Biostratigraphy, facies analysis and paleoecology of the Asmari Formation in the northwest of Behbahan, south-western Iran

Abstract

In this research, the biostratigraphy analysis, paleoecological interpretation and paleoenvironmental reconstruction of carbonate sediments of the Asmari Formation are based on the identified foraminiferal assemblages. The Asmari Formation was measured in the southern flank of Bangestan Anticline in north-western Behbahan (south-western Iran). Based on the foraminiferal assemblages, the Asmari Formation is late Oligocene–early Miocene (Aquitanian–Burdigalian) in age. Nine microfacies were identified and interpreted. These facies include: (1) anhydrite, (2) bioclastic mudstone, (3) peloidal wackestone–packstone, (4) mollusk packstone–grainstone, (5) bioclast imperforate foraminifera packstone–grainstone, (6) bioclast, bryozoa wackestone–packstone, (7) coral and corallinacea boundstone, (8) bioclast, foraminifera wackestone–packstone, and (9) ooid grainstone. The carbonate facies represent dominant marine conditions in a euphotic zone. The presence of non-skeletal grains such as ooids and peloids as well as the foraminifers and corals (Porites) indicates that the carbonate sediments of the Asmari Formation were deposited in a tropical to subtropical zone. Two third-order depositional sequences were recognized. These depositional sequences were separated by a type-2 sequence boundary. The faunal associations and the analyzed facies represent oligotrophic to mesotrophic conditions.