Constraints on the onset age of the Sturtian glaciation from the Southeast Yangtze Block, South China

Abstract

ABSTRACTThe Neoproterozoic glaciations represent a milestone in the Earth evolution due to their influence on atmosphere, biosphere and hydrosphere. Evidence for the Sturtian glaciation, the early stage of Cryogenian, has been recorded worldwide, but the precise timing and synchroneity of its counterpart, the Chang’an glaciation, in South China have been controversial. As such, new zircon U–Pb ages from the pre-Sturtian Gongdong Formation and the overlying the Chang’an Formation in southeastern Yangtze Block were reported. The youngest U–Pb zircon age from a tuff sample of the topmost Gongdong Formation was 716.8 ± 6.8 Ma, and that from a sandstone sample of the lower Chang’an Formation was 725.9 ± 4.4 Ma. The zircon weighted mean age of 716.8 ± 6.8 Ma was interpreted as the maximum depositional age of the termination of the Danzhou Group. This age, along with the ages reported from the bottom of the Danzhou Group, constrains deposition of the Danzhou Group to between ca. 820 Ma and ca. 715 Ma. The age of 716.8 ± 6.8 Ma from the top of the Gongdong Formation is consistent with the SIMS U-Pb age of 715.9 ± 2.8 Ma from the Sibao section, as well as ages from the Banxi Group, Liantuo Group, and Kaijianqiao Formation in the Yangtze Block, which further constrain the onset time of the Sturtian glaciation in South China at ca. 715 Ma. It is also, with uncertainties, consistent with ages from pre-Sturtian strata in Laurentia and Oman, which indicates a global synchroneity and extent for the Sturtian glaciation.