CALIFORNIA STATE UNIVERSITY, NORTHRIDGE

MARINE GEOLOGY OF THE WESTERN EXTENSION OF THE TRANSVERSE RANGES: POINT CONCEPTION TO POINT ARGUELLO

A thesis submitted in partial satisfaction of the requirements for the degree of Master of Science in

Geology

by

James Manfred Roush

May 1983 The Thesis of James Manfred Roush is approved:

California State University, Northridge

i i CONTENTS

Page

ABSTRACT ix

INTRODUCTION 1

General Statement 1

Acknowledgements 4

Geographic Setting 4

Bathymetric Setting 4

METHODS OF INVESTIGATION 5

General Statement 5

Types of Seismic Data 5 PREVIOUS WORK 10 REGIONAL GEOLOGY 12

TECTONIC SETTING 19

REGIONAL STRATIGRAPHY 29

General Statement 29

Pre-Cretaceous 32

Cretaceous 33

Paleogene Stratigraphy 34

Paleocene 34

Eocene 35

Neogene Statigraphy 39

Miocene 39

Pliocene 45 Pleistocene-Holocene 46

iii Q '

Page

OFFSHORE STRATIGRAPHY 47

Introduction 47

Acoustic Basement 4 7

Paleogene 51

Neogene 56

Miocene 56

Pliocene 60

Pleistocene 64

Holocene/Late Pleistocene 67

ONSHORESTRUCTURE 73

OFFSHORE STRUCTURE 77

Northeast Trend 77

Point Conception Syncline/Jalama Syncline Trend 80

Jalama Trend 87

Hueso Trend 87

Arguello Trend 94

F 1 Fault Trend 94

ONSHORE-OFFSHORE STRUCTURAL AND STRATIGRAPHIC CORRELATIONS 112

CENOZOIC EVOLUTION 124

General Statement 124

Paleogene 1 24

Neogene 127

iv " '

Page

SUMMARY AND CONCLUSIONS 133

REFERENCES 136 APPENDIX A 145 APPENDIX B 146

v LIST OF ILLUSTRATIONS

Figure Page

1. Location of study area 3

2. Tracklines of common depth point seismic lines in the study area 6

3. Generalized fault map west central California 14

4. Main structural features of the Santa Barbara Basin region 17

5. Interaction of the Pacific, Farallon, and North American Plates 22

6. Late Miocene generalized paleogeologic map of the Santa Maria pull-apart basin 25

7. Stratigraphic column of the western Transverse Ranges 31

8. Summary of the lithology and biostratigraphy of the test well OCS-CAL-78-164 No. 1 49

9. Paleogene and early Neogene seismic trends 54

10. Distribution of Miocene and early Pliocene units 62

11. Top middle to late Pliocene structure map 66

12. Seismic profile of the latest Pleistocene/ Holocene deposi tiona! sequence 69

13. Iospach of Holocene-Late Pleistocene sediments 72

14. Onshore structural cross section-Point Arguello 75

1 5. Structure map on the pre-Vaqueros unconformity 79

16. Restoration of the pre-Vaqueros erosional surface 82

17. Near top Monterey structure map 84

vi Figure Page

18. Point Conception Syncline-Jalama Syncline structural trend 86

19. Interpretation of seismic profile SLC-3 across fault A 89

20. Jalama and Hueso structural trends 91

21. Interpretation of USGS seismic profile 4 and 8 across fault E 93

22. Arguello structural trend 96

23. Interpretation of seismic profile USGS 14 across fault F 98

24. Interpretation of seismic profile SLC-5 across fault F 100

25. Interpretation of seismic profile SLC-114 across fault F 102

26. Interpretation of seismic profile SLC-203 across the F 1 tear fault 104

27. Interpretation of seismic profile SLC-9 across fault G 106

28. F 1 structural trend 109

29. Interpretation of seismic profile SLC-2 across F 1 fault tend 111

30. Correlation of stratigraphic units - Santa Barbara channel to the offshore Santa Maria 114

31. Interpreted pre-Vaqueros outcrop map 116

32. Interpretation of seismic profile SLC-3 showing potential pre-Vaqueros "high" 119

vii Figure Page

33. Generalized correlation of Cretaceous, Paleogene, and Neogene units of wells adjacent to the study area 122 34. Cenozoic paleobathymetry, and sedimentation and subsidence rates of the central Santa Ynez Mountains 126

35. Estimated northern boundary of Vaqueros deposition 129

36. Velocity functions used in depth/time derivation 148

Tables Page

l. Table of seismic coverage 8 2. Informal members of the Monterey Formation along the Santa Barbara Channel 43 3. Summary of major folds - Point Conception syncline - Jalama syncline trend 151

Plates

I. Bathymetry In pocket

II. Trackline Map 1 In pocket

III. Trackline Map 2 In pocket

IV. Structure Cross-Sections, A-A' and B-B' In pocket

v. Structure Cross-Sections C-C' and X-X' In pocket

VI. Bedrock/Late Pleistocene Geologic Map In pocket

viii ABSTRACT

MARINE GEOLOGY OF THE WESTERN EXTENSION OF THE TRANSVERSE

RANGES: POINT CONCEPTION TO POINT ARGUELLO

by

James Manfred Roush

Master of Science in Geology

The study area lies offshore of the western Santa Ynez Mountains and contains the northwestern corner of the Santa Barbara Basin and the offshore southern-most portion of the Santa Maria Basin. Two major geologic- geomorphic units, the western Transverse Ranges and the Coast Ranges

Provinces meet within this area. The junction of these provinces and their evolution during Cenozoic and Quaternary time were studied by using and correlating geological and geophysical data sets. These data sets include:

1. Seismic reflection data, including digitally processed common depth

point, 4- second profiles.

2. Surbsurface information from onshore and offshore core holes,

including the stratigraphic test hole OCS-CAL-78-164- No. 1.

3. Onshore mapping and stratigraphic analyses by Dibblee (1950, 1978),

Link (197 5), and other workers.

ix Methods used in this study include: shallow-bedrock geologic mapping of structural trends and stratigraphic units; correlation of seismic stratigraphic horizons; and structure contour mapping on key horizons (top mid-upper

Miocene, near top Monterey, and top pre-Vaqueros unconformity). In addition,

Quaternary fault activity was evaluated using high resolution seismic profiles.

In contrast to the results of previous studies, the transition or junction of the western Transverse Ranges and Coast Ranges Provinces was found to be abrupt, not gradual. This junction is mapped along a northerly continuation of the F-1 fault zone west of Point Conception. East of Point Conception the F-1 fault zone, trends east-west as is typical of the Transverse Ranges Province.

To the west of the point, the fault swings abruptly to the northwest-southeast.

Structures west of this area include the Hueso anticlinal trend, which is the location of a recently discovered major oilfield.

The Paleogene evolution of the study area is recorded by an onlapping regressive sequence of marine Paleocene-Eocene-Oligocene rocks. These rocks onlap a northeasterly trending erosional surface of Cretaceous rocks. However, details of this trend are not clear due to the tectonic overprinting of Neogene trends. In particular, the onland location of the eastern extension of the

Paleogene trend is unknown.

Neogene trends within the area are typical of their respective geomorphic province. The Neogene structures in the westernmost Transverse Ranges

Province are orientated east-west, while the Neogene structures in the offshore

Santa Maria Basin trend northwest-southeast. Many of the east-west trends are active today. These faults display sea-floor offsets, while folds show thickening of Quaternary sediments along synclinal troughs and a thinning over anticlinal crests.

X INTRODUCTION GENERAL STATEMENT

One of the major geologic features of Southern California is the

Transverse Range Province. This east-west-trending province lies between north-south-trending Coast and Penninsular Ranges to the north and south, respectively. The westernmost extension of the Transverse Ranges consists of the offshore Santa Barbara Trough and Channel Islands, and onshore to the north--the Santa Ynez Mountains (Figure 1).

This study consists of a geologic investigation of the offshore

Transverse Ranges structural grain between Point Conception and Point

Arguello. Within this area, two major problems are: I) How are the dominantly east-west-trending, left-reverse-slip faults of the Transverse

Ranges tectonically altered into the right slip, north-trending faults of the

Coast Ranges?; and 2) What is the structural and stratigraphic evolution of this complex westernmost extension of the Transverse Ranges?

To attempt an answer to these questions, well data and seismic reflection profiles were used. The latter data include deep penetration, common depth point (COP) and shallow- and intermediate- penetration sparker profiles. Seismic correlations are based on the deep test stratigraphic well CAL78-164 No. 1 south of Point Arguello and core hole and well data south and east of Point Conception. Where possible, onshore structure and stratigraphy are extrapolated offshore within the area of investigation.

1 2

Figure 1. Location of study area. I 11 , }' 111 C ', ~- , I It Ill ,,_ '',;" 4. , , -'7 , '9-9/ ,, , ~0 , '\. ,', ?o -,_ ~ p'\. SOUTHERN ..o,'·-~ -9__., ', ' ... , "Y~ COAST •,,' 4./1-' ',, G'~">._ "', '·,,./ ', ~ ,, ,,,,, --, --~ ( RANGES / II, ' ,, ,,,, '•,,,,- ,...,._____ I ... f I ', '•,,,,, '''IT'! 35° , / '•, 1 C{/''''''''•, • Y4A, I 11 ",, I I I I '"f4 ', , ',,,_ v4 ..... rTi'Ti"n .,.,.,...:(,- ~ ,,, ' 1 PACIFIC 1 I,, 1 '-t.("y ',, ''t,,,, ... OCEAN ', /'' ./, ', - ,,, ", ,.. ~ ~'''i7-- ,,,, ,,,,..,.~, I I ,, ,,''' .. ,, \ ', _.,../../ I I '\ \ lt,,l,~,, ' " TRANSVERSE -,,, ,,.,,,.. ".- I I -- I,/ RANGES Pt. - Arguello~ ------PROVINCE "\I I .,

,, II I I I\ 1 I 11\ \' ",. 1 o I , •' ' I ',, ""' '"" '' No. I ...... - Jl I I J "llt\11111' I I' I It I I I II/I '• 1\ t I II, I

I ,'I I I I I SANTA BARBARA : ''. '',,,',','' TROUGH I I J J 1 1 I 1 I 1 1 i Channel Islands

34° N C0 - PENINSULAR f ------RANGES • !·

w 4

ACKNOWLEDGEMENTS

The writer would like to thank Drs. Peter Fischer, George Dunne, and

Bruce Molnia for constructive advice and guidance in completing this project.

Special appreciation is directed to Kathleen Roush for her help and

patience.

GEOGRAPHIC SETTING

The area of investigation is located in the northwestern corner of the

Santa Barbara Channel and encompases 330 Km2 between Point Conception and

Point Arguello (Figure 1). Point Conception is 70 km west of the city of Santa

Barbara. The study area lies south and west of the Santa Ynez Mountain Range,

which trends east-west and forms the uplifted northern margin of the Santa

Barbara Basin.

BATHYMETRIC SETTING

The area of the continental shelf is 189 Km2 between Point Conception and Point Arguello. The shelf surface slopes westward approximately 20 (Plate

I). According to Yerkes and others (1980), an Arguello-North Channel slope

"extends for about 115 km from near Point Arguello to near Santa Barbara".

Incised into the outer shelf and slope, 6 to 10 km south of Point

Conception, are three submarine canyons. The canyons are generally V-shaped

(in cross section) and the canyon walls are steep with approximately 60m of relief. METHODS OF INVESTIGATION

GENERAL STATEMENT

For this study, several types of seismic reflection profiles were obtained from government and industry sources. The coverage consisted of: (1) 20 km of deep penetration (4 second sweep) digitally processed, common depth point

(COP) seismic profiles obtained from industry (figure 2); and (2) llOO km of processed industry and government sparker, acoustipulse, uniboom, and sonia profiles (Plates II and III) used for shallow and intermediate depth seismic coverage.

Cross sections (Plates IV and V) were constructed by correlating seismic profiles with the deep stratigraphic test well OCS-CAS-78-164 No. 1 south of

Point Arguello and well and core data south and east of the Point Conception

(figure 1). Their data were used to tie three reflectors over the study area:

1) Top of the acoustic basement (pre-Vaqueros unconformity)

2) Near top Monterey

3) Top middle to late Pliocene

Constraints imposed by a wide (deep penetration) seismic grid and marginal data quality in portions of the study area necessitated the presentation of structure contours on these reflectors as small scale figures.

A bedrock or subcrop geologic map below the Holocene and Late Pleistocene sediments was constructed using shallow and intermediate seismic profiles

(Plate VI).

TYPES OF SEISMIC DATA

The different types of seismic systems used in this study are listed in Table 1. Most of the systems are in the .06 to .4 KHZ frequency range and have shallow to intermediate penetration. These systems include uniboom,

5 6

•r-

Vl Q) s:: •r• ..- u •r- E Vl •r- Q) Vl +.1 s:: •r- 0 a. ..s:: +.1 a. Q) "0 s:: 0 ~ 0 u '+- 0 Vl Q) s:: •r• ..- ~ u co ~ I-

•r- LJ.... 7

Table I. Table of seismic coverage. Cruise Line Data Source Vessel-Date System Kilometers Quality

Intersea (for State R/V Paul- 1981 Sidescan sonar 3. 5 kHz 325 Fair Lands Commission sparker water gun PDR

Western geophysical R/V Western- 1981 Air gun 147 Good (for State Lands Commission)

McClelland engineers M/V Nidgeon - 1978 3. 5 KHz sparker 360 Good (for USGS) Acoustipulse

Fairfield (for USGS) M/V Peakcock - 1979 3. 5 KHz mini-sieve PDR 286 Good

():) 9

acoustipulse, and sparker profiles collected for the United States Geological

Survey (U.S.G.S.) by McClelland Engineers and Fairfield Industries to evaluate lease sales 48 and 53, respectively. Airgun and watergun systems collected for the State Lands Commission to evaluate the State tide and Submerged Lands between Point Conception and Point Arguello were also used in this study.

The deep seismic coverage consists of Common Depth Point (COP), digitally processed data obtained from industry. The data is 4800% stacked and has a four second sweep. The grid pattern is wide (4.3 km) and extends southwesterly 1.9 km from the shoreline (figure 2). Structure contours of the top of the acoustic basement, Monterey and the middle to late Pliocene are limited to the coverage of this deep penetration survey. The "bedrock map" incorporates seismic data from all the surveys. PREVIOUS WORK

Early marine geological studies in the Santa Barbara channel were made by Emery and Shepard (1945), Emery (1952, 1960), Hulsemann and Emery (1961), and Harman (1964). Later offshore work in the Santa Barbara Channel, which included the use of detailed seismic reflection profiling, was made by Moore

(1966, 1969), Vedder, et. al. (1969), Van Huene (1969), Curray (1970), Allen,

Schlueter, and Mikolaj (1970), Fischer and Kolpack (1971), Fischer (1972, 1976),

Fischer and Stevenson (1973), Fischer and Berry (1973), Moore and Beyer (1973),

Ashley (1974), Wagner (197 5), Green, et. al. (197 5), Wolf (197 5), Howell (1976),

Hoyt (1976), Henry (1976), and Vedder (1976).

Geologic studies of the northern Channel Islands and the surrounding shelf were completed by Weaver (1969), Yeats (1970), Howell (1976), and Junger (1979).

Studies by Raftery and others at California State University, Northridge are in progress at this time. Studies of the Quarternary sediments of the island shelf were completed by Day (1976) and Fischer (1972 and 1976).

