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Rôle des argiles dans la préservation et la fossilisation de la Matière Organique ±pétroligène±

Abstract : Several authors proposed that organo-mineral interactions, under aquatic environments, could influence transfers of organic matter (OM) to sediments. Despite these studies, the fixation mechanisms and the role of clays in the preservation of labile organic compounds remain obscure. The aims of this work are first to test the fixation of organic molecules on clay minerals, by in vitro and in vivo experiments under marine and lacustrine environments, and secondly to evaluate the stability of the organo-clay complexes formed. This study proves the lack of molecular intercalation in clay structure, and demonstrates that the fixation is restricted to sorption on clay edges and surfaces of the mineral. Lab experiments show that the nature of OM and more precisely the type of their functional groups play a major role in organo-mineral interactions. In vivo experiments demonstrate that "fresh" OM are selectively adsorbed. Surface charges of clays also control the nature and concentration of adsorbed molecules. The density of the cationic charges induces the selective sorption of aromatic compounds on the low charge clays, under the studied lacustrine environment. The failure of destabilisation by hard alkaline treatments performed on complexes obtained after experiments, under the two main conditions, points out the strength and probably the multiplicity of linkages between mineral and organic phases. These bond-strengths control the stability of the organo-clay assemblages, in natural environments. The labile organic compounds, durably adsorbed on clays, become unavailable to benthic fauna and bacteria. In this sense, the mineral sorption can be considered as one of the OM preservation mechanisms, like degradation-recondensation pathway, natural sulfuration or selective preservation. It leads the incorporation of metabolisable organic compounds into sediments.
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Sylvain Drouin. Rôle des argiles dans la préservation et la fossilisation de la Matière Organique ±pétroligène±. Géochimie. Université d'Orléans, 2007. Français. ⟨tel-00259467⟩

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