Abstract: Subsalt Origin of Exotic Blocks in Piercement Domes Reveals Probability of Oligocene-Miocene Salt in Gulf of Mexico Region

H. H. Wilson

The occurrence of exotic blocks of igneous and sedimentary rocks in piercement salt dome caprock is a common phenomenon around the world. Although salt piercements in many basins are known to have pierced through great thicknesses of sedimentary overburden, fragments of the sediments traversed do not appear to have been incorporated in the caprock. Jurassic, Cretaceous, or Tertiary material has not been found in salt piercements of the Gulf Coast interior salt basins nor have post-Cambrian sedimentary rocks been found in the Hormuz caprock detritus of the numerous Persian and Arabian Gulf piercements.

Empirical evidence from salt piercements suggests that insoluble caprock material is derived either from rocks interbedded with the parent evaporite or from subsalt formations as a result of glacier-like plucking from the salt subcrop during flow toward the diapiric exit.

In basins where bedded salt is too deep for penetration by the drill the age of exotic material in piercement caprock has often been used as an age indicator of the salt deposit when, in fact, the exotics probably represent presalt formations commonly lying unconformably below the evaporite deposit.

Evidence from the Isthmian salt basin in southern Mexico suggests that salt structures may be cored by Oligocene rather than Jurassic evaporite and, likewise, the salt in the Moron basin diapirs, northeast Cuba, may be Oligocene-Miocene rather than Jurassic as currently is supposed.

The possibility that Oligocene-Miocene salt may core many of the offshore Texas and Louisiana structures is suggested both by diapiric immaturity of many of the structures and by the presence of Oligocene-Miocene exotics in Belle Isle and Eugene Island piercements, Louisiana.

AAPG Search and Discovery Article #90978©1975 GCAGS-GC Section SEPM Annual Meeting, Jackson, Mississippi