Oxisol development along a compound catena of the Araguari river, Central Brazil

Several Oxisols, containing different parental materials, were studied along a compound catena of the Araguari River, central Brazil. Their development, age, and genetic features were analyzed by morphological, chemical, and mineralogical methods. Results indicated continuously decreasing weathering from tableland (also known as chapada) to valley floor. Soils on the chapada probably developed during middle and upper Tertiary, and are considered relict. Their different types of quartz sand clearly show that they derive from preweathered sediments of distinct locations, suggesting a polygenetic origin that may reach as far back as the Cretaceous. Soils on the pediment, inserted into the slope toward the Araguari River, developed in situ and may have been formed at the beginning of Pleistocene but still indicate ongoing ferralitization. A ferralitized paleosol that developed in situ near the river's present base level is apparently from late Pleistocene. Recent pedological processes are characterized by strong leaching and hillwash.