Abstract: There exists paleokarst unconformity on top of the Loushanguan Formation,western Hubei.Numerous marks of subaerial exposures and dissolution indicate that the generation of paleokarst surfaces was controlled by the sea level lowering event at the end of the Cambrian.They not only form the typical Ⅱ type sequence boundary of the carbonate platform,but also coincide with the Cambrian Ordovician chronostratigraphic boundary, the organic integration of sequence boundary,chronostratigraphic boundary and event boundary.