Remarkable geomorphologic and sedimentologic features observed in the middle valley of the Doce river (Minas Gerais State, Southeastern Brazil) have supported discussions concerning to paleoclimatic and neotectonic controls on the Cenozoic evolution. The most impressive feature is represented by a Quaternary barred lake system. Many authors have related the origin of the lakes to the damming of the mouth of tributary valleys by an intensive sedimentation at main channels. Another important feature corresponds to distinctive paleochannel traces developed on large infilled valleys which are parallel to the present course of the Doce river. These paleovalleys are bordered by lakes. This work presents new evidences of neotectonic controls on the development of these geomorphologic features. Detailed geomorphologic and structural analysis support neotectonic interpretations. Seismic stratigraphic survey of the main lacustrine body in the lake system (Dom Helvécio Lake) was carried out and has revealed meaningful submerged features. It is proposed that the beginning of the lacustrine evolution was influenced by an early Holocene E-W dextral transcurrent tectonic stage that strongly affects Pleistocene deposits. It would have obstructed the flowoff of the tributary drainages and promoted the filling up of the main fluvial valleys by a relatively thick Holocene alluvial sequence. The paleochannel traces are developed on this alluvial sequence and so they are younger than this deposition. The abandonment of the infilled valleys is directly related to the lake damming and both are controlled by neotectonic mechanisms. They are related to an abrupt migration of the Doce river channel that is controlled by an Holocene NW-SE extensional tectonic stage. Seismic profiles at the mouth of the Dom Helvécio Lake document a remarkable NE-SW normal fault related to this neotectonic stage. This extensional phase was responsible for the isolation of the lakes from the fluvial system leaving lacustrine bodies aligned in NE-SW direction, parallel to the paleochannel directions.
*Supported by FAPESP, CAPES and CEPG-UFRJ.