Petrography and diagenesis of Sarvak

he Sarvak Formation is a thick carbonate unit of the Bangestan Group with an age of Middle Cretaceous and has a wide distribution in the Zagros region in southwest Iran. Outcrops of Chenarbashi (754m thick) and Korhall (over 680m thick)، with 18km distance from each other، were studied in the Kabirkuh Anticline. At these outcrops، the Sarvak Formation can be subdivided into lower (thick bedded) and upper (thin bedded) units. The thick bedded unit is a neritic carbonate and consists of limestone and dolomite that contains chert nodules and bands. The thin bedded unit is a pelagic carbonate and consists of limestones with intercalation of calcareous shales. Morphologicaly، the thick bedded unit forms the scarpment and the thin bedded unit forms the lower areas. An investigation at the outcrops of Garau Formation at a distance of 4km from Chenarbashi outcrop shows that the boundary between these two formations is continuous without any erosinal discontinuity. Sarvak Formation occurs between Garau and Surgah formations، source rock، with a suitable potential to act as a reservoir rock. The microscopic and field investigations of the studied sections led to recognition of nine main microfacies، deposited in lagoon، bar، bar front and open marine sub environments. The Chenarbashi section forms in a deeper environment، where pelagic facies is more developed. Lagoon and bar facies are developed farther in southern areas such as the Korhall Section. Diagenetic processes confirm the influence of marine، burial and meteoric diagenetic environments. The microfacies successions diagrams illustrate that the Sarvak Formation consists of two sedimentary cycles (3rd & 4rd orders) and a part of a third cycle which was probably continued while the Surgah Formation was depositing in that area. A rimmed shelf carbonate platform is suggested for the depositional environment of the Sarvak Formation.