Sedimentary Dynamics of the Salt-Dominated Continental Slope, Gulf of Mexico: Integration of Observations from the Seafloor, Near-Surface, and Deep Subsurface

Winker, C.D., Shell E&P Technology Applications and Research, Houston, TX, and J.R. Booth, Shell Offshore Inc., New Orleans, LA.

Regional Scale: Depocenter shifts and eustacy cause intermittent pulses of high sediment flux to the slope. The Mississippi River can deliver sufficient sediment to quickly fill downdip, salt-controlled bathymetric depressions to their spill points; ponding in mini-basins is followed by bypass to submarine fans on the abyssal plain. When the updip sediment supply is shut off, tectonically controlled topography is rejuvenated.

Corridor Scale: Interbasinal channel systems originate at shelf-margin deltas and/or erosional features. Sand-rich turbidity currents and mud-rich debris flows follow the same channel systems. Turbidity currents tend to travel fa rther than debris flows and become increasingly dominant downslope. Channels develop graded profiles by both incision and levee aggradation. Channels, levees, and a variety of mass-transport complexes dominate upper slope deposits (bypass facies assembla ge), while fan lobes dominate minibasin deposits of the middle to lower slope (ponded facies assemblage).

Mini-Basin and Reservoir Scale: Multiple entry and exit points can exist within the same sequence, and can occur adjacent to active salt ridges. High net to gross, high continuity fan-lobe sands may be localized near the entry point, or displaced farther downdip in the mini-basin, depending on pre-existing topography. Discontinuous reservoirs can result from deposition in bypass channels, truncation by debris flows, and fragmentation by rotational slides. Mini-basins commonly sho w a repeated stacking pattern, attributed to cycles of (1) simultaneous filling of ponded and slope accommodation space, and (2) structural rejuvenation.