The age of Silurian regional stages of European north-eastern Russia

Results of palaeontological, biogeochemical and sedimentological studies of Silurian strata in the western Subpolar Urals and on the Chernyshev Swell revealed that assignment of the Marshrut Regional Stage and the lower part of the UstDurnayu Regional Stage to Wenlock, as it is indicated in the latest stratigraphical scheme, is not correct. Disappearance of the conodont Apsidognathus and appearance of brachiopod Spirinella nordensis indicate that the Llandovery-Wenlock boundary lies in the middle part of the UstDurnayu Regional Stage. Comparative analysis of palaeontological and lithological data from the Subpolar Urals, Estonia and Severnaya Zemlya suggest that the strata corresponding to the lowermost Wenlock are missing in the study region. The gap recognized divides the UstDurnayu Region Stage in two, lower and upper parts. Here, we propose to include the lower part of the stage into the Marshrut Regional Stage (as its upper part), to rename the upper part of it as Vojvyv Regional Stage, and not to use the name UstDurnayu for a regional stage in future.