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Vertical sequence analysis of late Pliocene pico formation sediments in Adams Canyon, Ventury County, California

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Vertical sequence analysis of late Pliocene pico formation sediments in Adams Canyon, Ventury County, California

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Content VERTICAL SE Q UENCE ANAL YSIS OF LATE PLIO CENE PICO FOR MATIO N SEDIMENTS IN ADAMS CAN YON, VENTUR A COUNTY , CAL IFORNI A by Thomas Martin Hartnett A Thesis Pre sented to the FACU LTY OF THE GRADUATE SCHOOL UNIVERSIT Y OF SOUTHER N CALIFOR NIA In Partial Fulfill ment of the Requi rem ents for the Degree MASTER OF SCIENCE (G eological Sc ien ces ) Septem ber 1980 UNIVERSITY OF SOUTHERN CALIFORNIA THE GRADUATE SCHOOL UNIVERSITY PARK LOS ANGELES, CALIFORNIA 90007 This thesis, written by ____________ :_��---��-::�-�-�---��-:.�::--��-!: __________________ _ :..;;) �/lj. under the direction of hi. f?.. ... 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 t·equirements for the degree of Master of Science ·················- �'--t� -� -d ................ . T� IS OM ITTEE ' � \ ·--- - -- - ------- -- � � �:.. . ' . () v .� �nt;;l . . 10.. _ _ __ . ... K .. r _ _rJUJ!l? h/ /_// I .p. - ____ a..; '-p,�- Dean D DEDICATION Dedicated to the memo ry of the late Dr . Richard 0. Stone , for mer Chairman of the Department of Geological Sc ien ces , who gave me his advice , support , and frie ndship . ii ACKNOW LEDGMENTS This thesis has rece ived hel p fr om vario us so urce s. Many thanks go to my Mother who has pr ov ided unders tanding and support throughout my ac ademi c car eer . I would li ke to thank Dr . Donn Gorsl ine for ch airin g my thesis co m mittee and for teaching me the principles of marine geology and sedi me ntary proc esses . I would also li ke to thank the other mem bers of my co mmi ttee, Dr . Bernard Pi pkin and Dr . Donald Lama � for visiti ng the study area with me , revi ewing earlier drafts of thi s thesis and off ering usef ul comm ents . Tal ks wit h Dr . Tor Nil sen and Dr . Mart y Lin k and turb idi te fiel d trips with them were very he lpful . Dr . Li nk visited my field area and pr ovided me wit h m any sug gestions. Dr . Rober t Bourro uilh helped decide which port io of Adams Canyon to me asure in detail after I had co mp leted a rec onnaissance of Adams Canyon and con necting Salt marsh Creek . The Mobi l Corp ora tio n was im porta nt in deve lopin g my in terest in ancient deep-sea fa n sys tems by givin g me the opportu nit y to map and interpret Eocene deep•sea fan deposits in so uthwester n Oregon . Gloria Lee did an exce ll ent jo b in typ ing the final iii co py of thi s thesis with pro m ptness above and beyond the call of duty . Special thanks go to Virginia Wong who has helped with the fiel d work and virtuall y did all the draft ing whil e cons tantly provi ding mo ral support . iv TABLE OF CONTENTS Page DEDICATION . ••• ii ACKNO \tJLE DG MENTS . iii LI ST OF IL LUSTR ATI0 NS . . ix LI ST OF TABLES . - . . . . . . • xiii ABSTRACT ••• . xi v INTRODUCT ION ••• . . . . . . . . . . . . 1 General Statem ent. . . . . . 1 Str ucture , Strat igraphy , Paleoeco logy and Sediment Type s . . . . . • • . • 2 Pre vious Work . 7 Fiel d Work .. 7 FAN FAC IES ASSOC IAT IONS AN D TH E ORGANI Z ATION OF THE MI DFAN SEDIMENTS IN ADAMS CAN YON. • • . • . 13 SE Q UENCE I •. 21 Sequence IA : In ter channe l • 21 Grain size and bed characte ri stics . • 4 0 Struc tur es •• 40 Summary 40 Sequence IB: Megasequence . 40 Grain size and bed characte ristics .•• 43 v -----� Page j Struct ures •• Summary Sequence IC : In ter channe l . Gra in size and bed characteri sti cs . Struct ures .• Summary SE Q UENCE II . Sequence II A: Megasequenc e. Gra in siz e and bed character istics .• Structure s. Summary • Sequence IIB: In ter channel. Grain siz e and bed character isti cs . Structures .. Summary . Sequence IIC : In ter channe l to Near- Channel. Gra in siz e and bed character istics .•. Structure s. Summary . SE Q UENCE III . Sequence III A: Megasequence 46 46 55 55 60 60 63 63 63 70 70 70 70 80 80 81 81 88 88 89 89 Grain size and bed character istics. . . . 89 Str uctur es . 90 Summary . 98 Sequence III B : In terchannel • 98 vi ----� �-�--- -----------, Pag e Grain size and bed characte ri sti cs . 98 Struc ture s. 107 Summary • . 107 Sequence III C : In terchanne l • 107 Gr ain siz e , be d character istics and structure s. . • • • . • . . . . 110 Summa ry • . . . . . . . . . . . . . Sequence IIID : Inter cha nnel . Gr ain size, bed charact eristics and structure s. . . ...•. Summary SEQ UE NCE IV • Sequence IVA : r1egasequence. . Grain siz e and bed charact eristics .• Structur es .. Summa ry •• Sequence IVB : Upper Channe l-Fi ll. Gra in size, bed ch aract eri stics and structure s. . . . .. . .. Summa ry • Sequence IVC : Overb ank to In terchan nel. • Grain size, bed cha racter istics and structu res .••.... Summary • SEQ UENCE V .. . . . . . . . Sequence VA: Megasequence • Gra in siz e and bed charac ter istics .. 110 110 110 113 118 118 122 122 130 130 130 138 138 139 144 14 7 14 7 147 vi i Struct ur es� •• • • • . . . . . . Summary . . . . . . . . . . . Pale ocur rents •• DISCUSSION. . CO NCL USIONS . REFERENCES .•. . . . . . . Page 157 160 167 172 180 182 viii LIST OF IL LUSTRATIONS Fig ure Page 1. Location and general struct ural features near Adams Canyo n. . . . . . • • • . . . . . . • 4 2. Stratigr aphy and paleoeco logy of Ojai Ventura Basin , Cali fornia . . • • . area , 3. Adams Canyon measured section locat ion and general geo logy • • • • • • • . . . • 4 . Di agra m showing fan facies assoc iations 5. Envi ronme ntal model of a deep- sea fa n used in 8 10 14 the pres ent study . . . . . • . . . 19 6. Contin uous sandstone bed thi ckne sses for Se- quence I, me ters 0 to 84. . • • . • • • 22 7. A continuous detail ed section of sequence IA and me gasequence IB . . . . . • . . 28 8. Sandstone bed perc entage for me ters 0 - 100 of sect ion and vertical sequence analysis of sequence IA. . . • . • . . . • . . . . . 41 9. Ama lga ma ti on of pebbly sandstone layers at meter 14 .6. . . . . . . . . . . . . . . . . 44 10 . Wavy bedding in 10 em thick silt bed at meter 14 . 6. . . . . 11. Shell ma terial orie nted conca ve upward in 47 med ium- thick granu le sand layer at meter 32 4 9 12 . Fla me struct ures and loadfor ms of several ce nti m eters relief at meter 30, Fi gure 7. • 51 ix Fi gure 13 . Pl astic defor ma tio n in thick me di um- grained Page i sand bed at meter 35. • • • . • . • . . . • 53 14 . Vertical sequence analysis of mega sequence IB 56 15. Detailed section of a po rtion of IC , in ter- channe l turb idi tes . • . • • • • • • . • 58 16. Facies D in terch annel tur bidites at meter 53. 61 17 . Amal gam ated ma ssi ve me diu m- to fin e-grai ned beds of facies B 2 bet ween me ters 84 and 94 whi ch are character ist ic of megas equence II A . . . . . . . . . . . . . . . . 18 . Contin uous detail ed section of me gasequence 64 II A fro m meter 84 - 94 . . • • • . . . . . . 66 19 . Vertical sequenc e analys is of mega sequence II A 71 20. Sandstone bed thicknes s data for mega sequenc e I IA . . . . . . . . . . . . • . . . . . 7 3 21. Contin uous sandstone bed thickness for me ter s 10 7 - 12 6, sequence II B, in ter channe l environment • . . . • . . • . • . . . . . • 75 22. Detailed section of in ter channel tur bidit es of a port ion of section IIB fr om meter 114 .5 - 116 . • . . • • . . . . . . . • 78 23. Sandstone bed thi ckne ss for sequence IIC . . . 82 24 . Detaile d sect ion diagra m for a portion of section IIC , in terc hannel turb idites fr om me ter 140 - 142. 7 • . . . • • . • • • . • • 84 25. Twenty em thick pebbly sandstone bed at meter 14 2.5 . . . . . . . . . . . . . . . . . 86 26. Contin uou s detail ed section dia gra m of mete rs 158 through 173 , megas equence II IA . . • . . 91 27 . Mass ive pebbly sandstone layer 70 em th ick wit h ripups of siltst one at meter 159 • . • 96 28 . a) Botto m photo . Dis h structu res to right of hamm er in thi ck (122 em) me diu m- to fi ne- grained sandstone at meter 168.5 . • . . . 99 X Fi gure 28 . b) Top photo . Close up of top of the bed seen in top port ion of photo below showing fl uid escape pi pes in co nvo lute beddin g . . . . • 99 29. Sandstone bed thickness of me gasequence III A fro m meter 158 - 170 showing a thinning upward tr end when co mp ared to overl ying bed thi cknesses of sect ion III B. • . • . . • 101 30 . Vertical sequence anal ysis of me gasequence III A 103 31. Sandstone bed thi ckness for me ter s 190 to 192 of in terc hannel sequence III B . . 105 32 . Detailed section diagram for a portion of sequence III B , in terc hannel tur bidi tes fr om me ter 190 to 191. 9 • . . • • . . • . . . . . 108 33 . Ph oto at me ter 344 of sequence IIIC, fac ies D in terch annel tur bidit es . . . . • • . . . 111 34 . In terbedded sandstone , sil tstone and mu dstone of in terchan nel sequenc e IIID. . . . 114 35. Cliff for ming expos ure of mega sequenc e IVA abru ptly over lyin g thi n-bedded turb idites of sequence III D just to left of geo logy student Gin ny Wong • . • • . • • . . • • • • 116 36. Contin uous sandstone bed thi ckne ss dia gra m for me ters 378 to 493 , me gasequenc e IVA. • . 119 37 . Contin uous detail ed sect ion of a port ion of me gasequence IVA fro m me ter 378 to 385.8 . . 123 38. 1'1u lti stor ie d , ama lga ma ted bod ies of me gase- quence IVA at me ter 390. . • . • . • • . . . 126 39 . Sketc h of lar ge siltstone and mu dstone ripups at meter 490 . . • . • . . . • • . . . . • . 12 8 40. Shallow dish stru ctures at meter 385 of me ga- sequence IVA • . • . . • . 41. Continuous ver tical sequence analysis of me ga- 131 sequence IVA . . . . . • . • . • • • . • 133 42 . Detaile d section of a portion of IVC , overbank deposits fro m me ter 520 to 521.9 . . • . • • 140 xi -- ---------, Fig ure 43. Ph oto taken at meter 586 near top of section Page IVC , facies D, inte rchan nel turb idites . . . 142 44 . Sandstone bed thic kness diagram for a portion of sequence IVC , in ter channe l tur bidit es . . 145 45. Continuous detail ed section of a portion of mega sequence VA from meter 588 to 614. . . . 148 46. Sandstone and co nglomerate bed thi ckne ss diagram for a port ion of meg asequence VA 155 47. Conglomerate bed pin chin g out beneath head of the ham mer . . . . . . . . . 158 48. Bou lder con glomerate in poorl y sorted sandy mu dstone at meter 590 of mega sequence VA 161 49 . Vertical sequence analysis of me gasequence VA. 163 50. Clast supporte d cob ble cong lomerate close to base of mega sequence VA near meter 586 . 165 51. Ro se dia gra m for paleocurrent mea sure ment s (T able 3) in the interchannel and channe l sedi men ts . . . . . . . . . . . . . . . . . • 169 I xii LIS T OF TABLES Table 1. FACIES CLASSI FICATIO N OF SEDHm NT GRA VITY Page FLOWS (A FTER WALKER AND MU TTI, 1973) . . • . . 3 2. KEY FOR DETAILED SECTI ON DI AGRAHS • 27 3. PA LEOCU RRENT MEASUREMENTS . 168 4 . COMPAR ATIVE STUD Y OF MIDF AN CHA NNEL-FI I�L SEQU ENCE . . • . . • . . • . . • • . . . 