Pedogênese em platôs de canga ferrífera e basaltos na Serra dos Carajás - PA

• Autor(a) principal: Corrêa, Guilherme Resende
• Data de Publicação: 2011
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1619
• topic: Concreções; Pedogênese; Evolução da Paisagem; Concretion; Pedogenesis; Landscape evolution; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::CIENCIA DO SOLO

Between Xingu and Araguaia/Tocantins rivers, in the state of Para (Brazil), is situated the Serra dos Carjás, worldly known for its enormous mineral reserves, specially the reserves of iron. The changeable environment between cerrado and rain forest helped the formation of the complex landscape, sustained by a big variety of soils. Among these environments, stand out on this research the ones related to the band iron formation (BIF) and basalt, which for millions of years form the big iron crust plateau or deep saprolite covered by oxisol in the case of mafic rocks. Such environments have different geomorphological in relation to regional patterns. Phisical, chemical, mineralogical and microchemical analysis were made, aiming at knowing the genesis ant the material which originated the soils in the Formção Carajás and Parauapebas. The results show that the soils of the iron crust plateaus of Carajas haveoriginated from the alteration of the superficial laterite, remains of ancient pedogenic cycles, with the exception of P9C profile, because it received imput from another areas of materials of Formação Águas Claras. The iron was preferential removed from the profiles, and elements as Al and Ti have concentraded on the soil. This process was more intense in P10C, because it is situated in hydromorphic environment. The present climate with precipitation beyond 2000 mm per year is dissolving/changing the laterite of the surface and originating soils with iron-aluminium plasma. In the areas consisted of mafic rocks the process is similar to the process which have been ocurring in the plateaus originated from BIF, highlighting that laterite crust rich in iron observed in the plateaus in the Formação Parauapeba, for instance the profile P15C, still remains in the landscape. This is due to the condition of less humidity (the plateaus are places where the drainage starts to be defined, where begins the water courses) and the groundwater exerts less influece, keeping the climate less humid. In such conditions the change of hematitic concretion is less and its stability kept longer in relation to the distant soils of the edge. In more humid climates the hematite concretion changes to goethita and gibbsita, as noted in the more central soils of the plateaus (P16P, P1P, P2P, P3P, P4P, P5P and P7P).