The Brazilian shield comprises two separate units. The Precambrian crystalline basement, in the eastern part of the shield, is divided into three parts distinguished by their lithology, structural trend, and mineralizations. The sedimentary cover contains a folded series of formations ranging in age from terminal Precambrian to early Paleozoic and an unfolded series represented by sediments of lower Devonian to Tertiary age which were deposited in epicontinental, intracratonic, and coastal basins. Four phases are recognized in the evolution of the unfolded sedimentary series. The effects of geologic processes active in the Brazilian shield from the end of the Precambrian to the end of the Mesozoic have been observed in the Parnaba-Sao Francisco intracratonic geosyncline. Results of age determinations are reported.

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