The current area of investigation between Point Conception and Point

Arguello has been studied by oil companies, the United States Geological

Survey, and the California State Lands Commission. Along the southeast corner of the study area, numerous studies were made for the proposed liquified natural gas (LNG) facility east of Point Conception. Non-proprietary work included two published reports by Fugro, Inc •• One report described the results of the shallow penetration seismic investigation of the offshore Hosgri fault between Point Sal and Point Conception published in the USGS Open File

Report, 79-1199. Technical Appendix D (1979) to the Environmental Impact

Report for Exploratory drilling on lease PRC 2879.1 prepared by Fugro concerned the geologic hazards of the Union Oil Company lease 3 km south of

10 11

Point Conception. The environmental impact report published by the State

Lands Commission in 1982 dealt with the offshore geology of three Texaco leases (PRC 2725.1, 2206.1, 2955.1) approximately 11 km east of Point

Conception. Faulting and shallow stratigraphy of the shelf south east of Point

Conception were investigated by Fischer and others (1978) as part of the LNG site evaluation. The geology of the offshore state lands between Point

Conception and Point Arguello was reviewed by the State Lands Commission

Environmental Impact Report (1982). Yerkes and others (1980) discussed major offshore structures, regional seismicity, and deformational rates in the Point

Arguello area. Willingham (1979), in an abstract, described the structural character of the western termination of the Transverse Range Province.

Geologic studies of the deep statigraphic test well (OCS-CAL-78-164 NO. 1) south of Point Arguello were presented in the United States Geological Survey

Open File Report 79-1218. REGIONAL GEOLOGY

The study area lies on the northern edge of the California Continental

Borderland (Shepard and Emery, 1941; Moore, 1969) between Point Conception and Point Arguello where the Conception-Arguello shelf forms the northwestern margin of the elongate Santa Barbara Channel at the opening into the Pacific

Ocean.

The Santa Barbara Basin forms the western edge of the Transverse Range Province (Figure 1), an east-west-trending structural and topographic feature of-. Southern California lying between northwest trending structures of the Coast and Penninsular Range Provinces (Figure 1). The Transverse Ranges are believed to be a microplate bounded to the north by the Lompoc-Solvang-Santa

Ynez fault zone, to the south by the Malibu Coast-Santa Monica-Raymond Hills fault zone, and the San Gabriel fault to the east (Figure 3), which is believed to have moved 70 km west and northwest since the middle Miocene (Hall, 1981).

The Santa Barbara Basin is the submerged western extension of the

Ventura Basin, a structural depression filled with over 15,000m of Cretaceous and Tertiary sediments (Vedder, Wagner, and Schoellhamer, 1969). To the west, the Santa Barbara Channel contains an estimated 7,000m to 10,153m of early

Cretaceous sediments and 7 ,OOOm to 13,000m of Cenozoic sediments

(McKelvey, 1976). In the study area south of Point Arguello, 250 meters of

Miocene through Holocene sediments were encountered in the test well OCS­

CAL-78-164 No. 1 (Cook and others, 1979).

The Santa Barbara Basin is bounded to the south by the Channel Islands and to the north by the offshore northern shelf and slope and the onshore Santa

Ynez Mountain Ranges and fault (figure 4).

12 13

Figure 3. Generalized fault map west central California (Hall, 198lb). 14

\

Bo 0

II ' ' \ \ \ \

FAULTS

BP Big Pine R Rinconada Cu Cucamonga RH Raymond Hill EH East Husana SA San Andreas F Foxen Canyon sea San Cayetano H West Huasna SG San Gabriel HG Hosgrl SJ San Jacinto LP Little Pine SJu San Juan MaC Malibu Coast SM Santa Monica SMR Santa Maria River Nl Newport -Inglewood Oz Ozena SY Santa Ynez PM Pine Mountain 15

Fischer (1972) defined this northern boundary as the Santa Ynez block and subdivided it into the onshore mountain subblock and the offshore northern shelf. His mountain subblock extends from the onshore area north and west of the study area (Arguello Plateau to Point Conception) to the San Gabriel fault and consists of the Santa Ynez Range (Figure 4). The subblock contains approximately 4,725m of a nearly complete sequence of marine sedimentary rock of Late Cretaceous to Late Miocene age (McCulloch, Vedder, Wagner, and

Brune, 1979). This entire succession of sedimentary rock is exposed as a south dipping homocline along the western edge of the subblock. Structurally or unconformably underlying the late Cretaceous strata are Franciscan basement rocks (Dibblee, 1966) in the west and granitic basement rocks (Crowell, 1966) in the eastern portion of the subblock.

The Santa Ynez fault zone marks the northern margin of the subblock along which the Santa Ynez range was uplifted (Dibblee, 1950, 1966). The fault extends nearly 135 km from the San Gabriel fault at its eastern end (Gordon,

1978) to the termination of its northern branch north of Point Conception

(Figure 4). West of Lake Cachuma the fault branches into northwest-trending fault splays (Sylvester and Darrow, 1978) which are believed to be part of the northern boundary of the Miocene Transverse Ranges Microplate (Hall, 198lb).

Near Gaviota Pass, a southern branch of the Santa Ynez fault strikes southwest to the ocean near Algeria Canyon and then bends westward offshore to merge with the North Channel slope (figure 4). The dip along most portions of the

Santa Ynez fault is nearly vertical. The South Branch is believed to have reverse and left-lateral slip (Fischer, 1978 and Yerkes, Greene, Tinsley, and

Lajoie, 1980).

Fischer's (1972) offshore northern shelf subblock (Figure 4) consists of 16

Figure 4. Main structural features of the Santa Barbara Basin region (from Fischer, 1976). 120° ' 1-'oc. ' "!)). ' ' "~, ...... 'o 0 ..... f\\· ' _ ,c-l,o: e\ll .. \,...

Sal\ cayel\tOI\0 ?-- TtlfUS, "\--( ---:INCON V ---~A SANTA ~ ENTURA ~Mf ' ------TROUG ANTICLINA BARBARA r- H l TROUGH ' --- ~PI;;;;- --- / -...... M- ) ...... _ ON TALVO ---- \. '"'"'- A N T I ? ...... ------<. ~t-'v I CLINO;--- v~~~o~"~ ' ------~IUM SO - I .____ UTHERN SHELF..... - AIIOCHANN EL T ---1 ' ------RO HANNEL ISLANds, - - "•" C ~ -- ...... ~ AI ~ ~0 M•l .. .. \------

...... 18

east-west-trending faults and folds and northwest-trending tear faults. The

northern shelf subblock and portions of the mountain subblock are underlain by

reverse faults. The area is undergoing active compressional deformation. The

Point Conception-Gaviota area has uplift rates of 3-4 mm per year with an

historic uplift rate from 1904 to 1914 of over 28 mm per year (Yerkes, Greene,

Tinsley, and Lajoie, 1980).

Modern tectonism is generally confined to the northern portion of the

Santa Barbara Basin where north-south compression is occurring. In the .. southern portion of the basin, extensional structures are predominant. Along

the Channel Islands shelf, four undisturbed transgressive-regressive cycles

I indicate that the area is relatively tectonically quiescent (Fischer, 1972).

In the study area and to the north and west, northwest trending, southeast dipping reverse faults with possible left lateral slip are believed to be predominant (Yerkes, and others, 1980). According to Willingham (199) a major

uplift along reverse faults parallels the coastline offshore between Point

Conception and Point Arguello. TECTONIC SETTING

A complex plate tectonic history involving subduction in the Paleogene, and right lateral shear and north-south compression in the Neogene characterizes the Cenozoic western Transverse Ranges.

The Upper Cretaceous through Oligocene tectonic setting in the vicinity of the western Transverse Ranges was one of active subduction of oceanic lithosphere of the Farallon plate beneath the continental North American plate

(Dickinson 1976, 1979; Atwater, 1973; Crouch, 1981). Subduction occurred along a north-south-trending magmatic arc/trench system which paralleled the present

California coastline and ~extended from "Central America to northernmost

California" (Crouch, 1980).

Cretaceous and Paleogene rocks in the Western Transverse Ranges show evidence of this arc-trench system. Franciscan "basement" rocks, which are exposed along portions of the Santa Ynez Mountains, are believed to represent accreted "deep sea radiolarian oozes and ultramafic crust" that was not subducted beneath the North American plate (Crouch, 1980; Ingle, 1980).

Cretaceous and early Paleogene sedimentary rock exposed in the western Santa

Ynez Mountains are deep sea fan deposits that were derived from the North

American plate and deposited over the floor of the trench (Nilsen and Clark,

1975).

The sedimentary package in the Santa Ynez Mountains represents a continuous regressive sequence from late Cretaceous to early Oligocene (Ingle,

1980). Deposited progressively in the Cretaceous-Paleogene trench were deep water shales and turbidites (Upper Cretaceous to Eocene) followed by shelf, littoral, and continental deposits of late Eocene to Oligocene age (Dibblee,

1966; Stauffer, 1967; Hamilton, 1978).

19 20

Relative to the present orientation of the Santa Ynez Mountains, deposition progressed southward and westward (Stauffer, 1967). Equivalent depositional slope, shelf, or littoral facies are progressively younger westward along the Santa Ynez Range (Van de Kamp and others, 1974). The regressive cycle culminated with the late Eocene/Oligocene non-marine Sespe Form.ation in the eastern Santa Ynez Mountains and a major Oligocene unconformity in the

Point Conception-Point Arguello area (Ingle, 1980).

Pyritized Eocene foraminifera suggest the formation of submarine sills which intersected the oxygen minimum layer during the middle Eocene (Gibson,

1973; Ingle, 1980).

A major reorganization of tectonic stresses occurred in the Southern

California area when the Farallon Plate/Pacific Plate spreading ridge intersected the trench in the late Oligocene, approximately 29 million years ago

(Atwater and Molnar, (1973), Blake and others, 1978) (Figure 5). The resulting plate interaction ended subduction, started the migration of the Mendocino triple junction northward and the Rivera triple junction southward, and initiated the San Andreas transform between the American and Pacific plates (Dickinson and Snyder, 1979). These events triggered Neogene basin formation, subsidence, and rapid transgression along the southern and central California margin (Ingle,

1980).

In the western Transverse Ranges, an unconformity exists between folded

Eocene units and the overlying Vaqueros Formation (Dibblee, 1950). The unconformity marks a period of uplift and erosion during the late Oligocene- early Miocene in the Point Conception-Point Arguello area equivalent to \ . Dibblee's (1950) Ynezian orogeny (Fischer, 1972). Throughout the Transverse

Ranges Province, regional subsidence and rapid transgression are indica ted 21

Figure 5. Interaction of the Pacific, Farallon, and North American Plates (modified from Crouch, 1981). 22

EXPLANATION

IT] Pacific plate ~ Patton Ridge area

Farallon plate fAKWC\~~~ California Continental Borderland IT] North American plate Oceanic ridge v v Subduction zone (trench) Transform fault Pacific plate motion c:::::> relative to the North American plate I

23

by overlying littoral-shelf, and slope deposits (Ingle, 1980}.

Subsidence of a linear east-west-trending trough, called the Capitan­

Santa Clara trough (Fischer, 1972}, occurred along the southeastern edge of the

present Santa Ynez Mountains in the early Miocene (Edwards, 1971). By middle

Miocene time this trough had subsided and widened so that it encompassed

much of the area that is now the Santa Barbara channel (Fischer, 1972}.

Between 15 and 17 million years ago, subaerial and submarine volcanics

of rhyolite, dacite, and basalt were extruded along a "leaky San Luis Obispo

transform" (Hall, l981a) that made up part of the eastward migrating San

Andreas Transform System (Blake and others, 1978). These volcanics fringe

the present Santa Maria Basin and are present as Dibblee's (1950) Tranquillion

and Solvang volcanic centers in the northwestern Santa Ynez Mountains.

Largely following deposition of the Santa Maria-northern Santa Barbara

volcanics, the Transverse Ranges microplate (defined by the Lompoc­

Solvang-Santa Ynez fault zone as the northern boundary and the Malibu

Coast-Santa Monica-Raymond Hills fault zone as the southern boundary)

moved northward and westward over 70 km between 8 and 14 million years

ago {Hall, 198lb). The Santa Maria Basin was formed during this same period

as a pull-apart structure between the northward-migrating,

counterclockwise-rotating Transverse Ranges microplate and the San Luis

Obispo Transform (now the Santa Maria River-Foxen Canyon-Little Pine­

Lompoc-Solvang fault system) (Figure 6) (Hall, 1981 a and b).

Kamerling and Luyendyk (1977) stated that the volcanics in the Santa

Monica mountains of the Transverse Ranges have rotated 750 clockwise. The discrepancy in direction of rotation is explained by Hall (1981b) as clockwise

rotation of individual blocks by right lateral faulting or 24

Figure 6. Late Miocene generalized paleogeologic map of the Santa Maria pull-apart basin (from Hall, 1981). 25

----'Ct.l•tU _= •: 1\,IO"'f'f!~

Arro undrrlo1n by Juross1C Ophtolite, chert, sholr, Fronmcon rocks, or Lospe (Sespe) Formation

COI'te•OtiCift~-· 26

extension within the larger northward and westward migrating Transverse

Ranges microplate.

Basins created by lower to middle Miocene plate interactions subsided

rapidly at rates of 200 to 850m per million years (Graham, 1976; Ingle, 1981).

The basins became starved as sedimentation could not keep up with subsidence.

Also, during middle Miocene time, oceanic cooling (Woodruff, 1981) and a

lowering of sea level (Vail and Hardenbol, 1979) produced upwelling in the

Southern California area (Isaacs and others, 1983). These factors, together with · a well developed oxygen minimum layer, produced the "laminated diatomites and diatomaceous mudstone" of the Monterey Formation (Ingle, 1981).

In the northwestern Santa Ynez Mountains, the Monterey and older

Miocene units thin or buttress against Eocene rocks (Dibblee, 1950). This relationship was used by Fischer {1972, 1976) to define the "Arguello Positive" and probably indicates uplifted remnants of the Ynezian orogen (Cenozoic

Evolution).

According to Blake (1978) and Isaacs and others (1983), new basins were formed regionally about 10 million years ago as a result of a "minor westerly change in relative plate motion between the Pacific and North American

Plates". Within the western Transverse Ranges microplate, subsidence rates leveled off between 10 and 15 million years ago when pa1eodepths reached IOOOm {Ingle, 1980).

During late Miocene and early Pliocene, an increase in terrigenous sediment supply, contributed partly by a global lowering of sea level (Vail and

Hardenbol, 1979), diluted biogenic deposition and started an east to west basin filling cycle of sedimentation "that became the dominant theme during the later Pliocene-Pleistocene" {Ingle, 1980). Late Miocene-early Pliocene uplift 27

in the Santa Ynez Mountains area and throughout the borderland to the south was also a major contributing factor in increased sedimentation (Ingle, 1980).

Uplift in the Santa Ynez Mountains area occurred simultaneously with the rejuvenation of the Capitan-Santa Clara trough to the south (Fischer, 1972).

Right slip along the San Gregorio-San Simeon-Hosgri (and possibly adjoining

Santa Ynez) fault zone may have occurred 4 to 8 million years ago (Hall, 1981).

With the establishment of the western Transverse Ranges microplate configuration (approximately 8 mybp) and the formation of the Santa Clara trough and Santa Ynez uplift (possibly 4mybp estimated by Hall, 1981), the present Santa Barbara-Ventura Basin structural trend was established. Along this trend, basin filling from east to west continued with the deposition of distal fan, suprafan channel and overbank, slope, shelf-littoral, and non-marine, deposits into latest Pleistocene (Ingle, 1980). The present Santa Barbara channel is the submerged extension of the filled Ventura Basin (Fischer, 1976).

