The First Discovery of Calcareous Nannoplankton in the Lower Berezovo Subformation (Upper Cretaceous, Coniacian–Campanian Stages) of Western Siberia

Nannoplankton was first discovered in the core of the Lower Berezovo Subformation from Borehole Russkaya 5_05 at a depth of 674.8 m in flaky clay-siliceous siltstones. The presence of Arkhangelskiella cymbiformis suggests that the age of the host beds are not older than the Late Santonian, and the age range can be defined as the Upper Santonian–Campanian–Maastrichtian. The radiolarian association is dated Campanian. The composition of foraminifers is typical of the upper part of the Lower Berezovian Regional Substage.