In the framework of a biostratigraphical study of the Albian–Cenomanian Butkov Formation attention is paid to the paleobathymetry of its basal part. The oldest planktonic foraminifers Thalmanninella ticinensis subticinensis (Gandolfi) appear in these beds. Usually, only the glauconitic moulds of the planktonic foraminifers are preserved; but in places there are also remnants of the original calcareous test. Their presence indicates sedimentation on a shallow-water raised bottom, surrounded by a deeper pelagic environment, precipitation of glauconite and the filling up of foraminifer tests with glauconite immediately after their death.