Determination of the origin of the neogene aged halite deposits in the southern part of the Tuz Gölü Basin

The study area located in the southern part of Konya Closed Basin is the largest Miocene inner basin in Central Anatolia. In the thesis, mineralogical, geochemical and isotopic investigations were conducted in halite samples taken from three deep drillings at the southern part of the basin in order to determine the chemical composition of the Miocene halite deposits and to evaluate depositional environments of Tuz Gölü lacustrine basin. The Cl- and Na+ contents of the halite-rich samples in the Tuz Gölü basin are characterized by ranging from 60.20 to 61.00 % and from 39.00 and 39.40 %, respectively but the Br- contents vary within a wide range (5-637 ppm). The Cl-, Br-, Ca, Mg2+, SO42-, K+ values and Cl/Br (948-86428) ratios of the halite samples and fluid inclusion analysis results from pure halite samples indicated that solutions with different composition and origin were effective on formation of the Miocene halites in Tuz Gölü basin. The high Br- (> 40 ppm) content of the pure halite samples indicates the marine origin while the low Br- content is related recycling (dissolution of re-precipitation) of the previously deposited halites. The reason of high Mg2+ and SO42- contents of the halites in Tuz Gölü basin is the dissolution of previously deposited gypsum in the study area and de-dolomitization process. The δ81Br, δ37Cl, δ7Li, and δ11B isotopic compositions of the pure halites are ranging from -0.06 to 0.82 ‰, -0.80 to 1.28‰, -0.70 to 30.60 ‰ and from -14.70 to 11.60 ‰, respectively. The low δ37Cl (from -0.06 to 0.06 ‰), low δ81Br (from 0.03 to 0.95 ‰), high δ11B (from -6.40 to 11.60 ‰) and high δ7Li (from 26.00 to 30.60 ‰) contents clearly show the solution in the deposition of halites in the Tuz Gölü basin was derived from seawater during the Mid-Miocene Climatic Optimum (MMCO) period. Furthermore, the Cl-, Br-, Ca2+, Mg2+, SO42- contents as well as intermediate δ81Br (0.34 – 0.95 ‰) isotopic values of halites from the Tuz Gölü basin indicate that the origin of the Miocene halites is not only marine composition but also the mixture of brines with different composition, ratio or origin (e.g., seawater or saline water and groundwater/fresh water). In the Tuz Gölü basin, which is a sedimentary basin formed by the effect of highly complex physico-chemical mechanisms, the possible effective mechanisms causing chemical differences; (1) seawater input (2) the changes in chemistry of Miocene halites due to dissolution and re-precipitation processes of ancient evaporites, and (3) de-dolomitization processes were first detected in this thesis. Besides, it is determined in this study for the first time that fault and karstic cavities play an important role in the seawater input into the basin as well as the rise of the sea level in the Mid-Miocene. Keywords: Evaporite; Halite; Konya Basin; Fluid inclusion; Tuz Gölü; Recrystalization