Soil-landscape Relationships in the Occidental Plateau of São Paulo State, Brazil: II. Soil Morphology, Genesis, and Classification
1977
Lepsch, I. F. | Buol, S. W. | Daniels, R. B.
Nine profiles representing the major soils in the Occidental Plateau of São Paulo State, Brazil, were characterized after detailed geomorphic and soil mapping were completed on a 70.8 km² area. The stable upland geomorphic surface had Oxisols, surrounded by younger erosional surfaces with Ultisols, Alfisols, and Inceptisols. Mollisols formed where the erosional surfaces exposed calcareous sandstone. The argillic horizons of the Ultisols and Alfisols in these positions apparently have formed in material that would qualify as an oxic horizon before it was exposed. Laterally moving water at these sloping sites is believed to initiate free Fe removal and lessivage. Lateral water movement at the contact between the surficial deposits of oxic composition and the underlying calcareous sandstones appears to supply the bases for the Alfisols developed in the oxic material. Kaolinite dominates the clay mineralogy of the soils formed in unconsolidated deposits, but attapulgite and smectite are present in the calcareous sandstone. In the soils shallow to calcareous sandstone the attapulgite apparently has weathered to smectite within a few centimeters of the rock.
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