Lower boundary age of the Nanhua System and the Gucheng glacial stage: Evidence from SHRIMPⅡ dating

In the newly revised Regional Chronostrati-graphic (Geochronologic) Scale of China, the original bipar-tite division of the Neoproterozoic is changed to tripartite division. The three 搒ystem?rank chronostratigraphic units are in ascending order of the Qingbaikou, Nanhua and Sin-ian Systems. This report presents SHRIMP zircon U-Pb dat-ing on volcanic tuffs from the candidate stratotype section of the Nanhua System at the Yangjiaping section that is geo-graphically located in Hupingshan Town, Shimen County, Hunan Province. Tuff from the upper part of the Xieshuihe Formation (equivalent to the Liantuo Formation) in the Lower Nanhua Series yields a zircon U-Pb age of 758 23 Ma, which may provide a constraint on the lower limit of the Gucheng glacial stage in the Nanhua System. Tuff from the Laoshanya Formation of its underlying Qingbaikou System (equivalent to the Banxi Group) gives a zircon U-Pb age of 809 16 Ma. The sampling locality lies 12 m from the upper boundary of the Qingbaikou System. According to the sedi-mentation rate it is estimated that the upper boundary age is about 800 Ma. The present studies also provide a resolution to the long-standing problems concerning stratigraphic cor-relation of the Late Precambrian in South China whether the Liantuo Formation is equivalent to the Banxi Group or not.