AGE DETERMINATION OF THE MID-PENNSYLVANIAN ELY LIMESTONE IN NORTH EASTERN NEVADA BASED ON CONODONT BIOSTRATIGRAPHY

Tectonism along the western margin of North America initiated foreland basin development, composed of a series of sub-basins and uplifted regions during the upper Paleozoic. The Pennsylvanian Ely Basin, one of these sub-basins within the Antler Foreland, experienced periods of quiescence and deformation as tectonism continued along the margin. Within the Ely Basin, the dominant lithostratigraphic unit, Ely Limestone, records a cyclic marine succession created by a combination of eustasy and tectonism. The lithologies are dominated by alternating layers of wackestone, packstone, grainstone successions. During periods of quiescence the Ely Basin provided a unique environment for Chaetetes, a coralline demo-sponge, and species of Syringopora to thrive, producing extensive carbonate accumulation. The purpose of this study was to determine the age of the horizon containing Chaetetes based on conodont biostratigraphy at a stratigraphic section measured along Hwy. 50, east of Eureka Nevada in the south Buttte Mountains. Conodont elements were recovered from twenty five to thirty three meters above base, straddling the Chaetetes horizon that occurs at thirty meters above the base of the section. The rock units containing the conodont elements are composed of a silty packstone containing crinoids, brachiopods, bryozoans, and miscellaneous shell fragments. The chaetetes horizon is a silty packstone containing crinoids, brachiopods, foraminifera, syringapora, and rugose corals. Species of Adetognathus, Idiognathodus, and Diplognathodus have been identified indicating that the Chaetetid/Syringopora carbonate buildup developed during the Middle Pennsylvanian, Atokan age. Fusulinacean species of Biseriamminid and Profusulinella recovered from the conodont bearing units and the Chaetetes horizon support the age determination of Atokan.