The significance of Spiroplectammina (Foraminifera) for Upper Cretaceous stratigraphy of Western Siberia

In the result of many years studies of Mesozoic and Cainozoic foraminifera especially species of Spiroplectammina genera their significance for stratigraphy Upper Cretaceous (Coniak-Maastrichtian) have been established. They are absent in Middle Cretaceous and Paleogene deposits. The species of Spiroplectammina genera have been used as speciesindex or characteristic species in foraminiferal Late Cretaceous assemblages. Such of them for example Maastrichtian Spiroplectammina species, earlier and now have been ented in content of characteristic species or species-index for Spiroplectammina variabilis and S. kasanzevi zones (lower and upper Maastrichtian). Establishing of these Spiroplectammina species are the basis for the Late Cretaceous stratigraphy. The middle Cretaceous and upper Paleogene deposits don't contein the Spiroplectammina species. The new subspecies Spiroplectammina optata Kisselman subsp. ksenevae Podobina subsp. nov. is characteristic for early Campanian of Western Siberia. In all foraminiferal assemblages of the Upper Cretaceous Spiroplectammina of Western Siberia have been found by auther. In Coniacian deposits of Sedelnikovsaya suite (such name of Horizon) single findings of Spiroplectammina orientalis Kisselman species (ealy S. senonana Lalicker orientalis Kisselman) have been established. This species has known in Coniacian zones: lower - Haplophragmium chapmani, Ammoscalaria antis, upper - Dentalina basiplanata, D. tineaformis. The findings of this species are in Sidelnikovskaya suite. In deposits of Slavgorodskaya suite (such name of Horizon) Spiroplectammina lata Zaspelova species have been found in lower Santonian Zone Ammobaculites dignus, Pseudolavulina hastata. In middle layers of Slavgorodskaya suite Spiroplectammina pocurica Balakhmatova species have been known as characteristic one (earlier was S. senonana Lalicker pocurica Balakhmatova subspecies). This species is characteristic for upper Santonian - Cribrostomoides exploratus, Ammomarginulina crispa zone. In lower Campanian deposits (upper layers of Slavgorodskaya suite) Spiroplectammina optata Kisselman ksenevae Podobina subsp. nov. have been described by auther in this article. This subspecies is very impotent for lower Campanian stratigraphy. For upper Campanian deposits S. optata Kisselman species is very characteristic for Cibicidoides primus zone. All Coniacian, Santonian and Campanian zones have been established by auther. Maastrichtian Spiroplectammina species - S. variabilis Neckaja - species index for Lower Maastrichtian zone and S. kasanzevi Dain - species-index for upper Maastrichtian zone.

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