Tim R McHargue, David Hodgson, Eitan Shelef

The most popular model for submarine unconfined lobate deposits has the following attributes: (1) a single feeder channel that delivers sediment, (2) a set of distributary channels present only in the proximal part of the lobate body, and (3) unchannelized tabular deposits present in the middle and distal part of the lobate deposit. This model has become a standard to guide interpretation of outcrop and subsurface examples of submarine lobate deposits. In this contribution, three well imaged subsurface lobate deposits are described that display three markedly different morphologies, all of which differ from the “standard” model. All three lobate examples are buried by less than 150m of muddy sediment and imaged with high resolution 3D reflection seismic data of similar quality and resolution. Distinctively different distributary channel patterns are present in two of the examples, and no distributaries are imaged in a third example. We conclude that if channels are not imaged, it is because channels are not present. The different distributary channel patterns are interpreted to have resulted from different processes: (1) a lobate deposit that is pervasively channelized by many distributaries that have avulsed from numerous nodes is interpreted to result from mud-rich, stratified, turbulent flows ; (2) an absence of distributaries in a lobate deposit is interpreted to result from collapse of mud-poor, turbulent flows remobilized from littoral drift; and (3) a lobate deposit with only a few, long, straight distributaries without avulsions is interpreted to be dominated by debris flows (laminar flows) . Reconciling 3D seismic morphologies with observations of channels, scours, and amalgamation zones in outcrops is problematic. It is concluded from this study that, when characterizing unconfined deep water deposits, multiple models with significant differences in predicted permeability structure should be considered.