Contribution to the Biostratigraphy and Microfacies Analysis of the OAE2 from the Kurdistan Region (NE Iraq)

The Cenomanian/Turonian Boundary sediments of the Gulneri Formation are characterized by a 1.5 m thick organic-rich calcareous black shale that can potentially represent the lithostratigraphic expression of the global Ocean Anoxic Event 2 (OAE2). It is bounded by double unconformities, with the underlying dolomitic limestone of the Cenomanian Dokan Formation and with the overlying white-weathered, thinly bedded limestone of the Turonian Kometan Formation. The high-resolution planktic foraminiferal biostratigraphic investigation of the Gulneri Formation reveals three main biozones: Whiteinella archaeocretacea Partial-Range Zone, Helvetoglobotruncana helvetica Taxon-Range Zone, and Dicarinella primitiva-Marginotruncana sigali Interval Zone that constrains it from Latest Cenomanian to late Turonian in age. The characteristics of the planktic foraminiferal lime mudstone, wackestone, and packstone microfacies suggest that the Gulneri Formation was deposited in an euxinic, stagnant, open marine environment of the middle shelf. The occurrence of fish detritus, the increased abundance of the low-oxygen tolerant species belonging to the Heterohelix genus, surface dweller Muricohedbergella, and the disaster opportunist Guembelitria cenomana all indicate that the organic-rich calcareous black shale of the Gulneri Formation is correlated with the OAE2 that is observed widely across the Tethys realm.