Biostratigraphy and microfacies of the Dariyan Formation in east of Gachsaran (Anneh anticline)

In this study, biostratigraphy, micofacies and sedimentary environment of Dariyan Formation in Anneh Anticline, near Hosein-Abad village (east of Gachsaran city) were investigated. Dariyan Formation at this study were consisted of 196 meters of thick, medium and thin layers of limestone, with orbitolinids, marl and marly limestone. The Daryian Formation is divided into the upper and lower parts, based on the existence of tongue with thin layer of limestone and laminated shale along with interlayer chert, with a large amount of radiolarids and planktonic foraminifera. In study area, Dariyan Formation conformably overlies the Gadvan Formation and is overlain by Kazhdumi Formation. A total of 114 thin sections were extracted from the study area and 22 benthonic foraminifera and 3 planktonic foraminifera have been identified in 4 biozones and 1 subzone: Praeorbitolina cormyi zone, Palorbitolinoides cf. orbiculata subzone, Hedbergella spp. Assemblage zone, Mesorbitolina texana zone, Mesorbitolina gr. subconcava zone. Based on identified zones in the study section, the age of Dariyan Formation is designated between Early Aptian to Albian. Sedimentary environment study of Dariyan Formation in Anneh Anticline led to identification of 9 microfacies related to open marine and lagoon. Due to the lack of a barrier facies, slumping and storm deposits, lump and grapston, an open shelf sedimentary environment was suggested for deposition of the Dariyan Formation in Anneh anticline.