Drainage rearrangements in the northern portion of the Amazonian Basin

Abstract

The Amazonas River Basin is the biggest in area and volume in the planet. Its high dimension was originally interpreted as a result of the climate and geological configuration of South America. However, in recent years, a series of studies has shown evidence that extensive drainage rearrangement processes are taking place in the region and that these favored the expansion of Amazon Basin. Among these broad processes, studies stand out that claim that the upper hydrographic basin of the Branco River flowed towards the Essequibo River and would have been captured by the Amazon Basin. However, the studies that affirm this do not present morphological evidence for this drainage rearrangement. In this context, through remote sensing, geoprocessing, cartographic analysis and fieldwork, the present work evaluated the morphological evidence that could prove drainage rearrangement processes in the upper hydrographic basin of the Branco River in the Northern Amazon. The results allowed to identify a series of geomorphological evidences integrated with each other and indicative of fluvial piracy processes, with emphasis on elbow drainages, low dividers and river paleochannels. Therefore, they confirm that in the past the Uraricoera and Tacutu rivers - which form the Branco River - were part of the Essequibo River Basin, that flows into the Caribbean. However, thanks to the regressive erosion of the paleo-headwaters of the Branco River, they were intercepted and integrated into the Amazon Basin.