CALIFORNIA STATE UNIVERSITY, NORTHRIDGE

THE GEOLOGY OF THE INNER BASIN MARGIN, NEWPORT BEACH TO DANA POINT, ORANGE COUNTY, CALIFORNIA

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

Geology by Stephen Charles Sterling

January, 1982 The Thesis of Stephen Charles Sterling is approved:

California State University, Northridge

i i CONTENTS Page ABSTRACT INTRODUCTION 1 General Statement 1 Geographic Setting

Bathymetric Setting 2

Previous Investigations 2

METHODS AND PROCEDURES 7 General Statement 7

Navigation 10

Velocity Analysis 10

Velocity Functions 11 Depth Migration 13

Ac know l edgemen ts 13 GEOLOGIC SETTING 15

REGIONAL STRATIGRAPHY 23

General Statement 23

Basement 23 Superjacent Rocks 26 Jurassic-Early Miocene 26 Middle to Late Miocene 27 Pliocene 32 Pleistocene 36 Holocene 37 SEISMIC STRATIGRAPHY 38 General Statement 38

iii Page

Basement 38 r1i ocene 39

Pliocene 43 ONSHORE STRUCTURE 48 OFFSHORE STRUCTURE 52 General Statement 52 Faults 52 The Newport-Inglewood Fault Zone 52

Other Faults 58 Structural Highs and Lows 61

Correlation of Onshore-Offshore Geologic Features 63

NEOGENE EVOLUTION OF THE INNER BASIN MARGIN 67

General Statement 67

Pre-depositional Events 67 Neogene Events 69

Depositional History 69 Structural Evolution 73 SUMMARY AND CONCLUSIONS 75 REFERENCES 80

iv LIST OF ILLUSTRATIONS Figure Page .,.. l. Location of study area 4 2. Bathymetry of the inner basin margin 5 3. Tracklines of common depth point seismic lines in the study area 9 4. Major structural blocks of the Los Angeles basin 17 5. Location of geologic features referred to in text 19 6. Composite sections showing regional correlation of units 24 7. The major structurally high and low areas in the basement surface 41 8. Location of stratigraphic sequences that onlap or downlap against the basement surface 47 9. Structural provinces in the study area 54 10. Earthquake epicenters, from 1933 to 1972, plotted along the Newport-Inglewood structural zone 57 11. Location of major faults displacing the basement surface 60 12. Apparent horizontal offset of geologic features along the Newport-Inglewood structural zone 65 13. Direction of sediment transport for upper Miocene through lower Pliocene strata 72

Plates

I. Structure contour map on top of the basement schist In pocket II. Structure contour map. on the top of the Delmontian stage In pocket III. Structure contour map on the top of the Repettian stage In pocket IV. Structure contour map on top of an arbitrary reflector within the Plio-Pleistocene stratigraphic section In pocket

v Plates V. Structure cross-sections: Oriented perpendicular to the coastline In pocket VI. Structure cross-sections: Oriented parallel to the coastline In pocket

vi ABSTRACT

THE GEOLOGY OF THE INNER BASIN MARGIN, NEWPORT BEACH TO DANA POINT, ORANGE COUNTY, CALIFORNIA by Stephen Charles Sterling Master of Science in Geology

Geological and geophysical data, which include common depth point seismic profiles, velocity analysis displays, borehole and other information, were used to study the structural evolution and Neogene sedimentation of the inner basin margin between Newport Beach and Dana Point. Neogene time, as used in this study, includes the Miocene and Pliocene epochs. Using these data four seismic horizons were mapped in the study area: (1) top of the acoustic basement (top Catalina Schist);

(2) top of the Delmontian (?) benthic foraminiferal stage; (3) top of the Repettian benthic foraminiferal stage; and (4) an arbitrary reflector within the Plio-Pleistocene stratigraphic section. Sedimentary rocks in the study area range from late Miocene to Recent. Late Miocene through Pliocene strata onlapped structurally

vii high basement areas and downlapped structurally low basement areas to the south-southeast. The southerly direction of sediment transport in the upper Miocene through Pliocene stratigraphic section from the .... San Pedro Bay area to the study area suggests sediment was channeled through the northwest-trending Wilmington graben. These sediments were probably transported by density currents. In the study area, strata accumulated on a basement surface in which structural highs controlled or blocked sediment transport to the southeast. South of Dana Point, sediment input from the northwest was blocked by the basement high associated with the offshore San Joaquin ridge, however, the strata in this area onlapped the basement ridge from the north to northeast. This north to northeast onlap involves strata probably corresponding to the upper Miocene-lower Pliocene Capistrano Formation. Onlap to the offshore San Joaquin ridge from the north­ northwest continued through Pliocene time until Plio-Pleistocene strata overlapped this structural high. Major ridges, troughs, and numerous faults are present in the surface of the basement Catalina Schist. The relatively continuous nature of these faults suggests that the area consists of a series of north to northwest-trending fault blocks which move independently. This is evidenced by differential displacement of the basement surface along single fault traces. Based primarily on basement structural elements, the study area is divided into three structural provinces: 1. Province I is located on the continental shelf and is characterized by chaotic reflectors. 2. Province II is the northwest portion of the area and is characterized by north to northwest-trending faults and ridges in

viii the basement surface. 3. Province III is the southeast portion of the area and is characterized by north to northeast-trending faults, ridges, and troughs in the basement surface. Faults in the study area are high angle normal. Most of these faults terminate within, or near the top of, the Repetto Formation. A number of them have a thicker sedimentary section on their downthrown side indicating that at least a portion of the displacement occurred contemporaneously with sediment deposition. The Newport-Inglewood structural zone extends offshore of Newport Beach to southeast of Dana Point in a series of four right-stepping en echelon fault segments. Lateral offset along the Newport­ Inglewood zone, using assumed similar or related geologic features as piercing points. has been right-lateral with an estimated horizontal displacement of 4250 meters.

ix I •

INTRODUCTION General Statement

The inner basin margin from Newport Beach to Dana Point is located at the southernmost extent of the Los Angeles basin and forms a portion of the northern flank of the San Diego trough. Since Middle Miocene time, this area has been the site of significant sedimentation and tectonic activity. No previous detailed investigations have been completed in the study area. The purpose of this investigation is, then, to delineate structural and stratigraphic features and to describe the geologic evolution of the area. For this study, industry geophysical and geological data were obtained including common depth point (COP) seismic profiles, post-plot navigation sheets (shot point locations), velocity analyses, and borehole information. Both geological and geophysical interpretations by the writer were limited to the use of the COP seismic profiles. Offshore extrapolations of onshore geologic structures were hindered due to the proximity of the offshore portion of the Newport-Inglewood structural zone. In the northern portion of the area interpretations were aided by good borehole information.

Geographic Setting

The area of investigation is part of the southern California Continental Borderland and encompasses nearly 360 square kilometers {approximately 40 km x 9 km) along the inner basin margin, between

l 2

Newport Beach and Dana Point (Fig. 1). Newport Beach is approximately 45 kilometers southeast of the city of Los Angeles along the southern California coast. Landward of the study area are the San Joaquin Hills which define the eastern margin of the Los Angeles basin. Directly offshore the ocean floor deepens into the northern end of the San Diego trough. The northernmost portion of the area overlies the southern edge of the broad San Pedro shelf.

Bathymetric Setting

The southern California continental shelf typically is narrow. The shelf southeast of the broad 25 kilometer wide San Pedro shelf tapers to approximately 2 km in width and broadens to a width of approximately 3.5 km near Dana Point (Fig. 2). The edge of the shelf generally is parallel to the coast, only diverging significantly near the San Pedro-Newport submarine canyon area. From the shelf break, at approximately 100m below sea level, the transition to a steep continental slope is abrupt. Further offshore, the continental slope rapidly grades into the basin apron and floor of the San Diego trough.

Previous Investigations

A majority of previous investigations were concerned with regional surveys of the entire California Continental Borderland. Moore (1960, 1969) utilized seismic data with subbottom penetration to evaluate geologic structures beneath the sea floor. Western Geophysical Company (1972) used common depth point seismic reflection 3

Figure 1. Location of study area. LOS 118° 00'

0-1 (~, 0 ~k ~

SAN PEDRO SHELF ',, "',f,,, ,, '"-:,,.. '', ": l{ 100m 0 km/ 15 SAN PEDRO ~· BASIN SCALE 1:500,000 - 33° 30' /

SAN CLEMENTE

~ ISLAND ';:) L·------~--~-----___.j

..j::>.

• • 5

Figure 2. Bathymetry of the inner basin margin (from Vedder and others, 1976, sheet 3). 6

118° 00' LOS ANGELES '..:ll BASIN

-0 km 5 10 .J ' SCALE 1:250,000

BATHYMETRIC CONTOUR INTERVAL: 50 METERS

AREA

33° 30' sao 7

and seismic refraction data to construct reflection-time structure contour maps from Miocene rocks to the acoustic basement between Palos Verdes and offshore of San Diego. Ziony and others (1974) reviewed published and unpublished data, supplemented by limited field investigations, to study the recency of faulting along the coastal portions of the Borderland. Vedder and others (1974) used subbottom seismic profiles, gravity and magnetic data, well and shallow core information, published papers, and unpublished data to describe the regional geologic framework of the Borderland. North of the study area, in the Santa Monica and San Pedro basins, Junger and Wagner (1977) used seismic reflection profiles and bedrock samples to evaluate the geologic evolution of these areas. Nardin and Henyey (1978) utilized seismic reflection profiles and bedrock samples to study the late Pliocene through early Pleistocene evolution of the Santa Monica and San Pedro shelves. Rudat (1980) assessed the Quaternary evolution of the San Pedro shelf using reflection profiles and dart core data. South of the Palos Verdes Peninsula, Jahns and others (1971) described structural elements along the continental shelf and Lee (1977) utilized seismic reflection profiles in the Newport submarine canyon area to construct a tectonic map and geologic cross sections.