174 5. TYPES OF GR AVITY-DR IVEN SEDIMENT FLOWS (A FTER HAM PTON, 1979 , TABLE 1) . . • . • . • • . • • 17 7 xii' ABSTRA CT Late Pliocene deep- water (300 m) tur bidites of the upper Pi co For m atio n for m a well -ex posed , near- com plete ver tical section in Adams Canyon , Cali forn ia. Appr oxi- :m ately 700 me ters (m) of section were exami ned in detail , ' rev ealing fi ve sect ions of channe l-fill sedi me nts up to 117 m thi ck domi nated by thi ck-bedd ed , coar se- to fi ne- grained sandstones , pebbly sandstone s and conglo mera tes . A thin nin g of bed thi ckne sses upward was fo und in all fi ve sect ions along wit h an assoc iated decrease in grain sizes. The channel-fill sedi men ts are separated by tens to hundreds of mete rs of fi ner grained pla ne -para llel inte rchann el turb idit es. The associati ons of facies ty pes ! along with the cyc lic nature of the bed thi ckne sses ' indicates that the entire sequence repr e sents a mi dfan envi ron me nt of deposition . A com pari son wit h equiva lent ' age midfa n channe l sedi ments exposed in Santa Paula Creek 2 km to the east indica tes mo re frequent depo sitio n for the midfa n sedi me nts of Adams Canyon . This is interpr eted as the result of a de crease in the midfa n gradient fro m i • I ·- -···- -- - �� east to west ca using in creas ed depos iti on of sedim ent gravity fl ows in the Adams Can yon area . Pale oeco logical studies have in dicated an infi llin g sedi mentary basin from earl y Pliocene to the begi nning of the Plei stocene . Pe bbles and other clast co mpo siti on indicate the source terrain was Eocene and Miocene sed im entary rock s to the nort heast and crysta ll ine basement toward s the east . A subm ar in e ca nyon tren din g west to sou thwest is indicat ed by th e paleocurrent data . Fl ow mechan isms indi cated by str uctu res within the sect ion show that sed iment was trans po rted by debr is, grai� fl uidi zed and turbu lent fl ows . A rate of 1 rom /year has been esti mated as the overa ll sedi menta tion rate for the Pliocene sedi men ts in the area . XV INTRODUCTION Genera l Statement The study of mo dern tur bidites has long been hindered by their ina cc essi bi lit y as they accu m ulated in deep waters . The recent examin ations of deep- sea fans at the base of the continental slope along with sm alle r fans in the sou thern Calif or nia bord erl and have provi ded a clearer picture of thei r mo rpho logy and sedi men to logy during the last decade . This has tre mend ou sly aid ed in the recog nition of ancient deep- sea environm ents in that much of the extensive turbidite deposits in the geologic record were for med as prograd ing deep-se a fans rapidly fil led ma rine basins. The analysis of these for mer ma rine basin s in cre asin gly re quires an in terpre tatio n of the sed im entary rocks in ter ms of their depos iti ona l environm ent. The study of turb idites has shown these sedi ment s to be mu ch mo re than monotonou sly rhyth mic beds . Repetiti ve sedi me ntary divis ions were re cog nized and ter med Bouma divi si ons . These divi si ons were found to be descr ipt ive of on ly some tur bidites and are now a subord inate 1 classif ication to turb idite facies and facies locations within a tur bidite basin (see Table 1) • Var ious subenvi ron me nts of deep-sea fans ca n be reco gnized in the fiel d by recently deve loped criteria for disting uishin g facies and assoc iat ions of faci es . Struct ure , Stratigra phy, Paleoecolog y and Sedi ment Type s The Pli o-Plei stocene section expose d in Adams Can yon and other canyo ns along the south fla nk of Sulp hur Moun tain , is distinctive because it is one of the thickest known marine sections in the wor ld, var ying fro m 4,545 m to 5,050 m (Baile y and Jahns, 1954) . At its thickest po int ! near the city of ventura the total Tertiar y section is 15 , 150 m (Y eats , 1976) . The Adams Canyon section for ms an east-we st strikin g hom oc li ne that dips steeply (70°) to the south along the south fla nk of the Sulp hur Mountain anti cl in orium. Uplif t of Sulp hur Mountain is pos t- late Pli o cene ti me acco mp anied by foldin g occurred along the east west tren d ing Sisar rev erse fa ult (s outh si de up) direc tl y north (F ig. 1) (Y eats , 19 76) . The Sulp hur Mountain uplif t li es within the larger east-w est tr endin g Santa Cl ara sy nc li ne . The San Cayentano Fault ma rks the nort hern boundary of the sy ncline and the Oakridge Fault the sou thern Boundary (Bai ley , 1954) . Al ong the San Cayentano Fault Eo cene age rocks have been thrus t ove r younger , 2 Bouma Sequence Not Applicable Bouma TABLE I FACIES CLASSIFICATION OF SEDIMENT GRAVITY FLOWS (AFTER WALKER AND MUI'TI 1 1973) Facies A: Coarse-Grained Conglomerate Sandstone A1 Disorganized Conglomerate A2 Organized Conglomerate A3 Disorganized Pebbly Sandstone � Organized Pebbly Sandstone Facies B: Medium Fine to Coarse Sandstone B 1 Massive Sandstone with Dish Structure B2 Massive Sandstone without Dish Structure Facies C: Interbedded Medium to Fine Sandstone and Sequence Mudstone, Proximal Turbidites Applicable Bouma Sequence Not Applicable Facies D: Interbedded Fine to Very Fine Sandstone, Siltstone, and Mudstone, Distal Turbidites Facies E: Interbedded Very Fine to Medium Sandstone, Overbank Deposits Facies F: Chaotic Deposits Formed by Downslope Mass Movement Facies G: Mudstone, Pelagic and Hemipelagic Deposits 3 Fig ure 1. Location and general struct ural fea tur es near Adams Canyon , striped area shown in Fig. 3 (a dapted fro m Cro well et al. , 1966 I Fig . 1) . 4 U1 santa Ynez Fault SANTA YNEZ HTNS . ----- ./) -1 0 -?' .;:.. -?' 0 ��t'· �<;-.<;. c� ,O U. S II �- 101 1 6 miles 1 i N steeply dipping rocks of Miocene and Pl iocene age which are locally overturned near the fault zo ne (Bai ley , 19 54) . The me asured section in Adams Canyon co nsists of late Pliocene (Wh eelerian) sedi men ts of the upper Pi co For ma ti on . The rocks include in ter bedded siltstone , sandstone , mu ds tone and co nglome rat e that are poor ly to mod erat e ly indura ted . The mud stone is usuall y gray wit h occas ional thin redd ish pelagic mu dstone la yers whil e the coa rse grained rock s are li ght gra y or tan. Beddin g thicknesses ra nge fro m lami nated to very thi ck-bedded (480 em ) . Sandstone and cong lom erate units gen erally show coa rse tai l grading or are ma ss ive. The sandstones are clas sifiec as ark osic wackes because they cont ain greater than 10 percent mud ma trix . The lenticular nature of the sand stones and co nglome rates can be seen in the fe w inst ances where beds can be traced laterally tens of me ters . Lit hif ied clasts are ma inl y siltst one and mu ds tone wi th lesser am ounts of che rt , quartzite , vo lcanic roc k fragments and ig neous rocks . So urce areas co nsis ted of Eocene and Miocene sed im entary rocks to the nort heast and cryst alli ne basement of the San Gabriel Mountain s to the east . The grain size s in the Pi co Form ation genera ll y grade lat era lly fro m coa rser gra ined rocks dominant in eastern Vent ura County to fi ner grained rocks in the west , suggestin g an in crease in water depth to the west during depos it ion (We ber et al. , 19 73) . 6 Pr evious Work Driver (1928) examined the foraminifera in Adams Canyon and conc luded that it consist ed of 4,150 m of unrepeated Pliocene sedi men ts . Nearby Santa Paula Creek wi th equiv alent (Pli o-P lei stoc ene) age sedi ment s has been studie d by Natland and Kuenen (1951) in their work on the sedi men tar y hist ory of the Ventur a Basi n . Natl and (1957) studied the stratigra phy in Wheeler Canyon only 2.4 km to the west of Adams Can yon . His analys is of paleoeco logical data indica ted prog re ss ive incr ease in water depths to greater than 1 ,200 m until early Pl iocene (R epettian) ti me . Basin filli ng and shallowin g to 600 m continued during middle Pliocene (Ventu rian) and depths of 300 m were present dur ing late Pli ocene (W heelerian) ti me (F ig. 2) . Cro well et al. (1966) also in vestigated Santa Paula Creek and desc ribed a var ie ty of turb idite struct ures . Fie ld Wo rk Nearly 700 m of poorly indurated late Pl iocene deep water sedi me nts were examined during the wi nter and spring of 1980 in Adams Can yon. The mouth of this ca nyon li es appr ox i mately 2 km west of the town of Santa Paula (F ig. 3) An abandoned dirt ro ad prov ides acc ess to the base of the section . The base of the mea sured sect ion is approx ima tel y 7 Fig ure 2. Stratigra phy and paleoec o logy of Ojai ar ea , Ventur a Basin, Cali fornia (aft er Natland , 19 57 , Pl.4} . 8 ... z ... u 0 � "" ... _, "- ... z ... v 0 ... z ... u 0 ::!: z 0 � < ::!: c.: 0 ... 0 .. a .II ... 0 < � "" c 0 - = .. a .: X D - c a "" c t) 0 - "' .. - . t:.. - .. •o �.::: Oa. .... 0 - - • " • c.: -� 0 .. -0 ""� I - � c. o .. �· • • ..::: c g - • " • c.: E 0 0 DE POSHIONAl. ENVIRONMENT bE?TH 0 600 900 1200 M ' I 1 I I 9 r-- ---- --------- I I i Fi gure 3. -- --- - -- - - --- ------------------------- - -- - - ---- - ------ -------, Adams Canyon measured sec tion location and general geology . Topogra phic map fr om USGS Santa Paula Peak , Calif ornia Qu adra ngle and the geology is after Weber et al , (1973) . Symbo ls and ex planation s- follo w; T p : Pi co For m ation, TO sb : Santa Barbara For mation , --r-70 : strike and dip of beds , B: base of me asured sec tion. f I i I i 1o I ·--- ··-�, . . .. ------ ·-�---�.,�-'""" -- -·--------�·-·--···,.--. - - -- --- - · - .... -- -·----�-- --! 25 m east of the inte rsec ti on of Adams Canyon and Salt marsh Creek roads (Fig . 3) . Str eam cu ttin g has been ra pid, leaving exc ellen t expo sures of beds dipping steeply so uth ward along mo st of the cr eek' s leng th. Steep gorg es up to severa l me ters in dept h oc cu r in the harde r str ata that are erod ed at right angles to the strike of the beds . Field desc riptions of the ro cks included atti tudes of beddin g , primary structure s, bedding co ntacts , textur al var ia ti on s and the presenc e or absenc e of ch annels. Where distinct ch anges oc c urred in these ch arac teristics, detai led obser vations were rec orded on data sheets which included sketches of the sec ti on . These fig ure s along with others nec essary for their interpr etatio n are pre sented in the desc riptions of the mea sured sec ti on . An advantage in working with these par tially lit hifi ed sedi me nts is the easy cl eaning and shaping of outc rops to better expose primary struc ture s and cros sbedding in three dim ensio ns for paleocurrent me asur em ents . Approx ima tely fi ft y days were spent in the fi eld . 12 FAN FAC IE S ASSOCI ATIONS AND THE ORGANIZ ATIO N OF THE MI DFAN SEDIMENTS IN ADAMS CAN YON Turbidites and assoc iated rese dimented beds are found in three ma jo r depositional enviro nm ents : slope , fan, and basi n plai n of eit her abys sal co ntin ental ma rgin or deep- sea basi n loc ations (Wa lker and Mutti, 1973) . The fan syst em is subdi vided using depo siti onal facies and cy cl es of sedi me ntatio n in diff er entia ti ng the in ner , mi dd le , and ou ter fa n enviro nm ents (Fig . 4) . Cy cl es of thi nnin g and fi nin g upward have been found ch arac teristic of midfa n tur bidites whi le thickening and co ar seni ng upward cy cl es indi c ate prograding outer fan turb idites (Ricci-L uc c hi, 1975) . The var ious depositional facie s (T able 1) of Wa lker and Mutti (1973) and Ricci -Luc ch i (1975) mo dified after Howell and Link (1976) are desc ribed as follows : facies A - orga nized and disor ganized co nglom erate and pebbly sandstone , co arse sandstone , thic k to ma s si ve bedd ing , lenticular beds with cut -a nd- fill struc tures , nongraded and graded , Bouma A or AE divisio ns ; facies B - pebbly sandstone and co arse sandstone with or wi thout di sh 13 Fig ure 4. Di agra m showin g fa n facies assoc ia tions (aft er Walker and Mutti, 19 73 , Fig . 10 ) . See Table 1 for facies cl assific ation. 14 ...... BASI C FACIES GROUPINGS fACIES IN EACH GROU P ENVIRONM ENT ClASSIFICATION FACIES ASSIGNED TO EAC H ENVIRO NMENT I PROXIMAL· EXOTIC PROXIMA L DIST A L F,G A 1 ,AJ A 2 , A 4, B l B2 C,E D,G � ) J ? • SLOPE, I CHANNELS F,G SOME A1,A3 inner fa n MIXTURE OF A1,A3,G SOME F, E \ J \ ? /\ SUBMARINE FANS BASIN PLAIN middle fan C,D t B 2 ,A3,A4 WITH outer fan fan fringe A4,+ 2 ,C f D,C G THICKENING THICKENING UP SEQUENCE UP SEQUENCE ' D,G THINN � NG UP I HQUENCE � structure , beds 50 to 200 em thi ck , beds often ama lga ma ted , br oad er osional co ncave lower surface , sole mar ks , gener all y nongr aded ; facies C - fi ne- to co ar se-g rained sand stone , beds 20 to 150 em thi ck , mu dstone or silt stone interbeds , genera ll y even and par allel beddin g surfac es , sole marks , equivalent to Bouma ABCDE to AE di visions , grad ed ; facies D, Bo uma BCDE to CE divisio ns , beds laterall y persi stant and in the past have been referred to as "dis tal" turb idit es ; facies E - ver y fi ne- to me diu m grained sandstone , mu dstone in terbeds, beds 3 to 20 em thi c k, lenticular bedd ing , para llel bases and wavy tops of beds , gener all y nongra ded ; facies F - chaotic slump depos its, pebbly mu ds tone , all retransported depos its; facies G pelagic mu dstone , ma ssive bedding. The in ner fan is one channel charact eri zed by associ ations of the various facies A and B along with levee depos its, facies E, enc losed by pe lagic mu ds , facies G. The hig h channe l wall s pr evented the overb ank fl ow of tur bidi tes and resulted in facies G, pelagic mu ds domi nating the sedi me nts outsid e the channeled are as (N ormark , 1970) . The change in gradi ent in the midfa n locat ion causes a br anch ing sys tem of sm all vall eys and channe ls that are progr essi vely less incised (N elson et al. , 19 70) . Midfa n sedi ment s com pri se the Adams Canyon me asured section whi ch is nearl y 700 m thi ck . This section 16 is part of the upper Pic o For mat ion and is late Pliocene in age . It is com po sed of br oadly lenticular ma ssive sandstones , co arse- gra ined co nglomerate and sandstone of fa cies B and A respec ti vely wit h alternating plane-par allel strata of med ium to fi ne sandstones , siltstones and mu d stone of facies D, E and C (T able 1) . The orga nize d , re cu rr ent groups of thic ker beds of facies A and B that form mu lti storied sand bodies up to 117 m thick within the sec tion are ref erred to as megas equenc es (R icci -Luc c hi, 1975) . By definiti on me gasequences have sand /shale rat i os of greater than one and in this sec tion the sand /shale ratio often exc eeds 50 to 1. The sand /shale rat ios were deter mined by to talli ng the thic knesses of the in di vi dua l sandstone beds and dividin g that number by the tota l thi c kness of the re mai nin g mu dstone wit hin eac h in terva l. The aver age bed thi ck ness of mega sequences in Adams Canyon range fro m 22 to 88 ce nti m eters . These mega sequences are separated by sequences 47 to 203 m thick that are defined as having sand /shale ratios less than one . Sequences are ch arac terize d by thinly bedded , plane parallel strata that may be fou nd in minor am ounts wi thin the megas equence . A com mon tr end in mega sequences is a thinning of beds , ter med a posi ti ve cy cle , and a dec re ase in gra in size fr om the base toward the top (R icci-Lucc hi, 19 75) . These type s of megas equenc es have been in ter prete d as the result of filli ng of sub ma rine ch annels (N or mark 17 and Pi per , 1969) . They diffe r fro m pr ograd in g oute r fan depos its whi ch thicken upward , ref erred to as a negativ e cy cl es (R i cci -L uc c hi, 1975) . A mid fa n envi ronment has been in dicated for the assoc ia tion of facies of the type desc ribed above on the basis of lateral and vertic al stratigraph ic re lationships and paleoc urrent trends by Walker and Mutti (1973) and Ricci-Lu cchi (1975) . Fi ve mega sequences are found within the sec tion at Adams Cany on, all ch arac terized by overa ll thinning of bed thickness and dec re ase in grain size s upsec ti on . The deep- sea fan mode l of Ri cci -L uc ch i (1978) (Fig . 