Vittorio Maselli, DaVID Iacopini, Ben Kneller, Olusoji Taiwo

In deep-water settings, the accommodation space for sediment transported by turbidity flows relates to the difference between the elevation of the depositional surface and its equilibrium profile. As a consequence, accommodation space creation, or disruption, may depend from changes in the physiography of the receiving basin, or changes in the flow properties. In topographically complex slopes, such where salt-withdrawal intra-slope basins occur, three different types of accommodation space have been recognized. Among other parameters, the ratio between flow thickness and depth of the intra-slope basin controls the partial, or full, ponding of the sediment in suspension, and consequently, the lithology distribution within the deposit. On a smaller spatial scale, the behavior of turbidity flows is affected by the topography of the sea floor. Indeed, the presence of large-wavelength bedforms may generate local topographic low compared to the adjacent sea floor that may trap part of the sediment carried by sediment-laden flows, such as turbidity flows or bottom currents.
With a beautiful example from the offshore Brazil, we show how ponded lobes accumulate on the convex-up stoss side of pre-existing sea floor bedforms and how the three-dimensional topography of the sea floor controls the flow behavior and the deposition farther downslope. In detail, using 3D seismic data and attributes we demonstrate that the stoss side of the bedform traps the coarse-grained fraction of turbidity currents flowing downslope, while the fine-grained cloud spills over its crest. Further studies are necessary to fully understand the behavior of sediment-laden flows on a complex sea floor topography, the preservation potential of such deposits and the role of stoss accommodation in the evolution of deep-water depositional systems.