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

Abstract

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.