Microfacies and Sedimentary Environments of Dalan Formation at Surmeh Mountain, Folded Zagros Zone, Southwestern Iran

Abstract

The Permian carbonates–evaporates Dalan Formation is one of the most important gas reservoir in the Zagros Basin. The Zagros are located on the boundary between the Arabian and Eurasian lithosphere plates and are the Orogenic response to a collision between Eurasia and advancing Arabia during the Cenozoic. The study area is located at the eastern part of Surmeh Mountain, ~120 km south of Shiraz in the Folded Zagros Zone. Dalan Formation at Surmeh Mountain, with a thickness of 650 meters, is formed of three lithostratigraphic units. These units, from bottom to top, consist of lower Dalan, Nar Member and upper Dalan. The careful examination of thin sections led to the recognition of 6 microfacies which was performed on the basis of skeletal and non-skeletal grains and matrix (Fenesteal dolomitic mudstone, Layered anhydrite, Lagoonal skeletal wackstone/packstone, Fine- grained ooid, peloid grainstone with lagoonal skeletal debris, Medium-grained ooid grainstone with oomoldic porosity, Open marine fossiliferous mudstone). Microscopic and macroscopic evidences show that Dalan Formation Facies can be divided into 4 facies belts, on the basis of depositional features, specific of carbonate platforms of homoclinal ramp type. These belts include tidal flats, lagoons, shoal and basin environments.