Document Type : Original Research
Department of Geology, Faculty of Basic Sciences, Sciences & Research Branch, Islamic Azad University, Tehran, Iran
Department of Geology, Faculty of Earth Science, Shahid Beheshti University, Tehran, Iran
Qom Formation with Oligo-Miocene age is the most important known hydrocarbon formation in Central Iran. The deposits of this formation in Band-Amir section in the northwest of Saveh have been studied in order to study stratigraphy, facies analysis and interpretation of sedimentary environments. The study area is located in the structural-sedimentary zone of Central Iran. The facies changes of the Qom Formation are so great that gypsum and gypsum-bearing marls are deposited when the sea level goes down and limestone and marl are left when the sea level rises. Thus, in many areas, the Qom Formation can be considered as a periodicity of marl and limestone along with gypsum and gypsum marl layers. This formation is located with a discontinuity on the lower red formation and also in a slope below the upper red formation. Due to the sedimentary environment of Qom Formation, the sequences of sediments in this formation have a significant diversity in terms of lithology and are of great importance in terms of reservoir rock, source rock and rock cover. The section of Qom Formation in the northwest of Saveh has a thickness of 198 meters. Extensive and detailed microscopic studies in Band-Amir section have led to the identification of various facies in the form of three facies groups related to the marine environments of the lagoon, dam and open sea. Wetland facies are made of rocks with Paxtonian and Waxtonian texture. Reef facies are of the coral bandstone type and have formed dam deposits. Offshore facies have the characteristics of turbidite facies and basin deposits. Absence of tidal facies and abundance of facies due to reef debris and turbidite deposits are the characteristics of Qom Formation in the study area. Investigation of lateral and vertical changes of facies shows that the deposits of Qom Formation in the studied section are deposited in a carbonate platform of marginal shelf type.