GEOLOGIA

GEONOMOS, 6 (1): 1-12

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

Rogério Rodrigues da Silva (*)
Abstract
This work deals with Sequence Stratigraphy concepts applied to the Proterozoic record of the São
Francisco Craton in Minas Gerais, southeast Brazil. The cratonic cover is characterized by eight sequence boundaries (unconformity and/or correlative conformity), which subdivide the Proterozoic stratigraphy into seven depositional sequences. These sequences initially filled an intracratonic rift basin (the Espinhaço
Basin), which evolved into a passive continental margin (the São Francisco Basin). The Espinhaço Basin was filled by six stacked depositional sequences. Their sequence boundary unconformities are indicative of taphrogenic 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 coarse alluvial 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. They usually show the unconformities and the basal conglomerates covered by shallow-marine transgressive sediments. 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 deposition of tillites on the proximal reachs and turbidites on the distal portions. A transgressive phase followed the glaciation and was marked by the deposition of fine-grained sediments (lutites) and carbonatic rocks overlaying the cratonic areas. Around 0.6 Ga, during the Brasiliano Orogeny, the Espinhaço and São