The role of tectonics and climate in the late Quaternary evolution of a northern Amazonian River

Author(s)

Cremon, Edipo Henrique ; Rossetti, Dilce de Fatima ; Sawakuchi, Andre de Oliveira ; Lisboa Cohen, Marcelo Cancela

• Document type: Journal article
• Source: Geomorphology; v. 271, p. 22-39, OCT 15 2016.
• Web of Science Citations: 13

Abstract

The Amazon basin has most of the largest rivers of the world. However, works focusing the geological evolution of the trunk river or its tributaries have been only partly approached. The Branco River constitutes one of the main northern Amazonian tributaries. A previous work proposed that, before flowing southward into the Negro-Amazon Rivers, the Branco River had a southwest to northeast course into the Caribbean Sea. The present work aimed to establish if the proposed change in the course of this river is supported by morphological and sedimentological data. Other goals were to discuss the factors influencing river development and establish its evolution over time within the chronological framework provided by radiocarbon and optically stimulated luminescence dating. The work considered the entire course of the Branco River downstream of the Precambrian Guiana Shield, where the river presumably did not exist in ancient times. The river valley is incised into fluvial sedimentary units displaying ages between 100 and 250 ky old, which record active and abandoned channels, crevasse splay/levees, and point bars. The sedimentary deposits in the valley include two alluvial plain units as old as 18.7 ky and which intersects a Late Pleistocene residual megafan. These characteristics suggest that a long segment of the Branco River was established only a few thousand years ago. Together with several structural anomalies, these data are consistent with a mega-capture at the middle reach of this river due to tectonic reactivation in the Late Pleistocene. This integrated approach can be applied to other Amazonian tributaries to unravel how and when the Amazonian drainage basin became established. (C) 2016 Elsevier B.V. All rights reserved. (AU)

• FAPESP's process: 10/09484-2 - Quaternary megafans in the state of Roraima, Northern Amazonia: sedimentological, climatic and tectonic implications
• Grantee: Dilce de Fátima Rossetti
• Support type: Regular Research Grants
• FAPESP's process: 13/50475-5 - Mapping Amazonian biodiversity at multiple scales by integrating geology and ecology
• Grantee: Dilce de Fátima Rossetti
• Support type: Regular Research Grants