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Anais da Academia Brasileira de Ciências

versão impressa ISSN 0001-3765versão On-line ISSN 1678-2690

Resumo

SANTOS, Maria-do-Carmo  e  VARAJAO, Angélica F.D.C.. Sedimentation and pedogenic features in a clay deposit in Quadrilátero Ferrífero, Minas Gerais, Brazil. An. Acad. Bras. Ciênc. [online]. 2004, vol.76, n.1, pp.147-159. ISSN 0001-3765.  http://dx.doi.org/10.1590/S0001-37652004000100013.

The clay deposit of Caxambu Hill occurs in a NW/SE oriented graben originated by syntectonic sedimentation during Cenozoic. Four facies were identified (fragmentary, nodular, massive and friable) and their differentiation is related to gravity mass-flow processes. The fragmentary facies is composed of extraclast fragments of the local Paleoproterozoic basement and sand size quartz-grains dispersed in a kaolinite-muscovite-goethitehematite matrix. The nodular facies is constituted by lithorelictal and pedorelictal nodules dispersed in a similar matrix as in the fragmentary facies. The massive facies is characterized by quartz grains dispersed in a kaolinite, hematite and goethite matrix with minor amounts of muscovite. The friable facies differs from the massive facies by its channel morphology, higher quartz and kaolinite content and the presence of millimetric clay-balls. The fragmentary facies is considered as deposited during the early stage of opening of the basin. After that, under sub-arid conditions, the slumping of lateritic materials from the surrounding regolith led to the formation of the nodular and massive facies. The friable facies was originated by the action of unidirectional flow that reworking the clayey sediments. The increasing of kaolinite content towards the top is related to the chemical weathering action after the deposition of the sediments.

Palavras-chave : kaolinite; lithofacies; micromorphology; gravity mass flow; chemical weathering.

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