Oxygen and carbon isotope records of Upper Cretaceous foraminifera from Poland: vital and microhabitat effects

Abstract

Oxygen and carbon isotope data of 11 Lower Campanian and 11 Upper Maastrichtian co-existing rotaliid foraminiferal taxa from Eastern Poland are presented. Pristine preservation of the studied material is documented by studies of cathodoluminescence, elemental contents and micro/nano-structures of foraminiferal tests. The variability in δ18O and δ13C values of the foraminifera is taxon-specific and relatively constant within the investigated intervals. It results from the combination of vital and microhabitat effects. A comparison of the measured isotope signatures with the published data of similar Cretaceous or modern taxa have allowed us to find benthic foraminifera which precipitated oxygen and carbon isotopes in near-equilibrium with bottom water. These are Praebulimina sp., Gyroidinoides globosus, Pullenia jarvisi, and Bolivina incrassata for oxygen, and Cibicidoides voltzianus and Cibicides beaumontianus for carbon isotopes.The observed differences between δ13C values of infaunal and epifaunal foraminiferal taxa are related to the presence of δ13CDIC (DIC - dissolved inorganic carbon) gradient in the sediment column, which was much higher in the Chełm section. Although planktic foraminifera studied are characterized by different lifestyles, this feature is not mirrored in their oxygen and carbon isotope compositions. This is probably due to effects of vital isotope fractionation and minor thermal and carbon isotope gradients in a part of the water column inhabited by these organisms. The thermal gradient between near surface and bottom waters is calculated to be ca. 4.0 °C, and ca. 7.5 °C for the Early Campanian and the Late Maastrichtian seas of East European Platform, respectively, based on the comparison of δ18O values of selected planktic and benthic foraminifera.