5) was appli ed in this study . These midfan sedi me nts were depos ited in water s bet ween 300 to 600 m deep on the basis of cor relations bet ween the same fora m ini feral spec ies found in these Plioc ene sedi ment s and the depth rang es they are found within pres ent- day offs hore waters (N atland , 1957) . 18 Fig ure 5. Enviro nm ental mo del of a deep - sea fa n used in the prese nt study (aft er Ricci Luc c hi, 19 78, Fig . 14} . 19 A: shelf B 1 : upper slope 82: lower slope C 1: inner fan C2: middle fan C 3: outer fan D: basin pl ain C: canyon Vp: principal volleys Vs: secondary volleys Cp: peripheral channels Aiv:inter valley areas r Separation scarps of submarine slides J Acc umulations of submarine slides 20 SEQ UE NCE I Hundreds of me ters of thinl y bedded turbidites oc cu r between the base of the me asured sec ti on and the junc tio n of Adams and Salt ma rsh Creeks (F ig. 3) . Sequenc e I is 84 m thi ck and for ms the base of the measured sec tio n . It is divided into three sub units IA , IB and IC . IA co nsists of near -chann el tur bidites and ma ke s up the bottom 5.5 m of the sec ti on . IB is ch annelize d sands co nsisti ng of thin to very thi ck beds that th in upward and extend upward to 47 m fro m the base of the sequenc e (m eter 47) . IC is ch arac terized by thin- b edded interchannel deposits that co ntin ue the thinning upward trend to mete r 84 at the top of the sec ti on (Fig . 6) . Sequence IA : Interc hannel The begin ning of the sec ti on is loc ated 25 m east of the inte rsec tion of Adams Can yon and Salt ma rsh Creek roads (Fig . 3) . The basal 44 m of the sec tion are depict ed in Fig ure 7 whi ch in cl ude s sequenc e IA and IB . See Tab le 2 for the key to the detailed sec tions . 2 Fig ure 6. Contin uous sands tone bed thicknesses for Sequenc e I, me ters 0 to 84 . The gra phs were pr epared by me asuring the thicknesses of eac h sands tone bed in Sequenc e I. Breaks in the gra ph rep resent co vered int erva ls. 22 p:) H p:) � H H 0 0 N 0 0 .-! 0 l[) 0 rl 0 0 N 0 0 .-! 0 l[) 0 .-! s tl s:: ·r-1 t:Jl Ul Q) s:: � tl ·r-1 ..c: 8 s tl s:: ·r-1 t:Jl t:Jl Q) s:: � tl ·r-1 ..c: 8 23 l!l H ..:ra:+aw l!l H L_________ ·---��--------�-----�- -- N (\"') 0 0 .--1 0 If) 0 .--1 s 0 s:: ·r-1 Ul Ul Q) s:: ...!>�: 0 ·r-1 ..c: 8 s 0 s:: ·r-1 Ul Ul Q) s:: ...!>�: 0 ·r-1 ..c: 8 C) H C) a:! H H 0 0 N 0 0 ...-! 0 lf) 0 0 N 0 0 .--i 0 I.(') 0 ...-! s u s:: ·r-l Ul Ul (l) s:: � u ·r-l ..c: 8 s u s:: ·r-l Ul Ul (l) s:: � u ·r-l ..c: 8 25 r------------------------------------ ------ () H () H 0 0 N 0 0 ...-! 0 L[) 0 0 N 0 0 r-1 0 L[) s 0 s:: ·r-1 Ul Ul QJ s:: ..lt: 0 ·r-1 ..c: E-i s 0 s:: ·r-1 Ul Ul QJ s:: ..lt: 0 ·r-1 ..c: E-i 26 TABLE 2 KEY FOR DETAILE D SECTIO N DI AGR AMS A. STRUCTURES B. TEXT URE --v- Load for m b Bou lder Sc our cb Cobble C'C7 !f Org anic ma ter ial p Pebble (w ood , plant, ch arc oal ) g Gran ule s Shell ss Sand -- Bi otur bati on struc ture Silt s - Lenticular , undulose or c Cla y wavy bedding _./L. Fla me struc ture (\f\) Convo lute lamina tio n z Par allel lami nation � Sm all-sc ale cr oss-s tratific atio n C. CONT ACTS Sharp , fl at Grad ati onal � Undulating D. DI RE CTION 270 - Pale oc ur rent direc tion 270 me asured from cro ss- bedding 27 Fig ure 7. A co ntin uous detailed sec tio n of sequenc e IA and me g asequenc e IB . See Table 2 for explanatio n . 28 l COLUMN METER SEQ. DIR. STRUCTURES TEXTURES �B fS H nl!_j �Q..OO�UlU l-4 • L -' IA Ill l� �..-. I"' _j. Ill [ ,. 1- IIIII - 3 I"' 1- l - --- - - � ... I � • � 2 ,.,:z:-� • • .- l I 280 � • --- - ------ ,_ __ ___ IA 29 I COLUMN _e=:::: � � � ···-: 0 • 0 0 • : \) ( • � .. I> 0 C::, 0 � .. e:::. . . .-:.... . - . . . ' .. I. -.-�:;..,;. iii;::: .. _.,· . . . ·r==== - -. p �,�� METER 8 7 � 6 � _...;..""' �-v:.-=-- � · · . =- 1 � -�--.-: _- 5 1 -. SEQ. DIR. STRUCTURES TEXTURES I�H'SH��N>1 l..o"Bc..o.o �en u I IB Ill 1- - • .. • 280 ----- ioi � I • • � 265 - TR TA � � 270 � - f- • lM • � 280 � IA ...____ 30 I COLUMN -- � . . . . . . . . 0 • Q . . I �- • • - -===- - - - � . . . . . . . . ·- - - - ;;--_--;: � ·. > � o � � r. . . � -..; 'D- . -� � � - �- - -...,....:.._ -=: � � � •.;.....:;:, ¥<=>�· · • - ,___ �� -v --=- cP - .... ,. ,. •= ... . .. �, . ' ·£7. . .-:�-.- o oC' • o co• a o o oc=:J o "o o ��._:_: �.J. ....... - ...... METER SEQ. DIR. STRUCTURES TEXTURES I? B r s � r � � N � l..c-e "' o.o.ccncnu 12 IB • • "' II 1- � � J � 1- I· � I• 275 I I I I..- I IHI - •"" 265 � 1- - 9 1- • IB l-8 31 COLUMN METER SEQ. DIR. STRUCTt.:RES TEXTt.:RES 16 IB 0 0 0 0 0 0 0 0 0 15 0 0 0 0 0 0 0 0 0 0 0 0 14 0 0 0 0 0 0 0 0 0 0 13 0 0 0 0 0 0 0 IB 0 0 12 32 t COLUMN METER �20 "",_,. -= � ,_ ., .� L - =-· • � � _.c:::: _ . 0 0 0 . 0 . . . 0 . 0 . . . 0 . 0 . 0 � t- � � . - LP =· ---'=-: o� o_.!. ; . . .&.....•. 1 � • E I • - � ::;. � �·- � ' . . 0 . . . 0 <::::> 0 ' - 0 0 . ' . 0 . ' 0 0 0 0 0 0 . 0 19 18 17 0 0 0 ' 0 o�l6 SEQ. DIR. STRUCTURES TEXTURES ?BtS �InN� l.o -5 "' c..occn:n IB • 1- � I I • • • I '21o � ""' � � 1- ""' 1- IB 33 0 0 0 0 COLUMN 0 0 0 0 • u . . � Q • 0 0 0 0 0 0 0 .o 0 METER SEQ. 24 IB 23 22 21 DIR. STRUC Tl"RES ;, B TEXTL.RES 34 .<> • a �· COLUMN , •• METER 28 27 25 SEQ. DIR. STRUCTURES TEXTt:RES IB 35 l COLU�1N � . - -- .� � � - .... �·-""� - .--: . _i.. c_O_.". c.!!..�· ..-. L . --:" ,_!. - . 0 . . ' . - '-' • � 0 � - � . · ·.� � _jf' ..- - � v - - 1-- - •. �· . - - � 2_� _ _._ -:: ' - . ' � , � 0 � � :___.:::: Ld�� -� METER SEQ. DIR. STRUCTCRES TEXTl.RES � s r s 11 � iii� l .o-: "' c...x;.:.n:..; ! I I I • I 32 I IB • � • 260 --- - ·� "' p. 31 � I • • �-'"" � � ---- � � 280 � r-!- "' = t- 2 9 • IB ·28 36 l COLUMN METER SEQ. DIR. STRUCTURES TEXTURES ?BfS � Hl N� lof?"3 o..oo � oo u � �� IB � I I I�YJ � f- 3 5 V '- --- " � � r�� - � - -= 34 _!/- ��;-� , -o-, • � . ..._ . "" '/ • _·<-: � :/ ../ , _!.. __... � ----� . ......... 33 ,.;;;_� � 1- � 0 c::::;::::::o ,?7 -=- - "" ii �- - • - I - � - . . . . � IB I :::;_ • � 37 r------------ I COLUMN METER SEQ. DIR. STRUCTURES TEX TURES ? B !f S � I � � N jl.c>"B"'" "' O.Omoou � ... � IB F= - . � """ I= - - - - - --r _j """ 39 • � � • � ...2_ 6( ---=-==--=- - ---- F= • I • 38 � '-!. 1- � �� . � i --- �= - 37 '1:::::::, Ill - ··� 1- . ---- 1- . • I l ��- ... 36 I ___, IB 3 8 ] I COLUMN METER SEQ. DIR. STRUCTURES TEXTURES ? B fS � U� �l.o"B "' 0..00 til ((.1 u -- 44 IB 1- 4 • � II � I � L 43 I "' r d . . I"' I I i= l 42 I - ! • : I t"' � f: I I _. 41 ·� f"D __ (§) � I'"' • - � I• r- 11 = _. I 40 IB 39 L__----------- ------------------- --------� Gr ain size and bed cha rac teri stics . Sec ti on IA is com posed of ver y thin- to thin- bedded often lenticular beds of mediu m sand and siltst one . The me di um sands are eit her mas si ve or gr aded siltst one . Many beds were observed to lense out wit hin a fe w me ters of the availab le outc ro p . Laminat ions, Bouma B, or cro ss- bedd ing , Bouma C di visi ons are very commo n. Structure s. The bottoms of the beds are fl at to gently undulating . Sc our in g was observed to oc cu r at the bases of appr oxi m ately a quarter of the beds and max imum re lief is 8 em but usuall y 1 to 3 ce nti m eters . The tops of mo st beds are wavy due to diff ere ntia l com pact ion. Orga nic mat erial was often obser ved in para llel and wavy la mina tions. Summ ary . This sandstone sequenc e is compo sed ma inly of Bouma BE and/or CE di visions , facies D and some Bouma AE and ABCE divisions, facies C (Fig . 8) . The beds beco me thicker upward near the ch annel-fill sedi ment s at me ter 5.5 . Sequenc e IB : Megasequenc e The first mega sequenc e is 42 . 5 m thi ck start ing at meter 5.5 where the sand to shale ratio first exc eeds 1 and ends at me ter 48 where the ratio beco mes less than 1. The sequenc e between me ters 5. 5 and 44 is depicted in 40 Fig ure 8. Sandstone bed perc entage for me ters 0 - 100 of section and ver tical sequence analysis of sequence IA . Partial stratigra phic colu mn shows per centage of sands tone deter mi ned by to talin g the thi ckne ss of all sands tone beds in each interval divi ded by re main ing thickness of mu ds tone . Layered co lumns show internal orga nizati on of section in to sands tone (w hit e} and mu dstone (bl ack } . Letters in dicate faci es int er pretation , see table 1. 41 ..:c: H H L{) C) I Cl C) C) H ttl H �--- �----------------------------------------------�� .--1 o--- 1--=- ___: -- ...L:... __..:.. __ _:_ ____ ;__ __ ....:.... -r-L.---- __..:.. -------=- ......J � 0 0 .--1 0 L{) 0 l 42 Fi gure 7. Gra in siz e and bed character istics . Sect ion IB is com posed of quite var ia ble thi ckne ss and sedi me nt types . Layers of pebbly sandstone to siltstone range fro m very thi ck- (214 em) to thinl y bedded (2 em) and have flat to undulating beddin g contac ts . Organized pebbly sandstones , facies A 4 (Ta ble 1) occ ur bet ween me ters 12 and 27 . Individual beds are ch aract erized by coa rse -t ail grading and rev erse grad in g especiall y near their bases . Ama lga ma tion between the pebbly sandstones as well as other gr anule an d coar se sand layers (Fig . 9) is co mmo n and the in ter venin g mud stone laye rs ar e co m pletely eroded and in co rpo rated into the beds as ripups . Rip ups of siltst one and sandstone are also common some ti mes up to 1 m in length. Where ama lga m atio n has not taken place the mud stone layers are hig hl y deformed and er oded as can be seen just above and below me ter 10 where the mu dstone layers ter minate in ripup zones . Sand injection struct ures and load pockets were obser ved at me ters 6, 7.2, and 22 .2 and are indica ti ve of the rapid rate of depos iti on of these beds . Beds of gr anule to sil t size sed ime nt range fro m thin (1-2 em) to thi ck (116 em) and the coar ser ma ter ial usuall y occurs in the thicker beds . They are found above and below the pebbly sands tones and are nor ma ll y gra ded or mas sive wit h occas ional reve rse gr ad in g . Very thin, 43 Fi gure 9. Ama lg am ation of pebbly sandstone layer s at me ter 14 .6. Top of section is to the right. No te change in grain sizes point ed out fro m gr anules in lower bed to sm all pebbles in upper bed . 44 45 lenticula r bedd ing occurs infre quentl y in the bottom two thirds of the sect ion. Structur es . Sc ou ring is very co mmon at the base of the coar ser grained beds and up to 27 em deep at the base of a pebbly sandstone layer . Loadfor ms were nearly as co mm on . The thinly bedded sandstone and sil t layers (6 - 60 em } are co mm only para llel to wavy la minated and/or cr oss -bedded as are the tops of a fe w of the medium - thick (90-100 em ) layers (Fig . 10 ) . Shell mat erial was obser ved in some gr anule to co ar se sand layers fro m meter 23 upward ; the shells are often ori ented conca ve upward (Fig ure 11) . Some exc elle nt examp les of fla me struct ures are found in thi s me gasequence, especially at meter 30 (Fi gure 12) and just above meter 35 where they attain 10 em of relief. These structure s usuall y for m in the fi ne sand to sil t upper port ion of a bed by loadin g of the coarse sand to gran ule ov er lyin g bed . The mediu m-grai ned sand bed at meter 35 (Fig . 