METHODS AND PROCEDURES General Statement

For this study, 340 kilometers of unmigrated time common depth point (COP) seismic profiles were obtained from industry (Fig. 3). 8

Figure 3. Tracklines of common depth point seismic lines in the study area. 9

118° 00'

~

HUNTINGTON 0 km 5 10 BEACH L J j I SCALE 1:250,000 I

LAGUNA 10

The profiles were collected on five separate surveys by four geophysical service companies. The surveys vary from 12 fold to 36 fold gathers (1200% to 3600% stack). Four of the surveys used airgun energy sources and a 100 Kj super sparker energy source was used for one. Borehole data were only available from the northern part of the study area. Using these data three reflectors corresponding to: the top of the acoustic basement (Catalina Schist), the top Delmontian (?) and top Repettian benthic foraminiferal stages of Kleinpell (1938), were correlated throughout the study area.

Navigation

Precision navigated 11 Shot point 11 location maps were furnished by industry for all of the seismic tracklines.

Velocity Analysis Velocity analysis, an integral part of seismic processing, utilizes the variation of normal moveout with seismic record time to determine velocity (Garotta and Michon, 1967; Telford and others, 1976). In an ideal model of parallel horizontal layers, an RMS (root­ mean-square) velocity is determined to remove normal moveout and to enhance primary reflectors (Sheriff, 1978). RMS velocity may be obtained from the equation: v12t + v22t2 + V3 2t3 + ... + Vn 2tn Vrms 2= tl + t2 + t3 + ... tn where: Vl, V2, V3 ... Vn are the interval velocities of the 11

respective horizontal layers, and tl, t2, t3 ... tn are the one-way travel times to their respective horizontal layers (Dobrin, 1976). During computer processing of an actual seismic line, a proper stacking velocity is determined for enhancement of primary reflectors. This is accomplished by assuming a stacking velocity and, then, normal moveout is examined for the offset of traces as a function of time. The degree of unison of all available traces to be stacked is measured until the coherence of reflectors is a function of stacking velocity and arrival time. \~hen this criteria for reflector coherence is attained, the stacking velocity is considered to ensure the proper amount of normal moveout removal to maximize the stacking of primary events {Telford and others, 1976; Coffeen, 1978). Stacking velocities, and RMS velocities, are determined from first arrival times and are typically a few percent faster than corresponding average velocities (Sheriff, 1973). Velocity analyses were completed at intervals of approximately one mile along each seismic line.

Velocity Functions

Velocity analysis displays were digitized and individually entered into a pre-written industry computer program designed to calculate a least-squares-fit for linear increase of velocity with depth. This least-squares-fit is termed a velocity function. The relation is expressed by the equation: 12

( 1 ) V(z) = Vo + kz where: V(z) = velocity at depth z below the datum plane (instantaneous velocity). ..,. Vo = velocity at the horizontal datum plane. k = acceleration factor or velocity gradient. z = depth (Dobrin, 1976; Telford, and others, 1976, Sheriff, 1973). The assumption of a linear increase of velocity with depth is more advantageous than a stepwise increase involving discrete layers. Not only is it easier to handle mathematically, but is also a good approximation of actual velocity functions in clastic basins (Dobrin, 1976). Using the calculated velocity functions, a time-depth relationship was established (assuming that shot and receiver are

coincident and ray paths are vertical) by using the equation:

(2) z = Vo/k (ekt/2- 1) or

(3) t = 2/k ln (1 + k/Vo z)

where: t = two-way reflection time. (other notation defined above). The projection of the top basement Catalina Schist, top Delmontian

(?) and Repettian benthic foraminiferal stages onto unmigrated time seismic profiles was accomplished by using the following procedure: 1. Depths (z) of the top of the above formation and stage tops were obtained from borehole data. 2. Velocity at the horizontal datum plane (Vo) and the acceleration factor (k) were calculated from the velocity analyses adjacent to the boreholes by using the velocity function computer 13

program. The program output is expressed by equation (1). The horizontal datum plane is water bottom and the given velocity (to be used in calculations) of the water column is 4850 feet per second. 3. The two-way reflection time to the formation and stage tops was obtained by entering depth (z) and the calculated (Vo) and (k) values into equation (3). 4. Projection of the formation and stage tops onto the seismic profiles was completed using ten different velocity analysis displays adjacent to the boreholes to ensure proper location of the correlated formation and stage tops on both strike and dip seismic profiles.

Depth Migration

Reflectors corresponding to the chosen formation and stage tops were correlated within the study area. The correlated tops from each seismic profile were digitized and entered into a pre-written, two dimensional depth migration industry computer program. Velocity functions, and their corresponding shot point locations, also were entered. Output from this program is individual plots of the seismic profiles with the digitized tops migrated to their proper positions in space and depth. The migrated formation and stage tops on the output plots were then checked for correlation misties at profile intersections.

Acknowledgements The writer would like to thank Dr. P. J. Fischer for suggesting this project and for his guidance, Dr. H. Adams for critically reading this manuscript and especially Dr. J. M. Evensen for the 14

critical reading of this manuscript and for his support and encouragement. The author is greatly indebted to Mr. W. J. Isaacs for his consultation in the velocity research phase of this work. The computer assistance by Mr. R. J. Grabyan and Mr. L. J. Rothenberg and the assistance in the determination of the correlated benthic foraminiferal stage tops from borehole data by Mr. G. Blake is appreciated. The writer is grateful to E. Kutz and C. Hutchens for typing, Mr. J. Donnelly for drafting, and Mr. M. C. Blundell for the critical reading of this manuscript and for his support throughout this project. Above all, the author would like to thank Dottie Sterling for her many hours of assistance, her patience and encouragement. This project could not have been possible without the financial support, computer use, and the release of proprietary data furnished by Union Oil Company of California. GEOLOGIC SETTING

The basement rocks of the Los Angeles basin have been divided into a western blueschist facies complex and an eastern granitic complex (Yerkes and others, 1965; Hill, 1971; Yeats, 1973). The basin contains a structural depression, parts of which have been sites of discontinuous deposition since the Late Cretaceous with continuous subsidence and predominantly marine deposition since middle Miocene time (Yerkes and others, 1965). Yerkes and others (1965) divided the Los Angeles basin into four large structural blocks based on rocks of contrasting lithologies (Fig. 4). Contacts of adjoining blocks are flexures in basement rocks or major fault zones. The present study area is within the southwestern block which extends from Santa Monica to Long Beach, and southeastward into San Pedro Bay. The basement rock is composed of the western blueschist facies complex. The sedimentary rocks of the southwestern block are approximately 6250 meters thick and are composed of chiefly marine sedimentary strata of middle Miocene to recent age (Yerkes and others, 1965). The Palos Verdes fault (Fig. 5) can be traced for more than 80 kilometers, extending offshore northwest and southeast of the Palos Verdes Hills (Junger and Wagner, 1977). Beneath the San Pedro shelf, the fault is most commonly expressed by an abrupt dislocation between folded strata and relatively undeformed layers, although locally it appears as a wide fault zone (Nardin and Henyey, 1978). Junger and Wagner (1977) describe the southward continuation of the Palos Verdes fault as the vertically distributed terminations of near-horizontal

15 16

Figure 4. Major structural blocks of the Los Angeles basin (from Yerkes and others, 1965). 17

NORTHWESTERN BLOCK

NORTHEASTERN BLOCK

~ .. , \...___./ LOS ANGELES ' '\. ' \ \ ' \ \ .\, \

CENTRAL BLOCK

0 km 15 / , / ' ' ~\:'.,~v ~ ' ' SCALE 1:500,000 'o -.:-,....._,, BOUNDARY OF STRUCTURAL BLOCK . IS' ',:--' ' J-v ' ', ' <>J- '

' ' ' -1-r-.·r~ ' ' '\ ' ''-1 ' ' ', ' ) ' / ' '/... / 18

Figure 5. Location of geologic features referred to in text. The offshore portion of the Newport­ Inglewood structural zone is from this study. All other features are from sources cited in. LOS 118" oo' ~ okrn 1 5 I l I I .<) \) ,o SCALE 1:500,000 '1( 0~

it-/ £.~ (1, /1> \ ~<) G')' ('lSI 0 ./"<. 1> / ~ (:> ' ~~._,:a{)"''""'''It ,,,,,,,, ")> ' ,y Q '',, &..0 ',-1~ ~ 1(. v1 \ '('"V ',1/ (.IS' 1' (~ ' ,(:' \... SAN PEDRO .>- ' &i- ..... BASIN ' ' ',,v.

'-0

j . 20

beds of the Wilmington graben against the steeper dipping beds of the Palos Verdes uplift. To the south, the Palos Verdes fault extends to the area adjacent to Lasuen Knoll. Near San Pedro, this fault shows late Pleistocene and possible Holocene tectonic deformation and separations. (Junger and Wagner, 1977; Nardin and Henyey, 1978). The Wilmington anticline (Fig. 5) is another major fold, approximately 30 kilometers in length, located eastward of the Palos Verdes Hills (Junger and Wagner, 1977). Its southeastern extent underlies a portion of the northern San Pedro shelf. The core of the Wilmington anticline consists of Catalina Schist which is overlain by as much as 3500 meters of Miocene and younger sediments. This northwest-trending anticline is complexly broken by northeast-trending faults (Mayuga, 1970). One of the major structural features in San Pedro Bay is the Wilmington graben (Fig. 5). The southwestern boundary of the graben is the Palos Verdes fault zone and the northeastern boundary is a discontinuous series of faults on trend with the onshore Newport­ Inglewood fault zone. Strata appear to be gently folded in the Wilmington graben with a structural high appearing against the Palos Verdes fault (Junger and Wagner, 1977). The San Joaquin Hills, immediately landward of study area, form a complexly faulted anticline, bordered by the Capistrano syncline to the east (Fig. 5). The stratigraphic sequence exposed contains Paleocene through Holocene marine and nonmarine sedimentary rock, locally cut by igneous intrusive rocks (Vedder, 1970). The Newport-Inglewood fault zone is one of the dominant structural elements in the Los Angeles basin. This northwest- 21

southeast trending zone separates the southwestern and central structural blocks of the Los Angeles basin. The Newport-Inglewood fault zone consists of cross-trending en-echelon anticlinal folds and discontinuous faults (Yeats, 1973) characteristic of wrench-style deformation (Harding, 1973). Cumulative right-lateral strike-slip displacement is approximately 3 kilometers (Yeats, 1973). Several workers continue this zone southward to the San Diego area (Emery, 1960; Barrows, 1974). REGIONAL STRATIGRAPHY General Statement The relationship and distribution of lithologic units can be grouped into two stratigraphic sections separated by the northwest­ trending Newport-Inglewood fault zone. To the southwest, Mesozoic schist basement is overlain by a succession of marine and nonmarine middle Miocene to Recent sedimentary rocks containing local igneous intrusions. Northeast of the Newport-Inglewood fault zone, Mesozoic granitic basement underlies the Cretaceous to Recent succession of marine and nonmarine sedimentary rocks and local intrusive igneous rocks (Yerkes and others, 1965). Figure 6 shows the regional correlation of these rocks. Basement Basement rocks of the southern California Continental Borderland consist of a western blueschist facies complex (Yerkes and others, 1965) and of metasedimentary rocks analogous to the Franciscan complex of northern and central California (Crouch, 1981). In the study area, basement rocks are composed of Catalina Schist, which belong to the western blueschist facies complex. In middle Miocene time, an extensive Catalina Schist highland west of, and subparallel to, the present coastline extended from Santa Monica to Oceanside (Woodford and others, 1954; Yeats, 1973; Stuart, 1979). Exposures of Catalina Schist are present on the Palos Verdes Hills uplift and on Santa Catalina Island (Woodford and others, 1954). Samples of Catalina Schist also have been obtained from submarine dredge and core samples (Vedder and others, 1974) as well as from clasts in the San Onofre Breccia (Stuart, 1976). These

