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

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 delta(13)C 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. (C) 2004 Elsevier B.V. All rights reserved.