Mixed evaporative and meteoric water dolomitization: isotope study of the Zechstein Limestone (Upper Permian), southwestern Poland

Abstract

Dolomites of the Zechstein Limestone in western Poland have high 13C values, characteristic of the Zechstein carbonates, and there is some variation in 18O profiles. Dolomites are mostly stoichiometric and well ordered and are characterized by variable crystal textures. The area studied underwent constant burial since the Late Permian and the isotopic curves, despite their complexity, show distinct regularities and signals of meteoric water input that in most cases could occur only during the Permian. Moldic porosity, interpreted as originated shortly after dolomitization, commonly occurs. Stratigraphic patterns and facies analyses suggest that dolomitization phases occurred at the top of each (eustatically controlled) subcycle of the Zechstein Limestone in association to subaerial exposures. Most of the dolomites, therefore, originated during the Permian.A significant proportion of the dolomites originated via meteoric—marine mixing during deposition of the Zechstein Limestone. The mixing mechanism was closely related to sea-level falls. Conventionally, evaporite-related dolomites are believed to have originated in a sabkha environment and/or by the reflux mechanism. The Zechstein Limestone case suggests that the mixing of evaporative and meteoric water may be responsible for dolomitization of other evaporate-related carbonates.