Qingbaikouan and Crygenian in South China: Constraints by SHRIMP Zircon U-Pb dating

The Qingbaikouan System is the lowest unit of the Neoproterozoic Erathem in Chinese stratigraphic succession, and it now provides a precise geochronological framework and geological time scale for mapping and stratal correlation in China. However, a sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon age date (1368 +/- 12 Ma) obtained from a bentonite in the Qingbaikouan Xiamaling Formation indicates that it belongs to the Mesoproterozoic Erathem instead. This change is a milestone in understanding the Precambrian Stratigraphic Time Scale in China, and it has had great influence on Precambrian correlations in Asia. Otherwise, a large amount of geochronological work has been done in the Jiangnan Orogen Belt of South China, and new isotopic data have redefined the traditional recognition of metamorphosed Mesoproterozoic strata from the Sibao orogeny to the Neoproterozoic Erathem. Based on SHRIMP zircon U-Pb age data, the authors regard the Sibao orogeny (equal to the Willing orogeny) as a movement at ca 820 Ma, meaning that the Sibao orogeny was not equivalent to the Grenvillian orogeny. Finally, we report here the first SHRIMP U-Pb age of the boundary between the top of the Qingbaikouan Gongdong Formation (786.8 +/- 5.6 Ma) and the bottom of the Chang'an (diamictite) Formation (778.4 +/- 5.2 Ma), which is the age of the lowest diamictite of the Nanhuan System in China.