The purpose of this study was to examine the geological, stratigraphic and organic geochemical features of the Küçükkuyu Formation outcropping on Biga Peninsula, NW Turkey. The Lower-Middle Miocene formation crops out around the Gulf of Edremit and near Bayramiç-Çan in the north of the Kazdağ Mountains. The unit is composed of shale, siltstone and sandstone intercalations. The shale is bituminous and represents a potential source rock in the region.Shale samples from the formation were investigated. Rock-Eval pyrolysis, vitrinite reflectance (Ro %), gas chromatography (GC), stable C isotope and total sulfur measurements were carried out. The shale is characterized by high total organic carbon (TOC) values (0.27 to 7.44 wt%, average 1.69 wt%), indicating a good potential source rock. The kerogen types are II and III, indicating the shale to be gas and oil-prone. T max values are between 352 and 453 °C, the average value suggesting early catagenesis. The pristane/ phytane (Pr/Ph) values reveal suboxic and anoxic environments. Carbon preference index (CPI) and C isotope values reveal terrestrial OM.Geological and stratigraphic evaluations and total sulfur (TS) figures indicate that the Küçükkuyu Formation was deposited in a suboxic-anoxic, freshwater environment (lacustrine), developing brackish water conditions from time to time.