پالئواکولوژی و اجتماعات کربناته سازند قم در منطقه چنار (شمال غرب کاشان)

Abstract

In This study, large benthic foraminifera of Qom Formation in Chenar area (northwestern Kashan) with 147 m thickness are investigated. 112 thin sections were prepared and distribution of benthic foraminifera was analyzed to reconstruct paleoenvironmental condition. Sea level fluctuations could be observed from bottom to top in the studied section. Based on large benthic foraminifera assemblages and microfacies features, three major depositional environments (inner shelf, middle shelf & outer shelf) were defined. The inner shelf facies is characterized by wackstone-packstone, dominated by miliolid and small perforate foraminifera. The middle shelf facies is represented by packstone-grainstone with diverse assemblage of large perforate benthic foraminifera. Outer shelf facies is dominated by large perforate benthic foraminifera as well as planktonic foraminifera. The distribution of the Oligocene large benthic foraminifera in the studied area indicates that shallow marine carbonate sediments of the Qom Formation were deposited in a photic zone of tropical to sub-tropical environments.