Late cretaceous foraminifera from the Kurdistan region, NE Iraq: palaeontological, biostratigraphical and palaeoenvironmental significance

The early Turonian-early Maastrichtian planktonic and benthonic foraminiferal faunas of the Kurdistan region, NE Iraq are evaluated. Some 93 planktonic foraminifera (24 species of the family Heterohelicidae are described in detail) from the Kometan and Shiranish formations, and 115 benthonic foraminifera from the Shiranish Formation are identified and illustrated. The fauna reveals new and important data bearing on the palaeontological, biostratigraphical and palaeoenvironmental significance of the Late Cretaceous successions in the Kurdistan region, NE Iraq. Based on the planktonic foraminiferal assemblages, nine biozones and two subzones spanning the early Turonian to late early Maastrichtian were identified. Sequential changes in planktonic foraminiferal assemblages map discrete intervals within the Kometan and Shiranish formations that suggest dominantly warm, nutrient-poor marine surface and near-surface conditions during the mid-Turonian to late Coniacian, latest Santonian, and late Campanian, and cooler more nutrient-rich surface and near-surface waters in the early Turonian, early to late Santonian, early Campanian and early Maastrichtian. Species of the benthonic foraminiferal genus Bolivinoides provide a refined biostratigraphic biozonation for the late Campanian to early Maastrichtian Shiranish Formation in the Kurdistan region, NE Iraq. Three biozones and two subzones are identified for the first time in Iraq: the Bolivinoides decoratus biozone (late Campanian) subdivided into a lower B. decoratus subzone and an upper B. laevigatus subzone; the B. miliaris biozone (earliest Maastrichtian); and the B. draco biozone (late early Maastrichtian). Combined, the Bolivinoides and planktonic foraminiferal biostratigraphy enables the informal recognition of lower and upper intervals within both the Globotruncana aegyptiaca and Gansserina gansseri planktonic foraminifer biozones that may be important for a more refined inter-regional correlation in the Middle East and North Africa. The new Bolivinoides biozonation precisely locates the Campanian-Maastrichtian boundary in NE Iraq. The benthonic foraminiferal assemblages are interpreted as representing outer shelf to middle slope environments, between ca 200 m to at least 600 m water depth, with maximum water depths in the late Campanian, followed by shallowing into the early Maastrichtian. The most likely control mechanism for the shallowing of sea level is the beginning of southern Neo-Tethys Ocean closure at this time.