Collapse of Submarine Channel Levees; Examples from Outcrop and Subsurface, and Reservoir Implications

Kneller, Ben¹, Mason Dykstra², Philip Thompson¹ (1) University of Aberdeen, Aberdeen, United Kingdom (2) University of California, Santa Barbara, CA

Submarine channels in mixed or muddy turbidite systems frequently build levees that can be tens to hundreds of metres thick. Often they form geometrically regular features whose thickness is greatest close to the channel and decays smoothly with increasing distance. Small scale surficial deformation is common in the form of minor slumps and debris flows, but generally high bed continuity makes these potentially excellent reservoirs. However, in many cases considerable portions of the levee show extreme and pervasive deformation, with disruption at all scales; large rotated blocks, slide sheets, slump folds and thick debris flows all occur. In extreme cases the entire levee has collapsed. The collapse process reduces gradients on the levee, and is presumably driven by gravitational instability as the depositional relief grows; this is borne out by the observation that the highest parts of the levee, close to the crest, tend to collapse first, and principally (though not exclusively) collapse inwards towards the channel. Also the higher levee (the right hand in the northern hemisphere) tends to collapse more frequently than the lower. Collapse may occur repeatedly during growth of a levee, producing internal unconformities related to each collapse event. Similar phenomena have been observed at outcrop and in the subsurface, and the frequency of occurrence of wholesale collapse observed in high-resolution seismic data suggests that this is a very common phenomenon. The effect of such collapse on bed continuity and reservoir predictability may be significant.