Deliberation of Cenomanian- Coniacian Boundary based on Biostratigraphic and Lithostratigraphic Studies in Bahregansar Field, Presian Gulf

I In order to investigate lithostratighraphical and biostratigraphical as well as determination of exact contact between the Sarvak and Ilam formations in oil well X-01 of Bahregansar field thin microscopic sections, final well reports and its illustrative diagram were studied. The Sarvak Formation with a thickness of 206 m overlies the black to dark-green marls of Kazhdomi Formation with a gradual contact. This formation can be divided into 2 members and consist mainly of dolomite and dolomitic limestone. The Ilam Formation is considered in a depth ranging from 2672 to 2678 m in the studied well based on studied section and is mainly formed of clay limestone and thin-bedded limestone. This formation is covered by Gurpi Formation with a gradual contact and has a disconformity contact with the Sarvak Formation.Moreover, the age of the Ilam Formation has been considered as Coniacian - Early Campanian which is formed of pelagic facies in the studied area. A number of 22 species belonging to 23 genera have been identified that 6 genera and 11 species belong to the Ilam Formation and 11 species of 17 genera belong to the Sarvak Formation. Considering the identified fauna in the Sarvak Formation, the three following biozones were identified conforming to biozones presented by Wind (1965):1-Nezzazata - Alveolinids Assemblage Zone # 25; 2-Rudist debris # 24;3-”Oligostegina”facies # 26. Presented biozones and principle of super position indicate Cenomanian age for the Sarvak Formation that consist of pelagic and neretic facies. Moreover, the age of the Ilam Formation has been considered as Coniacian - Early Campanian which is formed of pelagic facies in the studied area.