t s l a b b e d s u r f a c e s s h o w e d B o u a a T a - b s e q u e n c e s w i t h o r i e n t e d a i c a g r a i n s a c c e n t u a t i n g p l a n a r - l a a i n a t i o n s . i l l s a n d s t o n e s t r a t a h a v e f r e s h a n d w e a t h e r e d c o l o r o f g r a y i s h o r a n g e (1 0 IB 7 / 4 } . O u t c r o p d i s p l a y s a a r k e d i n c r e a s e i n a v e r a g e g r a i n s i z e f r o a l o w e r o u t c r o p s a s e n t i r e e x p o s u r e c o n s i s t s o f s a n d s t o n e s t r a t a t h a t r a n g e f r o a s i l t y , v e r y f i n e - g r a i n e d t o v e r y c o a r s e g r a i n e d s e d i a e a t s . B e d s r a n g e i n t h i c k n e s s f r o a 1 - 1 7 c a ( a v g . 2 c a ) and c o n m G n ly p i n c h a n d s w e l l a l o n g s t r i k e . F i n e - t o v e r y f i n e - g r a i n e d s a n d s d o a i - n a t e o u t c r o p a l t h o u g h m e d i n e - g r a i n e d , 1 - 6 a a - t h i c k , l e n t i c u l a r s a n d s t r i n g e r s f o u n d t h r o u g h o u t e x p o s u r e . F i n e g r a i n e d s a a d s d i s p l a y s h a r p u p p e r and l o w e r c o n t a c t s , c u t - a n d - f i i l s t r u c t u r e s , f a i n t p l a n a r s a a l l - s c a l e c r o s s - l a a i n a t i o n s , r a r e r i p p l e a a r k s , r i p u p c l a s t s , and a b u n d a n t wood and p l a n t f r a g a e n t s t h a t o c c u r a s b o t h c o n c e n t r a t e d o r g a n i c — r i c h l a n i n a e and d i s p e r s e d f r a g a e n t s w i t h i n s a n d s t o n e b e d s . F i n e - g r a i n e d s a n d s h a v e f r e s h c o l o r r a n g e o f d a r k y e l l o w i s h brow n (10 IB 4 / 2 ) t o b r o w n is h g r a y (5 IB 4 / 1 ) and w e a t h e r e d c o l o r r a n g e o f l i g h t brow n (5 IB 5 / 6 ) t o p a l e y e l l o w i s h b r o w n (10 IB 6 / 2 ) . T h i c k e r b e d s ( 1 0 - 1 7 c a ) a r e c o a r s e - t o v e r y c o a r s e - g r a i n e d , d i s p l a y g r a d e d b e d d i n g , l o a d c a s t s , f l a a e s t r u c t u r e s , T a - b s e q u e n c e s , s c a t t e r e d ' t r a c e f o s s i l s (T h a l a s s i n o i d e s ? ) , c u t - a n d - f i l l s t r u c 220 4283 ^ ) BS-25 — s ~ 8 0 - t u r e s , r i p a p c l a s t s , f r e s h c o l o r o f l i g h t o l i v e g r a y (S I 6 / 1 ) , a n d w e a t h e r e d c o l o r o f p a l e r e d (1 0 H 6 / 2 ) . S l a b b e d s e c t i o n s o f s a n d s t o n e s r e v e a l B o u a a T a - b - c - d - a , b - c - d , a nd a - b - c s e q u e n c e s i n f i n e - t o a e d i u a - g r a i n e d , a o d e r a t e l y - s o r t e d s a n d s . C o a r s e - t o v e r y c o a r s e - g r a i n e d s a n d s e x h i b i t a a s - s i v e b e d d i n g w i t h c o n c e n t r a t i o n s o f r i p u p c l a s t s i n u p p e r 2 c a o f s t r a t a . C o n c r e t i o n s v e r y r a r e i n t h e s e c o a r s e r s e d i a e n t s b u t fe w s l a b b e d s a a p l e s d i s p l a y e d v e i l d e v e l o p e d l a a i n a t i o n s 0 . 