U redistribution in the Vendian Siltstones of the Paleo Valley (NW Russia)

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• 作者：Alexander I. Malov ; ^{malovai@yandex.ru}
• 关键词：uranium isotopes ; groundwater ; rock
• 刊名：Procedia Earth and Planetary Science
• 出版年：2017
• 出版时间：2017
• 年：2017
• 卷：17
• 期：Complete
• 页码：658-661
• 全文大小：160 K
• 卷排序：17

文摘

This paper describes the occurrence and redistribution of U in the Vendian siltstones of the paleo valley at NW Russia. The main flow of U to the study area and its deposition as a result of hydrolysis, adsorption on natural sorbents and changes oxidizing conditions of the environmental in reducing conditions was in Vendian-Lower Carboniferous. During Mesozoic-Pliocene occurred main redistribution of accumulated U. As a result, almost all the U on the slopes of the paleo valley could be replaced by a newly formed hydrogenic (precipitated from groundwater) U with a higher 234U/238U activity ratio. Elevated concentrations of U have been preserved in not oxidized lenses at the paleo valley bottom. Now there is a hydrogenic U dissolution and desorption from the slopes of paleo valley, its concentration in fresh water with 14C Age to 6 ka reach 12 ppb, in the rocks downgraded to 1.2ppm. The maximum U concentrations are characteristic of old waters with 14C Age from 25 to 35 ka, located on the redox barrier. Behind the redox barrier, the U becomes restored to U4+ and precipitates, its concentration in the rocks reach 20ppm.