Mineralogical Characterıstıcs of Neogene Sulphate Minerals in the Southern of Tuzgolu Basin, Turkey

Abstract

The studied sulfate minerals are located in southern part of Tuz Gölü basin. The Na-Ca-Mg sulfate minerals determined in the basin range from the simple anhydrous salts such as anhydrite, glauberite, thenardite, to simple hydrous salts such as gypsum, eugsterite, starkeite, and also a series variably hydrated Na-Mg sulfates ranging from blöedite, mirabilite and epsomite to löweite. In this study, it has been aimed to investigate the depositional environments and syn-depositional or post-depositional properties of the sulphate minerals. Gypsum is generally the first sulfate mineral formed thermodynamically, and then the gypsum transforms to anhydrite when it just lost two mole H2O. Glauberite is the next sulfate mineral either precipitated with halite or form as a reaction product with anhydrite or gypsum. Mg-sulfate minerals initially precipitate as epsomite then altered to thenardite. Syn-depositional features identified in the sulfate minerals are bed-form structures, vertically oriented euhedral crystals, detrital substrate (siliciclastic sediments), pellets and dissolution or erosion surfaces, and these fabrics have been preserved at the levels including gypsum, anhydrite and glauberite. Porphyroblast, poikilitic growth determined in the sulphate minerals are also typical features of syn-depositional crystallization. Dissolution-reprecipitation features are generally common in gypsum, anhydrite and glauberite minerals which show rounding of euhedral crystals terminations, followed by new syntaxial growth. Additionally, biological processes being syn-depositional feature lead to the form of lenticular minerals. Post-depositional features are very susceptible to alteration caused by increasing in temperature and pressure during burial. Generally, gypsum and epsomite minerals have altered when waters hydration has been released. Disruption and destruction of sedimentary structures have been observed in the levels such as mosaic textures, folds, slabs, fractures, veins. Intrasediment growth of anhydrite nodules has been also detected in all levels of the bore holes. In addition to, different types of several paedomorphic replacements such as gypsum-anhydrite, gypsum/anhydrite-glauberite and glauberite/anhydrite-halite have been determined in the sulfate minerals. Sulfate mineralogy of the Tuz Gölü basin is a key role to understand the water hydrochemistry causing precipitation, and this brine may originate from i) reprecipitation of the Eocene-Oligocene evaporates ii) also inflow of seawater (mixing with non-marine or hydrothermal inflow, and iii) de-dolomitization process.