The Asmari Formation, north of the Gachsaran (Dill anticline), southwest Iran: facies analysis, depositional environments and sequence stratigraphy

The Asmari Formation is exposed at the Dill anticline in the Dezful Embayment of the Zagros foreland basin with 206 m thickness comprising thin, medium and thick to massive bedded carbonates. The Asmari Formation is Late Oligocene (Chattian)-Early Miocene (Burdigalian) in age at the study area. Ten facies characterizing upward gradual shallowing trend of an open marine (MF 1-3), shoal (MF 4), semi-restricted and restricted lagoon (MF 5-9) and near-shore lagoon (MF 10) depositional environments were identified. Based on environmental interpretations, a homoclinal ramp consisting of inner and middle parts prevails. MF 4-10 were characterized by the occurrence of large and small porcelaneous benthic foraminifera representing a shallow-water setting of an inner ramp influenced by wave and tide processes. MF 1-MF 3 with large and small hyaline benthic foraminifera represent a deeper fair water wave base of a middle ramp setting. Three-third-order depositional sequences were recognized. Sequence 1 mostly consists of an open marine to the lower part and is followed by semi to restricted lagoon facies. Sequences 2 and 3 are characterized by semi to restricted lagoon facies. Moreover, the relative sea-level change curves correlate with the global sea-level change curves.