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