This research focusses on the biostratigraphy and paleoecological implications of the carbonatesof the Asmari Formation. The Asmari Formation is located in the Siah Kuhanticline of Izeh, Zagros Basin, SW Iran. It is of Late Oligocene (Chattian) - Early Miocene (Burdigalian) age. In this stratigraphic section, the Asmari Formation overlies the Pabdeh Formation and underlies the Gachsaran Formation. It consists of cream-colored limestone intercalated with marl. 182 thin sections were prepared and the benthic foraminifera distribution analyzed. Examination of large benthic foraminifera from the 228 m-thick Asmari Formation led to the identification of 3 biozones: the Lepidocyclina- Operculina- Ditrupa Assemblage Zone, Miogypsina-Elphidium sp. Assemblage Zone and the Borelis melocurdica- Meandropsina iranica Assemblage Zone.