Quaternary sedimentation, neotectonics and the evolution of the Doce River Middle Valley lake system (Southeastern Brazil)

Abstract

The Doce River Middle Valley (State of Minas Gerais, Southeastern Brazil) is one of the most important areas in Brazil in the study of Quaternary evolution of the humid tropics. This area preserves a singular barred-Iake system which has been previously investigated by several authors, particularly on the 70's. Most previous studies have considered paleoclimatic controls as responsible for the origin and the evolution of the lake system. Some authors have also recognized evidences of neotectonic influence on the lacustrine development. In the present study, a new approach to the Quaternary evolution ofthis area is discussed. The origin and the evolution of the lake system are interpreted according to regional stratigraphic and structural investigations. Geophysical (seismic stratigraphic) data provide new insights about the lake stratigraphy. Detailed structural analyses of joints and faults affecting Quaternary sediments support neotectonic interpretations. Stratigraphic analyses confirm the beginning of the lacustrine sedimentation around 9,000 years BP, simultaneously with an important regional alluvial sedimentation. Seismic stratigraphic analysis performed at the dam of Dom Helvécio Lake shows a normal fault affecting Holocene alluvial sediments. It explains the damming of this lake and suggests neotectonic mechanisms as the main control for the origin of the Doce River Middle Valley lake system.