CENOZOIC PALEODRAINAGE EVOLUTION IN THE SOUTHERN SIERRA NEVADA/TEHACHAPI MTNS., CALIFORNIA AND PROVENANCE OF OIL AND GROUNDWATER RESERVOIRS IN THE SOUTHEASTERN SAN JOAQUIN BASIN INFERRED FROM NON-MARINE CONGLOMERATES AND RELICT STREAM CHANNELS

Previous studies of the provenance of southeastern San Joaquin Basin (SSJB) oil and groundwater reservoirs emphasized the importance of locally derived plutoniclastic sediment from the Sierra Nevada. Recent detrital zircon studies have suggested an extraregional source for some SSJB reservoirs. To test models of paleodrainage evolution, provenance, and basin formation Eocene-Quaternary fluvial conglomerate outcrops in a 70,000 sq km area were sampled for clast composition, paleocurrents, and heavy minerals. Clasts >2cm were counted in lab and by the area method at outcrop. Pebble counts pass tests of inter-method and inter-operator variability. Intra-SSJB conglomerates (ISJB) contain >50% locally derived plutonic and metamorphic clasts with low ratios of Kspar-rich granitoids (Pkg) to total plutonics (Pt). Most ISJB conglomerates are interpreted to have been deposited during periods of rapidly changing paleoslope, drainage derangement, beheading, and piracy in the late Eocene, early-mid-Miocene, and late Pliocene-Quaternary. Derangement was coeval with lacustrine deposits in eastern California and widespread fine-grained deposits in the SSJB. Extraregional-sourced conglomerates (ESJB) include the Paleogene Tejon petrofacies with high Pkg/Pt ratios and >50% Precambrian-Paleozoic miogeoclinal quartzites + Mesozoic felsic metavolcanics and the Neogene Mojave petrofacies with high Pkg/Pt ratios and >50% Miocene silicic + intermediate volcanics. ESJB conglomerates were deposited in the middle to late Eocene, Oligocene, and late Miocene coeval with deltaic deposits in the Tejon, Tecuya, and Kern River Formations and sandstone lithosomes (Metralla, Vedder, Stevens) which form the main oil and groundwater reservoirs of the SSJB. Relict bedrock channels, and low-relief graded surfaces continuous with Tertiary unconformities can be used to evaluate late Cenozoic tilting and fault offset. From Eocene to late Miocene, major river outlets, clastic sediment input, and deltaic deposition shifted northeast along the margin of the SSJB.