Origin and evolution of halite based on stable isotopes (delta Cl-37, delta Br-81, delta B-11 and delta Li-7) and trace elements in Tuz Golu Basin, Turkey

Abstract

The Tuz Golu 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 Golu basin were determined. Halite samples in the Tuz Golu basin are characterized by Cl (60.20-61.00%), Na (39.00-39.40%) and Br (5637 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 Golu basin, the mixture of solutions had different compositions/origins and that the dissolution, recrystallization and dedolomitization mechanisms were effective. The delta Br-81,delta Cl-37, delta Li-7 and delta B-11 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 delta Cl-37 (from - 0.06 to 0.06 parts per thousand), low delta Br-81 (from 0.03 to 0.95 parts per thousand), high delta B-11 (from -6.40-11.60 parts per thousand) and high delta Li-7 (from 26.00 to 30.60 parts per thousand) values clearly indicate that the brine involved in the formation of the halites of the Tuz Golu 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 delta Br-81 (0.34-0.95 parts per thousand) values of the Tuz Golu 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).