Origin and chronology of sandy substrates in Amazonia: implications for quaternary evolution of open vegetation ecosystems

Abstract

The Amazon is known worldwide for its high biodiversity and transcontinental drainage system. Changes in the physical landscape, like drainage expansion and precipitation variation, are recognized as an important driver of biota diversification. The rise of a transcontinental drainage system transformed large floodplains covered by várzeas and igapós into incised valleys limited by terra firme forests in Western Amazon. Such transformation became one of the main factors for biota diversification in the Amazon biome. And even though, the Amazon is better known by its terra firme forest, this biome also hosts non-flooded open vegetation ecosystems, such as savannas and white-sand ecosystems, which contain a specific biota and are considered as key environments for biota diversification in terra firme ecosystems under the lenses of vicariance, such as the Refuge Theory. The origins of sandy substrates that sustain savannas and white-sand ecosystems as the changes through time in these substrates are still a matter of debate. Thus, studying such sandy substrates associated to the patches of open vegetation ecosystems is important to understand their origins and factors controlling their expansion, retraction and maintenance e their role in environmental and biogeographical changes within the Amazon biome. This project proposes to study the spatial distribution, age and forming processes of the sandy substrates of savannas and white-sand ecosystems. With this study, it is expected to understand the relation among climate change, sedimentation, pedogenesis and expansion, stabilization and retraction of Amazon open vegetation ecosystems. The chronology for the formation of the sandy substrates will be determined with luminescence signals from quartz and/or feldspar, to try to expand the limit of the ages obtained so far (100-200 ka with quartz optically stimulated luminescence). Together with luminescence dating, provenance analysis based on luminescence signals will be performed to help understanding the origin of these substrates. Analysis textural (grain size) and compositional (environmental magnetism and elemental ratios) proxies will help reconstruct variations in the formation of the sandy substrate. Such data will be analyzed along with published climate change data for the Quaternary and with phylogeographical studies. That will allow us to trace the demographic history of the biota of the open vegetation ecosystems and compare it with abiotic changes registered in these substrates. Thus, it is expected that this project will contribute to the understanding of the relation between Amazon landscape changes and biota diversification. (AU)