Evidence of fluvial rearrangements in the Amazonas-Essequibo interfluve - Northern Amazon

Abstract

The Amazon region stands out, among several reasons, for presenting a mosaic of landscapes in the Amazon River’s large fluvial system. However, studies about the northern portion of this region still lack in depth, mainly in geology and geomorphology. In this context, the Branco River basin – located in the State of Roraima, in Brazil, which drains towards the Amazon River but is located in the triple hydrographic divisor with those of the rivers Orinoco (Venezuela) and Essequibo (Guiana) – presents evidence of drainage rearrangement in several of its tributaries, as occurs with the Maú River in the far northeast of the area, at the interflow between the Amazonas and Essequibo basins. Therefore, this study aims to interpret evidence of drainage rearrangement in Maú River’s medium/low course, such as river capture and alluvial deposits, by means of remote sensing images and morphometric data obtained from DEM’s. The analysis procedures were based on the interpretation of remote sensing images of the satellite SENTINEL-2, 10x10 meters, MSI sensor, together with morphometric data obtained from the MDE’s ALOS/PALSAR, 12.5x12.5 meters and SRTM/TOPODATA, 30x30 meters, in order to analyze the drainage network, morphological features and alluvial deposits. The interpreted data indicate that the fluvial system of Maú River’s medium/low course suffered little erosion because its regional base level had allowed lateral overflow and formation of a network of distributary paleochannels, constituting features of alluvial fans; the channels being tributaries of the Rupununi River (Essequibo Basin). Subsequently, a change in the regional base level of the Branco River apparently favored the capture of Maú River for the Amazon Hydrographic Basin, reorganizing the local drainage systems and, consequently, promoting changes in the landscape. These conclusions clear the path for future studies that aim to assess the dates of the sedimentary deposits and thus track down the age of the fan systems and the capture of the area drained by the Maú River into the Amazon basin.