Abstract: Flow and Deposits of Turbidity Currents and Submarine Debris Flows

Parker, Gary - University of Minnesota

Turbidity currents and submarine debris flows are major mechanisms for delivering sediment to the deep-water environment. Turbidity currents are dilute suspensions of solids which form downslope-moving bottom currents. They generally require turbulence in order to hold the sediment in suspension. Submarine debris flows are thick slurries of water-sediment mixtures in which grain-grain interaction is important. Both flows can be driven either by gravity or momentum. A review is provided of recent research on flow mechanics, depositional mechanisms, deposit structure and resulting morphology. Both turbidity currents and debris flows can run out long distances and form submarine fans. Turbidity currents tend to sort sediment downslope. The current may obtain much of its drive from clay in suspension, yet deposit relatively fines-free sand over long distances. Turbidity currents can also construct strongly meandering channels with high natural levees. They can be highly erosive as well as depositive. Submarine debris flows are poorer sorters of sediment. At least some fines are required in order to render the slurry mobile at slopes well below the angle of repose. Remobilization of antecedent deposits appears to be partially suppressed in the subaqueous environment. Strong turbidity currents can drive a subsidiary basal momentum-driven debris flow. Turbulence tends to drive fines out of this basal layer. Strong submarine debris flows can create subsidiary turbidity currents as sediment erodes from their heads. Implications for distinguishing the deposits created by the two flow types are discussed.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil