ICE 2022


The Argentine Basin is the deep-water basin located along the slope of South America north of the Agulhas Malvinas fracture zone. The western part of the margin is underlain by thick igneous bodies and volcanic rocks known as seaward dipping reflectors (SDRs), fed by magmatism parallel to the future continental-ocean transition (COT) zone. However, the southernmost segment of the margin resembles a transform margin, where at the Agulhas Malvinas strike-slip fracture zone, faults were deflected northwards against the Patagonian craton, creating a transform margin segment. Transition between this segment and the magmatic divergent margin occurs over a short distance, the northernmost branch marking the onset of the magmatic packages of the SDRs. South to north propagation of the volcanic divergent margin occurred stepwise, where each magmatic segment was bounded by fractures zones, which could accommodate stresses during the rotation between Africa and South America. They did not propagate into the continent, but occasionally reactivated preexisting basement heterogeneities. Reactivation occurred along the Colorado fracture zone (CFZ) which marks the northern end of the oldest segment of SDRs and the Rio de la Plata Fracture zone (RFZ). The CFZ is characterized by a change in propagation from N-S to NNE-SSW and pervasive volcanic intrusions. Further north, where SDRs are best developed, several smaller fractures zones with a little continuity landward. They show strike-slip structures and initially constituted isolated depocenters, first to be flooded during the onset of marine transgression and prone to source rock preservation. The RFZ is the northern first order boundary, with an counterclockwise offset of continental crust against oceanic crust and following another basement weakness zone. After breakup, a marine transgression occurred during Barremian-Early Aptian times. Transgression flooded first the fracture zones and then expanded onto the subsiding SDRs. Once the rate of transgression was outpaced by sediment supply, clinoforms prograded into a shallow water body (less than 300 m). A narrow shelf developed and most of the sediment bypassed the slope building up stacked levees and toe of slope turbidites, precluding basin floor fans and thermohaline reworking typical of deep-water environments. Deep water deposition occurred only after Cenomanian – Turonian boundary concomitant with the final separation between the Malvinas plateau and SW Africa.