The similarity in systematic composition of the new foraminiferal assemblages and litological affinity of such stages as Aptian, Albian, Cenomanian and Turonian have given opportunity to establish the Middle order of Cretaceous system. The first time these foraminiferal assemblages have been found in borehole sections of Samotlorskaya, Van-Eganskaya, South-Russkaya, Parusovaya and several areas of Yamal peninsula, which keep to Northern paleobiogeographical district of West Siberian province. The related connecting between species of foraminiferal assemblages of four stages have been united in one association of these taxons. Holding rocks of Viculian, Chanty-Mansian, Uvatskian horizons consisting of similar on litology argilit-alevrolit-silks have been united in Pocurskaya series of deposits, without opoka and carbonate infusions. Due to similarity in foraminiferal assemblages Kusnetsovskian horizon also offer to Middle Cretaceous. New data on Foraminifera and Biostratigraphy of each stage have been received during study kern specimens from borehole sections of these areas. Some species, subspecies and vicariant in foraminiferal assemblages have known in such age formations of Canadian province. On this base West Siberian and Canadian provinces belong to Arctic paleobiogeographical Realm of same name circum pole Belt.
