BIOSTRATIGRAPHIC CHARACTERIZATION IN THE TYPE CISURALIAN REGION (LOWER PERMIAN) AND CORRELATION TO WEST TEXAS

The stages of the Cisuralian series (Lower Permian) have been accepted as standards for the global stratigraphic scale and the biostratigraphic characteristic in the type region of southern Ural Mountains, Russia/Kazakhstan is important for correlation studies. Historically, fusulinaceans and ammonoids have been used for boundary definitions but tend to be endemic at the species level and, therefore, are not accurate enough to establish an international standard. Conodonts have proven to be useful for defining boundaries because they exhibit subtle morphologic changes within a stratigraphic continuum that can be correlated precisely world wide. The first appearance of Streptognathodus isolatus defines the Carboniferous/Permian boundary and base of the Asselian Stage at the GSSP (Global Stratotype Section and Point), Aidaralash type section. This boundary can be found within the upper beds of the Grey Limestone Member of the Gaptank Formation in West Texas. The working definition for the Sakmarian Stage is the FAD of Streptognathodus barskovi as proposed for the type section at Kondurovsky, and has been recovered from strata within the lower portion of the Neal Ranch Formation. Sweetognathus whitei and/or Streptognathodus florensis are currently the working definitions for the base of the Artinskian, however, in the Glass Mountains area, only sparse conodont faunas have been recovered from the largely conglomeratic Lenox Hills Formation, hampering precise correlation. Sweetognathus whitei may be more useful in this region as the definition for the Artinskian and a small population has been recovered from limestone units within the upper part of the Lenox Hills Formation in the Dugout Mountain area. Neostreptognathodus "exsculptus" is the current working definition for the Kungurian Stage boundary occurring in the lower part of the Skinner Ranch Formation. Correlation of this boundary is more problematic and more detailed biostratigraphic studies are needed.