Estratigrafia do Grupo Araí: registro de rifteamento paleoproterozoico no Brasil Central

Abstract (English)

The Araí Group is characterized by a succession of low-grade metassedimentary and metavolcanic rocks that overlaps the Aurumina Suit and the Ticunzal Formation. The related basin fill-succession of the Araí Group was probably deposited in an intracontinental rift, which evolution initiated before 1,77 My in the Paleoproterozoic. Originally this unit was subdivided in the Arraias Formation (continental sequence) and Traíras Formation (marine sequence). However, the analysis, compilation and integration of the geologic data, mainly related to the sedimentary geology and the tectono-stratigraphy, had shown the necessity to formalize four unit subdivisions, including the Água Morna, Arraias, Caldas and Traíras formations. The Água Morna Formation represents a braided river fluvial deposicional system, evolved in an intracontinental SAG basin type, during a pre-rift phase, and representing the Água Morna Tectonosequence submitted to thermal subsidence processes. The Arraias Formation represents a thick package of continental sediments, subdivided in four members: Cubículo (aluvial fans), Prata (braided river), Mutum (aeolian), Ventura (lacustrine) and Buracão (volcanic and pyroclastic), representing the Arraias Tectonosequence, which constitute the infilling of the main rift phase, under mechanic subsidence. The Caldas Formation represents the transitional depositional sequence of the Araí Group, subdivided in two informal members related to beach system: Lower Member (backshore and foreshore) and Upper Member (shoreface). The Traíras Formation represents the marine sequence, subdivided in the Boqueirão Member (mixed platform dominated by tides), Rio Preto Member (siliciclastic platform dominated by tides) and Rosário Member (mixed platform dominated by tides), integrating the Traíras Tectonosequence and developed during flexural subsidence (post rift phase). Here the rewied stratigraphy has shown well functional for mapping and regional correlations in different areas of occurrence of the Araí Group in Central Brazil.