Denudação química e rebaixamento do relevo em bordas interplanalticas com substrato granítico: dois exemplos no SE de Minas Gerais
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Data
2012
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Resumo
The interfl uves of major river basins of Eastern Brazil often correspond to escarpments between stepped reliefs. These escarpments are result of the differential erosion along the headwaters of these major basins, dividing highlands from lowlands.
This paper presents a study of chemical denudation along two of these escarpments dividing three levels in Minas Gerais: (i) the step of Cristiano Otoni (250m) which divides the São Francisco River basin (highland) from the Doce River River basin (lowland) and (ii) the step of São Geraldo (450m) which divides the Doce River basin (highland) from the Paraiba do Sul River basin (lowland). In order to understand the dynamics of chemical denudation of these two geomorphological steps, the
total dissolved solids (TDS), the Eh, the pH and the fl ow of the stream of 21 catchments have been monitored in the end of rain season (March) and dry one (August) for the same hydrological year (2009). Chemical denudation rates (ton.y-1.km-²) and average relief lowering rate (m.My-1) have been calculated by using TDS and fl ow. The results have revealed that the water of the studied geomorphological steps have different geochemical signatures: (i) in the highlands, the pH is always acidic (around 6.35) and in the escarpment fronts, slightly basic (around 7.10), (ii) the TDS values in the highlands (around 10.00 mg L-1) are smaller than those found in the escarpment fronts (around 35.00 mg L-1 for São Geraldo, and around 18, 00 mg.L-1 for Cristiano Otoni). The lowering rates of relief caused by chemical denudation are similar for both highlands (around 2.40 m.Ma-1). Otherwise, the escarpment front of the step of São Geraldo are higher (7.06 m.Ma-1) than the step of Cristiano Otoni (4.25 m.Ma-1). This difference has been interpreted as a direct consequence of escarpments height, 450 and 250 m respectively.
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Escarpas, Escarpments, Bordas interplanálticas, Denudação química, Interplateau edges, Chemical denudation
Citação
CHEREM, Luis Felipe Soares et al. Denudação química e rebaixamento do relevo em bordas interplanalticas com substrato granítico: dois exemplos no SE de Minas Gerais. Revista Brasileira de Geomorfologia, Curitiba, 13, n. 1, p. 73-84, jan./mar. 2012.