Lateritic crusts and related soils in eastern Brazilian Amazonia

The upland soils of Carajas and Paragominas in eastern Brazilian Amazonia are made up of yellow to reddish earthy-clayey to clayey materials, which cover iron-aluminum, aluminum-iron and aluminum lateritic crusts. These materials are closely related to each other and to lateritic evolution and are comprised by three horizons described from the base to the top as lower, intermediary and upper horizons that are identified by the type, amount and size of the lateritc fragments embedded into a matrix that increases towards the top. The three horizons show a strong lithological vertical transition into themselves and the degradation degree increases toward the top of the profiles where the main characteristics are the same geochemical signatures between the horizons of every profile, and the change in the mineralogical composition from hematite+gibbsite to gibbsite+Al-goethite in the N5 and IB, and from gibbsite to kaolinite+quartz in Paragommas. These transformations support a lateritic crust chemical reworking, which allows for its transformation into a friable and soft in situ matrix and then into soil in a progressively weathering process, which started in Amazonia probably in the Miocene, after the formation and exposure of the main lateritic crusts to landsurface. (c) 2004 Elsevier B.V. All rights reserved.