CALIFORNIA STATE UNIVERSITY, NORTHRIDGE QUATERNARY EVOLUTION ~ AND SEISMIC STRATIGRAPHY OF THE SAN PEDRO MARGIN, SOUTHERN CALIFORNIA A thesis submitted in partial satisfaction of the requirements for the degree of Master of Science in Geology By Juhani Henrique Rudat January, 1980 The Thesis of Juhani Henrique Rudat is approved: ~ Dr./Martin L. Stout California State University, Northridge ii ACKNOWLEDGEMENTS This author is indebted to Dr. Peter J. Fischer for his help, endless patience, and numerous ideas and suggestions, not to mention his invaluable experience in marine sciences. The numerous students of the CSUN Geoscience Department, whose enthusiasm and cooperation continues to be a source of support, provided assistance in data collecting and drafting. In particular, thanks to Calvin Lee who, from the earliest trials and tribulations, spent many hours with the author, including stints on various offshore platforms and assorted vessels. Funding for this project was obtained from Shell Oil Company, Houston, Texas, and from NOAA Sea Grants No. 04-5-158-20 and 04-6-158- 44021. The author is grateful to Scripps Institute of Oceanography and Dr. F. P. Shepard for providing boat time on the M/V GIANNA, and to Mr. Arne Junger for providing reproducible copies of R/V KELEZ data, as well as valuable discussion of the local seismic stratigraphy. Through the efforts of Mr. D. Clarke of the California State Lands Division, the author obtained microfilms of all R/V KELEZ data. This thesis is dedicated to my wife, Jane, for her support and understanding. iii CONTENTS CHAPTER PAGE ACKNOWLEDGEMENTS iii TABLE OF CONTENTS iv ABSTRACT vi 1. INTRODUCTION 1 General Statement and Previous Work 1 Physiographic Setting 7 Geologic ?etting 8 2. METHODS AND PROCEDURES 12 California State University, Northridge (CSUN) Surveys 12 Instrumentation 12 Navigation 13 "Beta Platform Sites" Survey 13 USGS (R/V Kelez) Survey 13 Data Reduction and Basis of Interpretation 14 3. MESOZOIC TO MID-PLEISTOCENE SEISMIC STRATIGRAPHY 18 Basement Rocks 21 Miocene Rocks 27 Pliocene Rocks 31 Pleistocene Rocks 37 4. SEISMIC-STRATIGRAPHIC MODEL, WILMINGTON GRABEN LATE PLEISTOCENE AND SHELF HOLOCENE UNITS 46 Introduction 46 Seismic-Stratigraphic Model 47 Late Quaternary Chronology 57 iv CHAPTER PAGE Late Pleistocene to Holocene Seismic Stratigraphy 67 LP IV 67 LP III 68 LP II 71 LP I 75 Holocene 83 5. STRUCTURE 94 Faults 94 Folds 101 6. EVOLUTION OF THE SAN PEDRO BASIN MARGIN 105 Pre-Quaternary Events 105 Qua ternary Evolution 108 Early Pleistocene 108 Middle Pleistocene (Oxygen-Isotope Stages 11 to 7) . 109 Pleistocene and Holocene (Oxygen-Isotope States 6 to 1) 110 San Gabriel Submarine Canyon 116 7. SUMMARY AND CONCLUSIONS 123 REFERENCES CITED 128 LIST OF FIGURES 134 LIST OF TABLES 136 LIST OF PLATES 137 v ABSTRACT QUATERNARY EVOLUTION AND SEISMIC STRATIGRAPHY OF THE SAN PEDRO MARGIN, SOUTHERN CALIFORNIA by Juhani Henrique Rudat Master of Science in Geology '~he San Pedro basin margin is a relatively wide platform located southeast of the Palos Verdes Peninsula and the Los Angeles-Long Beach Harbor. A departure from the normally narrow Southern California inner basin margins, the configuration of this area is the result of the Neogene evolution of two tectonic elements: the Palos Verdes uplift and the Wilmington graben. The interrelationships of tectonic events, sedimentation dominated by the Los Angeles, San Gabriel, and Santa Ana Rivers, and glacioeustatic sea level fluctuations, are critical factors in explaining the evolution of this area; Exposed and near-surface ~ocks on the outer San Pedro shelf (Palos Verdes uplift) include basement rocks (Catalina Schist?), folded Miocene (Monterey Formation) and Pliocene (Repetto Formation) strata (Mohnian vi to Repettian benthic stages), Pleistocene San Pedro Formation(?) and slope deposits. These are partly covered by Holocene sediments. A thicker post-Miocene stratigraphic section in the Wilmington graben is inferred from oil fields onshore. The interpreted seismic reflection data reveals the presence, near the edges of the graben, of middle Pleistocene (?) deposits ("unnamed upper Pleistocene deposits" of Poland and others, 1956) and the San Pedro (?) Formation:j tthe upper Quaternary section in the Wilmington graben is based on '---- a seismic-stratigraphic model of an upper Pleistocene slope unit (LP I), and the Holocene shelf sediments. Analogous older units (LP II-IV) are defined by unconformities and paleo-shelf breaks:, They are termed seismic-stratigraphic sequences and as such have chronostratigraphic significance. ('fhese units are believed to reflect glacioeustatic sea level fluctuations~ and are provisionally correlated with stages in the marine oxygen-isotope curve of Shackleton and Opdyke (1973). Periods of incision and aggradation of the Newport-Inglewood zone fluvial gaps are correlated with isotope stages 1 through 5, and with units LP III through Holocene·~, The lowest (first) marine terrace of the Palos Verdes Hills is correlated with unit LP II. LP III correlates with the lowest terrace in the town of San Pedro, and the fourth and possibly the third and second terraces of the Palos Verdes Hills. C!he high-angle reverse and right-lateral Palos Verdes fault separates the Palos Verdes uplift from the Wilmington graben. Slightly oblique-trending folds are suggestive of convergent dextral shear along the faultj Its late Quaternary seismic activity is shown by offsets of units LP IV through LP I. Activity appears to have diminished since vii the deposition of LP III (possibly starting about 140,000 years B.P.), the youngest horizon commonly disrupted on all splays. However, some seismic activity has continued until the present, as indicated by epicentral data and numerous offsets of the basal Holocene surface and the seafloor. [~n area off the Palos Verdes Peninsula is markedly bowed over the fault zone. The shoreward edge of the Wilmington graben is defined by another active fault zone, portions of which also offset the base of the Holocene interval. Abrupt upward tilting of LP IV and older strata, pinch out of LP III and LP II, and areas of no Holocene sediments on the upthrown side further delineate this fault;; viii Chapter 1 INTRODUCTION GENERAL STATEMENT AND PREVIOUS WORK The last decade has seen a revolution in knowledge about the geo­ logy of continental margins. In California, the use of seismic reflec­ tion techniques from the initial work of Moore and Shumway (1959) and Moore (1960) to efforts by universities and the U.S. Geological Survey, as well as the extensive work by the private industry sector, has brought the continental margins to the forefront in current geologic research. It has become increasingly evident that the submerged por­ tions of the continents will play a vital role in man's search for energy and resources. The region underlying San Pedro Bay (The San Pedro Basin Margin Figure 1), has been the focus of a great deal of academic research and economic interest. A progressive development in geophysical application to marine geology is chronicled by studies of this basin margin, particularly the shelf area. Moore (1954) contributed the first report on the area, including a discussion of surface sediments and foraminif­ eral and lithologic correlation of in-situ rock samples. The only geophysical data used for this study were fathograms. In his assess­ ment of the structure of the continental borderland, Moore (1960, 1969) utilized newer seismic systems, which produced subbottom penetration. The evaluation of an area immediately seaward of Balsa Chica Beach (Figure 2) for a proposed nuclear power plant involved a detailed survey of local structure and stratigraphy (Bechtel, 1967). Part of this project included several drillholes and numerous arcer seismic- 1 Figure 1 Index map 3 w a: :::> (!) LL 0 -a) .co .... + .. II 1: lit II .. 0 Dl 'D _, 1: co oC w a:: "'w > "'z <( ....a:: Figure 2 Location map SH-Signal Hill, RH-Reservoir Hill, All-Alamitos Heights, LH-Landing Hill, BCM-Bolsa Chica Mesa, HEM-Huntington Beach Mesa, NM-Newport Mesa ·:-- ..... ~ .. ' t '"'·----.. ..,.,.,,,1/lfllltl•ll,. 118 1 !} .,~-···/~ \i .... ""\I\IU~ ....,.,,hl'lolll/.t9~ ~ \ \":. \~··-. SH ,...... ... \ ''fiiNII,IH ,,,,, r··, ~ ,.~ ~ \ "••• RH "-. ,w""··· t~"' ~ or\ ~ NM i' •, (/'........ ,.J \ ., (. ........ ~ ............. ., ... ,............ l l 1; \ ~-. f ........ ,.,••'"' / / HBM \ ~\ i \ •. 0 ~- BCM i j ~- ~ ··~ \':~.... LONG { ! ~ ' \\ \ BEACH \.,.,,.,."'+•/ { \ '.,\-:.,.~~~~ i '·~·.... 8 1 NEWPORT 01 \~~ m-t-~n:-j " •• ch; ~ \ ·, \ (BEACH 0 \ ·- 1-·-.J Stotoe ih HUNTINGTON \ '•,,,, , .... ~' ,e....... ,,,,,,, ....... ,., BEACH.... ~ ,i '.. \ "'"'•"' BECHTEL CORP. ~ • "BOLSA ISLAND" ,--.c SURVEY AREA • • (f' ~· __,.,.,o ~.,o ---~sa, ~ ----- X . ..,..,,·"' \ q•o•• <;,.~ '\ 0 10km 33.30' FIGURE 2 6 reflection profiles. Junger and Wagner (1977) published a series of maps of the San Pedro and Santa Monica basins and surroundings based on several types of seismic profiling data, some of which provide rela­ tively more resolution and quality than systems used in previous studies of this area. Some of their work was incorporated in a USGS open-file report (Greene and others, 1975) discussing environmental aspects of selected continental borderland areas; also in a symposium volume (Howell, ed., 1976) on the geologic history of the borderland as a whole. Most recently, Nardin and Henyey (1978) published a study of the Palos Verdes uplift based on air-gun and magnetometer records, and bedrock samples.