Quaternary megafans in the state of Roraima, Northern Amazonia: sedimentological, climatic and tectonic implications

Abstract

Megafan consists of a large-scale depositional system with sedimentological, stratigraphic and morphological characteristics still poorly documented in both modern and ancient environments. In Brazil, the Taquari megafan in the Pantanal Matogrossense is the only known record of this type of depostional system. Preliminary analysis of remote sensing data suggests the presence of a remarkable megafans in the State or Roraima, northernmost of Amazonia Basin The goal of this project is to demonstrate the presence of two megafan systems preliminarily detected in the Branco-Negro interfluve and in the left margin of the Branco River, as well as discuss the factors that were potentially important to their development in an area today dominated by fluvial systems. The study will consist on the following phases: 1. analysis of remote sensing data, using Landsat, ALOS (Advanced Land Observing Satellite)-PALSAR (Phased Array type L-band Synthetic Aperture Radar), digital elevation model (DEM)-Shuttle Radar Topography Mission (SRTM), and drainage maps provided in digital format by SIVAM/IBGE; 2. analysis of sedimentological and stratigraphic data to be acquired from cores; 3. laboratorial analysis including total organic carbon (C), ´13C, 14C dating and optically stimulated luminescence (OSL). The presence of megafans in an area dominated by fluvial alluvial systems linked to tributaries of the Amazonas River has great implications to discuss the influence of climate and tectonics during the Quaternary of Amazonia. The results derived from this project will help to amplify the characterization of megafans, as well as understand the factors that might control their development in different geological contexts. (AU)