In recent years, in Zhangxia-Gushan area of Changqing district, Yaowangshan Mountains region in Qingzhou County, and the Huangyangshan area in Laiwu City, the Cambrian-Ordovician boundary has been determined biostratigraphically, using the conodont fossil “Cordylodus lindstromi”, to be within the Chaomidian Formation, respectively at 9.05 m, 58.10 m, and 4.00 m below the top of the Chaomidian Formation. Thus, the Chaomidian Formation should be regarded as a lithostratigraphic unit that crosses the Cambrian-Ordovician boundary.