Deep-Water Sedimentary Processes in from Active Continental Margin, Magdalena Fan, Offshore Colombia
The Magdalena deepwater fan, offshore Colombia, is the result of sediment accumulation in an accretionary prism initiated during the middle Miocene. It is fed by the Magdalena River, which drains the northern Andean Cordillera. Multibeam bathymetry and 2D seismic profiles reveal a series of seafloor deepwater channel-levee systems and mass transport deposits (MTDs) that have evolved as a result of changes in the processes controlling the sedimentation. This study compares channel evolution and basin floor morphology in tectonically deformed and undeformed areas.
The river delta migrated westward during Pliocene - early Pleistocene time, generating four channel-levee systems on the slope, formed by channel conduits that vary from constructive to destructive during their evolution. Each of them has evolved by avulsions and are now in a destructive stage. A major Late Pleistocene shift towards the east defined the western abandonment of the main fan area (Galerazamba).
Mass transport processes have smoothed sea bottom morphology alternating with channel geometries. MTDs were subdivided based on causal mechanisms: 1) detached (growth of thrust structures, instability of slope canyon and channel walls) and 2) shelf attached (major slope failures).
Depositional processes in the active fan are dominated by MTDs alternating with turbiditic and possibly hyperpycnal flows. Numerous submarine cable breaks have been reported in the area, indicating recent mass wasting activity. Slope instability associated with faulting in the area created collapse scarps and associated MTDs. Presence of channels in the head scarp and at the toe of the escarpment indicates that instability of the slope is not the only trigger for the sediment flows traveling basinward through this area.
This work provides new understanding of the processes involved in submarine fan evolution in an active margin setting, which has implications for both petroleum exploration and assessment of shallow hazards of submarine infrastructure in the area.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009