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Pervasively Anoxic Surface Conditions at the Onset of the Great Oxidation Event: New Multi-Proxy Constraints from the Cooper Lake Paleosol Michael G

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Pervasively Anoxic Surface Conditions at the Onset of the Great Oxidation Event: New Multi-Proxy Constraints from the Cooper Lake Paleosol Michael G Geological and Atmospheric Sciences Publications Geological and Atmospheric Sciences 1-3-2019 Pervasively anoxic surface conditions at the onset of the Great Oxidation Event: new multi-proxy constraints from the Cooper Lake paleosol Michael G. Babechuk University of Tübingen Nadine Weimar University of Tübingen Ilka C. Kleinhanns University of Tübingen Suemeyya Eroglu Iowa State University Elizabeth D. Swanner IFoowlalo Swta tthie Usn iaverndsit ay,dd eswitaionnnealr@i wasorktatse .aedut: https://lib.dr.iastate.edu/ge_at_pubs Part of the Atmospheric Sciences Commons, Geochemistry Commons, and the Oceanography See next page for additional authors Commons The ompc lete bibliographic information for this item can be found at https://lib.dr.iastate.edu/ ge_at_pubs/264. For information on how to cite this item, please visit http://lib.dr.iastate.edu/ howtocite.html. This Article is brought to you for free and open access by the Geological and Atmospheric Sciences at Iowa State University Digital Repository. It has been accepted for inclusion in Geological and Atmospheric Sciences Publications by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Pervasively anoxic surface conditions at the onset of the Great Oxidation Event: new multi-proxy constraints from the Cooper Lake paleosol Abstract Oceanic element inventories derived from marine sedimentary rocks place important constraints on oxidative continental weathering in deep time, but there remains a scarcity in complementary observations directly from continental sedimentary reservoirs. This study focuses on better defining continental weathering conditions near the Archean-Proterozoic boundary through the multi-proxy (major and ultra-trace element, Fe and Cr stable isotopes, μ-XRF elemental mapping, and detrital zircon U-Pb geochronology) investigation of the ca. 2.45 billion year old (giga annum, Ga) Cooper Lake paleosol (saprolith), developed on a sediment- hosted mafic dike within the Huronian Supergroup (Ontario, Canada). Throughout the variably altered Cooper Lake saprolith, ratios of immobile elements (Nb, Ta, Zr, Hf, Th, Al, Ti) are constant, indicating a uniform pre-alteration dike composition, lack of extreme pH weathering conditions, and no major influence from ligand-rich fluids during weathering or burial metasomatism/ metamorphism. The loss of Mg, Fe, Na, Sr, and Li, a signature of albite and ferromagnesian silicate weathering, increases towards the top of the preserved profile (unconformity) and dike margins. Coupled bulk rock behaviour of Fe-Mg-Mn and co-localization of Fe- Mn in clay minerals (predominantly chlorite) indicates these elements were solubilized primarily in their divalent state without Fe/Mn-oxide formation. A lack of a Ce anomaly and immobility of Mo, V, and Cr further support pervasively anoxic weathering conditions. Subtle U enrichment is the only geochemical evidence, if primary, that could be consistent with oxidative element mobilization. The leaching of ferromagnesian silicates was accompanied by variable mobility and depletion of transition metals with a relative depletion order of Fe≈Mg≈Zn>Ni>Co>Cu (Cu being significantly influenced by secondary sulfide formation). Mild enrichment of heavy Fe isotopes (δ56/54Fe from 0.169 to 0.492 ‰) correlating with Fe depletion in the saprolith indicates loss of isotopically light aqueous Fe(II). Minor REE+Y fractionation with increasing alteration intensity, including a decreasing Eu anomaly and Y/Ho ratio, is attributed to albite breakdown and preferential scavenging of HREE>Y by clay minerals, respectively. Younger metasomatism resulted in the addition of several elements (K, Rb, Cs, Be, Tl, Ba, Sn, In, W), partly or wholly obscuring their earlier paleo-weathering trends. The behavior of Cr at Cooper Lake can help test previous hypotheses of an enhanced, low pH-driven continental weathering flux of Cr(III) to marine reservoirs between ca. 2.48-2.32 Ga and the utility of the stable Cr isotope proxy of Mn-oxide induced Cr(III) oxidation. Synchrotron μ- XRF maps and invariant Cr/ Nb ratios reveal complete immobility of Cr despite its distribution amongst both clay-rich groundmass and Fe-Ti oxides. Assuming a pH-dependent, continental source of Cr(III) to marine basins, the Cr immobility at Cooper Lake indicates either that signatures of acidic surface waters were localized to uppermost