OSL dating and analytical techniques applied to the middle Negro River basin, Amazonia: implications on fluvial dynamics, sedimentation, landscape modifications and ichtyofauna

Abstract

Studies on the Quaternary fluvial dynamics in the Rio Negro Basin are still scarce, despite this river harboring the two largest fluvial archipelagos in the world, the Anavilhanas and the Mariuá. The Mariuá archipelago has few studies and keeps records of the main sedimentary, climatic and tectonic processes, which influenced the evolution history of this river in the last thousands of years and can provide important data for future projects of environmental and preservation in the area. In addition, paleoclimatic records associated with aeolian paleodune fields have been recorded in the middle stretch of the Rio Negro, which may help to define temporal intervals of climate change. The expressive width of the Rio Negro in the Mariuá archipelago may act as a barrier to certain species, mainly small fish in tributaries. For this reason, complementary data on the use of the molecular clock to estimate the time of divergence of several populations, today isolated in this river, may correspond to the time of implantation of the drainage system. The investigation of the types of fluvial and aeolian sedimentary deposits corroborated with the study of speciation of the species over time, through biological DNA analysis, will provide data for modeling the dynamics of the Rio Negro and tributaries and, consequently, in studies of changes in the past tense landscape. In the last decade, Optically Stimulated Luminescence (OSL) dating has been widely used in the geochronological positioning of river terraces, in certain stretches of the Solimões-Amazonas fluvial system and in the Lower Rio Negro region, allowing the knowledge of ages and sedimentation rates, fundamental in the analysis of fluvial dynamics and avulsion processes. Continuing this study, the site chosen for this project will be the Middle Rio Negro region, where the Mariuá Archipelago is located (Figure 1). The geochronological focus will be on the alluvial deposits and paleodunes deposited in this stretch of the Rio Negro, as well as the effect on the endemic biota. In this way, with the determination of the Ages of sediment deposition and river movements, depositional models can be elaborated and applied in the understanding of the evolution of fish populations. The region contains several old formations such as Viruá and aeolian dunes with Ages higher than the dating limit, using the conventional protocol, so one of the main focuses of this project will be to find a protocol that can extend the upper limit of Ages by LOE. In addition to geochronology and biological analysis, excellent and well-established analytical techniques will be used to characterize the various types of associated deposits, such as Instrumental Neutron Activation Analysis (INAA), Scanning Electron Microscopy (SEM), X-Ray Diffraction (DRX) and Sedimentological-Stratigraphic Analysis, the results will help in studies of sedimentary origin and in the supply of sediments in flooded areas, which recycle the ecosystem of the region. The integration of analytical and geochronological data will contribute to the development of depositional evolutionary models for the region, in the Quaternary. Knowledge of fluvial dynamics will provide subsidies for future research involving the Amazonian biota, proposing models for evolutionary and biogeographical studies. As the project has a strongly interdisciplinary character, the researchers come from different areas of knowledge. This will have the participation of researchers from National Institutions such as UNIFESP, IPEN-SP/CNEN, UFAM, UEA and International ones such as the University of Salzburg in Austria, National Centre for Scientific Research Demokrito, Greece and The Maharaja Sayajirao University of Baroda/MSU, India. (AU)