22 23

Figure 6. Composite sections showing regional correlation of units (from Yerkes and others, 1965; Rudat. 1980). California My I f." Epoch Verdes Uplift G~nthlc 'Nllmington Grnbcn San Jonquin Hills Area U.P Stnge 0

PLEISTOCENE!- ~~~~-_:~~'--~~ vn"t:E'-"~'~'"1'< -- 'i-il'l-\-tJI~I-1>-~'< t f\~p-0\~~N- "rPr:to FM -.,._ ..-· - -- -- REPETTO FM. 5 of.LMO~'~""N w MONTEREY SHALE z PUENTE FM. PUENTE FM. 0 t..~Orlt-1\P..~'< MalBQO Mudstone N T Valmonte Diatorn1te 10 Altamira Shale 1- _J r~~~---- :::> <:( u \_\)lSI I>-~'< ;--.____ TOPANGA z <:i" u.. 0 w 15 ~ I .:f'() "' SA~~- N ONOFRE-<:: D 0 0 - f>.tLI"Z.II>-~'<--- 0 z BRECCIA w --- 0 u $:

20

30·-

60-

UPPER CRETACEOUS 90- CATALINA SCHIST CATALINA SCHIST CATALINA SCHIST

LOWER CRET TO TRIASSIC

N ~

-~

"' 25

basement rocks typically consist of fine-grained chlorite-quartz schist, chlorite-muscovite-albite-quartz schist, crossite-bearing schist, chlorite-talc schist, quartz-chlorite-tremolite-lawsonite schist, and meta-gabbro (Woodring and others, 1946; Yerkes and others, 1965). The Catalina Schist on the mainland has been correlated with the type section that is exposed on Santa Catalina Island (Woodford, 1924). Whole rock, blue amphibole, white mica, and hornblende potassium-argon ages indicate that the schist on Santa Catalina Island was metamorphosed 95 to 109 m.y.b.p. (Suppe and Armstrong, 1972). Prior to metamorphism, the protolith of the Catalina Schist consisted of mafic volcanic rocks, conglomerate, graywacke, shale, and chert. These are similar in proportion to the unmetamorphosed portion of the Upper Jurassic to Eocene Franciscan Formation of the Coast Range and are considered to be equivalent to that formation (Woodford and others, 1954; Bailey and others, 1964). In the Los Angeles basin, the basement rocks of the southwestern block are composed of schist, which contrast sharply with the plutonic, metasedimentary and volcanic Mesozoic basement rocks of the other basinal blocks (Yerkes and others, 1965). The basement rocks have been divided into a western blueschist facies complex and an eastern granitic complex (Woodford, 1925; Yerkes and others, 1965; Yeats, 1973), which are separated by the Newport-Inglewood fault zone. Tertiary rock units older than middle Miocene are not known to occur in the southwestern block. It is unknown whether the absence of these rock units is the result of erosion or non-deposition. Yerkes and others (1965) suggested erosion because 4300 meters of Upper 26

Cretaceous to Oligocene rocks in the San Joaquin Hills probably extended across the present Newport-Inglewood structural zone to the southwestern block. It also has been suggested that the Catalina uplift may have occupied the western Los Angeles basin and shelf area as early as Paleocene time (Reed and Hollister, 1936; Woodring and others, 1946). The Catalina uplift could have been covered with Cretaceous sediments which were not eroded away until the end of Miocene time, therefore delaying exposure of the Catalina Schist. Yeats (1973), however, questioned whether pre-middle Miocene Strata could be removed entirely by erosion with none of the Catalina Schist having undergone erosion and subsequent deposition as sedimentary rocks. Yeats (1973) proposed that the Catalina Schist did not receive sediment nor was subjected to erosion in pre-Miocene time. The depositional history and the age of rock units overlying basement Catalina Schist in the study area are discussed in subsequent sections of this paper. Hill (1971) suggested that the Newport-Inglewood structural zone represents a Mesozoic subduction zone that juxtaposes basement rocks of contrasting lithologies .. This zone developed during Cretaceous time and altered or subducted any pre-Tertiary rocks in the southwestern block. Superjacent Rocks Exposures of Cretaceous through lower Miocene rocks are found in two areas of the Los Angeles basin: the Santa Monica Mountains and the San Joaquin Hills-Santa Ana Mountains. These rocks are not known to occur within the southwestern block (Yerkes and others, 1965). Jurassic - Early Miocene In the Los Angeles basin, the lithologically varied Upper Cretaceous rocks are chiefly marine. Paleocene and Eocene rocks 27

comprise a marine and nonmarine section and the upper Eocene (?) to lower Miocene rocks comprise a thick nonmarine red-bed section of the Sespe Formation. Sespe strata are overlain by, and interbedded with, lower Miocene marine strata (Yerkes and others, 1965). In the San Joaquin Hills, rocks of the Jurassic Bedford Canyon Formation and of the lower Cretaceous Trabuco, Ladd, and Williams Formations consist of sandstone, siltstone, and conglomerate beds. The Paleocene Silverado Formation contains marine and nonmarine coarse-to-medium-grained sandstone with conglomerate and claystone. The Eocene Santiago Formation consists of marine and nonmarine medium-to-coarse-grained sandstone with interbedded conglomerate, fine-grained sandstone, and claystone beds. Upper Eocene to lower Miocene rocks unconformably overlie Eocene rocks and comprise the Sespe and Vaqueros Formations. These rocks are unconformably overlain by the early Miocene Vaqueros Formation. The Vaqueros Formation consists of marine siltstone, arenaceous siltstone, and fine-to­ coarse-grained siltstone (Vedder, 1970; Tan and Eddington, 1976). Middle to Late Miocene The sedimentary rocks of the southwestern block are approximately 6250 meters thick and are composed predominantly of marine sedimentary strata of middle Miocene to recent age (Yerkes and others, 1965). Marked differences in rates and amounts of subsidence have produced pronounced lateral variations in thickness and lithology of these rocks. Contemporaneous faulting and folding, and local erosion, have produced regional and local unconformities, disconformities and stratigraphic discontinuities across faults (Yerkes and others, 1965). 28

In the Los Angeles basin, the middle Miocene rocks form a varied succession of volcanic and marine sedimentary rocks. In the western portion of the basin middle Miocene strata unconformably overlie the Catalina Schist basement (Yerkes and others, 1965). In the Palos Verdes Hills middle Miocene strata lie on Catalina Schist and are overlain by upper Miocene strata (Woodring and others, 1946). The Monterey Shale is the oldest middle Miocene formation exposed on the Palos Verdes Hills. Outcrops of Monterey Shale are present on the San Pedro shelf (Crouch, 1954; Moore, 1954; Junger and Wagner, 1977; Nardin and Henyey, 1978; Rudat, 1980). Miocene rocks thought to belong to the Monterey Formation have been dredged along the inner shelf offshore of Palos Verdes and from the outer Los Angeles Harbor (Moore, 1954). Rocks typical of the Monterey Shale (described as hard, porcelaneous, laminated, rhythmically banded shale) were dredged from the west­ central area of the San Pedro shelf by Moore (1954). Middle and upper Miocene siliceous shale and mudstone have been sampled along the crest of the Palos Verdes uplift as well as along its flank (San Pedro Escarpment). Seafloor samples indicate that the lithology of Miocene rocks differs in various parts of the area (Junger and Wagner, 1977). Upper Miocene strata of the Los Angeles basin form a widespread section of very fine-to coarse-grained, marine sedimentary rocks and local intrusive igneous rocks. Upper Miocene sediments onlap the western basement from the northeast (Yerkes and others, 1965). In the southeastern part of the Palos Verdes uplift, Miocene sediments buttress against the basement and pinch out against Miocene volcanic 29

or basement rocks on the northeast side of the San Pedro basin (Junger and Wagner, 1977). This pattern of sedimentation indicates that the subsidence of the Los Angeles basin in upper Miocene time began southeast of the southwestern block and spread north and west (Yerkes and others, 1965). Woodring and others, (1946) reported that subsidence and continuous deposition occurred in the Palos Verdes Hills area until early Pliocene time. The Wilmington oil field contains a thin middle Niocene section and a thick upper Miocene section (Mayuga, 1970). A majority of the strata belong to the upper Miocene Puente Formation, with a thin underlying section of the middle Miocene Topanga Group present. The Topanga Group along the crest of the Wilmington anticline consists of alternating layers of coarse-grained, poorly sorted sandstone and distinctly stratified shale (Mayuga, 1970). The upper Miocene Puente Formation consists of poorly sorted, fine- to coarse-grained sandstones interbedded with claystone, siltstone, shale and a few hard sandstone members (Mayuga, 1970). A majority of the oil sands in the Puente Formation, as well as portions of the Repetto Formation, show a southwest direction of transport (Truex, 1974). Along Newport Beach, the upper Miocene section has been correlated with the lower Mohnian Puente Formation (Hunter and Allen, 1956; Ingram, 1968). The Puente Formation generally is a fine to silty arkosic san.d with an upper massive, silty brownish-gray shale containing thin silt seams, sand, and hard chert lenses (Hunter and Allen, 1956; Ingram, 1968). Overlying the shale sequence is a characteristic bentonitic marker bed, the top of which marks an 30

