Stable isotope contents of porewater in a claystone formation (Tournemire, France): assessment of the extraction technique and preliminary results

Claystones are one of the types of geological formations that are considered for the isolation of radioactive wastes. The study of water transfer through these rocks comes up against a lot of difficulties. Among them is the problem of extracting representative samples of interstitial water from indu...

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Bibliographic Details
Published in:Applied geochemistry 1997-11, Vol.12 (6), p.739-745
Main Authors: Golvan, Yann Moreau-Le, Michelot, Jean-Luc, Boisson, Jean-Yves
Format: Article
Language:English
Subjects:
Earth sciences
Earth, ocean, space
Engineering and environment geology. Geothermics
Exact sciences and technology
Hydrogeology
Hydrology. Hydrogeology
Pollution, environment geology
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Summary:Claystones are one of the types of geological formations that are considered for the isolation of radioactive wastes. The study of water transfer through these rocks comes up against a lot of difficulties. Among them is the problem of extracting representative samples of interstitial water from indurated claystones with very low water contents (usually less than 10% vol.). The vacuum distillation technique considered here for samples from the Tournemire site (Toarcian argillite formation), is one of the few usable techniques to extract water from this type of rock in order to perform stable isotope investigations on porewater. Tests have shown that the isotope water content is not only influenced by the yield of extraction and the temperature of distillation (as already known), but also by the rain size and the contact time between the crushed sample and the atmosphere. This affects particularly 18O data. The first isotopic results on the Tournemire claystones suggest a meteoric origin for its interstitial water. Data show a depletion in heavy isotopes with respect to present day meteoric water, that could suggest a recharge under climatic conditions cooler than at present. A clear link appears between the isotope contents of water and the structural context: interstitial waters of rock samples taken in the fractured zone of the massif seem to have been affected by a secondary process (evaporation or water-rock exchange) leading to the enrichment in heavy isotopes.
ISSN:0883-2927
1872-9134
DOI:10.1016/S0883-2927(97)00044-9