The Parvicingulakhabakovi-Williriedellum salymicum Radiolarian Biohorizon in the West Siberian Bazhenov Formation (Berriasian-Valanginian)

Three-dimensional SEM images of the radiolarian species Williriedellum salymicum Kozlova, 1983 were obtained for the first time, from the Berriasian-Valanginian Parvicingula khabakovi - Williriedellum salymicum biohorizon of the Bazhenov Formation (based on material from the Gubkinskaya and Radonezh boreholes). Using computer tomography (CT) and scanning electron microscopy (SEM) methods, in addition to optical microscopy, we were able to confirm the validity of the species Williriedellum salymicum Kozlova, 1983 and we propose that this biohorizon be included in the Lower Cretaceous regional stratigraphic scheme of Western Siberia.