Caracteriza??o faciológica e evolu??o sedimentar da Forma??o Moeda (Supergrupo Minas) na por??o noroeste do Quadrilátero Ferrífero, Minas Gerais

摘要

The Moeda Formation, along the northwestern region of the Quadrilátero Ferrífero, registers the first stages of the Minas?basin, during the Neoarchean/Paleoproterozoic, south of the S?o Francisco Craton. This paper examines this unit from six?stratigraphic sections where nine sedimentary facies were characterized: four conglomerate facies (Gms, Gm, Gt and Gp),?three sandstones (St, Sp and Sh) and two predominant mudstones (Fl and Fsc). The stratigraphic sections were correlated allowing the grouping of the facies in five genetically related associations. The associations of facies AF1 and AF2 presents an alluvial fan system which evolved into interlaced fluvial plains. AF3 is related to a shallow marine associated lake system in the distal portions. Finally, the association of facies AF4 and AF5 represent interlaced fluvial plains enclosed by a marine transgression in the final evolution stage of the basin. Based on the geological-structural detail mapping of these facies associations and in a restored section, it is interpreted that AF1, AF2, AF3, and the basal portion of AF4 were deposited during the initial stages of the continental rift, and the other associations materialize the transition between the stages rift and passive margin.