Author(s): Joris T. Eggenhuisen; William D. Mccaffrey
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Abstract: A typical internal vertical organisation is often recognised in ancient deposits of submarine turbidity currents (the “Bouma-sequence”): A massive, poorly-sorted division is overlain by an upward-fining, laminated division. The lower division has been interpreted as the result of rapid deposition from a flow that is carrying a large surplus of sediment over its suspension capacity. The upper division is the result of various phases of bed-load transport beneath a regime of relatively slow sediment fall-out. The two divisions are commonly separated by a bypass surface, often coated with a thin coarse-grained veneer and scour features. Experimental reproduction of this full sequence has so far eluded researchers, so that the coupling between the fluid mechanics of turbidity currents and the vertical transitions observed in their deposits is still unclear. We present vertical profiles of velocity from supercritical experimental turbidity currents moving down a continuous slope and propose that the transition from the rapid suspension dropout of the Ta division to sediment by-pass and scouring may be linked to the passage of a moving hydraulic jump.
Year: 2009