Document Type : Original Research Paper


1 Ph.D., Department of Geology, Science and Research Branch, Islamic Azad University (IAU), Tehran, Iran

2 Professor, Department of Geology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran

3 Professor, Department of Geology, College of Science, University of Tehran, Tehran, Iran

4 Associate Professor, Exploration and Production Division, Research Institute of Petroleum Industry (RIPI), Tehran, Iran

5 Ph.D., Iranian Offshore Oil Company, Tehran, Iran


The Santonian – CampanianIlam Formation is one of the major reservoirs of Bangestan Group in the Zagros petroliferous basin. In the Siri Alvand Oilfield located in the Persian Gulf this formation with a total thickness of 130 m, consists of limestone. In this study, microfacies, depositional environments, diagenetic processes and sequence stratigraphy of the Ilam Formaton in Siri Alvand oilfield was studied. Based on thin sections studies, 8 microfacies and 4 facies associations were identified that  deposited in a homoclinal carbonate ramp environment. On the basis of petrographic studies, the main diagenetic processes affected these rocks include bioturbation, cementation, dissolution, dolomitization, stylolitization, pyritization and fracturing. The most important cement types in this formation are bladed calcite, fine equant calcite, drusy mosaic calcite, coarse blocky calcite and syntaxial calcite overgrowth. Sequence stratigraphic studies led to recognition of four third order depositional sequences in the Ilam Formation that all of them terminated to the type 1 sequence boundary. Finally, facies and diagenetic processes intensity were studied in each sequence.