Biostratigraphy Study of Gurpi Formation in Poldokhtar Section (Kuh-Soltan Anticline) based on Calcareous Nannofossils

Calcareous nannofossils are suitable for biostratigarphical studies since they are abundant, planktonic, rapidly evolving and largely cosmopolitan, especially in the late Cretaceous. In this regards, 131 microscopic slides from shale and marl sediments of Gurpi formation of Poldokhtar section with thickness of 320 meters were collected. Out of this, 22 genera and 35 species were determined and their range chart is plotted. The distribution of nannofossil species indicates that there are 9 biozones in the study Poldokhtar section that can be separated, based on first occurrence (FO) of index species. They can be placed in CC18-CC26 of Sissingh (1977) time zones. On this basis, the age of sedimentation of this formation can be suggested to be from lower Companion to late Masstrichtian. In addition, presence of index species of low latitude in Poldokhtar section of Gurpi formation shows that this sedimentary basin was located in low latitude at the time of sedimentation.