CYCLONIC BRINE-FLOW PATTERN RECORDED BY ORIENTED GYPSUM CRYSTALS IN THE BADENIAN EVAPORITE BASIN OF THE NORTHERN CARPATHIAN FOREDEEP

Abstract

In the middle Miocene (Badenian), within sulfate evaporites formed in the northern Carpathian Foredeep basin of Poland, Ukraine, and the Czech Republic, the apices of the primary, bottom-grown gypsum crystals (selenites) are similarly aligned over broad areas and have a common azimuth. This crystal orientation is interpreted as the product of a consistent direction of a brine inflow during gypsum crystallization, and such a unique commonality is used as a tool for paleocurrent analysis in order to recognize both the local and the regional brine paleocurrents in the basin. Earlier sedimentologic and stratigraphic studies proved that these beds of oriented selenites were deposited at the same or nearly the same time, in a brine not more than a few meters deep. It is interpreted that the oriented selenites recorded only the mean flow within the basin, mainly from the periods of mixing (in the dry-season lowstands), when the whole brine column down to the bottom was Ca-sulfate oversaturated. The measured paleocurrent vectors showed that the brines flowed along the marginal zone of the Carpathian Foredeep basin predominantly in a counterclockwise direction. This longshore flow is interpreted as a typical cyclonic circulation analogous to those present in recent lakes and semi-closed basins in the northern hemisphere where counterclockwise mean water drift is directly or indirectly forced by Earth rotation (the Coriolis effect). The detected brine flow directions do not reflect downslope gravity flow of dense brines into the central basinal depths or subbasins that were filling with the halite facies. Copyright © 2006, SEPM (Society for Sedimentary Geology).