Dependence of regional stratigraphy on tectonic movements (by example of Upper Cretaceous and Paleogene of Western Siberia)

Studies on Cretaceous and Paleogene foraminiferal zones of Western Siberia, their correlation with the zones of the adjacent regions (Kazakhstan, East-European Platform) resulted in establishing the omission of the most part of the Campanian, the Daman and the top of the Priabonian stages and some other stratons. This phenomenon is supposed to result from tectonic movements of different directions and scopes. Movements of the significant range (these of the first order) are suggested to be responsible for submergence or emergence of almost the entire territory of Western Siberia. In declining tectonic movements and transgressive cycles, marine sedimentary rocks accumulated. The ascending tectonic movements of the first order activated uplifting of the territory of Western Siberia and disintegration of emergent rocks formed previously. A new sediment body derived from subsequent transgressions was superimposed on the washed-out surface of previous deposits. The omission of almost whole stages corresponds chiefly to periods of changes in the direction of transgressions (boreal transgression to southern and conversely). This resulted in the formation of non-evident stratigraphic non-conformities identifiable by correlations of foraminiferal zones with the coeval ones of adjacent regions. The tectonic movements of the second order are responsible for omissions of a part of stratons from the section, and also to origination of straights (the Yenisei, Mariinsk, and other straights) in different times, which assured ways for foraminiferal fauna to migrate to adjacent areas and backwards. The activity of tectonic movements of the second order is assumed different in the western and eastern parts of Western Siberia. The border line between them is supposed to coincide with the location of the Koltogorsk-Urengoy Rift. The formation of different suites of the Ipatovskian Horizon exemplifies varied manifestations of the tectonic movements of the second order in this territory. In the unidirectional transgression, these tectonic movements seem to be responsible for the omission of single foraminiferal zones composing a small part of a straton (e.g. the top of the Thanetian Stage). The Yenisei riverside strait seems to form in the late Cenomanian, when almost the whole territory of Western Siberia was a continent. This straight connected the northern boreal and south-eastern basins. This is evidenced by the finds of the identical late Cenomanian foraminiferal assemblages in these basins. The Mariinsk Straight was tracked by the finds of Santonian inherent southern foraminiferal species together with the agglutinated forms in the south-east Western Siberia. The constantly manifesting oscillating tectonic movements of the third order elicited deepening of the basin, as well as widening or some constricting of marine basins against the background of extensive transgressions.

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