Early Cretaceous extension of Africa and South America: cause and consequences of the Late Aptian intraplate deformation
Résumé
The Jurassic-Cretaceous boundary corresponds to a major step in the Gondwana dispersal. The deformation regime indeed changed from localized, along the incipient ocean (Atlantic Tethys, Somali-Mozambique Ocean), to a highly distributed deformation along several rifts spanning from India to southern South America through Africa including Arabia. The last step of extension is marked by a major unconformity of Late Aptian in age known, since the pioneering work of Edward Suess at the end of the nineteenth century, as the Austrian Unconformity that corresponds to a world-scale plate kinematic reorganization.
We compiled a new map of the Early Cretaceous (Berriasian-Aptian) rifts in Africa and austral South America with a particular emphasis on southern Africa and the Falkland-Malvinas plateau:
At middle wavelength (few tens of kilometers) deformation scale, this Late Aptian event may have stopped the rift regime, corresponding to the transition to a sag setting (Chad and Sudanese rifts), and/or reactivated basement structures (e.g. neoproterozoic faults in the Illizi and Ghadames basins in southern Algeria and Libya). In the central segment of the future South Atlantic Ocean, Late Aptian corresponds to the end of the hyperextension period and the onset of the passive margin coeval with salt deposition.
At a longer wavelength of deformation (several hundreds to thousand of kilometers), the highlighted deformation regime may have changed regional subsidence pattern with for example the overall subsidence of northern Africa and the onset of large marine floodings (e.g. deposition of Nubian sandstones).The Late Aptian unconformity therefore records a major change in the stress within the African plate likely related, considering the scale of deformation, to a reorganization in mantle convection processes.