Depositional environments and the extension of Basal Anhydrite evaporitic facies of the Asmari Formation in ‎the Dezful Embayment and surrounding areas, SW Iran

The Oligo-Miocene Asmari Formation consists of carbonate facies with lesser amount of evaporites. The evaporite ‎unit deposited at the base of the Asmari Formation is called Basal Anhydrite. Depositional model was investigated ‎using field data, geophysical logs and the Basal Anhydrite facies in the Dezful Embayment (DE). Seven microfacies ‎were recognized in seven outcrops located in the Bangestan, Sefid, Asmari and Anaran anticlines. They were ‎deposited in tidal flat and lagoon environments of inner ramp. Anhydrite facies is a distinct and pure evaporite unit ‎with no carbonate components. Two main textures, fine crystalline (alabastrine) and coarse crystalline ‎‎(porphyroblast), were distinguished in samples indicating replacement of anhydrite by gypsum. Gamma ray, neutron, ‎sonic and density logs of 20 wells in 15 oilfields in the DE indicate that evaporite facies, present at the base of the ‎Asmari Formation, is composed of anhydrite and halite. Anhydrite is present in the most of the DE wells and halite ‎and small amount of anhydrite are present in three central wells. The results of geophysical logs and microfacies ‎studies of the Asmari Formation reveal shallow water-shallow basin environment for the Basal Anhydrite.‎