Document Type : Original Article
Department of Construction and Mineral Engineering, Technology and Engineering Research Center, Standard Research Institute (SRI), Karaj, Iran
Assistant professor Department of Remot sensing. Dezful Branch Islamic Azad University, Dezful, Iran
In order to study the biostratigraphy, and depositional environment of Gadvan and Dariyan formations in wells A and B, Gachsaran oil fields, a large number of microscopic thin sections have been studied. This oil field is located 220 km southeast of Ahvaz city. In this study, the Gadvan formation consists of three sections: lower shale, khalij limestone, and upper shale, and in both studied sections, the Kazhdami formation is disconformity placed on the Dariyan formation. The border between Gadvan and Dariyan formations is disconformity. In the studied field, the following biological zones were identified for Gadvan and Dariyan Formations, which include the following:1) Choffatella decipiens - Pseudocyclammina littus -Trocholina elogatus Assemblage Zone, 2) Mesorbitolina texana - Choffatella decipiens Assemblage Zone. Based on biostratigraphy data, the age of the former Aptian Gadvan and late Dariyan Aptian Formations was considered. Microfacies study of the Dariyan and Gadvan led to recognition of 6 microfacies in 3 facies belt inclusive, Inner ramp, Mid-ramp, Outer ramp. Microfacies interpretation which is done based on the fauna mainly indicates ramp environment. Also uniform variation of microfacies and absence of rim and buildup faunas predicted as hemoclinical carbonate ramp.