13) conta in s an unusuall y thick defor med strata indic atin g that the layer under went plastic defor mat ion dur in g cr eep fl owage downslope . Summary . The bed thickness dia gra m (F ig. 6) for megas equence IB shows a thinnin g upward trend and a fini ng upward of grain sizes also occurs wit hin this section (F ig. 7) . The or ganized pebbly sandstones are in ter preted as facies A 4 and the thi nner gran ule to silt stone beds are 4 6 Fi gure 10 . Wavy bedding in 10 em thick silt bed at meter 27 .2. The top of the sect ion is to the right. l----��-� - 47 r----------------------------- ------ -- 4 8 Fi gure 11. Shell mater ial orie nted conca ve upward in mediu m - thick gr anule sand layer at me ter 32. 4 9 50 Fig ure 12 . Fl ame struc tures and loadforms of sev er al centim eters relief at me ter 30 , Fig ure 7. Top of the bed is toward s the top of the photo . 51 r------------------- --------- ----·· ;-; o � ; ;;:� ·. ·. :! ' /;�, '· � :� r; 'ti� � :..) ... . : 52 ,----------------- -- --- -- -- -- ------ --- --- -- - 1 I Fi gure 13 . Plast ic deform ation in thick me di um grained sand bed at meter 35. 53 ______ ________ __) 5 4 facies B 2 , C and D turb idites (F ig. 14) . These beds are in terpre ted as channeli zed sands to upper ch annel- fill as a channel was progr essi vely fi lled and abandoned . Sequence IC : In terch annel This sequenc e begins above me ter 48 where the sand/ shale ratio decr eases to less than 1 and cont in ues to meter 84 (F ig. 8) . It is co nsis tent with the trend of thin nin g upward sandstones that begins in mega sequence IB . Its rel ati onship to the chan neli zed sands and upper channel fill below appears to be in terchan nel charact eri zed by thickening upward mu ds tone layers that beco me me di um - thick (40 em ) to thick (100 em } at the top of the sect ion. Above IC the thick sands of megas equenc e II begin abrupt ly at meter 84 . Gra in size and bed charact eristics . The bed thickness of in d ivi dua l sand layers as well as gra in sizes continues to decrease bet ween section IB and IC (F ig. 6) . Sandstone thicknesses average 22 em in IB but decrease upward to 6 em in IC (F ig. 15) . Above meter 80 sandstone all but disappears and is re placed by thick mud stone laye rs wit h minor thin silt lamin ations cr op out to the top of the section . Boum a divi s ions BE, CE and BCE were obser ved to occur in 56 percent of the 136 sand layers me asured in this se ction and whi le beds with Bouma A divi sions at the 55 Fi gure 14 . Ver tical sequence analysis of me gase quence IB . Refer to Table 1 and Fig ure 8 for explanatio n . 56 Ul -....) H Q) 0 1 % san d 100 I I I � 50 s 0 . . 100 I 10 - - IB �-� c B 2 D A 4 B 2 3 = ------------------ ------------------ c B 2 - A 4 c A 4 B 2 - C C-D B 2 C-D c A 4 - B 2 D C-D D c [1m C-D B 2 c D B 2 - C B 2 D c B 2 c B 2 20 A 4 35 1 - _ )_ Fi gure 15 . Detaile d sect ion of a portion of IC , int erchanne l tur bidit es . See Table 2 for explanation. 58 I COLU1-!N METER SEQ. IC 52 J �· � -.,.- " t- 51 �. � .� . . .. . 0 . • �� · 50 IC DIR. - 275 STRUCTURES TEXTU RES ?B!fsH nN�.o r= "" �� I= 1- .. ��- � � I II �� .0 "' U O.. COU )VlU I • I• I I j• !• ·- L I J1 ' 59 base co mpr ise the re m ain der . Str uctures . Contacts were usua ll y fl at wit h fe w undulatin g bottoms fro m min or sco ur in g (2 em ) • Par allel lamin ati ons , wavy beddin g and cr oss -bedd in g (Fig . 16) are abundant in this sect ion in dicati ng decre asin g and var ia ble current speeds (Cro well, 1966). Organic ma terial occurs in the la minated in ter vals . Ama lga ma ti on of sand layers is rare . Summary . The thinning upward of sand layers and associated in crease in the thickness of shale layers throughout thi s section indic ate continued channe l ret reat from this area and cons equently thin ner and thinner inter channel deposits. Most of the tur bidites lack basal Bouma A divis ions and start wit h eit her divis ion B or C, facies D, and are in terbedded wit h some turb idites starting with Bouma divis ion A, facies C. 60 Fig ure 16. Facies D in terc hannel tur bidit es at meter 53. Lower bed is par allel la mi nated silt stone , Bouma B, ca pped by mud stone , Bouma E divis ion. Upper silt bed is parallel lam in ated in it s basal portion and is trans it ional to slightl y wavy upper portion , Bouma C and is also ca pped by mud stone . 61 .-------------------- -------------------------------------------- ------------- 62 --- ·-- - · --- ---- ·- ---- - -- --- ----------- ------------ -- ----- � SEQUE NCE II Sequence II cons ists of three subunits, II A-C . II A, a me gasequence begins suddenly above the inte rch annel deposits of IC just above me ter 84 and cr op out to me ter 100 where there is 5 m of co ver . II B, inte rchanne l depos its, start at me ter 105 and con tin ue to me ter 140 . At that location near-c hannel deposits charact eri ze the third subsection , IIC to me ter 154 . Sequence IIA: Megasequence The sand/shale ratio is ver y hig h , 7 to 1 co mp ared to 1 to 4 for the in terchan nel deposits of sequence IC below. Grain size and bed characte ri stics . This sect io n is compo sed of me diu m- to fi ne-grained sand in beds for the ma in part 40 em to 154 em thick (F ig. 17 ) . These sand- stone beds alter nate with thin sandstone layers , and very thi n sil tstone and silty cl ay beds that some time s are ! I fissil e . The sandstone beds are ei ther mas s ive or display I slig ht normal grading (Fig . 18) . Bedding cont acts are I __ §_� � ��---- -- -l Fig ure 17 . Ama lga mated ma ssive mediu m- to fine grained beds of facies B 2 bet ween meter s 84 and 94 which are chara cteristic of me gasequence IIA . The top of the section is to the left. 64 65 Fig ure 18 . Conti nuous de tailed sect ion of me gase quence II A from me ter 84 - 94. See Table 2 for ex planatio n . 66 � COLUHN METER SEQ. DIR. STRUCTURES TEXTURES 1� 1 !f s � r � � N � l..c� o.. on�oou IIA I � . - 87 86 -= ._ -......;_..-;.__ � I :.. g .. . . .-,-. - � - -· - - • 1- -""- i I IIA 84 67 COLUMN · �.� .� c:::::;-::--:7 METER 92 91 90 - --, ! SEQ. DIR. STRUCTU RES TEXTt.:RE S IIA IIA 68 L----------------------------- ----------------- --------- ----------------� � COLUMN METER SEQ. DIR. STRUCTURES TEXTt:RES I? B f S � H � N � l.o"fl c..oo � "'u i - 94 I .\. IIA """" � � • • � r-:: � 93 • • - ..-· � l 0 • • • • � � I generall y fl at with minor sc ouring and occas ional load for ms of 1 to 3 em relief. However, ripups of underl ying mud stone and siltstone beds fro m a fe w to 75 em in le ngth and 10 em thic k with long- axis im brication were noted . Ama lga mat ion of sandstone beds is common . Structur es . Par allel la minat ion and cr oss -bedding was found in many ver y thin sil t beds and also in the sil ty to ps of the nor m all y grad ed , very thic k mediu m grained sand beds . Organ ic mate rial is fairl y common and , somet ime s associated with par allel lamina tions. Summary . Section II A rep resents at least 16 m of channe l sands of facies B 2 , ma ssive sandstone wi thout dish stru ctures along with some fa cies C and D tur bidites (Fig . 19 ) . The ov era ll bed thi ckne ss data (Fi g . 20) indi cate a thinning upward sequence charact eristic of midfa n channels. Sequence IIB: Inter ch annel The co ntin uous sequence II B cr op out for 35 m (mete r 105-14 0) . The sand/shale ratio dec lines to 1 to 4 in this se quence . Grain size and bed charact eristics . Bed thic knesses (F ig. 21) and grain sizes continue to decrease above section IIA. Sect ion II B (Fig . 22) is com posed of thin bedded fine sands , siltst one s and silt y mu ds tones. ________________ 7ol Fig ure 19 . Vertical sequence analysis of rne gase quence IIA. See Fig ure 8 and Table 1 for ex planation. 71 u 0 Cl I N N u o:1 o:1 u .::X:: H H � - l t--- �- ---1 'd �- [/) a.. o - - u H o:1 H u .::X:: H 0 ---�----��--�--�--��.�--��--------------�4 0 0 r-l 0 11') 0 I ' I Fig ure 20 . Sands tone bed thickness data for me ga sequence II A. 73 .:r.: H H 0 0"\ 0 0 N 0 0 r-t 0 I.() s 0 s:: ·r-l Ul Ul Q) s:: ...!.:! 0 ·r-l ..c: 8 - ]_ 4j Fig ure 21. Contin uous sands tone bed thickness for me ters 10 7 - 126 , sequence II B , in ter channe l envi ronm ent. 75 1]:1 H H 1]:1 H H ----- I 0 0 N 0 0 r-l 0 1.{) 0 0 N 0 0 r-l 0 1.{) 0 r-l I 6 -� Ul Ul � ·r-1 � 6 -� Ul Ul � ·r-1 � 76 It! H H 0 0 N 0 0 r-1 0 If) E1 () I=: ·r-1 (J) (J) Q) I=: ..!<: () ·r-1 ..c: E-1 77 Fi gure 22 . Detailed section of int erc hannel turb i dit es of a portio n of sect ion II B fro m me ter 114 .5 - 116 . See Table 2 for explanatio n . 78 r------- -- - -- � �- - -- - � - - �� - �-�� -�� - -��- - -��-� � � COLUMN METER SEQ . DIR . --- 116 IIB l I 245 --- • 115 l - IIB STRUCTURES �BY'S� f� �N� I ' TEXTURES ..0 <Jl ..Ot,J O.. ODCilCilU I � ] 79 Muds tone layers wit h thin la mi nations 1 to 2 mm thick are usuall y as thic k or thicker than the coa rser gra ined layers and beco me thicker toward the top of the section . Red mud stone s fro m 1 to 3 em thi ck comm only are inter bedded with or top gray mu ds tone laye rs . The fin e sands are gra ded or are ma ssive li ke the siltst ones . Fi ne sands and siltstones less than 3 em thick were noted to lense out in the lower part of the sequence but mo st beds have good lateral co ntinuit y . Beddin g contacts are fl at with sc our ing of 4 em re lief unc ommon . Structur es . The ma ss ive and graded fi ne sands to silts cons isti ng of Bouma divi si on s AE and ABE , faci e s C make up 52% of the 120 beds me asured in sequenc e II B . Par allel laminatio n and cross -bedd in g are also co mmon in the silty to sil ty mud stone beds of Bouma BE and BCE di visions , facies D, in the rem ainder of the beds . Summ ary . Inter bedded fi ne to very fi ne sandstone , siltstone and mud stone show a decrease in bed thi ckne ss fro m thin- to very thin-bedded and the avera ge thickness is less than 5 em wit hin this section . Facies C and D are interbedded in nearly equal amo unts upsection . The thin , fi ne- grained sand lenses noted in the lower par t of the section may have originated from dilute ove rbank depo sits filli ng shallo w depre ssions (Mut ti, 19 75) . Section IIB is co nsid er ed repres entati ve of in terchan nel turbidites deposited in creasingly further and further fro m a midfa n dist r ibutary channel. 80 I I Sequence II C: Inte rchan nel to Near -C hann � l I Sequence II C is co ntin uous wit h II B belo w and is located bet ween me ters 140 and 154 . It differs fr om the siltst ones and mu dstones of the upper part of II B by the in trodu ction of mo re frequent and thicker sandstone beds (Fig . 23) as well as pebbly sandstones (Fig . 24) . It is dif ferentiated from the overlyi ng me gasequence starting at mete r 154 by its sand/shale ratio which is just under 1. Gra in size and bed charact eristics . Sect ion II C co ntain s thin (30 em) to very thin (1 em ) beds of pebbly sandstone , fin e sandstone , siltstone , silty mu ds tone and mu dstone (Fig . 24) . The pebbly sandstone s (Fig . 25) make up the thickest laye rs with the ma xim um pebble dia me ters 2 em and the average size 1 centi me ter . The pebbles are subro unded and are com posed of li thifi ed sil tstone . The grave l port ion was found to vary fr om bein g found unif o rml � thr oughout the thinner beds (10-1 5 em ) to concentrated in the bottom two- thirds or cen tral port io n of thicker beds (20-31 em ) . Rounded , long-a xis im br icated clasts also co mposed of sil tstone up to 7 em in length are found in the cen tral port ion of some of the thicker beds along wi th mu dstone ripups . The grain size s of the ma trix ma terial range fro m me di um -g rained sand to cl ay and are poor ly 81 Fig ure 23 . Sands tone bed thickness for sequence II C. 82 r------------------------------------------------------------ --- - -- ----- (.) H H .:r<:qa w 0 0 N 0 0 .--i 0 11) s tl I=: ·r-1 UJ UJ Q) I=: .!>I: tl ·.-! ...c: 8 83 Fig ure 24 . Detailed sect ion diagra m for a portio n of section II C , int er channe l turb idit es fro m met er 140 - 142 .7. 84 r---- - - -- --- - -- -- -- -- - --- - -- ---- --- -- --- - -- - - -- l COL{]}IN .. - 0 <::::> 0 0 ·o· . _ . l.:_ - o_:o" . • ."'•;o. -- - � � 0 - . " . . 0 ., • .,CI *'• o" 0 o D 6�: -oo o o. •o 0 0 .- - >..!...!. � .- ·� ' � Q o C> 0 0 G 0 0--"- L METER SEQ. DIR. IIC � = 142 141 IIC 140 STRUCTURES TEXTURES I I � I i 85 Fig ure 25. Twent y em th ick pebb ly sandstone bed at me ter 142.5 . Top of the sequence is toward the top of the photo . Over lying fine-gra in ed sand to silt y bed in basal graded (B ouma A) , la mi nated siltst one (B ouma B) in central portio n and convo lute bedding (B ouma C) in silty top . Mudstone (B o uma E) ca ps beds . 