Position of the boundary between the Timan and Ust-Yarega formations (Middle-Upper Devonian) in the Southern Timan

New data on the lithological structure of the stratotype section (Outcrop 14) of the Ust-Yarega Formation of the Frasnian Stage in the Southern Timan are presented. Sedimentary cyclites are identified and relative sea level curve are reconstructed. Local erosion has been identified inside the sediments of the Ust-Yarega Formation, as well as a sharply transgressive unit, which are a good regional reference level and a reflection of the Genundewa event. The boundary of the Timan and the Ust-Yarega formations is located at the base of a unit of the fine-grained sandstones and siltstones, the lower part of which is represented by the oil-bearing bed I. On the surface, we have established only the upper part of this oil-bearing bed.