Biostratigraphy and Sedimentary Environment of the Qom Formation in Talenkuh Section in Southwest of Semnan

The Qom Formation in Talenkuh section with 605 meters thick is located 50 kilometers west of Semnan and includes six rock units which mainly consists of limestone, alternating of limestone and marl, marl, marly limestone, and gypsum. Lower boundary of the Qom Formation in this section with Lower red Formation is unconformable and its upper boundary is missing by faulting or erosion. By biostratigraphic studies, 34 genera and 18 species of benthic foraminifera were identified. Three assemblages have been recognized by distribution of these benthic foraminifera in the studied section that indicate Chattian? – Burdigalian age. Field evidences and petrographic studies together with microfacies analysis, led to recognition 1 conglomerate lithofacies, 1 evaporite facies and 10 microfacies that deposited in 5 sedimentary environments consists of: supratidal, tidal flat, lagoon, shoal and shallow open marine. Therefore, for the Talenkuh section, a carbonate platform in the homoclinal ramp has been suggested.