Biostratigraphy and paleobiogeography of the Gan’kino horizon (Maastrichtian) of the Western Siberia

Abstract

Research subject. This paper investigates Maastrichtian (Upper Cretaceous) foraminifera complexes present in various parts of the Western Siberia.Materials and methods. The materials of parametric drilling performed in the last century were reviewed in the context of new data. The characteristics of the main ecological microfauna groups in the Gan’kino horizon (Maastrichtian) were clarified by analysing their taxonomic composition, structure and diversity. Results. It was shown that, in the typical Yamal-Tyumen district, the Gan’kino horizon consists of three zones: Spiroplectammina variabilis, Gaudryina rugosa (with subzones Bolivina decurrens, Bolivinoides senonicus and Stensioeina caucasica transuralica), Spiroplectammina kasanzevi, Bulimina rosenkrantzi (with subzones Bolivina plaita, Bulimina rosenkrantzi and Heterostomella foveolata) and Brotzenella praeacuta. Here, the horizon volume is limited to the Maastrichtian stages. The Stensioeina caucasica transuralica and Brotzenella praeacuta zones were found to belong to the Upper Maastrichtian.Conclusions. It was established that, the Early and early Late Maastrichtian was characterized by a gradual increase in the diversity of foraminifera complexes due to immigrants from the Boreal-Atlantic realm. The widespread distribution of foraminifera complexes from the Northern district across the Western Siberia during the Spiroplectammina kasanzevi and Bulimina rosenkrantzi period was associated with the transgression of Arctic waters. The appearance of the foraminifera associations with Heterostomella foveolata reflects a wide levelling of the foraminifera composition throughout the Western Siberia. At the beginning of the Brotzenella praeacuta time, Boreal-Atlantic taxa were widely dispersed across the Western Siberian basin.