86 87 sorted . Sc ouring of 2 to 3 em relief usuall y occurred wi th the pebbly sandstones and at the base of some of the fin e-grain ed sands . The fi ne- gr ain ed sands were all less than 15 em thick and the siltst ones , silt y mud stones and mu dstones are less than 8 em thi ck . Red pelagic mu ds tone often capped gra y tur bi dit e mud stone layers . All the thin beds have fl at bases , fairl y unifor m thicknesses that can be traced latera ll y acr oss 15 m of avail able outc rop . Structur es . Para llel la mination was co mmon in the tops of beds of all gra in sizes espec iall y the fi ne sil ts and silt y mu dstones . The very thin (3 em } sil t beds were some tim es cross -bedde d as were the thin silt y tops of one pebbly sand layer . Most Bouma di visi ons cons ist of AE , ABE , ABCE cou plets of facies c. Summa ry . The tra nsition to coarser grain sizes , thicker beds , ripups of mud stone and cobb le siz e clasts in dicates the presence of a distr i butar y ch annel. The Bouma divisions are mainly of facies C (T able 1) , proxima l turb idit es . 88 SEQUENCE III Sequence III is divi ded into four subunits III A-D . III A is a mega sequence which begins at me ter 154 and crop out to meter 173 where there is 4 m of cover . Very thin bedded turb idites of facies D and C make up sequence II IB which begins at me ter 177 and extends upward to approx i ma tely meter 300. Sequence IIIC crops out from me ter 300 to meter 354 and conta ins hi ghly la min ated sil t and silty mud stone of facies D, distal tur bidit es . Above , in sequenc e IIID, facies c, prox i ma l turb idi tes , are found to meter 376 where mega sequence IV begi ns . Sequence II IA : Megasequence The third me gasequence is do minated by pebbly sand stones and other co arse -gr ained beds . The sand/shale rat io beco me s very hig h , 70 to 1. Gra in siz e and bed character istics . Megasequence II IA cons ists of thick (80 em ) to ver y thic k (125 em ) layers of pebb ly sandstone which are ma ss ive in the bottom part of the sect ion and are no rma ll y graded from basal 89 pebbles to sil tstones in the upper la y ers of the sec tion (Fi g . 26} . Maximum pebble dia meter is 1. 8 em and the average size is approxima tely 0.3 em . Pebbles are co mpo sed of quart z, red chert , vo lcanic rock , gnei ss and gran odiorit e set in a fin e- to coarse-grain ed sand ma trix. Mudstone and siltstone ripups up to 50 em in length, often wit h their long-a xis im bric ated , occur throug hou t the sect io n (Fig . 27) . Inter bedded wi th the pebbly sandstone s are gran ule and co arse- to fi ne-gr ain ed sandstones fr om 10 to 60 em thick which have slig ht norma l grading and occa si ona l strata of granules or pebbles for mi ng thin zones of rever se grad ing . Nearl y ever y bed is ama lgam ated , as a result mud stone layers are rare and scouring is common ; up to 70 em of relief occurs at the base of one pebbl y bed . An examp le of a deformed mud stone layer that was near ly detached and ripped up occ ur s just below meter 162 (Fig . 26) . Many of the beds prove to be hi ghly lenticular and thicken latera lly as much as half a me ter over 15 to 20 m of expo sed outc ro p . Stru cture s. Par allel and wav y lamin atio n , cr oss bedding and co nvo lute-bedding were seen in the infrequent very thinly bedded sil t layers and in so me of the fi ne grained sand to sil ty top s of the thicker laye rs . Load for ms and fl ame struct ures of several cen ti meters relief as well as sma ll loadpoc kets were common bedding contact fe atures throughout mega sequence III A. Dish struct ures up 90 Fig ure 26. Conti nuous detailed sect ion diagram of me ters 158 through 173, me gasequence III A. See Table 2 for explanation . 91 ��--- ! = " ..... ... . · .. .. .. .. COLUMN •• .. METER SEQ. DIR. II IA 16 1 16 0 159 STRUCTURES TEXTURES C/l Cl.O.O tll UJU 92 COLUMN METER SEQ. DIR. STRUCTURES TEXTURES III A 164 163 162 III A 93 I COUJNN ,- ·� , "' · "' . , , . , "' r.-. .� � . . ' -:' . � · �-..,...-�� ..___... .. � . . �· � �m f / { l )· / . . , .....__,;,_- � - � ------------- . ...._________.. � ----..:....-- . '---------" ------------- . ---------- '--.-----' � . 0 . . ·=·= 0 ·- ' . . 0 0 . . . . . � -"- ' · -=-- • . . . . , : . . . . . . . !:!._ •• . • . . . . . . ' . . . 0 . . . . . ' . 0 0 . 0 . . . --!.. �· . ____.;- . --:::::----- - . � -.._____;...---, . . . . . . � METER SEQ. DIR. STRUCTU RES TEXTURES ?Brs _tr �lN>i (..c� o.. o.o � rJlt.J III A - -169 • • • I"' -168 - -16 7 � I 166 III A 94 � --- 0 �- = • o . COL illiN = 0 - � = 0 0 0 0 o -o ..,.. "-' o 0 0 0 0 0 0 0 0 0 0 0 0 0 - = · - 0 �· C? . . METER SEQ. DIR. IIIA 171 170 IIIA STRUCTURES TEXTURES --- � ! 95 Fi gure 27. Massi ve pebbly sandstone layer 70 em thick wit h ripups of siltst one at meter 159 . Currents tr aveled from the left to the right. 96 97 to several centimet ers in lengt h and 1 em deep were seen in se veral medium - to fi ne-grai ned sandstone beds (Fig . 28a) . In a very thick (122 em) sandstone bed dish struc tures are trans it ional to fl uid escape pipes (Fig . 28b) indicatin g that they were for med by a ra pid dewater in g pro ce ss. The minor am ount of or ganic and shell mater ial observed was assoc iated wit h paral lel la minations and pebbly sandstone re spectively. Summ ary . Megasequence III A is co m prised of cy cl icall y thin nin g upward layers (F ig. 29) of or ganized pebbly sand stones , facies A 4 , med ium- fi ne- to coarse -grai ned sand stones wit h dis h struct ure , facies B 2 , and wit hout dis h struc ture , facies B 1 , along with minor am ounts of facies C and D (F ig. 30) . This mega sequence is int erpreted as a midfa n channe l that became inf ill ed and aban doned. Sequence III B: In ter channe l This sect ion is ma inly very thin -b edded , fi ne- to med ium -gra ined sandstones , siltstones , sil ty mud stones and mu dstones of facies D and C. It has an overa ll thi ckne ss of 123 m. Grain size and bed characte ristics . Sandstone bed thi ckne ss and average grain sizes are less in III B than II IA (Fi g . 31) . The sandstone thicknesses average 33 em in III A but drop to just under 2 em in III B . Massi ve sil tstones and silt y mud stones less than 4 em thick 98 Fig ure 28 . a) Bo ttom photo . Dish struct ures to ri ght of hammer in thick (122 em ) me di um- to fi ne-grained sands tone at me ter 168.5. b) Top pho to . Cl ose up of top of the bed seen in top portion of photo below showin g fl uid escape pipes in convo lut e bedding . 99 ,------------------------------------------------------------------ ------ ----- --- --------� ., ;.-'!'·:�·� •J .. 10 0 Fig ure 29 . Sands tone bed thickness of me gasequence III A from me ter 158 - 170 showin g a thinnin g upward tren d when com pared to overl ying bed thickne sses of sect ion III B (Fig . 31) . 10 ��- ---�---- -l � H H H .:r<:q.a rn 00 l() r-1 0 0 N 0 0 r-1 0 l() s () � ·.-I [J) [J) (]) � � () ·.-I ..c: 8 102 -- - -- ·-·------ --· ---· ----- --·--· ----------- -, Fi gure 30 . Vertical sequence analysis of me gase quence IIIA. See Table 2 and Fig ure 8 for explanation. 1-' 0 *"' lo-1 Q) 2 17 -1-l 15 Q) s 14 105 170 / ) ' B 2 B 1 B 1 B 2 B 1 B 2 A 4 2 4 2 4 [1m Fi gure 31. Sands tone bed thickness for me ters 190 to 19 2 of in ter c hannel sequence III B . 105 0 L{) E t:!l () H H I=! H ·r-i UJ UJ Q) I=! � 0 0 r-i ·r-i .c 8 r-i 0 C) 0\ r-i r-i .:ra:ta w 106 predo min ate wi thin sect ion III B and the rare beds of uni form to gr aded mediu m- to fin e- grained sandstone are alway s less than 7 em thick (F ig. 32 ) . The beds are separated by equall y thick or thi cker layers of gray mu ds tone somet imes wi th paper thin sil t la minati ons. Red , pelagic mu dstone 1 to 4 em thick c omm only cap or are in terbedded with the gre y mud stone . Bedding conta cts are fl at with minor sco ur in g of less than 2 em rel ief at the base of the med ium - to fi ne-gra ined sandstones . Some of the very thi n bedded siltst one laye rs were obser ved to lense out latera lly over the 2 to 3 m outcrop widt h . Ama lgam ation was ra rel y observed . Structure s. Silt stones and the silt y top s of gr aded sandstones are often par allel la minated or cr o ss -bedded . Si xty percent of the coar se-g ra in ed beds start wit h Bouma divi si on B or C, facies D and 40 perc ent begin with Bo uma A divis ion, facies c. Summ ary . Section III B cons ists of in terbedded very thin turb idites of facies D and C that beco me thinner upwards fro m III A and are interpreted as interchannel deposits. Sequence III C : In terc hannel Sequence III C is continuous wit h II IB below and II ID above . It starts just above meter 300 and extends upwards 107 Fig ure 32 . Detai led sect ion diagra m for a portio n of sequence IIIB, int erchanne l turb i dit es fro m me ter 19 0 to 191.9. 108 I COLUMN • l �� METER SEQ. DIR. STRUCTURES TEXTURES 1� 8-'f'S� H �N �I.<:>"S o.oc � ""' II II B - - • - il ! ·191 235 � ':: / � . - 190 -+I=-:I:..::I:.::B+---+-+-+-+-+++++++++-+-+--H• -- -- 1 I i 109 to meter 354 diff ering fr om the interchannel depo sits above and below it by being co mpo sed near ly exc lusively of facies D. Grain siz e , bed cha racter istics and structure s. Grain sizes and bed thicknesses decrease fro m sequence II IB to III C. III C is ma inly gre y and red mu ds tone with some sil tstone and sil ty mud stone . Bed thickn esses are al way s less than 4 em thick with fl at beddin g cont acts and good lateral cont inuit y that can be traced over 20 m of available outc rop . Near ly all beds begin wi th para llel 1 lami nations, Boum a B or cr oss - bedding , Bouma C divis ions, facies D (Fig . 33) . Summary . Sequence IIIC shows a slight thinn ing and fi nin g upward s character in re lation to III B belo w and cons ists al mo st entire ly of parallel lamin ated sil tstones and silt y mud stones of facies D, distal tur bidit es . It may re pre sent in terchan nel tur bidites depo sit ed by dilute 1 turb idit y currents further fro m a distr ibutary ch annel than sequence III B. Sequence II ID : In terc hannel Sequence III D continues above III C at me ter 354 and crop out to me ter 377 where me gasequence IV abrup tl y .b egins. Gr ain si ze, bed charact eristics and struct ures . A 11 - ----- --- -- -- - --- --- -----' Fig ure 33 . Photo at meter 344 of sequence III C, fa cies D in ter channel turb idi tes . Very thin-be dded (4 ern) siltstone bed wit h wavy bedding and fain t cros s bedding (B ouma C) in terbedded wit h thic k mu dstone layers (B ouma E) co mpr isi ng sequenc e III C . 111 112 r sli ght increase in grain siz e and bed thi ckne ss occur : in l sequence III D and ver y coar se- to fi ne-grain ed sand and siltstone are found in beds up to 15 em thic k . The sand/ shale ratio incr eases to just unde r 1 in com parison to 1 to 3 in sequence III C. Bedding co ntacts are fl at and minor sco uring is pres ent at the bases of some sandstone la y ers . Beds appear to have unif orm thi ckne ss ove r 50 m of exposed , though large ly inaccessibl e outc rop due to its steepness . Exami nation of available outcro p reve aled that Bouma di visi ons ABCE, ABE and ACE of facies C predo minate and Bouma divisio ns BE , facies D occur in minor am ounts (Fig . 34) . Summ ary . Sequenc e II ID is ma in ly com posed of fa cies C, pr oximal turbidites in ter bedded with minor amoun ts of I I I facies D, distal tur bi dites that show a slig ht increase in\ both grain size and bed thi ckne ss rela tiv e to III C below. Though sequence III D is still repre sentative of inter- I I ! : channe l depo sits it seems to indi cat e a deve loping channel I i source that begins abru ptl y (F ig. 35) wi th megas equence I IV , the thi cke st ch anneli zed sand body in the section at \ me ter 377 . i i I I 113 1 I Fig ure 34 . In terbe dded sandstone , siltst one and mud stone of interchannel sequence III D . The top of the section is to the right. 115 Fig ure 35. Cliff forming exposure of me gasequenc e IVA abrup tly overl ying thin - bedded tur bidit es of sequence II ID jus t to left of geo logy student Gin ny Wong . A sc oured contact bet ween ma ssive co arse-g ra ined ama lga ma ted sandstones is being point ed out by her . Note the broadly lenti c ular nature of these beds as they thicken fr om the upper left to the lower ri ght hand portio n of the photo . 