10:45 〜 11:00
[HCG20-01] Turbidity current circulation patterns in three-dimensional minibasins of various widths and lengths: why being short and wide is so stressful
★Invited Papers
キーワード：Turbidity currents, basins, experiments
The structure of many continental margins reflects a competition between the dynamics of mobile substrates and processes that control sediment transport and deposition. For example, movement of subsurface salt along some margins has produced depressions, often termed minibasins, with enclosed relief comparable to the thickness of turbidity currents. Minibasin shape is influenced by the initial spatial structure of salt deposits and local clastic sedimentation patterns. Here, we explore how the ratio of minibasin length-to-width influences turbidity current flow dynamics and resulting sedimentation patterns using physical experiments. Experimental minibasin length-to-width values are informed by minibasin scales in the Gulf of Mexico. Under sustained conditions, all experiments have inlet flows with significant turbulent mixing that extend towards the center of minibasins and feed ponded flow conditions covering the rest of the minibasins. Fluid and sediment are routed through the ponded flow by a set of horizontal recirculation cells. The development of these cells is influenced by the length-to-width ratio of minibasins, with greater horizontal recirculation in minibasins that are wide relative to their length. Weak horizontal recirculation in long but narrow minibasins influences the vertical structure of the velocity field, specifically the development of relatively stagnant near bed flow that forces peak velocities to be at the minibasin rim elevation. As such, flows entering short and wide basin produce greater near bed shear stress compared to minibasins of comparable volume that are long and narrow. This should influence the development of channels and lobes in minibasins and the heterogeneity of minibasin filling turbidites.