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Geochemical evidence for widespread euxinia in the Later Cambrian ocean


Widespread anoxia in the ocean is frequently invoked as a primary driver of mass extinction as well as a long-term inhibitor of evolutionary radiation on early Earth. In recent biogeochemical studies it has been hypothesized that oxygen deficiency was widespread in subsurface water masses of later Cambrian oceans1,2, possibly influencing evolutionary events during this time1,2,3. Physical evidence of widespread anoxia in Cambrian oceans has remained elusive and thus its potential relationship to the palaeontological record remains largely unexplored. Here we present sulphur isotope records from six globally distributed stratigraphic sections of later Cambrian marine rocks (about 499 million years old). We find a positive sulphur isotope excursion in phase with the Steptoean Positive Carbon Isotope Excursion (SPICE), a large and rapid excursion in the marine carbon isotope record, which is thought to be indicative of a global carbon cycle perturbation4,5. Numerical box modelling of the paired carbon sulphur isotope data indicates that these isotope shifts reflect transient increases in the burial of organic carbon and pyrite sulphur in sediments deposited under large-scale anoxic and sulphidic (euxinic) conditions. Independently, molybdenum abundances in a coeval black shale point convincingly to the transient spread of anoxia. These results identify the SPICE interval as the best characterized ocean anoxic event in the pre-Mesozoic ocean and an extreme example of oxygen deficiency in the later Cambrian ocean. Thus, a redox structure similar to those in Proterozoic oceans6,7,8 may have persisted or returned in the oceans of the early Phanerozoic eon. Indeed, the environmental challenges presented by widespread anoxia may have been a prevalent if not dominant influence on animal evolution in Cambrian oceans.

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Figure 1: Palaeo-reconstruction of the later Cambrian Earth.
Figure 2: Chemostratigraphies of the SPICE carbonate stratigraphic sections.
Figure 3: Chemostratigraphy from the Andrarum no. 3 Core of the Alum Shale, Sweden (Baltica).
Figure 4: Examples of the modelled carbon and sulphur isotope composition of the ocean during the SPICE.


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NSF-EAR and NASA Astrobiology provided funding. Fieldwork and sample collection were aided by S. Bates, L. Bongers, H. Dayton, S. Mason, P. McGoldrick, J. Owens, C. Seeger and E. Starbuck. Sulphur isotope analyses were aided by S. Bates and W. Gilhooly. We thank P. Ahlberg and M. Eriksson for allowing access to the Andrarum no. 3 drill core. Discussions with G. Love, N. Hughes, D. Johnston, P. Cohen and T. Dahl improved the manuscript.

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Authors and Affiliations



B.C.G., T.W.L., M.R.S. and S.A.Y. collected samples used in this study. B.C.G. did the chemical analyses and collected mass spectrometer and ICP-MS data. B.C.G. and L.R.K. built the geochemical box model. B.C.G. wrote the manuscript, with contributions from T.W.L., A.H.K. and L.R.K. All the authors contributed to discussions and interpretations of the data.

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Correspondence to Benjamin C. Gill.

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The authors declare no competing financial interests.

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This file contains Supplementary Samples and Geological Settings, Supplementary Methods, additional references, Supplementary Tables 1-6 and Supplementary Figures 1-14 with legends. (PDF 2979 kb)

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Gill, B., Lyons, T., Young, S. et al. Geochemical evidence for widespread euxinia in the Later Cambrian ocean. Nature 469, 80–83 (2011).

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