unconformity between the late Mohnian and Delmontian (?) stages (Hazenbush and Allen, 1958; Ingram, 1968). The validity of the benthic foraminiferal Delmontian stage is questionable. Pierce (1972) suggests that the Delmontian stage may be a facies of the Mohnian stage as evidenced by the finding of characteristic Delmontian fossils in rocks of the Mohnian stage as well as the finding of Mohnian fossils in rocks of the Delmontian stage. Furthermore, the Delmontian stage may transgress the Miocene­ Pliocene boundary within the upper portion of the Monterey Formation (Berggren and Van Couvering, 1974; Boellstroff and Steineck, 1975). Surface investigations have shown the middle to upper Miocene and upper Miocene to lower Pliocene rocks along Newport Bay belong to the Monterey and Capistrano Formations, respectively (Vedder and others, 1957; Vedder, 1970; Ingle, 1972). Outcrops of the Monterey Formation consist of silty and diatomaceous shales, clay and cherty shale, limestone lenses, and turbidite sand. Comparison of the middle to upper Miocene Monterey and the upper Miocene Puente Formations indicate that the Puente Formation generally is composed of coarser­ grained material (Woodford and others, 1946; Woodring and others, 1946; Hunter and Allen, 1956; Ingram, 1968). The Capistrano Formation conformably overlies the Monterey Formation and consists of siltstone, channel deposits, and interbedded white diatomaceous shale (Ingle, 1972). In the San Joaquin Hills, the stratigraphically lowest formation of middle Miocene age is the Topanga Group. Contact with the underlying Vaqueros Formation generally is gradational. 31

The middle Miocene marine and nonmarine San Onofre Breccia unconformably overlies the Topanga Group in the San Joaquin Hills. The upper portion is locally intertongued with Monterey Shale (Vedder, 1970). Stuart (1975, 1979) and Vedder (1971) have indicated that the San Onofre Breccia in the type region most likely is restricted to the upper Relizian and lower Luisian stages. Locally, the San Onofre Breccia contains sandstone, siltstone, and conglomerate, but dominantly consists of a distinctive coarse clastic unit composed chiefly of Catalina Schist detritus (Tan and Edgington, 1976). This unit is very lenticular and may be as thick as 900 meters near South Laguna. The San Onofre Breccia thins northward (Vedder, 1970; Stuart, 1979) to the point where no San Onofre Breccia is found in the Los Angeles basin north and west of Sunset Beach (Yeats, 1973). Vedder (1970) concludes that the bulk of the San Onofre Breccia was derived from exposures of Catalina Schist to the south and west near the present trace of the Newport-Inglewood structural zone. According to Junger (1974), the primary source terrane was a ridge, presently buried, that extended for about 30 kilometers south\vard from a point about 9 kilometers offshore of Laguna Beach. The San Onofre Breccia formed as a series of clastic wedges derived from uplifted Mesozoic metamorphic rocks. These clastic wedges were deposited as alluvial fan, fan-delta, and shallow marine deposits. The most complete sequences of alluvial fan and fan-delta deposits are exposed between Oceanside and Laguna Beach (Stuart, 1979). Overlying the San Onofre Breccia in the San Joaquin Hills is the Monterey Shale. The contact with the underlying San Onofre Breccia is locally gradational, but generally is unconformable (Vedder, 1970). 32

The upper Miocene to lower Pliocene rocks of the San Joaquin Hills belong to the Capistrano Formation which is composed predominantly of mudstone and the prominently sandstone Oso member. The Capistrano Formation unconformably overlies older rocks in the western portion of the Capistrano syncline but elsewhere it is gradational with the Monterey Shale. Igneous dikes, sills, and flows of Miocene age (probably limited to the last half of the epoch) disrupt the sedimentary section in the area west of Laguna Canyon in the San Joaquin Hills (Vedder, 1970). In the Capistrano Embayment, the Monterey Formation has nearly a uniform thickness and lithology and is conformably overlain by the

Capistrano Formation. These two formations are differentiated by the change of the thin bedded Monterey shale to the indistinctly bedded siltstone and fine-grained biotite-rich sandstone of the Capistrano Formation (Ehlig, 1979). On the west side of the embayment, the lower part of the Capistrano Formation contains sediments derived from the erosion of strata exposed in the San Joaquin Hills. This formation was deposited at bathyal depths (Ehlig, 1979). Pliocene In the central portion of the Los Angeles basin, sedimentation continued uninterrupted through late Miocene into Pliocene time. This contrasts with the periphery of the basin where uplift at the beginning of Pliocene time resulted in local unconformities (Yerkes and others, 1965). The Pliocene rocks comprise a repetitive succession of alternating fine to coarse clastic marine strata, which range in 33

thickness from 3000 to 4300 meters (Woodford and others, 1954; Yerkes and others, 1965). Pliocene rocks of the southwestern block of the Los Angeles basin have been assigned to the Repetto and Pico Formations. The Repetto Formation is not a formalized name, but is used to remain consistent with existing literature and the use of Pico Formation is actually restricted to areas outside the Los Angeles basin (Wissler, 1943; Woodring and others, 1946; Yerkes and others, 1965; Junger and vJagner, 1977). The Repetto Formation on the Palos Verdes Hills is represented by soft, massive, glauconitic siltstone containing Catalina Schist detritus apparently derived from the south or west. A majority of the sediment, however, was derived from the north (Woodring and others, 1946). The Repetto Formation in the Los Angeles basin and accumulated in seas as deep as 1829 meters (Woodring and others, 1946; Ingle, 1967). Strata of the lower Pliocene Repetto Formation have been reported on the north slope of the San Pedro basin by Emery and Shepard {1945), Moore (1954), and Jennings (1962). Pliocene rocks occur locally along ridges and slopes of San Pedro Basin but are covered by younger sediments in the basin proper (Junger and Wagner, 1977). Junger and Wagner (1977) established a relation of the Offshore Pliocene stratigraphic sequence to the underlying and overlying stratigraphic sequences by correlation of unconformities observed in the offshore basins with those described in the literature. Seismic profiles show a thin layer of sediment forming a dip slope and lying unconformably on an erosional surface of folded upper Miocene strata. Moore (1954) 34

described rocks of the Repetto Formation obtained from dredge hauls on the northern San Pedro shelf as massive, angular, olive-colored soft siltstone containing hard sandstone and mudstone concretions. Rudat (1980) recognized a seismic unit characterized by a lack of distinct bedding reflectors in the vicinity of the San Pedro Sea Valley and the San Gabriel Submarine Canyon suggesting the massive lithology of the Repetto Siltstone. This seismic unit is not deformed and rests unconformably on folded Neogene rocks. Junger and Wagner (1977) propose that the undeformed unit is the earliest post-Miocene strata in the San Pedro basin deposited prior to the steepening of the basin flanks.·· Hov.Jever, Nardin and Henyey (1978) show deformed Repetti an strata beneath the outer shelf in San Pedro Bay. In San Pedro basin, sediments .buttress against Miocene rocks on the basin flanks and the deeper sediments show growth structure caused by contemporaneous sedimentation and subsidence (Junger and Wagner, 1977). Other buttress unconformities associated with accelerated subsidence have been recognized by Junger and Wagner (1977). These are the unconformity at the top of the Repetto onshore and an intra-Repetto unconformity correlated with the Huntington­ Sunset Beach coastal area. Late Pliocene basin sediments (the Pico Formation) buttress against the basin flank, indicating that strata higher on the flank have been uplifted prior to the deposition of the late Pliocene sediments (Junger and Wagner, 1977). In the Wilmington oil field Pliocene strata (representing both the Repetto and Pica Formations) conformably overlie the upper Miocene Puente Formation (Mayuga, 1970). The Repetto shale beds are soft and poorly indurated, brown to greenish gray, and grade to very micaceous 35

siltstone toward the upper part of the formation. The Pico Formation unconformably overlies the Repetto Formation and consists of a series of sand and siltstone strata, with some claystone and hard shale beds (Mayuga, 1970). Faults in the offshore portion of the oilfield do not appear to extend above the Repetto Formation (Junger and Wagner, 1977). Allen and Hazenbush (1957) reported unconformities at the top of the Miocene Puente Formation and within and at the top of the Repetto Formation in the Sunset Beach oil field. A majority of the faults terminate at the Miocene-Pliocene unconformity or at the unconformity within the Repetto. In the Huntington Beach oil field, Hazenbush and Allen (1958) place erosional unconformities between the Miocene Puente Formation and the lower Pliocene Repetto Formation, between the Pliocene Repetto and Pica Formations, and within the Pico Formation. A majority of the faults in this oil field terminate within the Repetto Formation. Lee (1977) mapped seismic reflectors offshore of Newport Beach and the seismic profiles show an apparent northward dip and a southwestward thinning of strata towards a basement high. The contact between the basement and ~1i ocene reflectors, and between the Miocene and Pliocene reflectors show an angular relationship, indicating an angular unconformity exists between the corresponding strata. The fine-grained clastic rocks of early to late Pliocene age near Newport Bay have been assigned to the Fernando Formation. This formation is faulted against, or rests unconformably on, the Capistrano Formation (Vedder, 1970). 36

