Berriasian-Valanginian (Early Cretaceous) seaways of the Russian Platform Basin and the problem of Boreal/Tethyan correlation

The Russian Platform (RP) is one of the key-regions for the correlation of the Boreal and Tethyan stratigraphic successions. Zoogeographical analysis of ammonite distribution in the RP and adjacent areas demonstrates the existence of relations between different basins and the opening/closure of sublatitudinal and submeridional sea-connections in the RP area. Two epochs in the development of the RP were recognized. The Berriasian-Barremian time shows a close relation of the RP Basin to the Boreal Realm. During Aptian-Albian times the region was affected mainly by the Tethys Ocean. It is supposed that the Upper Volgian corresponds to the Lower Berriasian. The similarity of the Western Siberia and the Peri-Caspian-Mangyshlak fauna allows us to propose for the first time an existence of a direct connection between those basins. Berriasian-Valanginian sea-connections of the RP Basin are discussed in this paper.