Sedimentary evolution of Badenian (Middle Miocene) gypsum deposits in the northern Carpathian Foredeep

Abstract

In the northern peripheral part of the Carpathian Foredeep, the Middle Miocene (Badenian) gypsum deposits comprise two major, laterally extensive members: the lower is mostly autochthonous, of selenitic facies and the upper is allochthonous, of clastic facies and cumulate deposits. Towards the south, gypsum is replaced in the subsurface by anhydrite which displays relict textures of the primary gypsum. The facies variation and succession throughout the gypsum section, as well as geochemical indicators, reflect varied sedimentary conditions on the basin margin. Deposition took place on the periphery of a platform made up of a system of widespread shallow-water lagoons (sub-basins) separated by fault-controlled, NW-SE elongated islands or shoals. In these physiographically differentiated palaeoenvironments, facies relationships were largely diachronous. The water depth varied from a few metres to some tens of metres, and subaerial exposure episodically affected the gypsum deposition, as suggested from the sedimentary record and comparison of the facies with modem evaporitic environments. Variations in brine depth, salinity and water dynamics are expressed in the cyclic succession of the progressively changing facies associations. Sedimentary conditions changed drastically at the boundary of the lower (selenitic) and upper (clastic) members, and at the end of sulphate deposition, following major sea-level changes.