Bio-events, foraminiferal and nannofossil biostratigraphy of the Cenomanian/Turonian boundary interval in the Subsilesian Nappe, Rybie section, Polish Carpathians

The Rybie section (Subsilesian Nappe, Polish Carpathians) comprises hemipelagic and pelagic sediments of the Cenomanian/Turonian boundary (CTB) interval. In general, positioning of the CTB in such sediments is problematic owing to the absence or scarcity of index ammonites or inoceramids, but an integrated stratigraphy of nannofossils, foraminifera and microfacies allowed determination of the CTB within a narrow interval. The standard nannofossil UC zones have been used, and the standard planktonic foraminiferal Thalmanninella reicheli Zone combined with a new local zonation, which includes the Parathalmanninella micheli, Heterohelix and Marginotruncana zones is proposed. A few bio-events related to the CTB were identified, including the Heterohelix shift, the radiolaria domination, the roveacrinid abundance event, the planktonic foraminifera turnover, the deep-water agglutinated foraminifera extinction and the filament event. The CTB interval lies in the lower part of the nannofossil UC5c-6 Zone, and in the middle of the planktonic foraminiferal Heterohelix Zone and of the benthonic foraminiferal Bulbobaculites problematicus Zone. The boundary interval is also above the deep-water agglutinated foraminifera extinction event and below the filament event. The CTB lies between a package of black shales (an equivalent of the Bonarelli Level) and a level of ferro-manganese deposits.