Detrital Zircon Geochronology and Sediment Transport of the Miocene Stevens Sandstone

Abstract

The Upper Miocene Stevens turbidite sandstones are prolific petroleum reservoirs in the southern San Joaquin Basin of California and were deposited as a series of submarine fan systems and deep water channels sourced from paleodrainages emanating from the Sierra Nevada, Techachapi Mtns., and the Salinian block across the proto-San Andreas fault system. The stratigraphy of Stevens channel-fan complexes is complicated by syn-depositional faulting and folding in a deep marine basin and correlating the discontinuous sand bodies is not easily resolved with conventional electric logs or other methods. A combined detrital zircon U-Pb age and garnet+hornblende composition provenance study is reported here with the goal of identifying regional-scale sources and sediment-dispersal patterns across the full spatial and temporal distribution of the Stevens, and provides a statistical framework that enables detailed correlation and discrimination of sandstones widely across the region. Provenance shifts resulting in significant differences in detrital zircon and garnet populations are particularly significant in the southwestern portion of the basin where the Salinian block sediment sources were being transported to the northwest across on the San Andreas fault plate boundary during the late upper Miocene. By collecting detrital zircon populations from existing core and outcrop data, we hope to establish links between individual channel and fan complexes based on the composition of their provenance, challenge long-held paradigms about Stevens sedimentary distribution, and provide a new correlation tool to supplement conventional electric log correlation. This technique has implications for the exploration of new Stevens oil pools, and supplements detailed characterization of other reservoirs in existing oilfields by providing a new potentially high-resolution correlation tool in the San Joaquin Basin.

AAPG Datapages/Search and Discovery Article #90372 © 2020 AAPG Pacific Section Convention, 2020 Vision: Producing the Future, Mandalay Beach, Oxnard, CA, April 4-8, 2020 (Cancelled)