5 - 4 c a - t h i c k o f c o a r s e s i l t a n d f i n e - g r a i n e d s a n d , s h a r p u p p e r and l o w e r c o n t a c t s , s n a l l - s c a l e p l a n a r c r o s s - l a a i n a t i o n s , a nd s c a t t e r e d C h o n d r i t e s b u r r o w s i n s i l t l a a i n a e . I n t e r c a l a t e d s h a l e , s a n d s t o n e , a nd c o n c r e t i o n a r y s t r a t a . F i n e - t o c o a r s e - g r a i n e d s a n d s t o n e b e d s s p a r s e l y d i s t r i b u t e d i n o u t c r o p ( 1 - 2 / 2 a o u t c r o p ) sh o w r a p i d l a t e r a l t h i c k n e s s c h a n g e s a l o n g s t r i k e . S a n d s t o n e b e d s r a n g e i n t h i c k n e s s f r o a 1 - 1 2 c a ( a v g . 2 c a ) , h a v e s h a r p a n d i r r e g u l a r b a s a l c o n t a t s , b o t h g r a d a t i o n a l a n d s h a r p u p p e r c o n t a c t s , d i s p l a y r a r e f l u t e c a s t s , a nd h a v e f r e s h c o l o r o f o l i v e g r a y (5 IB 4 / 1 ) a n d w e a t h e r e d c o l o r o f l i g h t o l i v e g r a y (5 IB 6 / 1 ) . S l a b b e d s e c t i o n s o f s a n d s d i s p l a y f a i n t p l a - n a r - l a a i n a t i o n s w i t h c o n c e n t r a t i o n s o f r i p u p c l a s t s t o w a r d s u p p e r c o n t a c t , B o u a a T a - b s e q u e n c e s , and g r a d e d b e d d i n g . S h a l e s t r a t a h a v e f r e s h c o l o r o f d a r k g r a y ( 8 3 ) , w e a t h e r e d c o l o r o f m e d ia * l i g h t g r a y (8 6 ) , a n d d i s p l a y l o c a l c o n c e n t r a t i o n s o f t e r r e s t r i a l p l a n t f r a g a e n t s . F i v e r e s i s t a n t c o n c r e t i o n a r y b e d s a n d o u s e r o o s i n d i v i d u a l c o n c r e t i o n s d o a i n a t e o u t c r o p . S l a b b e d c o n c r e t i o n s d i s p l a y d o a i n a n t l y b l o t u r b a t e d t e x t u r e a l t h o a g h r a r e o c c u r e n c e s o f u n d i s r u p t e d a l t e r n a t i n g l a a i n a e o f f i n e - t o a e d i u a - g r a i n e d s a n d a n d b i o t o r b a t e d s i l t w e r e a l s o o b s e r v e d . B i o t u r b a t e d s e d i a e n t s p r e s e r v e a b u n d a n t C h o n d r i t e s , c a n n o n P l a - 221 BS-22 7 0 J COVERED -7 ^ - 651 p o l i t i e s . a nd r a r ® Z o o n h v c o s t r a c e s . S e n i s c u s b a c k f i l l i n g o f P l a n o l i t i e s a n d Z o o p h v c o s o b s e r v e d a s w as r e b a r — r o w i n g o f P l a a o l i t i e s by C h o n d r i t e s . C o n c r e t i o n s p r e s e v e d en s® c o n c e n t r a t i o n s o f p l a n t a n d wood f r a g a e n t s p a r a l l e l t o b e d d i n g . G ood p r e s e r v a t i o n o f o r g a n i c f r a g m e n t s a s c e l l u l a r s t r u c t u r e s t i l l v i s i b l e a l t h o u g h p a r t i a l p y r i t i z a t i o n a l s o l o c a l l y p r e s e n t . I n o c e r a a a s s h e l l f r a g a e n t s l o c a l l y a b u n d a n t i n c o n c r e t i o n s w h i l e o n e c o n c r e t i o n h a s e n t i r e v a l v e f o r n - i n g l o w e r f a c e o f c o n c r e t i o n . C a l - c i t e - f i l l e d s e p t a r i a n c r a c k s p r e s e a t i n a a n y o f t h e b i o t o r b a t e d c o n c r e t i o n s ( 2 - 2 0 X o f c o n c r e t i o n v o l u a e ; a v g . = 5 % ) . I n t e r b e d d e d s h a l e and s a n d s t o n e s t r a t a . S a n d s t o n e b e d s h a v e t h i c k n e s s r a n g e o f 1 - 3 . 