Fades analysis and carbonate ramp evolution of Oligo-Miocene Asmari Formation in the Gachsaran and Bibi-Hakimeh oilfields and the nearby Mish Anticline, Zagros Basin, Iran

摘要

A high-resolution well data in the Gachsaran and Bibi-Hakimeh oilfields and outcrops from nearby Mish Anticline, in the SE Dezful Embayment and the Izeh Zone of the Zagros Basin were used in this study to investigate facies and depositional settings of the Asmari Formation (Oligo-Miocene). The main skeletal constituents in the Asmari Formation include large benthic foraminifera, red algae, coral and planktonic foraminifera. Six foraminiferal assemblages have been distinguished and their palaeoenvironmental settings were suggested based on their position along the depositional profile as well as in comparison with published work. Six main facies have been distinguished, representing a shallowing upward cycles, including planktonic foraminifera dominated-facies, nummulitidae-lepidocyclinids facies, Nummulites facies, coral-coralline red algal facies, small benthic foraminifera facies and mudstone facies. Facies changes during the Rupelian- to Early Miocene are generally associated with carbonate ramp models. These including a number of distinct phases, namely: a Nummulites-dominated ramp with minor corals during the Rupelian, a nummulitidae and lepidocyclinids-dominated ramp during the Rupelian/Chattian, a coral- to algal-dominated ramp during the most of the Chattian and a dolomitized low angle benthic foraminifera-dominated ramp during Early Miocene.