Biostratigraphy of the Albian of the Samotlor area of Western Siberia (based on foraminifera)

For the first time in Western Siberia (the Khanty-Mansiysk Horizon of the Samotlor area, the northern paleobiogeographic district) V.M. Podobina has revealed the Albian foraminiferal assemblages in ten borehole sections. Previously, the Albian foraminifera were studied by Z.I. Bulatova, E.O. Amon and V.A. Marinov. Agglutinated quartz-siliceous foraminifera, often having coarse-grained microstructure of test walls, were encountered in all 93 studied samples from 10 borehole sections. In some samples, calcareous foraminiferal pseudomorphs were found preventing from determining their systematic position. The species composition of foraminifera permitted to date the Khanty-Mansiysk Horizon to the Middle and Upper Albian within the Samotlor area. Two foraminiferal assemblages were established: Ammobaculites fragmentarius Gaudryinopsis filiformis (Middle Albian) and Ammotium braunsteini Verneuilinoides borealis assanoviensis (Upper Albian) within the Albian zones of the same name. The Lower Albian deposits were not traced in the Samotlor area as based on foraminifera. The Middle and Upper Albian zones established in the Samotlor area differ significantly in systematic composition from those of Transuralia known from the latest stratigraphic scheme (2005). In the Middle Albian deposits, the foraminiferal assemblage of the Ammobaculites fragmentarius Gaudryinopsis filiformis Zone is noted for the prevalence of genera Haplophragmoides, Recurvoides, Ammobaculites, Ammo-marginulina, Ammotium, Pseudoverneuilina Podobina gen. nov., Gaudryinopsis. The integrity of tests varies, but destructed forms prevail. It should be noted that solitary species Verneuilinoides borealis Tappan assanoviensis (Zaspelova) are also encountered in the Middle Albian, but at this stratigraphic level they are not decisive for determining the Middle Albian age of the foraminiferal zone. The most characteristic for the Middle Albian is the index-species Recurvoides leushiensis Bulatova as well as the new species Pseu-doverneuilina albica Podobina sp. nov. In the overlying deposits of the Khanty-Mansiysk Horizon of the Samotlor area, the Upper Albi-an foraminiferal assemblage Ammotium braunsteini Verneuilinoies borealis assanoviensis of the homonymous zone was detected. The representatives of genera Haplophragmoides, Ammobaculites, Ammomarginulina, Verneuilinoides, Gaudryinopsis prevail. However, the species of these genera differ from forms of the Middle Albian assemblage. Species Ammomarginulina obscura (Loeblich), Spiroplectammina sibirica Podobina sp. nov., Gaudryinopsis oblongus (Zaspelova) together with index-species are characteristic for the Upper Albian. Many species of both Albian assemblages of the Samotlor area are analogues of those of the Canadian Province (Northern Canada, Northern Alaska), which are confined to the Arctic paleobiogeographic realm along with the West Siberian Province. Species of both Albian assemblages are illustrated on four paleontological plates. Three species and one genus of foraminifera are new.

Keywords

Authors

References