On the first discovery of calcareous nannoplankton in the Lower Berezovo sub-formation (Upper Cretaceous, Coniacian-Campanian Stages) of Western Siberia

Nannoplankton was first discovered in the core of the Lower Berezovo subformation from the Russian 5_05 well at a depth of 674.8 m in flaky clay-siliceous siltstones. The presence of Arkhangelskiella cymbiformis suggests that the age of the host sediments is not older than the Late Santonian, and the age range can be defined as Upper Santonian-Campanian-Maastrichtian Stage. The radiolarian complex indicates the Campanian Age. The composition of foraminifera is typical for the upper part of the Lower Berezovo subhorizon.