Stratigraphy, Microfacies, Paleoenvironments and Paleoecology of Asmari Formation (Oligocene- Miocene), Zagros Basin, Western Iran

The present work involves the study of the Asmari Formation from the viewpoint of the stratigraphy, microfacies, and depositional environment. The Khorramabad area, Zagros basin, west Iran, has been investigated for the first time. For this purpose, seventy-three samples were taken from the Shurab section. Eight microfacies have been identified in the Asmari Formation: Sandy wackestone (MF1), Peloidal Mudstone (MF2), Bioclastic milina Wackestone-Packstone (MF3), Bioclastic imperforate foraminifera Wackestone-Packstone (MF4), Coral boundstone (MF5), Bioclastic packstone - grainstone (MF6), Bioclastic imperforate foraminifera grainstone (MF7), Mudstone microfacies (MF8). Two benthic foraminiferal biozones were recognized, which are Archaias asparagus- Archaias Henson Assemblage Zone, which is restricted to Chattian, and the Eulepidina- Miogypsina Assemblage Zone, which is restricted to Aquitanian. The biostratigraphic correlation with other studies in and outside Iran, executed across the studied section, enveloping the Chattian to Aquitanian, divulges a progression in the biozone thickness, indicating a migration of the depositional center towards the northwest of the basin. The Asmari Formation is deposited from an outer ramp and open shelf lagoon and is defined as a tropical environment.