Stratigraphy and correlations of the Pouso Alegre Basin; Neoproterozoic-Cambrian; state of Minas Gerais; Brazil

Abstract

Remnants of Pouso Alegre and other essentially terrigenous basin deposits occur along the Ribeira Belt from Minas Gerais to Paraná State. Analysis of sedimentary fácies and depositional systems allowed discrimination of three stratigraphic units represented by deposits related to subaerial alluvial fans, fan-delta and proximal shelf. ln subaqueous environments these deposits were reworked by tidal currents and by normal or, eventually, storm waves. The acritarchs Soldadophycus bossii GAUCHER et al. 1996, Soldadophycus major GAUCHER 2000 e Symplassosphaeridium sp. were identified in the prodeltaic sediments, denoting participation of relatively oxygenated marine waters during sedimentation. Taking into account stratigraphic, paleontological and geochronological parameters, it is proposed that a correlation exists with the other basins along the Ribeira Belt, as well with others in Africa and South America. A palaeotectonic and palaeogeographic model was adapted to the evolution of the Westem Gondwana during the Neoproterozoic-Cambrian transition, in a scenario where cratonic blocks, tectonic collage and opening and closing of the oceans interacted. After the Varanger glacial event (ca 600 Ma) and the rising of the planet temperatures, ocean levels were also rising. Brazilides Ocean waters penetrated the southem subsiding areas af the Ribeira Belt and became a base leveI for infillings of strike-slip basins in the occidental areas of the Mantiqueira Orogen. Concomitant to these epicontinental basin infillings, sedimentation was also taking place in passive basins ofthe cratonic marginal areas. The connection between the Brazilides and Adamastor oceans allowed dispersion of similar microfossils, mainly Cloudina, in almost all basins. Convergence of cratonic blocks and closure ofthe oceans near 530 Ma allowed basin inversions, as revealed by isotopic signatures ofbasement and basin rocks.