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FONCTIONNEMENT HYDROGEOLOGIQUE ET ARCHIVES PALEOCLIMATIQUES D'UN AQUIFERE PROFOND MEDITERRANEEN
Etude géochimique et isotopique du bassin miocène de Valréas (Sud-Est de la France)

Abstract : A hydrogeochemical survey of the Valreas Miocene aquifer has been carried out from 1997 to 2000. The purpose of this survey is to have an improved knowledge of the system using a set of isotopic and geochemical data. The isotopes include those of water molecule (18O, 2H, 3H) and inorganic carbon (13C and 14C), whereas the geochemical data are noble gases and major ions. Radiocarbon activities decrease from 100 pmc in the recharge area to less than 1 pmc in the confined aquifer providing ages from present day to 30 000 years BP.18O and 2H data show a strong isotopic contrast between unconfined and confined aquifer, the later having depleted values. The 18O/2H relationship clearly distinguishes the atmospheric pattern?s influence of the Atlantic (d≈10) and the Western Mediterranean area (d≈14). Deuterium excess does not show demarcation between Pleistocene and Holocene waters. Palaeorecharge temperatures deduced from noble gases indicate that the Last-Glacial is 7°C cooler than the Holocene. Radiogenic helium concentrations increase gradually with groundwater residence time in the aquifer giving a relative age to water. Hydrogeochemical data from the recharge area show that groundwater is polluted by anthopogenic sources from their NO3-, SO42- and Cl- high concentrations. There is also evidence of water-rock interaction from the evolution of the chemical facies where Na+ and K+ tend to dominate in the deeper aquifer probably due to reaction with clay minerals as against Ca2+ in the recharge zone. Velocity of flow estimated for the confined aquifer using the radiocarbon data gives a rate of 0,2 m/year, however this contrasts with estimates of 2 m/year from hydraulic data. In conclusion a conceptual model has been produced to describe the functioning of the aquifer.
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Frederic Huneau. FONCTIONNEMENT HYDROGEOLOGIQUE ET ARCHIVES PALEOCLIMATIQUES D'UN AQUIFERE PROFOND MEDITERRANEEN
Etude géochimique et isotopique du bassin miocène de Valréas (Sud-Est de la France). Hydrologie. Université d'Avignon, 2000. Français. ⟨tel-00323650⟩

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