Seismic Stratigraphy, Seismic Geomorphology, and Process Sedimentology of Mass Transport and Other Non-Turbiditic Deposits in Deep-Water Environments

Extensive mass transport deposits are observed both in slope as well as basin-floor settings. Using 3D seismic data, such deposits can be characterized stratigraphically as well as geomorphologically. The integration of these two approaches provides great insight regarding the mode of deposition as well as the physical characteristics of these deposits. Mass transport deposits can take the shape of sheets, lobes, and channel fills, and can reach 150 m or more in thickness. Greater thicknesses are observed where successive flows are amalgamated. Mass transport deposits can be recognized seismically by certain geomorphologic and stratigraphic characteristics: 1) surfaces underlying such deposits commonly are characterized by scour, commonly taking the form of extensive linear grooves. These grooves are inferred to be formed by the passage of blocks imbedded at the base of the flow mass that are dragged across the underlying sea floor. 2) Upper surfaces commonly are characterized by irregular to hummocky relief and with steep to gentle flanks. 3) Internally, these deposits are characterized by transparent to chaotic seismic reflections. 4) In some instances mass transport lobes are characterized by extensive low-angle thrust faults associated with compression, commonly at their termini. 5) In basin floor settings larger mass transport deposits appear to be associated with a deep plowing process by which basin floor deposits “bulk up” the flow and steep-walled erosional margins are formed.

Other deposits that are observed in deep-water settings are sediment waves. These are observed in a variety of settings including 1) channel-levee overspill, 2) upper slope settings unrelated to channelized flow, and 3) near the slope to basin floor transition. Though channel-levee overspill deposits are turbiditic, the other two deposits likely are not. Nonetheless, they all seem to be associated with a waveform morphology and display a wave migration direction opposite to the direction of flow.