116 r------------------------- -��--�--� -�--� 117 SEQUENCE IV Sequence IV begins abru ptl y wit h med iu m-thick to 1 very thic k beds of pebbly , granule and coarse- to fi ne gra ined sandstone of megas equence IV . Sequence IV is divided in to thr ee subunits which dem onstrate a thinnin g and fi nin g upward sequence indi cat ing a progr ess ive change fro m channe l depos ition , IVA, to upper chan nel- fill , IVB , and overbank and interchannel deposit s , IVC . The thick ness of each uni t is approxi m ately 117 m for A, 16 m for B and 77 m for unit C. 1 Sequence IVA : Megasequence Sequence IVA is the thickest mega sequence studie d within the section conta in ing the thickest beds (485 em ) found wit hin the entire measured sec tion. IVA is ma de up of 117 m of or ganiz ed pebbly sandsto nes , facies A 4 , ma ssive gran ule to fi ne-gra ined sandstones, fa cies B 1 , B 2 as well as facies C, prox ima l tur bidit es . These layers for m a thin ni ng (Fig . 36) and fini ng up\va rds tren ds . Load defor ma tion and the effects of sco uring are the ma in structures in these roc ks . 118 Fig ure 36. Contin uous sand s tone bed thickne ss diagra m for me ters 378 to 493 , me ga sequence IVA . Breaks in the gr aph repre sent co vered int er vals . 119 0 l{) ""' � H � H 0 N ""' 0 0 N 0 0 r-1 0 1.{) 0 r-1 0 0 N 0 1.{) 0 r-1 s u s:: ·o-i Ul Ul Q) s:: � u ·o-i ..c: E-t 120 � H 0 00 -=::!' 0 0 1.() 0 0 N 0 0 r-1 0 1.() s u !=: ·r-1 [I) [I) Q) !=: � u ·r-1 ..c: E-t --- - --, I 1 2 1 r- -------- -··- --- -- -------- ----- ·-�-·--· 1 Grain size and bed characteri sti cs . Thick {12-105 em ) i to ver y thic k {485 em ) beds of pebbl y , granu le and coa rse Ito fi ne-grain ed sand abru ptly overlie the intercha nnel I I ! deposits of sect ion III D (Fig . 35) . These beds are usuall y � no rma ll y graded to fi ne-grain ed sand to sil t tops . Layers •o f pebb les , gra nules , and coar se-grain ed sand co mmo nly ·form reve rse grad in g wi thin beds greater than a me ter :t hick . The lenticular nature of these beds ove r hundre ds :o f me ters of outcro p is well expre ssed in a cliff exposure perpen dicular to strike (Fig . 35) . Beddin g conta cts are undulating with sc ouring (maxim um re lief of 25 em ) oc- cu rring at the base of nearl y every bed . Inter vening mu dsto ne lay ers are rare and hig hl y sc oured and de for med where they do cro p out (see me ter 384.3 , Fig . 37) . Near ly every bed is ama lga mat ed and on ly the change s in grain ·sizes rev eal the undulating bedding conta cts . Thi s result s in a 22 :1 sand/shale ratio . Mudstone and siltstone cl asts (2-30 em ) , often im bric ated , are co mmon and occ asional ripups ove r a me ter long occur (Fig s . 38 and 39) . Ig neous rock fragme nts , chert and charcoal fragment s are less co mmon and usuall y less than 3 em in leng th. Structure s. Loadfor ms and fl ame struct ures of several cen ti m eters relief are very co mmon along basal con tacts and oc casionall y have 25 em re li ef. Load pockets of coarse-gra ined sand or gran ules were also noted . Par- allel la mi nations, wavy beddin g and cross -bedding occur 12 Fig ure 37 . Contin uous detail ed sect ion of a po rt ion of megas equence IVA from me ter 378 to 385.8. See Table 2 for explanation. 12 3 COLUMN METER SEQ. DIR. STRUCTURES TEXTURES IVA 381 380 IVA 124 - --- - --- ----- -- - - - - 0 COLUMN METER 385 383 SEQ. DIR. STRUCTURES TEXTURES IVA 125 �------------------------ ---- -- -- ---------- --------- -------------- ---� Fig ure 38 . Multistor ied, ama lga mated bod ies of me gasequence IVA at me ter 390 . Note hammer beneat h me ter mark for scale . The top of the sec tion is to the left . Large ca vit y also beneat h me ter mark is weathered out mu dstone ripup approx imate ly 1 m long. 126 1 2 7 Fig ure 39 . Sketch of large siltst one and mud stone ripups at me ter 490. 1 2 8 .. ') 0 • 0 0 ) • 0 • �· 0 • . . · , .. .... : : - "' · . · : . . ) :� · · ) . • 0 ) • ) 0 0 ) 0 • • 0 • ) 0 0 ) -� .. 0 0 0 0 L.-- -� �- 1 2 9 r- - ---- -- ---- - --- ------- ----- ... --··-· ------ -------- ------- ------- ---- --------------- -, l in the silty top several cen ti me ters of many norm all y l graded beds . Shell mat erial , usually conca ve downward was ! I !o ft en associated wit h gr anule portions of beds . Dis h i structure s, several ce ntimete rs in length and 0.2- 0.3 em deep occur at me ter 385 and 451 in the top half of me diu m- to fi ne-grain ed sand (Fig . 40} . Summary . Thic k to ver y thi ck sandstone beds of facies B 2 , ma ssive sand wi thout dish structure , facies B 1 , .m ass ive sand wi th dish structure , with minor am ounts of facies A 4 , orga nized pebbly sandstone and facies C, pr oximal tur bidites make up mega sequence IV (Fig . 41} . The first cycle of very thick beds bet ween me ter 378 and 41 0 culminates in several beds 2 m thick or greater which then thin upward to me ter 435 wher e a 3. 5 m thi ck bed starts the next thin nin g upward trend . The thinning upward trend cont inue s to mete r 470 where a 4.85 m thick bed is noted (F ig. 36} which begins the last thinnin g upward cycle to the top of IVA . Sequence IVB : Upper Channel- Fill Sandstone/shale ratio , bed thi ckne ss and grain sizes dec rease fro m IVA through IVB as prox ima l turb idit e facies C sandstones dominate for the next 16 m in ter val. Grain size, bed charact eristics and structure s. Nor- ma ll y graded beds of med iu m- grained sand to siltstone I I 1301 �-- ·-- ... ---· -�-- -�--� ----··· ·- ···- ··- ----·-·- ---·-· ----- -·----------· ·- ------- .J Fig ure 40 . Shallow dish struc ture s at me ter 385 of me gasequence IVA . 131 I I L __ _ _ Fig ure 41. Contin uous vertical sequence analysis of me gasequence IVA . See Table 1 and Fi gure 8 for explanation. 133 � -�9 0 ! I 1-1 ()) .j...J ()) s I . % sand I I I 100 I ·II II . . II I IVA 3 78 I> · · ·. ·. · . . · J I I-' w ol:>o 3 9 1 A ) B 2 B 2 r I I ) A 4 B 2 B 2 B 2 c IC I I B 2 ) i B 2 �I � =4� 3 /� ) 3 9 8 l ) 3 9 2 A 4 c B 2 - C B 2 B 2 c B 2 c B 2 c 4 1 7 B 2 410 I I [1m -- J H (]) .jJ (]) s 0 100 I % sand 1 I I I 4 go,.- - --,- ____:. � 378..L-- " - - - --:.&.1 IVA B 2 430 420 B 2 42 X 1 B 2 A 4 A 4 ) B 2 l 450 44 B l c A 4 B 2 A 4 c A 4 A 4 I A 4 I 1-' w "' )...j (1) +J (1) s 0 1 % sand 490 I I I 378 ...L: ·_ .:.___ __ -1.1 IVA B 2 460 � - -- ....... B 2 I t c c c B 2 c B 2 c c B 2 470 4 2 A 4 I I I I 8 2 I I B 2 I I 488 480 J 2 2 A 4 A 4 c A 4 B 2 [1 m N '<:!' '<:!' u u m� u � u 0 ---�--------�--��----------�----------��----� 00 r C"") 137 vary ing fro m very thin- (5 em ) to thick- ll20 em) bedded , usuall y wit h in terve ni ng mu ds tone layers , in dicat e a tra nsiti on fr om the channeli zed sands of IVA to upper channel - fill deposits of IVB . Beddin g cont acts are mo stly fl at wit h min or scouring (less than 3 em relief) . Load forms are rare within IVB and are only found where sand stone beds are ama lga m ated . Rip ups cons ist ing of mud stone clasts (2 em ) are inf re quent and found only within the thick- bedded sandstones . The silt y and silt y mud stone tops are ofte n para llel la mi nated and/or cr oss -bedded and cons ist of Bouma divis ions ABCE, ABE , ACE and AE , charac teristic of facies C, proxi ma l tur bi dit es . A 2 rn thick sl ump struct ure , fa cies F, wi th hi ghly dist urbed beddin g was found at meter 497. It was pro bably for med by local slump ing off the edge of the banks of the channel. Summa ry . The decre ase in bed thickness and grain siz e along wit h the increased amo unt of traction struct ures ' (B ouma B and C di visi ons ) in the tops of the sandstone beds cha racte rize IVB . These layers can be clearly iden tifie d as facies C, prox ima l turbidites. The sedi ment s are in terpre ted as upper channe l deposits of IVA to over bank and interchannel tur bidit es of IVC. Sequence IVC : Overban k to In terc hannel Bed thi ckne sses continue to decrease fro m sequence IVB 138 to IVC , and average 2.2 em thick in IVC , but grain sizes rema in the same in the lower one- -third of IVC and gradu all y decrea se in its upper portion . Facies E, overbank depo si ts are in terbedded wit h in creas in g am ounts of facies D, in terch annel depo sits fro m the bottom to the top of sequence IVC . Gra in siz e , bed chara cter istics and struct ure s. Thin- (7 em ) to very thin- (1 em ) bedded med ium- to fine grained sandstone , sil tstones and silt y mud stones are found : , in sect ion IVC (Fig . 42) . These beds are separated by equall y thick or thicker (33 em) layers of gray to red ' mud stone , often wit h very thin (0.1 em ) silt y la minatio ns . Bedding cont acts are fla t, and infre quent shallow (2 em ) sc our s occur at the base of a fe w me di um- to fi ne-grain ed sand laye rs . In the lower third of the section one-ha lf of the mediu m- to fi ne-g rained sandstone and si ltst one beds were observed to lense out abru ptly wit hin the li mited outcr op . These lenticular beds prod uce AE Bo uma divi sions which Ricc i-Lucchi (1978) descri bed as the overbank product of large by -pass in g turb idit y curre nts . The overbank deposits are in terbedded wit h incre asin g am ounts of para llel la minat ed , Bouma B di visi on and cr oss -bedded , BoQ ma C divisio n sil tstones and silt y mud stones of facies D (F ig. 43 ) . Bouma divis ions ABE , facies C, were also found in terbedded in the lower third of the section but decre ase in abundance in the upper port ion. Organic 139 Fig ure 42 . Detailed sect ion of a portion of IVC , overbank depo sit s from meter 520 to 521.9. See Table 2 for explanation . 14 0 �--- ------- --- ------ �--- -� --- --- �----- - - l COLUMN METER I � - � -=- t-521 I; � • I f-520 SEQ. DIR. STRUCTURES ?B!fq H �N� IVC 2.li!. IVC TEXTURES .0 "' ..CU0. 0DU)U)U I • 141 ---- --�-- ------ �-- -- -- � ------ l Fig ure 43. Photo taken at meter 586 near top of section IVC , facies D, int erc hannel tur bidit es . Thick mu ds tone laye rs are seen in bottom half of photo over lain by wavy and fai ntly cro ss-bedded (B ouma C) fin e-gra in ed sandstone and par allel lami nated (B ouma B) top bed which is directly beneath handle of the hamm er . I 142 14 3 ma ter ial is co mmon in silty, paral lel laminated layers . Summ ary . A thi nning (Fig. 44) and fini ng upward trend co ntin ues from IVA through IVB and IVC which is in terpre ted as a change in envi ron m ents fr om channel, IVA , to upper channel-f ill , IVB , to overbank and in terchan nel depos its, IVC . - -- - -- -- -l Fig ure 44 . Sandstone bed thi ckne ss diagra m for a portion of sequence IVC , interchannel tur bidi tes . 145 0 r..n s 0 C) :> s:: H ·r-1 Ul Ul Q) s:: ,..!>/.! 0 u M ·r-1 ..c: 8 ....-l 0 N N lf) r..n .:re:}.e w 14 6 SEQUENCE V Sequence VA: Megasequence Megasequence VA is the hig hest, coar sest and mo st debris- laden mega sequence me asured . It is at least 97 m thick and near the top is cove red by alluvium . Above the cove red part of the mega sequence near - channe l turb idites of facies C were noted . Conglomerate s, pebbly sandy mud sto nes , and mas si ve sandstones domi nate this section I and ' i co nglom er ates are concentrated wit hin the bottom 39 me ter s ·• Fig ure 45 describes the basal thi rd of the me gasequence. Gr ain size and bed ch aract eristics . The con glome r- atic layers are com posed of poo rly sort ed sandstone with greater than 30 perc ent sma ll pebbles and gran ules of quartz , che rt , and ig neou s ro ck . Large pebbles (2-6 em ) , cobbles (6-22 em) , and boulders (22-75 em ) of sandstone , mu dstone and ig neous rocks infre quentl y compo se up to 90 perc ent of the basal portion of the mega sequence and usuall y cons titute less than 5 percent in the re m ainin g con glome rat ic beds . Beds range fro m thin (7 em ) to very i thi ck (196 em) (Fig . 46) and are cru dely orga nized, facies I - -- - .. - -- ---· - 1 �� Fi gure 45. Conti nuous detailed sect ion of a por tion of megas equence VA from meter 588 to 614. Dia mete rs of large co bbles and boulders are indic ated in ce ntime ters within spec if ied clasts . See Table 2 for explanatio n . 14 8 ---- ----- - --�-- --- -··-·-· --- - -- �-- - - - - - COLUMN .. 0 .. " 0 0 0 0 METER 590 589 SEQ. DIR. STRUCTURES VA VA TEXTURES 14 9 COLUMN . . . 0 0 0 0 0 0 0 0 D 0 0 0 0 0 0 0 0 = C> 0 =o 0:; 0 <;::, <:::::> - METER SEQ. 592 0 591 DIR. STRUCTURES TEXTURES til O.. O.Ooooou 150 ____ " ___ ______ ___ " _____ _ - METER SEQ. DIR. STRUCTURES TEXTURES ):, B f S ll � � N � l..o"8 "'oo �"''"' I COL ill!N VA - - I 602 I 601 . . . . . . 0 0 0 0 0 0 0 0 - 600 -5 99 l��-r��-rv_m�r-�++++++++++++++�� 151 l COLL �!N . . . . . . 0 .��c-'?>;b-=. �� P= . � ·· · � • • • •• • • 0 • c:) c::: � o ':-o o_ o �� -�,4?.-0 r- ....,. ......_:I- . � �o O . o o c: ·. · . · . · -· ·. �' .. . . � � .. ._ " ' . . . . ·. """-f#' :· ·. · · ' ;/.- .. - � 0 . � .. . -' . - ., L '- ' . . .C. . . METER SEQ. DIR. STRUCTURES TEXTURES I� B � s � f � � N � ...o'f: Q.. co � f/.1 VA � 607 II �I II �60 6 � • "" 605 � ,. ,. 