Detailed geophysical surveys were conducted over five intraslope basins on the northern Gulf of Mexico slope off Texas and Louisiana. Analysis of the seismic reflection data shows that these depressions are the result of coalescence of diapiric salt structures. They are filled with numerous thick sedimentary sequences with variable drape and onlapping relations. The difference in bedding attitudes which distinguish the sequences are believed to be a result of episodic salt movement. The five intraslope basins show great individual variability in the details of their physiography and structure. However, they may be classified into two main structural types: (1) eastern basins that are generally deep depressions with steepened slopes which display evidence of recent vertica motion and mass sediment movement and are underlain by salt at relatively shallow depths; and (2) western basins which are broad and shallow, formed between elongate ridge systems and which have undergone less deformation. The marked structural difference east to west is believed to be the result of differences in the thickness of the underlying salt. A thicker accumulation of salt to the east allowed for greater relative vertical motion in response to differential loading, and consequently more localized subsequent deposition. Differential loading on a thinner layer of salt may be expected to produce less vertical motion and broader basins, such as in the west. The composition and structure of the sedimentary sequences reflect complex interactions of sea-level fluctuations, thick sedim nt deposition, relative vertical motion of salt structures, related faulting, and mass sediment movement. Once formation of intraslope basins is initiated, they become the main loci of deposition for sediments reaching the continental slope.

End_of_Article - Last_Page 568------------