Tectonic and stratigraphic evolution of the Cretaceous Western South Atlantic

Abstract

The Cretaceous evolution of the Argentine margin between the Agulhas Malvinas Fracture Zone and the Rio de la Plata Fracture Zone is key in understanding the development of a volcanic divergent margin. In order to outline the evolution, more than 50000 km of 2D Seismic data were the foundation for the identification of the tectonic events and the sequence stratigraphic interpretation of the margin. However, ages of these events remain uncertain, as well data is limited to continental and shallow marine sequences with few biostratigraphic records.Rifting during late Jurassic-early Cretaceous times preserved under the current shelf seems not to be mechanically linked to the crustal thinning, breakup and subsequent generation of oceanic crust, as rifts entered into sag stage before the onset of crustal breakup.Four main turning points in the evolution of the passive margin have been identified: (i) crustal breakup associated with the SDRs emplaced during the late fault-extensional stage of the margin (ii) top of the first marine transgression creating accommodation for shallow marine carbonate and clastic deposits by Late Aptian times, followed by the development of a stratigraphic shelfbreak in overall shallow marine (300 m) paleowater depth during Albian times; (iii) a regional unconformity after which deep marine conditions with a structurally enhanced shelfbreak and thermohaline currents came into being (Late Cenomanian – Turonian), likely to be associated to final split off between SW Africa and the Malvinas plateau; (iv) a regional unconformity followed by a widespread transgression which marks the end of the Cretaceous (Maastrichtian-Danian) and a margin-wide reorganization of the sediment dispersal systems.