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Paper No. 52-5
Presentation Time: 2:30 PM
DEPOSITING COMBINED-FLOW TURBIDITES BELOW WAVE BASE: EXPERIMENTAL EVIDENCE FOR TELECONNECTION OF SURFACE WAVES AND THE DEEP SEAFLOOR BY TURBIDITY CURRENTS
Recent studies of sediment-gravity flows and their deposits have highlighted the importance and complexity of turbidity currents interacting with water-surface waves. We investigate whether turbidity currents can transport an oscillatory flow field generated by water-surface waves into deeper water. A set of experiments have been designed to answer the following questions. How do oscillatory and unidirectional flow fields combine to produce wave-influenced turbidity currents? Can wave-influenced turbidity currents transport an oscillatory flow signal into water depths that exceed the effective wave base and what is the magnitude of this teleconnection? Turbidity currents composed of quartz silt with initial volume concentrations of 5% were released at a constant rate into a tank at a water depth of 0.66 m and then travelled down a 9-degree sloping bed for 3.3 m, followed by a 2-m long horizontal segment. Steady surface waves with a 2-second period were generated by a motor-driven paddle placed at the distal end of the tank. Maximum oscillatory velocities generated by these waves ranged from ~20.0 mm/s at 0.15 m depth to ~3.5 mm/s at 1.01 m depth. Currents interacted with this wave field as they travelled downslope into deeper water. The oscillatory velocities measured within the wave-influenced turbidity currents decreased with distance travelled downslope. Even so, the maximum oscillatory velocities in the combined-flow currents at 1.01 m depth were five - six times larger than those measured at the same depth under the wave field only. Results suggest that combined-flow turbidity currents are capable of transporting oscillating-flow signals beneath the effective wave base. These wave-influenced turbidity currents can deposit combined-flow bedforms below the effective wave base, suggesting that additional lines of evidence should be used in order to unambiguously define the effective paleo-wave base.