604 • 603 VA I I � � 152 COLUNN METER SEQ. DIR. STRUCTURES TE XTURES VA II 0 608 O o 153 COLUNN METER SEQ. DIR. STRUCTURES TE XTURES 0 0 0 VA 0 0 <) �0 CJo 0 " 0 0 0 0 0 0 0 0 0 0 0 0 613 0 0 0 0 o a Oo 0 0 0 0 0 0 0 0 0 0 0 0 0 c::::;/ 0 - 0 15 Fig ur e 46. Sandstone and cong lome rate bed thickness diagr am for a portion of me gasequence VA. 155 ,-----------------------� -�-�-- 0 r-1 \.0 � 0 0 \.0 00 00 L{) 0 0 N 0 0 r-1 0 L{) 0 r-1 s () s:: ·.-I U) U) Q) s:: � () ·.-I .£: 8 156 A2 and A 4 have pebbles, cob bles and boulders co ncentrated towards the bottom of beds bet ween mete rs 592 and 614. Very thi ck (150 em ) beds of pebb ly sandy mud stone , facies F, are found in the top of the conglo m eratic part of section V to me ter 620. Si xty perce nt of the orga nized pebbly sandstones, facies A 4 , norma ll y gra de upwards to thin tops ' of la minated siltstone whereas just under 30 perc ent of the . or gani zed conglo m er ates , facies A2 , do the same . It is poss ible to trace laterall y a fe w of these co nglomerate layers and they were found to lense out latera ll y wi thin 50 m (Fig . 47) . The pebbly sandstones and co nglo m er ates usually form ama lgama ted laye rs wit h undulati ng bottoms . These coarser grain ed beds are in ter bedded with thin (8 em ) ' to thick (95 em ) beds whose grain sizes ra nge from gra nule to siltstone of fa cies B2 , mas sive sandstone wi thout dish structure s, and facies C, pro xi ma l turb idite s. These facies cons tit ute the upper 59 m of sect ion . Facies C tur bidites are usually ma ssive or gr aded fro m gran ules or coa rse-gra ined sand to sil tstone . Many of the facies B2 have gran ule or coar se-grain ed sand bases . Muds tone layers , where present , are al mo st always sc oured and hig hl y defor med . Str uct ures . Sco uring is found at the base of nearly all beds , espec iall y the thicker beds and has a maxim um re lief of 15 centi met ers . Loadfor ms are pr evalent at the ' bases of the pebbly sandstones usually being 6 em or less Fig ure 47. Conglo m erat e bed pin chin g out beneath head of the hamme r. Bed is 30 em th i ck at the right. 158 .--------------------- ---�·----· l I 159 deep but rang ing up to 35 em at the base of a boulder con- gl om erate unit (F ig 48) . Sm all fl ame struct ures (2 to 3 em } resulting from loadin g oc cur at the silty top s of some beds . Par allel and wavy la mination frequently are found in the sil tstone top s of the facies C turb idi tes . 1 Organic mate rial is fairly co mmo n, usuall y in coar se- i grained sand or gr anule portions of beds . Sum mary . Megasequence VA defi nes a thin nin g upward trend in the top 59 m of the sect io n starting at meter 625 associated with a decre ase in grain size upward . It is co m posed of facies A2 , A4 , F, B2 and C wit h the latter two facies dominat ing the top 59 m of me gasequence {Fig. 49) . The cong lomerates in the lower 39 m of megas equence ' show var ia ti ons in the rel atio nship of clasts to ma trix . The basal 5 m of the mega sequence cons ists of clast supported boulder layers , 30 em thick in terbedded wit h ma ssive med iu m- to fi ne- grained sands (Fig . 50) . The central port ion conta ins poor ly so rted , ma tr ix supported cobb les and pebbles which decreas e in size upward within each bed and genera ll y have greater than 50 percent ma trix ma ter ial (Fig . 45) . The third and upper port ion cons ists of pebbly sandy mud stones si mila r to pre viously descri bed debr is fl ow depos its (C r owell, 1957) . The charact eristics suggest that the co nglomerate units rep rese nt sedi men tation. L: :�:: l ::::: _ :: c ::::: :� t:�a ::: m :::: �:::i: uld � a l: J Fig ure 48. Boulder co nglome rat e in poor ly so rt ed sandy mud stone at me ter 590 of me gase quence VA . The top of the sect ion is to the left . Seventy-fi ve em thick boulder has com pr essed underl ying sand bed ca using 35 em of re lief along bed ding cont act . 161 ,------------------------ "------- ---� 162 Fig ure 49 . Vertical sequence analysis of mega se quence VA. See Table 1 and Fig ure 8 for ex planation. 163 ....... 0'1 � H Q) +l Q) s 684 586 0 100 I %· sand 1 I I I A 2 B 2 c B 2 iiiiiiii& A 2 6 1 4 608 I � c B 2 c [1m Fi gure 50. Clast support ed cobb le conglo me rat e close to base of me gasequence VA near me ter 586 . 165 ,---------------- ------ ----- 166 con sisti ng of debr is fl ows , tur bidit es , and submar ine lands lides (Middlet on and Hamp ton , 1973) . The central crudely graded zone shows the eff ects of turbu lence by its poor sort ing of grain sizes but also resedimenta tion because the ma trix was unable to support all of the clasts , at least temp orari ly . Conglomer atic lit ho logies of si mi lar descr iption have been reco gni zed as being upslope and downslope facies of a si ngle ma ss move ment deposit (Cosse y and Ehr li ch , 1979) . The co nglom eratic lit hologies seen in me gasequence VA were depo sited fro m a numb er of seperate ma ss move ments downslope that ind ivid uall y canno t be obser ved to be latera ll y grad ational bet ween con glome r atic type s but may repres ent diffe rent facies of debris fl ows . Pale ocurrents Sma ll scale cr oss- bedding was examin ed in the field for paleocurrent data which is pr esented in Table 3 and Fig ure 50. In the ro se diagra m (Fig . 51) paleoc urrents were in dicated as bein g found in eit her ch annel or inter cha nnel environmen ts . The cross -bedded uni ts were usuall y less than 1 em thick and some of the thin and fain t units were unuseable. The measure me nts were ma de by cleaning two surfaces at right angles to one another to see the cross -bedd ing in three di me nsions. The thr ee di men si ona l 1 LOCAT IO N 1. 0 4.0 5.0 5.5 6.7 9.5 10.6 17 .3 24 .2 29 .8 31 .5 38.5 51.1 92. 0 115.2 142 .1 160.2 191. 0 521.1 TABLE 3 PA LEOCU RRENT MEASUREMENTS ENVI RONMENT In terchannel In terchannel I nter channe l Channe l Channe l Channel Channe l Chan nel Chan nel Channe l Chan nel Cha nnel In terc hannel Cha nnel Inter channel In ter channe l Channel In terch annel In ter ch annel DIRECTION° 28 0 280 270 265 280 265 275 270 2 40 280 260 260 275 ?.75 245 255 270 235 260 168 Fig ure 51. Rose diagra m for paleocurrent me asure me nts (T able 3) in the int erc hannel and channe l sed im ents . 169 w ----- ------ ------- "" ____________ " N s � Inter cha nnel �C hannel 170 orie ntation of the cro ss- bedd ing was found and the sense of move ment perpend icular to the cr oss- bedding was then deter mi ned . The pre- tilti ng direc tion was found by rotat ing the plane of cr oss - bedd in g ar ound the strike li ne into the hori zontal. The directio n of current fl ow ove rall was west to south west for both channel and in terch annel deposits . This agrees with the paleocurrent me asure ments of Hsu (1977) and Crowe ll et al. (1966), for ear ly and late Plioc ene age sed im ents respectively in the area . Ac cord ing to Barker (1976) the Pliocene sedi men ts•co mpo - siti on indicate s an inf lux of ma terial from the eros ion of upli fted older form ations to the northeas t. Thi s source terrain would have been Eocene and Miocene sed im entar y rocks of the ancest ral Topatopa Mountains and crysta lline basement fr om the San Gabriel Mountain s further to the east . The Pliocene subma rine can yon was probab ly orie nted northeast to sou thwest and trans ferred sedi me nts fro m the basi n ma rgin to the east- west trough axis. Hsu's (1977 ) studies of the Ventura oil fiel d lower Pliocene tur bidit es , which was the first rele ase of information of Shell Oil Company work in the Ventura Basin in the 1950's empha size 1 longit udinal sedi ment transport in the basin and de- em phasi zes fan depos it ion. Walker (1978) prese nts a mo dern interpretation of the same data in ter ms of outer subm arine fan deposits . 17 DISCUSSION The Adams Canyon me asured sect ion is character ist ic of midfa n facies assoc iations that for m broadly lenticular bodies of ch anneli zed sandstones wit h lesser am ounts of conglomerate of facies A, B and c. These sed iments alternate wit h plane-para llel in terc hannel depos its of facies D , C and somet ime s E. Conformab ly over ly ing the sect ion are intermit tently exposed thin sa ndstone and mu dstone beds also of the upper Pic o For m ation and the poorly expo sed Pli o-P lei stocene marine Santa Barbara For mation which is compr ised of mu ds tone and i some sands tone� Under lyin g the section are 200 m of upper Pic o thin sand- stone and mu dstone beds and poorl y exposed sandstone , mud stone , and con glom erat e of the lower Pliocene Repetto Form ation. Walker (1978) , inte rpret ed the Repetto sedi- men ts as depositi ona l lobes in an outer fan environme nt. Natland (1957) establis hed that the Repetto was deep water (1, 200 m) fro m paleoe co logical studies. A deep- sea fa n pro grad ati onal cyc le is indicated as the Pl iocene tur bi dite basin inf il led and shallowed . A tr end of fan prograd ation was re ported by Johnson (1977) for the mid dle -- ----- -- -- - 17 2 J I to late Pl iocene sedi men ts exposed along Santa Paula Cree k which are 2 km along strike to the east. A co m parison of the megas equence s me asured in Adams Canyon to those fo und in midfa n channel-f ill sequences in Santa Paula Cree k by Johnson (1977) and the northern Apennines by Ricci - Lucchi (1 975) is pre sented in Table 4. The thick ness of interch annel sedi ments separating mega - sequences are very si milar between Adams Canyon (47-203 m) and Santa Paula Creek (40-210 m) whil e the Apennines me gasequence s have much less thick in terc hannel intervals (10-80 m) . Most of the int erchannel sedi ments in Adams Can yon are 90m or less thic k , which co rrelates well with the Appenines, with the except ion of the 203 m in terval bet ween mega sequence III and IV. The thick in terch annel in terv al probab ly owes itself to coars e-grained sedi me nts bei ng transported to another area of the mid fan during that ti me . The max imum average layer thickness within individ ua l mega sequenc es in Adams Canyon (88 em ) is thicker in co m parison to Sa .nta Paula Creek (5 6 em) but both are much less thick than the Apennines (5 00 em) . This suggests that there was a higher rate of depos ition in the Adams Can yon midfan sect ion com pared to the Santa Paula midfa n i I sect ion and is supported by the greater minim um and maxim um I thickness of mega sequences in thi s section (16- 117 m) than I I in eit her of the other two sect ions. The middle fa n TABLE 4 CO HPARATIVE STUDY OF HIDFAN CH AilNE L- FILL SEQ UENCE SEPARATIO N OF MEGASEQUENCE AVERAGE LAYER THI CKNESS THI CK NESS OF MEGASEQ UENCE SA ND/SHALE APENNI NES 10-80 m 40-500 em 2.5-62 .0 m 1. 5-50 ADAMS CANYON 47-203 m 22-88 em 16-117 m 4-50 SANTA PAULA CREEK 40-210 m 25-56 em + 2.0-70 m 3. 6-50 17 envi ronment in mo dern fans forms as the resu lt of an abrupt ch ange of gradient in the subm ar ine topogr aphy (Nelson et al. , 1970) . It is possi ble that the Adams Can yon midfan sedi men ts were depo si ted in incr easin g am ounts on a portion of the midfan farther basin ward accord ing to paleocurrent data , wit h a lower gradient than the Santa Paula Cree k midfa n sedimen ts . An expla- nati on for the thinner average layer thi ck ness in this ' area (88 em ) in com pariso n to the Apennines (5 00 em ) sedi me nts was suggested by Johnson (1977) by a possible narro w shelf ma rgin and/or a direct deltaic feed of sedi- ment to the head of a subma rine canyon . It may be si mi lar to the Pl i oc ene de lt a reported by Baldwin (1959) in the Fill mo re area 24 km east of Santa Paula. The sand/ shale ratios are si mi lar wit hin the mega sequenc es bet ween Adams Canyon (4-50 ) and Santa Paula Creek (3.6-50 ) and both are roughly equiva lent to those of the Apennines (1.5-50) . The paleogeog rap hic recon structio n of thi s late Plioc ene basin pre dicts basi n plain sedi me nts were being depos it ed farther west ward dur in g the ti me of mid fan deposition in the areas of Santa Paula Creek and Adams 1 Can yon . Basin plain pelagic mud stone of late Pl iocene age re ferred to as the "m udpit shale" is nearly 1, 000 rn thick and is expose d in Hall Can yon near the city of Ventura 19 krn to the west (Baile y and Jahns, 1954) . I I A number of ty pe s of gravity- driven sedi ment fl ows 1 •------ ------ -- ---- -- --- -- -- ---- -- -- - -- --- --- -- -- --- - -- ---- - ---- - - -- - -- - ---- 1 7 � were recog nized wi thin the measured sect ion and are summ ar ized in Table 5. The dense , conc entrated turb idit y depos it s , facies c, were found in the megas equenc es and in terbedded wi th facies D, dilute turb idit y current deposits of the in ter channe l areas . The ma ssi ve sandstones of facies B 2 and various facies! ! A con glome rates ca nnot be classifi ed under the classic I I turb idit y current mo de l and are thought to re pre sent gra in i I fl ows , disper s ions conta inin g hig h concentrat ions of grainsl that fl ow ra pidly on a slope . The disper si ons are fre - ! quentl y channelize d and lose their energy very ra pidl y at the base of the slope res ulting in depo sit ion of their entire load , wi thout tractio n support at the base or i selecti ve sorting of grains (Mi ddleton and Hampt on , 19 73) . Grain fl ows have recen t ly been found for the fi rst time on the deep ocean fl oor off the Bahamas by Mulli ns and ' Van Buren (1979) • The dis h struct ures characte ri stic of facies B 1 are co nsidered indicat ions of fl uidi zed (l iqu efied) fl ow where the sedi men t was supporte d by pore -fl uid expulsi on . Dish struc tur es descr ibed in mega sequence III (F ig. 26) were obser ved to be tra nsi ti ona l to fl uid esca pe struc - tur es . It has been suggested by Lowe (1975) that these sedi ments were depo si ted initially by norma l turb idity I I I I I currents and that imm ediat ely aft er depositi on large I I • I underly 1ng l ! 