Isotopic composition of salt efflorescence from the sandstone castellated rocks of the Bohemian Cretaceous Basin (Czech Republic)
Abstract
Sulphate efflorescences on quartz sandstones with a clay matrix, exposed in rural areas of the Czech Republic are interpreted based upon an isotopic study of S and O. The low variability of S and O isotopes indicates a common source of the sulphur and a similar mode of sulphate formation.
Atmospheric sulphates with a similar isotopic signature occur in the area, due to the combustion of sulphurous coal in power plants. The sulphates crystallize from supersaturated pore waters that represent atmospheric precipitation, rich in sulphates, having percolated through the porous sandstone system.
The previously proposed model of efflorescence growth due to the oxidation of pyrite can be excluded, due to both the rare occurrence of pyrite and also to its different isotopic signature. Gypsum prevails in the central and eastern part, the north and north-west of the Bohemian Cretaceous Basin exhibits presence of alums that grow due to the dissolution of clay minerals or feldspars in acid environment.