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Communication dans un congrès

Salinity origin and groundwater circulation in a large sedimentary aquifer system (Adour-Garonne district, SW France): a multi-isotopes approach (O, H, S, B, Sr, Li)

Abstract : The tertiary multi-layers aquifer, located in the SW-France (1/5th of the land surface), is a large sedimentary aquifer system identified as being of primary importance and/or at risk by the local authorities. As large water abstractions for human activities can induce complete modification of the natural functioning of such aquifer systems, e.g. leakage between aquifer layers leading to water quality degradation, the characterization of such large system constitutes a key point to prevent further deterioration of the ecosystems. This study provides further characterization insight on this large aquifer through a geochemical approach which has to deal with the limited number of borewell where groundwater sampling is possible. Combined geochemical analysis, and isotope systematics (O, H, S(SO4), O(SO4), Sr, Li, B) have been applied to the tertiary demonstrative aquifer systems, made up of five four aquifer systems layers: Paleocene, Infra-Molassic Sand (Eocene), Early Eocene, Middle Eocene and Late Eocene with a mineralized area, north of the basin where the groundwaters show strong mineralization and anomalous levels of critical elements (SO4, F...), leading to difficulties of resource management. Extreme heterogeneities of geochemical composition and isotope signatures of groundwater between the aquifers but also within a single aquifer are discussed in terms of lithological control induced by lateral and vertical variation of facies and interconnections between aquifers. Strong control of evaporate dissolution (both gypsum and halite) was evidenced in three domains in the Adour-Garonne district by means of S and B isotopes. Weathering of silicate and carbonate rocks has also been demonstrated to be partly responsible of the spatial variability of groundwater geochemistry within an aquifer through Sr and B isotope tracing. In addition to this strong lithological control, different relations between the Infra-Molassic Sand aquifer and the other aquifers, depending on the part of the district, water/rock interaction processes (dissolution and formation of alteration minerals traced by Li isotopes) and age of the recharge (through O and H isotopes of the water molecule) have been demonstrated.
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https://hal-brgm.archives-ouvertes.fr/hal-00921097
Contributeur : Emmanuelle Petelet-Giraud <>
Soumis le : jeudi 19 décembre 2013 - 16:18:33
Dernière modification le : lundi 18 mai 2020 - 14:54:13

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  • HAL Id : hal-00921097, version 1

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Philippe Négrel, Emmanuelle Petelet-Giraud, Agnès Brenot, Romain Millot, Eline Malcuit. Salinity origin and groundwater circulation in a large sedimentary aquifer system (Adour-Garonne district, SW France): a multi-isotopes approach (O, H, S, B, Sr, Li). 9th South American Symposium on Isotope Geology, Apr 2014, Sao Paulo, Brazil. pp.PAP014514. ⟨hal-00921097⟩

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