Seismic Stratigraphic and Seismic Geomorphologic Expression of Mass Transport Deposits and Sediment Waves — Examples from Slope and Basin Floor Settings

Henry W. Posamentier
ETC, Chevron Energy Technology Company, Houston, TX

Mass transport deposits (MTD's) and sediment waves are common in many deep-water settings. In some areas, they comprise in excess of 50% of the section. Less common are sediment waves, which seem to be best developed in base of slope to basin floor settings. Both types of deposits tend to be sand poor.

MTD's can range from below seismic resolution to greater than 300m thick. They are characterized by erosional bases sometimes indicative of failure along a basal decollement surface, and sometimes characterized by significant rugosity. Most MTD's are not viable exploration targets because of their fine-grained nature, largely because they originate in sand-poor staging areas. In the uncommon event that MTD's contain sand, their viability as exploration targets depends on the style of mass transport deposition - i.e., slump vs slide vs flow. Internal deformation commonly characterizes MTD's so that reservoir continuity is severely compromised, thus yielding a deposit with limited producibility.

Sediment waves are common in some base of slope settings and tend to resemble very large-scale climbing current ripples. The direction of climb commonly is in the upslope direction. The resulting seismic pattern, when sediment waves are encountered at exploration depths may be incorrectly interpreted as progradational clinoforms or extensional listric faults. Sediment waves in excess of 200 meters thick and a wavelength of 1.5 to 2.5 km are not uncommon. Smaller sediment waves can be observed in upper slope settings and can be associated with contour-parallel currents such as the loop current in the Gulf of mexico. Still other sediment waves can be associated with flow-stripping processes associated with overbank flow from turbidity current channels. In some instances such deposits can contain sand though in most instances these deposits also are commonly mud prone.

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