5 c a , p i n c h a n d s w e l l l a t e r a l l y , and d i s p l a y s h a r p i r r e g u l a r l o w e r c o n t a c t s a n d b o t h s h a r p a n d g r a d a t i o n a l u p p e r c o n t a c t s . . B e d d i n g p l a n e s w i t h i n s a n d s t o n e s t r a t a e x h i h i t c o n c e n t r a t i o n s o f t e r r e s t r i a l p l a n t a n d wood f r a g a e n t s . S a n d s t o n e f r e q u e n c y m e a s u r e m e n t s h o w s 9 t e d s ( a v g . t h i c k 2 - 5 c « ) i n 2 i o f s t r a t i g r a p h i c s e c t i o n . So p r i a a r y s t r u c t u r e s v i s i b l e i n f i e l d d u e t o i n t e n s e w e a t h e r i n g , b u t s l a b b i n g i n l a b o r a t o r y sh o w e d p l a n a r - l a a i n a t i o n s i n g r a d e d s a n d w i t h a l t e r n a t i n g l a a i n a e o f f i n e r - g r a i n e d a i c a - r i c h a nd c o a r s e r - g r a i n e d a i c a - p o o r s e d i a e n t s , w e l l - d e v e l o p e 4 l o a d 222 6 0 ” 5 5 ' c a s t s , l o c a l i z e d c h a o t i c b e d d i n g w i t h f l a n e s t r u c t u r e s a n d s m a l l b a l l - a n d - p i l l o w s t r u c t u r e s (4 x 2 am) - S a n d s t o n e b e d s c o n t a i n common t o a b u n d a n t C h o n d r i t e s an d P l a n o l i t i e s b u r r o w s a nd h a v e f r e s h c o l o r o f d a r t y e l l o w i s h brow n (10 I S 4 / 2 ) a n d w e a t h e r e d c o l o r o f l i g h t b ro w n (5 IB 6 / 4 ) . S h a l e s t r a t a h a v e f r e s h c o l o r o f l i g h t o l i v e g r a y (5 I S 5 / 2 ) a n d w e a t h e r e d c o l o r o f p a l e y e l l o w i s h brow n (10 IB 6 / 2 ) a n d c o n t a i n a b u n d a n t c o n c r e t i o n s * C o n c r e t i o n s c o a l e s c e on o n e s t r a t i g r a p h i c h o r i z o n a n d f o r a a d i s c o n t i n u o u s c o n c r e t i o n a r y b e d - C o n c r e t i o n s p r e s e r v e s e d i m e n t t e x t u r e s r a n g i n g f r o a f i m e l y - l a & i n a t e d t o c o m p l e t e l y b i o t u r b a t e d s e d i a e n t s . F i n e l y - l a m i n a t e d s e d i a e n t s d i s p l a y a l t e r n a t i n g s i l t a n d f i n e g r a i n e d s a n d l a a i n a e a n d w e l l d e v e l o p e d c o n v o l u t e b e d d i n g w i t h f l a a e s t r u c t u r e s - So v e r t i c a l s e d i m e n t t e x t u r e t r e n d s a r e e v i d e n t . C o n c e n t r a t i o n s o f o r g a n i c f r a g m e n t s o r i e n t e d p a r a l l e l t o b e d d i n g a r e p r e s e n t l o c a l l y , b u t s p a r s e , p a r t i a l l y - p y r i t i z e d o r g a n i c f r a g a e n t s a r e m ore com m on. B i o t u r b a t e d t e x t u r e s p r e s e r v e C h o n d r i t e s . P l a n o l i t i e s . and C h o n d r i t e s r e b o r r o w i n g P l a n o l i t i e s b u r r o w s . C a l - c i t e - f i l l e d s e p t a r i a n f r a c t u r e s o c c u r i n b i o t u r b a t e d c o n c r e t i o n s a nd com p r i s e <5X o f c o n c r e t i o n v o l u m e . L o c a l l y c o n c r e t i o n s p r e s e r v e s c a t t e r e d f o r a n a n d r a d i o l a r i a n t e s t s , many o f w h ic h h a v e b e e n p y r i t i z e d . One u n u s u a l c o n c r e t i o n a r y o c c u r e n c e o c c u r s n e a r t o p o f o u t c r o p w h er e f i v e s e p a r a t e c o n c r e t i o n s a r e s t a c k e d o n t o p o n e a n o t h e r a n d a r e s e p a r a t e d b y t h i n s h a l e p a r t i n g s (<1 c m - t h i c k ) t o fo r m a n a a a a l g a a a t e d c o n c r e t i o n 0 . 7 5 m - t h i c X . S h a l e s s u r r o u n d i n g c o n c r e t i o n s a r e d e fo r m e d a r o u n d c o n c r e t i o n s . 223 ^ l e n t i c u l a r s a n d s t o n e d e p o s i t c o a - p r i s e d o f a a a a l g a a a t e d c o a r s e - g r a i n e d t o p e b b l y s a n d s t o n e s r a n g i n g i n t h i c k n e s s f r o a 15 c a t o 0 . 5 a . S a n d s t o n e s t r a t a c o a a o n l y d i s p l a y s c o u r e d b a s a l c o n t a c t s , w e l l - d e v e l o p e d g r a d i n g , a b u n d a n t r i p u p c l a s t s , p o o r l y - s o r t e d t e x t u r e , l o c a l i z e d f l a a e s t r u c t u r e s , a nd a b u n d a n t c o n p l e x T h a l a s s i n o i d e s b u r r o w n e t w o r k s on b e d d i n g s u r f a c e s . S o l e s a r k s n o t w e l l d e v e l o p e d a n d i n c l u d e o n l y i r r e g u l a r l o a d c a s t s . P r i m ary s e d i a e n t a r y s t r u c t u r e s i n c l u d e S o u s a T a - b s e q u e n c e s , r a r e s a a l l - s c a - l e p l a n a r c r o s s - l a a i n a t i o n s , a n d v e r y r a r e , p o o r l y - d e v e l o p e d , s t r a i g h t - c r e s t e d s a a . l l r i p p l e s . H u a e r o u s s t r a t a d i s p l a y a a s s i v a b e d d i n g w i t h c o n c e n t r a t e d z o n e s o f p a r a l l e l a l l i g n e d r i p u p c l a s t s a nd o c c a s i o n a l c o b b l e s l o c a t e d c e n t r a l l y w i t h i n s a n d s t o n e b e d s . S a n d s t o n e s t r a t a o c c a s i o n a l l y a r e s e p a r a t e d b y t h i n (<5 c a - t h i c k ) , o r g a n i c - r i c h , d i s c o n t i n u o u s b e d s o f f i n e l y - l a a i n a t e d c o a r s e s i l t t o v e r y f i n e - g r a i n e d s a n d - s i z e d s e d i n e n t . 1 d i s t i n c t l a c k o f a b u n d a n t c o n g l o a e r a t - i c s t r a t a i s e v i d e n t i n t h i s l e n t i c u l a r d e p o s i t w i t h t h e s i n g l e e x c e p t i o n o f a 30 c a - t h i c k , r e v e r s e g r a d e d p e b b l e — c o n g l o a e r a t e * T h i s l a t e r a l l y d i s c o n t i n u o u s b e d c o n t a i n s s u b r o u n d e d t o a n g u l a r i g n e o u s p e b b l e s , a b u n d a n t s h a l e r i p u p c l a s t s , a n d d i s p l a y s a s c o u r e d b a s a l c o n t a c t . S a n d s t o n e s t r a t a h a v e f r e s h c o l o r o f s o d e r a t e y e l l o w i s h brow n (10 I £ 5 / 4 ) a nd w e a t h e r e d c o l o r o f l i g h t brown (5 YE 6 / 4 ) . 