THE MILK RANCH CANYON SECTION, EAST-CENTRAL NEVADA: A NEOGENE COARSE CLASTIC SUCCESSION

The Milk Ranch Canyon (MRC) section is an informally-named, poorly described succession of coarse fluvial and alluvial sandstone and conglomerate located in the Egan Range of east-central Nevada. The MRC section rests unconformably on the Late Eocene to Oligocene Garrett Ranch Group volcanic sequence, and is capped by Late Miocene to Pliocene(?) volcanic flows and younger conglomerates of the Cave Valley Formation. The MRC section was measured at 275 m thick below a fault repeated interval. Conglomerate clast count and paleocurrent data were obtained at regular intervals through the section, and 2 samples for LA-ICP-MS detrital zircon dating were collected from the basal and upper portion of the section. Clast counts show a dominance of carbonate (70%) and quartzite (20%) clasts with a minor contribution from the Garrett Ranch Group (10%). Paleocurrent data (N=86) indicate a transport direction toward the W/NW. Detrital zircon age spectra indicate a dominance of Miocene (ca. 24-16 Ma) zircons, with a major contribution from the Garrett Ranch Group (ca. 36-30 Ma). Lesser contributions from Jurassic (ca. 200 Ma) and Mesoproterozoic (ca. 1 Ga and 1.7 Ga) sources were identified. Provenance and paleocurrent data suggest derivation of the MRC sediments from unroofing of the southern Schell Creek Range (Mount Grafton vicinity) or additional source areas to the east. The MRC section is potentially correlative to widespread conglomerates within the Schell Creek Range, specifically the Miocene North Creek Formation, as well as the Miocene Horse Camp Formation of the northern Grant Range to the west. The MRC section forms part of an approximately 2 km thick Late Cretaceous to Neogene sedimentary and volcaniclastic succession in the southern Egan Range, which includes the Sheep Pass Formation and Garrett Ranch Group. Together these data may provide insight into the Paleogene to Neogene extensional and paleogeographic histories of east-central Nevada.