Lithostratigraphy and study of planktonic foraminifera of the Abderaz Formation at type section, Kopet-Dagh basin, IRAN

Abstract

AbstractIn order to study the fossil contents of the Abderaz Formation for biostratigraphical purposes the 300 meters thick section was sampled at type section. The sequence is mainly made up of grey shales and marls with two units of chalky limestone in upper part. The lower contact of the formation with Aitamir Formation is disconform while the upper contact with Abtalkh is continuous. There are huge amounts of inoceramids and ammonite. In the chalk limestone bonds of this formation which is belong to Santonian time planktonic, would exist some foraminifera with a less diversity because during the Santonian, the members of morphotype group three (M3) shows a regression in the above-mentioned section, with association of tegilla shapes decreases in the area and sea water. The study of the planktonic foraminifera in isolated form led to differentiate three morphotype groups. The first group is characterized by trochospiral tests usually indicate shallow waters, the second group contains forms with strong ornamentations and the primary keels representing mid waters and finally compact trochospiral tests with keels known as deep water indices are included in the third group. Studies on the morphotypes showed a regressive cycle for Abderaz Formation.