In this research, biostratigraphy and paleo-ecological reconstruction of the Qom Formation deposits in Bijegan village, northeast of Delijan, are discussed. The studied section is situated in the western margin of the Urumieh-Dokhtar magmatic arc (the intra-arc basin). The Qom Formation deposits at the studied area are Rupelian-Chattian in age. Larger benthic foraminifers are used for biostratigraphy with the occurrence of 14 genera and 16 species, which led to the identification of two faunal assemblages: 1 Nummulites vascus- N.fichteli, and 2. Lepidocyclina-Operculina-Ditrupa. Oligocene coral assemblages from the studied section are investigated with regard to its palaeoecological implications. These corals comprise four species of four genera and are compared with faunas from the Mediterranean Tethys and Indo-pacific Ocean, and they have an affinity to corals of the Mediterranean Tethys. Re-deposited branching Porites coral assemblages probably occurred in patchy dense frameworks which were destroyed during storm events and re-deposited in the present stratified horizons. The Porites-Faviidae assemblage represented a common feature of Oligocene coral faunas and increasing water energy.

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