Tectonic stresses in the last 4 million years have been affected by

"about 250 km of right slip along the San Andreas Fault" (Crowell, 1962, Hall,

198lb). Within the western Transverse Ranges, Fischer (1972) described evidence of the Pasadenan phase of the Cascadean Orogeny in the middle

Pleistocene (less than 1.5 mybp). The evidence includes a "strong angular unconformity at the base of Ventura area marine terraces" that indicates uplift of the Santa Ynez Range. Jackson and Yeats (982) assign a middle to late Pleistocene age to the formation of the Carpinteria basin south of the

Santa Ynez Mountains. Regional evidence that the Pasadenan Orogeny continued at least into the latest Pleistocene includes 1) seismicity associated with east-trending, left-oblique reverse faults in the Santa Barbara Basin that parallel the bend in the San Andreas (Yerkes and 28

Lee, 1979), and 2) historical earthquakes associated with a portion of the sinistral Santa Ynez River wrench fault (Sylvester and Darrow, 1979).

Evidence of uplift in the Point Conception area includes the deflection of the

Point Conception fan (Fischer, 1972; 1976) and offset of an early Holocene or late Pleistocene stream terrrace by the South Santa Ynez fault (Yerkes and others, 1981). REGIONAL STRATIGRAPHY

GENERAL STATEMENT

Onshore stratigraphy east of the study area in the Santa Ynez Mountain range consists of a nearly complete sequence of homoclinaly south marine and non-marine strata of Cretaceous through Holocene age (Dibble, 1966). These rocks are exposed along the Santa Barbara Channel coastline from Point

Conception to Canada de Santa Anita (Cook, 1979). This Cretaceous through

Holocene sequence unconformably or structurally overlies intensely deformed pre-Cretaceous (Upper Jurassic?) "basement" rocks (Vedder and others, 1969).

Wells drilled offshore near the middle of the Santa Barbara Channel have encountered 1829m of Pliocene and Pleistocene rocks which are not present to the north in the Santa Ynez Mountains (Vedder and others, 1976). North of the study area, between Point Conception and Point Arguello, the stratigraphy is complicated by the presence of several unconformities. Cretaceous rocks may be unconformably overlain by early Eocene, late Eocene, early Miocene or middle Miocene sediments at different locations in the western Santa Ynez

Mountains (State Lands Commission, 1982).

Stratigraphic units are generally the same in the western Santa Ynez

Mountains as they are east of Point Conception. However, 370m of rhyolitic extrusives are present near Point Arguello which are absent to the east

(Dibblee, 1950).

Foraminiferal stages by Kleinpell {1938) have been found to be time transgressive (Bandy, 1971; Lipp, 1971; Gibson, 1973). There is, however, general agreement as to the relationship of these benthic stages to planktonic correlations and formation boundaries (Ingle, 1980). The stratigraphy of the western Transverse Ranges is shown by figure 7.

29 30

·.

Figure 7. Stratigraphic column of the western Transverse Ranges (from Dibblee, 19 50 and Van de Kamp and others, 1974). 31

0 Pocel•neovl 0 Ct.ert, Sili&eo••• 0 .. S"ele MONTEAE I 0 0 Ort•" Ia llll•t• a 2 Tl'h' Lhneatofte

0 z ~,o• 0 R~yolito a loaoll "' o.'' !:! Anlo•oroto Toft u "(, .... lentoRite "'0 ·~ 0 i RINCON CLAYSTONE

_j;·.·:,;; "J~': I 0 'loft4ato•• a YAOUEIIOf~·;~.:::::·: 0~ CoRgiOftltrate Varittatef lanll• · stone a Slttltoflt "'z u "'0 .SANDI TONE !:! a SILTSTONE ...1 Upptr (SS) 0 "COLDWATER" Middle -(Shale) SANDSTONE Lower {SSI a CLAYSTONE uDD"er (Shale) COZY DELL Cozy De II Sand

CLAYSTONE Lower (Shale) zI&J MATILI.JA Ill ...... Upper u 0 AIIKDSIC 0 -:.:==.:.:.• 11.1 MATILL~ ...... ·.-.•: ! lANDS TONI .JUNCAL Camino Cielo )-~!'S:./! I Sand ~.·.-:-:·.· 0 SHALE a Lower CLAYSTONE SIERRA BLANCA Alaor Li••••••• f'- ANITA (PALEOCENE) CloJ&I ..o a SittlteRe.,,.,,...... 'i•e- - CRETACEOUS •'•"' at top ··~ ......

II) :::..~:..:.. ::I 0 === "'~ ~~!! I&J IE u CAIIBONAC:EOUI IE SHALE a TNIIt I&J 3t IANDITONI 0 ...1

- u IASAL I'EIILES SANDSTONE IE iii I&J II) D. .. D. "··· IE ...... ::I .,::I s.,,• ...... ••••• ,,.,, ••• 32

Onshore stratigraphy between Point Conception and Point Arguello is believed to typify most of the offshore stratigraphy in the study area. Epstein and Nary (1982) correlated Miocene and early Pliocene units in the offshore

Union PRC-2879 well with equivalent units in onshore wells at Point Conception and Point Arguello. Pre-Miocene rocks that outcrop in the western Transverse

Ranges were penetrated in the subsurface in wells drilled at Point Arguello.

(Dibblee, 1950) and can be extrapolated offshore. The following descriptions of lithologic units between Point Conception and Point Arguello are from Dibblee

(19 50).

PRE-CRETACEOUS

Franciscan basement rocks are exposed in the western-most Santa Ynez

Mountains north of Canada Honda Creek where they are in fault contact with the overlying Honda Formation (Cook, 1979). The Franciscan complex is also exposed as fault slivers adjacent to the Santa Ynez fault (Vedder and others,

1969).

Exposures of Franciscan rocks in the San Rafael Mountains to the northeast consist of highly deformed sandstone, clay shale, radiolarian chert, and basalt which have been intruded by serpentine rocks. The sandstone is hard, massive and jointed and consists of medium grained, arkosic, angular feldspar grains. Irregular lenses of red and green cherts approximately 80mm thick are found within the shales. The basalts are amygdaloidal with pillow structures and have been partially altered to greenstone.

The chert, basalt, sandstone, and shale are all cut by serpentine sills.

Franciscan Basement is believed to underly the Santa Ynez Mountains west of Carpinteria and most of the Santa Barbara Channel (Fischer, 1972). 33

However, a transition from Franciscan to "granitic" basement must exist under

the channel since schistose metamorphic rocks intruded by hornblende diorite are present on Santa Cruz Island (Vedder and others, 1969).

Exposures of Franciscan rocks in the northern and central portions of

California are generally interpreted as accreted deep sea siliceous oozes and

ultramafic material of a major north-south trending arc-trench system (Ernst,

1970; Ingle, 1980; Crouch, 1981). The Franciscan is upper Jurassic to Paleogene

in age (Crouch, 1981).

Faulted against the underlying Franciscan assemblage is several hundred

meters of marine clay shale of Dibblee's (1950) Honda Formation. The Honda

Formation is only exposed at the Canada Honda Creek in the westernmost Santa

Ynez Mountains where it consists of sheared, greenish-brown clay shale with calcareous concretions and thin layers of fine grained sandstone. Fossil evidence suggest the Honda Formation is Late Jurassic and Early Cretaceous in age (Cook, 1979).

CRETACEOUS

Overlying the Honda Formation is the Lower Cretaceous, marine, Espada

Formation (Dibblee, 1950) which consists of over !200m of dark greenish-brown, silty shales interbedded with thin, fine-grained sandstones. The Espada shale contains black carbonaceous specks along cleavage planes and occasional thin conglomerate lenses.

At the type locality in the Canada Honda, the Espada unconformably overlies the Honda Formation. However, the Espada Formation is believed to conformably overlie the Honda in the Tranquillon Mountain area (Cook, 1979).

The Jalama Formation (Dibblee, 1950) is Late Cretaceous in age and 34

consists of !200m of clay shales and sandstones. The sandstones are grey to white, hard, well bedded to massive, well sorted, medium to fine grained, and inter-bedded with siltstones and silty clay stones. The clay shales are dark grey to brown and slightly carbonaceous.

According to Nilsen and Clarke {197 5) and Ingle {1980), these sand sand shales described above are considered "abyssal and lower bathyal" submarine fan sediments that were deposited westward into the north-south-trending

Cretaceous trench (Nilsen and Clarke, 1975; Ingle, 1980).

PALEOGENE STRATIGRAPHY

Overlying the Cretaceous Jalama Formation is a Paleocene-Eocene­

Oligocene marine sequence consisting of a "turbidite and marine lutite" facies, a "proximal turbidite" facies, and a "shallow marine" facies that together make up the major regressive cycle in the western Transverse Ranges (Van de Kamp and others, 1974; Ingle, 1980). The contact between Paleogene and Cretaceous units is unconformable in the Point Arguello area (Dibblee, 19 50; Cook, 1979), but it is considered to be conformable in other portions of the Santa Ynez

Mountains (Gibson, 1973; Ingle, 1980).

Paleocene

Two hundred meters of interlayered marine sandstone, claystone, and conglomerates that make up the lower portion of Dibblee's {1950) Anita Shale are Paleocene in age (Gibson, 1973; State Lands Commission, 1982). Van de

Kamp and others (1974) confine Dibblee's (1950) Anita Shale to the Paleocene portion of that Formation. They also redefine Dibblee's (1950) western Santa

Ynez Eocene and Oligocene formations based on "facies distribution" and

"lithostratigraphical sequence" correlations within the eastern and central

Santa Ynez Mountains. Stratigraphic correlations in the western Santa Ynez

Mountains are summarized in Figure 7. 35

Eocene

The Eocene-lower Oligocene sequence in the western Santa Ynez

Mountains consists of 1300 meters of conformable marine sandstones and shales

originally mapped as the Tejon Formation (Arnold and Anderson, 1907; Effiner,

1936). Dibblee (1950) divided this series into five formations; the Anita Shale,

the Matilija Sandstone, the Cozy Dell Shale, the Sacate formation, and the

Gaviota formation. The Sierra Blanca Limestone is present at the base of the

Eocene section but only as small outcrops at three localities in the western

Santa Ynez Mountains.

The Eocene-lower Oligocene sequence is thickest east of Gaviota Canyon.

North of Jalama Creek the sequence thins rapidly to the south and west

(Roubanis, 1963). In the Point Arguello-Tranquillon Mountain area, disconformities exist between the Cozy Dell, Matilija and Anita Formations

(Roubanis, 1963; Cook, 1979).

The Anita Shale (Kelley, 1943) consists of 300m of dark-grey clay shales with thin beds of micaceous sandstone and thin calcareous sandstone beds. Van de Kamp and others, (1974) subdivide the Anita Shale of Dibblee (1950) and

Kleinpell and Weaver (1963) into a Paleocene Anita Shale Formation, the Sierra

Blanca Formation, and the lower Juncal Formation. The Paleocene Anita Shale

Formation consists of siltstone and shale with a small percentage of "very thin to medium bedded, graded sandstones" that together indicate "turbidite and marine lutite deposition in a bathyal basin" (Van de Kamp, 1974).

The "Sierra Blanca Formation" consists of limy silt and mud deposited at

"lower bathyal depths" that represent "redeposited bioclastic and glauconitic debris from coeval banktops and shelves fringing a Paleogene" high that existed north of the study area (Gibson, 1973; Van de Kamp and 36

others, 1974; Ingle, 1980). In the western Santa Ynez Mountains, these limy muds interfinger with radiolarian tests and "foraminifera rich" terrigenous sediments that Dibblee (1950) named the "Poppin Shale" (Van de Kamp and others, 1974; Ingle, 1980). The transition from predominantly "arenaceous fauna" to "calcareous fauna containing lower bathyal-abyssal species" may mark the Paleocene calcium compensation depth (Gibson, 1973; Ingle, 1980).

The upper portion of Dibblee's (1950) Anita Shale, correlated with the

Lower Juncal Formation by Van de Kamp and others, (1974), marks a -- continuation of terrigenous sediment deposition at bathyal depths during the early Eocene.

The Matilija Sandstone (Kelley, 1943) consists of 300m of massive, medium-grained, white to buff sandstone beds separated by micaceous, sandy shales. These upper bathyal "thick accumulations of thicker bedded proximal turbidites" are "lithostratigraphically" equivalent to the "Camino Cielo member" of the Juncal Formation of the eastern Santa Ynez (Van de Kamp and others, 1974). The position of these "thick bedded proximal turbidities" above and below deep water sediments indicates "deep-sea submarine fan and channel deposition" (Link, 1975).

The Cozy Dell Shale (Kerr and Schenck, 1928) consists of 200m of well bedded, gray clay shales interbedded with thin, greenish sandstone at the base and thin, siliceous, brown clay shale in the upper portion of the formation.

Dibblee's (1950) Cozy Dell Formation becomes sandy near the top anq grades into the overlying Sacate Formation.

Van de Kamp and others (1974) determined that Dibblee's (1950) Cozy Dell

Shale Formation is lithostratigraphically equivalent to the Upper Juncal

Formation of the central and eastern Santa Ynez Mountains. Both 37

represent upper bathyal deposition of laminated basin muds and thin fan sands and silts.

The Sacate (Kelley, 1943) and Gaviota (Effinger, 1935) Formations are not differentiated in the Point Arguello area because there is no distinct fauna or lithology change to separate the two formations. The Eocene-Oligocene boundary is in the upper portion of these undifferentiated marine sediments

(Dibblee, 19 50).

In the Point Conception area, Dibblee (1950) subdivided the Sacate and

Gaviota based on mega fossils and foraminiferal fauna in the Sacate of Upper

Eocene age. The Gaviota formation was identified by Schenck and Kleinpell

(1936) as belonging to the "Refugian" Stage (upper Eocene to lower Oligocene).

Van de Kamp and others (1974) correlate the Sacate and Gaviota with the

Matilija, Cozy Dell, and "Coldwater Formations" of the central and eastern

Santa Ynez Mountains. Lithostratigraphic and paleontologic correlations are summarized in Figure 7.

The Sacate Formation (the Matilija Formation of Van de Kamp and others,

1974) consists of 300m of fine-to medium-grained, hard, well bedded to massive gray sandstone interbedded with gray, bedded and laminated, micaceous shales.

The lower portion of the Sacate was deposited by turbidity currents (Jestes,

1963) at bathyal depths (Blaisdell, 1955). These fine grained, thinly bedded sandstones are over lain by coarser grained, thicker bedded sandstones. Link

(197 5) interpreted this sequence in the central and eastern Santa Ynez

Mountains as proximal turbidites overlain by shallow-marine "coastal and restricted-coastal lithofacies" which together make up a "progradational deltaic complex".

A similar depositional environment is suggested for the Sacate/"Matilija"

Formation in the western Santa Ynez Mountains (Van de Kamp and others, 1974) 38

Kamp and others, 1974). They conclude that the "predominantly proximal turbidite sequence", and the "local occurrence of conglomeratic, sandfilled channels" indicate "progradation of shallow marine sediments" from a probable source area to the north.

The Middle and Lower Eocene formations discussed to this point make up a single regressive cycle. Beginning with the "basin plain and submarine fan deposits" of the Anita and Juncal Formations (Ingle, 1980), the regressive cycle continues with prograding shallow marine deposits of the Sacate/"Matilija"

Formation (Link, 1975). Van de Kamp and others (1974) interpret a minor transgression followed by a second regressive cycle during the deposition of the

Gaviota and Alegria Formations of Dibblee (1950). Ingle (1980) identifies a single regressive cycle for the entire Eocene--Oligocene stratigraphic sequence.

