INTEMPERISMO E MORFOGÊNESE NO PLANALTO DE CAMPOS DO JORDÃO (SP)

MAY CHRISTINE MODENESI

Resumo


Weathering phenomena on the Campos do Jordão Plateau have been studied from a geomorphological point of view. The geochemical type of evolution and degree of weathering were analysed in order to show their relationship to geomorphic units and morphogenetic dynamics. Soils, elluvium and sedimentary deposits are highly weathered and consist mainly of quartz,gibbsite and kaolinite. Aluminous vermiculite may occur in incipiently weathered granite and in some soils. Correlations between the degree of weathering of surficial materials and the geomorphic units are more evident in weathered rock than in soils. In the highest areas of the plateau gibbsite is the most important secondary mineral and bauxite is common. At lower topographic levels kaolinite prevails. Two weathering processes, alitization and monossialitization are thus defined and may be interpreted as different stages in a general alitic weathering trend. In some hillslope deposits, the degree and sequence of weathering is frequently related to downslope movement processes, rather than to the still incipient pedogenetic action. The superposition of colors, frequent in hillslope surficial materials, reflects two opposing pedogeochemical trends, the more ancient being ferralitic and the more recent tending towards podzolization. The identification of past ferralitic weathering phenomena on the Campos do Jordão Plateau allows the correlation of the "superfície dos campos" (Campos Surface) to degradational processes active at lower altitudes prior to the uplift of the plateau to its present level and the consequent modification of climatic characteristics.


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