224 4 0 - P o o r l j e x p o s e d o u t c r o p o f h i g h l y - f r a g a e n t e d a nd w e a t h e r e d s h a l e s t r a t a w i t h t h r e e , t h i n (< 3 c a - t h i c k ) , a e d i - u a - t o f i n e - g r a i n e d , d i s c o n t i n u o u s s a n d s t o n e s t r a t a l o c a t e d n e a r b a s e o f o u t c r o p . Ho v i s i b l e c o n c r e t i o n s i n o u t c r o p . Top o f o u t c r o p c a p p e d by l e n t i c u l a r s a n d s t o n e d e p o s i t w h ic h a p p e a r s t o h a v e c u t i n t o u n d e r l y i n g s h a l e s t r a t a a l t h o u g h c o n t a c t n o t v e i l v w w y l e x p o s e d . COVERED 35 225 30 232: COVERED I n t e r c a l a t e d s h a l e s a nd 2 - 8 c a - t h i c k ( a v g . 2 . 5 c a ) , a e d i a a - t o v e r y f i n e - g r a i n e d s a n d s t o n e b e d s . S a n d s t o n e b e d s a r e r e s i s t a n t i n o u t c r o p , p i n c h a n d s w e l l l a t e r a l l y , h a v e i r r e g u l a r b a s a l c o n t a c t s , a n d g e n e r a l l y a r e d i s c o n t i n u o u s i n o u t c r o p . S i n g l e 8 c a - t h i c k s a n d s t o n e s t r a t u s d i s p l a y s g r e a t e r l a t e r a l c o n t i o n i t y a n d a o r e c o n s i s t e n t t h i c k n e s s a l o n g s t r i k e t h a n do t h i n n e r s a n d s . T h i s o u t c r o p c o n t a i n s g r e a t e r f r e q u e n c y c f s a n d s t o n e b e d s ( a v g . 6 b e d s / 5 a o f s e c t i o n ) t h a n l o v e r o u t c r o p s a nd d i s p l a y s g e n e r a l i n c r e a s e i n f r e q u e n c y t o w a r d s t o p o f s e c t i o n . S a n d s t o n e s h a v e f r e s h c o l o r o f x o d e r a t e b ro w n (5 TS 3 / 4 ) a nd w e a t h e r e d c o l o r o f g r a y i s h o r a n g e (10 IB 7 / 4 ) . T h e y d i s p l a y no v i s i b l e p r i - a a r y s t r u c t u r e s i n f i e l d , b u t s l a b b i n g i n l a b o r a t o r y h a s r e v e a l e d B o u a a T a - b - a a n d T c - d - « s e q u e n c e s . S h a l e s h a v e f r e s h and w e a t h e r e d c o l o r o f b r o w n i s h g r a y (5 IB 3 / 1 } a n d c o n t a i n a b u n d a n t c o n c r e t i o n s . S l a b b i n g o f c o n c r e t i o n s s h o w s d i s t i n c t i n c r e a s e i n b i o t u r b a t i o n f r o a l o w e r o u t c r o p . Con c r e t i o n s d i s p l a y a b u n d a n t C h o n d r i t e s and o c c a s i o n a l P l a n o l i t i e s b u r r o w s i n b i o g e n i c a l l y d o a i n a t e d s e d i a e a t a r y t e x t u r e , a b u n d a n t c a l c i t e - f i l l e d s e p - t a r i a n c r a c k s (5-10% v o l u a e ) , s c a t t e r e d o r g a n i c f r a g a e n t s s h o w i n g p a r i - t a l p y r i t i z a t i o n a n d l o c a l l y a b u n d a n t I n o c e r a a u s f r a g a e n