Comparative study of major element geochemistry of gypsum-ghost limestones and selenite lithofacies from the Miocene of northern Carpathian Foredeep: implication to the model of massive replacement of solid sulphates by calcium carbonates

Gypsum-ghost limestones and selenite gypsum facies, commonly believed to be as lithological equivalents caused by massive replacement of selenites by limestones, occur in the same Miocene evaporitic series of the northern Carpathian Foredeep (southern Poland) and differ considerably with regard to their sedimentological features and major element compositions. The differences (dealing with variation of contents, ranges, means, patterns of distribution, correlations, and interelement ratios of the major elements) clearly do not indicate any geochemical similarities between the gypsum-ghost limestones and the selenite gypsum lithofacies. Mass-balance chemistry shows a deficit of calcium and sulphur contents in the limestones compared to the composition of the selenitic gypsum and implies that the gypsum-ghost limestones system was open to mass transfer and cannot be related to simple and regionally extended replacement of solid sulphate rocks by limestones plus native sulphur. The major element geochemistry of the gypsum-ghost limestones and the selenites represent their original compositions which in turn reflect original depositional settings, rather than pore water chemistry during replacive diagenesis. Both the lithological units developed in co-eval depositional domains (carbonate and sulphate) constituting an evaporitic system but corresponding to different sedimentary settings of the system. The gypsum-ghost limestones reflect the unique situation of simultaneous formation of carbonate and selenites in a sedimentary, transitional milieu between the carbonate and gypsum domains, where bottom calcium carbonate deposition was alternating with the growth of selenite crystals. The results are clearly inconsistent with the epigenetic model of formation of the Polish sulphur deposits which assumes massive and regionally extended replacement of sulphate deposits by carbonates.