GIN: 0cm 0cm 0pt" class=MsoNormal>The base of the Middle Ordovician series and Dapingian has been defined at a point 10.57 m above the base of the Dawan Formation in the Huanghuachang section at Yichang, Hubei Province, South China by the first appearance of the conodont Baltoniodus? triangularis. The results of acritarch investigation into the Dawan Formation at the Huanghuachang and the nearby Daping sections indicates that based on their FADS, some of the acritarch taxa may be of biostratigraphical potential for recognition of the Lower-Middle Ordovician boundary.