The upper "Matilija"/Sacate is interpreted as a "short-lived local excursion of a nearby delta front onto the shelf and slope (Link, 1975; Ingle, 1980).

Dibblee's (1950) Gaviota Formation (Cozy Dell and Lower "Coldwater"

Formations of Van de Kamp and others, 1974) consists of 500m of siltstone and sandstone which Dibblee (19 50) divided into three members. The lower member is a soft gray siltstone; the middle member consists of well sorted, fine- to medium-grained sandstone, and the upper member consists of interbedded sandy siltstone and fine-grained sandstone.

The lower member of the Gaviota Formation was deposited at bathyal ' depths (Wilson, 1954; Kleinpell and Weaver, 1963). This lower member is equivalent to the Cozy Dell Formation of Van de Kamp and others (1974) and marks their Eocene-Oligocene boundary.

Oligocene The middle and upper members of Dibblee's Gaviota Formation and 39

the Alegria Formation (equivalent to the "Coldwater" Formation of Van de

Kamp and others, 1974) consists of "neritic and littoral lithofacies and biofacies

(Wilson, 1954; Obrien, 1972; Ingle, 1980).

The Algeria Formation (Dibblee, 1950) is absent in the Point Arguello area

but present in the Point Conception area where it consists of 300m of medium­

to coarse grained, buff to grey, well bedded sandstone. Grey, fine grained

sandstone, greenish siltstone, and brown clay shale are also present. The

Alegria is the marine facies of the continentia! Sespe Formation found in the

eastern Santa Ynez Mountains.

NEOGENE STRATIGRAPHY

The upper Oligocene--lower Miocene Vaqueros Formation (Hamlin, 1904)

lies disconformably on the Alegria with up to 100 of angular discordance

between the two formations in the western Santa Ynez Mountains (Fischer,

1972). In the northwestern Santa Ynez Mountains, the Vaqueros unconformably

overlies previously folded Gaviota and older formations.

The Vaqueros consists of 190m of marine, greenish-brown or buff, fine- to

medium-grained sandstone interbedded with massive grey siltstone; and basal

conglomerates.

The marine lower Miocene Rincon Shale (Kerr, 1931) conformably overlies

the Vaqueros formation in the western Santa Ynez Mountains. In the Point

Arguello area to the north, the relationship is unconformable.

The Rincon shale consists of 460m of brown-grey massive clay shale. The shale is lower Miocene in age.

The Vaqueros and Rincon Formations represent a transgressive cycle of sedimentation in the western Santa Ynez Mountains. The coarse clastics of the

Vaqueros represent shelf deposits (Ingle, 1980) consisting of "offshore 40

massive highly burrowed fine-grained sands", coarse grained bank top deposits, and "thin deposits of coarse sand and conglomerate" formed over active structural ''highs" (Edwards, 1971; Fischer, 1972). The Rincon shale consists of

460m of brown-grey massive clay shale, which represent outer shelf and slope deposits (Ingle, 1980).

Over 300m of middle Miocene rhyolite, agglomerate, and ash of the

Tranquillion Volcanics are present in the Tranquillon Mountains near Point

Arguello in the western-most Santa Ynez Mountains. Unconformably overlying the Rincon Shale and conformable with the overlying Monterey Formation, the volcanics consist mainly of buff, dense to porphyritic, rhyolite flows. Fischer

(1972) suggests that the distribution of Tranquillon Volcanics "indicate subaerial flows extending southwards from east-west trending faults."

Several other middle Miocene volcanic centers are present in the Santa

Barbara Basin area. They include "Conejo" andesite and basalt flows in the

Santa Monica Mountains, and volcanic sequences separated by the Monterey

Formation on the Santa Cruz and Santa Rosa Islands. The Channel Islands volcanics are made up of the lower unit called "Conejo" and the upper andesitic and rhyolitic unit called the "Santa Margarita Formation" (Vedder and others,

1969).

The Monterey Formation (Blake, 1855) of middle to late Miocene (Luisian­

Mohnian) age consists of predominantly biogenic sediments deposited in a sediment starved anaerobic basin (Ingle, 1980). The Monterey is found extensively around the Santa Barbara Basin area and the western Santa Ynez

Mountains and consists of up to 600m of siliceous shales which can be divided into an upper and lower member.

The lower member consists of up to 500m of phosphatic shales, 41

organic shales, diatomite, siliceous shales, limestone beds, and volcanic ash. In

the western Santa Ynez Mountains, the upper member consists of opaline cherty

shales with layers of chalcedonic chert and laminated diatomite. Thick lenses

of well-bedded conglomerates are present at the top of the upper member along

the shoreline west of Gaviota Canyon and Sacate Canyon (Isaacs, 1981; Dibblee,

1950).

Isaacs (1981) divided the Monterey Formation along the Santa Barbara

Channel into five informal members. With the exception of dolomite nodules,

the upper member contains no carbonate. All the lower members contain

carbonate and two of them contain organic phosphatic calcareous shales. Isaacs

(1981) correlates the siliceous member, upper calcareous shale member, and

transition member with Dibblee's Lower Monterey. A description of each of the

members and their approximate age and thickness is given in Table II.

A regional facies analysis of the Monterey in the Santa Maria Basin and

Coast Ranges by Isaacs and others (1983) identified three regional deep water

marine facies. They are a--

1) Siliceous facies (equivalent to Isaac's (1981) siliceous and upper

calcareous shale members in the northern Santa Barbara Channel).

2) Phosphatic facies (equivalent to the transition and organic shale

members).

3) Calcareous facies (equivalent to the lower calcareous shale

member).

Isaacs and others (1983) associated these deep water facies with major

"climatic-oceanographic events" during the Miocene. They believe the calcareous facies was deposited during the early to early middle Miocene because "plankton (mainly coccolithophorids) predominated in the 42

Table II. Informal members of the Monterey Formation along the Santa Barbara Channel (from Isaacs, 1981). Mineral abundance 1n cll!'11l10n rock tyres, wt t -"'..,_ !i.,.,._ ...... c:"' !i .:= ~ Average u"' ... 0\­ ..,..., -... 41 .001 c:"' thickness .,._... c: .. <:""--' 0. ~mber Common rock typt>s • V'l ~-~ we C[ .5~ ~eddin~ characteristics (m) Age • I I I Siliceous Porcehnit~. siliceous 2~-90 10-65 <0.2 0-1 1-17. ..,eter-thick units of re~ularly 150 late Mohnian mpmber mudstone, siliceous shale, laminated porcelanite and cherty and cherty porcelanite. ror·cel anne interbedded ~

Uppt>r Cherty porcelanite, ?0-90 5-50 2-60 0-3 2·10 Meter-thick units gradinq upward 25 late Mohnian calcareous (siliceous) shale, porce­ frtll'l irregularly laminated shale lanite, and chert--all detr1tal-ri.ch carbonate-burin<] member calcareous and/or shale to regularly laminated dolomitic. carbonate-bear i n

Transition (Siliceous) shale, organic­ 5-90 5-50 5-60 0-20 2-~0 V3riable. In places, silica­ 40 Early and late member rich phos:>~~at 1c shale, nch rocks and hard shales arc Mohnian parcel anile, cherty por­ bedded as above (as thick as celanite, and chert--all i m) or phosphatic shales are calcareous and/or bedded in thick {as much as I n) dolmtit1c. un•ts. In other places, roc~s .1re Intimately interlayered.

l)rganic Or<]anic-rich calcareous J-25 15-50 25· IS 0-~0 "-~~ Sh.llc-units {dS thick as 15m) RS luisian and shale shale, commonly phosphatic. "' th unc(J11mon interbeds of chert early Mohn1an l'lel'lber or rorcelanite (l cm-7 m thick}.

lower (Siliceous) nud~tone, 5-90 S-50 5-80 0-10 1-19 In u~per strata, rocks are 100 Latest Saucesian, calcareous (si\ iceous) shale, rorcc­ irro·~uldrly laminated shalP; in Rrlt1ian, and sh~le lanite, and c~ertv rur­ \~,~r strc11ta, rock\ c11re •nass1ve e-1rly luisian menber celanite--all calcar~ou~ ,,n,1 t hI Ci hPr1ctP.f1 • .1nd/or dol!J'lltlC.

..J::a w

""' 44

warm, low-fertility seas" during that time, resulting in sediments that were carbonate rich. Later, ''higher nutrient levels engendered by late middle to late

Miocene cooling and intensified upwelling led to phytoplankton populations dominated by diatoms and the consequent predominantly siliceous sedimentation of the upper siliceous facies." They believe the phosphatic facies is related to the "maximum Miocene sea-level stand and the onset of Antarctic glaciation" during the Middle Miocene.

Up to 1500m of marine diatomite and diatomaceous shale of the Sisquoc

Formation (Porter, 1932) outcrop along the Santa Barbara coastline and extend into the western Santa Ynez Mountains to Jalama Canyon north of Point

Conception. The Sisquoc formation is late Miocene to early Pliocene in age and lies conformably on the Monterey except in the Jalama Canyon area where the relationship is unconformable. Uplift and erosion to the north and w~st has resulted in an absence of Sisquoc in the Point Arguello area. The Sisquoc

Formation is equivalent to the "Santa Margarita Formation" in the eastern

Santa Barbara and Ventura Basins where it has a higher sand content and less diatomite (Fischer, 1972).

In the Jalama Canyon-Point Conception area, the following description of the Sisquoc section was described by Dibblee (1950):

Top of section eroded Cream-white massive to poorly bedded somewhat punky silty diatomite with conchoidal fracture...... 800 feet Light brownish gray massive to poorly bedded silty to diatoma- ceous claystone, crumbly, with spheroidal fracture 1400 feet Light brownish gray well-bedded clay shale with splintery fracture, to laminated thin-bedded siliceous shale with platy fracture...... 1000 feet Brown massive compact sandy siltstone, highly bituminous; disappears west of Cojo Canyon; between Cuarta and Gaviota Canyons contains lenses up to 7 5 feet of well-bedded breccia-conglomerate composed of Monterey cherty shale debris in tar-soaked sandstone matrix 0-100 feet 45

Disconformity Monterey porcelaneous shale

The boundary between the Monterey and Sisquoc Formations is gradational at most exposures. However, the upper portion of the Monterey contains a higher average silica content, thinner mudstone units, and a greater percentage of porcelanite and diatomite. The boundary between the two formations can be indentified in the field within 5 meters (Isaacs, 1981). On electric logs, the upper portion of the Monterey is identified by an increase in resistivity, spontaneous potential, and velocity near the Sisquoc-Monterey boundary.

The Sisquoc depositional sequence marks an increase in the "late Miocene- early Pliocene (Delmontian) terrigenous sedimentation rate, cessation of subsidence, and consequent shoaling" in the vicinity of the study area (Ingle,

1980).

Pliocene

Middle and upper Pliocene sediments are not present in the western Santa

Ynez Mountains. To the east, in the Ventura Basin, over 3500 meters of a marine Pliocene sequence have been deposited (Vedder and others, 1969).

In the offshore western Santa Barbara channel, Pliocene marine sediments are present as the "Pico-Repetto Formation" which consists of sandstone and conglomerate beds alternating with mudstone, clay stone, and siltstone beds

(State Lands Commission, 1982). The Pico-Repetto boundary is not a true formational boundary but rather a deep water foraminiferal facies change

(Vedder and others, 1969). The stratigraphy of the "Pico-Repetto" Formation in the offshore Point Conception area is summarized below from Fischer, 1978-- 46

Unconformity

Early "Pico" siltstone - only preserved along the outer shelf and Pleistocenebasin slope in the study area, unconformably overlaps to "Repetto" and Sisquoc Formations. May be transitional Late Pliocene into upper Pliocene sediments.

Unconformity

Early "Repetto" Shale - brown mudstone, siltstone and minor Pliocene sandstone, poorly indurated, onlaps Sisquoc Formation with angular unconformity near the modern shelf edge.

Unconformity

Early Sisquoc Formation Pliocene to Late Miocene

Pleistocene-Holocene

Pleistocene terrace deposits up to 20m thick unconformably overlie the older formations in the western Santa Ynez Mountains and are composed of sands, silts, conglomerates, and mudstone derived from the older rocks. The terrace deposits are generally unlithified and poorly stratified.

Recent alluvial sands, silts, and gravels occur as thin deposits in some of the canyons. OFFSHORE STRATIGRAPHY

INTRODUCTION

Offshore stratigraphic correlations in the study area are based on onshore stratigraphy, the offshore stratigraphy of the northern Santa Barbara Channel, and the lithologic and paleontologic analysis of the Point Conception deep stratigraphic Test well OCS-CAL-78-164 No. 1 by the United States Geological

Survey (Cook, 1979). The test well is located 1 km west of the study area and approximately 16 km southwest of Point Arguello at latitude 34°28'56.6" north and longitude 120°47'0" west (Figure 1).

A summary of the lithology and biostratigraphy of the test well is presented by Figure 8. Using seismic profiles, test well correlations were extrapolated 1.2 km along strike into the study area.

ACOUSTIC BASEMENT

A continuous, high amplitude reflector can be traced throughout the area of investigation on the processed multichannel seismic reflection coverage. In the well, this reflector marks an angular unconformity between lower middle Miocene and lower Cretaceous or uppermost Jurassic marine sedimentary rocks.

Mesozoic rocks are present in the well from 2957m subsea to TO

(3212m). The lower Cretaceous or uppermost Jurassic age designation of these rocks is based on coccolith biostratigraphy from the test well (Bukry,

1979). McLean (1979) describes the sediments from this interval as:

2957- 3193m--

Siltstone and mudstone, dark gray and dark greenish gray, massive with calcite cement interbedded with sheared and polished dary gray mudstone.

at 3132m (from a sidewall core sample)--

47 48

Figure 8. Summary of the lithology and biostratigraphy of the test well OCS-CAL-78-164 No. 1. 49

OCS-CAL. 78-164 No. I Test Well

DIP Lltholo~lc

(l'r••llf) 447 mtllfl 1,485 flit

2- •• I • SE

PLIOCENE ~ANOOM PLIOCENE

LOWER ,_,. PLIOCENE u ANO UPPER MIOCENE 0 ...1- c i= ...z ..."' , ...... i5 NE •[ z ::>

T.o. nzs Mtlltl 10.571 ,,., 50

Sandstone (arenite), grayish brown, fine grained, well sorted, quartz, plagioclase, altered volcanic rock fragments, mica, chlorite, and opaque minerals. Rare calcite and diatoms? Sub­ angular grains cemented by grain contacts and pseudomatrix. Volcanic ground-mass glass alternating to chlorite. No visible porosity.

3193m to TD

Sandy siltstone, gray, contains grains of quartz, plagioclase, chlorite, mica, calcite, and opaque laminae and has a zeolite matrix.

Dibblee's (1950) Espada Formation is upper Jurassic to lower Cretaceous in

age and may be equivalent to the Mesozoic rocks described above. Both are

predominantly siltstone and have a dark green coloration. Minor interbeds of

hard, fine grained sandstones in the Espada may be equivalent to the COST well

sandstone described above.

The Mesozoic reflectors are generally chaotic on seismic profiles that

were collected near the well site. This is most likely due to a loss of seismic

energy at the interphase between the Miocene sediments and the underlying

well cemented and compacted Mesozoic rocks. Beyer (1979) reports "sizeable

acoustic impedance contrasts" related to a series of sandstones above the

unconformity and the unconformity itself. Since the seismic energy is absorbed

at the unconformity and there are no traceable reflectors on seismic profiles

below this boundary, the term "acoustic basement" is applicable and corresponds with the Jurassic and Cretaceous rocks at the base of the well.

