Brine palaeocurrent analysis based on oriented selenite crystals in the Nida Gypsum deposits (Badenian, southern Poland)

Abstract

Unique sedimentary structures indicating the direction of brine currents are present in the Middle Miocene (Badenian) evaporite basin in Carpathian Foredeep. They occur within widespread gypsum deposits cropping out along the northern margin of the Foredeep, in Ukraine, Poland and the Czech Republic. The primary bottom-grown selenite crystals show apices turned horizontally in the same or similar directions, and are interpreted as the direction of inflowing calcium sulphate oversaturated brine. The upstream directed crystals are used to reconstruct brine palaeocurrents in outcrops of the Nida Gypsum deposits in NW margin of the Foredeep evaporite basin in Poland. Palaeocurrent analysis is based on simplified measurements which consisted in the determination of azimuth intervals enclosing groups of conformably oriented crystals. Measurements revealed that the brine flowed into the study area mainly from north and east, and outflowed farther towards the SW. This palaeoflow is roughly parallel to the basin margin contour and is a part of the longshore counterclockwise brine circulation well documented in other areas of the basin. Local deviations from the uniform flow directions suggest presence of shoals and islands forming obstacles for the brine streamlines on the Nida area.