U-series constraints on aquifer groundwater residence time; the Adour-Garonne district case (southwest France)
U-series constraints on aquifer groundwater residence time; the Adour-Garonne district case (southwest France) (in Geochemistry of the Earth's surface, Mark E. Hodson (prefacer))
Mineralogical Magazine (February 2008) 72 (1): 321-324
- actinides
- Adour Basin
- aquifers
- C-14
- carbon
- carbonate rocks
- Cenozoic
- clastic sediments
- Eocene
- Europe
- France
- Garonne River
- ground water
- isotope ratios
- isotopes
- limestone
- metals
- O-18/O-16
- oxygen
- Paleogene
- radioactive isotopes
- residence time
- S-34/S-32
- sand
- sedimentary rocks
- sediments
- stable isotopes
- sulfur
- Tertiary
- U-234
- U-238/U-234
- uranium
- Western Europe
U-series were investigated in groundwaters from two water bodies of the Eocene sands aquifer, southwest France. The (super 234) U/ (super 238) U activity ratios are always larger than the equilibrium value, some waters being highly enriched in (super 234) U (as large as 13.5). In the southern water body, (super 234) U/ (super 238) U ratios correlate with (super 14) C ages (with one exception). Such U isotopic signatures may allow the evaluation of the residence time of groundwaters within their aquifer using an open-system model based on U activity ratios and concentrations. It is suggested that the "oldest" groundwaters from the southern water body are no older than 38 ky, whereas the maximum "age" of groundwaters from the northern water body, though overall of the same order of magnitude, could be slightly younger (25 ky).
