Abstract: The Bantang pelitic dolomite in the Chaohu Lake area, Anhui, is widespread, with distinct upper and lower boundaries and markers. Its geological age varies from place to place and shows a southwestward-younging trend, which reflects that the boundaries of the lithostratigraphic units are oblique to those of the geological age. The place where the earliest Bantang pelitic dolomite was deposited is Bantang, characterized by the presence of more Early Cambrian Redlichia; while the place where the dolomite was deposited is Suosong, characterized by the occurrence of large amounts of Middle Cambrian ptychopariids such as Kunmingaspis, Ptychoparidae and Chittidilla. The regional distribution shows striking diachronism. Besides, there also appears a concurrent-range zone composed of Redlichia and Kunmingaspis in places. It extends laterally for about 27 m and vertically for about 2 m. The range of this zone is late Early Cambrian.