بررسي محيطهاي رسوبي و چينه شناسي سكانسي سازند دالان در ناحيه زاگرس (نواحي كوه دنا و كوه سورمه )

Sedimentary Environments and Sequence Stratigraphy of Dalan Formation in The Zagros Area (Kuh-Dena And Kuh-Surmeh Sections)

Dalan Formation is known as a largest gas reservoir in the Zagros and Persian Gulf areas. The Dalan carbonate succession was placed between early Permian Fraghan and early Triassic Kangan Formations at the base and top, respectively. Microfacies and sedimentological studies indicate the ooilithic facies would be a main reservoir facies, which is restricted to the Upper Dalan unit. Based on the study at least 5 distinct facies belt has been distinguished along the Dalan ramp carbonate platform. The above-mentioned facies belt consists of 9 facies groups in which were arranged from Sabkha, restricted lagoon, oolithic shoal to open marine settings. All facies groups are characterized by special sedimentological and diagenetic properties in the study areas (Kuh-Surmeh and Kuh-Dena). In terms of sedimentary environments, all facies group were controlled by eustatic sea-level changes, in the study areas. The sequence stratigraphical study has led to accurate recognition of 6 significant third-order cycles or depositional sequences consisting of several meter-scale parasequences. All depositional sequences were bounded by sequence boundaries (type 1 and 2) or big sub aerial exposures. It is notable that each depositional sequence was deposited on the different sea-level flactuation with large scale shallowing-upward trend. Nevertheless, most depositional sequences are comprised of TST and HST intervals. As a result each depositional sequence represents a different sedimentary regime, sea-level changings and subsidence rate which were occurred during the Dalan carbonate deposition.