t s - 226 COVERED 20 ^ ,r tA .ii5 > A A -r~ T -> • S'f fc±: -c= > - V W v W \ COVERED /v_ys. /S. I v H i g h l y f r a g s e a t e d s h a l e s i n t e r b e d d e d w i t h f i v e , 2 - 5 c a - t h i c k , f i n e - t o m e d i u m - g r a i n e d s a n d s t o n e b e d s - 1 1 1 s t r a t a h i g h l y w e a t h e r e d s o no p r im a r y s t r u c t u r e s v i s i b l e i n f i e l d . S l a b s e c t i o n s o f s a n d s t o n e s sh o w m a s s i v e b e d d i n g , c r u d e g r a d i n g , a n d l o c a l b i o - t u r b a t i o n w i t h C h o n d r i t e s . S a n d s t o n e b e d s a r e l a t e r a l l y c o n t i n u o u s , h a v e s h a r p u p p e r a n d l o w e r c o n t a c t s , a n d l a c k s o l e n a r k s . S a n d s t o n e b e d s h a v e f r e s h c o l o r o f g r a y i s h o l i v e g r e e n (5 GT 3 / 2 ) a n d w e a t h e r e d c o l o r o f n o d e r a t e y e l l o w i s h b ro w n (1 0 IB 5 / 2 ) . S h a l e s t r a t a h a v e f r e s h c o l o r a nd w e a t h e r e d c o l o r r a n g e o f l i g h t brow n (5 I S 6 / t ) t o d u s k y brow n (5 IB 2 / 2 ) . l b u n - d a n t c a r b o n a t e c o n c r e t i o n s i n s h a l e s t r a t a sh o w f i n e l y - l a m i n a t e d (2 an a v g . ) , o r g a n i c - r i c h s e d i m e n t s . . S i l t l a m i n a t i o n s o c c u r i n 0 . 5 - 2 c a - t h i c k p a c k a g e s s e p a r a t e d b y < 1 c a - t h i c k f a i n t l y l a m i n a t e d c l a y b e d s . L a m in a t e d c l a y b e d s d i s p l a y i r r e g u l a r b a s a l c o n t a c t s w i t h c u t - a n d - f i l l s t r u c t u r e s , n u m e r o u s n o r m a l m i c r o f a u l t s (< 2 cm o f f s e t ) , s m a l l l o a d s t r u c t u r e s , m in o r s lu m p f o l d i n g , and s m a l l f l a a e s t r u c t u r e s . Two c o n c r e t i o n s c o l l e c t e d f r o a t o p o f o u t c r o p sh o w t r e n d t o w a r d s g r e a t e r b i o t u r b a t i o n ( a b u n d a n t Chon d r i t e s a n d o c c a s i o n a l P l a n o l i t i e s ) and d i s r u p t i o n o f l a a i n a e u p s e c t i o n . B i o - t u r b a t e d c o n c r e t i o n s sh ow l a r g e c a l - c i t e - f i l l e d s e p t a x i a n c r a c k s ( a v g . 5X v o lu m e ) a n d s c a t t e r e d , p a r t i a l l y - p y r i - t i 2e d o r g a n i c f r a g a e n t s . H i g h l y f r a g s e n t e d s h a l e s e c t i o n w i t h v e r y p o o r l y - d e v e l o p e d b e d d i n g and i n t e r b e d d e d t h i n ( 2 - 5 c a ) , m ed iu m - t o c o a r s e - g r a i n e d s a n d s t o n e s t r a t a . S p a r s e c a r b o n a t e c o n c r e t i o n s ( 7 - 2 0 c a i n d i a m e t e r ) s c a t t e r e d t h r o u g h s h a l e s t r a t a s h o w i n g p e n e c o n t e m p e r a n e o u s d e - 227 3 ~zsr^ f o r m a t i o n o f s h a l e b e d s a r o u n d i n d i v i d u a l c o n c r e t i o n s . S a n d s t o n e b e d s i d e n t i c a l i n c o l o r a n d t e x t u r e t o l o w e r t h i n s a n d s t o n e s t r a t a . S h a l e s h a r e w e a