FORWARD MODELING OF SHALE/SALT-CORED ANTICLINES AND LISTRIC NORMAL FAULTS IN THE GULF OF MEXICO USING AREA-CONSTANT GEOMETRIC MODELS WITH GROWTH SEDIMENTS

For shale/salt-cored anticlines, three different geometric models aid significantly in interpreting areas of poor quality seismic data and in estimating the amount of horizontal shortening and of material that was mobile. Three different geometric models can be applied: only detachment folding, detachment folding with a withdrawal basin, and a withdrawal basin only with no detachment folding. All three models result in different dip patterns, rate of growth of the anticline and associated layer-parallel strains in the pre-growth sediments. In the case of overfill of growth sediments, limb dips in the growth sediments and layer-parallel strains (elongation) decrease upward to zero at the top of the growth sediments. The elongating growth sediments would facilitate the development of normal faults that die out upward and propagate downward into elongating pre-growth sediments and die out without becoming layer-parallel. The models predict the amount of stretching at the propagating fault tip. Forward modeling of the anticlines, using the calculated/observed ductility, can then be performed to model the development of the normal fault with time. In listric normal, growth faults, changes in the curvature of growth axial surfaces can reflect changes in sedimentation rate, fault displacement rate, and/or differential compaction of hanging wall growth strata. Antithetic faults that form at the fault bend commonly propagate to the top of growth sediments present at that time. Thus, the upper termination of each antithetic fault reflects the position of the growth axial surface when that antithetic fault formed and the resulting location and shape of the growth axial surface. When combined with high-resolution chronostratigraphy, these models represents a powerful tool for interpreting the history of listric normal faults and detachment folds and for understanding possible charge, reservoir, and trap relationships in the Gulf of Mexico Hydrocarbon Province.