Carbon isotope stratigraphy of the Lower Triassic in northwestern Poland – first results from the Gorzów Wielkopolski IG 1 borehole

Abstract

The Lower and Middle Buntsandstein succession (Baltic and Pomerania formations) from the Gorzów Wielkopolski IG 1 borehole was examined in terms of δ13C and δ18O variability. The section is located in northwestern Poland, representing the eastern part of the epicontinental Central European Basin System. Forty-six powder samples from predominantly oolitic limestone intercalations were analysed for these stable isotopes, following microfacies, petrographic and geochemical analyses of these rocks. The δ13C values obtained range between –3.95 and +1.43‰ (VPDB); (average –1.13‰). The Baltic Formation is isotopically much heavier than the Pomerania Formation. δ18O values range between –4.06 and –8.68‰ (VPDB); (average –6.62 ‰). An increasing upwards trend can be observed throughout the succession. The d13C record suggests the possibility of correlation with four global events: the Mid-Griesbachian Event, Late Griesbachian Event, Dienerian-Smithian Boundary Event and Late Spathian Event. Correlation of the positive anomaly around a depth of 2120.0 m with the pronounced global positive Smithian-Spathian Boundary Event is less likely. The record of low and decreasing δ13C within the Pomerania Formation corresponds very well to the global decrease of this isotopic indicator through the Dienerian to early Spathian. Comparability of the local δ13C record with the global record suggests the suitability of using isotopic stratigraphy on such oolitic intercalations for improvement of the Early Triassic chronostratigraphy of the epicontinental Central European Basin System.