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

Resumo

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