Pulsed oxidation and biological evolution in the Ediacaran Doushantuo Formation

doi:10.1073/pnas.0708336105

Pulsed oxidation and biological evolution in the Ediacaran Doushantuo Formation

*Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061;
^†Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;
^§Department of Geoscience, University of Nevada, Las Vegas, NV 89154;
^¶Department of Geology, University of Maryland, College Park, MD 20742; and
^‖State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China

Edited by Paul F. Hoffman, Harvard University, Cambridge, MA, and approved January 9, 2008 (received for review September 5, 2007)

Abstract

Recent geochemical data from Oman, Newfoundland, and the western United States suggest that long-term oxidation of Ediacaran oceans resulted in progressive depletion of a large dissolved organic carbon (DOC) reservoir and potentially triggered the radiation of acanthomorphic acritarchs, algae, macroscopic Ediacara organisms, and, subsequently, motile bilaterian animals. However, the hypothesized coupling between ocean oxidation and evolution is contingent on the reliability of continuous geochemical and paleontological data in individual sections and of intercontinental correlations. Here we report high-resolution geochemical data from the fossil-rich Doushantuo Formation (635–551 Ma) in South China that confirm trends from other broadly equivalent sections and highlight key features that have not been observed in most sections or have received little attention. First, samples from the lower Doushantuo Formation are characterized by remarkably stable δ¹³C_org (carbon isotope composition of organic carbon) values but variable δ³⁴S_CAS (sulfur isotope composition of carbonate-associated sulfate) values, which are consistent with a large isotopically buffered DOC reservoir and relatively low sulfate concentrations. Second, there are three profound negative δ¹³C_carb (carbon isotope composition of carbonate) excursions in the Ediacaran Period. The negative δ¹³C_carb excursions in the middle and upper Doushantuo Formation record pulsed oxidation of the deep oceanic DOC reservoir. The oxidation events appear to be coupled with eukaryote diversity in the Doushantuo basin. Comparison with other early Ediacaran basins suggests spatial heterogeneity of eukaryote distribution and redox conditions. We hypothesize that the distribution of early Ediacaran eukaryotes likely tracked redox conditions and that only after ≈551 Ma (when Ediacaran oceans were pervasively oxidized) did evolution of oxygen-requiring taxa reach global distribution.

Footnotes

^‡To whom correspondence may be addressed. E-mail: kaufman{at}geol.umd.edu, xlchu{at}mail.igcas.ac.cn, ganqing.jiang{at}unlv.edu, or xiao{at}vt.edu
Author contributions: X.C., G.J., A.J.K., and S.X. designed research; K.A.M., J.H., X.C., G.J., A.J.K., C.Z., X.Y., and S.X. performed research; X.C., G.J., A.J.K., and S.X. contributed new reagents/analytic tools; K.A.M., J.H., X.C., G.J., A.J.K., C.Z., X.Y., and S.X. analyzed data; and K.A.M., J.H., X.C., G.J., A.J.K., C.Z., X.Y., and S.X. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0708336105/DC1.