Microfacies Analysis, Sedimentary Environments and Diagenesis of the upper Carbonates of the Dalan Formation in the Persian Gulf, Iran

The Dalan Formation (Upper Permian) is mainly composed of limestone and dolostone with minor evaporite interbeds. Upper carbonates of the Dalan Formation constitute one of the main gas reservoirs in the Zagros fold thrust belt especially in the Fars and the Persian Gulf. The upper part of the Dalan Formation consists of oolitic grainstone with high reservoir quality. Based on sedimentological studies in the upper Dalan unit، seven microfacies have been recognized. This microfacies have been deposited in warm، arid intertidal، lagoon and shoal. They deposited in a homoclinal ramp. Different diagenetic process affected this unit are bioturbation، micritization، neomorphism، replacement، dolomitization، anhydritization، mechanical and chemical compaction، cementation، dissolution and fracturing. Based on the evidence like widespread dissolution، formation of moldic and vuggy porosity and precipitation of different types of meteoric cements and based on paragenetic sequences، it can be concluded that the studied interval، have not buried after the deposition، but at least some parts like oolitic shoal exposed subearially and was affected by meteoric diagenesis that was followed by deep burial diagenetic environment.