Shallow Mass Transport Complex in a Pleistocene Shelf Margin Delta, Northern Gulf of Mexico
3D seismic data allow evaluation of soft-sediment deformation features in a Pleistocene shelf margin delta within a salt dome mini-basin, offshore Louisiana. The delta consists of a series of offlapping sandy clinoforms, interpreted as being associated with a prolonged forced-regression and ensuing lowstand of sea-level, Oxygen isotope Stage 6, which lasted for about 25Ky. The lowstand delta is onlapped by a transgressive mud wedge and is capped by regionally persistent highstand mudstones. The central part of the clinoforms shows severe disruption, suggestive of soft-sediment deformation. Two types of deformation are observed. Synsedimentary intradeltaic deformation forms a series of slumps and growth faults, indicated by rotated beds associated with listric faults. The central part of the delta also shows post-depositional extradeltaic deformation caused by a shallow-water mass transport complex (MTC) that erodes into the delta. The MTC shows well defined pressure ridges and forms two lobate complexes that show clear truncation of the older clinoform delta deposits. Mapping of the MTC’s show that sediment transport was almost perpendicular to the direction of the regional delta progradation that it replaces. The shallow mass transport complex is interpreted to have formed in water depths of around 100 m and is likely induced by the uplift of the adjacent salt dome. Tributive channels downdip of the delta front are interpreted as submarine slope channels possibly connected with distributary channels and formed near the end of the prolonged lowstand. These channels have a high potential of transporting coarse grained sediment down the slope and onto the basin floor.
We hypothesize that the high degree of syn- and post-depositional deformation, as well as the well developed shelf-edge channel-network are related to the prolonged nature of the lowstand. In contrast, shelf-edge deltas formed during shorter-term eustatic drops seem to lack the deformation features.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009