Preprint Article Version 1 This version is not peer-reviewed

Evolution of the Uranium Isotopic Compositions of the Groundwater and Rock in the Sandy-Clayey Aquifer

Version 1 : Received: 4 October 2017 / Approved: 4 October 2017 / Online: 4 October 2017 (16:45:54 CEST)

A peer-reviewed article of this Preprint also exists.

Malov, A.I. Evolution of Uranium Isotopic Compositions of the Groundwater and Rock in a Sandy-Clayey Aquifer. Water 2017, 9, 910. Malov, A.I. Evolution of Uranium Isotopic Compositions of the Groundwater and Rock in a Sandy-Clayey Aquifer. Water 2017, 9, 910.

Journal reference: Water 2017, 9, 910
DOI: 10.3390/w9120910

Abstract

Uranium isotopes actively investigated as mechanistic or time scale tracers of natural processes. This paper describes the occurrence and redistribution of U in the Vendian aquifer of the paleo valley at NW Russia. Forty-four rock samples were collected from boreholes, and twenty-five groundwater samples. The U, Fe concentration, and 234U/238U activity ratio were determined in the samples. We estimated the 14C and 234U-238U residence time of groundwater in an aquifer. It has been established that the processes of chemical weathering of Vendian deposits led to the formation of a strong oxidation zone, developed above -250 m.a.s.l. The inverse correlation between the concentrations of uranium and iron is a result of removal of U from paleo valley slopes in oxidizing conditions and accumulation of U at the bottom of the paleo valley in reducing conditions, and accumulation of Fe on the slopes and removal from bottom. Almost all U on the slopes replaced by a newly formed hydrogenic U with a higher 234U/238U activity ratio. After that dissolution and desorption of hydrogenic U was occurred from the slopes during periods without any glaciations and marine transgressions. Elevated concentrations of U preserved in not oxidized lenses at the paleo valley bottom.

Subject Areas

aquifer, rock, radioactive isotopes, groundwater dating

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