COMPARTIMENTAÇÃO E EVOLUÇÃO TECTÔNICA DA BACIA DO PARANÁ

V. J. FULFARO, A. R. SAAD, M. V. SANTOS, R. B. VIANNA

Resumo


The Paraná Basin was developed on one of the younger areas of the South American platform, and its basement cratonization had continued up till the Eopaleozoic. The Brazilian South-Southeast folded belt, with a NE-SW strike in Upper Pre-Cambrian, probably had watched the development of subsequent aulacogenic trenches with NW-SE trends in the Cambro-Ordovician. extending easterly from the present Andean belt. These "rift" type zones had controlled the pericratonic sedimentation on the western border area of the present basin during the Silurian. During the Devonian, a portion of the future Paraná Basin, belonging to the present Andean belt, had been divided into sections by the uplift of the Asuncion arch. However, the NW·SE weakness zones, which were previously impressed on the basin basement, had strongly controlled the Devonian sedimentation, the Lower Carboniferous tectonic reactivation and erosion, and the very early Permocarboniferous sedimentation. In these espisodes, the vertical movements had been controlled by the old "rift" pattern which is related to the aulacogenic channels in the basement. The basin had acquired an intracratonic sineclise character, which was clearly defined during the Middle-Upper Permian and which was maintened up till the Lower Triassic. In southern Brazil, a wide uplift of the crust, which had begun in the Jurassic-Cretaceous, had caused the vulcanism phenomenon and the old aulacogen zones of weekness and fault had been the tracks for the extrusion of the lava. The consequent shrinking of this crustal uplift area had controlled, subsequently, the subsidence process of the coastal basins, such as Campos and Santos, as well as the reactivation and the sedimentation of the Bauru Group at the continent. The successive boundaries of this contracting movement in the domic area were controlled by the NE-SW alignments. The rift phase of the coastal basins of that time had caused the elevation of the coastal margin of the old NE-SW folded belt and step faults were formed in both direction through the marginal basins and through the continental interior. The structures of Piratininga. Agudos, Artemis, Anhembi, etc, are examples of these step fault structures. Contemporaneously, the Upper Cretaceous sedimentation had begun in the northern area of the basin. The zones of NW-SE alignments had subdivided the Parana Basin, and had controlled the areas of maximum sedimentation, until the Tertiary, when the basin had been even more subdivided by the reactivation of these zones. This subdivision included the northern area which is still receiving sedimentation at the present time. The "riff" control of the basement, especially during the early Paleozoic sedimentation and reactivation and the "rift" strong influence during the Mesozoic evolution, allows the classification of the Parana Basin as an intracontinental, cratonic, type 2A complex basin, similar to the west Siberian basins.

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