Facies analysis and diagenetic features of the Aptian Dariyan Formation in Zagros Fold–Thrust Belt, SW Iran

Abstract

The Aptian Dariyan Formation (upper part of the Khami Group), is one of the important reservoir rocks in the Zagros Fold–Thrust Belt. The Zagros Fold–Thrust Belt is located on the boundary between the Arabian and Eurasian lithospheric plates and formed from collision between Eurasia and advancing Arabia during the Cenozoic. In these studied area, the Dariyan Formation with a thickness of 136 meters (Fahliyan section) and 100 meters (Kuh-e-Rahmat section), consists of carbonate rocks. Based on the facies analysis and sedimentological data, 16 microfacies were identified. The microfacies are attributed to five facies belts: tidal flat (lime mudstone, dolomitic mudstone and stromatolitic boundstone), lagoon (bioclastic packstone, orbitolinids bioclastic packstone and orbitolinids peloidal packstone), shoal (orbitolinids grainstone and peloidal grainstone), restricted (peloidal packstone, rudist floatstone/rudstone and orbitolinid wackestone), and open marine (orbitolinid floatstone, dasycladacean algae floatstone, bioclast pelagic foraminiferal wackestone/packstone, pelagic foraminiferal mudstone/wackestone, and calcispere packstone/wackestone). The depositional model relates to the carbonate ramp. The allochems of the Dariyan Formation are dominated by foraminifera, bioclasts and green algae. Peloids, and intraclasts are less abundant in this formation. Due to the great diversity and abundance of the foraminifera, this carbonate ramp is referred to as a “foraminifera-dominated carbonate ramp system”. This carbonate system reflects a local regression in the Fahliyan section which can be related to the vertical movement of the Kazeroon Fault. The carbonates of Dariyan Formation have been affected by a variety of diagenetic processes such as compaction, dissolution, cementation, neomorphism, and dolomitization.