CLAST PROVENANCE, TEPHROCHRONOLOGY, AND DETRITAL ZIRCON DATING OF PLIOCENE FLUVIAL CONGLOMERATE, DEEP SPRINGS VALLEY, CA: IMPLICATIONS FOR EASTERN CALIFORNIA PALEOHYDROLOGY

The paleohydrology of the western Great Basin has long been a concern of geologists and biologists interested in reconstructing dispersal pathways for various biota. Deep Springs Valley, eastern California, is a closed basin with present-day streams from the White Mountains flowing into the valley and the terminal playa. Previous studies described a fluvial conglomerate and an interbedded 3.1 Ma tuff that crop out on the 270-m-high Deep Springs ridge (DSR; informal name) that separates Deep Springs Valley from Eureka Valley; however, the provenance of this conglomerate was debatable. The normal-slip Deep Springs Fault bounds the east side of Deep Springs Valley and uplifts DSR and the Pliocene fluvial conglomerate. The fluvial conglomerate is a boulder-to-gravel-sized clasts interbedded with cross-bedded coarse, moderately to well-cemented sandstone. The dominant clast types are quartz monzonite and basalt with lesser amounts of Paleozoic sandstone and limestone. Tephrochronology correlates the tuff layer with the tuff of Mesquite Flats. Using the updated monitor ages, the corrected ⁴⁰Ar/³⁹Ar age is 3.135 ± 0.08 Ma. U-Th/Pb dates on 273 of 305 detrital zircons from the sandstone matrix are Jurassic (183.6–167.6 Ma; mean of 175.33 ± 0.38 Ma). Six Proterozoic zircons derived from Paleozoic metasedimentary rocks were found with U-Th/Pb ages ca. 1.1, 1.4, and 1.8 Ga that are similar to known North American provenances. Based on the clast types and dominant Jurassic detrital zircons, we infer that the provenance of this Pliocene fluvial conglomerate is Crooked Creek (dominant) and Wyman Creek drainages in the White Mountains across Deep Springs Valley. These data show that a northwest-to-southeast-flowing stream crossed Deep Springs Valley and DSR and into Eureka Valley at 3.135 Ma and that, the Deep Springs Fault initiated after 3.1 Ma. Previous studies showed that this paleohydrologic connection persisted until at least 750 ka.