CLAY MINERAL COMPOSITION OF MODERN SEDIMENTS IN THE PANTANAL FLOODPLAIN, BRAZIL

Clay mineral composition of modern sediments in tropical floodplains are useful to decipher the variable influences of weathering, climate, vegetation, soils, and bedrock lithology. The Pantanal is the world's largest freshwater wetland and is a world-class environment to examine weathering patterns and processes in a tropical lowland riverine basin. Here, we present the results of modern sediments (n = 40 samples) from the Pantanal rivers. Sample collection was informed by pour point analysis of sub-watersheds, to ensure broad spatial coverage downstream of major river channel confluences. Each sample was sieved to obtain the silt+clay fraction and chemically pre-treated to remove carbonates and organic matter, and subsequently fractionated by centrifugation following Stoke's Law. The resulting clay fraction was then freeze-dried and prepared as oriented clay mounts for X-ray diffraction scans. Semi-quantitative analyses of the peak areas were used to determine clay mineral composition for each sample. Preliminary results demonstrate distinct changes to clay mineral assemblage at different sampling points. These results create a modern snapshot to understand how the interacting environmental factors influence weathering and sediment transport, which are recorded in clay mineral composition.