Enhanced pedogenic weathering of aeolian dust as a Pleistocene carbon sink on the Chinese Loess Plateau

“Allochthonous weathering”—the continued weathering of plateau-derived detritus after its transport to climatically more favorable lowland basins—is a key mechanism by which tectonic uplift sustains high continental weathering fluxes. However, isolating these allochthonous weathering signals has remained challenging. To address this, we developed a novel methodological framework to extract post-depositional pedogenic weathering signals from a 6-million-year loess−paleosol and red clay sequence in the south-central Chinese Loess Plateau. This approach is predicated on the observation that post-depositional pedogenesis increases weathering intensity while reducing the mean grain size of aeolian sediments. Simultaneously, owing to its chemical stability, quartz undergoes passive enrichment as mobile elements are preferentially leached. Consequently, the relationship between quartz enrichment, weathering intensity, and mean grain size deviates from patterns dictated by dynamic sorting, leading to a measurable decoupling of these parameters. Using this method, we reconstructed the pedogenic weathering history since the late Miocene. Our results reveal that Pliocene red clay exhibits significantly stronger pedogenic intensity than Pleistocene loess−paleosol, which is primarily governed by dust accumulation rates. Crucially, the weathering-driven carbon sink flux in the Chinese Loess Plateau was higher during the drier, cooler Pleistocene than in the warmer, more humid Pliocene, providing direct evidence of enhanced land-surface weatherability. These findings suggest that allochthonous weathering of Tibetan Plateau−derived sediments represents a potentially important mechanism in the global carbon cycle. Future research should investigate how sediment source-to-sink evolution modulates erosion−weathering processes and the carbon cycle under coupled Cenozoic tectonic and climatic forcing.