Geochemical data from subsurface sands of the lower Brahmaputra (Jamuna) River are presented to reconstruct sediment provenance, evaluate weathering intensity, and infer tectonic setting. The analysis of major, trace, and rare earth elements (REEs) in these sands indicates that they predominantly consist of quartz, primarily classified as litharenite to sublitharenite, suggesting a deficiency in mineralogical maturity. The significant enrichment of LREEs, along with a relatively flat HREE fractionation (La/Yb)N = 9.91-10.98, and pronounced negative Eu anomalies (Eu/Eu* = 0.51 to 0.80), suggest a source dominated by felsic materials with minor contributions from mafic sources, aligning with the hypothesis of derivation from Himalayan orogenic lithologies. Low to moderate levels of chemical alteration, together with geochemical discrimination diagrams, indicate that sediments originated and were transported under semi-arid climatic conditions. Geochemical provenance and tectonic discrimination diagrams further suggest that the lower Brahmaputra sands were influenced by collisional orogeny and were dominantly derived from an active continental margin, highlighting their strong relationship with Himalayan tectonics. The low weathering index and chemical immaturity imply that both tectonics and climate play crucial roles in controlling sedimentation in the Bengal Basin.