This study investigates the boundary between the Upper Cretaceous Kometan (Turonian–Campanian) and Shiranish (Late Campanian–Maastrichtian) formations at the Sarchinar and Goizha surface sections in the Sulaymaniyah area, northeastern Iraq, in order to refine their biostratigraphic framework and reconstruct the depositional evolution across the formation boundary. The two formations are characterized by thin- to medium-bedded chalky and marly limestones overlain by blue to grey marls and marly limestones, which record a transition from outer-shelf to upper-bathyal ramp carbonates into deeper hemipelagic basinal deposits within the Zagros fold–thrust belt. A total of 100 rock samples were collected from the exposed successions and were prepared either as washed residues or standard thin sections, allowing for integrated analysis of planktonic foraminifera and microfacies. Planktonic foraminiferal biostratigraphy identifies five biozones within the Kometan and lower Shiranish formations: the Dicarinella primitiva Interval Zone, Dicarinella concavata Interval Zone, Dicarinella asymmetrica Total Range Zone, Globotruncanita elevata Total Range Zone in the uppermost Kometan, and the overlying Globotruncana aegyptiaca Interval Zone at the base of the Shiranish. The absence of the intervening Globotruncana ventricosa and Globotruncanella havanensis zones suggests a short intra-Campanian hiatus or condensed section at the Kometan–Shiranish transition. The combined stratigraphic and biostratigraphic data demonstrate that the contact is generally unconformable in the studied sections, thus providing a key reference for constraining the Late Cretaceous tectono-stratigraphic evolution of the northeastern Arabian Plate margin in Iraq.
