Research progress on the chronostratigraphic study of Nanhua System in South China.

The Nanhuan system in South China correlates with the Cryogenian, depositional age of which remains disputed. In the past decade, key depositional age points of the Nanhuan system have been ascertained by means of high precision zircon U-Pb geochronology. The basal Chang’an Formation is constrained to be ca. 717 Ma, whereas the top Liantuo Formation is constrained to be ca. 714 Ma. Glacial retreat during the middle Chang’an glacial period is constrained to be ca. 690 Ma, and the final glacial retreat for the Chang’an glacial period is constrained to be ca. 659 Ma. In combination with radiometric ages reported from other worldwide regions, the initiation and termination age of the Sturtian glaciation is constrained to be ca. 717-659 Ma. The onset and termination ages of Nantuo glaciation are roughly constrained to be ca. 649 Ma and ca. 635 Ma, respectively. In combination with radiometric ages reported from other worldwide areas, the onset age of the Marinoan glaciation can be constrained to be ca. 649-639 Ma. With ongoing work in future, age span for the initiation of Marinoan glaciation can be further shortened. Precisely dating the depositional age of the Nanhua System in South China will aid us in understanding the global geological and biological events during the glaciation. The duration of Marinoan glaciation is constrained to be ca. 14 Myr, which is much shorter than that of the Sturtian glaciation (ca. 58 Myr). Large-scale magmatism in the end of glaciation is the main reason that induced the difference in the time span of these two glaciations. By means of calculation and climate modelling, we found that magmatism in the northern Yangtze Block can foreshorten the Marinoan glaciation to 2-5 Myr.