Abstract

Early (Late Jurassic to Eocene) extension in the northern Gulf of Mexico was detached on the Louann salt, whereas late (Oligocene to Recent) extension typically detached on allochthonous salt canopies or weak shales. However, significant late Oligocene to Miocene shortening was accommodated in the deepwater Perdido and Atwater foldbelts, which are detached at the Louann level. This requires that late extension must have occurred at the deep level, thereby locally deforming the shallow canopies or shale detachments. We present several kinematic models in which extension is transferred from a shallow level to a deep level, either by slip on basinward-dipping faults, reactivation of counterregional faults and welded feeders, or extensional collapse of remnant primary diapirs. In all cases, the shallow canopy is deformed and anomalous supra-canopy growth geometries develop. We illustrate several of these geometries using data from the Louisiana shelf and the Corsair fault trend on the Texas shelf. Finally, we suggest that the transfer happens because the thickness and mechanical strength of the canopy overburden become greater than those of the overburden near the distal toe of the Louann salt, thereby favoring gravitational failure of the margin on the deeper detachment.