TRANSPORT AND DEPOSITION IN LINKED SUBMARINE MINIBASINS: PRELIMINARY EXPERIMENTAL RESULTS

Submarine minibasins affect deep-water sedimentation processes on the continental slope of the Gulf of Mexico. A network of channels carved by turbidity currents connects many basins. In general, when sea level is low the activity of these channels increase, and sediment is gradually deposited for the repeated passage of turbidity currents. When the turbidity current reaches the downdip ridge of a basin, it is reflected and an updip migrating hydraulic jump forms. In the case of a sustained current, the hydraulic jump migrates updip until flow reaches a sort of quasi-steady state condition, in which the location of the bore slowly varies in time. As the minibasin fills, an increasing rate of sediment spills into the next basin. Laboratory experiments on sediment transport and deposition in two linked submarine minibasins for the case of non-uniform sediment and three-dimensional geometry are in progress at the University of Illinois Urbana-Champaign. The three-dimensional geometry of the model should favour the natural formation of lobes, and enhance the deposition of coarse sediment in the upstream part of the minibasin due to the flow expansion. Data acquisition includes measurements of volumetric concentrations and grain size distributions of the suspended sediment, bathymetry and stratigraphy of the bed deposit. Preliminary results show that 1) as the upstream minibasin fills, the amount of sediment spilling into the basin downstream increases and its grain size becomes coarser, 2) the volumetric concentration and grain size of suspended sediment in the upstream basin, where the coarser fraction of the sediment is trapped, significantly vary in the vertical direction, 3) as the upstream basin fills, the layer of fine sediment deposited on the lateral side of the model becomes negligible, and 4) depositional features that may be interpreted as lobes form in the upstream basin in the experiments with the lower inflow rates.