North of İstanbul, a thick Upper Cretaceous volcanic and volcanoclastic sequence of the Yemişliçay Group is nonconformably overlain by the neritic clastic and carbonate 2 sequence of the Zekeriyaköy Formation. This unit, either placed within the volcanic sequence or interpreted to overlie it, was studied near Zekeriyaköy for its larger foraminifera, previously recurrently referred to the Maastrichtian. The basal epiclastic sandstone beds of the Zekeriyaköy Formation immediately above the volcanic sequence contain Praesiderolites dordoniensis and rare rudist shells. The higher sandstone and limestone beds comprise assemblages of Lepidorbitoides campaniensis, Orbitoides megaloformis, Vanderbeekia catalana, Siderolites gr. calcitrapoides, Sirtina orbitoidiformis, Praestorrsella roestae, Lenticulina rotulata, Planorbulina (?) sp., agglutinated and rotaliid foraminifera, rudist fragments, bryozoans and red algae. Lepidorbitoides, the most abundant foraminifera in the studied material, has predominantly L. campaniensis-type embryons with a single auxiliary chamberlet, and rarely L. bisambergensis-type embryons, characterized by having two such chamberlets. The Praesiderolites dordoniensis-Lepidorbitoides campaniensis-Vanderbeekia catalana assemblages, recorded for the first time from Turkey, suggest a late Campanian age for the Zekeriyaköy Formation, with the implication that Late Cretaceous volcanism terminated in the İstanbul region during or prior to the late Campanian. The faunas show a great resemblance to those from the late Campanian type section at Aubeterre (SW France) and late Campanian fauna of Pyrenean Basin (N Spain), and correspond to the most eastern record of the European Faunal Province of the Tethys.