Study of main planktonic foraminifera(Turonian-Santonian) in Kopeh-Dagh sedimentary environment, NE Iran

In order to study the fossil contents of the Abderaz Formation for biostratigraphical purposes the ۵۰۰ 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. Fifty six species belonging to ۱۶ genera were identified and four biozones were differentiated. These are: Helvetoglobotruncana helvetica (Sigal)total range Zone, ۲-Marginotruncana sigali - Dicarinella primitiva (Premoli Silva and Sliter)Partial range Zone, ۳- Dicarinella concavata (Sigal)interval Zone and۴-Dicarinella asymetrica (Postuma)total range Zone. Based on, these an age of Turonian-Late Santonian is quoted to the formation. Also it was shown that Helvetoglobotruncana helvetica, the index species for middle Turonian exists at the base of the formation while, in the samples immediately below this belonging to Aitamir Formation Rotalipora appenninica, the index for middel cenomanian was recorded. Therefore, lack of index species for late Cenomanian- early Turonian shows a gap spanning this period between the Aitamir and Abderaz formations. This could be a result of sub Hersinian orogeny.

Keywords:

Abderaz Formation , Biostratigraphy , Biozone , Planktonic foraminifera , Sub Hersinian orogeny