Stratigraphy, geochemistry and depositional environment of the celestine-bearing gypsiferous formations of the Tertiary Ulaş-Sivas Basin, East-Central Anatolia (Turkey)

Abstract

Celestine-bearing evaporite mineralization is widespread in the Tertiary evaporitic units of the Ulaş-Sivas Basin, east-central Anatolia. The oldest deposition of gypsum, which is of laminated character, occurred in a shallow inner-lagoonal environment or in depressions during Late Eocene regression. Thick gypsum and overlying beds composed of alternating bedded, nodular gypsum and sandstone developed in coastal sabkhas and abandoned channels within a meander-river complex during Oligocene time. The last occurrence of evaporitic units, namely massive and bedded gypsum alternating with sandstones and fossiliferous limestones, resulted from limited marine transgression of an Early Miocene sea along the southern margin of the Sivas Tertiary Basin. The celestine deposits are predominantly found within the gypsum beds throughout the Tertiary basin and in subordinate amounts in the limestones of the uppermost Eocene and as open-space fillings in gypsum, and as nodules in the some of the Oligocene fluvial sandstone, claystones and massive gypsums. Large-scale lenses of celestine occur within Early Miocene massive gypsums. The celestine samples were studied by scanning electron microscopy (SEM), ore microscopy, and electron-microprobe (EMP), fluid-inclusion, selected trace-element (XRF) 18O/16O, 34S/32S and 87Sr/86Sr isotope geochemistry. Field observations and analytical results indicate that the celestine did not develop via primary sedimentary processes. Rather, high-temperature conditions prevailed during late-diagenetic or epigenetic celestine formation.