The core from the drillinghole of Mao 206 in the Songliao Basin was obtained by the China Cretaceous Continental Scientific Drilling Project. The interval of the Qingshankou Formation is 497.02 meters long and is the material of present study. According to the biostratigraphic constrain, the authors suggest that the anoxic event might be happened in the Songliao Basin and corresponds to the marine oceanic anoxic event occurred at the Cenomanian-Turonian boundary. Based on both biostratigraphy and chemostratigraphy, the age of the Qing-shankou Formation should be Late Cenomanian to Turonian.