Marine and nonmarine sedimentary rocks of late Pliocene age which unconformably overlie the Monterey Shale and Capistrano Formation in the central part of the Capistrano syncline are assigned to the Niguel Formation. Pleistocene During early Pleistocene time subsidence occurred in the southwestern block of the Los Angeles basin and as much as 305 meters of coarse marine sediments were deposited. At the end of early Pleistocene time a majority of the southwestern block was only slightly submerged and a series of shoals may have existed along the Newport-Inglewood structural zone (Yerkes and others, 1965). The Lower Pleistocene rocks of the Los Angeles basin comprise a succession of marine silt, sand, and gravel. Exposures occur in the southwestern block, in several of the low hills and mesas along the Newport-Inglewood structural zone, and in portions of the central block (Yerkes and others, 1965). Upper Pleistocene deposits consist of marine terraces, nonmarine terrace cover, nonmarine fluvial and lagoonal deposits, and probable stabilized dune deposits. These deposits are widely exposed in the Los Angeles basin (Yerkes and others, 1965). In the Palos Verdes Hills, lower Pleistocene deposits have been assigned to the San Pedro Formation and unconformably overlay the Monterey Shale or, less cowmonly, the Repetto Formation (Woodring and others, 1946). Upper Pleistocene marine sand and gravels that occur as terrace deposits on the Palos Verdes Hills belong to the Palos Verdes Sand (Woodring and others, 1946). 37

Junger and Wagner (1977) suggest that the base of the cross bedding in the uppermost part of the stratigraphic sequence in San Pedro Bay is the base of the Pleistocene. These offshore crossbedded deposits extend to the shelf edges where foreset beds continue into the basins as slope deposits. Rudat (1980) mapped several middle to late Pleistocene units in the Wilmington Graben which are believed to be correlative with the Palos Verdes Sand. In the San Joaquin Hills area, limited exposures of early Pleistocene sandstone, conglomerate, and siltstone beds belong to the San Pedro Formation. Late Pleistocene rocks include marine and nonmarine terrace deposits (Vedder, 1970). Holocene Holocene deposits in the onshore region include alluvial and modern stream deposits, sediments on flood plains, beaches, embayments, and dunes (Yerkes and others, 1965; Vedder~ 1970). Offshore Holocene deposits have been described by Rudat (1980). SEISMIC STRATIGRAPHY General Statement

Good borehole data was obtained in the area offshore of Newport Beach to aid in the correlation of offshore stratigraphic sequences within the study area. Correlations of post-basement strata are based on Kleinpell •s (1938) benthic foraminiferal stages (borehole data references only benthic foraminiferal stages). It is apparent that provincial benthic foraminiferal stages can be time-transgressive as well as affected by tectonically or climatically induced environmental changes (Ingle, 1967; Bandy, 1972). However, the use of benthic foraminiferal stages for local correlations in the study area probably is valid because the paleobathymetry of the upper Miocene and lower Pliocene depositional environments appears to be uniformly deep water.

Basement

The basement rocks in the northern extent of the study area are known to be composed of Catalina Schist (from borehole data) and therefore belong to the western blueschist facies complex of the southern California Continental Borderland. The high-continuity and high-amplitude doublet reflector (Sheriff, 1973; Sangree and Widmier, 1977; 1979) corresponding to this basement surface is correlated approximately 33 kilometers to the south. The distinctive seismic signature of this reflector is consistent throughout the area. Below the top of the basement, reflectors are chaotic, indicating a near total reflection of energy from the basement surface.

38 39

The basement surface, as shown by Plate I, is cut by numerous faults with varying magnitudes of vertical displacements. This surface ranges from 1000 to 3150 meters below sea level with the major structurally high area located 4.3 kilometers southwest of Dana Point (named the offshore San Joaquin anticline by Western Geophysical Company (1972) but will be referred to as the offshore San Joaquin ridge) and a structurally low area (the offshore south Newport trough) located 7.3 kilometers south of Newport Harbor (Fig. 7). The basement reflector corresponds to the acoustic basement (Horizon C) mapped by ~Jestern Geophysical Company (1972). The contoured unmigrated time values utilized by Western Geophysical Company (1972) in the area offshore of Dana Point are equivalent to the unmigrated time values digitized from seismic profiles by the writer.

~1i ocene

The lowest correlated reflector above the basement surface in the study area corresponds to the top of the Delmontian (?) benthic foraminiferal stage (Plate II). This reflector shows an angular relationship with underlying reflectors in the area offshore of Newport Beach, and is considered to be equivalent to the Miocene­ Pliocene unconformity recognized onshore. Lee (1977) also reported this angular relationship as the unconformable contact between Miocene and Pliocene strata. The middle Miocene San Onofre Breccia was not encountered by the boreholes offshore of Newport Beach. It is probable, however, that this formation is present in the study area. Seismic profiles east of 40

Figure 7. The major structurally high and low areas in the basement surface. 41

H 1 0 km 5 10

SCALE 1:250,000

OFFSHORE SOUTH NEWPORT RIDGE

30'

OFFSHORE SAN JOAQUIN RIDGE 42

the offshore San Joaquin ridge show a high-amplitude reflector which may be the top of this formation. Hunter and Allen (1956), Hazenbush and Allen (1958), and Ingram (1968) stated that the upper Miocene section along Newport Beach is correlative with the Puente Formation. However, Lee (1977) reported that borehole data offshore of the Santa Ana River and southwest of the Newport-Inglewood structural zone indicate the upper Miocene strata belong to the ~1onterey Formation. Core descriptions from Lee (1977) indicate a fine-grained lithology, mostly shale, not typical of the onshore section. Throughout the study area pre-Pliocene reflectors are characteristically discontinuous (hummocky clinoforms?) (Mitchum and others, 1977). This suggests that the upper Miocene strata in the study area belong to the Puente Formation because the well bedded character of the upper Miocene Monterey Shale should appear as continuous to semi-continuous, parallel to subparallel reflectors. To clarify the question of the proper formation to assign the upper Miocene strata, additional borehole data is necessary. In addition, a facies transition from the Monterey Formation to the coarser Puente Formation also may occur southward from the San Pedro shelf area. Upper Miocene sediments filled the structurally low areas in the basement surface from the north to northwest. This south to southeast direction of sediment transport is shown by the onlapping sequences of strata against the north flank of the offshore south Newport ridge and the west flank of the offshore San Joaquin ridge. Additional evidence for this transport direction is the downlapping sequ~nces of strata observed on the south flank of the offshore south Newport ridge and in the offshore south Newport trough. Strata of 43

undetermined age onlap the east flank of the offshore San Joaquin ridge from the north to northeast. Truncation of upper Miocene strata occurs along the northeast-trending offshore south Newport fault located approximately 9.2 kilometers south of Newport Harbor. The thickness of upper Miocene strata varies from less than 50 meters to greater than 1000 meters (vertical isochore values, not true thickness). Major changes in thickness are controlled by the basement surface (i.e. greatest thickness on down dropped blocks). An exception to this is in the offshore south Newport trough where strata thin due to downlap prior to truncation against the offshore south Newport fault.

Upper r~iocene strata commonly are cut by faults (Plates II, V, VI). The faults predominantly are high angle normal and originate in basement rock. Subsidence of a number of basement fault blocks is contemporaneous with sediment deposition as evidenced by faults with thicker sedimentary sections on their downthrown side.

Pliocene

The reflector correlated within the Pliocene stratigraphic section is the top of the Repettian benthic foraminiferal stage (Plate III). This reflector is characteristically high-continuity and variable-amplitude and is relatively undisturbed, except by the offshore south Newport fault where it is displaced vertically approximately 200 meters. The sequence of reflectors below the top of the Repettian stage characteristically are parallel to subparallel, high-continuity with 44

generally high amplitude. The outstanding feature of these reflectors is their marked parallelism. Offshore of Newport Beach, Repettian strata unconformably overlie steeper dipping upper Miocene Delmontian strata. To the southeast, the Repettian strata appear to parallel the underlying upper Miocene strata. In the vicinity of the offshore south Newport trough, the Repettian strata onlap the more gentle dipping upper Miocene strata from the northwest. The onlapping nature of the Repettian strata continues to the southeast against the basement surface of the offshore San Joaquin ridge. The inability to recognize the angular unconformity between Miocene and Pliocene strata in certain areas may be the result of the limited resolution of the seismic profiles or the contact actually may be locally conformable to disconformable. The Repetto Formation gradually thickens to a maximum of approximately 850 meters in the offshore south Newport trough. To the southeast, Repettian strata onlap the offshore San Joaquin ridge and eventually thin to a zero thickness (the zero edge is located approximately 6 kilometers offshore of Laguna Beach and generally trends north-south). Varying stratigraphic thicknesses across some faults indicate displacement occurred contemporaneously with deposition. A majority of the faults, which are continuations of those originating in basement rock, terminate within or at the top of the Repetto Formation. Reflectors within the middle to upper Pliocene strata belong to the Pico Formation. Reflectors are variable-continuity, variable­ amplitude, parallel to subparallel and are subparallel to the reflectors associated with the underlying Repetto Formation. Strata of 45

the Pica Formation dip to the southeast toward the offshore south Newport trough and onlap the basement surface of the offshore San Joaquin ridge from the north to northwest. Onlap of this basement surface by the post-Repettian strata continues to the southeast until the strata completely overlap this basement high. Plate IV shows the structure along the top of an arbitrary reflector within the upper Pliocene to Pleistocene stratigraphic section that overlaps the offshore San Joaquin ridge. Thickness of the post-Repettian strata ranges from approximately 500 to 1600 meters. In summary, the major basement structural highs impaired or blocked sediment transport during the deposition of the overlying strata. Upper Miocene through Pliocene strata buttress (onlap) against the flanks of these structural highs, predominantly from the north to northwest, and locally, upper Miocene strata drape off (down1ap) the basement surface to the southwest. On1ap of strata against the eastern flank of the offshore San Joaquin ridge from the north to northeast is observed on seismic profiles as well. The areas of onlapping and downlapping stratigraphic sequences are shown in Fig. 8. 46

Figure 8. Location of stratigraphic sequences that onlap or downlap against the basement surface. 47

118°00'

0 km 5 1 0

SCALE 1:250,000

DIRECTION OF ONLAP/DOWNLAP

33° 30'

PT.

