LABORATORY EXPERIMENTS AND NUMERICAL SIMULATION OF SEDIMENT WAVE FORMATION BY TURBIDITY CURRENTS

Deep-water sediment waves are common features on levees of submarine channels, and have been interpreted as large antidunes produced by turbidity currents. The main reason for this interpretation is their internal layering displaying upstream wave migration. This study suggests, from the results of flume experiments and numerical simulations, a possible mechanism of sediment wave formation by turbidity currents that does not require antidune-type sedimentation.

The upstream migration occurs as a result of differential deposition between both sides of the waves. The experimental turbidity currents confirmed that an increase in deposit mass occurred on the upstream flank of a wavy topography. The increase, however, occurred even when the flow conditions were out of a stability field for antidune-type sedimentation.

Numerical model calculations were explored to extend the experimental results to natural settings of deep-sea sediment waves. The model used layer-averaged, quasi-two-dimensional equations and included topographic effects to describe the motion of and deposition from turbidity current on sediment waves. Application of the model to the settings simulating spillover turbidity currents on levees of submarine channels predicted development of wavy structure after accumulation of a number of turbidites. The wavy structures were similar to deep-sea sediment waves for their dimensions and the pattern of internal layering. The developing process of the structure showed that the waves were a succession of mounds, each of which was developed individually by preferential deposition after slope inflections.

These results suggest that antidune-type sedimentation is not necessary for sediment waves to form, and therefore sediment waves should not be interpreted as antidunes based only on their upstream migration.