CALIFORNIA STATE UNIVERSITY, NORTHRIDGE MARINE GEOLOGY AND GEOLOGIC EVOLUTION OF THE NORTHERN CHANNEL ISLANDS PLATFORM WEST OF SAN MIGUEL ISLAND A thesis submitted in partial satisfaction of the requirements for the degree of Master of Science in Geology by Peter John Raftery May 1984 p • is approved: California State University, Northridge ii CONTENTS Page LIST OF ILLUSTRATIONS v ABSTRACT viii ACKNOWLEDGMENTS xi i INTRODUCTION 1 General Statement 1 Geologic & Bathymetric Setting 1 Previous Work 6 INVESTIGATIVE METHODS 7 Seismic Data 7 Seismic Data Traverse Locations 7 Data Preparation 10 Sources of Lithologic and Age Data 11 Interpretation Techniques 11 Velocity Considerations 13 TECTONIC SETTING 16 SAN MIGUEL ISLAND AND POINT CONCEPTION STRATIGRAPHY - 23 General Statement 23 Pre-Cretaceous 25 Cretaceous 26 Paleocene-Eocene 28 Eocene 29 Oligocene 32 Miocene 33 Miocene-Pliocene 41 Pliocene 42 iii Page Quaternary 43 · ONSHORE STRUCTURAL GEOLOGY 46 OFFSHORE SEISMIC STRATIGRAPHY 47 Cretaceous to Lower Miocene 49 Middle to Upper Miocene 50 Upper Miocene to Lower (?) Pliocene 58 Lower (?) Pliocene to Quaternary 63 Quaternary 66 OFFSHORE STRUCTURAL GEOLOGY 72 Structural Region 1 72 Structural Region 2 74 Structural Region 3 80 CENOZOIC EVOLUTION 85 Paleogene 85 Neogene 86 SUMMARY AND CONCLUSIONS 88 REFERENCES CITED 92 APPENDICES 101 A. Sample Data and Descriptions 101 B. Velocity Data 116 iv LIST OF ILLUSTRATIONS Figure Page 1. Location of study area with respect to nearby 2 physiographic features 2. Location of study area with regard to major fault 3 zones and geomorphic provinces 3. Seismicity of Santa Barbara Channel region 5 4. Oligocene to Recent tectonic evolution of the 17 California Borderland 5. Approximate correlation of stratigraphic units 24 from Point Conception to San Miguel Island 6. Cenozoic depositional and bathymetric history of 34 central Santa Ynez Mountains and Santa Rosa Island regions 7. Generalized chronostratigraphic correlations 44 from Point Conception to to San Miguel Island, through boreholes 8. Approximate correlations of seismic stratigraphic 48 units in the study area to formations at Point Conception and San Miguel Island 9. Interpretation of R/V Kelez sparker profile number 51 713 illustrating pre-Monterey unit and Santa Rosa Island Fault 10. Interpretation of M/V Mediterranean Seal sparker 53 profile number 47 illustrating well developed Monterey reflectors and Ferrelo Fault 11. Interpretation of R/V Kelez uniboom profile 709 54 illustrating well developed Monterey reflectors 12. Interpretation of M/V Mediterranean Seal sparker 57 line 37 illustrating data limitations northwest of platform 13. Interpretation of M/V Mediterranean Seal 60 sparker line 53 illustrating well developed Sisquoc reflectors 14. Map illustrating onlap of post-Miocene sediments 64 onto platform 15. Interpretation of R/V Widgeon sparker profile 65 number A-76, illustrating 11 Pico 11 and southward thinning of units v Figure Page 16. Interpretation of M/V Mediterranean Seal 67 minisparker profile number 55 illustrating terrace deposits 17. Interpretation of M/V Mediterranean Seal sparker 69 line 33 illustrating buried channels and levee deposits 18. Interpretation of R/V Widgeon sparker profile 70 illustrating buried channels 19. Map of structural regions defined by this study 73 20. Interpretation of M/V Widgeon sparker profile 78 A-94 illustrating faulting at north margin of platform 21. Quaternary faulting at sea floor 79 22a. Interpretation of M/V Mediterranean Seal sparker 81 profile number 49 22b. Interpretation of M/V Mediterranean Seal sparker 82 profile number 48 22c. Interpretation of M/V Mediterranean Seal sparker 83 profile number 47 22d. Structure trend map combining data from Figures 84 22a-c 23. Time vs depth curves for platform wells 117 TABLE 1. Comparison of reflection profiling system 9 characteristics 2. Geologic significance of reflector characteristics 14 3. Comparative stratigraphy of Monterey Formation in 38 vicinity of study area 4. Mineral composition of Monterey Formation along the 40 Santa Barbara coast 5. Diatom zonation used in dart core descriptions 105 6. Summary of interval velocities used for isopach maps 118 and structure cross sections vi PLATE (in Back Pocket) 1. Bathymetry 2a. Seismic Trackline Map (northern part) 2b. Seismic Trackline Map (southern part) 3. Geologic Map 4. Terrace and Shelf Deposit Isopach Map 5. Post- 11 Pico 11 Isopach Map 6. 