Infrazonal Subdivision of the Volgian Stage in its Type Area Using Ammonites and Correlation of the Volgian and Tithonian Stages

The Volgian Stage of the Russian Platform is subdivided into 3 sub-stages and 9 zones, within which 37 biohorizons are recognized. Only the lower Volgian is characterized by occurrences of ammonites of Sub-Mediterranean origin, which permits direct correlation to be made with the Tithonian Stage. Rare records of Haploceras in the basal middle Volgian are not able to be used for correlation, and the overlying part of the Volgian stage lacks any Sub-Mediterranean or Mediterranean faunal elements in the ammonite faunas. Recent advances in magnetostratigraphic studies of the upper part of the Volgian Stage in northern Siberia lead to a correlation of the uppermost middle and upper Volgian of this area with the Tithonian succession. These results can also be effectively used for correlating the Volgian ammonite zones of the Russian Platform with those of the Tithonian Stage.