The foraminiferal assemblages of the uppermost Kimmeridgian-Volgian succession of Western Siberia and their correlation potential[/b]

Abstract

The present study summarizes the data on the continuous stratigraphic sequence of foraminiferal assemblages from the Volgian deposits of the south-east of Western Siberia. Microfaunal analyses of 650 core samples from 18 boreholes of Volgian deposits were performed. Eighty two foraminiferal species, identified from the samples, were combined into the Volgian assemblages. On the basis of these assemblages, four biostratigraphic units were established in the range of foraminiferal zones and foraminiferal beds with characteristic species. These biostratigraphic units correspond to the upper part of the Kimmeridgian/ lower part of the Volgian, the Middle Volgian (lowermost and uppermost beds), and the Upper Volgian. A detailed biostratigraphic analysis of the Volgian beds was carried out, which enabled a correlation scheme to be developed for major regions of Russia. West-Siberian foraminiferal assemblages were correlated with those of Europe and North America within thePanboreal Superrealm. The species composition of foraminiferal assemblages was analyzed, and correlatable species were established. This provided an opportunity to correlate coeval strata from Western Siberia, East European (Russian) Platform, northern territories of Siberia and Arctic Islands, Canada, Spitsbergen and England.The possibility was established for correlating Volgian-Tithonian deposits of the Panboreal and Tethys-Panthalassa Superrealms through the Dnieper-Donets Basin where faunas of both southern and Boreal-Arctic types are met.