Abstract: In the Armutlu Peninsula, the aim of the investigation made in the ragion between Karamürsel and Lake İznik, is to detemmne the relation between the Cretaceous and Pateoeene units interms of rock specifications and fossil groups, and to bring classification to the subject by comparingthe results with regional data. Merdigöz formation and Dereköy formation which overlies It comformably are the metamorphie units making up the basement of the Pre-Permian of the region.Kokarca formation, which is unconformable on this basement, and is made of rocks as iitMc arenite, biomicrite and clayey biomicrite is the sedimentary product of a sea which is getting deepertowards end of Upper Cretaceous (Maastrichtian). This unit is graded transitional with Lower-UpperPaleocene (Bam&n-Thanetian) aged Yağhane limestone which overlies it conformably and consist .ofrocks as calcisiltite, biomicrite, clayey biomicrite, sandy biosparite and biosparite. Yağhane limestone is a product of a sea which gets shallower gradually. Kokarca formation and Yağhane limestone is covered nonconformably by Kizderbent andésite lying in east-west direction.