Quaternary alluvial continental sedimentation in tropical areas: the Conceição River valley case, Southeastern Brazil

Abstract

The aim of this paper is to discuss the influences of litho-structures, tectonics, and climate on the pattern and chronology of Quaternary alluvial sedimentation in the Conceicao River valley, a mountain tropical area. The area is located in the northeastern Quadrilatero Ferrifero, one of Brazil’s most known mountainous domains and the world’s major iron-producing regions. The methods used were based on field research and laboratory analyses of sediments, including optically stimulated luminescence dating. Eight alluvial depositional levels were identified, most of which were morphologically uncharacterized (they do not have the configuration of terraces). River diversions, sediment traps, tilting, and terrace staircases indicate tectonic conditioning on fluvial dynamics. The formation of cyclic alluvial levels with gravel-bed facies cemented by iron oxides–hydroxides could be related to climatic fluctuations. Although luminescence data offer critical information for the understanding of regional Quaternary fluvial evolution, several geological and geomorphological inconsistencies require careful analysis.