Microfacies and depositional environments of the Qom Formation in Barzok area, SW Kashan, Iran

Abstract

Qom Formation (Oligo-Miocene marine deposits of Middle Iran) in the southwestern Kashan was studied to determine its microfacies and depositional environments. Outcrops of the Qom Formation in the study area with 410 m, consist mainly of limestone, sandy limestone, shale and marl. Study section is unconformably underlain by the Eocene volcanic rocks and overlain by alluvium. Biogenic components of the Qom Formation comprise mainly of larger benthic foraminifera, coralline red algae and corals. Based on the presence of Nummulites spp. (Nummulites fichteli, Nummulites vascus, Nummulites cf. vascus, Nummulites sp.) throughout the study section, the Qom Formation is considered to be Rupelian in age. Microfacies analysis and field investigations on the study section led to recognition of six carbonate microfacies and two marl and shale facies. Two major depositional environments were identified in the study area including lagoon and open marine. Based on the recognized microfacies and field investigations, deposition of the Qom Formation in Barzok area took place on a carbonate ramp; besides, most of the carbonate parts of the study section are deposited in the open-marine settings. The high abundance of larger benthic foraminifera, coralline red algae and corals indicates that deposition took place in the tropical warm waters.