NÍVEIS DE EROSÃO E FORMAÇÕES SUPERFICIAIS NA REGIÃO DE ITU-SALTO, SP

MAY CHRISTINE MONDENESI

Resumo


The Itu-Salto region is characterized by seven inlaid topographic levels considered as remnant erosional forms related to pediplanation and pedimentation processes in semiarid climatic conditions. Humid alternating phases were responsible for level dissection and inlayment. In this paper, different levels and superficial deposits are tentatively correlated. The two highest levels correspond to a paleogenic surface (Pd2) whose remnants are at the top of the Serra de Itaguá. Below this topmost surface an extensive pediplane of neogenic age (Pdl) occurs, unfolded as three different levels. Two lower levels P2 and P1 inset in the neogenic surface are related to Mindel and Riss respectively. Correlative deposits are rare but only one was related to the neogenic surface (lateritic crust). Most levels are covered by extensive colluviation, more recent than erosion surfaces, in situ regolith is rare. Level and slope deposits differ in characteristics and soil profiles. Level deposits are thick, intensely weathered and often high in iron content. Latosols are common. Old ferruginous colluvium occurs on the highest levels of the granitic area, Sucessive redistributions explain its presence on lower and more recent levels. Neogenic surface is characterised by specific soils rich in organic matter (humic red yellow latosol). On the other hand, slope materials are thinner, less weathered, giving rise to less evolved podsolie soils. The colluvium-elluvium contact is frequently marked by stone lines. Several gravel material horizons alternating pedogenic ones are frequent on lower slopes, indicating at least four climatic fluctuations, probably holocenic. Most of these colluviums indicate short-range transportation being closely related to bedrock (granite or glacial deposits), Ferralitic soils are exceptions, uniform throughout the whole region.

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