Considering the former and the recentprints of the 1/500.000 Scale Geological Maps of Turkey, an approximately 40 km(2) area between Seydiler, Agh town and Imranlar village located at the north of Kastamonu city in westhern Blacksea Region ispresented as orange colored Eoceneflysch in the former one while in the recent as unidentified Cuaternary. The same area is presented as Quaternary and Neogene in Tunoglu 1991a and 1991b. The unit spread out widely in this region is namedfor the first time as "Seydiler formation". The formation in question shows a paraconformable relation with Lutetian Gurleyikdere formation at the basement but an obvious hardground surface can be observed between them. At the top, it is overlaid by recent alluvival deposits and observed as errosional surfaces. Litostratigraphical and paleontological investigations were carried but on 184 samples collected from 7 measured stratigraphic sections that completes each other, whole rock analysis and related clay mineralogy and sandstone petrography examinations were realisedon labratory research levelfor litostratigraphy and paleontological observations were carried out particularly on planktic and benthic foraminifera, ostracoda, nannoplankton and dinoflagellate assemblages. Considering all together the present microfauna, the age of Seydiler formation is assigned as Late Lutetian-Bartonian. In addition to environment determinating characteristic of the ostacod fauna, taking in consideration the other microfauna and flora present, besides lithological aspects and theirfacies characteristics, the deposition of Seydiler Formation is thought to be occured in a marine environment and at depths changing from neritic to bathial under transgressive conditions.