Secular variation in the magnitudes of Phanerozoic and Precambrian weathering

Abstract

An investigation of terrestrial weathering reveals that the magnitude of Phanerozoic weathering was greater than that of Precambrian weathering; specifically, 36 ± 3 % of the labile constituents, SiO2, CaO, Na2O, and K2O, were removed from the protoliths of five modern soils, 37 ± 11 % from four Cretaceous protoliths, 24 ± 4 % from four Cambrian protoliths, 18 ± 2 % from nine Proterozoic protoliths, and 17 ± 2 % from four Archean protoliths. Potassium metasomatism is a common phenomenon in paleosols, and fourteen of seventeen of the Cambrian and Precambrian paleosols record the post-weathering addition of potassium, which was corrected for in calculating mass fluxes of weathering. The greater magnitude of Phanerozoic weathering compared to Precambrian weathering is attributed to the effects of elevated concentrations of organic acids in the critical zone, which were produced by land plants that evolved in Cambrian time and eventually colonized the continents.