Abstract: Şahinkaya Member, represented by reefal limestone, of Tonya Formation is first defined as Maastrihtian-Danian aged by Korkmaz (1983). Korkmaz1 s (1983) type locality for Şahinkaya Member was not standardized. Thus, Çalköy section is chosenfor a representative type locality in this study The bottom of Şahinkaya Member is constituted by nidist- bearing biosparite,which contains Orbitoides apiculatus Schlumberger and Siderolites calcitrapoides Lamarck. The same lithology is continuingwith miliolidea, algea bryzoa-bearing intraclast sparites and passing through Caskinolina sp., Gyroidina, sp., Gyroidina sp. Anomalina sp., miliolidea, algea and bryozoa-b earing algal biosparites. At the top level section, algea-bearing biospantescontains Idalina sinjarica Grimsdale, Miscellanea sp., algae, biyzoa, annelid tubes, echinoid spine and crinoids. This facie slocally contains iron-bearing sandy limestone beds. At the top level of this unit is consisting of Discocyclina seunesi Douville. The fossil fauna above indicate that the age of Şahinkaya Member is Maastrihtian-Thanetian. K/T transition in the Eastern Pontides with benthic fauna is first defined in this study.