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Fossilisation des apatites biologiques : approche cristallochimique et applications géochimiques

Abstract : Chemical and stable isotope compositions of fossil remains of vertebrates provide unique palaeo-environmental information. However, its reliability depends on the preservation of the biogenic geochemical record during the fossilisation process. This work aims to undersand how the geochemical record is acquired and preserved by studying the isotopic fractionation properties of apatite, the main inorganic constituent of vertebrates bones and teeth, and the crystal-chemical transformations occuring during fossilisation. These transformations are probed at the atomic scale using ATR-FTIR and solid-state NMR spectroscopies and their interpretation is supported by the modelling of ATR-FTIR spectra and DFT calculations of theoretical equilibrium isotopic fractionation properties. Atomic scale transformations of bones altered in aqueous solutions consist of partial dissolution of the biogenic apatite and formation of secondary carbonated fluor- or hydroxy- apatite, depending on the presence or absence of fluoride in the solution. These results were then applied to the study of the transformation of fossil bones from the karstic environments of Bolt’s Farm cave system (Cradle of Humankind, South Africa) and from the fluvio-lacustrine environments of the Tugen Hills (Gregory Rift, Kenya). Systematic formation of secondary carbonated fluorapatite is observed, as well as formation of secondary carbonated hydroxyapatite in the less fluorinated Bolt’s Farm fossils, highlighting the potentiality of fossil bones to record local physical-chemical conditions prevailing in fossilisation environments. The ~ 60 % maximum fraction of secondary apatite observed in fossils and modern bones altered under controlled conditions suggests it has a protective role against further dissolution of the primary apatite.
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  • HAL Id : tel-02611818, version 1

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Julie Aufort. Fossilisation des apatites biologiques : approche cristallochimique et applications géochimiques. Paléontologie. Sorbonne Université, 2018. Français. ⟨NNT : 2018SORUS484⟩. ⟨tel-02611818⟩

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