t h e r e d c o l o r o f l i g h t brow n (5 IS 6 / « ) a n d f r e s h c o l o r o f d u s k y y e l l o w i s h brow n {10 2 / 2 ) . ____________________ P e b b l y a u d s t o n e z o n e d i s p l a y i n g l o c a l c o n c e n t r a t i o n s ( 5 - 3 0 c a - t h i c k ) o f v e r y c o a r s e - g r a i n e d s a n d and r o u n d e d t o s u b r o u n d e d i g n e o u s p e b b l e s a n d c o b b l e s i n a m ix ed c l a y a n d s i l t m a t r i x . B e d d in g v e r y p o o r l y d e v e l o p e d , b u t s h o w s r a n g e f r o a p l a n a r - l a a i n a t i o n s t o c o n t o r t e d b e d d i n g . A l s o g e t i s o l a t e d p e b b l e s a n d c o b b l e s i n a n d s t o n e a a t r i x a nd i n t e r b e d d e d v e r y c o a r s e - t o c o a r s e - g r a i n e d , p o o r l y - s o r t e d , 2 - 5 c a - t h i c k s a n d s t o n e s t r a t a . P e b b l y a u d s t o n e d i s p l a y s s a n e c o l o r r a n g e a s s h a l e s b e lo w and s a n d s t o n e s h a v e s a n e c o l o r r a n g e a s l o w e r s a n d s t o n e s . _________ I n t e r b e d d e d s h a l e s and 2 - 1 5 c n - h i c k , . a e d i u a - g r a i n e d t o p e b b l y s a n d - i l s t o n e b e d s w it h s h a r p , p l a n a r u p p e r || and l o w e r c o n t a c t s , m a s s i v e b e d d i n g , | a b u n d a n t o r g a n i c f r a g a e n t s , and p o o r - I l y - s o r t e d t e x t u r e s . S h a l e s a r e h i'g h - l y - f r a g a e n t e d , h a r e w e a t h e r e d c o l o r o f l i g h t b r o w n (5 IB 6 / 4 ) a n d f r e s h c o l o r o f d u s k y b ro w n (5 1 8 2 / 2 ) , a n d c o n t a i n s c a t t e r e d c a r b o n a t e c o n c r e t i o n s ( 5 - 1 8 c a i n d i a m e t e r ) . 28 c a - t h i c k , v e r y c o a r s e - g r a i n e d , l e n t i c u l a r g r a d e d s a n d s t o n e c o n t a i n s s c a t t e r e d m a t r i x - s u p p o r t e d i g n e o u s p e b b l e s and c o b b l e s . L e n t i c u l a r s a n d h a s s c o u r e d b a s a l c o n t a c t , a a s s i v e a m s a l g a a a t e d b e d d i n g , s p a r s e r i p u p c l a s t s , few l o a d c a s t s , p o o r l y - d e v e l o p e d f l u t e m a r k s , and s c a t t e r e d c o b b l e s r e s t i n g a t o p t h e b e d . S a n d s t o n e s t r a t a h a v e f r e s h c o l o r r a n g e o f g r a y i s h r e d (1 0 B 4 / 2 ) t o g r a y i s h o r a n g e (10 IB 7 / 4 ) and w e a t h e r e d c o l o r r a n g e o f y e l l o w i s h brow n (10 IB 6 / 2 ) t o g r a y i s h o r a n g e (1 0 IB 7 / 4 ) . 228 Appendix B CONCRETION COMPOSITION ANALYSIS. RESULTS LECO gasom etric d e te rm in a tio n s of carbonate c o n c re tio n s (o rg an ic carbon and carbonate c o m p o sitio n s). 229 LECO GASOHETRIC DETERMINATIONS: C o n c r e tio n Sample Calcium Organic S i te Loca t i o n : C a r bon a te : Ca r bon : (we i ght %) (weight %) BS-9 58.41 0.28 BS-1 0 62.23 0.00 B S - 1 6 55. 