Intensity of Chemical Weathering in the Late Precambrian: New Data on the Riphean Stratotype, South Urals

The Ni/Co, La/Sc, and Th/Cr ratios (indicators of composition of rock complexes eroded on paleodrainages) typical of the South Urals Riphean fine-grained clastic rocks, as well as the CIA, Rb/Al, K/Al, and K/Rb values (indicators of intensity of terrestrial chemical weathering), are compared with data provided by G. Bayon, I.N. Bindeman, A. Trinquier, G.J. Retallack, and A. Bekker in the paper "Long-Term Evolution of Terrestrial Weathering and Its Link to Earth's Oxygenation" (Earth Planet. Sci. Lett., 2022, v. 584, 117490). It is shown that the Rb/Al-av value (0.0014 +/- 0.0006, n = 66) typical of the South Urals clayey rocks together with other data indicates a relatively low intensity of chemical weathering on paleodrainages for more than 1.10 billion years (from similar to 1.75 to similar to 0.60 Ga). This is in agreement with data of Bayon et al. (2022). Our material gives grounds to suggest that the composite world K/Al, Rb/Al, and K/Rb curves suggested by Bayon et al. (2022), as well as the curves for the South Urals Riphean clayey rocks, are comparable. Thus, the lithogeochemical characteristics of the fine-grained clastic/clayey rocks of a Riphean stratotype significantly expand our knowledge on processes of terrestrial chemical weathering in a range of 1.75-0.60 Ga.