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Clast Provenance Constraints, Late Cretaceous Pigeon Point Formation, California

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Clast Provenance Constraints, Late Cretaceous Pigeon Point Formation, California San Jose State University SJSU ScholarWorks Master's Theses Master's Theses and Graduate Research Fall 2010 Clast Provenance Constraints, Late Cretaceous Pigeon Point Formation, California Anne Sanquini San Jose State University Follow this and additional works at: https://scholarworks.sjsu.edu/etd_theses Recommended Citation Sanquini, Anne, "Clast Provenance Constraints, Late Cretaceous Pigeon Point Formation, California" (2010). Master's Theses. 3893. DOI: https://doi.org/10.31979/etd.gbfk-zfc9 https://scholarworks.sjsu.edu/etd_theses/3893 This Thesis is brought to you for free and open access by the Master's Theses and Graduate Research at SJSU ScholarWorks. It has been accepted for inclusion in Master's Theses by an authorized administrator of SJSU ScholarWorks. For more information, please contact [email protected]. CLAST PROVENANCE CONSTRAINTS, LATE CRETACEOUS PIGEON POINT FORMATION, CALIFORNIA A Thesis Presented to The Faculty of the Department of Geology San José State University In Partial Fulfillment of the Requirements for the Degree Master of Science by Anne Sanquini December 2010 © 2010 Anne Sanquini ALL RIGHTS RESERVED The Designated Thesis Committee Approves the Thesis Titled CLAST PROVENANCE CONSTRAINTS, LATE CRETACEOUS PIGEON POINT FORMATION, CALIFORNIA by Anne Sanquini APPROVED FOR THE DEPARTMENT OF GEOLOGY SAN JOSÉ STATE UNIVERSITY December 2010 Dr. Ellen P. Metzger Department of Geology Robert J. McLaughlin United States Geological Survey Dr. Richard L. Sedlock Department of Geology ABSTRACT CLAST PROVENANCE CONSTRAINTS, LATE CRETACEOUS PIGEON POINT FORMATION, CALIFORNIA by Anne Sanquini The depositional location of the Late Cretaceous Pigeon Point Formation, which crops out between San Francisco and Santa Cruz on the California coast, is unknown. Petrographic and chemical analysis of the conglomeratic clasts in the formation revealed several types of clasts that were helpful to constrain provenance. These included clasts of the recently identified underlying Pescadero felsite, clasts of dark porphyries with salmon-colored phenocrysts that have been identified at four other depositional locations, and granitoids for which isotopic data existed. Synthesis of research performed for this thesis with previously published data leads to a hypothesis that suggests the Pigeon Point Formation was deposited in the mid-Campanian at a paleolatitude south of the current United States, onto the Pescadero felsite, in an accretionary compleX setting. By the late Miocene, it was transported northward to a position near the present-day location of San Luis Obispo, then brought to its current location, within the past 10 Ma, by dextral slip on the San Gregorio-Hosgri fault and the San Andreas fault system. ACKNOWLEDGEMENTS Thank you to my thesis advisor, Ellen Metzger, for her thoughtful and patient support throughout this project, and to my thesis committee members Bob McLaughlin, who introduced me to this area and provided inspiration and constructive criticism along the way, and Richard Sedlock, for his enthusiastic and thorough review of the text. Many experts generously shared of their knowledge. Thank you to Karen Grove, Don Lowe, Diane Moore, Gary Ernst, Dave Anderson, Robert Lopez, Kathleen Burnham, Cal Stevens, Carl Jacobson, Duane Champion, Gail Mahood, Rick Stanley, Russ Graymer, and Rolfe Erickson. I appreciate the quick availability of permits from the State of California department of Parks and Recreation for geological investigations and collections, and I am also grateful for access given by Susan and Ken Miller to collect samples on their property. Thank you to my fellow students: to field assistants Rachel Unger, Morgan Mendoza, Ryan McKee, and Elaine Miller, as well as to Brendon Johnson, who assisted with several of the illustrations. Finally, thank you to my spouse, Richard Sanquini, who just now walked by and said he would be glad to have me back, soon. v TABLE OF CONTENTS INTRODUCTION..........................................................................................................................................1 GEOLOGIC SETTING..................................................................................................................................2 Fault Relationships.....................................................................................................................2 Underlying Units..........................................................................................................................4 Overlying Unit...............................................................................................................................8 PREVIOUS WORK ON THE PIGEON POINT FORMATION.........................................................9 General Structure and Stratigraphy.....................................................................................9 Paleontology and Palynology............................................................................................... 11 Geochronology ........................................................................................................................... 12 Conglomerate Clasts ................................................................................................................ 12 Paleomagnetic Data.................................................................................................................. 14 METHODS................................................................................................................................................... 15 Field................................................................................................................................................. 15 Laboratory.................................................................................................................................... 19 vi PETROGRAPHIC OBSERVATIONS.................................................................................................... 20 Pigeon Point Formation........................................................................................................ 20 Vaqueros(?) Formation ......................................................................................................... 24 MAJOR AND TRACE ELEMENT CHEMISTRY............................................................................... 27 Pescadero Felsite Samples.................................................................................................... 27 “Smoked Salmon” Clasts......................................................................................................... 30 INTERPRETATION OF DATA.............................................................................................................. 32 Age of Pigeon Point Conglomerates and Timing of Key Events........................... 32 Conglomerate Age Analysis.................................................................................... 32 Key Events..................................................................................................................... 34 Linkage to Underlying Units................................................................................................ 35 Comparison to Overlying Unit ............................................................................................ 37 Comparison to Upper Cretaceous Atascadero Formation...................................... 38 Paleontology and Inferred Paleolatitudes.........................................................38 Underlying Rocks Differ ........................................................................................... 39 Overlying Rocks Differ .............................................................................................. 39 vii Depositional Locations of the “Smoked Salmon” Clasts .......................................... 40 Synthesis of Depositional Environment ......................................................................... 41 Speculative Reconstruction.................................................................................................. 43 CONCLUSIONS .......................................................................................................................................... 48 REFERENCES CITED .............................................................................................................................. 50 viii LIST OF FIGURES Figure 1. Key faults, locations and geologic units mentioned in teXt.................................................3 2. Local geologic map, including fossil and zircon sampling locations...............................6 3. Simplified composite stratigraphy ................................................................................................7 4. Pigeon Point Formation outcrop photograph........................................................................ 17 5. Vaqueros(?) Formation outcrop photograph......................................................................... 18 6. Photomicrographs, Pigeon Point................................................................................................. 22 7. Photomicrographs, Vaqueros(?).................................................................................................. 26 8. REE diagram of Pescadero felsite samples.............................................................................. 29 9. Th-Hf/3-Ta tectonic discrimination diagram .......................................................................
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