The Cebecikoy Limestone from the Variscan flysch of the Istanbul Terrane is assigned to the foraminiferal MFZ11 zone (late early Visean, formerly V2a). This zone is essentially the range zone of Uralodiscus rotundus. Additional bioevents are proposed for characterizing the upper part of this biozone (MFZ11B subzone): the LAD of Eoendothyranopsis and the FAD of Pararchaediscus and Conilidiscus. The majority of foraminifers and algae, belonging locally to MFZ11 are well-known, except for the following taxa: Issinella luteotubulifomis sp. nov., I. enormis sp. nov., Vicinesphaera parasqualida sp. nov., Planogloboendothyra modesta sp. nov. and Endothyra irinaeformis sp. nov. The Istanbul Terrane is connected with the southern branch of the Palaeotethys, whereas the Zonguldak Terrane is connected with the northern branch of this one.