Pb?Pb ages of Neoproterozoic Doushantuo phosphorites in South China: constraints on early metazoan evolution and glaciation events

Abstract

The Pb–Pb isochron ages of 576±14 Ma for the upper part of the Upper Phosphorite Bed (UPB, this study) and 599±4 Ma for the lower part of the UPB [Earth Planet. Sci. Lett. 201 (2002) 203] in the Doushantuo Formation in the Weng’an area, South China, suggest that the deposition of the UPB lasted at least 5 Ma, and indicate that the observed microfossil assemblage (animal remains, multicellular algae, and giant process-bearing acritarchs) in the Doushantuo Formation predates all well-dated diverse Ediacaran assemblages and represents the earlier paleontological record of eukaryotes radiation on Earth. The 576±14 Ma age in the upper part of the UPB approximates the age of a negative δ13C excursion near the boundary between the Doushantuo and the overlying Dengying Formation if the Doushantuo–Dengying boundary at the Weng’an area is equivalent to that in the Yangtze Gorges area. This negative excursion might correlate to a post-Marinoan glaciation in South China, suggesting that the ice age following Doushantuo sediment deposition is younger than 590 Ma. The 599±4 Ma age in the lower part of the UPB [Earth Planet. Sci. Lett. 201 (2002) 203] represents the minimum age of the Nantuo diamictites, which are generally correlated with the Marinoan glaciation.