Detrital Zircon-Garnet-Hornblende Provenance Study of the Middle to Late Miocene Stevens Sandstone: Implications for Evolution of the San Joaquin Basin, California

Mark Korte Nahabedian

Mark Korte-Nahabedian
MS Candidate
Advisor: Dr. Dave Kimbrough

Friday May 10th, 2019
CSL 422 – 9:30 am

The Stevens Sandstone Member of the Miocene Monterey Formation is a prolific petroleum reservoir in the southern San Joaquin Basin of California. These sandstones were deposited as a series of prograding submarine fan systems and deep-water channels sourced from paleodrainages emanating from the Sierra Nevada Mountains, Techachapi Mountains, and the Salinian block across the proto-San Andreas fault system. The stratigraphy of Stevens channel-fan complexes is significantly complicated by syn-depositional and post-depositional faulting and folding, and consequently correlating the discontinuous sand bodies is not easily resolved with conventional electric logs or other methods. A combined heavy mineral (zircon-garnet-hornblende) provenance study is reported here, identifying regional-scale sources of sediment and sediment-dispersal patterns within the Stevens Sandstones. Combined heavy mineral analysis provides independent yet complimentary data to substantiate correlation and discrimination of Stevens Sandstones widely across the region, and in some cases challenge long-held paradigms about the sedimentary distribution networks that delivered these sandstones into the sedimentary depocenter in the central southern San Joaquin Basin. Provenance shifts are documented in the detrital mineralogy of Stevens Sandstones in the southwestern portion of the basin, where Salinian block sediment sources were being transported to the northwest on the San Andreas fault plate boundary during the late Miocene. Sedimentary provenance at the extreme southern margin of the basin on the Tejon Platform changed dramatically from Eocene to Miocene time, and again from Miocene to recent time. Stevens Sandstones in the central portions of the basin show evidence of mixed provenance, and likely represent the interaction of multiple sediment distribution networks operating simultaneously. By evaluating combined heavy mineral assemblages from existing, publicly available core and outcrop data, we group individual channel and fan complexes based on the unique U-Pb age and compositional signature of their provenance, providing a new correlation/discrimination framework to supplement conventional electric log correlation. Combined heavy mineral studies, such as the one presented here, have implications for the discovery and development of new Stevens oil pools and carbon sequestration projects, and supplement reservoir characterization by providing a new potentially high resolution, bias-free correlation tool in the San Joaquin Basin.