LITHOFACIES, DEPOSITIONAL ENVIRONMENTS, DIAGENESIS, AND RESERVOIR CHARACTERESTICS OF MIDDLE TO UPPER JURASSIC STRATA IN THE KOPET DAGH BASIN OF NORTHEASTERN IRAN

Three formations are recognized in the Middle to Upper Jurassic interval of the Kopet Dagh Basin of Iran. Upward they include: the Mozduran-1 Formation, the Chaman Bid Formation, and the Mozduran-2 Formation. Lithologically, they consist primarily of limestone and dolomite with abundant skeletal and non-skeletal particles. Regionally, the Chaman Bid Formation disappears in the eastern part of the basin where dominant lithofacies include dolomite, anhydrite, and siliciclastics.

Detailed analyses of microfacies and sedimentary structures indicate that the Mozdooran-1 and the Chaman Bid formations were deposited in deep waters, perhaps in an outer shelf environment. The Mozdooran-2 Formation, however, formed in a shallow, marginal sea setting. Sabkha, fluvial, and deltaic environments dominated the eastern part of the basin.

A depositional model for the area includes a shelf in the western part of the basin which included barrier islands, lagoonal, sabkha, and tidal flat environments toward the east. Sedimentation began during a major transgression by depositing the Mozdooran-1 Formation. The fine grained strata of the Chaman Bid Formation formed during the maximum deepening. The Mozdooran-2 Formation deposited during the regression.

Marine diagenesis was dominated by micritization, boring, and cementation. A strong meteoric diagenesis influenced the area resulting in grain dissolution, generation of moldic porosity, and cementation in vadose and phreatic meteoric environments. Passive margin burial diagenesis included compaction, stylolitization, and burial cementation. Post orogenic diagenesis caused oxidation, dedolomitization, fracturing, and compaction. Diagenesis destroyed the majority of pore space in the area. However, vuggy and intercrystalline porosity types still occur in the Mozdooran-2 Formation making it a suitable hydrocarbon reservoir in the region.