New constraints on the ages of neoproterozoic glaciations in south China

The most complete Neoproterozoic successions in south China contain three diamictite intervals in the Changan, Tiesiao, and Nantuo Formations. The youngest and most widespread Nantuo glacial deposit overlies the Datangpo Formation and underlies the fossil-rich Doushantuo Formation. Previous authors have correlated the Nantuo diamictite to either Sturtian or Marinoan glacial deposits elsewhere. Here we report sedimentary and delta(13)C chemostratigraphic data of the Doushantuo cap dolostone, which overlies the Nantuo Formation. Facies-dependent variation in delta(13)C is interpreted as evidence for spatial heterogeneity in delta(13)C and/or temporal diachroneity in the initiation of cap carbonate sedimentation. Sedimentary and chemostratigraphic data are indicative of a Marinoan age for the Nantuo glaciation. This inference is supported by a new U-Pb zircon age of 663 +/- 4 Ma from a tuffaceous bed in the Datangpo Formation. The new date and other isotopic ages from south China constrain the age of the Changan and Tiesiao glaciation(s) as between 761 +/- 8 Ma and 663 +/- 4 Ma, and the Nantuo glaciation as between 663 +/- 4 Ma and 599 +/- 4 Ma.