Seismic correlations and well data confirm that deep-water carbonate beds of Mesozoic age have been found above the shallow allochthonous salt canopy in the northern Gulf of Mexico. These rafts of carbonate strata often overlie equivalent age Mesozoic carbonates in their correct stratigraphic position below the salt canopy. The presence of displaced Mesozoic carbonate rafts above the canopy raises two important questions: 1) how did Mesozoic strata get to such a shallow level in the basin statigraphy? and 2) what effect do high velocity carbonates have on seismic imaging below shallow salt?
The origin of keel structures is presently not well understood. Empirical observations suggest that keels form in response to at least two types of subsalt deformation. The first of these two types links keels to a detachment within Oligocene-to-Eocene strata. The second type of keel-related deformation links keel formation to faults associated with extension over deep salt structures. As deformation occurs after shallow canopy emplacement, the keels are fairly recent developments geologically. Volumetrically few but intriguing observations suggest possible basement involvement in keel formation.