Clast Provenance Constraints, Late Cretaceous Pigeon Point Formation, California

Abstract

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.