Belemniters stabila isotopsammansättning : paleomiljöns och diagenesens betydelse

Sammanfattning: Stable isotope compositions (δ18 0 and δ13 C) and cathodoluminescence characteristics were determined in 112 belemnite rostra, including Belemnellocamax grossouvrei, Belemnitella alpha, Belemnellocamax mammillatus, Belemnellocamax balsvikensis, Gonioteuthis quadrata scaniensis, Belemnitella mucronata and Belemnella lanceolata. The main aims were to determine palaeoenvironmental and diagenetic influences on the fossil tissue, and to discuss the marine palaeotemperatures during Late Cretaceous times. The specimens were collected from strata in the Kristianstad Basin, southern Sweden. The strata included sediments spanning the earliest Campanian to earliest Maastrichtian interval. The belemnites are composed of low-magnesium calcite. EDX and cathodoluminescence microscopy indicated partial re-crystallisation, and thin sheets of cemented "growth rings" ( filled voids after organic tissue). Regardless of petrographic status, δ18 O and δ13 C data appear very uniform and plausible for Cretaceous palaeoenvironments. This may imply that the isotope data represent biologic as well as marine early diagenetic conditions. The oxygen isotope data were re-calculated to sea surface and/or early diagenetic temperatures. Accordingly, Campanian sediments reflect 15,6°C ± 0,1 °C, whereas the superimposed succession show gradually declining calculated temperatures down to, 12,5°C ± 1,9°C. This is in agreement with palaeoecological studies of vertebrates within the same basin, as well as with other studies of Late Cretaceous belemnites in northern Europe.