Biostratigraphy and palaeoecology of the Surgah Formation based on calcareous nannofossils in shah-Nakhjir section (south west Ilam)

Economically the Surgah Formation is the most significant in the Zagros sedimentary basin. In this study, the calcareous nannofossils have been investigated of the Surgah Formation from the Shah-nakhjir section. The thickness of the Surgah Formation is about 147 meters and composed of marly limestone deposits with diversity and well-preservation of calcareous nannofossil assemblages. In total, 41species belong to 22 genera were determinate and ultimately have compared with nannofossil standard zones. According to identified nannofossils, the age of the Middle Cenomanian- Middle Santonian corresponding to CC10- CC17 (Sissingh, 1977) includes Microrhabdulus decoratusZone (CC10), Quadrum gartneri Zone (CC11), Lucianorhabdus maleformis Zone (CC12), Marthasterites furcatus Zone (CC13), Micula decussataZone (CC14), Reinhardtites anthophorus Zone (CC15), Lucianorhabdus cayeuxii Zone (CC16), Calculites obscurus Zone (CC17) were suggested for the Surgah Formation in the studied section. Palaeoecological interpretations based on the identified species show warm climate and low depth conditions in low latitudes for deposits of the Surgah Formation in southwest of Ilam city (Shah-nakhjir section).