LA-ICP-MS U-Pb zircon age constraints on the termination of Sturtian glaciation and the onset of Marinoan glaciation in the Yangtze Block, South China

Radiometric dating of the Neoproterozoic Cryogenian glacial deposits is critical for constraining the duration of the Sturtian and Marinoan glaciations and understanding the evolution of the climatic, geochemical and biological events related to the ice ages. However, the termination of the Sturtian glaciation and the onset of the Marinoan glaciation remains controversial. Here we present new LA-ICP-MS U-Pb zircon age data from two tuff layers in the interglacial Datangpo Formation on shallow-water platform in the Yangtze Block, South China. The analyses of volcanogenic zircon yield U-Pb concordia ages of 660.1 ± 3.6 Ma and 651.3 ± 3.4 Ma for the two tuff layers are from the base and topmost part of the Datangpo Formation at one single section. The 660.1 ± 3.6 Ma age obtained from a 3-cm-thick tuff layer within the siltstone ca. 110 cm above the base of the Datangpo Formation. This new zircon U-Pb age is corresponded to those from previous studies well. The consistency indicates that globally synchronous termination of the Sturtian glaciation may have occurred before ~660 Ma. The age of 651.3 ± 3.4 Ma is from a 3-cm-thick tuff layer that is ca. 35-40 cm below the boundary between Marinoan glacialgenic diamictites and the non-glacial Datangpo Formation. This 651.3 ± 3.4 Ma age is well consistent with previously reported CA-ID-TIMS zircon U-Pb age of 651.69 ± 0.64 Ma from the Thorndike submember in Death Valley (USA). Our data can provide the maximum age (~651 Ma) constraint on the initiation of the Marinoan glaciation in South China. Additionally, the existing age of the radiometric age obtained in this study and previous cyclostratigraphic results demonstrate that the interglacial period in Cryogenian time might have lasted for at least 9 m.y. and the duration of the Marinoan glaciation is possibly <16 m.y. Keywords: U-Pb zircon age; Cryogenian chronostratigraphy; Sturtian glaciation; Marinoan glaciation; Datangpo Formation; South China