and typically unpreserved regolith horizons or were geographically restricted to acid-generating point sources. However, in given detrital pyrite preservation in fluvial sequences overlying the paleosol, we propose that the oxidative sulphide corrosion required to drive surface pH(δ53/52Cr: -0.321 ± 0.038 ‰, 2sd, n=34) that cannot be linked to Cr(III) oxidation and is instead interpreted to have a magmatic origin. The ombc ined chemical signatures and continued preservation of detrital pyrite/uraninite indicate low atmospheric O2 during weathering at ca. 2.45 Ga preserved in the rift-related sedimentary rocks of the Lower Huronian. The quea ous flux from the reduced weathering of mafic ockr s was characterized by a greater abundance of transition metals (Fe, Mn, Zn, Co, Ni) with isotopically light Fe(II), as well as higher Eu/Eu* and Y/Ho. In most models of Precambrian ocean element inventories, hydrothermal fluids are viewed as the This article is available at Iowa State University Digital Repository: https://lib.dr.iastate.edu/ge_at_pubs/264 main supplier of several metals (e.g., Fe, Zn), although the results herein suggest that a riverine metal supply may have been substantial and that using Eu-excess as a strict proxy for hydrothermal flux may be misleading in near-shore marine sedimentary environments. Keywords paleosol, Cooper Lake, Huronian Supergroup, stable Cr isotopes, stable Fe isotopes, redox-sensitive trace elements, anoxic weathering, atmospheric oxygenation, U-Pb detrital zircon geochronology Disciplines Atmospheric Sciences | Geochemistry | Oceanography Comments This is a manuscript of an article published as Babechuk, Michael G., Nadine E. Weimar, Ilka C. Kleinhanns, Suemeyya Eroglu, Elizabeth D. Swanner, Gavin G. Kenny, Balz S. Kamber, and Ronny Schoenberg. "Pervasively anoxic surface conditions at the onset of the Great Oxidation Event: new multi-proxy constraints from the Cooper Lake paleosol." Precambrian Research (2019). doi: 10.1016/j.precamres.2018.12.029. Posted with permission. Creative Commons License This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License. Authors Michael G. Babechuk, Nadine Weimar, Ilka C. Kleinhanns, Suemeyya Eroglu, Elizabeth D. Swanner, Gavin G. Kenny, Balz S. Kamber, and Ronny Schoenberg This article is available at Iowa State University Digital Repository: https://lib.dr.iastate.edu/ge_at_pubs/264 Accepted Manuscript Pervasively anoxic surface conditions at the onset of the Great Oxidation Event: new multi-proxy constraints from the Cooper Lake paleosol Michael G. Babechuk, Nadine E. Weimar, Ilka C. Kleinhanns, Suemeyya Eroglu, Elizabeth D. Swanner, Gavin G. Kenny, Balz S. Kamber, Ronny Schoenberg PII: S0301-9268(18)30321-8 DOI: https://doi.org/10.1016/j.precamres.2018.12.029 Reference: PRECAM 5251 To appear in: Precambrian Research Received Date: 9 June 2018 Revised Date: 22 December 2018 Accepted Date: 27 December 2018 Please cite this article as: M.G. Babechuk, N.E. Weimar, I.C. Kleinhanns, S. Eroglu, E.D. Swanner, G.G. Kenny, B.S. Kamber, R. Schoenberg, Pervasively anoxic surface conditions at the onset of the Great Oxidation Event: new multi-proxy constraints from the Cooper Lake paleosol, Precambrian Research (2018), doi: https://doi.org/10.1016/ j.precamres.2018.12.029 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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. Pervasively anoxic surface conditions at the onset of the Great Oxidation Event: new multi-proxy constraints from the Cooper Lake paleosol Michael G. Babechuka-c*, Nadine E. Weimara, Ilka C. Kleinhannsa, Suemeyya Eroglua,d, Elizabeth D. Swannerd, Gavin G. Kennyb,e, Balz S. Kamberb, Ronny Schoenberga aIsotope Geochemistry Group, Department of Geosciences, University of Tübingen, Tübingen, Germany bDepartment of Geology, Trinity College Dublin, Dublin, Ireland cDepartment of Earth Sciences, Memorial University of Newfoundland, St. John’s, Canada dDepartment of Geological & Atmospheric Sciences, Iowa State University, Ames, USA eDepartment of Geosciences, Swedish Museum of Natural History, Stockholm, Sweden *Corresponding author, present address: Department of Earth Sciences, Memorial University of Newfoundland, St. John’s, Canada. Contact information – email: [email protected]; phone: 1-709-864-6095 Abstract Oceanic element inventories derived from marine sedimentary rocks place important constraints on oxidative continental weathering in deep time, but there remains a scarcity in complementary observations directly from continental sedimentary reservoirs. This study focuses on better defining continental weathering conditions near the Archean-Proterozoic boundary through the multi-proxy (major and ultra-trace element,
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