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| Registros recuperados: 13 | |
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| Bonnand, P.; Lalonde, Stefan; Boyet, M.; Heubeck, C.; Homann, M.; Nonnotte, Philippe; Foster, I.; Konhauser, K.o.; Köhler, I.. |
| Precambrian banded iron formations (BIF) are chemical sedimentary deposits whose trace element signatures have been widely used to interrogate the chemical composition and redox state of ancient seawater. Here we investigated trace element signatures in BIF of the 3.22 Ga Moodies Group, Barberton Greenstone Belt (South Africa), which are interbedded with near-shore siliciclastic sedimentary rocks and represent one of the oldest known shallow-water occurrences of BIF. Unusual rare earth element (REE) signatures, notably with pronounced negative Ce anomalies in shale-normalized spectra, have been previously reported for chemical sediments of the Moodies Group, which we confirm here through an expanded dataset for Moodies BIF spanning three different... |
| Tipo: Text |
Palavras-chave: Trace element signatures; Ce anomalies; La-Ce geochronology; Rare earth element mobility. |
| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00641/75328/75861.pdf |
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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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| Dekov, Vesselin M.; Barry Maynard, J.; Kamenov, George D.; Rouxel, Olivier; Lalonde, Stefan; Juranov, Sava. |
| The large manganese (Mn) deposit at Obrochishte (NE Bulgaria) is part of a cluster of similar Early Oligocene deposits located around present-day Black Sea. They collectively constitute the Earth’s second largest endowment of Mn, after the Kalahari Manganese Field in Africa. We have employed a battery of isotopic techniques (C, O, Fe, Sr, Nd, Pb) to help understand the genesis of this deposit. Carbon isotope data indicates that some sections of the Mn-ore layer have diagenetic MnCO3 mineralization, formed by reaction of Mn oxides with organic carbon (Corg), whereas other sections have MnCO3 precipitated directly from the seawater column. Oxygen isotopes show that the high-grade Mn mineralization had seawater as the fluid source, whereas some lower-grade... |
| Tipo: Text |
Palavras-chave: Mn metallogenesis; C-O-Fe-Sr-Nd-Pb isotopes; Early Oligocene; Submarine groundwater discharge; Water column anoxia; Proto-Black Sea geochemistry. |
| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00624/73591/73025.pdf |
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| Guillermic, Maxence; Lalonde, Stefan; Hendry, Katharine R.; Rouxel, Olivier. |
| Although dissolved concentrations of germanium (Ge) and silicon (Si) in modern seawater are tightly correlated, uncertainties still exist in the modern marine Ge cycle. Germanium stable isotope systematics in marine systems should provide additional constraints on marine Ge sources and sinks, however the low concentration of Ge in seawater presents an analytical challenge for isotopic measurement. Here, we present a new method of pre-concentration of inorganic Ge from seawater which was applied to measure three Ge isotope profiles in the Southern Ocean and deep seawater from the Atlantic and Pacific Oceans. Germanium isotopic measurements were performed on Ge amounts as low as 2.6 ng using a double-spike approach and a hydride generation system coupled to... |
| Tipo: Text |
Palavras-chave: Stable isotopes; Germanium; Silicon; Sponges; Southern Ocean; Chemical oceanography. |
| Ano: 2017 |
URL: http://archimer.ifremer.fr/doc/00388/49956/50529.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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| Dekov, V. M.; Lalonde, Stefan; Kamenov, G. D.; Bayon, Germain; Shanks, W. C., Iii; Fortin, D.; Fouquet, Yves; Moscati, R. J.. |
