Petrology of modern river sands in China across tectonic, topographic and climatic gradients: Implications for sediment generation

Sandstone composition is widely used to infer tectonic setting, yet the combined effects of parent‐rock lithology, climate and topography on sand composition and texture within sedimentary routing systems remain difficult to constrain. This study investigates modern river sands across diverse tectonic, topographic, climatic and bedrock‐lithological settings in China, integrating quantitative compositional and textural data from 376 sediment samples. Our results show that sand composition is controlled primarily by parent‐rock lithology rather than the tectonic setting of the bedrock. Sands derived from most lithologies broadly reflect their parent‐rock characteristics, whereas carbonate and basaltic detritus exhibit more variable sedimentary behaviour owing to their higher susceptibility to weathering. Under strong physical erosion, rapid denudation and limited chemical weathering, carbonate and basaltic lithic fragments are preferentially preserved; conversely, they are readily decomposed or eliminated under more intense chemical weathering. Parent‐rock lithology also governs the morphology of lithic fragments: low‐grade metasedimentary rocks tend to produce elongated grains with high aspect ratios, whereas higher‐grade metasedimentary or more resistant lithologies typically yield coarser and equant fragments. We contend that tectonic setting affects river sand composition mainly by establishing the regional parent‐rock framework through ancient tectonic evolution and by shaping modern topography through neotectonic activity. Climatic influence on coarse‐grained sediments is most clearly recorded by carbonate lithic fragments, which decrease systematically from arid to humid regions. Given the distinct source‐to‐sink behaviours of sands and muds, we recommend conducting integrated mineralogical, petrographic and geochemical analyses on both detrital fractions, jointly considering tectonic, topographic, lithological and climatic controls to better understand river sediment generation processes. These findings suggest that tectonic interpretations based solely on sandstone composition should be treated with caution and provide a quantitative framework for extending modern river sand datasets to deep‐time sedimentary systems.