The geometry and evolution of allochthonous salt and its impact on petroleum systems, northern Gulf of Mexico Basin: Studies in three- and four-dimensional analysis

The geometry and evolution of allochthonous salt in the northern Green Canyon and Ewing Bank region of the northern Gulf of Mexico Basin are examined using a variety of techniques. Regional two-dimensional restorations illustrate the complex geometry of a multi-level salt system and the types of interactions between counter-regional and salt-stock canopy models of allochthonous salt system evolution. Salt geometry commonly changes dramatically through time as it provides much of the accommodation for sediments and absorbs much of the extension and contraction within its overburden.; Sequential restorations of a N-S megaregional cross section across the entire northern Gulf of Mexico recognized several salt provinces. These restorations place the local study area into perspective relative to the entire basin. Salt sheet formation and evacuation occurred progressively basinward through time in response to basinward shifts of major Cenozoic sedimentary depocenters. The cross-sectional area of autochthonous salt represents at most 45% of its maximum along this transect. The total cross-sectional area of salt through time is more stable with variations of only 30% from its maximum. Little translation/extension (1.46%) occurred at the autochthonous salt level during the evolution of the basin. Most of the translation/extension occurred above allochthonous salt sheets (25%) and was compensated laterally by salt flow.; Petroleum systems are significantly impacted by the evolution of allochthonous salt. The high thermal conductivity of salt retards the thermal maturation of subsalt petroleum source rocks and causes late generation. Oil generation varies spatially and temporally as a function of the overlying allochthonous salt evolution. The impermeability of salt causes petroleum migration pathways to be deflected laterally up dip along the base salt. Where salt welds form, petroleum migration continues vertically. All fields/discoveries within the study area are associated with predicted zones of paleo-subsalt petroleum concentration.; Finally, three-dimensional structural restorations constrain the evolution of allochthonous salt, its influence on sediment pathways, and the geometry of salt welds through time. Analysis of the changing salt geometry and salt welds is used to model petroleum migration pathways and zones of petroleum concentration through time.