AS BACIAS PROTEROZÓICAS DO ESPINHAÇO E SÃO FRANCISCO EM MINAS GERAIS: UMA ABORDAGEM DO PONTO DE VISTA DA ESTRATIGRAFIA DE SEQUÊNCIAS

Abstract

This work deals with Sequence Stratigraphy concepts applied to the Proterozoic record of the SãoFrancisco Craton in Minas Gerais, southeast Brazil. The cratonic cover is characterized by eight sequenceboundaries (unconformity and/or correlative conformity), which subdivide the Proterozoic stratigraphyinto seven depositional sequences. These sequences initially filled an intracratonic rift basin (the EspinhaçoBasin), which evolved into a passive continental margin (the São Francisco Basin). The Espinhaço Basinwas filled by six stacked depositional sequences. Their sequence boundary unconformities are indicative oftaphrogenic periods, when tectonic displacements were mainly accomodated along a master listric fault,but also along synthetic and antithetic subsidiary normal faults. The unconformities are covered by coarsealluvial conglomerates, deposited by the combined effects of source area uplift and depocenter subsidence.The depositional sequences of the Espinhaço Basin show impressive cyclical depositional patterns. Theyusually show the unconformities and the basal conglomerates covered by shallow-marine transgressivesediments. The São Francisco Basin, a passive continental margin, was developed at approximately 0.9 Ga.Coevally, a continental glatiation occurred over the craton, which produced a relative fall in the sea level,erosion and hence unconformity development. During that time, the basin was characterized by the depositionof tillites on the proximal reachs and turbidites on the distal portions. A transgressive phase followed theglaciation and was marked by the deposition of fine-grained sediments (lutites) and carbonatic rocksoverlaying the cratonic areas. Around 0.6 Ga, during the Brasiliano Orogeny, the Espinhaço and São FranciscoBasins were inverted.