Facies analysis and sequence stratigraphy of the Asmari Formation in the northern area of Dezful Embayment, south-west Iran

Abstract

This paper concerns the sequence stratigraphy of the Oligocene (Rupelian–Chattian)–Early Miocene (Burdigalian) Asmari Formation based on microfacies analysis of the sediments in the Ghale Nar Oilfield, central area of Zagros fold-thrust belt. Fourteen facies types typical for upward shallowing trend from open marine (MF 1–3), to shoal (MF 4-5), semi-restricted and restricted lagoon (MF 6–12) and finally to near-shore lagoon (MF 13-14) depositional environments were identified. Based on the environmental interpretations, we reconstructed a homoclinal ramp mainly represented by its inner and middle sectors. Facies types MF 4–14 are 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. MF1 (Pabdeh Formation), and 2 -3 with planktonic, large and small hyaline benthic foraminifera represent between FWWB and SWB. Four third-order depositional sequences were recognized. In this study, in order to better correlate the identified sequences with pre-defined sequences of the Asmari Formation in the Dezful Embayment and the Izeh zone that are chronologically well-defined, we use their number instead of their name. Sequence 2 mainly consists of an open marine environment in the base, followed by semi-restricted to restricted lagoonal facies. Sequences 36 are characterized by semi-restricted to restricted lagoonal facies. Moreover, the regional relative sea-level change curves correlate well with the global sea-level change curves.