ON THE CHAOMIDIAN FORMATION OF THE JIULONG GROUP IN SHANDONG PROVINCE

The Cambrian-Ordovician in Shandong Province has been determined on basis of trilobite and nautiloid biozones. However, due to lack of these biozone fossils in strata near Cambrian-Ordovician boundary at many sections, this important chronostratigraphic boundary is placed lithostratigraphically at base of Member b of Sanshanzi Formation. At Fanzhuang section in Gushan, Changqing district, this boundary is placed lithostratigraphically at top of Chaomidian Formation. As such, Chaomidian Formation is regarded as the topmost lithostratigraphic unit of upper Cambrian System. In recent years, in Zhangxia-Gushan area of Changqing district, Yaowangshan mountains region in Qingzhou county, and Huangyangshan area in Laiwu city, Cambrian-Ordovician boundary has been determined biostratigraphically, using conodont fossil cordylodus lindstromi, to be within Chaomidian Formation, respectively at 9.05 m, 58.10 m, and 4.00 m below top of Chaomidian Formation. Thus, Chaomidian Formation should be regarded as a lithostratigraphic unit that crosses Cambrian-Ordovician boundary.