Facies distribution and paleogeography of the Oligocene-Miocene succession in southwestern Iran

Facies analysis and paleogeographical reconstruction of the Asmari Formation in the Lorestan and Dezful Embayment Zones are documented by studying eight outcrop sections and two wells. The new observations provide a basis for correlation and description of the carbonate ramp evolution during the Early Oligocene-Middle Miocene time. Petrographic examinations on 877 thin sections revealed 16 facies which are deposited in tidal flat (4 facies), lagoon (4 facies), shoal (2 facies), shallow open marine (4 facies), and deep marine (2 facies). Tidal flat and lagoon facies associations are extended in the north and east, whiles shoal and shallow open marine facies are more frequent in the south and west of the study area. Detailed analysis of sedimentary facies indicates that in the Oligocene interval, the depositional system of the Asmari Formation was a distally steepened ramp. From northeast Lorestan towards central and south-west Lorestan, the Asmari Formation is replaced by pelagic deposits of the Pabdeh Formation. In the early Miocene, the depositional system changed to a NE-SW trending homoclinal ramp.