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A Look at Salt Keels in the Deepwater Northern GOM

Carl Fiduk

Keels in the base of salt have been observed since modern 3D seismic data shot in the deep northern Gulf of Mexico has been able to image beneath the shallow allochthonous salt canopy. The majority of these structures were the result of incomplete salt models input into the data processing. Failure to continue the base of salt interpretation (and top of salt 2 surface) down to their true levels produced artificially shallow bases. Restricting the salt models thus produced keels in the base of salt which extended below the sub-regional emplacement level of the shallow canopy but did not reflect their actual geometry. Many of these keels turned out to be feeders.

However, a subset of these structures has turned out to be true downward extensions in the base of the shallow salt canopy that do not directly connect with a deeper salt level. The size of this subset of keels range from seismic resolution limits to kilometer scale structures with corresponding offsets in the canopy’s base of salt. The origin of keel structures is incompletely understood but relates to at least two types of subsalt deformation. The first of these two types links keels to a detachment within Oligoceneto- Eocene strata. The location for detachment initiation appears to have some relationship with deeper salt structure. The second type keel-related deformation links keel formation to faults associated with extension over deep salt structures. In both cases deformation occurs after emplacement of the shallow canopy and is therefore geologically recent. Furthermore, there may be linkages to the deep salt level and/or basement that are as yet unseen.

 

AAPG Search and Discovery Article #90158©2012 GCAGS and GC-SEPM 6nd Annual Convention, Austin, Texas, 21-24 October 2012