Provenance, weathering, climate and tectonic setting of Padma River sediments, Bangladesh: A geochemical approach

The major, trace, and rare earth element (REE) compositions of sediments from the Padma River, Bangladesh have been examined using XRF and INAA analysis to determine their geochemical compositions, provenance, climate, weathering intensity and tectonic setting. The Padma River sediments from the region were remarkably comparable, demonstrating elemental depletion and pointing to a low geochemical maturation. Sediment samples are classified as arkose which are considered as chemically immature sediments, deposited under semiarid to semi-humid climatic conditions due to the weakening of Indian summer monsoon. The low CIA values (48.6-58.8), PIA (48.1-63.4) and Rb/Sr ratios of the river sediments suggest low intensity of chemical weathering in the source area. The Padma River is originated from the Higher Himalaya and the sediments derived from metasediments (Higher Himalayan Crystalline Series) as are evident by major, trace elements discriminate diagram and REE pattern. Most of the sand samples were derived from felsic source rock (granite) whereas some samples are plotted in the intermediate rock types (granodiorite) in the A-CNK-FM and discriminant function diagrams. High LREE enrichment and relatively flat HREE fractionation in chondrite-normalized REE patterns (LaN/YbN = 7.50-13.20) demonstrated felsic source origin. TiO2 versus Zr plot shows that Padma River sediments have felsic to intermediate provenance. According to Log (K2O/Na2O) vs. SiO2 discriminant diagram and La-Th-Sc, Th-Sc-Zr/10 ternary plot, the Padma River sediments were deposited in passive continental margin. The Padma River sediments have been compared with Yarlung Zangbo River (YZR), Brahmaputra-Jamuna River (BJR), Ganges River (GR) and Upper Meghna River (UMR), which results suggest that there is contrast among the sediments of different Himalayan Rivers in relation to provenance, weathering intensity and tectonic setting.