Ammoniteand bivalve-based biostratigraphy and Panboreal correlation of the Volgian Stage

The current ammoniteand buchiid-based biostratigraphical successions of the Volgian Stage are outlined, with an analysis of the most important data that support correlation throughout the Panboreal Superrealm. Updated ammonite zonal schemes were proposed for the Volgian of the type region (the Russian Platform) and Svalbard. The lower Volgian successions in all areas except the Russian Platform, with its eudemic1) virgatitid lineage and Submediterranean faunal elements, were dominated by Pectinatites and Eosphinctoceras-Subdichotomoceras. The last two genera were especially common eastwards from the Ural Mountains. During the middle Volgian, provincialism developed quickly within the ammonites, and unified assemblages with early Palvovia and Dorsoplanites at the base of the substage were replaced by numerous local eudemic faunas. Despite this, migrations of species of Crendonites, Laugeites, Epivirgatites Epipallasiceras, Epilaugeites, and Taimyrosphinctes occurred at regular intervals and these enable precise correlations between the faunal sub-provinces. The zonation of the upper Volgian is mainly based upon the succession of Craspedites (on Subcraspedites in England and North Sea), and can be traced throughout the Arctic. Zonation based on the bivalve Buchia enables correlations to be made between the successions over much of the Northern Hemisphere, including Northern California, British Columbia, Arctic areas, and the Russian Platform. Each substage of the Volgian is characterized by buchiids with different types of the ontogenetic development. Research on the infrazonal subdivision of the Volgian Stage based on buchiids is currently in progress. Our analyses of the ammonite and buchiid successions of the Panboreal Superrealm lead us to conclude that there are no major faunal gaps in Volgian successions of the Russian Platform and Northern Siberia.