Biostratigraphy, facies analysis and sequence stratigraphy of the Sachun Formation (Interior Fars, Zagros, SW of Iran)

Two sections of the Maastrichtian–Lower Eocene Sachun Formation, crossing Interior Fars zone, Zagros basin in SW Iran, were selected. To biostratigraphy, facies analysis, paleoenvironment and sequence stratigraphy, foraminifers and lithofacies were studied. Three foraminifer assemblage zones were observed in the studied areas. According to stratigraphic distribution of the identified foraminifers, the Sachun Formation is assigned to Upper Cretaceous (Maastrichtian)—Lower Eocene (Ypersian) age. The sedimentation of the Sachun Formation was controlled by the sea-level fluctuation. According to the sedimentary records, Sachun Formation has been deposited in a tectonically unstable basin. Microscopic investigation confirms the presence of seven microfacies, which can be grouped into four depositional environments: tidal flat, lagoon, shoal, and open marine. A carbonate shallow shelf is suggested for the depositional environment of the Sachun Formation, with the depth of sedimentary basin of the Sachun Formation decreasing from the study area to the south of Fars zone. Sachun Formation facies have been deposited in a shallow depositional basin characterized by permanent sea level changes. The vertical distribution of the investigated lithofacies supports two third-order cyclic sequences in the Sachun Formation, based on shallowing upward patterns in the determined lithofacies.