Carbon, oxygen and strontium isotopes as a tool to decipher marine and non-marine environments: Implications from a case study of cyclic Upper Cretaceous sediments

Abstract

AbstractThe interplay of Late Cretaceous basin subsidence and oscillations in sea level produced a mixed freshwater–marine succession within the Upper Cretaceous Gosau Group of the Northern Calcareous Alps. Cored sections from wells of the Glinzendorf and Gießhübl Syncline, as well as sediments from the outcrop area of Grünbach–Neue Welt and Slovakian equivalents have been investigated for their stable isotopic composition. Bulk carbonate δ13C and δ18O values of 116 fine-grained samples (shales, siltstones, marls) and 87Sr/86Sr values of 10 samples from the borehole Markgrafneusiedl T1 were analysed in order to distinguish between non-marine and marine deposits and to compare and correlate isotope characteristics of the different Gosau synclines and basins.Non-marine samples have significantly lower mean δ13C values compared to the mean of marine samples. The discrimination between a marine and non-marine group using δ18O is also highly significant statistically, even though the difference between the average non-marine and marine values is small. Strontium isotope values of marine intervals are near the range of values of normal Upper Cretaceous sea water but show a trend towards higher ratios in marginal marine and non-marine deposits. Although diagenesis and the detrital carbonate admixture partly influence the isotopic composition, the original environmental signal can still be reliably identified.