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Stability of Turbidites Deposited on the Sidewalls of Subaqueous Channels

James Buttles and David Mohrig
Massachusetts Institute of Technology, Cambridge, MA

We present results from a series of laboratory experiments which illustrate the bank stability of submarine channels in strongly depositional systems. The stability of channel sidewall deposits is generally not considered with regards to the evolution of a channel form and its resulting stratigraphy, but topographic measurements collected following the release of depositional turbidity currents in the laboratory show that these deposits are particularly prone to remobilization by successive currents. Initial conditions for each of these turbidity currents were held constant and channel topography was mapped following each flow using an ultrasonic transducer. The stability of the channel sidewall deposits was determined by examining the differences between the topographic maps from individual flows at a given cross-section as the bank aggrades. The difference maps reveal that channel sidewalls are at times the site of maximum or minimum sediment deposition. This alternating character of bank deposition appears to be controlled by local sediment failure events which are aided by gravity acting on the sloping bank surface. Sidewall failure during passage of a depositional current leads to a local minimum in deposition. Interestingly, the topographic indentations associated with failure focus sedimentation by subsequent currents, producing a thick deposit. This process has been observed to repeat itself, producing a complicated stratigraphy for sidewall deposits that is characterized by episodes of both focused sediment removal and sedimentation. The implications of these experimental results to the potential continuity of channel-margin deposits will be discussed.