Age and composition of the upper part of the Upper Visean - Lower Permian petroleum-bearing formation of the southern part of Kosyu-Rogovaya depression

New data on age and composition of the upper part of Upper Visean - Lower Permian petroleum-bearing formation are considered. The study area comprises the Inta area (Inta-2 and Inta-16 boreholes) and the southern part of Tchernyshev Ridge (Izyayu River section). Bioclastic carbonates compose the Serpukhovian, Middle Carboniferous, and Lower Permian parts of the sequence dated with conodonts. Data on conodonts from the Lower Artinskian carbonates are considered in this region for a first time. Conodont alteration indexes suggest mesocatagenesis (MK1-2) of the upper part of Upper Visean - Lower Permian petroleum-bearing formation. The apocatagenesis (AK) is supposed for the lower part of the formation.