Reference : Polyphased karst systems in sandstones and quartzites of Minas Gerais, Brazil
Scientific congresses and symposiums : Paper published in a book
Physical, chemical, mathematical & earth Sciences : Earth sciences & physical geography
Polyphased karst systems in sandstones and quartzites of Minas Gerais, Brazil
Willems, Luc mailto [Université de Liège - ULiège > Département de géologie > Pétrologie sédimentaire >]
Rodet, Joël [Université de Rouen > Géologie > > >]
Pouclet, André [Université d'Orléans > ISTO > > >]
Melo Da Silva, Sergio [Universidade Federal de Minas Gerais (Brazil) > Instituto de Geociências > > >]
Rodet, Maria-Jacquelines [Université de Paris X Nanterre > > > >]
Auler, Augusto [Universidade Federal de Minas Gerais, Belo Horizonte, Brazil, > CPMTC – Instituto de Geociências > > >]
Proceeding 14th UIS Congress, Athens-Kalamos, 23-28 august 2005, Abstract Book : 71.
UIS Congress, Athens-Kalamos, 23-28 august 2005
du 23 août au 28 août 2005
[en] karst ; quartzite ; Brazil
[en] The state of Minas Gerais (Brazil) exhibits several major karst areas located in sandstone and quartzite terrains, that display a complex suite of underground and surface karstic forms. In the Espinhaço Ridge, central Minas Gerais, several caves, up to a few hundred metres long, occur in the surroundings of the town of Diamantina. Some of these caves, such as Salitre, represent swallow-holes and show dome pits. Other horizontal caves are characterized by corrosion forms generated into the phreatic zone. In some places, such as in the Rio Preto area, these phreatic forms have been overprinted by ceiling tubes, suggesting a polyphase karst evolution, prior to the draining of the cave. Relicts of passages, with circular cross section up to a metre in diametre, can be found amidst the residual tower-like surface landforms, which constitute a typical scenery in the landscape. Their dissection is due to a generalised karstification in the area, resulting in closed canyons, megakarrens and kamenitzas. In southern Minas Gerais, close to the Mantiqueira Ridge, the caves of the state park of Ibitipoca can extent 2 km in length. These caves are associated with a very large hanging geological syncline. Several of these caves contain active streams, that flow for hundreds of metres before disappearing in sand-choked passages. Keyhole cross sections characterize steeply descending passages in these caves, indicating a change from slow phreatic flow towards a faster vadose flow responsible for the vertical incision of the passage. Such change is probably related to base level lowering and/or to turn in the direction of the water flow. Several generations of wall-pockets, from a few centimetres to over a metre long, occur into the caves. These features are good indicators of the initial phase of speleogenesis, generating the initial conduits by their coalescence. This mechanism is also responsible for cut-off meanders. The main river in the area, which flows along the syncline axis, cuts through a rock barrier, generating a tunnel-like passage. This cave drains, through resurgences in its walls, part of the water that flows in other caves located in the flank of the syncline. The non-carbonate karst features observed in the state of Minas Gerais demonstrate the complex organisation of polyphase karst systems due to the linkage of underground and surface forms not previously connected. As in carbonate areas, these systems may play an important hydrological role.
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