The Permian-Triassic in the Paraná Basin in Brazil and Uruguay: an approach to stratigraphic systematization

Abstract

The continental deposits of the Paraná, Chaco-Paraná, and Norte basins (Brazil, Argentina, and Uruguay), accumulated from the end of the Permian until the extrusion of the enormous volumes of lava in the Early Cretaceous, are intimately linked to the new paleogeographic configuration associated with the geological processes of the southwestern margin of Gondwana. This fact led to the implementation of a progressive continentalization of these basin areas that housed essentially siliciclastic deposits of aeolian, fluvial, and subordinately lacustrine origin, which followed one another throughout that time. In the Uruguay - Rio Grande do Sul/Brazil region, a large part of these continental records crop out. Their lithological similarities, the difficulties in recognizing unconformities, and the lack of marker horizons are part of the causes of many conflicting conceptions about the area’s stratigraphy. The work was based on a broad review of the geological literature on the historical evolution of the different proposals addressing the spatial and temporal arrangement of the sedimentary rocks developed between the Rio do Rasto Formation and the Serra Geral basalts. This review was accompanied by fieldwork aimed, in particular, at reviewing the lithological characteristics and distribution of the Buena Vista (Upper Permian) and Sanga do Cabral (Lower Triassic) formations exclusively on the surface, with the ultimate goal of adjusting the geological cartography in the area of the Uruguayan-Brazilian border. In addition, aspects related to the departure from good stratigraphic practices are discussed, such as the mixture of litho-bio-chrono correlation criteria and the unnecessary proliferation of names, as well as the importance of the application
of correct stratigraphic techniques and procedures in the discussion on the use and protection of the Guarani Aquifer System, a water resource shared between the two countries.