About This Item
Share This Item
A regional study of the Barreirinhas Basin, located in the Brazilian equatorial Atlantic margin, revealed that this basin does not fit the classical rifted Atlantic margin model and that it should be interpreted as a transform basin.
Three major stratigraphic sequences, Canarias, Caju, and Humberto de Campos, limited by unconformities, represent the principal evolutionary steps of the basin. The basin evolved from an initial rift phase dominated by tension (early or pre-Aptian?) to a transform phase dominated by lateral motion with tension/compression produced by a wrench system (late Aptian). These events were followed by a more quiet period as final separation (Albian-Cenomanian) and subsequent continental drifting (Upper Cretaceous to Holocene) occurred.
The Aptian sediments (Canarias) were formed by clastics representing fluvial-deltaic and fan delta, slope, and basinal depositional systems. The Albian-Cenomanian sediments (Caju) comprise cyclical deposits of carbonates and shales representing carbonate shelf and slope depositional systems. The Upper Cretaceous to Holocene sediments (Humberto de Campos) are composed of mixed coarse clastics, carbonates, and shales representing fan delta, carbonate platform, and slope-basinal depositional systems.
Structural and isopach maps, based on seismic and well data, allowed the determination of the structural framework and displayed several features not related to a normal rift basin. The structural grain of the basin at the end of the Aptian is formed by a succession of folds arranged in a consistent north-northeast en echelon pattern displaced by normal and strike-slip faults. Also, inversion structures affecting deep sedimentary sections and local shale mobilization associated to fault zones are present in the central and eastern area of the basin. All these features indicate that the area was affected by a right-lateral motion in connection with the separation of African and South American plates. The motion was directly related to the Romanche fracture zone, as shown by the reconst uction of continents at the end of the Aptian.
From east to west, the complexity and magnitude of the wrench tectonics gradually decrease, and in the westernmost area (Plataforma de Ilha de Santana) only horst-and-graben rift tectonics is observed. The stratigraphy, controlled by tectonics, also changes from a thick Aptian section in the east to a thick Upper Cretaceous to Holocene section in the west.
End_of_Article - Last_Page 449------------