Stable carbon and oxygen isotope composition of Late Cretaceous benthic foraminifera from the southern South Atlantic

Interspecific differences vary between samples probably reflecting temporal changes in organic carbon fluxes to the sea floor. Constantly lower delta 13C values for Pullenia marssoni and Pullenia reussi suggest the deepest habitat for these species. The strong depletion of delta 13C values by up to 3 per mil within lenticulinids may be attributed to a deep infaunal microhabitat, strong vital effects, or different feeding strategy when compared to other species or modern lenticulinids.

The mean delta 18O values reveal a strong separation of epifaunal to shallow infaunal and deep infaunal species. Epifaunal to shallow infaunal species are characterized by low delta 18O values, deep infaunal species by higher values. This result possibly reflects lower metabolic rates and longer life cycles of deep infaunal species or the operating of a pore water [CO3]2- effect on the benthic foraminiferal stable isotopes.

Pyramidina szajnochae shows an enrichment of oxygen isotopes with test size comprising a total of 0.6 per mil between 250 and 1250 µm shell size. Although delta 13C lacks a corresponding trend these data likely represent the presence of changes in metabolic rates during ontogenesis. These results demonstrate the general applicability of multi-species stable isotope measurements of pristine Cretaceous benthic foraminifera to reconstruct past microhabitats and to evaluate biological and environmental effects on the stable isotope composition.