Microfossils of the Albian and Cenomanian shales from the Stramberk area (Silesian Unit, Outer Western Carpathians, Czech Republic)

Abstract

Microbiostratigraphic study of sporomorphs, dinoflagellate cysts, foraminifers and calcareous nannofossils documented the age and paleoenvironmental features of black and grey-green, organic-rich sediments in the classical area of Stramberk (Baska Formation, Silesian Unit, Outer Western Carpathians). Age-assessments suggest Late Albian and Cenomanian age (foraminiferal Zones Rotalipora appenninica, R. reicheli and R. cushmani; nannoplankton Zones BC27/UC0-UC4). The character of dinoflagellate cyst assemblages (e.g. presence Pterodinium) reflects open-sea environment. The presence of calcareous foraminifers and nannofossils gives an evidence of depositional conditions above the carbonate compensation depth (CCD). The presence of some terrestrial and non-marine aquatic palynomorphs (e.g. Tetraporina, Lecaniella) documents the proximity of a continent and fluvio-lacustrine influences. The presence of microfossils tolerating low-oxygen bottom conditions such as foraminifers of genus Lingulogavelinella and jaws of polychateous annelids (scolecodonts) reflect a dysaerobic bottom environment. Co-occurrence of Boreal and Tethyan species encountered in foraminiferal and palynomorph assemblages documents the influences from the higher latitudes on the depositional area of northern Tethys. Moreover, Lower-?Middle Cenomanian sporomorphs (angiosperms) have similar character to others of the same age from the Blansko Graben, in the SE part of the Bohemian Cretaceous Basin, which is situated on the SE border of the West European plate.