Bohemian Cretaceous Basin – Cenomanian-Turonian boundary based on calcareous nannofossils


Lilian Švábenická

Geoscience Research Reports 37, 2004 (GRR for 2003), pages 44–47

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Based on studies of calcareous nannofossils Cenomanian-Turonian boundary was recognized in the Bohemian Cretaceous Basin, in polygon of towns Turnov-Hořice-Kolín. Cenomanian deposits provided poor and poorly preserved calcareous nannofossils with stratigraphically significant species Axopodorhabdus albianus. Its last occurrence marks the upper part of the "geslinianum" zone. In the overlying strata, Ahmuellerella octoradiata and Quadrum intermedium are scarcely present. State of nannofossil preservation is probably caused by dysaerobic paleoenvironmental conditions. Turonian base is marked by abundant, diverse and well preserved nannofossil assemblages with Eprolithus octopetalus and Quadrum giganteum that reflect a deepening of the depositional area. The first occurrence of Eprolithus moratus probably indicates the upper boundary of macrofossil zone Watinoceras devonense.