11 Pico 11 Isopach Map 7. Sisquoc Isopach Map 8. Cross Sections vii ABSTRACT MARINE GEOLOGY AND GEOLOGIC EVOLUTION OF THE NORTHERN CHANNEL ISLANDS PLATFORM WEST OF SAN MIGUEL ISLAND by Peter John Raftery Master of Science in Geology An investigation of the northwestern Channel Islands Platform, using geological and geophysical data including seismic reflection profiles, dart core descriptions, and borehole information, was com­ pleted. The primary purpose of the study was to determine the Cenozoic geologic history of the western portion of the northern Channel Islands Platform and surrounding continental shelf. Seismic stratigraphic units, generally corresponding to onshore formations, were established and the stratigraphic relationships, thickness variations, and sea floor distribution of these units were defined. Formations studied range in age from Late Cretaceous through Recent and represent deep basin to subaerial environments. From Late Mesozoic through Oligocene time, marine deposition occurred in a shoal­ ing trench environment, associated with subduction tectonics. During viii Oligocene time a plate/spreading ridge collision resulted in the ex­ tensive subaerial erosion and deposition, which occurred during this period of maximum uplift. In early Miocene time, deep sediment starv­ ed basins formed as the result of plate boundary readjustments. These basins received dominantly biogenic sediments (the Monterey Formation) until the end of Miocene time. Clastic deposition (the Sisquoc Form­ ation) followed renewed deformation and uplift. Additional clastic facies occur in the ••pico" and younger units in the study area. Pliocene to Recent depositional features include the large scale on­ lap of the north margin of the Channel Islands Platform by units originating to the north. Other depositional features include buried and modern submarine channels, terrace deposits, and modern channel levee deposits. Structural features of the study area include: the major anticlin­ al fold belt and its associated faults, which trend approximately north 45 degrees west, the Ferrelo Fault zone with Cretaceous to late Miocene (or younger) offset, and the Santa Rosa Fault with Quaternary offset. Dip separation along the Ferrelo Fault zone is evidenced by uplift at the southwestern margin Channel Islands Platform in the study area. Strike-slip motion is evidenced on the Santa Rosa Island Fault where it offsets Quaternary units on Santa Rosa Island and the sea floor. Numerous unnamed faults occur in the region and can be placed in two major groups: those that do not cut the late Miocene unconformity and those that cut the unconformity and in some cases offset the sea floor. Geophysical profiles and dart core descriptions from the Miocene and younger units, particularly in the immediate vicinity of the ix northern Channel Islands Platform, permit the assignment of seismic reflectors to geologic formations. Unconformities between the Monter­ ey, Sisquoc, and 11 Pico" seismic stratigraphic units are well defined and may be correlative over a large portion of the study area. The investigation has shown that: 1) deformation in the study area was contemporaneous with known regional tectonic events and (2) that it is possible to correlate onshore formations to seismic strati­ graphic units. The investigation has also shown that the northern portion of the Channel Islands Platform is structurally related to the Peninsular Ranges Province. The boundary of the Transverse Ranges and Peninsular Ranges Provinces may be along the north margin of the Chan­ nel Islands Platform in the study area. X ACKNOWLEDGEMENTS The writer would like to thank Dr. P. J. Fischer for guidance and editorial comment throughout the project, Dr. B. Molnia for his numer­ ous helpful suggestions, and Dr. G. Simila for his reading of the man­ uscript. The author is grateful to William Richmond for suggesting the project. The stratigraphic correlations by Frank Webster are highly appreciated. The comments on geophysical interpretration techniques made by David McCulloch were very helpful and appreciated. Thanks are extended to Donald Krotser, Jack Vedder, and Pamela Utter for assist: ance in obtaining basemaps and data from the U.S. Geological Survey. Appreciation is extended to Susan Lee and Scott Sorensen of the Miner­ als Management Service for their constructive editorial assistance. xi INTRODUCTION General Statement The northern Channel Islands Platform is the major feature along the southern margin of the Santa Barbara Channel. The platform is located near the western boundary of the east-west trending Transverse Ranges Province and the northwest-southeast trending, Peninsular Ranges Province (Figures 1 and 2). The Channel Islands Platform and adjacent areas of the southern California Continental Borderland were part of a convergent plate margin until 29 M.Y. ago (Atwater and Mol­ nar, 1973). A subsequent spreading ridge-plate collision changed the margin from a convergent to a transform plate boundary. Wrench tec­ tonics associated with the transform boundary are largely responsible for the