The Pontides forming the south-western continental margin of the Black Sea consist of two tectonic units, the Istanbul Zone in the west, and the Sakarya Zone in the central and eastern parts. The Sinop Basin in the Sakarya Zone is filled, from base to top, by Hauterivian to Albian turbidites, Cenomanian-Turonian red pelagic sediments, Turonian-Campanian magmatic-arc and related deposits, and by the uppermost Campanian to middle Eocene post-magmatic units developed on the southern passive margin of the Black Sea. Based on nannofossil, dinoflagellate, Foraminifera and Radiolaria data we describe the Kapanbogazi Formation, a Cenomanian-Turonian unit in the Sinop Basin, represented by red calcareous/siliceous pelagic shales, limestones and cherts passing gradually from the Albian black shales. These sediments possibly represent deepest depositional conditions of the basin during the Cenomanian-Turonian interval and also reflect the transition from an anoxic to an oxic palaeoenvironmental setting. The Istanbul Zone to the west was emerged during the deposition of the Kapanbogazi Formation in the Sakarya Zone.