LAUSR

Abstract Sulfur, oxygen and strontium isotope compositions of the sulfate minerals (gypsum and anhydride) of the Miocene evaporites in the Tuz Golu basin which is the largest, closed and inner basin of Turkey located in the Central Anatolia, were investigated to evaluate the origin of the sulfates and interpret the precipitation paleoenvironment. The isotopic, mineralogical and chemical properties and composition of the samples collected from drillings were investigated. The δ34SCDT and δ18OSMOW values of the sulfate minerals range from 18.78 to 35.90‰ and 7.55–22.57‰, respectively. Most of the δ34S values are similar to marine (Messinian) water. In addition, the 87Sr/86Sr ratios of the minerals vary from 0.707803 to 0.708209. Most of the δ34S and δ18O values and 87Sr/86Sr ratios of the investigated samples in the Tuz Golu basin are similar to those of the isotopic values of the Messinian marine sulfates indicating that the minerals were precipitated mostly from marine water. The 34S and 18O values of some samples are higher than those of the evaporites precipitated from the Miocene seawater and indicate that the evolution of the sufates in the basin was also controlled by the recycling-dissolution of the predeposited marine sulfates (Oligocene-Eocene), arid conditions and bacterial sulfate reduction (BSR) processes. Additionally, the low δ18O values and 87Sr/86Sr ratios with high Sr content of some samples other than those of the Miocene marine sulfates may have been caused by the influence of volcanic emanations, hydrothermal fluid, re-oxidation of sulfur and partially the contribution of the external or internal nonmarine water to the basin (e.g., meteoric water or groundwater/surface water). The Ca-sulfate minerals with high Sr contents and low 87Sr/86Sr ratios may have precipitated under the seawater-dominated hydrothermal fluid mixing conditions.