Trace fossils have been found for the first time in the Tavda Formation shallow marine facies, and their possible indicative value has been evaluated. The results of the ichnofossil study suggest that the Tavda Basin had low hydrodynamics. Under these conditions boreal and thetic waters of different characteristics were blended, which caused periodic formation of thermohaline water stratification and anoxic conditions in bottom water levels. Such periodic events conditioned mass extinctions of a wide variety of the Eocene marine biota thus preconditioning the development of freshwater fauna in the upper levels of the Tavda Sea along with saturation of the index beds of the Tavda Formation with micro- and macrofossils.
