Sedimentation Patterns in Zones of Flow Separation along the Inner Banks of Bends in Submarine Channels

David Mohrig¹, Kyle Straub¹, James Buttles¹, Brandon McElroy¹, and Carlos Pirmez^2
1 Massachusetts Institute of Technology, Cambridge, MA
² Shell International E&P, Inc, Houston, TX

A set of laboratory experiments reveal that turbidity currents commonly separate from channel sidewalls along the inner banks of bends. Points of separation are located close to bend apexes and currents reattach to a sidewall within a downstream distance that is less than a few channel widths in length. These pairs of points define the extent of eddies, zones of recirculating flow with very low velocities relative to the downstream current. Suspended sediment is transported into an eddy across the shear layer that separates it from the core flow. In some cases, sedimentation rates and patterns within eddies are sufficient to construct bar forms that are attached to the channel sidewalls and represent an important yet unrecognized mechanism of turbidite channel filling. These bar forms consist of inclined strata that might be mistaken for the deposits of point bars and internal levees, even though the formation mechanism and its implications to channel history are quite different. We will present laboratory data that constrains the conditions under which pronounced eddy bars are expected to develop and will present data that highlights compositional differences between eddy zone deposits and those filling the adjacent active channel. Finally, we will explore geometric properties of eddy bars that can be used to separate them from point bar and internal levee deposits.