Nannobiostratigraphic Study of Dokan Formation (Cenomanian) in the Kosrat Anticline, Northeastern Iraq

The Dokan Formation is distributed during the Cenomanian at northern and central Iraq. The research region is located in northeastern Iraqi's Kosrat anaticline, where the Dokan Formation is exposed at its southwestern flank. The formation is composed of marl, dolomitic limestone, and limestone, with interspersed chert nodules. The Qamchoqa Formation is documented to have an unconformable contact below the Dokan Formation, whereas the Kometan Formation is conformable at the top above Dokan Formation. We have determined 46 species of calcareous nannofossils belonging to 28 genus: Heterococcoliths: Chiastozygaceae (Ahmuellerella, Chiastozygus, Neocrepidolithus, Placozygus, Reinhardtites, Staurolithites, Tranolithus, Zeugrhabdotus), Eiffellithaceae (Eiffellithus), Biscutaceae (Biscutum), Prediscosphaeraceae (Petrarhabdus, Prediscosphaera), Cretarhabdaceae (Cretarhabdus, Retecapsa), Watznaueriaceae (Cyclagelosphaera, Watznaueria), Arkhangelskiellaceae (Arkhangelskiella, Broinsonia); Holococcoliths: Calyptrosphaeraceae (Calculites, Octolithus); Nannoliths: Microrhabdulaceae (Lithraphidites, Microrhabdulus), Polycyclolithaceae (Eprolithus, Lithastrinus, Micula, Quadrum, Uniplanarius), Schizosphaerellaceae (Ceratolithoides).We identified two nannobiozones, Eiffellithus turriseiffelii Interval Biozone (CC9) and Microrhabdulus decorates Interval Biozone (CC10). By comparing these biozones with those of other calcareous nannofossil biozones from local sections and regional countries, we identify that these fossils are of Cenomanian age.