Mass-transport deposits in confined mini-basin settings, Mad Dog area, Gulf of Mexico
3D seismic data in the Mad Dog area show numerous episodes of mass-transport deposition
(MTCs), each characterized by chaotic, mounded seismic facies and fanlike geometry. Four types of
are identified based upon seismic morphology and character. These include::
Type 1 have a long run-out distance from slump scars to terminus. There is a central basal erosional
“channel” that is U-shaped with lateral collapse features. Basal cats claw scours are common and
parallel the central scour. Numerous small thrusts occur in aligned pressure ridges at the termimal end
of the flow and seismically transparent intervals of fine-grained turbulent cloud deposits drape the
distal ends.
Type 2. have a high seismic coherency and appear to be formed as a large slide block moves down
slope, and disintegrates into numerous smaller blocks of various sizes. Type 2 MTCs have a relative
short run-out distance. The MTCs terminate abruptly, and pressure ridges can be seen, but they lack
basal scours and show no presence of overlying turbulent clouds deposits
Type 3 MTCs are complicated or compound with abundant basal scours but lacking the central
erosional core seen in Type 1 complexes. These scours originate high on the slope near the origination
point of the flow, but converge together further downslope
Type 4 MTC’s show scours that are dramatically different from the other three types. Scours are linear
features, that cut deep, narrow erosional channels. Scours may merge downslope and can extend for
long run-out distances, sometimes running the entire diameter of the mini-basin.
The types of MTCs are controlled by gradient of slope, viscosity of flows, and component of
sediment. Among these factors, viscosity of flow, strongly influenced by clay content, is a key
variable. Based upon observation of run out distance, geometry and erosive degree character of the
composing material can be interpreted from morphology.