CISURALIAN (LOWER PERMIAN) TIME-SCALE IN SOUTHERN URALS

The Working Group to establish Cisuralian stages during a passed decade has achieved a significant progress in developing time scale. Although GSSP of the base of the lowermost Cisuralian Asselian stage is already established at the Aidaralash section, NW Kazakhstan (Davydov et al., 1998) , we are proposing to establish Auxiliary Stratotype Section for the Global Stratotype section and Point for the Carboniferous-Permian boundary at Usolka section to adjust some of the features that are not present in Aidaralsh section. Particularly, conodont succession at the Carboniferous-Permian boundary beds in Usolka section seems to represent much more details. Most importantly is the presence of numerous volcanic ash beds recently recovered in the section that makes radiometric control of the boundary possible. The base of Sakmarian Stage proposed to be defined by the FAD of the conodont species St. barskovi(s. str.) or Sweetognathus merrilli and two sections are considered for the GSSP establishment: Usolka, and the historical Sakmarian stratotype - Kondurovsky section. We are expecting the GSSP of this boundary to be established within a very short period of time. The base of Artinskian proposed to be defined by the FAD of the conodont species Sweetognathus whitei. Several sections for the GSSP establishment are under recent consideration. The base of Kungurian proposed to be defined by the FAD of conodont species N. pnevi and/or N. "exculptus". Transition from N. pequopensis to N. pnevi has been found in the type area in the Urals (Mechetlina section), and in the western U.S.A. (West Texas and Nevada).