Variations of the 238U/235U isotope ratio in metasedimentary rocks and evidence of changes in sedimentation conditions during the Ediacaran period of the Neoproterozoic

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Abstract

The isotopic composition of uranium is a new geochemical indicator that facilitates reconstruction of the redox conditions of geological processes. In this paper the results of study of the 238U/235U isotope ratio in the Neoproterozoic metasedimentary rocks of the Baikal–Patom fold belt (Northern Transbaikalia) were obtained using the MC-ICP-MS method and 233U+236U double spike. The scale of 238U/235U ratio variations (δ238U = –0.37 to –0.11‰) is within the range of (–0.39 to +0.15‰), typical of metasedimentary terrigenous rocks of marine origin. In terms of the δ238U values, uranium of the BPB rocks studied is heavier than seawater uranium (δ238U = –0.41 ± 0.03). There is a correlation between the δ238U value in the rocks and their position in the stratigraphic section. Variations of the 238U/235U ratio in the terrigenous-carbonate sequences of BPB indicate that the sedimentation conditions changed and euxinic conditions were established in the course of evolution of the paleobasin in the Late Ediacarian Period.

About the authors

A. V. Chugaev

Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry of the Russian Academy of Sciences

Author for correspondence.
Email: chug@igem.ru
Russian Federation, 35, Staromonetny, Moscow, 119017

I. V. Chernyshev

Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry of the Russian Academy of Sciences

Email: chug@igem.ru

Academician of the RAS

Russian Federation, 35, Staromonetny, Moscow, 119017

A. E. Budyak

Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences

Email: chug@igem.ru
Russian Federation, PBox 9, 1a, Favorsky street, Irkutsk, 664033

G. V. Mandzhieva

Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry of the Russian Academy of Sciences

Email: chug@igem.ru
Russian Federation, 35, Staromonetny, Moscow, 119017

A. S. Sadasyuk

Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry of the Russian Academy of Sciences

Email: chug@igem.ru
Russian Federation, 35, Staromonetny, Moscow, 119017

B. I. Gareev

Kazan Federal University

Email: chug@igem.ru
Russian Federation, 18, Kremliovskaya street, Kazan, 420008

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