1 1 0.00 BS-17 71 .32 0.00 BS-22 75.02 0.00 8 S - 2 3 56.84 1 .26 BS-39 67.56 0.86 BS-46 69.91 0.00 BS-64 62.82 0.00 BS-68 71 .01 0.31 23C Appendix C MICROFOSSIL IDENTIFICATION TABLE Faunal l i s t of fo ra m in if e ra and c a lc a re o u s nannoplankton. 231 O J on CM MlCROFOSS L IDENTIFIXATION TAB LE : Sample S i t e Loca t i on s : Taxonom i c L i s t : o C M o n LA ~ct vO o > . C M -3- CM CM o n LA vO t— cm o n -cr LA vD 1 r ''- 1 • • r t GO 1 GO l GO 1 CO 1 to i to 1 to E to i to to o <_> o o o o o Fo ram i n i f g rs i O f t CD CD CD CD C O ca CD CD CD — — ” ” “* * * “* * * “ Allomovphica of. A.han't X Allomovphica c reta cea X Ammobaculites s p . X X X Anomalina poponoei X Astacolus j a r v i s i X Bathysiphon sp. X X X X X X X X X Bathysiphon v i t t a X X X X X X X X X X X Budashevaella s p . X X X Cribrostomoides creta cea X X X Dentalina catenula X Dentalina s p . X Gaudvyina pyramidata X X G lo b o r o ta lite s mi ohe U n i anus X Haplophragmoides of. E.exoavatus X X X X X Haplophragmoides s p . X X X X X X X X X X Hyperammina elongata X L e n ticu lin a sp. X X X X X Nodosaria s p . X Psammosphaera la e v ig a ta X S ilio o s ig m o ilin a c a l i f o m i c a X X X X Thalmannamina s p . X X X X X X X X X X Tvoohamminoides of. T.velasoo X X X X X X X Taxonom i c List: Calcareous Nannofossi1s : E 'tffe ttith u s eximius L ith o s trin u s g r i l l i i M a rth a ste r ite s furoatus Mi-oula staurophora Watznaueria barnesae Zygodiscus diplogrammus Sample Site Locations 04 04 I G O CD -3 * -J- ■ I < /> C Q O vD I < /> CO I o vD I O 233 Appendix D MACROFOSSIL IDENTIFICATION TABLE Faunal l i s t of m a c ro fo ssil specimens c o l l e c t e d from Holz Shale outcrops in Black S ta r Canyon. 23* Propeamus sium s p . Anomalodesmacea Indogrammatodon sp MACROFOSSIL IDENTIFICATION TABLE: Sa mple S i t e L o c a t i o n s : Taxonomic List: O x O co -tr o - CO L O CO Q CO LA -3 - C O » — co « — C X I C X I C x | ro CO CO -3 ‘ x D x O B i v a lv e s : CO CO CO CO CO CO ' CO CO CO CO CO CO CO CO co c q ca CD ca CD CO ’ CD CD CD CD CD CD CD CD CD Inocevamus sp. X X X X X X X X X X Ammon I te s : Bostrychocevas elongation B aou lites sp. Eupachydiscus haradai (?) M i see 11a n e o u s : B i v a 1ve f ragmen t s Gastropod fragments Arthropod fragments Scaphapod fragments L T i on c\j

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Creator Buck, Steven Paul (author)

Core Title Paleoenvironmental analysis of late Cretaceous continental slope deposits (Holz Shale Member, Ladd Formation), Black Star Canyon (Santa Ana Mountains), Southern California

Contributor Digitized by ProQuest (provenance)

Degree Master of Science

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

Tag Marine Geology,OAI-PMH Harvest

Language English

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c30-120722

Unique identifier UC11225342

Identifier usctheses-c30-120722 (legacy record id)

Legacy Identifier EP58715.pdf

Dmrecord 120722

Document Type Thesis

Rights Buck, Steven Paul

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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...

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