EVOLUÇÃO CLIMÁTICA DO GONDWANA NA REGIÃO CENTRO-SUL DO BRASIL E SEUS REGISTROS GEOLÓGICOS CONTINENTAIS DURANTE O MESOZÓICO, ENFATIZANDO O ARCO DO PARANAÍBA, A BORDA NNE DA BACIA DO PARANÁ E A PORÇÃO MERIDIONAL DA BACIA SANFRASCISCANA, NO OESTE DO ESTADO D

Abstract

Current theories suggest the the main cause of the temperature changes in Earth surface along thegeological time, seems to be, as a concensus, the anomalous concentration of CO2 , CH4 and other gasesin the terrestrial atmosphere. There are however divergences about the origin of these gases which are themain responsables for the greenhouse effect.This study discusses questions about the global climate changes in the geological past, commentingthe mass-extinction periods of the Permian-Triassic (P/Tr) and Cretaceous/Tertiary (C/T) boundaries. Therelationship between unusual high CO2 levels in the atmosphere and mass-extinction events is commented.The origin of the greenhouse gases are attributed to: a) extensive outgassing of volatiles through of largevolcanic events, or b) asteroid or cometary impact by bodies ranging up to 10 Km in diameters, or c)marine and terrestrial organic production by living organisms.Climatic changes have been detected in all the geological records, from Precambrian to Cenozoic.Tillites and varvites in Gondwana are features of Proterozoic and Paleozoic ice ages. The Mesozoic, onthe other hand, had a global warm climate, exhibiting generally high level sea and low thermal variationbetween the poles and the equator. The Mesozoic continental geologic records in Gondwana are consequenceof this arid climate, and the sedimentary rocks are mainly red-beds seguences or other related with arid/semi-arid environments.The relationship between the climate, geological records and paleogeographical aspects in the MesozoicCentral-South Gondwana are presented, focussing the NNE border of the Paraná and the SouthernSanfranciscana basins, which occur in the western part of Minas Gerais state. The Parecis Basin thatoccurs in Mato Grosso State is also mentioned.These basins show sequences of varied rock types -volcanicand sedimentary ones -, and exhibit ages ranging from early to late Cretaceous.Other important paleogeographic feature studied occurs as a strip of intensely deformed Precambrianrocks forming a NW-SE tectonic arch, preserved as a succession of thrust slices. This is known as Alto doParanaíba Arch or Alto do Paranaíba Anteclesis, (Ladeira et al. 1971, Grossi Sad et al 1971, respectively),a regional structure related with the emplacement of the Cretaceous Paraná and Sanfranciscana basins.