MORPHODYNAMIC AND STRATIGRAPHIC EVOLUTION OF SELF-CHANNELIZED SUBAQUEOUS FANS EMPLACED BY TURBIDITY CURRENTS

The formative mechanisms of many geologic features attributed to the passage of turbidity currents are still obscure due to the difficulties in documenting the dynamics of turbidity currents in the field. Submarine channels and lobes have been extensively documented using seismic tools and outcrops. The actual morphodynamics of their emplacement remain, however, only poorly understood. In this paper we present experimental research that documents the morphodynamic and stratigraphic evolution of self-channelized subaqueous fans emplaced by turbidity currents. A large-scale facility is used to document the fan structure and internal stratigraphy that developed after repeated flow events. The fan surface tended to prograde and aggrade from event to event. Within this general pattern, the experiments exhibited the formation, migration, and abandonment of well-defined depocenters that tended to stack compensationally. These depocenters were typically characterized by one or more channels bounded by levees. The deposits of successive runs showed a tendency to cyclically expand contract in the strike direction, and extend-backstep in the dip direction. The overall pattern of grain-size variation consisted of downstream fining. The sediment in the channels, however, tended to be coarser than in the levees bounding it. As the fan evolved from flow event to flow event, successively more of the sediment fed in bypassed the platform on which it developed. The evolution of morphologic and stratigraphic patterns observed in the experiments shows several key similarities with channelized fans at field scale.