Major and trace element geochemistry of Brahmaputra River sediments in Bangladesh and implications for provenance and contamination

The Brahmaputra River, a major sediment conveyor from the Himalayan orogen, provides valuable insights into geological processes such as lithologies, weathering regimes, and environmental conditions. This study presents a holistic multi-proxy investigation integrating polarizing microscopy, X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), and pollution assessment using the pollution load index (PLI) and geo-accumulation index (Igeo). Microscopic and mineralogical analyses reveal that the sediments are dominated by quartz, feldspar, and mica, along with resistant heavy minerals including magnetite, rutile, and monazite. SEM analysis shows textural heterogeneity of sediment grains, characterized by sub-angular to well-rounded morphologies. Geochemically, the sediments are enriched in SiO2 (66.36–74.34 wt%) and rare earth elements including La, Ce, Pr, and Nd, reflecting derivation from felsic-intermediate Himalayan source-rocks. The Chemical Index of Alteration (CIA: 58.47–62.77) indicates a mixed felsic-intermediate provenance from the Higher and Lesser Himalayas, having undergone weak chemical weathering. Contamination assessment indicates that As and Cd are the primary pollutants, showing moderate to strong enrichment, while Cr enrichment is predominantly lithogenic, and pollution load index (PLI: 2.07–9.42) values suggest moderate to high cumulative contamination at several sites. These findings provide comprehensive insights into sediment provenance, weathering intensity, and contamination impacts in the Brahmaputra River system. Future studies should focus on temporal monitoring and advanced isotopic tracing to better understand sediment evolution and anthropogenic impacts in the river system.