Most of the topographic highs on the hummocky Gulf of Mexico continental slope off Texas and Louisiana are underlain by diapirs. The continuous upward growth of the diapirs can cause local blockage of canyons to such an extent that positions of thalwegs may be in error if based solely on currently available bathymetry. Seismic facies studies can help identify the different types of intraslope basins from which the courses of submarine canyons can be unraveled.

Three types of intraslope basins have been recognized in the Texas-Louisiana slope area: blocked canyon, interdomal, and collapse basins. As sea level rises and bottom transport decreases, the topographic effect of diapiric growth in canyons may be unchecked by erosion and infilling; thus canyon blockage can form an intraslope basin. The interdomal-type basin results where adjacent diapirs move upward, and an intervening section of sea floor is left at about its original depth. Collapse basins are formed from tensional collapse of the crest of domal and anticlinal diapirs. During a relative fall in sea level only the blocked canyon basins can receive sandy terrigenous material, shown in the seismic reflector facies pattern as onlapping onto diapiric flanks. The seismic facies pattern hat results from a relative rise in sea level consists of parallel reflectors owing to the deposits of fine-grained sediments that drape the sea floor. The interdomal and collapse types of intraslope basins are characterized by parallel reflector patterns only.

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