The lower part of the Late Cretaceous Tomalar Formation (Devrekani Basin, Central Pontides, northern Turkey) is characterized by the presence of light-green ribbon cherts and cherty mudstones (approximately 10 m thick) with abundant well-preserved Radiolaria. The presence and coexistence of such taxa as Acaeniotyle macrospina, Archaeospongoprunum salumi, Becus horridus, Cavaspongia euganea, Dactyliodiscus longispinus, Halesium sexangulum, Hexapyramis pantanellii, Pessagnobrachia irregularis, Pyramispongia glascockensis, Savaryella quadra, Vitorfus brustolensis, Novixitus dengoi, N. weyli, Phalangites telum and others clearly indicate the Cenomanian age. The Tomalar Formation covers the whole Upper Cretaceous due to the presence of Maastrichtian planktonic Foraminifera from the upper part of this formation. The radiolarian assemblage of the Tomalar Formation correlates well with the coeval fauna of the Western Mediterranean.