Isotopic composition of the crystallization water of gypsum in the Badenian of the northern Carpathian Foredeep: a case study from the cores Przybor6w 1 and Strzegom 143

Abstract

The isotopic composition of a crystallization water of gypsum is considered representative or the mother brine. In order to determine its origin for the Badenian primary gypsum in the northern peripheral part of the Carpathian Foredeep, two sections were sampled for the oxygen and hydrogen isotope analyses. The measured dD and d18O values for the crystallization water vary from -94.9 to -41.2‰ and from -7.2 to 0.8‰, respectively. Overall, these values are distinctly lower than those expected from isotopic exchange interactions during the gypsum crystallization from the marine brines, which is most likely due to (1) mixing of the original marine (sedimentary) waters with the isotopically light meteoric waters, or (2) isotopic exchange of the crystallization water with secondary solution. There is a clear relationship between the differentiated isotopic composition and variation in lithofacies. Both isotopic components calculated for the mother brine change in parallel fashion and show a decreasing-up trend of changes throughout the section. Most of these values, however, fall above the present-day meteoric water trend line, suggesting either (a) formation of gypsum from connate waters with distinct isotopic signatures, or (b) variation in the isotopic composition of the meteoric waters generated by the general climatic conditions since the late middle Badenian. The difference in the slope of the mother water line for both studied sections may be also explained by differentiated kinetics of tile isotopic exchange interactions. Based on the slope of this line and its relationships to the local meteoric water trend line, it may be assumed that the crystallization water in studied gypsum samples has been largely, if not completely, replaced by the meteoric waters or circulating ground waters under relatively cool and humid climatic conditions. Thus, the isotopic signature for gypsum reflects rather very recent history of its diagenesis.