Characterization of surface materials and the relationship with topographic positions: case study in the Serra da Canastra, Brazil

Quartzite regions tend to present incipient and unconsolidated surface materials, even in areas with humid tropical climates. The degree of weathering of surface materials and its relationship to topography in these environments remains unknown. Therefore, the objective of this study is to analyze the relationship between topography and the mineralogy of the clay fraction of surface materials developed in quartzite bedrock. We selected three representative slopes along which transects were installed from the crest to the valley floor. Nine geocover samples were collected for analysis by X-ray diffraction. The results were analyzed using the Principal Component Analysis method. The results show a correlation between the identified materials, their position on the slope, the slope profile, and the presence of natural barriers. In the first transect, representing a quartzite ridge with extremely incipient weathering material, minerals indicative of highly weathered environments with poor drainage, such as kaolinite and illite, were found. In the second transect, representing broad interfluves with long slopes and low gradients, samples presented Fe and Al oxides and hydroxides, demonstrating the advanced degree of weathering in the area. The third transect, conducted in a secondary divide with a convex profile, collected a deeper sample containing goethite and siderite, indicating a poorly drained environment with water remaining in the system for a short time. Thus, it can be seen that, despite the predominantly quartzite basement, the shape of interfluves and slopes allows for differentiated development of the weathering mantle materials, strongly dependent on drainage dynamics and varying along the slope as a function of changes in longitudinal profiles.