This investigation is concentrated on biostratigraphy, facies distribution, palaeoecology and palaeoenvironment of the Asmari Formation with 276m in thickness on oil field of Aghajari (well #66) with an anticlinal structure, in the fold–thrust zone of the Zagros Baisn in southwest of Iran. According to the lithology properties, four lithostratigraphic units were recognized, dolomitic limestone, sandy limestone, dolomitic and marly limestone are predominant. The Asmari carbonate system was dominated by foraminifera and corallinacean assemblage. 24 genera, 15 species were encountered in the studied area and 4 assemblage zones have been recognized. Based on distribution of the larger foraminifera, the Asmari Formation is Late Oligocene (Rupelian - Chattian) -Early Miocene (Aquitania and Burdigalian) in age. Based on petrographical studies of 320 thin sections, 12 carbonate microfacies were identified within the Asmari Formation. These microfacies belong to inner ramp, shoal and middle ramp environments. As a result of this study, the Asmari Formation deposited in tropical waters and oligotrophic to slightly mesotrophic conditions. Our itemized analysis of microfacies and paleoecology display that the Asmari Formation deposited on a carbonate shelf dominated by heterozoan and subordinately, photozoan skeletal assemblage.
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