Research ArticleECOLOGY

Extensive marine anoxia during the terminal Ediacaran Period

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Science Advances  20 Jun 2018:
Vol. 4, no. 6, eaan8983
DOI: 10.1126/sciadv.aan8983
  • Fig. 1 Reconstructed Ediacaran depositional environments on the Yangtze Craton with the location of the study sections and integrated lithostratigraphy and biostratigraphy of the terminal Ediacaran Dengying Formation, South China.

    (A) Simplified map showing the location of the Yangtze Block (31, 32). (B) Paleogeographic map of the Yangtze Block showing the location of the Wuhe section and the Gaojiashan section. (C) Simplified stratigraphic column of the Ediacaran Doushantuo and Dengying formations and the Early Cambrian Yanjiahe Formation (YJH), as well as the chronology for the evolution of major Ediacaran animal groups (15).

  • Fig. 2 Geochemical profiles of the terminal Ediacaran Dengying Formation at the Wuhe and Gaojiashan sections.

    Stratigraphic columns and δ13C data of Gaojiashan (GJS) are from Cui et al. (31). δ238U data from the Hamajing Member and samples with Mn/Sr > 2.5, Rb/Sr > 0.02, and Al > 0.35% are excluded in this plot, but they are shown in fig. S2. PC-C denotes Precambrian-Cambrian boundary. Red and black circles represent data from limestone samples and from dolostone samples, respectively.

  • Fig. 3 Model results.

    (A) The fraction of oceanic U inputs removed into anoxic/euxinic sediments (horizontal axis) varies as a function of the fractionation factor (Δanoxic; vertical axis) between seawater and anoxic/euxinic sediments. The estimates are based on calculations using the average carbonate δ238U of the Shibantan/Gaojiashan members (δ238U = −0.95‰). (B) Mass balance calculations show variations of seawater δ238U values as a function of anoxic seafloor area, keeping suboxic seafloor area fixed at 0% of total seafloor area and testing the sensitivity to possible Δanoxic values. In reality, suboxic seafloor area would co-vary with anoxic/euxinic seafloor area; thus, this modeling exercise gives us the lowest estimation of anoxic/euxinic seafloor area.

  • Fig. 4 Summary of global ocean redox chemistry in the Ediacaran and Early Cambrian periods.

    Data sources: 1, Fe-S-C systematics and redox-sensitive metal enrichments in euxinic shales from South China (14); 2, S and C isotopes in carbonates and siliciclastic rocks from Oman (16) and South China (15); 3, redox-sensitive metal enrichments and Mo-U isotopes in organic-rich shales from South China (14, 50, 52); 4, U isotopes in carbonates from South China (this study); 5, U isotopes in carbonates (this study), Mo isotopes in phosphorites (49), and redox-sensitive trace metal enrichments in euxinic shales from South China (14); 6, U isotopes in carbonates (this study). I to IV: Members I to IV of the Doushantuo Formation. The Ediacaran temporal distribution is modified after Laflamme et al. (3).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/6/eaan8983/DC1

    fig. S1. Simplified schematic representation of the major source and sinks of U in the modern ocean along with their isotopic compositions (sources) or associated isotopic fractionations (sinks) [modified after Tissot and Dauphas (54) and Wang et al. (55)].

    fig. S2. Geochemical profiles for the study sections.

    fig. S3. Petrographic images of the Hamajing Member.

    fig. S4. Petrographic images of the Shibantan Member.

    fig. S5. Petrographic images of the Baimatuo Member and the Yanjiahe Formation.

    fig. S6. Chemostratigraphic profiles of δ238U, Sr content, Mn content, Mn/Sr ratio, and δ18O for the study sections.

    fig. S7. Chemostratigraphic profiles of δ238U, Mn/(Mg + Ca) ratio, and Sr/(Mg + Ca) ratio for the study sections.

    fig. S8. Cross-plots of δ13C-δ18O for the study sections.

    fig. S9. Chemostratigraphic profiles of δ238U, Al content, Rb/Sr ratio, U/Al ratio, and Mg/Ca molar ratio for the study sections.

    fig. S10. Chemostratigraphic profiles of U and Mo concentrations, Ce anomalies, U/(Mg + Ca) ratio, and Mo/(Mg + Ca) ratio for the study sections.

    fig. S11. Mass balance modeling calculations show variations of seawater δ238U values as a function of anoxic/euxinic seafloor area while keeping Δanoxic constant (+0.6‰) and testing various suboxic areal extents.

    fig. S12. Calculated combination fanoxic and fsuboxic to account for latest Ediacaran seawater average δ238U of −0.95‰.

    table S1. The sample-dissolving procedure.

    table S2. Cross-correlation coefficients (R2) and P values calculated to test the influence of diagenetic indicators on δ238U (confidence interval, 95%).

    table S3. Summary of the parameters used in the modeling excise.

    database S1. δ238U data with associated geochemical data at the Wuhe section.

    database S2. δ238U data with associated geochemical data at the Gaojiashan section.

    database S3. Analytical results of standard summary (Wuhe measurements).

    database S4. Analytical results of standard summary (Wuhe measurements).

    References (54100)

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Simplified schematic representation of the major source and sinks of U in the modern ocean along with their isotopic compositions (sources) or associated isotopic fractionations (sinks) modified after Tissot and Dauphas (54) and Wang et al. (55).
    • fig. S2. Geochemical profiles for the study sections.
    • fig. S3. Petrographic images of the Hamajing Member.
    • fig. S4. Petrographic images of the Shibantan Member.
    • fig. S5. Petrographic images of the Baimatuo Member and the Yanjiahe Formation.
    • fig. S6. Chemostratigraphic profiles of δ238U, Sr content, Mn content, Mn/Sr ratio, and δ18O for the study sections.
    • fig. S7. Chemostratigraphic profiles of δ238U, Mn/(Mg + Ca) ratio, and Sr/(Mg + Ca) ratio for the study sections.
    • fig. S8. Cross-plots of δ13C-δ18O for the study sections.
    • fig. S9. Chemostratigraphic profiles of δ238U, Al content, Rb/Sr ratio, U/Al ratio, and Mg/Ca molar ratio for the study sections.
    • fig. S10. Chemostratigraphic profiles of U and Mo concentrations, Ce anomalies, U/(Mg + Ca) ratio, and Mo/(Mg + Ca) ratio for the study sections.
    • fig. S11. Mass balance modeling calculations show variations of seawater δ238U values as a function of anoxic/euxinic seafloor area while keeping Δanoxic constant (+0.6‰) and testing various suboxic areal extents.
    • fig. S12. Calculated combination fanoxic and fsuboxic to account for latest Ediacaran seawater average δ238U of −0.95‰.
    • table S1. The sample-dissolving procedure.
    • table S2. Cross-correlation coefficients (R2) and P values calculated to test the influence of diagenetic indicators on δ238U (confidence interval, 95%).
    • table S3. Summary of the parameters used in the modeling excise.
    • References (54–100)

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    Other Supplementary Material for this manuscript includes the following:

    • database S1 (Microsoft Excel format). δ238U data with associated geochemical data at the Wuhe section.
    • database S2 (Microsoft Excel format). δ238U data with associated geochemical data at the Gaojiashan section.
    • database S3 (Microsoft Excel format). Analytical results of standard summary (Wuhe measurements).
    • database S4 (Microsoft Excel format). Analytical results of standard summary (Wuhe measurements).

    Download Tables S1 to S8

    Files in this Data Supplement:

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