Foraminiferal changes and geochemical profiles across the Cenomanian/Turonian boundary in central and south‐east Poland

Abstract

ABSTRACTTwo sections of the Upper Cenomanian and Lower Turonian in central and south‐east Poland were investigated for foraminifers, CaCO3content, carbon content insoluble in HCl (Corg) and in the carbonates (Ccarb), carbon and oxygen isotopic composition of bulk‐rock carbonates and elemental abundances. The Cenomanian/Turonian boundary interval is characterized by the appearance of more marly facies, a δ13C and δ18O stable isotope 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 +2 (PDB) occurs in the lowermost Whiteinella archaeocretacea Zone. The late Cenomanian δ13C anomaly is associated with heavy δ18O values. The peak value of δ13C corresponds to the minima in P/B ratio and in diversity of foraminiferal assemblages. A late Cenomanian anoxic event is thought to be responsible for changes in foraminiferal assemblages. However, elemental abundance analyses do not show changes in the concentrations of trace elements. This may be explained by the long distance between studied area and a source of enrichment which was probably located in the western hemisphere.