The behavior of uranium and manganese under the diagenesis of carbonate sediments in small lakes of the Baikal region

Abstract

This report considers the experimental studies of diagenetic processes involving uranium and manganese in lacustrine sediments, especially to prove the possibility of formation of UO 2 + x reduced phases. Comparative research was performed for two lakes of different depths, hydrological conditions, mineraliza tion, and chemical composition of waters. The layerwise successive leaching of sediments was carried out, with subsequent measurement of the contents of the uranium 238 and 234 isotopes in chemogenic fractions of the sediment. By means of ESR and successive leaching, the profiles of the manganese oxide and hydroxide content over the section were obtained. The performed studies confirmed the hypothesis of the formation of UO 2 + x reduced phases in sediments. The sediments of the deeper freshwater Alyaty Lake are characterized by an increase in the content of the UO 2 + x reduced phases and a decrease of manganese oxides and hydrox ides downwards and upwards through the section, respectively. This conforms quite well to the behavior of these elements in oceanic sediments. The shallow saline Tsagan Tyrm Lake is characterized by the reverse sit uation: the bulk of the UO 2 + x reduced phase occurs in upper layers where, in turn, the oxide phases of man ganese are simply absent. This is caused by different reductive conditions in the sediments.