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www.hydrol-earth-syst-sci.net/8/35/2004/
doi:10.5194/hess-8-35-2004
© Author(s) 2004. This work is licensed
under a Creative Commons License.
234U/238U Disequilibrium along stylolitic discontinuities in deep Mesozoic limestone formations of the Eastern Paris basin: evidence for discrete uranium mobility over the last 1–2 million years
1GEOTOP-UQAM-McGILL, P.O. Box 8888, Succ. Centre-Ville, Montréal, QC, Canada H3C 3P8
2CEREGE, Europôle méditerranéen de l'Arbois, BP 80 13 545 Aix-en-Provence, France
3Université Blaise Pascal, CNRS (UMR 6524), Observatoire de Physique du Globe de Clermont-Ferrand, 5 Rue Kessler, 63038 Clermont-Ferrand Cedex, France
4ANDRA, 1-7 rue Jean Monnet, 92298 Châtenay Malabry, France
Email for corresponding author: deschamps@cerege.fr
Abstract. The (234U/238) equilibrium state of borehole core samples from the deep, low-permeability limestone formations surrounding the target argilite layer of the Meuse/Haute-Marne experimental site of the French agency for nuclear waste management -ANDRA- (Agence nationale pour la gestion des déchets radioactifs) was examined to improve understanding of naturally occurring radionuclide behaviour in such geological settings. Highly precise, accurate MC-ICP-MS measurements of the (234U/238U) activity ratio show that limestone samples characterised by pressure dissolution structures (stylolites or dissolution seams) display systematic (234U/238U) disequilibria, while the pristine carbonate samples remain in the secular equilibrium state. The systematic feature is observed throughout the zones marked by pressure dissolution structures: (i) the material within the seams shows a deficit of 234U over 238U ((234U/238U) down to 0.80) and (ii) the surrounding carbonate matrix is characterised by an activity ratio greater than unity (up to 1.05). These results highlight a centimetric-scale uranium remobilisation in the limestone formations along these sub-horizontal seams. Although their nature and modalities are not fully understood, the driving processes responsible for these disequilibria were active during the last 1–2 Ma.
Keywords: uranium isotopes, multiple-collector ICP-MS, waste management, remobilisation, migration
Final Revised Paper (PDF, 1408 KB) Special Issue
Citation: Deschamps, P., Hillaire-Marcel, C., Michelot, J.-L., Doucelance, R., Ghaleb, B., and Buschaert, S.: 234U/238U Disequilibrium along stylolitic discontinuities in deep Mesozoic limestone formations of the Eastern Paris basin: evidence for discrete uranium mobility over the last 1–2 million years, Hydrol. Earth Syst. Sci., 8, 35-46, doi:10.5194/hess-8-35-2004, 2004. Bibtex EndNote Reference Manager XML