17 61 .. --- --· --------- --1 TABLE 5 TYPES OF GRAVITY- DRIVEN SEDIMENT FLOWS (AFTER HAM PTO N , 19 79 , TABLE 1) TYPE OF FL OW Tur bid ity Current Grain Fl ow Liq uefied Fl ow Debris Fl ow SEDIMENT SUPP ORT MECH ANIS M Turbu lence Grain Interaction (Dis pers ive Pres sure ) Upward In tergr anular Flo w (P ore-Fluid Expulsi on ) Matrix Str ength 17 7 beds undergoing loading con solid ation which could tr igger rene wed fl owage . The con vo lute la mination that over lies the dish struct ures at meter 169 (Fi g . 28B) are cohes ive upper laye rs that res isted fl uidi zation and defor m hydro plastically in to co nvo lute la mi nation (L owe , 197 5) . The debris fl ow deposits in the basal port ion of megase quence VA (F ig. 45) were noted to have var iations in clast and mu ds tone content between individ ual flo ws . The debr is fl ows may repre sent lateral or longit udina l var i- , ati ons wit hin a si ngle debris flo w or may owe itself to dif fere nt clast sizes avail able in the source mate rial . Facies cha nges within a si ngle debr is fl ow were reported by Cossey and Ehrlic h (1979) . Their upslope facies co nsisted of boulders in conta ct repres enting cl asts too large for suspensi on , the in ter m ed iate facies was a poo rl y sorte d boulder y pebble mud stone wit h a downslope fac ies 1 of unsorted , pebbly mu dsto ne . These pebbly mu dstone s were traced in outcrop into tur bidites and in dicate that turbidites can rep rese nt downslope re mnant s of large ma ss fl ows that are rou ghl y ti me equiv alent to the boulder depo sit upslope . Lowe (1972) descri bed si mila r li thologic variations in the Cretaceous of Calif ornia wit h boulder s in contact in the basal portio n of the Logan rid ge memb er while its distal two-thirds cons ists of pebbly mud stones with fe w clasts . The depo siti onal rate for the Pli ocene sedi me nts in thi s area has been ca lculated by Yeats (1976) as 1 mm/yr . This is equi valent to the rate of accum ulatio n for outer fa n deposits in an Apennine tur bidit e basin (M utti et al. , 197 6) . The Upper Pl iocene tur bidit e basin sh all owed toward s the east and eroding Eoc ene and Mi ocene sed iment ary rock s to the northeast and cr yst alli ne basement to the east pro vided so urce ma terial to a rap idl y infi lli ng basin (B ark er , 19 76) . A subm arine ca nyon transported sedi ment s in a so uth westward direction and depos ited them in a cha nneli zed midfa n portion of a deep-se a fan in the are as of Adams Canyon and Santa Paula Creek . 17 9 CONCL USIO NS A prog rading deep- sea fa n would be expec ted to for m a stratigra phic co lumn of midfa n sedim ents over lying oute r , fan sedi me nts. The earl y Pl iocene Repett o For ma ti on in thi s area has been interpreted by Walker (1 978) as being , compr ised of outer fan sedi ment s and the lat e Pli oce ne : upper Pi co For ma tion in Adams Can yon is here interpreted as midfa n sedi ment s. Continued sha llowi ng of this basin is in dicated wit hi n the overl ying Pl io-P leist oce ne Santa i Barbara For ma ti on by Natland's (1957) foraminiferal corre lati ons . Fi ve mega sequences were found in Adams Can yon all of which dem ons trat e thin nin g and finin g upward trends character isti c of inf il led and abandoned mid fan channels. I These broadly lenticular , coa rse - grained channe lized 1 facies are separated by fi ne-gra ined, plane-para llel layers of in terch annel depos its ranging fro m tens to hundreds of meters thick . These sedi ments ori gi nated fr om ' older expo sed for ma tio ns to the northea st and east and were rapidly tra nsfe rred int o a subm arine canyon that transported them in a southwestward direc ti on . At the i L_ ____ ____ ---- - -- - ·-- -- -- - . --- ---- ·-------- - --·-- -- 180 mouth of the subm ar in e can yon the sedi me nts for med a deep sea fan and in the area of Adams Can yon and Santa Paula Creek the sedi me nts were depo si ted in a midfa n envi ron m ent. Pale ocurrent direct ion mea surements in dicate that the Adams Can yon sedi me nts were depo si ted on a port ion of the midfa n fa rt her basim vard (w estward ) than the Santa Paula , Creek sedimen ts . As the slope of the deep-s ea fa n decreased towards the west sedi me nts tve re dep os ited in greater am ounts and fr equenc y in the Adams Can yon area co mp are d to Santa Paula Creek . This interpretation is supported by the mu ch thicker megas equenc es and greater ' average layer thickness wit hin the mega sequences of Adams Can yon com pared to Santa Paula Creek (Ta ble 4) . The . mi dfan sedi me nts of the Adams Canyon and Santa Paula Cree k area laterall y change facie s to basin plain mu dstones westward near the city of Ventura . The deep-sea fan mo del can therefor e be used as a pred ictor in the paleogeogra phic reconstr uc ti on of this late Plioce ne basin . Sedi ment gra vit y fl ow types obser ved were those of turb idit y curren ts , grain flo ws , fl ui dized flo w, and debris fl ows . The overa ll rate of sedi me ntation for Pliocene sedi men ts in the area is 1 mm /yr . (Y eats , 1976) . REFER ENCES Baldwin , E. J. , 1959, Pliocene tur bidit y crr ent deposits in Ventura Basin, Californi a: unpub. M.S. Thesis, Univ . of Southern Calif ., Los Angeles , 64 p. Bailey , T. L. , 1954, Geology of the western Ventura Basin , Santa Barba ra , Ventura , and Los Angeles count ies: Cali f. Div . Mine s Bull. 170 , Map Sheet No . 4. Bailey , T. L. , and Jahns , R. H. , 1954 , Geo logy of the Trans verse Range Pr ov ince, Southern Cali fornia: Calif . Di v . Mines Bull. 170 , Cha pt . II , p. 83-106 . Bark er , c. T. , 1976, Pliocene geology and the Santa Paula oil fi eld area : Am . Asso c . Petro leum Geologists and Coast Geol . Soc . Spr ing Field Trip Gui debook , Pacific Sect ion, 18 p. Cossey , S. P., and Ehrlic h , R. , 1979 , A cong lome rat ic , ca rbonate fl ow deposit , northern Tunisia: a lin k in the genesis of peb bly mud stones: Jour . Sed . Petr o logy , vo l . 49 , p. 11-2 2. Cro well, J. c. , 1957, Origin of pebbly mu dsto nes : Geol . Soc . Am erica Bull., vol . 68, p. 993-1010 . Cro well, J. C., Hope , R. A., Kahle , J. E. , Ovenshine , A. T. , and Sams , R. H. , 19 66 , Deep-water sed im entary str ucture s, Pl iocene Pi co For mat io n , Santa Paula Cr eek , Ventura Basin , Cali forn ia: Cali f. Div . Mine s Spec . Rept. 89 , 40 p Driver, H. L. , 192 8, Forami ni feral section along Adams Cany on , Ventura County , Cali fornia : Am . Assoc . Petrole um Geologis ts Bull., vo l. 12 , p. 753-7 56 . Hampt on , M. A. , 1979 , Buoyancy in debris fl ows : Jour . Sed . Petrolo gy , vol . 49 , p. 753-7 58. Howell, D. G. and Lin k , M. H. , 1979 , Eoc ene cong lome ra te sedi men tology and basin analys is, San Dieg o and southern Cali fornia borde rl and : Jour . Sed . Petrol ogy , vol . 49 , no . 2, p. 517-5 39 . 18 2 Hsu , K. J. , 1977 , Studies of Ventura fiel d , Cali forn ia, 1: fa cies geometry and genesis of lower Pliocene tur bid ites: Am . Assoc . Petroleum Geologists Bull., vol. 61, p. 137-1 68. Johnson , B. A. , 19 77 , Vertical sequence analysis of Santa Paula Cree k , Ventura , Calif or nia: unpub. M.S. Thesis , Univ . of Southern Calif., Lo s Angeles , 204 p. Lowe , D. R. , 1975 , Water esca pe str uc ture s in coar se grained sedi me nts : Sedi mento logy , vol . 22 , p. 157- 204 . Lowe , D. R. , 1972, Im plicatio ns of three subma rine ma ss moveme nt depos its, Cretaceo us , Sacra me nto Valley , Cali for nia: Jour . Sed . Petro logy , v. 42 , p. 89- 101 . Middle ton , G. V. and Hamp ton , M. A. , 1973 , Sediment gravity fl ows : mech anics of fl ow and depos it ion in Middlet on , G. V. and Bouma , A. H. , (e ds .) Tur bi dites and deep-wate r sedim entatio n : So c . Ec on . Paleontologists and Mineralogi sts Pacific Coast Section , Los Angeles , p. 1- 38. Mulli ns , H. T. and Van Buren , H. M. , 1979 , carbon ate grain flo w depos it, Jour . Sed . p. 747-7 58. Moder n modifie d : Petrology , v. 49} I Mutti, E. , 1975, Dis tinctive thin -bedded turb idite fa cies and re lated depos it ional envi ro nme nts in the Eoc ene Hecho Group (s outh- central Pyrenee s, Spain): Sedi ment ology , vol. 24 , p. 107-131 . Mutti, E. , Nilsen , T. H., and Ricci-L ucch i, F. , 1976, Sedim entology of outer fan depositio nal lobes of upper Miocene-P li ocene Laga For m ation, east-central Italy , (A bst.): Am . Assoc . Petro leum Geolo gists Bull., vol. 60, p. 701 . Natla nd , M. L. , 1957, Pal eoec ology of west coast Terti ary sedi me nts in Ladd , H. s. , (ed.), Turb idit y Currents and the Transportation of Coarse Sediment into Deep Water : Soc . Econ . Paleontologists Mineralogists Pacifi c Coast Section , Los Angeles , Cali for nia, p. 39-78 . Natland , M. L. , and Kuenen, Ph. H. , 1951 , Sedi me ntar y history of the Ventura Basi n , Cali forn ia, and the action of tur bidit y curren ts : Soc . Econ . Paleontologists Mine ralo gists Spec . Pub. No . 2, p. 76-1 07 . 18 i I r-:-e lson , C. H. , Car lson , P. R. , Byrne , G. V � �n d Alpha, -l T. R. , 1970 , Development of the Astoria Can yon - fan phys iogr aphy and co mpa riso n wit h si milar sy stems : Mar ine Geo logy , vol. 8, p. 259-2 91. Normark , W. R. , 1970 , Gro wth patterns of deep- sea fans: Am . Assoc . Petrole um Geologists Bull., vol. 54, p. 2170- 2195 . Normark , W. R. , and Pi per , D. J. W. , 1969, Deep-sea fa n vall eys , past and pres ent: Geol. Soc . Am . Bull., vo l . 80 , p. 1859-18 66 . Ricci -Lucchi , F., 1978 , Tur bidites of the northern Appennines: in troduc tio n to facies analys is: In ternat . Geology Rev. , vo l. 20, no . 2, p. 127-1 66 . Ricci-Lucchi , F., 197 5, Depos itional cyc les in two tur bi dite for mat ions of nor thern Appenn ines (Italy) : Jour . Sed . Pet rolo gy , vol . 45, no . 1, p. 3- 43 . Walker , R. G. , 1978, Deep-w ater sandstone facies and ancient subm arine fans: mo de ls for explorat ion for strat igraphic traps : Am. Assoc . Petro leum Geologists Bull., vol. 62, p. 932-966 . Walker , R. G. and Mutti, E. , 1973, Tur bidite facies and facies associati ons in Middleton , G. V. and Bouma , A. H. , (e ds. ) Tur bidit es an � deep- water sed iment ation: Soc . Ec on . Paleontologists Mi neralog ists Pacifi c Section Shor Course , p. 119-159 . Weber , F. H. , Jr . , Cle veland , G. B. , Kahle, J. E. , Kiessli ng, E. F. , �H ller , R. V. , Mills, M. F. , Mor ton , D. M. , and Ci lweck , B. A. , 1973 , Geology and Min era l Reso urc es Study of southern Ventura County , Calif ornia : Cali f. Div . Mines Pre li m. Rept. 14 , p. 1- 39 . Yeats , R. S. , 1976, Neogene tectonics of the ce ntr al Ventura basin, Cali forn ia in Fritsche , A. E. , Ter best , Jr . , H. , and Worna rt , \'1 . W - . - ( eds .) , The Neogene Sy m posi um , selected technical papers on : Pal eonto logy , Sedi mento logy , Petro logy , Tecto nics , Geo logic Hi story of the Pacifi c Coast of Nort h Am erica , Annual Meetin g I Pacifi c Sect i on Soc . Ec on . Paleontologists Mi neral ogists1 P· 19-32 . I -- - -�-------� l J

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Vertical sequence analysis of late Pliocene pico formation sediments in Adams Canyon, Ventura County, California.

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Creator Hartnett, Thomas Martin (author)

Core Title Vertical sequence analysis of late Pliocene pico formation sediments in Adams Canyon, Ventury County, California

Contributor Digitized by Interlibrary Loan Department (provenance)

Degree Master of Science

Degree Program Geological Sciences

Defense Date 09/01/1980

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

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Permanent Link (DOI) https://doi.org/10.25549/usctheses-c3-392771

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