Intensity of Chemical Weathering in Late Precambrian: New Data on the Riphean Stratotype (Southern Ural)

Abstract

The values of Ni/Co, La/Sc, and Th/Cr (indicators of the composition of rock complexes eroded in paleowatersheds) and the values of CIA, Rb/Al, K/Al and K/Rb (indicators of the intensity of chemical weathering on land), typical for fine-grained clastic rocks of the Riphean of the Southern Urals were compared to the data given in the publication “Long-term evolution of terrestrial weathering and its link to Earth’s oxygenation” by Bayon G., Bindeman I.N., Trinquier A., Retallack G.J., and Bekker A. (Earth Planet. Sci. Lett., 2022, v. 584. 117490). It was shown that the average Rb/Al ratio (0.0014 ± 0.0006, n = 66) typical of the Riphean clayey rocks of the Southern Urals, together with other data, suggests that for more than 1.10 Ga (from ~1.75 to ~0.60 Ga) the intensity of chemical weathering in paleowatersheds was relatively low. This is in good agreement with the data obtained by Bayon et al. The material presented in the article allows us to consider that the composite “world” curves of K/Al, Rb/Al, and K/Rb by Bayon et al. and the same curves for clayey rocks of the Riphean of the Southern Urals are sufficiently comparable. Thus, data on the lithogeochemical characteristics of fine-grained clastic/clayey rocks of the Riphean stratotype significantly expand our understanding of the nature of chemical weathering processes on land in the interval 1.75–0.60 Ga ago.