Provenance, transport and storage of sediments in Amazon rivers

Abstract

Understanding the factors controlling the origin, flux and fate of sediments through space and time is now an objective of the surface processes research. In this context, the Amazon region encompasses the major watershed (7,050,000 km2) of the Earth, forming a continental scale "source to sink" system. The tributaries of the Amazon River drain areas with different bedrock geology, tectonic regime, geomorphology, climate, vegetation and land use, producing high variability in the production and flux of sediments. The Quaternary evolution and the present dynamics of the Amazon rivers are related to many aspects of the Amazonia biodiversity, human activities such as hydroelectricity production, deforestation and land use. Many studies about the provenance, supply and storage of sediments in the major tributaries of the Amazon River focus on short timescales (days to few years). Few studies investigate the provenance and flux of sediments transported by Amazon Rivers during the Quaternary and considering the present knowledge about the Amazon geology, climate and biology and the current analytical techniques. This research proposal deals with the sediment provenance and supply within the Amazon watershed in the lower reach of three great tributaries: the Negro, Madeira and Xingu rivers. The Negro, Madeira and Xingu rivers supposedly have different sedimentary dynamics, delivering sediments with different characteristics to the Amazon River channel. The sediments in the lower portion of these three tributaries will be characterized through the analysis of inorganic and organic components using a multi-proxy approach (grain size, heavy minerals, clay minerals, luminescence, organic compounds and carbon isotopes, major chemical elements and radionuclides). These data will be evaluated under a geochronological-geological-geomorphological framework. We hope to improve the knowledge about how the Amazon Rivers work in a decadal to millennial timescale through the study of their Pleistocene and Holocene sedimentary record. This can give valuable information about the Amazon River dynamics, which is fundamental for a better understanding of distribution of animal species, carbon cycling, delivery of nutrients to the ocean and impacts of future climate change. Regarding the development of research methods, the luminescence sensitivity is a promise provenance proxy for terrigenous sediments. This project will be a robust test for this method. The scientific results will be disseminated through papers in journals, scientific conferences and outreach activities. (AU)