A.I. MALOV (FCIARctic)

Evolution of uranium isotopic composition in the sandy-­clay aquifer of the paleo­-valley in the Northern Dvina depression

The origin and redistribution of U isotopes in the aquifer of Vendian sandy­-clay deposits of a paleo-­valley in northwestern Russia is described. Chemical weathering of Vendian deposits led to the formation of a thick oxidation zone developed above 250 m.b.s.l. The inverse correlation between U and Fe concentrations is a result of U removal from paleo-­valley slopes under oxidizing conditions and its accumulation on the bottom under reducing conditions, and accumulation of Fe on the slopes and its removal from the bottom. Accordingly, the groundwater near the redox barrier is characterized by the highest U concentration and the activity of the ²³⁴U isotope that handicaps their use for drinking and medicinal purposes. Radiologically, the groundwater located near recharge zones is the safest.
Keywords: radioactive isotopes, Vendian deposits, groundwater dating.