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| Marin-carbonne, Johanna; Rollion-bard, Claire; Bekker, Andrey; Rouxel, Olivier; Agangi, Andrea; Cavalazzi, Barbara; Wohlgemuth-ueberwasser, Cora C.; Hofmann, Axel; Mckeegan, Kevin D.. |
| Iron and sulfur isotope compositions recorded in ancient rocks and minerals such as pyrite (FeS2) have been widely used as a proxy for early microbial metabolisms and redox evolution of the oceans. However, most previous studies focused on only one of these isotopic systems. Herein, we illustrate the importance of in-situ and coupled study of Fe and S isotopes on two pyrite nodules in a c. 2.7 Ga shale from the Bubi Greenstone Belt (Zimbabwe). Fe and S isotope compositions were measured both by bulk-sample mass spectrometry techniques and by ion microprobe in-situ methods (Secondary Ion Mass Spectrometry, SIMS). Spatially-resolved analysis across the nodules shows a large range of variations at micrometer-scale for both Fe and S isotope compositions, with... |
| Tipo: Text |
Palavras-chave: Pyrite nodules; Fe and S isotopes; Archean; SIMS. |
| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00177/28824/27324.pdf |
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| Bankole, Olabode M.; El Albani, Abderrazak; Meunier, Alain; Rouxel, Olivier; Gauthier-lafaye, Francois; Bekker, Andrey. |
| Red beds are extensively used as evidence for an oxygenated atmosphere in the Paleoproterozoic. Red beds in the unmetamorphosed, ca. 2.15 Ga FA Formation of the Franceville Basin, Gabon were geochemically, petrographically, and mineralogically characterized to constrain the process of their formation and their relationship to atmospheric oxygenation in the early Paleoproterozoic. Petrographic observations indicate that ferric oxides are dispersed in clay filling intergranular pores and along platy cleavage in altered phyllosilicates. Grain-coating hematite is generally rare to absent in most samples suggesting hematite precipitation after sediment deposition and during burial diagenesis. Textures and geochemical data suggest that iron was likely sourced... |
| Tipo: Text |
Palavras-chave: Red beds; Atmospheric oxygenation; Diagenesis; Iron isotopes; Franceville Basin; Oldest sandstone-type U deposit. |
| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00358/46966/48278.pdf |
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| Gueguen, Bleuenn; Rouxel, Olivier; Ponzevera, Emmanuel; Bekker, Andrey; Fouquet, Yves. |
| Although initial studies have demonstrated the applicability of Ni isotopes for cosmochemistry and as a potential biosignature, the Ni isotope composition of terrestrial igneous and sedimentary rocks, and ore deposits remains poorly known. Our contribution is fourfold: (a) to detail an analytical procedure for Ni isotope determination, (b) to determine the Ni isotope composition of various geological reference materials, (c) to assess the isotope composition of the Bulk Silicate Earth relative to the Ni isotope reference material NIST SRM 986 and (d) to report the range of mass-dependent Ni isotope fractionations in magmatic rocks and ore deposits. After purification through a two-stage chromatography procedure, Ni isotope ratios were measured by MC-ICP-MS... |
| Tipo: Text |
Palavras-chave: Nickel; Stable isotopes; MC-ICP-MS; Geological reference materials; Bulk Silicate Earth; Abiotic fractionation. |
| Ano: 2013 |
URL: http://archimer.ifremer.fr/doc/00159/27069/25332.pdf |
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| Asael, Dan; Rouxel, Olivier; Poulton, Simon W.; Lyons, Timothy W.; Bekker, Andrey. |
| The early Paleoproterozoic witnessed Earth's first major oxygenation, referred to as the Great Oxidation Event or GOE. The GOE began around 2.45 billion years ago (Ga) and progressed over hundreds of millions of years, as evidenced by multiple redox indicators, before coming to an abrupt end by ca. 2.06 Ga. The details of the GOE and the extent of oxygenation are still not resolved, however, and it is not dear how redox conditions across the GOE compare with those during the middle Proterozoic. In order to investigate the evolution of deep-ocean redox conditions during the GOE, we present Mo concentration and isotope data together with Fe speciation values for three key organic matter-rich shale units of the early Paleoproterozoic age (2.32-2.06 Ga). In... |
| Tipo: Text |
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| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00442/55330/60642.pdf |
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| El Albani, Abderrazak; Bengtson, Stefan; Canfield, Donald E.; Riboulleau, Armelle; Bard, Claire Rollion; Macchiarelli, Roberto; Pemba, Lauriss Ngombi; Hammarlund, Emma; Meunier, Alain; Mouele, Idalina Moubiya; Benzerara, Karim; Bernard, Sylvain; Boulvais, Philippe; Chaussidon, Marc; Cesari, Christian; Fontaine, Claude; Chi-fru, Ernest; Garcia Ruiz, Juan Manuel; Gauthier-lafaye, Francois; Mazurier, Arnaud; Pierson-wickmann, Anne Catherine; Rouxel, Olivier; Trentesaux, Alain; Vecoli, Marco; Versteegh, Gerard J. M.; White, Lee; Whitehouse, Martin; Bekker, Andrey. |
