Pre-Salt Rift Morphology Controls Salt Tectonics In The Campos Basin, Offshore Se Brazil

Classic models of gravity-driven salt tectonics commonly depict kinematically linked zones of overburden deformation, characterised by updip extension and downdip contraction, separated by a weakly deformed zone associated with downdip translation above a relatively smooth base-salt surface. We use 2D and 3D seismic reflection and borehole data from the south-central Campos Basin to show that these models fail to adequately capture the complex range of structural styles forming during salt-detached gravity-driven deformation above a rugose base-salt surface. In the Campos Basin, the base-salt is defined by broadly NE-trending, margin-parallel, generally seaward-dipping ramps that have up to 2 km of structural relief. We define three domains of overburden deformation: an updip extensional domain, an intermediate multiphase domain and a downdip contractional domain. The multiphase domain is defined by large, partly fault-bounded, ramp-syncline basins, the stratigraphic record of which suggest ca. 28 km of seaward gravity-driven translation of salt and its overburden since the end of the Albian. We also identify three main types of salt structures in the multiphase domain: (a) contractional anticlines that were subjected to later extension and normal faulting; (b) passive-to-active diapirs that were later extended and widened, and which are bound on their landward margins by landward-dipping, salt-detached normal faults and (c) reactive (extensional) diapirs that were subsequently squeezed. We argue that this multiphase deformation occurs because of basinward translation of salt and its overburden over complex base-salt relief, consistent with the predictions of physical models and several other seismic reflection data-based studies. Critically, these complex local strains overprint margin-scale patterns of deformation.