Relief-Rock-Soil relationship in the transition of Atlantic Plateau to Peripheral Depression, Sao Paulo, Brazil

Abstract

This paper presents an atlas of physical geography at a detailed scale for an area located between two large morphostructural units: the Atlantic Plateau, a crystalline shield of rough landforms, and the Peripheral Depression, a transition unit from Plateau to the Parana Sedimentary Basin, whose smooth landforms are generally sculpted over sedimentary terrain. The transition between these two land systems creates contrasting landforms as a function of bedrock structure and soil type. Smooth landforms underlain by sedimentary rocks and reddish clayey soils alternate with small hills with abrupt slopes sustained by igneous or metamorphic rocks. These soils, developed from weathering of siltstones can rapidly change to brownish and pale colors indicating leaching and weathering of stratified sandstones or massive structured quartzites. A geomorphopedological classification at 1:10,000 scale was performed initially by delimiting units according to landforms. Secondly, other themes were added by combining them with different types of rocks and soils. The geomorphological map was produced by using thematic maps including a topographic base map, hypsometric map, slope map and morphological map. Also the geological and pedological maps were created based on field data collection, morphological analysis of soil profiles and physical, chemical and mineralogical laboratory analysis. Finally, the geomorphopedological units were defined using all the mapped data. Each of these units has peculiar features concerning developed or undeveloped soil formation, with mineralogy and structure very often linked to underlying rock. The landform shape is either controlled by geologic structure or originated from weathering processes that make the relief flatter.