EVOLUÇÃO POLIGENÉTICA DAS BAUXITAS DO DISTRITO DE PARAGOMINAS-AÇAILÂNDIA (ESTADOS DO PARÁ E MARANHÃO)

摘要: The aluminous laterite surfacing the area of Acailândia-Paragominas (Eastern Amazonia) displays a profile characterized by ferruginous lateritic crust underlain alumina-rich bauxite. lithology is complex origin marked multiple mechanical reworking and mobilization Al Fe. Five successive stages in evolution history are recognized: initial laterization, formation iron-aluminious "hard cap" its partial reworking, first main phase "gibbsitization" hard cap, second deposition as pseudo-pisolites affecting upper part laterite. Epeirogenetic movements rate erosion drainage with superimposed climatic changes were important factors controlling pedogenesis. Based on analogy Surinam occurrences because studied profiles Upper Cretaceous sediments, an early tertiary age proposed for Eastern Amazonia bauxitic laterites.