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On the Potential Joint Use of Uranium and Carbon Isotopes for Groundwater Dating
  • Alexander Malov
Alexander Malov
Federal Center for Integrated Arctic Research of Russian Academy of Sciences: Arkhangelsk, RU

Corresponding Author:malovai@yandex.ru

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The well-investigated aquifer in southern Tunisia have been selected from the literature to test the potential use of uranium isotopic compositions as a groundwater dating method. This is the Senonian carbonate aquifer of the Nefzaoua basin (https://doi.org/10.1016/j.quaint.2020.01.024). For the this aquifer, an increase in U concentrations along the generalized flow path is observed in proportion to an increase in total dissolved solids, which may indicate the predominance of dissolution processes over alpha-recoil processes under oxidizing conditions for uranium. There is also an increase in U concentrations with a decrease in 14C values. For this aquifer, positive results were obtained on uranium-isotope dating. It was found that the groundwater residence time in the aquifer increases from 440 to 11,300 years from the recharge area along the generalized flow path (Figure). Uranium age correction model under oxidizing conditions in the aquifer is given in “Malov, 2018. Evolution of the groundwater chemistry in the coastal aquifers of the south-eastern White Sea area (NW Russia) using 14C and 234U-238U dating. Science of the Total Environment. https://doi.org/10.1016/j.scitotenv.2017.10.197” It is shown that for uranium-isotope dating of groundwater, three main conditions must be met: i) oxidizing conditions for uranium in the aquifer, ii) an increase in uranium concentrations with a decrease in 14C activities, and iii) the homogeneity of the aquifer in terms of hydraulic conductivity and lithological composition. The author understands the reality of the fact that groundwater dating methods are under development and improvement. Nevertheless, analysis of the evolution of the chemical and isotopic composition of groundwater, analysis of the geological and hydrogeological history of the region, hydraulic estimates of groundwater velocities in aquifers, hydrodynamic and balance justifications for the formation of groundwater, and analysis of the composition of stable isotopes can increase the reliability of dating. In the future, it is necessary to continue studies to assess the retardation factor and recoil loss factor in order to improve the uranium-isotope method for dating groundwater under oxidizing conditions for uranium. This work was supported by the RFBR (project no. 20-05-00045_A)