Research ArticleGEOCHEMISTRY

Constraining the rate of oceanic deoxygenation leading up to a Cretaceous Oceanic Anoxic Event (OAE-2: ~94 Ma)

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Science Advances  09 Aug 2017:
Vol. 3, no. 8, e1701020
DOI: 10.1126/sciadv.1701020
  • Fig. 1 Geochemical profile of ODP Site 1258 from Demerara Rise.

    (A) Spliced section analyzed for this study. OAE-2 is identified by the area in gray, as delineated by the carbon isotope excursion (33), and the shaded yellow region represents the onset of the Tl isotope shift. Vanadium concentrations are from previous studies (15, 37). (B) Zoomed-in view of the profile immediately preceding OAE-2, highlighting the timing between the Tl isotope shift and disturbance of the global C cycle. Error bars represent 2-SD uncertainty of multiple sample analyses or the long-term reproducibility of SCO-1, whichever is greater.

  • Fig. 2 The modeled decrease in Mn oxide burial associated with the Tl isotope shift from this study.

    Percentage of Mn oxide drawdown is calculated using the range of reported values for Tl isotope fractionation during incorporation into altered oceanic crust (AOC) and Mn oxides (MnOx) (inset boxes) (28). This yields a range of drawdown between 40 and 80% during OAE-2 (see the Supplementary Materials).

  • Fig. 3 Temporal constraints for pre–OAE-2 trigger mechanisms and changes in oceanic redox.

    All estimates are derived from constant sedimentation rates for ODP Site 1258 and depend on an estimate for the duration of OAE-2 of 600 ky (see the Supplementary Materials). LIP activity time constraints are from Os isotope data (10, 11). The expanded marine deoxygenation estimate is based on the drawdown of the oceanic V reservoir (15, 37), and the expansion of anoxic sedimentation estimate comes from this study (see the Supplementary Materials for more information). Error bars represent the difference between upper and lower time estimates, as explained in the Supplementary Materials.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/8/e1701020/DC1

    Supplementary Text

    fig. S1. Paleogeographic locations of the sites analyzed in this study during the Cenomanian-Turonian boundary Anoxic Event (OAE-2: ~94 Ma).

    fig. S2. Geochemical data from interbedded shales of the Furlo section in Central Italy.

    fig. S3. Tl isotope composition of the authigenic fraction alongside that of the detrital fraction to show similarity.

    table S1. Tl isotope and concentration data.

    table S2. Reproducibility of Tl isotope composition with one column versus two columns.

    table S3. Reproducibility of USGS shale standard SCO-1.

    References (4650)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Text
    • fig. S1. Paleogeographic locations of the sites analyzed in this study during the Cenomanian-Turonian boundary Anoxic Event (OAE-2: ~94 Ma).
    • fig. S2. Geochemical data from interbedded shales of the Furlo section in Central Italy.
    • fig. S3. Tl isotope composition of the authigenic fraction alongside that of the detrital fraction to show similarity.
    • table S1. Tl isotope and concentration data.
    • table S2. Reproducibility of Tl isotope composition with one column versus two columns.
    • table S3. Reproducibility of USGS shale standard SCO-1.
    • References (46–50)

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