3D Seismic examples of differential compaction in mass-transport deposits and their effect on post-failure strata

A 3D seismic volume from southeast Brazil is used to investigate the role of mass-transport deposits (MTDs) in the shaping of the post-failure seafloor morphology. In particular, it is documented the effect of differential compaction of failed sediments on the thickness of post-MTD strata. Variations in seafloor morphology above the studied MTDs are signed as: a) local thickening of post-MTD strata; b) small-scale depressions and furrows striking perpendicularly to the slope gradient; and c) submarine channels and younger mass-wasting units emplaced above compacted MTD strata. In addition, depressions up to 55 ms deep, within the scale of salt minibasins in the Gulf of Mexico, were formed immediately above the studied MTD, which detaches deep-rooted extensional faults from overlying units. This work suggests that most part of the subsidence related to differential compaction occurs soon after the sediment failure. However, inferred rheological differences within failed strata (i.e. related to the presence of uncompacted remnant strata and other lithological heterogeneities) affected seafloor morphology several million of years after slope instability occurred. Consequently, the studied landslide strata, of probable Miocene age, still control the modern seafloor topography.