Print this pageShelf-Edge Collapse, Mass Transport Complexes and Megaturbidites
Deep-water slope and fan deposits commonly include a significant, but under-appreciated, signal that stems from large to regional-scale collapse of shelf-edges. Instantaneous detachment of sediment from the shelf-edge generates a sliding mass that can either remain relatively coherent and deposit a mass transport complex, or can disaggregate and transform into an exceptionally high volume turbidity current. In both cases the sector down-dip of the collapse scar experiences by-pass and significant erosion, either by shear at the base of the sliding mass, or by turbulence. The depth of erosion is often meters to tens of meters and has the effect of re-sculpting the sediment surface directly down-dip of the collapse scar and across a large sector of the pre-existing deepwater fan.
Following the collapse event the scar becomes a site of extreme slope disequilibrium with continued fluvio-deltaic sediment supply largely by-passing the shelf margin via turbidity currents triggered by frequent, smaller scale failures. These early, post-collapse sediment gravity flows are guided by the newly created erosional topography created during the collapse event and may increase the linkage between erosional lows, creating a new network of deep-water channels.
Depositional elements created by this suite of collapse related events include i) a shelf margin scar filled by a wedge of mud-prone and anomalously deep-water sediments; ii) a large-scale mass transport complex (slumps/debris flows); iii) a new channel/lobe fan system related to the by-pass and early healing phase of the collapse scar; and iv) an exceptionally thick, widespread mega-turbidite created either by the high volume turbidity current or via the mass transport complex as linked debrites/turbidites. Megaturbidites generated in this way are deposited in very distal locations, often beyond the limits of the basin floor fan system.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009