PRELIMINARY CHEMICAL WEATHERING INTENSITY INFERRED FROM MODERN FINE-GRAINED FLUVIAL SEDIMENTS OF THE PANTANAL BASIN (BRAZIL)

Elemental analysis provides an understanding of how sediments are generated by chemical weathering in a source-to-sink system. This study was undertaken to resolve the chemical composition of fluvial fine-fraction (silt+clay) sediments from the Pantanal Basin in western Brazil. The Pantanal, the world’s tropical largest wetland, lies in a low elevation basin that accumulates sediment from megafan rivers draining the surrounding plateau. Wavelength-dispersive X-ray fluorescence analysis was performed on sediment samples (n=38) prepared as fused glass discs, which resulted in a suite of major element oxide data including SiO2, Al2O3, Fe2O3, K2O, Na2O, CaO, MgO, P2O5, TiO2, and MnO. These elemental abundances have been used to calculate the chemical index of alteration (CIA) and the Weathering Index of Parker (WIP), which provides a basis for evaluating the weathering intensity at each sample site. Preliminary results indicate a relative increase in weathering intensity towards the Paraguay River from E-W, and a gradient from N-S towards the basin’s southern outlet. The results provide a better understanding of sediment generation and transport in the Pantanal, and how hydroclimatic and other environmental factors influence patterns of modern sediment accumulation in the tropical lowlands.