Analysis of texture, structure and depositional environment of evaporites in the Kond Formation, Saran section, Central Alborz, based on field data, petrography and XRD analysis

The late-Eocene Kond Formation in Saran section, Central Alborz, is a carbonate, marl, volcano-clastic and evaporite succession and the lower and upper boundaries with Karaj and Lower Red Formation is unconformable. The main thickness of the studied section consists of evaporite deposits. Based on the field studies, petrography and XRD data, these evaporite deposits are mostly consist of gypsum, anhydrite, dolomite, calcite and quartz. Field and petrographic study, imply that the gypsum and anhydrite are present in three types: primary (type one), secondary (type two) and Tertiary (type three) and dolomites are related to very early diagenesis. The primary evaporites which are laminated and layered gypsum, were deposited in a subaqueous shallow environment (salina) due to solar evaporation. Secondary evaporites with nodular texture and enterolithic and chicken-wire structures, were formed during epigenetic and shallow burial diagenesis (coastal sabkha). Moreover, tertiary evaporites with alabasterian, porphyroblastic and satin spar textures are related to burial and uplifting of primary and secondary evaporites in telogenesis and phreatic meteoric conditions. The abundance of evaporite minerals as well as other evidences of this sediments in the Saran section indicates a warm and dry climatic conditions during deposition of the Kond Formation. Due to the layered nature of evaporites of the Kond Formation in the Saran section and their association with shallow marine facies and the presence of significant thickness of volcano-clastic deposits of the Karaj Formation below these deposits, Eocene seawater and also migration of ions from older tuffs is suggested as the source of ions required for the deposition of these evaporite units.