ON LAP ONSHORE STRUCTURE

The structural grain of the southern California Continental Borderland and the Peninsular Ranges is characterized by northwest­ southeast-trending folds and faults (Emery, 1960; Moore, 1969; Vedder, and others, 1974; Junger, 1976). These northwest-southeast-trending features are bordered or truncated on the north by the east-west structural grain of the Transverse Ranges. The major structural element in the study area is the offshore extension of the northwest-southeast-trending Newport-Inglewood structural zone. In the Los Angeles basin, the Newport-Inglewood structural zone is characterized by a belt of northwest-southeast­ trending, en echelon faults and subparallel west-northwest-trending folds which extend from Beverly Hills to Newport Beach. Reed and Hollister (1936) summarize early investigations and suggest that the en echelon structural character indicates that a basement or master fault exists along which dextral shearing stresses are operative. Basement contrasts on either side of the zone tend to support the master fault hypothesis. The NevJport-Inglevmod structural zone is considered by most workers to be a major tectonic boundary separating Catalina Schist (western blueschist facies complex) from predominantly granitic basement (eastern granitic complex) (Yerkes and others, 1965; Hill, 1971). The placement of contrasting basement lithologies along this zone occurred between Late Cretaceous and middle Miocene time (Yerkes and others, 1965). The Newport-Inglewood structural zone separates the Los Angeles basin's southwestern and central structural blocks. To the northwest,

48 49

the zone is terminated against, or merges with, the east-northeast­ trending Santa Monica fault zone. At its southeast end, the zone trends offshore of the San Joaquin Hills (Yerkes and others, 1965). This structural trend is a zone of complex faulting and related folding. It contains west-trending reverse faults, north-trending normal faults, northwest-trending right-lateral en echelon strike-slip faults, and right-handed en echelon anticlinal folds (Yeats, 1973; Harding, 1973). The development of the structural style of the Newport-Inglewood structural zone has been attributed to strike-slip deformation (Barrows, 1974). Early investigators (Eaton, 1923; Ferguson and Willis, 1924) noted that lateral movement was responsible for the formation of the en echelon anticlinal structures. Moody and Hill (1956) recognized that various faults associated with the structural zone are not a part of a single clear-cut faul,t trace, but rather~ they are parallel faults in a narrow zone. Harding (1973) stated that the "parallel faults" in different parts of the Newport-Inglewood structural zone demonstrate different directions, magnitudes, and histories of displacement. He attributed the structural trends to wrenching and used the Newport­ Inglewood structural zone as an example of a wrench zone of small displacement analogous to experimentally produced structural patterns produced in model studies by Wilcox and others (1973) The amount of right lateral displacement along the Newport­ Inglewood structural zone is controversial. The anticlines associated with Dominguez Hill, Baldwin Hills, and Signal Hill have displacement, as measured across fold axes or on flank bulges, that range from 750 to 1980 meters (Harding, 1973). Wright and others (1973) suggest 1220 meters of dextral offset. Large scale right lateral separation of as 50

much as 3000 meters also has been suggested (Yerkes and others, 1965; Hill, 1971; Yeats, 1973). Vertical separation of basement rock is as much as 1220 meters. This displacement progressively decreases in younger strata (Yerkes and others, 1965). A northwest-southeast compression and the propagation of basement anisotropies into overlying strata along the present trace of the Newport-Inglewood structural zone began at the end of Miocene time. However, localization of shear strain and deformation along the zone began during the initiation of the Pasadenan orogeny in late Pliocene time (Yeats, 1973). An offshore continuation of the Newport-Inglewood structural zone has been shown by many authors (Tabor, 1920; Eaton, 1933; Emory, 1960; Yerkes and others, 1965; Morton, 1973; Jennings, 1975; Rodgers, 1979).

Hill (1971) suggested that the ~ctive fault zone does not extend south of Newport Beach, rather, a much older Cretaceous fault zone extends south to Baja California. On the basis of seismic reflection profiles and active seismicity, others have suggested the (active?) fault zone extends south to San Onofre (Western Geophysical Company, 1972; Fischer and others, 1979; Tieken, in prep.). Some writers continue this zone south to the San Diego area (Emery, 1960; Barrows, 1974) whereas others suggest a connection between the Newport-Inglewood fault zone and the Rose Canyon fault in San Diego (Corey, 1954; Moore, 1972; Kennedy, 1975; Moore and Kennedy, 1975; Greene and others, 1979). A major onshore structural feature adjacent to the study area is the complexly faulted anticline of the central San Joaquin Hills. The anticlinal structure is defined by the regional bedding dips of the Topanga Formation (Tan and Edgington, 1976). The dominant structural 51

control is faulting, not folding, since homoclinally dipping beds generally are present in fault blocks. The exception is the Monterey Shale where folding is apparent (Tan and Edgington, 1976). The San Joaquin Hills are transected by numerous northwest­ trending faults including the Pelican Hill, Shady Canyon, and the Laguna Canyon fault. Also present are north and east-trending faults (the northern portion of the Laguna Canyon fault and the Temple Hill fault) (Tan and Edgington, 1976). The Pelican Hill fault zone extends from Newport Bay to northwest Laguna Beach. This fault displays vertical and inferred lateral movements that were recurrent in Miocene and Pliocene time (Vedder, 1970). Furthermore, higher-level Pleistocene marine terraces are displaced by this fault zone indicating that it moved during Late Quaternary time (Tan and Edgington, 1976). The greatest vertical stratigraphic separation along the fault is 760 meters (Tan and Edgington, 1976). Southeast of the San Joaquin Hills is the Capistrano Embayment. This embayment is a flat-bottomed trough, which is bounded by the Peninsular Ranges on the east and the San Joaquin Hills on the west and extends from the coast near San Juan Capistrano to the Santa Ana Mountains (Ehlig, 1979). The trough was formed by down-warping along the east side of the San Joaquin Hills and downward displacement along the west side of the Cristianitos fault. The trough began to form approximately 10 m.y. ago and was a depocenter for the upper Miocene to lower Pliocene Capistrano Formation (Ehlig, 1979). OFFSHORE STRUCTURE General Statement

The study area is divided into three structural provinces based primarily on basement structural elements (Fig. 9): 1. Province I is located on the continental shelf landward of the seaward margin of the Newport-Inglewood structural zone, and is characterized by chaotic reflectors (because of which the basement rock type cannot be determined). 2. Province II is the northwest portion of the area and is characterized by north to northwest-trending faults and ridges in the basement surface. 3. Province III is the southeast portion of the area and is characterized by north to northeast-trending faults, ridges, and troughs in the basement surface.

Faults

The Newport Inglewood Fault Zone The major fault in the study area is the Newport-Inglewood fault zone (Fig. 9). This tectonically active structural zone has a maximum width of approximately 5 kilometers in the region extending from Huntington Beach to Newport Beach (Morton, 1973). Numerous faults show surface to near-surface displacements and the Long Beach earthquake of 1933 is generally attributed to movement of this fault zone. According to Harding (1973), the structural style of the zone is the result of wrench-style deformation.

52 53

Figure 9. Structural provinces in the study area. 54

118~ 00'

0 k m 5 10 ' SCALE 1:250,000

X RIDGE NEWPORT

;< TROUGH

\ FAULT 55

The Newport-Inglewood structural zone was mapped by the writer offshore of Newport Harbor and found to continue southeastward past Dana Point (Plate I). Lee (1977) mapped offshore fault splays within this zone from Huntington Beach to the Newport Beach River. Within the study area the Newport-Inglewood structural zone is characterized by chaotic reflectors (discontinuous and discordant) which are the result of severely deformed rock units. No attempt to correlate reflectors across the zone was made. The maximum mappable width of the offshore continuation of the zone is 3 kilometers, however, the seismic coverage was insufficient to delineate the landward margin of this zone. The uppermost reflectors in the Plio-Pleistocene sequence appear to be disrupted within the offshore portion of the Newport-Inglewood structural zone. Fischer and others (1979) utilized 3.5 kHz high resolution profiles to show late Pleistocene, Holocene, and sea floor displacement in this offshore portion. Seismicity studies show activity along the zone (Henyey and Teng, 1976) (Fig. 10). Four right-stepping, en echelon segments form the seaward margin of the Newport-Inglewood structural zone (Plate I). The right-stepping, en echelon character is consistent with the onshore right-handed, en echelon structural pattern of anticlinal culminations and strike-slip faults (Harding, 1973). This seaward margin was mapped at the basement surface, where the basement reflector was disrupted beyond recognition. Overlying reflectors become chaotic at approximately the same location as the basement reflector suggesting a near vertical attitude of the zone. This southern boundary of the zone is defined as the change from chaotic reflectors (Characteristic of the internal zone) to the high-continuity reflectors to the southwest. The 56

Figure 10. Earthquake epicenters, from 1933 to 1972, plotted along the Newport-Inglewood structural zone (from Henyey and Teng, 1976). ,. l>e LOS ••• 118° 00' t{ O 0 ANGELES • ~• • 0 O • ..OBASIN Okm 15 .• •';_ ::• SCALE 1:500,000 EARTHQUAKE ..~!'\ ~ •": •• • EPICENTER NEWPORT- \ INGLEWOOD FAULT ~--(!).• ~-. @I ~- ". 0 o ti\~ j·o • " ""' o$ e8 .,.. ..<~o •~A·· ( ...... \'<~ , ''9 ...... , ' ' .... SAN PEDRO ' . IS' ... , BASIN ', )-(/, ' ' '0;... " .... , -1-s:-<' ',, ', -1 ' ', ) ' f ', / './

U1 -....j

., 58

northernmost offshore segment extends to within 2.5 kilometers of Newport Beach and the southernmost segment is approximately 3.8 kilometers offshore of Dana Point (Plate I).

