Detlef Hans-Gert Walde

Geological evolution of the Neoproterozoic Corumbágraben system (Brazil). Depositional context of the stratified Fe and Mn ores of the Jacadigo Group

Abstract The Corumbaregion is located near the junction of two young (545–480 Ma) Brasiliano provinces: the Chiquitos-Tucavaca aulacogen which cross cuts the Amazon craton-Rio Apa block, and the Paraguay fold belt. Formation of the aulacogen and the Paraguay basin, which is interpreted as a foreland basin, was roughly synchronous with the 590 Ma metamorphism in the neighbouring old Brasiliano Brasilia fold belt. Deformation and metamorphism in the Paraguay belt are bracketed between 545 and 500 Ma, whereas folding in the aulacogen occurred between 500 and 480 Ma ago. The NE–SW-trending, Corumbagraben system is located on the eastern part of the WNW–ESE-trending, Chiquitos-Tucavaca aulacogen. The extensional structures of the Corumbagraben system are attributed to flexure of the Amazon craton along the western border of the Paraguay basin. Stratigraphic successions in the Corumbagraben system resemble those of the adjacent cover rocks of the Amazon craton: a lower detrital unit (Jacadigo Group and Boqui, Puga, and Cadieus formations), partly of glacial origin, and an upper carbonate-rich unit, (CorumbaGroup and Pororo, Cerradinho, Bocaina, and Araras formations) with local preservation of an Ediacara-like fauna. The whole sequence is probably Vendian. In the cover sequence around Cuiaba, the carbonate unit is capped by siliciclastic sediments. In comparison to the cratonic cover rocks, the Jacadigo Group, which is filling the Corumbagraben system, differs on three points: it is thicker, contains chemical manganese and iron sedimentary intercalations and was affected by a diagenetic to epimetamorphic event during which temperatures reached 250–280°C. These features are in good agreement with sedimentation of the Jacadigo Group in an extensional environment where Fe and Mn, of probable hydrothermal origin, would be generated by leaching of hypothetical, hidden intrusive mafic plutons associated with graben formation.

Challenges of an integrated water resource management for the Distrito Federal, Western Central Brazil: climate, land-use and water resources

Land-use/cover change (LUCC) and climate change are major controlling factors for water resources in the Distrito Federal in Western Central Brazil. Dynamic LUCC in the region has severe impacts on water resources, while climate changes during the last three decades is thought to have only moderate effects. LUCC affects water quantity mostly during base flow conditions. River basins with substantial expansion of agriculture since the end 1970s show a dramatic decrease of base flow discharge by 40–70%, presumably due to irrigation. In contrast, the effects of urbanization on runoff are less distinct, since factors controlling runoff generation might be more variable. For water quality, we found urban areas to have a strong influence on the parameters CSB, NH4+, and suspended solids. In addition, we assume emerging pollutants, e.g. organic (micro)pollutants, might play a major role in the future. The project IWAS-ÁGUA DF focuses on creating the scientific base to face these problems in frame of an IWRM concept for the region. Results of our study will be a contribution to an IRWM concept for the Distrito Federal and will help to maintain high standards in water supply for the region.