The chaotic reflectors typical of the acoustic basement do not exist on seismic profiles to the east. Although the continuous, high amplitude reflector corresponding to the top of the Mesozoic rocks in the test well is traceable to

the east, other very weak reflectors with variable amplitude become apparent below this main reflector. These underlying reflectors 51

are present in the eastern half of the study area. Their continuity is variable but none of the reflectors can be traced for more than a few thousand meters.

The transition from the chaotic "basement" to the discontinuous variable amplitude reflectors is fairly abrupt and is interpreted as a major southeast dipping unconformity (cross section X-X').

Both northwest- and northeast-trending seismic profiles near the COST well show an unconformable relationship between the high amplitude, continuous reflector and the underlying "chaotic" zone. In the COST well,

Mesozoic rocks dip 18o to 220 to the southeast from 3068 to 3153m below sea level (Prensky, 1979). Along seismic profiles in the eastern portion of the study area, the weak, discontinuous reflectors dip gently to the south and are truncated by the more continuous high amplitude reflector. Where northeast and northwest seismic profiles intersect and reflectors can be matched on intersecting profiles, dips range from Qo to 120 to the southeast below this continuous reflector.

It is concluded then, that the continuous, high amplitude reflector is a major unconformity present throughout the study area that truncates southeast dipping late Jurassic-Early Cretaceous and younger units. The transition from chaotic to weak variable amplitude reflectors below this major unconformity is believed to be a second unconformity separating Paleogene and Cretaceous rocks. This relationship is illustrated in cross section X-X'.

PALEOGENE

There are no Paleogene rocks in the Point Conception stratigraphic test well. Therefore, all inferences concerning the lithology and stratigraphic units within the Paleogene are based on seismic stratigraphic relationships of different packages of reflectors, the onshore stratigraphy 52

of the western Santa Ynez of Dibblee (1950) and other workers, and limited data from nearshore and offshore wells in the northwestern Santa Barbara Channel.

In the western Santa Ynez Mountains, late Paleocene and Eocene marine strata unconformably overlie Cretaceous and older "basement" rocks. This stratigraphic relationship is believed to extend offshore where industry sources estimate that !200m of Paleogene sediments overlie the Cretaceous and older units (although no confirmining well data has been made available) directly east of the eastern boundary of the chaotic zone mapped in figure 9.

The discontinuous, variable amplitude package of reflectors onlaps the chaotic zone at angles of 12o to 180. This onlapping of reflectors indicates an unconformity between the chaotic zone (Jurassic-Cretaceous rocks) and the

(Paleogene) discontinuous reflectors. This unconformity is truncated by

Neogene rocks above the high amplitude continuous reflector. The net result is the removal by erosion or lack of deposition of the late Paleocene, Eocene and

Oligocene rocks west of the chaotic zone boundary traced in Figure 9.

This interpretation of the chronostratigraphic relationship of reflectors below the high amplitude, continuous unconformity explains why Eocene rocks are present in the Santa Barbara channel and onshore in the Santa Ynez

Mountains but are absent in the Point Conception stratigraphic well. A problem with this interpretation is that Eocene rocks are present in the onshore Point

Arguello area (Dibblee, 1950). The extrapolation of the western boundary of the offshore Paleogene rocks onshore north of that portion of the study area where deep seismic coverage is available would suggest an absence of Eocene rocks in the onshore Point Arguello area to the west (Figure 9). However, Eocene rocks are present to the west of this line and Eocene rocks were penetrated in wells drilled at Point Arguello (Dibblee, 1950; State Lands Commission, 1982). Several 53

Figure 9. Paleogene and early Neogene seismic trends. 2 4km -----~~ ' ~ 0L------~--- -~ _,~ ~.,o Onshore ~~ProjectedExtrapolation of ·-~~ -~"$v'lJ~c? Boundary · ~ 1'--·

.., -~ ) -~ ) DISCONTINUOUS REFLECTORS -v ZONE (Paleogene) >..,) ) _.., ) CHAOTIC ZONE ·) (Jurassic- Cretaceous) _.., ~ BASELAPS POST­ ·•) PALEOGENE ... UNCONFORMIT~ )... ) --.l CONTINUOUS HIGH ) \ AMPLITUDE REFLECTORS ·") .-.) (Vaqueros I Rincon?) ) -v ) ·v ) . .,) )., >

U"l ~ 55

explanations are possible for this discrepancy and are discussed in Onshore­

Offshore Structural and Stratigraphic Correlations.

In the southeastern portion of the study area, the high amplitude, continuous reflector that defines the post-Paleogene unconformity becomes less distinctive on seismic profiles and is overlain by a set of high amplitude, continuous nearly parallel reflectors. The loss of reflected energy at the unconformity is interpreted as a gradual reduction of travel time, density, and lithology change across the unconformity as the sediments become nearly conformable to the south and east in the Santa Barbara channel. This interpretation agrees with onshore stratigraphic relationships, where along the northern margin of the Santa Barbara Channel a nearly complete sequence of

Paleogene strata crop out (Dibblee, 1950). Between Point Conception and Point

Arguello, the Paleogene sequence is interrupted by a major unconformity that separates the Eocene and Oligocene from the late Oligocene-early Miocene

Vaqueros Formation. A second unconformity separates middle Miocene

TranquiUon volcanics and the Monterey Formation from underlying Rincon and Vaqueros rocks.

A set of continuous, high amplitude nearly parallel reflectors overlies the post-Paleogene unconformity. These reflectors are believed to be equivalent to the Vaqueros and Rincon Formations and are mapped as a package of reflectors that baselaps the unconformity to the northwest. The western and northern boundary of this series of reflectors is approximately mapped in Figure 9. An unconformable relationship appears to exist on seismic profiles between the

Vaqueros/Rincon continuous reflectors and an overlying zone of discontinuous reflectors believed to be Middle Miocene in age (See Miocene). This 56

unconformable relationship is believed to correspond to an onshore (Post­

Rincon/Vaqueros-Pre Monterey /Tranquillon volcanics) unconformity.

The interpreted relationship of the post Paleogene unconformity and the post-Rincon unconformity to underlying and overlying units is illustrated in cross sections C-C' and X-X'. NEOGENE

Miocene

McCulloch and others (1979) separate the Miocene section in the Point

Conception stratigraphic test well into three units based primarily on lithology.

The uppermost unit is considered equivalent to the Sisquoc Formation (late

Miocene-early Pliocene) and consists of calcareous shales and siltstone. Below the Sisquoc are siliceous shales, mudstones, procelanite, and chert of the

Monterey Formation. Between the Monterey and Mesozoic rocks are siltstones, sandstones and pebbly sandstones composed of reworked Mesozoic rocks. No definite onshore equivalent of this lowest unit was identified although

McCulloch and others (1979) compared the lithology to the Vaqueros Formation exposed along the northern flank of the Santa Barbara channel.

Unfortunately, most of the Miocene section in the test well was non­ diagnostic or barren of micro-fossils (McDougal and others, 1979). Only the benthic foraminifera and coccoliths were useful in deciphering the Miocene biostratigraphy (Figure 8). McDougal and others {1979) indentified calcareous benthic foraminifers between 2569 and 2578m and 2744 to 27 53m in the well that are indicative of the late Luisian Stage. Samples from 2800 to 2809m and

3215 to 3224m were assigned an early Luisian age. The latter of these sample intervals was considered to be reworked. This agrees with seismic data which indicate that the base of the Miocene is approximately 300m at well depth. 57

This is supported by other evidence such as dipmeter logs (Prensky, 1979), density and sonic logs (Beyer, 1979), and nannofossils.

Bukry (1979) correlated coccoliths from 2523 to 302lm in the well with

"assemblages near the internationally recognized lower Miocene to middle

Miocene boundary."

On seismic profiles near the well, three distinctive seismic facies are present above the acoustic basement. These seismic units are believed to correspond with the Sisquoc, Monterey, and the "sandy unit," all from the

Miocene section of the well described by McCulloch and others (1979).

Overlying the "acoustic basement" unconformity is a seismic unit with few traceable reflectors. What reflectors are present have very low amplitude and no continuity or parallelism. This unit is believed to correspond to the basal pebbly sandstone interval. On seismic lines, this massive appearing unit continues eastward and terminates against the "acoustic basement high".

Northward, it becomes less distinct and is no longer traceable. The boundaries of the unit are difficult to define but appear to be confined to the southwest corner of the study area. According to test well descriptions by McLean (1979) this unit consists of reworked sand, silt, and pebbles possibly derived from the uplifted basement source. Descriptions of sediments from the well that correspond in depth to the massive unit (2385 to 2995m) were generally described as sandy siltstone, sandstone and pebbly sandstone. The sandstone is grey to greenish grey, medium to fine grained, calcareous, well rounded and poorly sorted. The siltstone is dark reddish brown with laminated clayey matrix or calcareous matrix. Some siltstone is tuffaceous with tuff altering to clay.

The pebbly sandstone contains green and light brown chert fragments with calcite cement. From a petrographic study of the sandstones, McLean (1979) 58

concluded that both ophiolitic and granitic source terraines for the sandstones may have existed.

The stratigraphic position of this sandy "massive" appearing unit is above the inferred pre-Miocene unconformity. As previously discussed, microfaunas suggest a lower to middle Miocene age for this basal Neogene unit.

The Monterey Formation is composed of porcelanite and siliceous mudstone in the stratigraphic test well. The porcelanite is grayish brown, laminated, partly dolomitic. Near the base of the Monterey, the porcelanite is described by McLean (1979) as silty, dolomitic, partly laminated siliceous shale.

The siliceous mudstone is soft and plastic. Chert and dolomite fragments were also found in this basal unit.

On seismic profiles, the Monterey Formation is characterized by dicontinuous reflectors with variable amplitudes. High amplitude, discontinuous reflectors at different depths in the formation probably indicate the chert, limestone, dolomite, and porcelanite beds.

Reflectors in the Monterey baselap the pre-Vaqueros unconformity. The

Monterey is significantly folded so that the regional dip was difficult to determine. Where unfolded, the Monterey was early horizontal. Where deep seismic data is available (Figure 2), the Monterey ranges from 300 to 700m in thickness throughout most of the study area.

Isaacs (1981) distinguishes nondiatomaceous Monterey rocks from nondiatomaceous Sisquoc sediments in outcrops north of the Santa Barbara channel by a greater average silica content and higher proportions of porcelanite in the Monterey. In the Point Conception stratigraphic test well, an increase in porcelanite at a depth of approximately 2000m marks the upper boundary of the Monterey. On most of the seismic profiles, this upper boundary 59

is defined by a transition from discontinuous, variable amplitude reflectors to continuous reflectors of the Sisquoc formation. The first continuous reflector

in the transition zone on all seismic profiles was mapped as the top of the

Monterey. The Monterey Formation is present throughout the study area.

Conformably overlying the Monterey Formation are calcareous shales and silts of the late Miocene/early Pliocene Sisquoc Formation. McCulloch and

others (1979) estimate the Sisquoc was penetrated in the Point Conception well at a depth of 1445m.

McLean (1979) describes the lithology for this interval as consisting of siliceous siltstone and mudstone, and porcelanite. The siltstones are siliceous, grayish brown, and friable. The mudstone is siliceous, grayish brown, noncalcareous, and weakly friable. The porcelanite is confined to the bottom

180m of the Sisquoc where it is described as partly thinly laminated with minor dolomite and chert.

A silty, very fine grained, grayish brown, friable, sandstone occurs at

1060m in the well. Calcareous feldspathic fine grained sandstones are interbedded with siliceous mudstone at approixmately !300m.

On seismic profiles, the Sisquoc Formation consists of continuous, medium amplitude, parallel reflectors.

The Sisquoc Formation varies considerably in thickness throughout the study area. In the western corner adjacent to the OCS well, the Sisquoc is

480m thick. The Formation thins eastward and is truncated in the southeast corner of the area by a major Pliocene unconformity. This unconformity is present throughout the area investigated and truncates the Monterey, Sisquoc, and younger sediments. The approximate intersection of the top of the 60

Monterey, Sisquoc, and Foxen (described below) with the unconformity is mapped in Figure 10.

Pliocene

Conformably overlying the Sisquoc Formation is a series of siliceous mudstones and calcareous siltstones which McCulloch and others (1979) believe may be equivalent to the middle (?) Pliocene Foxen Mudstone of the Santa

Maria Basin. In the OCS well, this unit is truncated by the Pliocene unconformity discussed above at a depth of !120m.

In the OCS well, McLean (1979) describes the Foxen interval from 1120 to·

!369m as consisting of siltstone, mud and sandstone. The siltstone is grayish brown to brown and calcareous. The mud is dark grayish brown and soft. The sandstone is brown to grayish brown, fine to very fine grained, with calcite cement and tuffaceous matrix. The bottom interval from 1369 to 1449m consists of brown to grayish brown siliceous mudstone.

On seismic profiles, the reflectors of the Foxen are indistinguishable from the underlying continuous, parallel reflectors of the Sisquoc Formation. The

Foxen Mudstone and the unconformity within the Formation are truncated ,to the west by the same regional Pliocene unconformity that truncates the Sisquoc and Monterey. The Foxen Mudstone is present in the western and southwestern portions of the study area.

Disconformably overlying the Foxen Mudstone is a package of continuous, variable amplitude reflectors that are traceable throughout the study area. In the Point Conception stratigraphic well, these reflectors correspond to an interval of siltstone and sandstone from 927m to 1128m. This interval is considered to be lithostratigraphically equivalent to the "Repetto" of the central and eastern Santa Barbara Channel. 61

Figure 10. Distribution of Miocene and early Pliocene units. 0 2 4 km -~-----_,----- ·0~ ! 0

MONTEREY / SISQUOC ' ~"ffvq.~'"" (,0 / 1'--.· / 0 ~ / _., (

s SISQUOC ~ Eastern Limit of / Foxen{?) MONTEREY. FOX EN{'?) SISQUOC MONTEREY

SISQUOC ' MONTEREY

Southeastern Limit of ....___ MONTEREY ONLY Sisquoc.

en 1"\) 63

Siliceous nannofossils in this interval indicate a late Pliocene age

(McDougall and others, 1979). They assign the interval in the well from 1164 to

!219m to the Repettian benthic foraminiferal stage and the interval from 618m

to lll8m to the Venturian-Repettian stages. Diatom and radiolarian

biostratigraphic analysis by McDougall &: others (1979) (figure 8), indicate that

the top of these late Pliocene reflectors marks the boundary between

Pleistocene and Pliocene sediments.

In the Santa Barbara channel, the "Repetto" is the name given to a

lithologic unit within the Pliocene Pico-Repetto Formation that contains

benthic foraminifera of the Repettian stage (State Lands Commission, 1982;

Vedder and others, 1969). In the central and eastern Santa Barbara Channel, the

"Repetto" is considered to be early to middle Pliocene in age and the "Pico" is

considered upper Pliocene to lower Pleistocene (State Lands Commission, 1979).

In spite of the discrepancy between the lower to middler Pliocene age of

the "Repetto" in the Santa Barbara channel and the upper Pliocene age of the

siltstone and sandstone unit between 927 and 1128m, both are considered to be

lithostratigraphically equivalent. The evidence for this correlation is primarily

from seismic reflection data. There is a very slight change in dip above the

package of reflectors considered here to be the "Repetto" equivalent. In addition, if this unit is traced shoreward (northeast), it can be tied into a

shallow seismic profile that shows an unconformable relationship between the overlying reflectors (Pico?) and underlying reflectors (Sisquoc?).

