Abstract
The Middle and Late Triassic Santa Maria Basin, exposed in southernmost Brazil, and Waterberg Basin, in Namibia, are herein interpreted as part of en échelon small basins in southern West Gondwana. The main structures are the Waterberg-Omaruru Fault which can be connected to a NW-strike anastomosed fault zone in Brazil. Based on field structural and stratigraphic analysis two populations of NW-strike fractures, named A-type and B-type, are recognized. A-type fractures (Az = 280°-290°) occur in the Sanga do Cabral Supersequence, underlying units of Santa Maria Basin, as extension of the Waterberg-Omaruru Fault during the Early Triassic. B-type fractures (Az = 295°-345°) are observed in all studied stratigraphic units, from the Triassic Sanga do Cabral Supersequence to the Early Cretaceous Botucatu/Serra Geral formations. Based on the structural analysis we propose that NNE-SSW extension reactivated structures of the Damara Belt, Namibia, with a propagation towards Rio Grande do Sul State forming an anastomosing normal fault system and related-rift basin by Early-Middle Triassic time. The A-type fractures were preferentially active by this phase and the B-type ones are interpreted as secondary link segments within the anastomosing system. During the Gondwana break-up and South Atlantic opening (rift to proto-oceanic phase, Aptian) the B-type fractures were reactivated as normal faults by N50°E-S50°W extension.
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