Tracing Sediment Provenance From the Upper, Middle and Lower Yangtze River: Insights From Source Rocks, Recycling and Weathering

ABSTRACT Large rivers are powerful agents in shaping Earth‐surface processes, strongly influenced by interactions among tectonics, climate, and sediment supply. However, the mechanism of how fluvial sediments respond to weathering and provenance remains poorly understood. This study investigates provenance and weathering processes in the Yangtze River, located in subtropical China, by analysing major and trace elements along with geochemical indices such as the Chemical Index of Alteration (CIA) and the Mafic‐Felsic‐Weathering (MFW) index. The Yangtze River exhibits physical erosion turning to chemical weathering from upper to lower reaches, suggesting low to medium weathering densities across the drainage. These spatial differences can be attributed to complex topography, climate variations, and lithological differences. The upstream feature diverse source rocks, including felsic, mafic, intermediate igneous, and quartzose sedimentary types, while felsic and quartzose sedimentary rocks dominate the mid‐lower reaches. Monsoonal climate dominates the weathering in mid‐lower reaches rather than the tectonics in upstream. Sediment sorting is slightly stronger in the upstream than the lower reaches, causing limited impacts on CIA assessment for weathering. The Songpan‐Garze Terrane and Yangtze Craton are the dominated source areas. Human activities like mining and dams, as secondary factors, affect sources and weathering. Overbank sediments effectively characterise source rock compositions, recycling, and weathering. This study advances the understanding of sediment geochemistry and provides a representative sampling to better evaluate weathering.