| An inactive vent field comprised of dead chimneys was discovered on the ultrafast East Pacific Rise (EPR) at 18°S during the research campaign NAUDUR with the R/V Le Nadir in December 1993. One of these chimneys was sampled, studied and found to be largely composed of silica-mineralized bacterial-like filaments. The filaments are inferred to be the result of microbial activity leading to silica (± Fe-oxyhydroxide) precipitation. The chimney grew from the most external layer (precipitated 226 ± 4 yr. B.P.) towards the central chimney conduit. Hydrothermal activity ceased 154 ± 13 yr. B.P. and the chimney conduit was completely sealed. Mixing between an end-member hydrothermal fluid and seawater explains the Sr–Nd isotopic composition of the chimney.... |
| Tipo: Text |
Palavras-chave: Chimney; C-O-Si-Sr-Nd-Pb-Th-U isotopes; Hydrothermal; Seafloor; Silica. |
| Ano: 2015 |
URL: http://archimer.ifremer.fr/doc/00280/39143/37698.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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| Finke, N.; Simister, R. L.; O'Neil, A. H.; Nomosatryo, S.; Henny, C.; Maclean, L. C.; Canfield, D. E.; Konhauser, K.; Lalonde, Stefan; Fowle, D. A.; Crowe, S. A.. |
| Development of Archean paleosols and patterns of Precambrian rock weathering suggest colonization of continents by subaerial microbial mats long before evolution of land plants in the Phanerozoic Eon. Modern analogues for such mats, however, have not been reported, and possible biogeochemical roles of these mats in the past remain largely conceptual. We show that photosynthetic, subaerial microbial mats from Indonesia grow on mafic bedrocks at ambient temperatures and form distinct layers with features similar to Precambrian mats and paleosols. Such subaerial mats could have supported a substantial aerobic biosphere, including nitrification and methanotrophy, and promoted methane emissions and oxidative weathering under ostensibly anoxic Precambrian... |
| Tipo: Text |
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| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00637/74908/76143.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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| Philippot, Pascal; Avila, Janaina N.; Killingsworth, Bryan A.; Tessalina, Svetlana; Baton, Franck; Caquineau, Tom; Muller, Elodie; Pecoits, Ernesto; Cartigny, Pierre; Lalonde, Stefan; Ireland, Trevor R.; Thomazo, Christophe; Van Kranendonk, Martin J.; Busigny, Vincent. |
| The Great Oxidation Event (GOE) has been defined as the time interval when sufficient atmospheric oxygen accumulated to prevent the generation and preservation of mass-independent fractionation of sulphur isotopes (MIF-S) in sedimentary rocks. Existing correlations suggest that the GOE was rapid and globally synchronous. Here we apply sulphur isotope analysis of diagenetic sulphides combined with U-Pb and Re-Os geochronology to document the sulphur cycle evolution in Western Australia spanning the GOE. Our data indicate that, from similar to 2.45 Gyr to beyond 2.31 Gyr, MIF-S was preserved in sulphides punctuated by several episodes of MIF-S disappearance. These results establish the MIF-S record as asynchronous between South Africa, North America and... |
| Tipo: Text |
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| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00638/74983/75853.pdf |
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| Killingsworth, B. A.; Sansjofre, P.; Philippot, P.; Cartigny, P.; Thomazo, C.; Lalonde, Stefan. |
| After permanent atmospheric oxygenation, anomalous sulfur isotope compositions were lost from sedimentary rocks, demonstrating that atmospheric chemistry ceded its control of Earth's surficial sulfur cycle to weathering. However, mixed signals of anoxia and oxygenation in the sulfur isotope record between 2.5 to 2.3 billion years (Ga) ago require independent clarification, for example via oxygen isotopes in sulfate. Here we show <2.31 Ga sedimentary barium sulfates (barites) from the Turee Creek Basin, W. Australia with positive sulfur isotope anomalies of Delta S-33 up to +1.55% and low delta O-18 down to -19.5%. The unequivocal origin of this combination of signals is sulfide oxidation in meteoric water. Geochemical and sedimentary evidence suggests... |
| Tipo: Text |
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| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00637/74903/76109.pdf |
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| Registros recuperados: 13 | |
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