Early Devonian Vascular Plants Enhanced Chemical Weathering: Insights From Paleosols in South China

Abstract

The colonization of land by plants during the early Paleozoic is hypothesized to have significantly intensified global chemical weathering, thereby triggering climatic and environmental change. To test this hypothesis, we investigated Lower Devonian paleosols from Qujing, South China, using mineralogical, elemental, and lithium isotope analyses of both bulk samples and clay fractions (<2 μm). The chemical Index of Alteration (CIA) for these paleosols ranges from 66.8 to 82.7, with clay fractions containing an average of 15% kaolinite, indicating moderate chemical weathering. Lithium and rare earth element concentrations in the clay fraction (Li _clay and ΣREE _clay ) average more than three times those in bulk samples (Li _bulk and ΣREE _bulk ), suggesting that secondary clay mineral formation during weathering preferentially incorporates these elements. The most negative δ ⁷ Li _clay value (−7.0‰), coincident with peak CIA, Li _clay /Li _bulk , and ΣREE _clay /ΣREE _bulk ratios, occurred in the early Pragian Stage, indicating a pulse of intensified chemical weathering. Together with abundant fossilized vascular plant traces in the Lower Devonian succession, these results suggest that enhanced weathering is linked to plant radiation during this interval. This study provides multi‐proxy terrestrial evidence from South China for a pronounced intensification of chemical weathering during the late Lochkovian‐early Pragian, directly correlating this pulse with the regional radiation of early vascular plants.