The onset of oxidative weathering traced by uranium isotopes

Brüske, Annika; Martin, A.; Rammensee, Philipp; Eroglu, Suemeyya; Lazarov, Marina; Albut, Gülüm; Schuth, Stephan; Aulbach, Sonja; Schoenberg, Ronny; Beukes, Nicolas J.; Hofmann, Axel; Nägler, Thomas F.; Weyer, Stefan

doi:10.1016/j.precamres.2019.105583

Cited by 24 publications

(18 citation statements)

References 89 publications

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“…The understanding of sedimentary U isotope signatures is particular important, as they are frequently used to reconstruct the redox evolution of Earth’s oceans and atmosphere. − However, ligands likely existed in the environment since the mid-Archean (e.g., by the degradation of organic materials and metabolites by microorganisms) , and may have mobilized small amounts of U, imposing the associated U isotope fractionation. In particular, in the Archean, the findings of our study may challenge the interpretation of variable δ 238 U, which are commonly interpreted as the onset of oxidative geochemical U cycling. ,, Heavy isotope signatures in Archean or early Proterozoic shales may be interpreted to be the product of partial U reduction during the deposition of the sediments. In such a model, it is assumed that U was mobilized during U weathering with little isotope effects and that the heavy shale signature, thus, indirectly indicated the onset of oxic weathering with quantitative U mobilization.…”

Section: Implications For the Use Of U Isotope Proxymentioning

confidence: 67%

“…In particular, in the Archean, the findings of our study may challenge the interpretation of variable δ 238 U, which are commonly interpreted as the onset of oxidative geochemical U cycling. 79,82,83 Heavy isotope signatures in Archean or early Proterozoic shales may be interpreted to be the product of partial U reduction during the deposition of the sediments. In such a model, it is assumed that U was mobilized during U weathering with little isotope effects and that the heavy shale signature, thus, indirectly indicated the onset of oxic weathering with quantitative U mobilization.…”

Section: Implications For the Use Of U Isotope Proxymentioning

confidence: 99%

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Uranium Isotope Fractionation during the Anoxic Mobilization of Noncrystalline U(IV) by Ligand Complexation

Roebbert

Rosendahl

Brown

et al. 2021

Environ. Sci. Technol.

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Uranium (U) isotopes are suggested as a tool to trace U reduction. However, noncrystalline U(IV), formed predominantly in near-surface environments, may be complexed and remobilized using ligands under anoxic conditions. This may cause additional U isotope fractionation and alter the signatures generated by U reduction. Here, we investigate the efficacy of noncrystalline U(IV) mobilization by ligand complexation and the associated U isotope fractionation. Noncrystalline U(IV) was produced via the reduction of U(VI) (400 μM) by Shewanella oneidensis MR-1 and was subsequently mobilized with EDTA (1 mM), citrate (1 mM), or bicarbonate (500 mM) in batch experiments. Complexation with all investigated ligands resulted in significant mobilization of U(IV) and led to an enrichment of 238 U in the mobilized fraction (δ 238 U = 0.4−0.7 ‰ for EDTA; 0.3 ‰ for citrate; 0.2−0.3 ‰ for bicarbonate). For mobilization with bicarbonate, a Rayleigh approach was the most suitable isotope fractionation model, yielding a fractionation factor α of 1.00026− 1.00036. Mobilization with EDTA could be modeled with equilibrium isotope fractionation (α: 1.00039−1.00049). The results show that U isotope fractionation associated with U(IV) mobilization under anoxic conditions is significant and needs to be considered when applying U isotopes in remediation monitoring or as a paleo-redox proxy.

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Section: Implications For the Use Of U Isotope Proxymentioning

confidence: 67%

Section: Implications For the Use Of U Isotope Proxymentioning

confidence: 99%

Uranium Isotope Fractionation during the Anoxic Mobilization of Noncrystalline U(IV) by Ligand Complexation

Roebbert

Rosendahl

Brown

et al. 2021

Environ. Sci. Technol.

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“…As discussed by Bone et al (2017), the role of adsorption could be critical in aqueous systems with low U concentrations, as adsorption could lower the dissolved U(IV) concentration below the level required for uraninite precipitation. Based on studies of U concentrations in Precambrian BIFs (Partin et al 2013b), shales (Partin et al 2013a), and carbonates (this study; Gilleaudeau et al 2019;Brüske et al 2020a), it is likely that the U concentrations in the Archean and Proterozoic oceans were factors of 10 to 100 lower than they are in today's oceans. In this context, the pathway for U removal into anoxic sediments could have been very different compared to the modern oceans, where both precipitation and adsorption are involved.…”

