THE EFFECT OF FLOW STRIPPING ON SUBMARINE LEVEE CONSTRUCTION AND STRATIGRAPHY

Submarine channels are ubiquitous features of continental slopes and fan systems. They may have complex meandering patterns, in which channel and levee deposits are built by repeated turbidity currents. Due to the remote location and to the episodic nature of the turbidity currents, very limited field data are available. As a consequence, the morphodynamics of submarine channels is still poorly understood compared to the subaerial environment. It is generally recognized that flow spilling and stripping are the main processes responsible for submarine levee formation. While the former process is responsible for the overbank deposition of relatively fine sediment transported in the upper part of the flow, the latter allows for the overbank deposition of relatively coarse bed material when a turbidity current travels through a meander bend. Here we present results of laboratory experiments on the formation of a submarine channel-levee complex in which the levees are built by stripping of 21 repeated and sustained turbidity currents. The turbidity currents are released in a multiple bends sinuous model channel with initial trapezoidal cross section and axial slope of 4\%. The morphodynamic evolution of the system is recorded via high-resolution measurements of bathymetry and stratigraphic sections. Special care is taken to monitor the stratigraphic record of the bedforms that appeared on the outer bank of the channel and on the levee. Finally, core samples are collected and divided in multiple layers to characterize how the spatial distribution of coarse and fine sediment in the channel and on the overbank area changes as the initial channel fills. The temporal variation of the geometric characteristics e.g. amplitudes and wavelenghts, and of the migration rates of the bedforms inferred from the stratigraphic sections, along with the grain size distributions of the core samples, should allow for a rough and preliminary characterization of the flow in the channel and on the overbank area in different stages of the depositional experiment.