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  • 207-1258A; 207-1258B; 207-1258C; AGE; Carbon, organic, total; Chromium; Depth, composite; DRILL; Drilling/drill rig; Event label; Fraction; ICP-MS, Agilent 7500-ce; Joides Resolution; Leg207; Molybdenum; Ocean Drilling Program; ODP; Sample code/label; South Atlantic Ocean; Titanium; δ53Cr  (1)
  • Bahamas  (1)
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  • 1
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    Unknown
    PANGAEA
    In:  Supplement to: Wang, Xiangli; Reinhard, Christopher T; Planavsky, Noah J; Owens, Jeremy D; Lyons, Timothy W; Johnson, Thomas M (2016): Sedimentary chromium isotopic compositions across the Cretaceous OAE2 at Demerara Rise Site 1258. Chemical Geology, 429, 85-92, https://doi.org/10.1016/j.chemgeo.2016.03.006
    Publication Date: 2024-01-09
    Description: In order to advance our understanding of the emerging chromium (Cr) isotope system as a paleoredox proxy, we measured the 53Cr/52Cr of black shales deposited before, during, and after Cretaceous Oceanic Anoxic Event 2 (OAE2). We observed a 〉 1 per mil coherent negative 53Cr/52Cr excursion and significant drawdown in Cr enrichments during OAE2 coincident with a large positive carbon isotope excursion. Our observed negative 53Cr/52Cr excursion during OAE2 is most easily linked to an increase in the ratio of euxinic to reducing conditions. Additional work on other OAE sections is needed to determine the spatial significance of this Cr isotope trend.
    Keywords: 207-1258A; 207-1258B; 207-1258C; AGE; Carbon, organic, total; Chromium; Depth, composite; DRILL; Drilling/drill rig; Event label; Fraction; ICP-MS, Agilent 7500-ce; Joides Resolution; Leg207; Molybdenum; Ocean Drilling Program; ODP; Sample code/label; South Atlantic Ocean; Titanium; δ53Cr
    Type: Dataset
    Format: text/tab-separated-values, 261 data points
    Location Call Number Limitation Availability
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  • 2
    Publication Date: 2022-05-25
    Description: © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 463 (2017): 159-170, doi:10.1016/j.epsl.2017.01.032.
    Description: The Proterozoic Eon hosted the emergence and initial recorded diversification of eukaryotes. Oxygen levels in the shallow marine settings critical to these events were lower than today’s, although how much lower is debated. Here, we use concentrations of iodate (the oxidized iodine species) in shallow-marine limestones and dolostones to generate the first comprehensive record of Proterozoic near-surface marine redox conditions. The iodine proxy is sensitive to both local oxygen availability and the relative proximity to anoxic waters. To assess the validity of our approach, Neogene-Quaternary carbonates are used to demonstrate that diagenesis most often decreases and is unlikely to increase carbonate-iodine contents. Despite the potential for diagenetic loss, maximum Proterozoic carbonate iodine levels are elevated relative to those of the Archean, particularly during the Lomagundi and Shuram carbon isotope excursions of the Paleo- and Neoproterozoic, respectively. For the Shuram anomaly, comparisons to Neogene-Quaternary carbonates suggest that diagenesis is not responsible for the observed iodine trends. The baseline low iodine levels in Proterozoic carbonates, relative to the Phanerozoic, are linked to a shallow oxic-anoxic interface. Oxygen concentrations in surface waters would have at least intermittently been above the threshold required to support eukaryotes. However, the diagnostically low iodine data from mid-Proterozoic shallow-water carbonates, relative to those of the bracketing time intervals, are consistent with a dynamic chemocline and anoxic waters that would have episodically mixed upward and laterally into the shallow oceans. This redox instability may have challenged early eukaryotic diversification and expansion, creating an evolutionary landscape unfavorable for the emergence of animals.
    Description: TL, ZL, and DH thank NSF EAR-1349252. ZL further thanks OCE-1232620. DH, ZL, and TL acknowledge further funding from a NASA Early Career Collaboration Award. TL, AB, NP, DH, and AK thank the NASA Astrobiology Institute. TL and NP received support from the Earth-Life Transitions Program of the NSF. AB acknowledges support from NSF grant EAR-05-45484 and an NSERC Discovery and Accelerator Grants. CW acknowledges support from NSFC grant 40972021.
    Keywords: Proterozoic oxygen ; Shuram isotope anomaly ; Carbonate diagenesis ; Bahamas ; Iodine ; Metazoan evolution
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
    Location Call Number Limitation Availability
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