A belt of Upper Eocene-Lower Oligocene marine sedimentary rocks extends from Kiyikoy on the Black Sea coast to Pinarhisar in the Thrace Basin, suggesting a marine connection between the Black Sea and the Thrace Basin during this period. The Cenozoic succession of this marine corridor was studied in the vicinity of Kiyikoy along two measured stratigraphic sections. The sequence lies unconformably over metamorphic basement rocks and consists of similar to 75 m of bioclastic limestone and sandstone of the Sogucak Formation, overlain by similar to 40 m of limestone, marl, mudstone, sandstone, and acidic tuff, which are assigned to the newly defined Servez Formation. Larger benthic foraminifera indicate that the lower part of the succession is Late Eocene in age, and nannoplankton from the upper part of the succession suggest an Early Oligocene age; these age determinations are also supported by the Sr-isotope data. A U-Pb age from zircons from a tuff bed is 33.9 +/- 0.4 Ma, which falls on the Eocene-Oligocene boundary. The Kiyikoy Upper Eocene-Lower Oligocene sequence was deposited in shallow marine conditions below 50-m water depth. The depositional setting, as well as the relatively reduced thickness of the sequence, shows that any marine connection between the Black Sea and the Thrace Basin along the Kiyikoy-Pinarhisar corridor was not significant. The Late Eocene-Early Oligocene marine connection between the Black Sea and the Thrace Basin occurred along the Catalca gap southeast of Kiyikoy. In the Catalca gap the Upper Eocene-Lower Oligocene sequence is much thicker (350 m) and was deposited at much greater water depth.