Stable chlorine isotope evidence for non‐marine chloride in Badenian evaporites, Carpathian mountain region

Abstract

Routine trace‐element geochemistry suggests that components in putative marine halite evaporites may be partly of nonmarine origin, but such interpretations are commonly ambiguous. Stable chlorine isotopes may provide a less‐ambiguous marker of chloride origin where δ37Cl departs from the range predicted for evaporite formation from seawater. Bedded halite with primary sedimentary textures preserves original δ37Cl values. Measurable change in δ37Cl can be generated by incongruent dissolution of halite, but only if less than half the original halite remains. Badenian (middle Miocene) halite from the Forecarpathian and from the East Slovakian and Transcarpathian basins has a δ37Cl range of – 0.2 to 0.8‰. Two phenomena cannot be explained by simple evaporation of 0.0‰ seawater. At Wieliczka, the Shaft Salt has distinctive δ37Cl values (– 0.2 to 0.0‰) relative to neighbouring salt beds (0.2 to 0.6‰), requiring a large, abrupt input of brine with negative δ37Cl. Halite with high (0.6 – 0.8‰) δ37Cl near the base of the East Slovakian and Transcarpathian evaporites requires a large input of chloride with positive δ37Cl into the basins. Expulsion of basin brine with non‐0‰δ37Cl into the evaporite basins may account for the nonmarine chloride sources.