Isotope Signs (234U/238U, 2H, 18O) of Groundwater: An Investigation of the Existence of Paleo-Permafrost in European Russia (Pre-Volga Region)
Author:
Yakovlev Evgeny,Tokarev Igor,Zykov Sergey,Iglovsky Stanislav,Ivanchenko Nikolay
Abstract
The isotopic (234U/238U, 2H, 18O) and chemical composition of groundwater on the right bank of the Volga River along the middle reach (European Russia) was studied down to a depth of 400 m. These data allow diagnosis of the presence of a three-component mixture. The first component is modern/young fresh recharge water of the Holocene age. It has the isotopic composition of water δ18O → −12.9 ‰ and δ2H → −90 ‰, close to modern precipitations, and the equilibrium isotopic composition of uranium 234U/238U → 1 (by activity). The second component is slightly salted water of the late or postglacial period with δ18O → −17.0 ‰ and δ2H → −119 ‰, and a small excess of uranium-234 234U/238U ≈ 4. The third component is meltwater formed as result of permafrost thawing. It is brackish water with δ18O ≈ −15.0 ‰ and δ2H ≈ −110 ‰, and a maximum excess of uranium-234 234U/238U ≈ 15.7. The salinity of this water is associated with an increase of the SO42−, Ca2+ and Na+ content, and this may be due to the presence of gypsum in water-bearing sediments, because the solubility of sulfates increases at near-zero temperature. We explain the huge excess of uranium-234 by its accumulation in the mineral lattice during the glacial age and quick leaching after thawing of permafrost.
Funder
Russian Science Foundation
Subject
Water Science and Technology,Aquatic Science,Geography, Planning and Development,Biochemistry
Cited by
1 articles.
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