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Mass-Transport Deposits in Distal Confined Mini-Basin Settings, Mad Dog Area, Gulf of Mexico

Ruan, Wei 1; Wood, Lesli 1; Huang, Jie 1
1 Bureau of Economic Geology,Jackson School of Geosciences, The University of Texas at Austin, Austin, TX.

3D seismic data in the Mad Dog area show numerous episodes of mass-transport complexes (MTCs), each characterized by chaotic, mounded, seismic facies and fanlike geometry. Four types of MTCs can be identified on the basis of seismic morphology and character: (1) Type 1 has a long run-out distance from slump scars to terminus and a U-shaped central basal erosional “channel” having lateral collapse features. Ubiquitous basal cat-claw scours parallel the central scour, and numerous small thrusts occur in aligned pressure ridges at the terminal end of the flow. Seismically transparent intervals of fine-grained turbulent cloud deposits drape the distal ends. (2) Type 2 has a high seismic coherency and appears to have formed as a large slide block moving downslope, disintegrated into numerous smaller blocks of various sizes. Type 2 MTCs have a relatively short run-out distance, terminating abruptly. Pressure ridges can be seen as well, although they lack basal scours and show no evidence of overlying turbulent cloud deposits.
3 Type 3 MTC’s show abundant basal scours, although 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 farther downslope.
4 Type 4 shows scours that are differ dramatically from those of the other three types. Scours are linear features that cut deep, narrow, erosional channels. The scours may merge downslope and can extend for long run-out distances, sometimes crossing the diameter of the minibasin. Type of MTC is controlled by gradient of slope, viscosity of flow, and component of sediment. Among these, viscosity of flow, strongly influenced by clay content, is the key variable. By observing run-out distance, geometry and degree of erosion, the composing material can be interpreted from morphology.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009