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| Mand, Kaarel; Lalonde, Stefan; Robbins, Leslie J.; Thoby, Marie; Paiste, Kart; Kreitsmann, Timmu; Paiste, Paarn; Reinhard, Christopher T.; Romashkin, Alexandr E.; Planavsky, Noah J.; Kirsimae, Kalle; Lepland, Aivo; Konhauser, Kurt O.. |
| The oceans probably remained well-oxygenated for millions of years after the Palaeoproterozoic Lomagundi-Jatuli Event, according to high concentrations and isotope signatures of redox-sensitive metals in the 2-billion-year-old Zaonega Formation, Russia. The approximately 2,220-2,060 million years old Lomagundi-Jatuli Event was the longest positive carbon isotope excursion in Earth history and is traditionally interpreted to reflect an increased organic carbon burial and a transient rise in atmospheric O-2. However, it is widely held that O-2 levels collapsed for more than a billion years after this. Here we show that black shales postdating the Lomagundi-Jatuli Event from the approximately 2,000 million years old Zaonega Formation contain the highest... |
| Tipo: Text |
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| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00663/77461/82873.pdf |
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| Mänd, Kaarel; Lalonde, Stefan; Paiste, Kärt; Thoby, Marie; Lumiste, Kaarel; Robbins, Leslie J.; Kreitsmann, Timmu; Romashkin, Alexander E.; Kirsimäe, Kalle; Lepland, Aivo; Konhauser, Kurt O.. |
| The Zaonega Formation in northwest Russia (~2.0 billion years old) is amongst the most complete successions that record the middle of the Palaeoproterozoic era. As such, geochemical data from the formation have played a central role in framing the debate over redox dynamics in the aftermath of the Great Oxidation Event (GOE). However, uncertainty over local redox conditions and the degree of hydrographic restriction in the formation has led to contradictory interpretations regarding global oxygen (O2) fugacity. Here, we provide new iron (Fe) isotope data together with major and trace element concentrations to constrain the local physiochemical conditions. The Zaonega Formation sediments show authigenic Fe accumulation (Fe/Al ≫ 1 wt.%/wt.%) and δ56Fe... |
| Tipo: Text |
Palavras-chave: Isotope geochemistry; Redox stratification; Benthic Fe shuttle; Dissimilatory iron reduction. |
| Ano: 2021 |
URL: https://archimer.ifremer.fr/doc/00688/79959/82885.pdf |
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| Wilmeth, Dylan T.; Nabhan, Sami; Myers, Kimberly D.; Slagter, Silvina; Lalonde, Stefan; Sansjofre, Pierre; Homann, Martin; Konhauser, Kurt O.; Munoz-saez, Carolina; Van Zuilen, Mark A.. |
| Siliceous sinter deposits from El Tatio, Chile, preserve a wide variety of depositional environments and biosignatures, from high-temperature (~85 °C) vent-proximal facies to distal deposits dominated by silicified microbial mats. Four cores were drilled into an El Tatio sinster mound and associated distal apron to investigate changes in hydrothermal environments over geologic timescales. Sedimentary and geochemical analysis of multiple sinter cores records the initiation and accretion of diverse depositional features still observed today in El Tatio. Facies adjacent to hydrothermal vents are dominated by laminated sinter crusts on the steep margins of a high-temperature pool, with sparse microbial preservation. Outer margins of the same pool contain... |
| Tipo: Text |
Palavras-chave: Siliceous sinter; Hot springs; El Tatio; Microbialites; Microfossils. |
| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00641/75332/75994.pdf |
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| Fru, Ernest Chi; Somogyi, Andrea; El Albani, Abderrazzak; Medjoubi, Kadda; Aubineau, Jeremie; Robbins, Leslie J.; Lalonde, Stefan; Konhauser, Kurt O.. |
| The Great Oxidation Event (GOE) at 2.45 Ga facilitated the global expansion of oxidized compounds in seawater. Here, we demonstrate that the GOE coincided with a sharp increase in arsenate and arsenic sulfides in marine shales. The dramatic rise of these oxygen-sensitive tracers overlaps with the expansion of key arsenic oxidants, including oxygen, nitrate, and Mn(IV) oxides. The increase in arsenic sulfides by at least an order of magnitude after 2.45 Ga is consistent with the proposed transition to mid-depth continental-margin sulfide-rich waters following the GOE. At the same time, the strong increase in arsenate content, to similar to 60% of the total arsenic concentration in shales, suggests that the oxidative component of the arsenic cycle was... |
| Tipo: Text |
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| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00637/74946/76142.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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