Evolução de um perfil laterítico em domo estrutural de Sobradinho, Distrito Federal

Abstract

The study of lateritic profiles has contributed to improve current knowledge on the evolution of residuals plateaus, a common form of relief found in tropical landscapes, being an object of intense debate in several geomorphological studies fora. It is classified, in geomorphologic maps of the Brazilian Federal District, as Pediplains and Etchplains. This thesis presents a morphologic, chemical, mineralogic and micromorphological study of a lateritic profile located in a plateau in the northern area of the Federal District. Its findings led to the differentiation of seven horizons are associated to the dismantlement of the lateritic cuirasse. The solum in the area studied derives from the weathering of the deepest horizons, thus characterizing an in situ evolution. The presence of pedorelics and lithorelics in the deepest horizons shows the evolution of the lateritic profile from the massive courace. The structure of microaggregates in superficial horizons evolves from biological activity in horizons marked by massive structures. The mineralogic evolution of the profile (base to the top) is compatible with the decrease of haematite and the corresponding gain of goethite, as well as with desilication and gain of gibbsita. The geomorphological model that best applies to such lateritic profile is Etchplanation, as it portrays the evolution of relief in tropical climate conditions, favoring the evolution of a horizon with iron accumulation that, after dehydration (climate change towards drier conditions), positions itself on soil surface as a massive courasse, making the relief plain; after degradation, it evolves to the formation of latossoils.