The Sheep Pass Formation, a record of late Cretaceous and paleogene extension within the Sevier hinterland, East-Central Nevada

Abstract

The Sheep Pass Formation, a record of Late Cretaceous and Paleogene extension within the Sevier hinterland, east-central Nevada by Peter Alexander Druschke Dr. Andrew Hanson, Examination Committee Chair Associate Professor of Geology University of Nevada, Las Vegas The Sevier hinterland of western North America is considered by many to be an ancient proxy for the modern Andean Puna-Altiplano or Tibetan Plateau. However, controversies exist as tectonic setting and overall paleogeography of the Sevier hinterland during the Late Cretaceous and Paleogene. The Sheep Pass Formation type section within the southern Egan Range of east-central Nevada comprises a > 1 km thick sedimentary succession spanning the latest Cretaceous to Eocene, and provides a rare opportunity to test prevailing tectonic and paleogeographic models for the Sevier hinterland. New 1:12,000 scale field mapping in the southern Egan Range indicates that up to three km of stratigraphic throw occurred along the Ninemile fault, a presently low-angle down-to-thenorthwest normal fault, during deposition of the Sheep Pass Formation type section. Subsequent reactivation of the Ninemile fault produced an additional ~1 km of stratigraphic throw during deposition of the Garrett Ranch Group, which unconformably overlies the Sheep Pass Formation type section. New U-Pb and (U-Th)/He detrital zircon dating and U-Pb carbonate age analyses from the Sheep Pass Formation type section