In the Point Conception area, an unconformity marked by a very slight change in dip separates the "Pico" from the "Repetto" units (State Lands

Commission, 1982). In addition, a second unconformity separates the Pico­

Repetto Formation from the underlying Sisquoc Formation. The "Repetto"- 64

Sisquoc unconformity at Point Conception is considered to be the same unconformity that separates the lithostratigraphically equivalent "Repetto" package of reflectors from underlying Foxen Mudstone, Sisquoc, and Monterey

Formations in the southern and eastern portions of the study area.

The structure on the top of the middle to late Pliocene package of reflectors is illustrated in Figure 11. It thins from approximately 150m in the southern portion of the study area to 0 meters near the coastline where it is truncated by Pleistocene reflectors (cross section X-X').

Pleistocene

The interval of siltstone and sandstone from 682m to 927m in the Point

Conception stratigraphic test well is considered to be equivalent to the "Pico" and is Pleistocene in age. The "Pico" disconformably overlies the middle to late

Pliocene reflectors and is in turn disconformably overlain by undifferentiated

Pleistocene and Holocene sediments.

McDougall and others (1979) and Bukry (1979) do not subdivide the

Qua ternary. However, the upper boundary of what is considered the

Pleistocene "Pico" is identified on seismic profiles by a line of small diffractions between underlying continuous, low amplitude reflectors and overlying continuous, high amplitude reflectors. In the OCS well, this inferred upper boundary of the "Pico" is marked by a change from siltstone and conglomerate (Post-"Pico") to sandstone ("Pico").

A relatively abrupt change from low amplitude to high amplitude reflectors marks the boundary between the "Pico" and "Repetto". This inferred boundary is marked in the OCS well by a change from siltstone and silty claystone (Pico) to sandstone, silty sandstone, and conglomerates (Repetto). 65

Figure 11. Top middle to late Pliocene structure map. 66

0 ·~o.: ~ ',\ \ ~J \ ~- t-• I V ~"o-v. ,tO' \ \.\ ~ 8 I ~ I / ' \ ~· I ~ \ t / \ \ \ \ :.oilI ' '\' \

I Jl'\ \ ~I I I r-· r-· \ I I I I § I I \ \ I 0 0 Cl) I

0 0 ":! \ \ \, ~I E \ ' .% q- \. \. ' N \ \ \).

c:: >. Q) .c ~\'',,, u .. "' .0 c:: ~ J ·- "'C .. 0 0 a::~u(\:' .. 8 .2 0 ~ ~ 0., .__a..,§ -~ .2 = I ..JI-C..-...Q: 0 ~o) "6'.....:>- 1 IQ .... ~ ~

I I 67

The interval in the well correlated with the Pico-Repetto Formation has

been described by Mclean (1979) as consisting of sandstone and siltstone with

some mudstone. The sandstone is silty, very fine to fine grained friable and

calcareous. The siltstone is brown to grayish brown, semiconsolidated to

friable, occasionally calcareous, poorly sorted and occassionally tuffaceous.

Rounded white tuff pebbles, tuff, tuffaceous mudstone, and soft brown mud are

also present.

Overlying the Post-"Pico" unconformity are undifferentiated Pleistocene

and Holocene siltstones and conglomerates which appear on seismic profile as

continuous, high amplitude reflectors. From 610 to 671m in the well,

conglomerates with clasts of rhyolitic volcanics are present which may be

derived from the Tranquillon Volcanics of Dibblee (1950) (McCulloch and others,

1979). Pebbles of chert and epidote hornfels are also present (Mclean, 1979) in

the well at 673 meters--just above the Post-"Pico" unconformity.

The undifferentiated Pleistocene-Holocene sediments from the Post­

"Pico" unconformity to the ocean floor have a thickness of 240m in the well.

These sediments thin shoreward and are completely removed by faulting near

the Point Conception-Point Arguello shelf.

Holocene/Pleistocene

Holocene sediments could not be identified on seismic profiles adjacent to

the well. However, the approximate Holocene-Late Pleistocene boundary may be mapped using shallow penetration seismic profiles near the coastline. Figure

12 is an interpretation of the stratigraphy of the upper 80m of the ocean floor along a seismic profile (1150). An unconformity is present at approximately 75m which may represent a low sea level stand approximately 18,000 to 20,000 years ago. A warming trend during this time is indicated in deep sea cores(Fischer & 68

Figure 12. Seismic profile of the latest Pleistocene/Holocene depositional sequence. 69

0 0 0 0 0 0 0 L() 0 L() L() !Q N N trJ 10

0 L.') I <[

(/) (!) (/) ::l

L() N

0 N

0 70

Parker, 1980). This warming trend produced glacial melting and a transgression of the sea to present sea level. Sediments deposited during this transgression may have produced the overlying low amplitude, continuous reflectors in figure

12.

On the San Pedro Shelf, Rudat (1980) mapped this late Pleistocene­

Holocene transgressive sequence as the LP-1 and Holocene units. The Holocene boundary was estimated to be part way through the transgressive sequence. If the transgressive sequence in the Point Conception area is equivalent to Rudat's

LP-1/Holocene sequence, then the Holocene/Late Pleistocene boundary should be approximately 35m below the sea floor.

East of Point Conception, Fischer (1978) identified a wedge of upper

Pleistocene sediments near the shelf break that he interpreted as terrace deposits similar to the "four-fold sequence of Upper Quarternary marine terrace deposits along the southern or Channel Islands shelf of the basin." Such a relationship suggests that multiple transgressive-regressive cycles may be preserved on the northern shelf in relatively undisturbed areas and that older cycles are present west of Point Conception below the LP-1 equivalent.

Uplift of the shelf between Point Conception and Point Arguello has resulted in the removal of Pleistocene sediments and the deposition of a thin veneer of Holocene (and latest Pleistocene) nearly horizontal, unlithified sands and muds (State Lands Commission, 1980). Figure 13 is an isopach map of the

Holocene-Late Pleistocene sediments in the study area. 71

Figure 13. Isopach of Holocene--Late Pleistocene sediments. 72

0 0 N .,; J l 0,, I/ I I / / \._--- 0 . \"- ...... ' I o I (- ~- \ ' / \ 1-- /

, ,

N

;;...J a::: LLJ 1- ~ a::: ::l I 0 1- I z 0 u ONSHORE STRUCTURE

The onshore structure in the western Santa Ynez Mountains adjacent to the study area was mapped by Dibblee (19 50, 1978). He divided the area between Point Conception and Point ArgueUo into two structural blocks separated by the Santa Ynez-Pacifico Fault zone.

The southern block consists of the southward dipping Cretaceous through

Quaternary strata that crop out along the coast north of the Santa Barbara channel. From Point Conception to the Pacifico fault, the monoclinal sequence swings northward so that lithologic units dip to the southwest in the study area.

The only major onshore break in the homoclinal dip is the Point Conception syncline. The hinge surface strikes N70°W and trends offshore 2 km north of

Point Conception and approximately 3 km east of Government Point.

The southern block is being uplifted in the Point Conception area at rates of at least 3 to 4mm per year (Yerkes and others, 1980). Historic uplift rates based upon leveling surveys between Point Conception and Gaviota may be as high as 28mm per year (Yerkes and others, 1980).

North of Jalama Canyon, Dibblee (1950) described the northern block -in the Point Arguello-Tranquillon Mountain area as containing minor Miocene folds that form a broad anticlinorium with a trend of roughly N75°W. The older formations are also folded with roughly the same trend. However, they are truncated to the north by the overlying Miocene rocks and dip regionally southward (figure 14).

Several periods of deformation have occurred in this northern block. Six or seven unconformities near the Tranquillon Mountains are evidence of this episodic deformation (Dibblee, 1950).

73 74

Figure 14. Onshore structural cross section - Point Arguello (modified from Dibblee, 1950). 75

-- N

CROSS SECTION:

A A' 76

The Santa Ynez fault trends east-west along the northern base of the

Santa Ynez Mountains. At Gaviota Pass, a southern branch of the Santa Ynez fault cuts south and westward and goes offshore near Alegria Canyon. Howard and Fischer (personal communication, 1983) believe that this fault is not genetically related to the Santa Ynez fault. The northern branch continues westward as the North Santa Ynez and Pacifico Faults (Figure 4). The Pacifico fault has been mapped to the mouth of Jalama Canyon and may extend 2.4 km offshore into the study area (Cook, 1979).

The Pacifico fault is upthrown on the south and displays 1530m of stratigraphic separation. According to Dibblee (1978) it also has a left slip component. The northern branch of the Santa Ynez fault zone is separated from the Pacifico fault by 800 meters. The North Branch has been displaced upward to the south a maximum of 1500 meters and has left lateral offset

(Dibblee, 1950). It dies out in the overturned Pacifico anticline.

The amount of left lateral separation along the eastern portion of the

Santa Ynez fault (east of Lake Cachuma) may be as large as 60 km, but the western segment has considerably less lateral separation (Sylvester and Darrow,

1979). The Santa Ynez fault is a vertical to slightly south dipping reverse fault

(Dlbblee, 19 50, 1966). The North Branch of the fault does not show major evidence of Quaternary displacement (State Lands Commission, 1982). The

South Branch does show evidence of movement during the Quaternary along the offshore portion of the fault (Fischer 1972, 1976). OFFSHORE STRUCTURE

The structure of the study area can be loosely divided into six major trends--the F 1 trend, the Jalama trend, the Hueso trend, the Point Conception syncline/Jalama syncline trend, the nearshore Arguello trend, and the northeast trend. Four of these trends contain both faulting and folding. Only the northeast trend appears to have no associated folding. The reason for this is probably three fold-- 1) The northeast trend is developed in deeper Paleogene and older units. 2) Younger sediments appear to deform by folding while the less ductile formations below the pre-Vaqueros unconformity tend to deform by faulting. 3) The Northeast trend is only apparent onthe widely spaced deep penetration seismic data, which may not resolve older folding.

NORTHEAST TREND

A single fault trending N40°E is traceable on southeast-trending deep penetration, seismic profiles (cross section X-X' and Figure 15). This fault offsets the basal Vaqueros unconformity, but it does not appear to cut reflectors in the upper portion of the Monterey. There is an apparent separation of correlative reflectors across the fault of approximately 140m upward to the south. The fault dips 100 to 14o to the northwest. Disrupted reflectors at the base of the Monterey indicate an early middle Miocene age of this fault, making it the oldest fault mappable with the available deep seismic grid. This Miocene fault is offset by the younger F1 fault (described below).

South of the F1 this older fault is laterally offset approximately 1.9 kilometers by smaller faults of the F1 trend. It is not traceable north of the Fj fault.

A pre-Vaqueros uplift and a subparallel linear depression near the center of the study area (figure 15) trend approximately NlOOE toward the coastline.

Both features are believed to be the result of differential

77 78

Figure 15. Structure map on the pre-Vaqueros unconformity. 79

/ I I / 'I / I / I I ---- I I 80

erosion of the Paleogene and older units that were uplifted to the northwest and dip regionally to the southeast. Cross section X-X' shows the inferred relationship between the pre-Vaqueros unconformity and the underlying pre­

Miocene units. Figure 16 is a restoration of the pre-Vaqueros erosional surface, which shows a general northeast orientation of underlying Paleogene and late

Cenozoic units.

Restoration was accomplished by contouring the pre-Vaqueros erosional surface (in seconds) starting inthe southwest corner of the study area and assuming all faults were predominantly reverse slip. The south side of faults served as datum when restoring this erosional surface. The pre-Vaqueros unconformity appears to deform predominantly by faulting so the effects of younger folding are negligible.

A slightly elevated area in the southern corner of Figure 15 is interpreted as a local, early to middle Miocene intrusion that has uplifted the pre-Vaqueros unconformity and overlying units in the basal Monterey. Seismic reflectors at the base of the Monterey have been folded and are parallel to the unconformity while deformation appears less significant near the top of the formation. A structure map of near contours on top of the Monterey (Figure 17) shows little or no effect of the underlying intrusion. Coarse grained sediments identified in the stratigraphic test well as possibly equivalent to the Vaqueros Formation may have been partially derived from this intrusion.

POINT CONCEPTION SYNCLINE/JALAMA SYNCLINE TREND

This trend is a continuation of the onshore structural trend mapped by

Dibblee (1950) and consists of N75°W-trending faults and folds (Figure 18).

Three major folds, the Point Conception syncline, Government Point 81

Figure 16. Restoration of the pre-Vaqueros erosional surface. 82

Ul :I: 1-z w 1-o zz_o u Ulw a::Ul ::l ~

Figure 17. Near top Monterey structure map. 84 p •

/ 1r / 0 Q7 ~.)~, ·v I I I I I 1 / / I 85

Figure 18. Point Conception Syncline - Jalama Syncline structural trend. 86

/ 11' / 87 anticline, and Jalama syncline characterize this trend. These are summarized in Table III.

Fault "A" lies north of these major folds and trends subparallel to them

(figure 18). The southern portion of the fault has been folded and uplifted and resembles a south dipping thrust fault at shallow depths (figure 19). Fault "A" is parallel to three faults onshore to the northwest (figure 18) that Dibblee (1950) mapped as upthrown to the south.

JALAMA TREND

A series of faults and folds trending N70°E meet the coastline near

Jalama Canyon (Figure 20). The onshore Pacifico fault is believed to extend into the area (Dibblee, 1950; Cook, 1979) and may be the eastern boundary of this trend. The Jalama trend is intersected to the west by the F 1 fault trend near the center of the study area (Discussed below).

The trend of fault E in Figure 20 is interpreted from seismic profiles as a sharp transition from chaotic reflectors south of the fault to somewhat continuous reflectors north of the fault (figure 21).

HUESOTREND

Faulting and folding west of the F 1 trend in the southwest corner of the study area are designated the Hueso trend.

Faults B, C, and D in Figure 20 are nearly vertical and have apparent reverse dip slip of 500 to 900m (cross section A-A'). Faults B and D are upthrown to the north while C is upthrown to the south~

A large anticlinal feature is developed in the Monterey and younger strata

(figure 17) above faults C and D and north of fault B. It appears that faulting occurs in the more "brittle" pre-Miocene rocks while folding occurs in the overlying less competent late Miocene and younger units. Fault B is an exception because it appears to offset Pleistocene sediments. 88

Figure 19. Interpretation of seismic profile SLC-3 across fault A. NW SHOT POINTS SE 650 600 550 500 450 400 350 300 250 200 150 0.0-J Msl- . ··· -LIA~-t :;( =~ _····~~

0.8

1.2

1.6

2.2

2.4

2.6

2.8

STATE LANDS COMMISSION 03

CX> \.0 90

Figure 20. Jalama and Hueso structural trends. 91

/ (. "¥

/ ::::> ..... <[ :I: ...... u.~"' \ ' ~·\ "

\ 92

Figure 21. Interpretation of USGS seismic profiles 4 and 8 across fault E. 93 ARGUELLO TREND

In the vicinity of Point Arguello, several faults and folds appear to converge and swing northward to trend between N25°E and N20o (figure 22).

Fault F is interpreted as a major fault that terminates as an anticline south of the Jalama syncline. The fault swings northward directly off Point Arguello and is believed to continue beyond the study area. Figures 23, 24, and 25 are a series of interpreted seismic profiles across this fault. The sharp contact between the east and west dipping Cretaceous and pre-Vaqueros unconformities on either side of Fault F may indicate that this fault has a strike slip component (seismic profile 119-figure 24). Other faults in the Arguello area probably also have lateral offset but the direction and amount of slip cannot be determined with the available seismic coverage.

