Effects of gradual increase of kaolinite concentration on experimental turbidity current flow dynamics and related deposits

Abstract

Clay particles are common elements in many natural flows such us fluvial, lacustrine and deep water flows. The addition of a small amount of clay causes changes in the fluid-dynamics of a flow and in the architecture of depositional systems. Eleven successful experimental turbidity flows with a constant 13% volume concentration were performed. Five runs correspond to the first set of experiments that have different ratios between sand and clay at a constant slope angle of 9 degrees at which all sand was bypassing. Six more runs correspond to two additional sets of experiments with constant sediment fraction but decreasing slope angles (clay at 4% sand at 9% vc in the first set and 13% sand 0% clay vc in the second set). There is a decreasing trend in Umax, and shear velocities as the clay content becomes higher, also the distance between Umax and the bedding plane becomes higher with larger clay concentrations. Thickness and sedimentation rates increase as the slope and clay content decrease. Also sand body deposits show to be coarser-grained than the tail deposits and these being coarser-grained than the input sediment. Closed-channel fluid dynamics reveal to be comparable to open-channel flow-dynamics, since similar phases were observed as clay content increases (1) turbulent flow; (2) turbulence-enhanced transitional flow; (3) upper transitional plug flow; and (4) quasi-laminar plug flow, these transitions are explaining by the capacity of clay to suppress local shear stresses, reducing velocity gradient and turbulence intensity. Clay is more efficient than silt on reducing the equilibrium and thus enhance the transport efficiency of sand. When looking at the experiments as a window along the continental slope to the basin plane in real-world systems, thick coarse grained sandy-packages are generated at relatively low slopes in the laboratory, or distal parts in nature under a clay laden flow. On the other hand, free-clay laden flows produce thick coarse grained sandstones at higher angle slopes in the laboratory or proximal areas in nature. Finally is also demonstrated that clean sand packages can be deposited from clay-laden flows.