Paleoecology, Microfacies and Depositional Environment of Surgah Formation based on Planktonic Foraminifera in Pol-e-Dokhtar district of Lorestan Province

In this research, paleoecology and depositional environment of Surgah Formation at the Maleh Kuh section have been investigated. The thickness of Surgah Formation is 82 meters and consists of argillaceous limestone, calcareous shales with intercalated limestones. Based on the planktonic foraminifera, the age of Surgah Formation at the study area is late middle Turonian to Early Santonian. Statistical studies of the morphotype groups of Epicantinental Sea Forms (ESF), Shallow Water Forms (SWF) and Deep Water Forms (DWF) show that these foraminifera are related to DWF, which indicate specific condition of oligotrophic. Also high planktonic/benthic foraminifera ratio confirms the semi deep to deep marine condition of sedimentary environment. The salinity as an ecological parameter in the section was changed to very low amount at the Late Turonian-Early Santonian based on abundance of Muricohedbergella and Whiteinella. Finally, four mirofacies have been identified based on stratigraphic and biostratigraphy position of planktonic foraminifera which formed in the semi deep to deep open marine. This microfacies belongs to the outer ramp of a carbonate platform.