Salt-influenced Morphodynamics: the Coevolution of Turbidity Currents, their Deposits and Mobile Substratum

Rich styles of landscapes emerge on salt-hosting continental slopes where the co-evolutions of turbidity currents, their deposits, and salt deformation occur. Salt-influenced morphodynamics are not well understood from seismic imaging of these systems because of high present-day structural complexity, and because properties of the depositing currents are not preserved. Here we avoid these shortcomings by performing a set of fully three-dimensional experiments that were specifically designed to capture the dynamic evolution of submarine fans underlain by a mobile substratum. Turbidity currents were released from a confined channel and spread across an unconfined, originally flat surface. When traversing a rigid surface, the currents in each experiment produced the same fan-shaped deposit. When the rigid surface was replaced by a thin layer of long-chain silicone polymer that possessed a salt-mimicking rheology, turbidite loading drove salt flow that applied tractions to the overlying fan and induced extensional faulting within the depositional lobe. Subsequent sedimentation events led to further structural segmentation that produced seafloor topography with significant enough relief to guide the subsequent currents. Over the uniformly thick salt, turbidite loading produced a minibasin that deepened as more sedimentation occurred. Over-steepening of the basin walls led to sediment failure that facilitated salt breaching and formation of allochthonous salt sheets that eventually sutured and encased the minibasin. Deposition of a similar deepwater lobe on top of a layer of basinward thickening salt created multiple minibasins with migrating depo-centers. As these linked minibasins evolved, the growing seafloor relief guided and promoted sediment bypass associated with subsequent currents. Our work highlights the need to incorporate substratum deformation into morphodynamic models for margins underlain by salt and demonstrates that salt-sedimentation interactions must always be considered when reconstructing basin evolutions in these provinces.