Późnocenomańskie zdarzenie beztlenowe w Polsce Środkowej

Abstract

LATE CENOMANIAN ANOXIC EVENT IN CENTRAL POLAND Summary In the Puławy IG 2 borehole (Central Poland) in the Upper Cenomanian and Lower Turonian strata, foraminifers, CaCO3 content, stable isotopes (13C, 180), carbon content insoluble in HCI (Corg) and in the carbonates (Ccarb) and elemental abundances have been investigated. The Cenomanian/Turonian boundary interval is characterized by the appearance of more marly facies, a δ13C and δ180 anomaly, a considerable increase in Corg content and decrease in Ccarb content and substantial changes in the foraminiferal assemblages. A major carbon stable isotope excursion with a shift of up to + 1.6°100 (PDB) occurs in the lowermost Whiteinella archaeocretacea zone. Heavy b180 values are associated with δ13C anomaly. The peak value of δ13C corresponds to the minima in P/B ratio and in diversity of foraminiferal assemblages. At the Rotalipora cushmani/Whiteinella archaeocretacea zones boundary a majority of the typical Cenomanian groups of benthonic foraminifers as well as two plantonic species Rotalipora cushmani (Morrow) and Rotalipora greenhornensis (Morrow) became extinct. A late Cenomanian anoxic event is thought to be responsible for carbon stable isotope anomaly and changes in foraminiferal assemblages. Elemental abundance analyses do not show remarkable changes in the concentrations of trace elements. It may be explained by a long distance between studied area and proto- Caribbeanl Gulf of Mexico where hot spot activity or intense pulses of spreading center in the late Cenomanian occurred.