The role of autochthonous salt inflation and deflation in the northern Gulf of Mexico

Abstract

The deep-water Gulf of Mexico can be divided into seven structural provinces on the basis of particular histories of mother (autochthonous) salt movement. Variations in sediment isopachs suggest that most of the deep-water region was underlain by an inflated mother salt layer during the Cretaceous to middle Miocene. The southern edge of this mega-pillow was either the depositional edge of the salt or a basement structure. Partial deflation of this mega-pillow during Late Miocene–Pleistocene sedimentation resulted in the formation of large structures overlying the mother salt. This process of ‘deep’ structuring was synchronous with progressive emplacement of shallow (allochthonous) salt to form the Sigsbee canopy in the southern part of the present-day deep-water area. Recent seismic imaging of the large structures, which are predominantly located below emplaced shallow salt, allows interpretation of a range of structural geometrical styles including turtles, folds, thrusts and extensional faults. Salt feeder systems link the shallow salt via sub-vertical or inclined stems. Numerous large structural traps are therefore developed between the shallow and mother salt levels (sub-salt traps), due frequently to the geometrical interaction of the feeder systems and the deep geometries induced by mother salt flow. Deflation of emplaced salt produces welds, which may be key to petroleum charge delivery to shallow traps. Common subsidence histories for individual basins within the seven proposed structural provinces suggest that basins largely developed as primary basins floored by flowing mother salt. A positive implication of this model is that deep structures are likely to incorporate Mesozoic source rocks.