زیست چینهنگاری و پالئواکولوژی سازند قم در ناحیه قهرود (جنوب کاشان)

Abstract

The Qom Formation in Ghohrud area, have been investigated in order to determine its biostratigraphy and palaeoecology. The thickness of Qom Formation is 325 meters at the study area and consists of thin, medium to thick bedded and massive limestons. They underline on Eocene volcanic with disconformably and its upper boundary is overlain by alluvium. Based on thin section studies 14 genera and 26 species of the benthic foraminifera was determined. The Assemblage of benthic foraminifera represents the Late Oligocene (Chattian) to Early Miocene (Aqitanian?) age. Large benthic foraminifera with thin hyaline wall such as large lepidocyclinidae and nummulitidae with symbiont bearing algae are present. This is due to increase in water depth, low energy, normal salinity and prevailing of a deeper open marine environment. In shallower open marine environment foraminifera’s wall (with hyaline wall) become thicker and smaller in size that represents decrease in water depth, and increase in light and energy. In this section in semi-restricted lagoon environment foraminifera with porcelaneous wall and foraminifera with hyaline wall are present together. In shallow water (restricted lagoon) foraminifera with porcelaneous wall such as Austrotirillina, Borellis, Miliolids and peneroplis are present, that reveals decrease of depth and increase light and salinity factors.