The São Francisco Basin

Abstract

The intracratonic São Francisco basin covers almost the whole NS-trending lobe of the São Francisco craton, encompassing multiple and superimposed basin-cycles younger than 1.8 Ga. Underlain by a relatively thick and cold lithosphere, the basin contains three major Precambrian first-order sequences. The Mesoproterozoic to Early Neoproterozoic Paranoá-Upper Espinhaço sequence consists of a sand-dominated rift-sag succession that grades laterally into the sediments of a rift-passive margin basin developed along the western São Francisco plate between 1.3 and 0.9 Ga. The main occurrence of this sequence is associated with the NW-trending Pirapora aulacogen, a prominent graben nucleated in the early stages of São Francisco basin evolution (Paleoproterozoic?). The Neoproterozoic Macaúbas sequence and its correlatives record extensional events that affected the São Francisco-Congo in same time period of the dispersal of Rodinia. The Ediacaran Bambuí sequence covers large areas of the basin and marks the onset of a foreland basin-cycle triggered by the successive Brasiliano orogenies that involved the cratonic margins during the West Gondwana assembly. Diamictite-bearing successions of both Macaúbas and Bambuí sequences record important glacial ages that might have covered low latitudes during the Neoproterozoic. The Precambrian fill units of the basin are involved in foreland fold-thrust belts of opposite vergences, the Brasília, on west, Rio Preto on the north, and the Araçuaí, on the east. The Proterozoic assemblages are unconformably overlain by the Paleozoic Santa Fé Group, as well as the Cretaceous Areado, Mata da Corda and Urucuia groups. The glaciogenic Santa Fé Group is exposed in a few portions of the central and northern São Francisco basin and records the passage of the Gondwana through polar latitudes in the Late Carboniferous to Early Permian. The Lower Cretaceous Areado Group contains a package of sand-dominated strata deposited under arid to semi-arid conditions. They are overlain by Upper Cretaceous volcanic and epiclastic successions, generated during a magmatic event that affected large areas of the central and southeastern Brazil. This event is probably coeval with the deposition of the widespread Urucuia desertic successions and marks an important uplift phase of the Alto Paranaíba arch, a 350 km long and 80 km wide structure that separates the Paraná and São Francisco hydrographic and sedimentary basins. The Cretaceous cover assemblages are contemporaneous to the South Atlantic opening and the consequent separation of the São Francisco and Congo cratons.