Origin and evolution of halite based on stable isotopes (δ37Cl, δ81Br, δ11B and δ7Li) and trace elements in Tuz Gölü Basin, Turkey

Abstract

The Tuz Gölü basin located in Central Anatolia contains ancient (Miocene) and recent evaporite deposits. The aim of this study is to determine the origin and evolution of the ancient halite deposits in the basin, particularly whether there is a marine origin. For this purpose, the mineralogical, geochemical and isotopic properties of halite samples taken from three different drillings at the southern part of the Tuz Gölü basin were determined. Halite samples in the Tuz Gölü basin are characterized by Cl (60.20–61.00%), Na (39.00–39.40%) and Br (5-637 ppm) contents. The Cl−, Br−, Ca, Mg2+, SO42−, and K+ values and Cl/Br (948-86428) ratios indicated that during the formation of the ancient halites in the Tuz Gölü basin, the mixture of solutions had different compositions/origins and that the dissolution, recrystallization and dedolomitization mechanisms were effective.The δ81Br, δ37Cl, δ7Li, and δ11B isotopic compositions of the pure halites range from −0.06 to 0.82, −0.80 to 1.28, −0.70 to 30.60 and −14.70 to 11.60, respectively. The low δ37Cl (from −0.06 to 0.06‰), low δ81Br (from 0.03 to 0.95‰), high δ 11B (from −6.40–11.60‰) and high δ7Li (from 26.00 to 30.60‰) values clearly indicate that the brine involved in the formation of the halites of the Tuz Gölü basin was largely derived from seawater during the Mid-Miocene Climatic Optimum (MMCO) period. Additionally, the Cl−, Br−, Ca2+, Mg2+, and SO42− contents, as well as the intermediate δ81Br (0.34–0.95‰) values of the Tuz Gölü samples, indicated that the origin of the ancient halites in the basin is not only a marine composition but also a mixture of solutions having different compositions, ratios or origins (e.g., seawater or saline water and groundwater/fresh water).