Section: Non-uniformitarian U Isotopic Fractionation During Depositiomentioning

confidence: 91%

“…In order to reconstruct the long-term redox evolution of the ocean, a large suite of marine carbonates ( Table 1) was assembled and the U concentrations and isotopic compositions of 95 carbonate samples spanning the Archean to Neoproterozoic were measured and combined with previously published data (Brennecka et al 2011;Dahl et al 2014Dahl et al , 2017Dahl et al , 2019Azmy et al 2015;Hood et al 2016;Lau et al 2016Lau et al , 2017Elrick et al 2017;Jost et al 2017;Song et al 2017;Bartlett et al 2018;Chen et al 2018aChen et al , 2018bClarkson et al 2018;Herrmann et al 2018;Phan et al 2018;White et al 2018;Zhang et al 2018aZhang et al , 2018bZhang et al , 2018cZhang et al , 2019aZhang et al , 2019bZhang et al , 2020aZhang et al , 2020cGilleaudeau et al 2019;Tostevin et al 2019;Brüske et al 2020a;Bura-Nakić et al 2020;Cheng et al 2020;Li et al 2020;del Rey et al 2020;Zhao et al 2020). The age and detailed description of the geological settings can be found in the references provided in Table 1 and in Supplementary Materials.…”

Section: Samplesmentioning

confidence: 99%

The uranium isotopic record of shales and carbonates through geologic time

Chen

Tissot

Jansen

et al. 2021

Geochimica et Cosmochimica Acta

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This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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“…For example, progressively heavier Mo isotope compositions are found in sedimentary rocks formed between about 2.6 and 2.5 Ga and inferred as evidence of a progressive rise in atmospheric and oceanic O 2 levels (Wille et al, 2007;Kurzweil et al, 2015). Yet, in some of these same rocks, generally invariant C (Fischer et al, 2009) and U (Brüske et al, 2020) isotope compositions are inferred as evidence of little to no change to Earth's surface O 2 levels. To summarize, emerging evidence clearly identifies brief, single-million-year O 2 accumulation events on the eve of the GOE, but no clear consensus yet exists for the O 2 levels that persisted over much longer, tens-of-million-year timeframes.…”

Section: Introductionmentioning

confidence: 99%

Shale Heavy Metal Isotope Records of Low Environmental O2 Between Two Archean Oxidation Events

et al. 2022

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Evidence of molecular oxygen (O2) accumulation at Earth’s surface during the Archean (4.0–2.5 billion years ago, or Ga) seems to increase in its abundance and compelling nature toward the end of the eon, during the runup to the Great Oxidation Event. Yet, many details of this late-Archean O2 story remain under-constrained, such as the extent, tempo, and location of O2 accumulation. Here, we present a detailed Fe, Tl, and U isotope study of shales from a continuous sedimentary sequence deposited between ∼2.6 and ∼2.5 Ga and recovered from the Pilbara Craton of Western Australia (the Wittenoom and Mt. Sylvia formations preserved in drill core ABDP9). We find a progressive decrease in bulk-shale Fe isotope compositions moving up core (as low as δ56Fe = –0.78 ± 0.08‰; 2SD) accompanied by invariant authigenic Tl isotope compositions (average ε205TlA = –2.0 ± 0.6; 2SD) and bulk-shale U isotope compositions (average δ238U = –0.30 ± 0.05‰; 2SD) that are both not appreciably different from crustal rocks or bulk silicate Earth. While there are multiple possible interpretations of the decreasing δ56Fe values, many, to include the most compelling, invoke strictly anaerobic processes. The invariant and near-crustal ε205TlA and δ238U values point even more strongly to this interpretation, requiring reducing to only mildly oxidizing conditions over ten-million-year timescales in the late-Archean. For the atmosphere, our results permit either homogenous and low O2 partial pressures (between 10−6.3 and 10−6 present atmospheric level) or heterogeneous and spatially restricted O2 accumulation nearest the sites of O2 production. For the ocean, our results permit minimal penetration of O2 in marine sediments over large areas of the seafloor, at most sufficient for the burial of Fe oxide minerals but insufficient for the burial of Mn oxide minerals. The persistently low background O2 levels implied by our dataset between ∼2.6 and ∼2.5 Ga contrast with the timeframes immediately before and after, where strong evidence is presented for transient Archean Oxidation Events. Viewed in this broader context, our data support the emerging narrative that Earth’s initial oxygenation was a dynamic process that unfolded in fits-and-starts over many hundreds-of-millions of years.

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The onset of oxidative weathering traced by uranium isotopes

Cited by 24 publications

References 89 publications

Uranium Isotope Fractionation during the Anoxic Mobilization of Noncrystalline U(IV) by Ligand Complexation

Uranium Isotope Fractionation during the Anoxic Mobilization of Noncrystalline U(IV) by Ligand Complexation

The uranium isotopic record of shales and carbonates through geologic time

Shale Heavy Metal Isotope Records of Low Environmental O2 Between Two Archean Oxidation Events

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