Evolution of Permian seawater: evidence from fluid inclusions in halite

The examination of primary fluid inclusions in sedimentary halite from several Permian evaporite basins of East and Central Europe (Asselian and Sakmarian Dnipro-Donets Basin of Ukraine, Sakmarian Dvina-Sukhona Basin of Russia, Kungurian Solikamsk Basin of Russia, Zechstein Basin of Poland and Peri-Baltic Russia) revealed that the brines were of Na-K-Mg-Cl-SO4 (SO4-rich) chemical type. They are characterized by minor content Of SO4 ions, when compared with modem seawater concentrated to the corresponding stage. The lowest SO4 content was recorded in the Kungurian; a higher SO4 content was found in the Asselian and Sakmarian; and the highest content in the Late Permian. The bromine content in halite of the Permian salts of East and Central Europe (mostly 30-160 ppm) correlates with ion concentration in brine inclusions. The marine origin of salt in most of the studied sections is supported by isotopic composition of sulphate sulphur. During salt deposition in every basin, local factors - such as the inflow of surface or subsurface waters, sulphate reduction, and water-rock interaction - have exerted important influences on the K, Mg, and SO4 ion ratios. However, these changes did not lead to the change of the chemical, SO4-rich type that is characteristic for the Permian evaporite basins.