Equilibrium in Submarine Channel-Levee Systems: New Insights from Physical Modeling

Sinuous submarine channels are significant conduits for the transport of sediment from the shelf into deep marine basins. Channel systems are major morphological features that vary greatly in size from a few metres wide to a few kilometres, with the levee crest several hundred of metres above the channel floor and can extend for thousands of kilometres into the basins. Turbidity currents are considered the key agents of sediment transport in submarine channels. Due to the nature of turbidity currents, direct measurements are difficult to obtain in active channels and therefore the interaction between turbidity currents and sediment transport is poorly understood.

The relationship between the evolution of turbidity currents and sinuous channels is investigated through physical modelling of scaled experiments using a channel model with 15 bends, allowing for the examination of velocity distribution, inner-channel and overspill flow properties, alongside their associated deposits. A known initial mass concentration of silica flour was used to create nominally identical particulate turbidity currents. Flow morphology evolves and adjusts to the channel form progressively along the system. Velocity and overspill is greatest in the proximal bends forming coarse-grained overbank deposits. In the distal bends the deposit becomes progressively finer, until the final five bends, as flow velocity decreases and overspill is predominantly confined to the outer edge of the bend apex stripping the flow of the coarse grains as the basal part of the flow runs up the outer bank. The intra-channel deposit grain size decreases down channel and remains finer grained than the overbank deposits in distal areas. Additional experiments attempt to address the relationship between axial slope and turbulence. Current understanding of flow development led to the prediction that the turbulence of the flow would decrease as the axial slope was lowered. Preliminary data show an unexpected trend in the results whereby turbidity current turbulence decreases from a 3° to 2° slope and increases from a 2° to a 1° slope, indicating a turbulence low at the mid slope angle. The initial findings question the present understanding of the development of equilibrium flow state and turbulence propagation through a sinuous channel system.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California