Large river deposits in the Solimões River area of the Brazilian Amazon: Neogene evolution and role as biogeographical barriers

Abstract

The origin and evolution of the large biodiversity of the Amazon is one of the main interdisciplinary field of research that relies in studies of fluvial sedimentology. Among the major hypothesis regarding biodiversity patterns of the Amazon , the hypothesis of Riverine Barriers as a mechanism of isolation and speciation stands out as one of the most frequently adopted. According to this hypothesis, the development of big rivers promotes the segregation of populations and limits genetic exchange, causing the arise of new species. Evolutionary studies suggests a chronology for the development of riverine barriers in the Amazon set during the Quaternary, after the paleogeographic and climate change that took place during the Miocene and the Pliocene. The scarcity of detailed studies regarding the fluvial successions from the Neogene and particularly from the Pleistocene prevent the independent assessment of the evolutionary studies, and limits paleogeographical reconstitutions in the Amazon to broad overviews with little use to the test of specific hypothesis. Additionally, paleogeographical models for the Amazon spanning since the Miocene consider the presence of a large lake in the foreland, drained by an axial fluvial system flowing northwards. This lake was bridged at some point during the Neogene, by the progradation of megafans from the Andes. Thus, such bridging event would establish the inception of the current transcontinental drainage pattern, and consequently, the placement of the riverine barriers. Furthermore, the cease of lacustrine or riverine barriers between east and west would give way to the invasion of the Amazon by higher altitude species during colder climate events, regarded by a number of specialists as an important factor for the current biodiversity. The present project aims to contribute to the interdisciplinary study of the evolution of the biota and its environment in the Amazon, through acquisition and interpretation of sedimentological data in selected targets on the Amazonian alluvial plain in the area of the medium Solimões River, integrated to Optically Stimulated Luminescence dating. The main focus of this project is the development of better detailed models regarding the evolution of the Amazonian plain, which will be confronted with hypothesis of riverine barriers brought by studies of evolutionary biology. This proposal is integrated to the Thematic Project "Estruturação e evolução da Biota Amazônica e seu ambiente: uma abordagem integrativa" (FAPESP-BIOTA-NSF DIMENSIONS), Process 2012/50260-6, which will be running from March, 2014 to August, 2017, of which the supervisor of this proposal is a main researcher. (AU)