| The Paleoproterozoic Era witnessed crucial steps in the evolution of Earth's surface environments following the first appreciable rise of free atmospheric oxygen concentrations similar to 2.3 to 2.1 Ga ago, and concomitant shallow ocean oxygenation. While most sedimentary successions deposited during this time interval have experienced thermal overprinting from burial diagenesis and metamorphism, the ca. 2.1 Ga black shales of the Francevillian B Formation (FB2) cropping out in southeastern Gabon have not. The Francevillian Formation contains centimeter-sized structures interpreted as organized and spatially discrete populations of colonial organisms living in an oxygenated marine ecosystem. Here, new material from the FB2 black shales is presented and... |
| Tipo: Text |
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| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00202/31356/29754.pdf |
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| Hofmann, Axel; Bekker, Andrey; Dirks, Paul; Gueguen, Bleuenn; Rumble, Doug; Rouxel, Olivier. |
| Trojan and Shangani mines are low-grade (<0.8 % Ni), komatiite-hosted nickel sulfide deposits associated with ca. 2.7 Ga volcano-sedimentary sequences of the Zimbabwe craton. At both mines, nickel sulfide mineralization is present in strongly deformed serpentinite bodies that are enveloped by a complex network of highly sheared, silicified, and sulfide-bearing metasedimentary rocks. Strong, polyphase structural–metamorphic–metasomatic overprints in both the Trojan and Shangani deposits make it difficult to ascertain if sulfide mineralization was derived from orthomagmatic or hydrothermal processes, or by a combination of both. Multiple S, Fe, and Ni isotope analyses were applied to test these competing models. Massive ores at Shangani Mine show... |
| Tipo: Text |
Palavras-chave: Komatiite-hosted nickel deposit; Zimbabwe craton; Archean; Sulfur isotopes; Iron isotopes; Nickel isotopes. |
| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00171/28207/26508.pdf |
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| Heard, Andy W.; Dauphas, Nicolas; Guilbaud, Romain; Rouxel, Olivier; Butler, Ian B.; Nie, Nicole X.; Bekker, Andrey. |
| The role that iron played in the oxygenation of Earth's surface is equivocal. Iron could have consumed molecular oxygen when Fe3+-oxyhydroxides formed in the oceans, or it could have promoted atmospheric oxidation by means of pyrite burial. Through high-precision iron isotopic measurements of Archean-Paleoproterozoic sediments and laboratory grown pyrites, we show that the triple iron isotopic composition of Neoarchean-Paleoproterozoic pyrites requires both extensive marine iron oxidation and sulfide-limited pyritization. Using an isotopic fractionation model informed by these data, we constrain the relative sizes of sedimentary Fe3+- oxyhydroxide and pyrite sinks for Neoarchean marine iron. We show that pyrite burial could have resulted in molecular... |
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| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00657/76889/78193.pdf |
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| Swanner, Elizabeth D.; Planavsky, Noah J.; Lalonde, Stefan; Robbins, Leslie J.; Bekker, Andrey; Rouxel, Olivier; Saito, Mak A.; Kappler, Andreas; Mojzsis, Stephen J.; Konhauser, Kurt O.. |
| Cobalt (Co) is a bio-essential trace element and limiting nutrient in some regions of the modern oceans. It has been proposed that Co was more abundant in poorly ventilated Precambrian oceans based on the greater utilization of Co by anaerobic microbes relative to plants and animals. However, there are few empirical or theoretical constraints on the history of seawater Co concentrations. Herein, we present a survey of authigenic Co in marine sediments (iron formations, authigenic pyrite and bulk euxinic shales) with the goal of tracking changes in the marine Co reservoir throughout Earthʼs history. We further provide an overview of the modern marine Co cycle, which we use as a platform to evaluate how changes in the redox state of Earthʼs surface were... |
| Tipo: Text |
Palavras-chave: Cobalt; Trace element proxies; Ocean redox; Shale; Iron formation; Pyrite. |
| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00174/28575/26986.pdf |
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| Little, Crispin T. S.; Johannessen, Karen C; Bengtson, Stefan; Chan, Clara S; Ivarsson, Magnus; Slack, John F; Broman, Curt; Thorseth, Ingunn H.; Grenne, Tor; Rouxel, Olivier; Bekker, Andrey. |
| Modern marine hydrothermal vents occur in a wide variety of tectonic settings and are characterized by seafloor emission of fluids rich in dissolved chemicals and rapid mineral precipitation. Some hydrothermal systems vent only low‐temperature Fe‐rich fluids, which precipitate deposits dominated by iron oxyhydroxides, in places together with Mn‐oxyhydroxides and amorphous silica. While a proportion of this mineralization is abiogenic, most is the result of the metabolic activities of benthic, Fe‐oxidizing bacteria (FeOB), principally belonging to the Zetaproteobacteria. These micro‐organisms secrete micrometer‐scale stalks, sheaths, and tubes with a variety of morphologies, composed largely of ferrihydrite that act as sacrificial structures, preventing... |
| Tipo: Text |
Palavras-chave: Arizona; Fe-oxidizing bacteria; Hydrothermal vents; Jasper; Late Paleoproterozoic; Verde mining district. |
| Ano: 2021 |
URL: https://archimer.ifremer.fr/doc/00680/79162/81674.pdf |
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