UPPER PALEOZOIC BIOSTRATIGRAPHY OF NEVADA: KEY FOR UNRAVELING THE TECTONOSTRATIGRAPHY

The Pennsylvanian and Cisuralian strata exposed in Nevada reflect deposition within several tectonically formed basins of the Antler Foreland. A series of cyclic carbonate to mixed siliciclastic-carbonate successions separated by unconformities, and defined as tectonostratigraphic units, record an interaction between eustasy and tectonism. Formulating a biostratigraphic framework for the region has been challenging, because the depositional packages are laterally discontinuous and restricted to individual basins. However, recognition of common fossil elements has provided an important role in deciphering individual basins and outlining the tectonostratigraphic history of the region. Conodont species of Neognathodus, Idiognathodus, and Adetognathodus; fusulinid species of Profusulinella and Beedeina along with a new ammonoid species of Glaphyrites provide the temporal framework for deposition during the Pennsylvanian. Unique occurrences of Chaetites in the Pennsylvanian strata provide important paleoenvironmental information and serve as a marker bed for regional field correlation across laterally discontinuous successions. Cisuralian tectonostratigraphic units are characterized by the conodont species, Sweetognathodus, Mesogondollela, and Streptognathodus, along with species of fusulinids and diverse Artinskian ammonoids. Linking the detailed biostratigraphic and tectonostratigraphic data has significantly enhanced the understanding of the geologic history of east central Nevada and has provided a tool to aid in the delineation and correlation of the unconformable-bounded units. Despite the utility of the existing biostratigraphic framework, further detailed studies must be conducted in order to address a variety of issues such as: extinction and speciation, provincialism, paleogeography, global correlation, refinement of the time scale, and numerous issues of regional interest in upper Paleozoic geology.