Foraminiferal biostratigraphy of the Callovian-Volgian sediments and biofacies of the southwestern West-Siberian Lowland

Abstract The study explored the taxonomic composition of foraminiferal assemblages from cores sampled in the Sil’ga and Yamal-Tyumen’ facies regions—the southern and southwestern West Siberian sedimentary basin. A complete sequence of biostratons was established for the Callovian-Kimmeridgian sediments of the southwestern West Siberian Lowland and was correlated with the units of the General Stratigraphic Scale. A number of biostratons have been revealed for the south of West Siberia. The biofacies analysis of the foraminiferal assemblages revealed that the Yamal-Tyumen’ facies region belonged to a relatively deep marine environment, far away from the Jurassic Sea littoral zone, in the Callovian through the Kimmeridgian and that the Sil’ga facies region was a relatively shallow marine environment in the Oxfordian through the Middle Volgian.