Other Faults Most other faults in the study area are high angle normal with varying magnitudes of vertical displacement. Evidence of strike-slip displacement could not be determined on any faults in the study area. Faults originate in basement rock and terminate at various levels in the overlying sedimentary section. Few faults extend through the top of the Repetto Formation and those that do have relatively small displacements. An exception is the offshore south Newport fault which displaces the top Repettian reflector more than 200 meters. Three faults in the study area vertically displace the top basement reflector more than 200 meters. Two of the faults are in Province II and trend north to northwest (the offshore Newport Mesa fault and the offshore Newport Harbor fault) (Fig. 11). The offshore Newport Mesa fault has a maximum displacement of 200 meters and the offshore Newport Harbor fault has a maximum displacement of 600 meters at its southern-most extent. The third fault is the offshore south Newport fault in Province III, which trends north to northeast. A maximum displacement of 900 meters was mapped along this fault (Plate I). This fault displaces the top Repetto reflector approximately 200 meters, and bifracates with decreasing throw to the south. Typically, faults within the study area show differential displacement of the basement surface along their length, which is due to numerous intersections with other faults. These fault intersections 59

Figure 11. Location of major faults displacing the basement surface. 60

118" 00'

0 km 5 1 0

SCALE 1:250,000

NEWPORJ BEACH )

" Q NEWPORT ~ ~' MESA ~cs FAULT

FAULT \

33° 30'

' 61

give Province II and the northwest portion of Province III the appearance of consisting of a series of 11 basement-rooted 11 fault blocks, each moving independently (Plate I). In the area of investigation, numerous faults show a greater thickness of sedimentary section on their downthrown side (Plates V and VI). This suggests that at least part of the vertical displacement along the faults was contemporaneous with sediment deposition. Faults vary in trend direction and lateral continuity. Faults in Province II generally are more continuous and have a predominantly northwest trend. Faults in Province III generally are discontinuous and have a predominantly northeast trend.

Structural Highs and Lows

The structural trends in the study area primarily are developed in basement rock. These trends, and the major structural relief of the basement surface, were developed prior to upper Miocene time. This is evidenced by the onlapping and downlapping sequences of upper Miocene strata against the basement surface. Apparent large scale folding of upper Miocene to Pliocene strata is due to the draping of strata over the basement highs and to post-depositional faulting. The major trend axes are located on Fig. 7. The largest high is the north-south trending offshore San Joaquin ridge in Province III. The crest of this high is 1000 meters below sea level and the west flank dips to a depth of greater than 3000 meters below sea level. The offshore San Joaquin ridge was formed primarily by plastic deformation 62

and faulting of the Catalina Schist prior to sediment deposition, by being a remnant high area on an erosion surface, or by a combination of both. Vertical fault displacement has also contributed to the overall relief of this ridge. The offshore south Newport ridge is a northwest-trending high in Province II with a relief of approximately 1000 meters on the basement surface. The origin of this ridge was due to faulting rather than by plastic deformation or differential erosion. Faults on the northeast flank have downdropped blocks to the northeast and faults on the southwest flank have downdropped blocks to the southwest. The offshore Newport Mesa and offshore Newport Harbor faults are primarily responsible for control of the relief of the offshore south Newport ridge. Both the offshore San Joaquin and the offshore south Newport ridges are buttressed by upper Miocene strata indicating growth prior to deposition. Syndepositional faults indicate continued relative growth of structural relief of these highs through time. Folds within the sedimentary section are relatively minor. The offshore south Newport ridge extends into the sedimentary section with a relief of approximately 300 meters in the top Delmontian (?) strata. This appears to be the result of post-depositional faulting and the draping of strata over the basement structural highs (supratenuous fo 1ding). The offshore south Newport trough and the offshore San Joaquin ridge have no expression in the sedimentary section. 63

Correlation of Onshore-Offshore Geologic Features

Correlation of reflectors across the offshore continuation of the Newport-Inglewood structural zone is difficult. Therefore the estimation of lateral offset along the zone is based upon assumptions. If it is assumed that the counterpart of the anticlinal structure of the San Joaquin Hills is the offshore San Joaquin ridge, then the lateral offset along the Newport-Inglewood structural zone is approximately 4250 meters since late Miocene time. This estimate is based upon the projection of the onshore anticlinal trend to the seaward margin of the zone (Fig. 12). The assumption of the equivalence of the positive structures is supported by their middle to late Miocene time of inception. The offshore San Joaquin ridge formed prior to upper Miocene deposition as indicated by the buttressing of the upper Miocene strata. The anticlinal structure associated with the San Joaquin Hills formed in response to Miocene faulting (Vedder, 1970; Tan and Edgington, 1976). The San Onofre Breccia was deposited as clastic wedges derived from western schist basement highs (Stuart, 1979). It should follow that the thickest deposits are adjacent to these basement source highs. The offshore San Joaquin ridge may have been the source terrain for the thickest package of San Onofre Breccia exposed on the San Joaquin Hills (Junger, 1974) and because this thick package is on trend with the axis of the offshore San Joaquin ridge (Fig. 12), a minimum of offset along the Newport-Inglewood structural zone is implied. Stuart (1979) reports that the Newport-Inglewood fault zone extends along the easter·n boundary of the offshore San Joaquin ridge where evidence supports an 64

Figure 12. Apparent horizontal offset of geologic features along the Newport-Inglewood structural zone. 65

00'

0 km 5 1 0

1:2 50. 000

PELICAN HILL FAULT

Thickest package of San Onofre Breccia exposed SAN JOAQUJN HILLS ANTICLINE

~' 3 3 ° 30'

OFFSHORE SAN JOAQUIN RIDGE 66

essentially fixed position of the ridge relative to San Onofre Breccia deposits. Lateral offset may also be estimated by assuming the onshore Pelican Hill and the offshore south Newport faults were once a continuous zone. The amount of estimated offset varies according to the azimuth of the line used to project the Pelican Hill fault to the seaward margin of the Newport-Inglewood structural zone. If the line of projection parallels the onshore fault trend, then the offset is approximately 7300 meters. If the line of projection is perpendicular to the seaward margin of the Newport-Inglewood structural zone, then the offset is approximately 4250 meters (Fig. 12). The assumption that these faults are the offset segments of a formerly continuous fault is based upon the following: (1) both faults have a northwest downdropped block (Vedder and others, 1957); (2) movement along both faults was recurrent in Miocene and Pliocene time (Vedder, 1970); and (3) the greatest stratigraphic separation on these faults is similar (Pelican Hill fault, 760 meters (Tan and Edgington, 1976) and offshore south Newport fault, 900 meters). It should be noted that the offset of 4250 meters is the same for the Pelican Hill-offshore south Newport fault and the San Joaquin Hills anticline-offshore San Joaquin ridge estimates. NEOGENE EVOLUTION OF THE INNER BASIN MARGIN General Statement

The present configuration of the inner basin margin can be attributed primarily to the deformation of basement rock and subsequent Neogene sedimentation. The study area did not become a depocenter until Mohnian time. The area developed in conjunction with major tectonic events associated with the deformation of the California Continental Borderland.

Pre-Depositional Events

The positioning of contrasting basement rock complexes (western blueschist facies complex and the eastern granitic complex) is thought to have occurred between Late Cretaceous and middle Miocene time (Yerkes and others, 1965). This basement contact is believed to be the Newport­ Inglewood structural zone and is thought to mark the location of the southern California subduction zone, which was active during Cretaceous time. This subduction zone extended both northwest across the Transverse Ranges, delineated by the Sur Nacimiento fault zone, and southeast along Baja California (Hill, 1971). Atwater (1970) and subsequent workers (Yeats, 1973; Blake and others, 1978) attribute the origin of the Neogene borderland basins to the impingement of a spreading ridge system against western North America and to subsequent interactions. Extensionists (Yeats and others, 1974) suggest that early middle Miocene east-west extension occurred in the southern California Continental Borderland as a result of the intersection of the East Pacific Rise and the North American

67 68

plate. Proponents of oblique extension (Howell and others, 1974) cite strike-slip movement as the main cause of basin inception. Recent work suggests the relative change in motion between the North American plate and Pacific plate to a more westerly direction about 10 m.y.b.p. produced the component of extension required to form the Neogene basins (Blake and others, 1978). Nardin and Henyey (1978) propose that a subsequent divergence between plate motions and the orientation of the tectonically soft boundary between the North American and Pacific plates occurred between 12 and 3 m.y.b.p. creating a degree of convergence along the existing strike-slip faults. This produced a change in deformational style from crustal dilation, regional block faulting and basin formation to narrow zones of folding and post-Miocene discontinuous faulting. (Nardin and Henyey, 1978; Junger, 1976). These tectonic events, or combination of events. resulted in the inception of the Los Angeles basin in middle Miocene time, as evidenced by a thick sedimentary section of upper Miocene to Pliocene rocks (Yerkes and others, 1965). In middle Miocene time, a fairly continuous basement schist-ridge system extended from Santa Monica to Oceanside (Stuart, 1979). The San Onofre Breccia was derived from this schist ridge and deposited in a structural 1ov1 between the ridge to the west and the San Joaquin Hills uplift to the east (Stuart, 1979) . The offshore San Joaquin ridge was the main source for the thickest exposed section of San Onofre Breccia in the San Joaquin Hi 11 s according to Junger ( 197 4) and Stuart (1979). The schist-ridge system subsided at the end of middle Miocene time and deposition of the San Onofre Breccia ceased. At this time, the basement surface in the study area attained its present

r 69

ridge and trough configuration with high angle normal faults. This ridge and trough configuration may be attributed to differential erosion of the basement rock surface in middle Miocene time, plastic deformation and faulting of the schist creating highs and lows, or a combination of both.

