Major, trace, and REE geochemistry of the Meghna River sediments, Bangladesh: Constraints on weathering and provenance

The major, trace, and rare earth element (REE) compositions of sediments from the Meghna River in Bangladesh have been examined to infer their sediment type, compositional maturity, chemical weathering intensity, provenance, and tectonic setting. Geochemically, the sediments are classified as litharenites, shale, and wacke. The ICV (Index of Compositional Variability) values (0.92 to 1.10) indicate that the sediments have low compositional and mineralogical maturity. Major and trace element abundances display marked depletion of Na2O, CaO, MgO, K2O, Fe2O3T, Sr, and Ba relative to UCC (upper continental crust), suggesting loss of feldspars during chemical weathering in the source. Zirconium, Th, Ce, and Y are enriched relative to UCC, indicating that these elements are primarily controlled by resistant heavy minerals. The CIA (Chemical Index of Alteration), PIA (Plagioclase Index of Alteration), and Rb/Sr and K2O/Rb ratios of the river sediments suggest low to moderate intensity of chemical weathering in the source area. Chondrite-normalized REE patterns show that high LREE enrichment, nearly flat HREE fractionation (La-N/Yb-N = 7.62 to 8.73) and marked negative Eu anomalies (Eu/Eu* = 0.49 to 0.69) suggesting a felsic source provenance. Several discriminant function diagrams and immobile trace element ratios (Th/Sc, Zr/Sc, Ce/Sc, and Ti/Zr) and REEs ( n-ary sumation LREE/HREE, Eu/Eu*, and Gd-N/Yb-N) parameters indicate that the river sediments were primarily derived from a common felsic source rock, with composition close to the average rhyolite, granodiorite, granite, and UCC. Tectonic setting signatures of the Meghna River sediments are both active continental margin and passive margin environments.