Fault F may be connected to fault E of the Jalama trend by a N6 0 E trending tear fault considered part of the Ft fault trend discussed below.

Figure 26 shows this tear fault.

Fault G in figure 27 is upthrown on the west side. The apparent dip slip along seismic profile SLC-9 to 170m.

Faults of the Arguello trend may mark the beginning of right lateral offset characteristic of north-trending faults rn the Coast Ranges north of the study area. The Arguello fault G is uplifted to the west and may develop right oblique slip as it swings towards the Coast Range province. However, there is no direct evidence of this with the available seismic coverage.

Fl FAULT TREND

South of Point Conception, the east-west-trending F 1 fault mapped

94 95

Figure 22. Arguello structural trend. 96

/ - 1,-- // /

f w :r 0 ; ~ z LL.. w / 0 ~ /

/

\ \ E I ""' o;t ) \

N \ '\

0 97

Figure 23. Interpretation of seismic profile USGS 14 across fault F. 98

w z

~ 1 i I I I

I I I

I Q . I '

i I , I I{) 0

(/) z~ 5 c..

q~ C\J v 0 0 b 99

Figure 24. Interpretation of seismic profile SLC-5 across fault F. SHOT POINTS NW 1150 1100 1050 1000 950 900 850 800 SE

2

C> C> 101

Figure 25. Interpretation of seismic profile SLC-114 across fault F. 102

w f.!) z Q

v

z 0 0 U'J U'J ::2' ::2' 0 u

U'J 0

0 (\J

I() N

0 r

U'J 1- z 0 ll.

1- 0 J: v U'J !2 i I 3: Cf) U'J I() I() I() 0 :t (\J 1'- d 0 0 0 103

Figure 26. Interpretation of seismic profile SLC-203 across the F 1 tear fault. l 04

i . I 8 I I C\J I I I i I

It \ I I t g I I I

I I I I I I I

(/) 1- z 0 a.. 1-N 3;z (/)~!!2 N I{) d d 105

p '

Figure 27. Interpretation of seismic profile SLC-9 across fault G. NW SHOT POINTS 585 570 550 500 450 400 350 300-

STATE LANDS COMMISSION 09

__, 0 0) 107

by Fischer {1978) swings northward and terminates as a series of N4°E-trending fault splays (Figure 28). Tight anticlines are developed between several of these splays.

The Ft fault is nearly vertical, is upthrown to the north, and has dip separation of 300m south of Point Conception (Cross Section C-C'). The fault trend separates bedrock of Monterey and Sisquoc to the north from a thick section of Pleistocene strata south of the trend. The F 1 fault system terminates the east-west-trending Jalama syncline-Point Conception synclinal trend. The Ft fault trend is a Quaternary fault system that has uplifted

Pleistocene units on the shelf north of the fault trend (figure 28). Subsequent erosion has removed all of the Pleistocene except a thin veneer of latest

Pleistocene and Holocene sediments.

Figure 29 is an interpreted seismic profile (SLC-2) across the F 1 trend. 108

Figure 28. F 1 structural trend. 109

\ w 0 z~ -~o: wu Olo " s uo 00:: V ~"o- t;o 0_ I ~·\\~I\ ~- -w "<>' ' ~Ill I c.. / - C'· 1-- / I C'. I ::::> 0 / 'I

/ / 0z I / tf \ C( I ( u ~ I I I I ffi~t;;g:S ~ 'I!I I ::;,/Q ~ w ~ ii> m (f_ I / I ::E t // I / I / / ~~~I

\ WC( I ~:Eo -l-lw \ C(~ E I u. 0 I

0 110

Figure 29. Interpretation of seismic profile SLC-2 across F 1 fault trend. 111

N 0 z 0 Vi (/) ::::!E ::::!E 0 u

(/) Cl z <{ ...J

w I­ <{ I­ (/)

0 l() l()

s0

0 l() (,!)

Zo (I) q 6 0 N ONSHORE-OFFSHORE STRUCTURAL AND STRATIGRAPHIC CORRELATIONS

The onshore stratigraphy in the study area consists of Miocene and

younger sedimentary rocks unconformably overlying southeast dipping pre­

Vaqueros rocks of Late Paleocene, Eocene, and Oligocene age. These in turn

unconformably overlie east-dipping Cretaceous and older units. This same

stratigraphic relationship exists onshore between Point Conception and Point Arguello. The Neogene section is laterally continuous across the study area and

eastward into the Santa Barbara Channel. According to Epstein and Nary (1982)

the Miocene and Pliocene section can be correlated between the offshore Santa

Maria Basin and the western Santa Barbara channel (Figure 30). The Neogene

rocks, therefore, mask Oligocene and older stratigraphic and structural trends

except in the onshore Western Transverse Ranges where uplift and erosion have

removed Vaqueros and younger sediments. A pre-Vaqueros geologic map of

Paleogene and older rocks can thus be compared with the structural and

stratigraphic relationships of pre-Vaqueros units observed on deep seismic

profiles in the study area. Figure 31 is a map of pre-Vaqueros units from

Dibblee's (1950) Western Santa Ynez geologic map that outcrop between Point

Conception and Point Arguello. The figure also shows an interpretation of the

structure and lithology that is masked by the Vaqueros and younger sediments.

This pre-Vaqueros geologic map shows two major faults. One is the inferred extension of the Pacifico fault. The second fault (Fault H in Figure 31) has

lateral displacement and may be a northwest-trending branch of the Pacifico fault, or it may be related to faulting along the edge of the Transverse Ranges microplate. Both faults have been extended because they terminate abruptly against Monterey outcrops and are thus inferred to extend under

112 113

Figure 30. Correlation of stratigraphic units - Santa Barbara channel to the offshore Santa Maria. 114

~ . ;!~ 18 !~ .. 18 • g • 8 o• o• o• D • o• 0 ~ ~-~~~4 ~ ! ! i ! l! ~ l ~ i ~ ~ ; ! J ~ ~ i . I ; . • .• ! ~ i i a l t 2 i ~ ! J J ! ! j . f ~ i i ~~--~~J---~-----t------1 j .. 1 v ·w.:t .A. lUI OliN OW •w.:t 1YS .LHIO.. i f<~ ,.g ::•' •' ..q•' .:: ' '

~ .. ~1~ ?:~ =~= ;~~: ~·§ ~! ~ !~ ' . ; ~·~ . ~ ; : j ~ v I I a I ! z t• ~ ~ ~ ! c z iu 5 • ..z 0 i r i 0 .. ~ . • ~ i ; i .. N z 1 : . ~ • .. ~ • 0 • . i •... I t .' f liNOZ S00li;)I11S I ; .. 1 l .A.OIHOiiNOW HO!ddn .A.OIHOiiNOW Hi1M01 / 115

Figure 31. Interpreted pre-Vaqueros outcrop map (modified from Dibblee, 19 50). 0 2KM 4KM I I I

EOCENE 8 OLIGOCENE

-N-~ - Kj -Jalama Ke- Espada J CRETACEOUS 8 JURASSIC ~ Jh- Honda

...... 0"1 117

these younger units. This also infers an episode of movement along the Pacifico fault, or a northward extension of this fault, that is pre-Vaqueros.

The pre-Vaqueros rocks south of the northwest trending fault H in Figure

31 consist of Paleogene strata baselapping against and unconformably overlying

Cretaceous and older formations. This same relationship is interpreted offshore on the deep penetration seismic profiles (Cross Section X-X').

The inferred offshore contact between the Cretaceous-Paleogene unconformity and the pre-Vaqueros unconformity is mapped in Figure 9. West of this line, Paleogene units should be absent. Onshore, Paleogene rocks were penetrated in wells drilled near Point Arguello and out crop east of Point

Arguello.

There are two possible explanations for the presence of Paleogene rocks at Point Arguello but not in the offshore southwestern portion of the study area. The first explanation is that the Pacifico fault continues offshore west of

Jalama Creek and that Paleogene rocks on the north side of the fault have been faulted westward. A western termination of the Paleogene strata would then be expected offshore west of Point Arguello (but still within the Transverse

Ranges microplate) and an extension of the Pacifico fault would extend across the shelf between the area of deep seismic coverage and the shoreline.

The offshore evidence partially supports this explanation. The Jalama trend extends near the shoreline where the Pacifico fault is believed to extend

(Cook, 1979). Therefore some left slip may occur offshore along the Jalama trend. If the interpretation of seismic profile 113 is accurate (Figure 32), than the post-Paleogene "high" that resulted from erosion of the steep dipping

Oligocene and older units observed in cross section X-X' may also occur near the shoreline. Also, the truncation of all of the eastward dipping Paleogene . 118

Figure 32. Interpretation of seismic profile SLC-3 showing potential pre-Vaqueros ''high". NW · 600 550 500 450 400 350 SHOT PTS I I I I I I I SE

0.4

0.8

1,2

1.6

2.0

2.4

STATE LANDS COMMISSION 03

__,

1.0

.. 120

rocks by the pre-Vaqueros unconformity may be repeated or nearly repeated in

profile 113. If these correlations are accurate, then the pre-Vaqueros units have

been offset left laterally approximately 3 km between the southern and

northern boundaries of the study area.

The second explanation for Paleogene rocks at Point Arguello is that the

Oligocene-Miocene unconformity has truncated all Paleogene units offshore but

not in the Point Arguello area and that major left lateral offset has not

occurred offshore. Near the center of cross section X-X', the Vaqueros and

younger rocks truncate Paleogene rocks as they do onshore south of Jalama ·

Canyon. North of Jalama Canyon, Neogene strata unconformably overlie the

Jalama Formation.

Figure 33 is a generalized correlation of Cretaceous, Paleogene, and

Neogene rocks in wells adjacent to the study area. The removal of over llOOm

of Paleogene occurs between Arco "Conception" Ill and Union "Sudden" 111. This

rapid removal can be explained by 1) pre-Miocene faulting of the Paleogene

(upthrow to the north) or 2) truncation of steeply east dipping Oligocene and

older rocks by Miocene sediments. This occurs in cross section X-X' offshore

directly south of Jalama canyon (Figure 1). This second explanation allows the

correlation of onshore--offshore stratigraphy without major lateral movement

along faults in the study area.

The stratigraphic correlation preferred here is a combination of both

· explanations. It is believed that the onshore stratigraphy between Point

Conception and Sudden is similar to cross section X-X' offshore. Uplift of the

Paleogene and Cretaceous units before the deposition of the Vaqueros

formation resulted in steeply east dipping Paleogene units. These were

subsequently truncated by Miocene erosion. This occurred throughout the study 121

Figure 33. Generalized correlation of Cretaceous, Paleogene and Neogene units of wells adjacent to the study area. OCS-CAL TESORO UNION ARCO CHEVRON EXXON 78-164 Sudden I Sudden I Conception Gerber I GCS-P-0197-3 No.I I 2 3 4 5 6 I ',- ,. /'\--/' ' ', ' ,• \ ~ '· , ::_ .. ..: ~X~'\,;-i~~.·~l/ • ,' oc< '~:·~·~:',, '' EOCENE , 1 ' I 'I',:,\'' . I ' ' ··:.:;•,'(:··"':'.... I/ I i '.!: ·~TD' '' I I ''j /,! / '/ '. ·\/•<'···:··. ".":.·\;,:, 1 ' I; I ' ' I ' I I I I I ~ ,'.·,: ,, .... ; r' I / /, I I/ ' /I/// I I I l..,..... !~ ,;·;.,., .. . ;' 11: ·:,, ,, I J I ' .'ri•Jil~' I I I 1 . ' ' I I '··~""·' ' 1 'I ! . : ' I/ I I I ' ' ' I I II I : I I I 'i 'I '.' ' ' I " ;,, '';;,

I , / t

TD E3 CRETACEOUS INDEX MAP: (NEAR K)

\~?~ PALEOGENE

Et.-1 NEOGENE

__, N N

., 123

area. Some left lateral movement has occurred on the shelf, possibly along the

Jalama trend. This explains the interpretation of the seismic profile 113 in

Figure 32. CENOZOIC EVOLUTION GENERAL STATEMENT

The marine Cenozoic depositional history of the study area is similar to that of the Central Santa Ynez Mountains studied by Ingle (1980, 1981} (figure

34). In the central Santa Ynez Mountains, a major regressive cycle of southward and westward basin filling marks Paleogene time. The Paleogene culminated with 1) complex plate interactions, which reorganized the Oligocene

Boardland; 2) a major period of pre-Vaqueros erosion; and 3) the inception of the transgression that continued into the early Neogene.

Neogene depositional history is characterized by a regional early to late

Miocene transgressive cycle followed by a late Miocene to early Pliocene regressive cycle of sedimentation. Basins were filled by Pliocene and

Pleistocene sands and silts from east to west. PALEOGENE

The Cretaceous uplift or ''high" mapped in the central and western study area is believed to represent the northwestern boundary of Paleocene and early

Eocene onlapping units. If the offshore Paleogene stratigraphy correlates with the onshore stratigraphy (Onshore-Offshore Structural and Stratigraphic

Correlations), then the following conclusions can be made concerning the offshore Paleogene--

!) Paleocene (?) through middle Eocene units consisting of the

Anita(?), Matilija, and Cozy Dell Formations onlap Cretaceous rocks

to the north and east.

2) The Cretaceous and older formations (the Jalama, Espada,

Honda (?) Formations) and the overlying Paleogene units dip to the

east.

