pdf: http://rogov.zwz.ru/Zakharo....RGG.pdf

In 1996 the Volgian Stage was divided into the Jurassic and Cretaceous units, removed from the Geological Time Scale, and substituted
by the Tithonian Stage according to the guidelines of the Interdepartmental Stratigraphic Committee of the Russian Federation (ISC RF).
Consequently, the Upper Volgian Substage including three zones (five subzones) was placed into the Berriasian Stage (the Cretaceous)
proceeding from ammonite fauna, and the Cretaceous lower boundary was defined by the base of the Kachpurites fulgens Zone. Some
stratigraphers, however, contested that decision and suggested to restore the former status of the Volgian Stage. Their idea has been validated by magnetostratigraphic studies carried out in 2003 in Jurassic-Cretaceous boundary strata in the Nordvik Peninsula (the Laptev Sea), which bear the most complete record of Boreal deposition and biostratigraphy. The new data prove that the Volgian Stage, in its nearly full stratigraphic volume, rather belongs to the Jurassic period.