Water stable isotopes, radiocarbon, noble gases and krypton-81 study of thermal groundwater from Upper to Mid-Pleistocene recharge age in deep aquifers of Argentina.

MARTINEZ D.E.; ALBOUY R.; BERTOLIN L.; JIANG W.; KRUSE E.; LEXOW C.; LU Z.; MABRY J.; MASUMOTO T.; MAURICIO QUIROZ LONDOÑO; RITTERBUSCH F.; ROMEO N. ; YANG G.; ZÁRATE, M.

Viena

Congreso; EGU General Assembly 2021; 2021

European Geophysycal Union

Recharge environmental conditions and residence time, can be studied by the application ofdifferent tracers. Several tracers are useful as proxies of the environmental recharge conditions,such as water stable isotopes deuterium and oxygen-18, and the dissolved noble gases. Othertracers are applied in order to know when the recharge occurred. Carbon-14 dating is a widelyapplied method for dating old groundwater, having an application range up to around 30 ky.Noble gases, as non-reactive and water-soluble substances, constitute useful tracers for studyingdifferent processes in hydrologic cycles. One of the applications is dating very old groundwaterbeyond the range of 14C. It can be done in a semi-quantitative way by the accumulation of 4He, andquantitatively through the radionuclide 81Kr (t1/2 = 229,000 y), a more robust method for datinggroundwater up to 1.3 million years.The province of Buenos Aires, Argentina, hosts three deep sedimentary basins, from north tosouth, Salado, Claromecó and Colorado, with areas of 85,000 km2, 3,100 km2 and 125,000 km2,respectively. In these basins, a thick continental sequence of Neogene sediments containsconfined thermal aquifers, at depths from hundreds meters to more than 1 km. The rechargeconditions and the water age of the Neogene aquifers are studied through water stable isotopes,4He and 81Kr tracers. 10 deep wells were sampled for δ2H, δ18O, 3H, 14C, for noble gases usingclamped copper tubes, and for 81Kr with a gas extractor. 4He analyses were performed at the IAEAlaboratory by mass spectrometry, and 81Kr at the ATTA laboratory of USTC.3H contents were not detectable in all of the cases, thus no young water components exist. Byplotting the isotopic results in a δ2H vs δ18O diagram, four groups of samples can be recognized.