气候变化领域集成服务门户(CCPortal): Post-depositional REE mobility in a Paleoarchean banded iron formation revealed by La-Ce geochronology: A cautionary tale for signals of ancient oxygenation

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DOI	10.1016/j.epsl.2020.116452
	Post-depositional REE mobility in a Paleoarchean banded iron formation revealed by La-Ce geochronology: A cautionary tale for signals of ancient oxygenation
	Bonnand P.; Lalonde S.V.; Boyet M.; Heubeck C.; Homann M.; Nonnotte P.; Foster I.; Konhauser K.O.; Köhler I.
发表日期	2020
ISSN	0012821X
卷号	547
英文摘要	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 localities. We find negative Ce anomalies as low as 0.2 Ce/Ce⁎ that are associated with unusual enrichment of LREE relative to HREE in the sample set. While total REE abundances and certain REE features appear strongly related to the concentration of detrital indicators (e.g., Zr), and are likely primary, other features, notably LREE enrichment, cannot be explained as a primary feature of the sediment. This is better explained by later addition of REE from a LREE-enriched but Ce-depleted fluid that generated the significant negative Ce anomalies observed in surface samples of Moodies Group BIF. This REE addition event influenced both Sm-Nd and La-Ce isotope systematics, the latter yielding an isochron of 60 ± 32 Ma, thus constraining the timing of emplacement of the negative Ce anomalies to the past 100 Ma, possibly upon surface exposure of the Barberton Greenstone Belt to wetter conditions during the Cenozoic. Our findings constitute a cautionary tale in that even the most immobile elemental redox proxies may be more sensitive to post-depositional modification than previously thought, and demonstrate the clear advantage offered by paleoredox proxies coupled to radiometric geochronometers to enable the direct dating of ancient signals of Earth surface oxygenation. © 2020 The Authors
关键词	Ce anomalies La-Ce geochronology rare earth element mobility trace element signatures
英文关键词	Binary alloys; Deposition; Economic geology; Geochemistry; Geochronology; Iron; Iron deposits; Lanthanum alloys; Neodymium alloys; Oxygenation; Rare earths; Samarium alloys; Sedimentary rocks; Sedimentology; Trace elements; Banded iron formations; Cautionary tales; Chemical compositions; Chemical sediment; Element signatures; Greenstone belts; Negative Ce anomaly; Sedimentary deposits; Cerium; Archean; banded iron formation; deposition; element mobility; emplacement; geochronology; oxygenation; rare earth element; Barberton Greenstone Belt
语种	英语
来源期刊	Earth and Planetary Science Letters
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/202503
作者单位	Laboratoire Magmas et Volcans, Université Clermont Auvergne, CNRS, IRD, OPGC, Clermont-Ferrand, F-63000, France; CNRS-UMR 6538 Laboratoire Géosciences Océan, European Institute for Marine Studies, Technopôle Brest-Iroise, Plouzané, 29280, France; Department of Geosciences, Friedrich-Schiller-University Jena, Jena, 07749, Germany; Department of Earth Sciences, University College London, 5 Gower Place, London, WC1E 6BS, United Kingdom; Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2E3, Canada; Geozentrum Nordbayern, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, 91054, Germany
推荐引用方式 GB/T 7714	Bonnand P.,Lalonde S.V.,Boyet M.,et al. Post-depositional REE mobility in a Paleoarchean banded iron formation revealed by La-Ce geochronology: A cautionary tale for signals of ancient oxygenation[J],2020,547.
APA	Bonnand P..,Lalonde S.V..,Boyet M..,Heubeck C..,Homann M..,...&Köhler I..(2020).Post-depositional REE mobility in a Paleoarchean banded iron formation revealed by La-Ce geochronology: A cautionary tale for signals of ancient oxygenation.Earth and Planetary Science Letters,547.
MLA	Bonnand P.,et al."Post-depositional REE mobility in a Paleoarchean banded iron formation revealed by La-Ce geochronology: A cautionary tale for signals of ancient oxygenation".Earth and Planetary Science Letters 547(2020).