Analysis of the Qom Formation microfacies and controlling factors on their deposition, Varkan area (Southwest of Kshan), Sanandaj-Sirjan fore arc basin

The Qom Formation in southwest Kashan in Sanandaj-Sirjan fore arc basin has a thickness of 190 meters and is composed of medium to thick and massive bedded limestone، marly limestone، sandy limestone، marl and coglomerates. Study of these deposits led to recognition of nine microfacies related to a carbonate platform. The high presence of perforate foraminifera in most of the recognized microfacies، the absence of lagoonal and near-coast microfacies indicate that the study section deposited in open marine with normal salinity. In addition، abundant of larger benthic foraminifera، corallinacea red alga and patch-reef indicate that deposition took place in tropical warm water. Abundance of Neorotalia is indicator of abundant nutrient، which causes to incrteases water turbidity. This in turn prevents the growth of continues coral and real reef.