The section Usolka and duplicating its section Dal’ny Tulkas (Bashkortostan) are proposed as the stratotypes of the Lower Sakmarian stage boundary and Lower Artinskian stage boundary of the International Stratigraphic scale. We give the description of sections with the indication of conodont, fusulinid and ammonoid level findings and the results of studying U-Pb geochronology as well as Sr, C, O isotopes.
