Investigation of sedimentological and petrographic minerological properties of evaporite sediments in the northeast of Eli̇acik and Alacayar villages (Catak-Van)

This study examines the sedimentological, petrographic–mineralogical, and geochemical characteristics of the Oligocene–Early Miocene evaporites in the Van–Çatak region, and reveals their diagenetic evolution and paleo-depositional conditions. Field data show that the evaporites developed in alternation with schist–phyllite at the base and marble–dolomite levels at the top, and were repeated along tectonic contacts as thrust slices. The location of the region within the Eastern Anatolian Compression Zone explains the strong deformation and slicing geometry. The Çatak basin is interpreted to have represented a semi-closed, highly evaporative platform basin during the Oligocene–Miocene. Sedimentological analyses indicate that the basin is represented by eight facies: lagoonal carbonate–conglomerate, fine-grained marl–claystone, laminated gypsum, massive gypsum, selenitic gypsum, nodular ("chicken-wire") gypsum, marl-rich/altered evaporites, and fan deposits related to basin closure. Petrographic and SEM–EDS analyses show that the evaporites consist mainly of gypsum with lesser anhydrite, exhibiting granoblastic, fibrous, and recrystallized textures; preserved anhydrite relics reflect multi-stage diagenesis. XRD data confirm the presence of gypsum, anhydrite, quartz, illite, muscovite, kaolinite, and locally berlinite, the latter indicating restricted basin conditions. The marble–dolomite alternation overlying the evaporites reflects the dolomitizing influence of evaporation-derived fluids. Diagenesis proceeds in three stages: primary gypsum precipitation, burial-related gypsum → anhydrite transformation, and late-stage rehydration of anhydrite to secondary gypsum along tectonic fractures. Major and trace element data indicate dominantly marine, hypersaline deposition with intermittent continental input. ⁸⁷Sr/⁸⁶Sr (0.7085–0.7091), δ³⁴S (+14‰ to +22‰), and δ¹⁸O (+10‰ to +17‰) values confirm a marine sulfate origin and deposition within a semi-closed lagoon system. In conclusion, the Van–Çatak evaporites represent lagoonal to shallow-marine deposits formed under active tectonics and semi-arid climatic conditions, having undergone multi-stage diagenesis and low-grade metamorphism, and constitute an important paleogeographic marker unit for the region.