Neogene Events

Depositional History

Upper Miocene deposition in the study area was contemporaneous with the principal phase of subsidence in the Los Angeles basin (Yerkes and others, 1965). During this time, sediments were derived from north to northwest of the area, as evidenced by the south to southeast onlapping and downlapping sequences of strata onto the basement surface. In the southeastern part of the Palos Verdes uplift, Miocene sediments buttress against the basement rock indicating deposition by turbidity currents rather than hemipelagic sedimentation which would have formed blanket-like deposits on the basin floor and flanks (Junger and Wagner, 1977). Truex (1974) reports a southwest direction of sediment transport during the deposition of the upper Miocene Puente and the lower Pliocene Repetto Formations in the Wilmington area. In the central part of the Los Angeles basin sedimentation was continuous from late Miocene into Pliocene time and was contemporaneous with continued basin subsidence (Yerkes and others. 1965). Conrey (1967) described the deposition of the lower Pliocene strata of the Los Angeles basin as resulting from turbidity currents entering the 70

Whittier Narrows (Montebello) spreading coarse sediment over the entire basin floor. Truex (1974) suggested that the early Pliocene (Repettian) sands in the Wilmington oil field represent turbidite sequences. In the study area, sedimentation was probably continuous from late Miocene through Pliocene time. The consistent south to southeast onlap and downlap of strata indicates a consistent direction of sediment transport. The upper Miocene through Pliocene sediment transport was controlled and blocked by the basement structural highs. As proposed for the areas to the north, sediments were probably transported by density currents into the study area. The Palos Verdes uplift may have blocked sediment transport to the southwest towards the deeper basin, restricting sediment transport to the northwest-southeast-trending Wilmington graben (Fig. 13). Sediment from the San Pedro bay and Wilmington areas would have been transported into the study area and eventually diverted into the deeper basin along the western flank of the offshore San Joaquin ridge. To the southeast, the Capistrano Embayment originated 10 m.y. ago and formed a marine basin of sedimentation for the upper Miocene to lower Pliocene Capistrano Formation (Ehlig, 1979). Capistrano sediments infilled this structural trough at approximately the same rate as the trough subsided. Numerous south to southwest-trending backfilled submarine channels exposed within the Capistrano Formation suggest that excess sediments were frequently carried by turbidity currents into a deeper offshore basin (Ehlig, 1979). Offshore of the Capistrano Embayment, reflectors onlap the east flank of the offshore San Joaquin ridge. 71

Figure 13. Direction of sediment transport for upper Miocene through lower Pliocene strata. LOS 11s• oo' J( ANGELES Ok m 15 BASIN

WILMINGTON SCALE 1:500,000

Direction of '\ sediment transport

J \

SAN PEDRO 33° 30' BASIN

\4 "

""-..J N

'i . ., 73

Deposition in the study area continued through Pliocene time as strata overlapped the offshore San Joaquin ridge from the north to northwest (age of the strata immediately overlying the basement surface could not be determined). As sediments overlapped this high from the north to northwest, the area east of the ridge no longer received sediment exclusively from the Capistrano Embayment area. In the Wilmington graben cross-bedded sequences indicate a continued southwesterly direction of transport in Quaternary time (Junger and Wagner, 1977). The Quaternary sediment filled the Wilmington graben from the present coastline toward the Palos Verdes uplift. A large portion of these sediments were transported southeastward into the Gulf of Catalina (Junger and Wagner, 1977).

Structural Evolution Growth of the Wilmington anticline was initiated in late Miocene time and continued through the lower Pliocene (Truex, 1974). Similar late Miocene uplift occurred in the San Pedro basin as evidenced by the thin or absent Miocene sediments from the central and southwestern parts of the basin (Junger and Wagner, 1977). In addition, strata buttress against the Miocene rocks on the basin flanks and the deeper sediments sho'.'J growth structure caused by contemporaneous sedimentation and subsidence of the central parts of the basin (Junger and Wagner, 1977). Concurrently, the flanks of the San Pedro basin rose primarily by folding. Late Pliocene subsidence of the basin was caused by steepening of the flanks with a majority of faults terminating at the top of the Repetto Formation (Junger and Wagner, 1977). In the study area, late Miocene to early Pliocene 74

tectonics are present. Late Miocene to early Pliocene faulting may be the result of continued subsidence of the structurally low areas, structural uplift of the positive areas, or a combination of both. Unconformities within the sedimentary section are associated with the highs, suggesting that widespread uplift within the area did not occur. Faults in the study area typically terminate within or near the top of the Repetto Formation. However, post-Repettian uplifts are present. The origin and uplift of en echelon anticlinoria beneath the Santa Monica and San Pedro shelves can be interpreted to be the products of convergent dextral shear along the Palos Verdes fault during late Pliocene and Pleistocene time (Nardin and Henyey, 1978). The emergence and formation of the modern Wilmington anticline began during the early part of the upper Pliocene (Mayuga, 1970). Woodring and others (1946) considered the absence of upper Pliocene strata north of the Palos Verdes Hills as indicative that this was the period of strongest deformation in the Palos Verdes Hills. Post-Repettian tectonics are present in the study area (i.e. the top of the Repetto Formation is downdropped over 200 meters along the northwest side of the offshore south Newport fault). The localization of right-lateral shear along the Newport-Inglewood structural zone during late Pliocene time (Yeats, 1973) could be neither substantiated or disproved. SUMMARY AND CONCLUSIONS

Seismic stratigraphic analysis demonstrates that the Neogene structural evolution and depositional history of the study area was relatively uniform. The area developed in conjunction with pre-upper Miocene tectonic events associated with the deformation of the California Continental Borderland. The basement surface in the study area ranges in depth from 1000 to 3150 meters bel ov1 sea 1evel. Basement rocks are schist and be 1ong to the western blueschist facies complex characteristic of the California Continental Borderland. Based primarily on basement structural elements, the area is divided into three structural provinces: (1) Province I is the continental shelf area, (2) Province II is the northwest portion of the area, and (3) Province III is the southeast portion of the area. During middle Miocene time, a schist ridge existed west of the present coastline and shed detritus (the San Onofre Breccia) toward the San Joaquin Hills area (Stuart, 1979). The exposure of this schist high resulted in differing sedimentary sections present in the San Joaquin Hills and the study area. The San Joaquin Hills area contains thousands of meters of late Cretaceous to Paleogene sediments whereas the study area contains no pre-Neogene rocks. The presence of middle

Miocene San Onofre Breccia in the st~dy area is probable, however, the majority of sediment deposition occurred only after subsidence of the ridge at the end of middle Miocene time. The source for the thickest sedimentary package of middle Miocene San Onofre Breccia exposed in the San Joaquin Hills may be the offshore San Joaquin ridge (Junger,

75 76

1974; Stuart, 1979). With the subsidence of the schist ridge, the present configuration of ridges and troughs in the basement surface was established. This basement configuration may be attributed to pre-Neogene plastic deformation and faulting of the schist, differential erosion of the basement surface during middle Miocene time, a combination of both, or an original discontinuous schist ridge. Upper Miocene sedimentary rocks, probably belonging to the Puente Formation, are downlapped on basement structural lows and onlapped on basement structural highs from the north to northwest. Indications are that from the San Pedro Bay area to the west flank of the offshore San Joaquin ridge the apparent mode of deposition was by turbidity currents with a southerly transport direction. During Pliocene time the depositional patterns established during late Miocene time continued. The lower Pliocene Repetto Formation onlapped the offshore San Joaquin ridge from the north to northwest until this unit thinned to a zero thickness. Sediments in the study area accumulated on a basement surface whose configuration was established prior to late Miocene time. Upper Miocene through lower Pliocene sediments were derived from north to northwest of the offshore Newport Beach area and their transport to the southeast was controlled or blocked by basement highs. This depositional pattern continued until Plio-Pleistocene strata overlapped the offshore San Joaquin ridge from the north to northwest. The consistent southerly direction of sediment transport during late Miocene through Pliocene time may indicate that sediments were channeled down the northwest-trending Wilmington graben. The 77

southwest border of the Wilmington graben (the Palos Verdes uplift) was uplifted along the Palos Verdes fault. The time of inception of the Palos Verdes fault probably was 10 to 15 m.y.b.p. at which time it blocked sediment transport to the deeper basin (Blake and others, 1978). Sediments, instead, were deflected to the southeast, eventually to be diverted seaward along the west flank of the offshore San Joaquin ridge. South of Dana Point, strata probably belonging to the upper Miocene to lower Pliocene Capistrano Formation onlapped the east flank of the offshore San Joaquin ridge from the north to northeast. Onlap occurred while sediment transported into the Capistrano Embayment was being shed offshore in a southerly direction (Ehlig, 1979). This offshore area received additional sediment from the northwest when sediment transported offshore of the Newport Beach area overlapped the offshore San Joaquin ridge. Unconformities within the sedimentary section reported in the San Pedro Bay area and in onshore oil fields are, for the most part, not observed in the study area. The unconformity between the Miocene and Pliocene strata is present offshore from Newport Beach to an area south of the Newport syncline. It can be recognized only where the divergent angular relationship between the strata is great enough to be resolved by the seismic data. Other unconformities were not mapped because the seismic data probably lacks the detailed resolution necessary for their recognition. Syndepositional faulting occurred during the upper Miocene and resulted in a relative subsidence of the structurally low areas. 78

Furthermore, faults with thicker sections of Repettian strata on their downthrown blocks indicate that this faulting continued through Repettian time. A majority of faults terminate within, or at the top of, the Repetto Formation. This suggests a slowing of relative subsidence during the lower Pliocene. The upper Pliocene sedimentary section is relatively undisturbed except along the offshore south Newport fault where the base of the upper Pliocene is displaced vertically approximately 200 meters. The Newport-Inglewood structural zone extends offshore of Newport Beach to southeast of Dana Point in a series of four right-stepping en echelon fault segments. Lateral offset along the Newport-Inglewood structural zone, using assumed similar or related geologic features as piercing points, has been right-lateral with an estimated horizontal displacement of 4250 meters. The late Pliocene time of inception of the Newport-Inglewood structural zone as suggested by Yeats (1973) could be neither substantiated or disproved as reflectors within the zone are chaotic and no attempt to correlate formation tops or reflectors through the zone was made. Recent work by Fischer and others (1979) and Tieken (in prep.) suggests the offshore extent of the zone has been active in Holocene time. Faults in the area are high angle normal. The attitude and sense of displacement of these faults suggests that a tensional regime was active from late Miocene through at least lower Pliocene time. The northern portion of the area probably underwent subsidence during late Miocene through lower Pliocene time similar to that which occurred in the nearby Los Angeles basin. This portion of the study area may have originated as an irregular pull-apart basin during 79

middle Miocene.time. Crowell (1974) suggested a similar origin for the Los Angeles basin. The relatively continuous nature of these faults suggests that the area consists of a series of 11 basement rooted 11 fault blocks which move independently. This is evidenced by differential vertical displacement of correlated reflectors along single fault traces. The major tectonic events of the California Continental Borderland are reflected in the geologic evolution of the study area. Subsidence of the western schist ridge and establishment of the basement configuration subsequent to the North American and Pacific plate interactions and prior to late Miocene sedimentation occurred in the area. The transition to a regime of convergent dextral shear is evident by the presence of the Newport-Inglewood structural zone. The noted northwest-trending structures of the Borderland are present, primarily in the northwest portion of the area. The study area may be an extension of the nearby Los Angeles basin as evidenced by similar depositional patterns and the timinq of tectonic subsidence. 80

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