124 125

Figure 34. Cenozoic paleobathymetry, and sedimentation and subsidence rates of the Central Santa Ynez Mountains (from Ingle, 1980, 1981). CENTRAL SANTA YNEZ MOUNTAINS. CALIFORNIA ® ® TIME EPOCH/ TIME EPOCH/ RATES OF SEDIMENTATION IMY8 Pf SERIES STAGE FORMATION' LITH TMIC. PALEOBATHYMETRY IM.Y.B PI SERIES STAGE FORMATION' PALEOBATHYMETRY B SUBSIDENCE H[J J'([f ru:r , • ., 0 2-r--\~~HALLIA'f ,'"'~ .. PLST HALLIA. L....;':..:":_.J-__...,.. ______f 8AR8ARA .. :_ 0 . J-: SLoPf ..''( .. !.!'.'!!! - - U) R[P[fT!AN ~!!t I·-=-·...... ,!1, PLIO [lf.:LioiOfol· SISQUOC '\ SL?~ _J _J --- . ..,_. ~tllltlto•lf.'' \ 1- ·-_T!.!,_N_ SISQUOC · - 0...0. DEL~· I •\ ,\ - TIA1'4 "'HNIAN ----~--~ I 'lOOIIoCBAS•N ~ I 'II .. 10 IO.SJ~ _?_ NOH~IA· : I . w r-- lleiiONT[ ..[Y I MONTEREY(_-~~ z --- I 0 w9 :..... : ., -:- ~ ~~LI~~ ·,·· IS U :t_ , ...... Qr~ .!_£~·!!. --- / Q ffi t •--c ~~:~'~·:1. I ,.!,.. i :! 3: SAUCUIAN TAANOUIL~ON > / . :::i:w / Sl'r" / ~ SAUCE SIAN RtMCON / _,; 22 ~ 9 "INCON .:.. ~-- /I •o ...;:, ·•I S ..(l;'. f--~--- ___ 1' ·;· - ·~'"''""•on••rt '-''tOitAl S"fLr­ VAQUEROS LITTOIIIt•t. 1 LtfT~:••U•L 7 .. 1._ ~ I I l ... , ZE""""••• \ S'1L' -~ u ~:J ~/%// ~ 0 ., I "' !21- 0; \ ··- 0 SACATE ' I 5 -·-r-·-~~ ' _I_ -' ' ~;.<.;~:G-4------~~-..., -,- LITT()tlt&l.- f- f- llt[f'UGIAN ~~~~ " ~~~\.c::­ 40 z .... NARIZIAN '>."!L' W\wwo t-----f __ ) . GAVIOU ' !Oil~·~-~~"'-'~ .. , ~~ \ \ ! '5 UQ WI------'-...._ S&.O"' COZY ' I : 0::; Z SACAT[ ...... DELL . w '1 \ ·~~l~'iwr W .ARIZIA. --- " 0 111110 •out£" I \ u i con OE:LLI '- " N S.t."'n I.Oitl\. ,__ L__l----f-··· . ,_ I \ , >0 ~- --- -;-.;-;z.J-;- ' ll •• I . .. 0 ULATtSI.&N --- "\ ;'tUT[ ',.,. _,--- I !-.&~0 ' t-- I- P[~tAN I !Jl$· :~s:.~:::':! ~-:-~ u ~ BULITIAN ANIU \ &!I- ..,._, ·~lo' •r.o ,•rol ~~,,.,· •• , ' ~ N'EZ"IAN I ,._C()(vAl, AlGAl.. J . HA~IN P!..A10t,1' M[TflltS -y- - RAlri•S \ 60 _J~ ~OIMOtUTIIJ'( / L::::...:::.L___ .,_"'"',_..,....""'...,.> .. ~--~ ··,, :~~;:"';:,_~-~i·;,.Lo;~·- ..... ~ 3 ''DANIAN'" ' _,-"!...... !l.YSOCLIN[I I ."wO:LUotS I';OtUfO •L_ ...... L_ -- . ----- .1.'-"--'t !AN" TC'PS '-'---~---' :"oofllhT•Ct "'" *fLL AS ('oSPLlC[n 111G.11 loi[T[I't$ .. [T[ItSIIIY IOltlfi(O ... It••"~ Qll' •••uruto '"•r•'f'SS ~f.!I,_•S W :::- ., •• \ "" , .. ,..... , ...... (l&lo"'AL 0(POS!TS • ...... ,::...... r.t. '""'! ~, •...,,, ...... c .... .; ...,.,, ~:::~~~.~... ·.• t •III•••.. G(IO~ .,,.. Will···- !t.SIOf •• '!'~',· ;~..,\j':;,Y'••s a• • ,., ro h•f r•n

...... N "'

<> 127

3) A marine regression during middle Eocene time produced silled

basin conditions (Ingle, 1981; Gibson, 1973) in the southeast and central

portions of the study area.

4) Oligocene uplift and subsequent erosion which occurred

throughout the Point Conception/Point Arguello area marks Dibblee's

(1950) Ynezian orogeny. At least 800 meters of Paleogene sediments

have been eroded west of Point Conception. NEOGENE

The deposition of the basal conglomerates and sands of the Vaqueros

Formation, followed by the overlying muds of the Rincon Shale, represent a

northward marine transgression from the Santa Barbara channel region

towards the present day Santa Ynez block during the upper Oligocene and

lower Miocene (Fischer, 1972 and Ingle, 1980). In the study area, the

Vaqueros and Rincon Formations are either absent or not distinguishable

from the Monterey on seismic profiles. They may simply be a package of

reflectors as mapped in cross section C-C'. This package thickens to the

southwest, but to the northwest it rapidly thins beyond the limits of

resolution and baselaps acoustic basement.

Onshore, the Vaqueros is thin in the Jalama Canyon and is absent to

the northeast where the basal unit of the Monterey unconformably overlies

Paleogene rocks. According to Dibblee (1950) there is no unconformity

between the Vaqueros Formation and the Rincon Shale. Therefore, onshore

outcrops where the Rincon is in direct contact with Paleogene rocks

probably represent subsurface onlapping of the Vaqueros against a pre-

. Vaqueros erosional surface. If contacts of the Vaqueros against Paleogene

rocks are also assumed to represent onlapping, then the northern boundary

of the baselapping Vaqueros Formation can be crudely mapped (figure 35). 128

Figure 35. Estimated northern boundary of Vaqueros deposition. WESTERN LIMIT (,MISSING VAQUEROS a RINCON OF VAQUEROS _/ BELOW MONTEREY

'"'\ ) ; ( . (' \ J ~ ' ...... ---} t! __,_.J- ' ') /. ~ I -- ~'MONTEREY DIRECTLY Pt. Arguello I ("······., '\ - _,,.. J AGAINST OLIGOCENE AND t •.... "'"" \ •• ,' ··-~ OLDER UNITS \ __ .. ,J

NORTHERN EXTENT OF VAQUEROS --:

PACIFIC OCEAN .-~. '-... ?

N

Pt. Conception" 0 2 4km

...... N I.e

., 130

Onshore and offshore, the Vaqueros appears to have been derived from either remnant "highs" or from areas undergoing uplift during the early Miocene. The offshore Vaqueros may therefore represent onlapping coarse clastics derived from erosional "highs" from the northward transgression onto the Ynezian orogen. The Rincon Formation represents a deepening basin, finer grained, clastic facies deposited in a deepening basin. This transgressive sequence filled in depressions on the ocean floor and baselapped lower Oligocene and older marine sediments.

The initial opening of the Santa Maria pull-apart basin is marked by the middle Miocene Tranquillion Volcanics in the Point Arguello area. The extension of the volcanics from a "leaky" pre-Santa Maria Basin transform fault system may have created seafloor volcanic flow ridges (Hall, a and b).

An unconformity at the base of the Tranquillion and Monterey Formations at Point Argueloo may be related to these ridges.

The richly organic Monterey Formation unconformably overlies

Cretaceous, Paleogene, Vaqueros, and Rincon rocks in the onshore Point

Conception-Point Arguello area. Interpretation of offshore seismic profiles reveals two explanations for basal Monterey unconformities--

!) The unconformable relationship between the Monterey and the

Cretaceous and Paleogene units is believed to be similar to the

relationship shown by cross-section X-X'. Here Monterey onlaps and

over laps resistant, east-dipping Cretaceous and Paleogene

formations, and

2) The rapid thinning of a seismic facies, which probably

represents Vaqueros and Rincon (?) Formations south of Point

Conception (Cross section C-C') may be caused by the top lapping of 131

Vaqueros and Rincon Formations against a "local" pre-Monterey

unconformity. This offshore unconformity is believed to correspond

with Fischer's (1972) "Arguello Positive". It may be related in part to

initial activity along the Transverse Ranges microplate boundary

north of Point Arguello (Tectonic Setting).

An influx of terrigenous material during the late Miocene and early Pliocene time (Ingle, 1981), was caused by a lowering of sea level and increased regional deformation. Stratigraphically, deposition of the progressively less siliceous mudstones, shales, and sands of the Sisquoc and Foxen Formations resulted.

On seismic profiles, a regional unconformity cuts across the Foxen (?),

Sisquoc, and Monterey Formations. If the original erosion surface was nearly flat, then these formations were tilted to the southeast, immediately prior to early Pliocene erosion. Figure 10 is a subcrop map of the Foxen, Sisquoc, and

Monterey below this unconformity. Erosion has completely removed the

Sisquoc and Foxen Formations from the southeast portion of the study area.

Nor are they present to the south, because cross section C-C' was extrapolated to the northwest edge of the Channel Islands Platform (cross section D-22 of

Junger (1979). This southward extrapolatian shows that the unconformity mapped by Junger above the Monterey is equivalent to the early Pliocene unconformity of the study area. It may be concluded that beginning in latest

Miocene time the area was lifted upward to the southeast.

Regional late Miocene-early Pliocene uplift of the western Transverse

Ranges is apparent on offshore seismic profiles within the area of investigation.

The Pliocene and Pleistocene "Pica" Formation onlaps the folded Sisquoc

Formation northwards towards Point Arguello. An interuption in the east to 132

west, Pliocene/Pleistocene basin filling depositional sequence (Fischer, 1972) is apparent as an unconformity between Pico and Repetto units.

From late Pleistocene to the present, faulting and folding have occurred in the study area along several structural trends. The F 1 fault trend has uplifted the shelf west of Point Conception resulting in the removal of most of the Pleistocene section and the deposition of only a thin veneer of latest

Pleistocene/Holocene sediments. Sea floor scarps and topographic positives overlie most anticlines and several faults. The Arguello and Hueso trends show evidence of latest Pleistocene/Holocene deformation. SUMMARY AND CONCLUSIONS

Seismic analysis suggests that the Cenozoic history of the western-most

Transverse Ranges Province was dominated by two distinct tectonic trends, one during Paleogene and the second during the Neogene time. Neogene structures, which trend east-west and northwest-southeast, are overprinted on a broad northeasterly trending Paleogene basin margin. Along the southeast flank of this margin, Paleogene sediments onlap southeast dipping Mesozoic rock.

Neogene faults and folds between Point Conception and Point Arguello are oriented east-west to northwest-southeast. High angle reverse faulting and associated folding are predominant in the westernmost extension of the east­ west structural grain of the Transverse Ranges. West of Point Conception the northerly trending Coast Ranges structures mark the termination of the

Transverse Ranges Province. This termination apparently occurs along the F1 fault zone (Fischer, 1978; Yerkes and others, 1981). The fault swings northward around Point Conception and cuts the Government Point anticline and Point

Conception synclinal trend. These folds mark the westernmost extent of the

Transverse Ranges structural grain. Their western termination defines the border of the offshore Santa Maria Basin of the Coast Ranges Province and the

Transverse Ranges Province. The gentle bending of structural trends around

Point Conception from east-west to northerly trends as shown by Yerkes and others (1981) was not substantiated by this study.

Seismic stratigraphy was used to define a cyclical depositional history within the study area that can be correlated with major plate tectonic events.

Four major depositional and tectonic cycles are recorded in the western

Transverse Ranges and the offshore Santa Maria Basin:

133 134

1) A Paleogene regression that culminated with a period of uplift and

erosion which marks the collision of the Pacific and North American

plates about 29 mybp (Atwater and Molnar, 1973; and Dickinson, 1983).

2) Initial subsidence of the Transverse Ranges Microplate resulting in

late Oligocene-early Miocene transgression. The onlapping transgressive

Vaqueros sandstone and Rincon Shale unconformably overlie Oligocene to

Cretaceous rocks in the offshore area of this investigation. The

outpouring of subaqueous flows of the Tranquillion Volcanics extended

west of Point Arguello along faults or perhaps "leaky transforms" that

bounded the microplate.

3) Deepening of local basins continued, probably in response to a

clockwise rotation of structural blocks within the "mega shear regime" of

the San Andreas transform (Kamerling and Luyendyk, 1977 and Dickinson,

1983). These basins were filled with the biogenic, organic rich Monterey

Formation. Later, as the clastic contributions from adjacent upland

areas increased, the Sisquoc and Foxen (?) Formations were deposited.

4) Uplift of the Transverse Ranges block occurs along the Santa Ynez

and Honda fault zones. This uplift' occurred in response to compression

presumably initiated by the formation of the "big bend" of the San

Andreas fault (Allen, 1981). This uplift and adjacent subsidence cycle,

which began during Pliocene time, is continuing today. Late Pleistocene

uplift along the F1 and related faults document continuing modern

tectonism.

Pliocene angular unconformities near the shelf break mark the initiation of, and pulses within, the corresponding depositional cycle. A 135

westerly on lap and basin filling is recorded by these relationships. The

Late Pleistocene-Holocene seismic sequence marks the latest stage of this ongoing cycle. 136

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APPENDIX A

FACTORS AFFECTING TYPE OF

SEISMIC COVERAGE

The relationship of the frequency (f) to wavelength ( ), and velocity (v) of sound is given in the formula:

f = v/

The velocity of sound penetrating different rock units will be the same for any type of seismic coverage employed along a given traverse. Therefore, differences in the type of seismic coverage are based on frequency and its reciprocal wave length.

On a seismic record, the ability to clearly distinguish a certain feature, its resolution, depends on its magnitude compared with wave length. The resolution of an object is generally 1/8 to 1/4 wavelength (Sheriff, 1977). In order to decrease the wavelength, the frequency of the sound source is increased. Wavelength will increase with depth because the velocity increases with depth and frequency decreases (Sheriff, 1977). Therefore, an object at depth must be much larger than a shallow object in order to be resolved on a seismic record.

The frequency-wavelength relationship also affects the penetration of seismic energy. High frequency energy is more likely to be absorbed or scattered in the earth than lower frequency energy. (Dobrin, 1976). High frequency energy is used to resolve details at shallow depths. Seismic energy writh longer wavelengths offers deeper penetration but significantly less

·esolution.

145 APPENDIX B

VELOCITY FUNCTION

The velocity-depth relationship used throughout most of the study area was derived from the Arguello stratigraphic test well and extrapolated to the north and east. The integrated one way travel time to all the depths of 500 foot increments from the ocean floor to the total depth were obtained from the

Schlumberger Borehole Compensated Sonic Log run in the test well. These values were converted to two way travel time and plotted against depth.

The relationship of velocity to depth can be closely approximated with a linear velocity function in clastic basins (Dobrin, 1976). The relationship is given in the equation:

V(z) = V0 + Kz where offshore: V(z) = Velocity at a depth z below the ocean floor Vo = Velocity at the ocean floor K = Velocity Gradient z = Depth (Dobrin, 1976; Sheriff, 1973).

Pre-plotted velocity functions with varying veolocity gradients were

:>Verlain on the plotted travel time/depth values from the Arguello well in

>rder to determine a function with a least squares fit. There is a noticeable

~ncrease in velocity in the well approximately 5000 feet below the sea floor. rherefore two velocity functions were derived: the function Vz = 4864 + .8z

:or the interval from 0 to 5000 feet below the ocean floor and Vz = 4385 +

.lz for all depths below the 5000 foot mark (Figure 36).

The two velocity functions were used to determine either time or depth

n a seismic record with the equation:

146 147

Figure 36. Velocity functions used in depth/time derivation. DEPTH (FEET FROM DATUM)

200 ~ ~ 400 0 :E 600 )> -< BOO -~ 3: 1000 -rr1 1200 3: en

1400 .., ::0 0 1600 3: 0 VI =4'385 + l.ll V2 = 4474 + 1.04 l t'BOO ~ V3 = 4864 + .8 l 2000 -3: 2200

2400

__, ~ 00 149

z (ekt/2 -n = K

t 2 In (1 + K/V Z)) = 0 K where tis equal to the two-way reflection time.

The travel time or depth from the ocean floor to a given reflector were determined from one of these two equations. The K and V0 values were taken from one of the two previously defined velocity functions.

At shallow depths in the vicinity of Point Conception, time vs. depth values derived for the Fugro shallow seismic study of the offshore UnionPRC

2879.1 lease were used (State Lands Commission Environment Impact Report,

November 1979).

Velocity analysis is not available for the deep penetration industry profiles. 150

Table III. Summary of major folds - Point Conception syncline - Jalama syncline trend. Fold Trend Axial Plane Flanks

Government Point N. 76 0 W. Nearly vertical, slight 20°- 30° North Anticline dip toward the North 20° - 40° South

Point Conception N. 80 0 W. Dips to the North 25°- 35° North Syncline (4° or 5°) 24°- 30° South

Jalama Syncline N. 75 0 W. Vertical 17 0 - 35 0 North 33 0 - 40 0 South

...... t.11