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Dégradation de schistes argileux fossilifères (bassin d’Autun, France, Permien), partie I : caractérisation de la spéciation et de la réactivité du fer par spectrométrie Mössbauer, diffraction des rayons X, porosimétrie et mesure de perméabilité

hal.structure.identifierCentre de recherche sur la Paléobiodiversité et les Paléoenvironnements [CR2P]
hal.structure.identifierCentre de Recherche sur la Conservation [CRC ]
dc.contributor.authorODIN, Giliane P.
hal.structure.identifierCentre de Recherche sur la Conservation [CRC ]
dc.contributor.authorCABARET, Thomas
hal.structure.identifierCentre de Recherche sur la Conservation [CRC ]
hal.structure.identifierLaboratoire de recherche des monuments historiques [LRMH]
dc.contributor.authorMERTZ, Jean Didier
hal.structure.identifierLaboratoire Géosciences et Environnement Cergy [GEC]
dc.contributor.authorMENENDEZ, Beatriz
hal.structure.identifierInstitut de Chimie de la Matière Condensée de Bordeaux [ICMCB]
dc.contributor.authorETIENNE, Laetitia
hal.structure.identifierInstitut de Chimie de la Matière Condensée de Bordeaux [ICMCB]
dc.contributor.authorWATTIAUX, Alain
hal.structure.identifierCentre de Recherche sur la Conservation [CRC ]
dc.contributor.authorROUCHON, Véronique
dc.date.created2014-01-07
dc.date.issued2015
dc.identifier.issn0753-3969
dc.description.abstractEnFossil-bearing shale specimens that include sulfides in their compositions are chemically reactive and sometimes also mechanically fragile. This decay is often related to iron sulfate efflorescence resulting from the oxidation of sulfide compounds. The processes underlying these degradations are poorly known, thus impeding the elaboration of curative or preventive treatments. The present contribution aims to identify the origin of museum specimen alterations. It focuses on the Flouest collection housed at the Muséum national d’Histoire naturelle (MNHN, Paris, France) and originating from the Autun Basin (Saône-et-Loire,France; Permian). To evaluate the alteration of MNHN specimens, it appeared necessary to compare their composition with that of unaltered shale so as to identify chemical changes occurring during ageing. Therefore new material was collected in the Autun Basin, among others on the locality of Muse that corresponds to the same lithostratigraphic unit than that of the MNHN specimens. The present article focuseson the combined use of X-ray diffraction and Mössbauer spectrometry for characterizing the speciation and reactivity of iron within the shale matrix. Crystalline pyrite was evidenced by X-ray diffraction (XRD) on one sample only and elemental analysis showed that iron is present in large excess with respect to sulfur. Iron sulfide, if present, involves a minor fraction of iron. A more complete characterization of iron-bearing phases was achieved with Mössbauer measurements, showing that a great part of iron, between approx. 25% and 65%, corresponds to iron(II) incorporated in clay minerals (illite and vermiculite weredetected by XRD). Similar percentages of these iron(II) signatures were found for MNHN specimens and new shale samples, suggesting that iron(II) present in clays is not affected by ageing. This point is complementary highlighted by porosity and permeability measurements showing that the pore size distribution of the samples originating from Muse is mostly unimodal and narrow (average radius below 10 nm). As a result, the shale is poorly permeable to water and almost fully impermeable to oxygen. This might explain the poor reactivity of iron(II) during ageing. Iron(III)-bearing phases were also identified. On new shale samples, they exclusively involve clay minerals. On MNHN specimens, poorly crystallized iron(III) sulfates are additionally observed. The presence of iron(III) oxyhydroxides appeared unlikely. The change of iron speciation provoked by the alteration of the matrix also mainly corresponds to the emergence of more or less crystallized iron(III) sulfates probably formed though iron sulfide oxidation. These phase show ever remain in the inner part of shale and cannot account for the large efflorescence of iron(II) sulfates observed nearby the fossil.
dc.language.isoen
dc.publisherElsevier Masson
dc.subject.enShale
dc.subject.enFossil
dc.subject.enPyrite
dc.subject.enAutun Basin
dc.subject.enOxidation
dc.subject.enIron Sulfide
dc.subject.enClay
dc.subject.enMössbauer
dc.titleDégradation de schistes argileux fossilifères (bassin d’Autun, France, Permien), partie I : caractérisation de la spéciation et de la réactivité du fer par spectrométrie Mössbauer, diffraction des rayons X, porosimétrie et mesure de perméabilité
dc.title.enAlteration of fossil-bearing shale (Autun Basin, France; Permian), part I: Characterizing iron speciation and its vulnerability to weathering by combined use of Mössbauer spectroscopy, X-ray diffraction, porosimetry and permeability measurements
dc.typeArticle de revue
dc.identifier.doi10.1016/j.annpal.2015.01.002
dc.subject.halPlanète et Univers [physics]/Sciences de la Terre/Géochimie
dc.subject.halPlanète et Univers [physics]/Sciences de la Terre/Minéralogie
dc.subject.halPlanète et Univers [physics]/Sciences de la Terre/Paléontologie
bordeaux.journalAnnales de Paléontologie
bordeaux.page75-85
bordeaux.volume101
bordeaux.issue2
bordeaux.peerReviewedoui
hal.identifierhal-01428942
hal.version1
hal.popularnon
hal.audienceInternationale
hal.origin.linkhttps://hal.archives-ouvertes.fr//hal-01428942v1
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