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Ammar, F.H.; Deschamps, P.; Chkir, N.; Zouari, K.; Agoune, A.; Hamelin, B. |
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Title |
Uranium isotopes as tracers of groundwater evolution in the Complexe Terminal aquifer of southern Tunisia |
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Journal Article |
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2020 |
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Quaternary International |
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547 |
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33-49 |
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CT southern Tunisia, Holocene, Mixing, Radicarbon, Uranium isotopes, Water-rock interaction |
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Abstract |
The Complexe Terminal (CT) multi-layer aquifer is formed by Neogene/Paleogene sand deposits, Upper Senonian (Campanian-Maastrichtian limestones) and Turonian carbonates. The chemical composition and isotopes of carbon and uranium were investigated in groundwater sampled from the main hydrogeological units of the (CT) aquifer in southern Tunisia. We paid special attention to the variability of uranium contents and isotopes ratio (234U/238U) to provide a better understanding of the evolution of the groundwater system. Uranium concentrations range from 1.5 to 19.5 ppb, typical of oxic or mildly reducing conditions in groundwaters. The lowest concentrations are found southeast of the study area, where active recharge is supposed to take place. When looking at the isotope composition, it appears that all the samples, including those from carbonate levels, are in radioactive disequilibrium with significant 234U excess. A clear-cut distinction is observed between Turonian and Senonian carbonate aquifers on the one hand, with 234U/238U activity ratios between 1.1 and 1.8, and the sandy aquifer on the other hand, showing higher ratios from 1.8 to 3.2. The distribution of uranium in this complex aquifer system seems to be in agreement with the lithological variability and are ultimately a function of a number of physical and chemical factors including the uranium content of the hosting geological formation, water-rock interaction and mixing between waters having different isotopic signatures. Significant relationships also appear when comparing the uranium distribution with the major ions composition. It is noticeable that uranium is better correlated with sulfate, calcium and magnesium than with other major ions as chloride or bicarbonate. The 14C activities and δ13C values of DIC cover a wide range of values, from 1.1 pmc to 30.2 pmc and from −3.6‰ to −10.7‰, respectively. 14C model ages estimated by the Fontes and Garnier model are all younger than 22 Ka and indicate that the recharge of CT groundwater occurred mainly during the end of the last Glacial and throughout the Holocene. |
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1040-6182 |
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THL @ christoph.kuells @ ammar_uranium_2020 |
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119 |
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Hamutoko, J.; Mapani, B.; Ellmies, R.; Bittner, A.; Külls, C. |
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Title |
A fingerprinting method for the identification of uranium sources in alluvial aquifers: An example from the Khan and Swakop Rivers, Namibia |
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2014 |
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Physics and Chemistry of the Earth, Parts A/B/C |
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72 |
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34-42 |
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Pergamon |
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THL @ christoph.kuells @ Hamutoko2014fingerprinting |
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19 |
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Grodek, T.; Enzel, Y.; Morin, E.; Jacoby, Y.; Dahan, O.; Benito, G.; Kulls, C.; Geller, A.; Van Langenhove, G.; Seely, M. |
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Flood hydrology, flood routing, paleohydrology and the estimation of water resources along the shallow alluvial aquifers of the Kuiseb River, Namibia |
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2008 |
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Abstracts – Israel Geological Society |
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2008 |
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37 |
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Israel Geological Society |
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THL @ christoph.kuells @ Grodek2008flood |
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56 |
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Stone, A.E.C.; Thomas, D.S.G. |
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Casting new light on late Quaternary environmental and palaeohydrological change in the Namib Desert: A review of the application of optically stimulated luminescence in the region |
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2013 |
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Journal of Arid Environments |
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93 |
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40-58 |
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Namib Desert, Optically stimulated luminescence dating, Palaeoenvironment, Palaeohydrology, Quaternary, Southern Africa |
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The application of optically stimulated luminescence (OSL) dating in the Namib Desert is casting new light on late Quaternary environments. OSL has been applied to: (i) complex linear dunes, alongside ground penetrating radar stratigraphy in order to establish dune migration rates, (ii) fluvial lithofacies associations that distinguish between flood deposits and river end points, in order to constrain the timing of periods of higher discharge and conditions relatively drier than present and (iii) aeolian sand interbedded with carbonate deposits in order to provide chronologies for water-lain interdune sediments. We present and review the contribution of these data to enhancing reconstructions of the palaeoenvironments and palaeohydrology of the west coast of Namibia, particularly the increased confidence in interpretations provided by lithofacies analysis of the river deposits. This includes major silt deposits, which have had a contested palaeohydrological interpretation, such as the Kuiseb River Homeb Silts. We conclude that OSL should remain a key chronological technique to further elucidate the palaeoenvironmental history of southern Africa. |
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0140-1963 |
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THL @ christoph.kuells @ stone_casting_2013 |
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98 |
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Stone, A.E.C.; Edmunds, W.M. |
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Naturally-high nitrate in unsaturated zone sand dunes above the Stampriet Basin, Namibia |
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2014 |
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Journal of Arid Environments |
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105 |
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41-51 |
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Kalahari, Namibia, Nitrate in the unsaturated zone, Stampriet Basin, Transboundary basin, Unsaturated zone recharge |
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Elevated groundwater nitrate levels are common in drylands, often in excess of WHO guidelines, with concern for human and animal health. In light of recent attempts to identify nitrate sources in the Kalahari this paper presents the first unsaturated zone (USZ) nitrate profiles and recharge rate estimates for the important transboundary Stampriet Basin, alongside the first rainfall chemistry records. Elevated subsurface nitrate reaches 100–250 and 250–525 mg/L NO3–N, with NO3–N/Cl of 4–12, indicating input above evapotranspiration. Chloride mass balance recharge rates range from 4 to 27 mm/y, indicating a vertical movement of these nitrate pulses toward the water table over multi-decadal timescales. These profiles are sampled from dune crests, away from high concentrations of animals and without termite mounds. Given low-density animal grazing is unlikely to contribute consistent spot-scale nitrate over decades, these profiles give an initial estimate of naturally-produced concentrations. This insight is important for the management of the Stampriet Basin and wider Kalahari groundwater. This study expands our knowledge about elevated nitrate in dryland USZs, demonstrating that it can occur as pulses, probably in response to transient vegetation cover and that it is not limited to long-residence time USZs with very limited downward moisture flux (recharge). |
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0140-1963 |
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THL @ christoph.kuells @ stone_naturally-high_2014 |
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91 |
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