LITHOSTRATIGRAPHY AND BIOSTRATIGRAPHY OF THE ELY LIMESTONE, ILLIPAH SECTION, NORTHEASTERN NEVADA

Late Paleozoic tectonic activity along the western margin of North America is most commonly attributed to the latest Devonian – earliest Mississippian Antler orogeny. However continued tectonism during the upper Paleozoic created basins and associated uplifts that have been recognized regionally. The Pennsylvanian strata of northeastern Nevada was deposited within the Morrowan – Desmoinesian Ely Basin, the Desmoinesian Hogan Basin, and the Missourian through Asselian (Early Permian) Strathearn Basin. A stratigraphic succession at the Illipah section along highway 50 west of Eureka, Nevada was measured and a lithostratigraphic and biostratigraphic study was conducted. Coarsening upward cycles consisting of micrites and wackestones at the base to grainstones at the top dominate the stratigraphic succession. Wackestones commonly contain carbonate mud with varying amounts of pelmatozoan, bryozoan and brachiopod fragments. Bioclasts of pelmatozoans, brachiopods, bryozoans, and small forams are also common within the grainstone units with minor amounts of siliciclastic debris. These cyclic units observed within the Ely suggest that eustasy along with basin subsidence controlled deposition. Unique occurrences of a chaetetid-dominated carbonate buildups at 90 meters above the base of the measured section provides important paleoenvironmental data, clues to the depositional environment, and support for a Pennsylvanian (Atokan) age. The presence of the chaetetid-dominated carbonate buildup at this interval indicates a stabilization phase within the basin and a period of tectonic quiescence along with favorable environmental conditions for chaetetid growth such as well-aerated, normal marine salinity and depths just below normal wave base. The firm substrate on which the chaetetids grew is characterized by the presence of Syringopora, brachiopods, and pelmatozoan and bryozoan fragments. Chaetetid-dominated carbonate buildups are significant regional marker beds and have aided in regional field correlation studies across northeast Nevada. Results of the detailed lithostratigraphy and biostratigraphy support the notion that cyclical shallow water carbonate facies dominated deposition within the Morrowan – Desmoinesian Ely Basin.