Geochemical characteristics of shoreline sediments from the Bay of Bengal, Bangladesh: Implications for provenance and source‐rock weathering

The detrital mode and geochemical composition of sediments from a coastal section of the Bay of Bengal, Bangladesh, were examined to identify sediment distribution, maturity, provenance and source-area weathering. The sediments are quartzrich with little feldspar and few lithic fragments (Q(78)F(10)L(12)), indicating derivation from a quartzose recycled orogen. The sediments exhibit high SiO2 (88-94 wt%) and low Al2O3 (4-5 wt%) contents. SiO2 shows a marked linear trend and strong negative correlation with Al2O3(r = -0.95), consistent with the high quartz content. The upper continental crust (UCC) normalization patterns for the sediments show marked depletion in Na2O, CaO, MgO, Sr, Sc and Fe-V, but slightly increased Th and SiO2, indicating a felsic UCC source. The sediments have low to moderate compositional maturity and are classified as sublitharenite. The Al2O3/TiO2 ratio (15-38) suggests that the sediments were derived from intermediate to felsic igneous rocks. Rareearth element profiles, discrimination diagrams and various elemental ratios are all consistent with the derivation of the sediment from a felsic igneous source area. The values of the chemical index of alteration (-65-69), chemical index of weathering (-75-84) and plagioclase index of alteration (-70-81) indicate that the source rocks underwent moderate chemical weathering. Comparison with potential Himalayan sediment sources and rocks support derivation of the investigated shoreline sediments from felsic quartzose recycled detritus of that area.