Papers

Neo-Cenozoic superficial deposits. geomorphic surfaces and soils in the Monte Alto, São Paulo State.

Author: José Marques Júnior, Igo Fernando Lepsch

Keywords: geomorphic surfaces

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Summary

geomorphic surfaces and soils were identified, mapped and characterized in a 612 ha around the Monte Alto plateau from 700 m on plateau to 600 m on footslopes of scarpment surrounding it. This place is a portion of the Occidental Plateau of São Paulo State, Brazil. Sand distribution patterns with depth, soil mechanical, chemical, analysis were performed. Three geomorphic surfaces, their respective slope elements and superficial deposits were identified. Soils on highest part of landscape developed from the Sub-Recent Neo-Cenozoic superficial deposits are under the two oldest surfaces, even when differently classed, and have similar properties related to mineralogy and sand morphology and sorting. Soils over the younger surfaces are mostly derived from the underneath Cretaceous sub-arkosean sandstone from the Bauru Formation. Joint interpretation of geomorphic surfaces, old superficial deposits characteristics and past references to Tertiary tectonic and Pleistocene climate variations lead to the conclusion that the now high elevated superficial deposits were once derived from reworking of the Cretaceous sub-arkosean sandstone. They were first deposited inside a Neogene graben were they stood a long time uneroded and under continuously chemical weathering conditions; latter erosive processes removed the surrounding higher sandstone probably during Quaternary tropical semi-and phases (relative to glacial periods). The deposits of the past tectonic low are nowadays the current topographical high with deep soils, the more weathered of the area, and developed on Neo-Cenozoic deposits, formerly preserved in lowered area.