The opening of the central segment of the South Atlantic: symmetry and the extension discrepancy

The rifted margins of the central segment of the South Atlantic are considered in terms of magmatism, symmetry and the amount and timing of extension, in comparison to the margins of the North Atlantic. It is suggested that the South Atlantic margins are probably moderately magmatic, with most of the magmatism occurring in the Hauterivian-Barremian, after the onset of rifting in the Berriasian. Most of the crustal extension took place between the Berriasian and early Barremian, before focusing along a narrow line of breakup in the Aptian. The changing locus of the rifting with time led to the development of considerable late asymmetry, and the stranding of the large part of the salt basins on variously the African and South American margin. The amount of Berriasian-Barremian extension may have been underestimated and may be sufficient to explain most of the observed crustal thinning. The apparent limited subsidence by the time of deposition of the Aptian evaporites may result from either delayed thermal subsidence due to the influx of hot asthenosphere or indicate that Early Cretaceous global sea level was well above the local water level within this isolated, partly empty basin.