title: Early Cambrian ocean anoxia in South China.
abstract: The cause of the most marked changes in the evolution of life, which define the first-order stratigraphic boundary between the Precambrian and the Phanerozoic eon, remains enigmatic and a highly topical subject of debate. A global ocean anoxic event, triggered by large-scale hydrogen sulphide (H(2)S) release to surface waters, has been suggested by Wille et al., on the basis of two data sets from South China and Oman, to explain the fundamental biological changes across the Precambrian/Cambrian (PC/C) boundary. Here we report a new precise SHRIMP U-Pb zircon age of 532.3 +/- 0.7 million years (Myr) ago (Fig. 1) for a volcanic ash bed in the critical unit that reflects the ocean anoxic event, the lowermost black shale sequence of the Niutitang Formation in the Guizhou Province, South China. This age is significantly younger than the precise PC/C boundary age of 542.0 +/- 0.3 Myr ago, approximately 10 Myr younger than the extinction of the Ediacaran fauna, and thus challenging the view of a major ocean anoxic event having been responsible for the major changes in the direction of evolution at the PC/C boundary.
authors.affiliation: State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing 210093, China. shyjiang@nju.edu.cn
authors.forename: Shao-Yong
authors.initials: SY
authors.lastname: Jiang
authors.forename: Dao-Hui
authors.initials: DH
authors.lastname: Pi
authors.forename: Christoph
authors.initials: C
authors.lastname: Heubeck
authors.forename: Hartwig
authors.initials: H
authors.lastname: Frimmel
authors.forename: Yu-Ping
authors.initials: YP
authors.lastname: Liu
authors.forename: Hai-Lin
authors.initials: HL
authors.lastname: Deng
authors.forename: Hong-Fei
authors.initials: HF
authors.lastname: Ling
authors.forename: Jing-Hong
authors.initials: JH
authors.lastname: Yang
mesh_terms: D005075:Biological Evolution; D002681:China; D049690:History, Ancient; D009792:Oceans and Seas; D010100:Oxygen / Q000032:analysis* / Q000378:metabolism*; D012623:Seawater / Q000737:chemistry*; D018707:Volcanic Eruptions
chemical_list: D010100:Oxygen