NEW GEOMETRIC MODEL FOR DETACHMENT FOLDS IN THE DEEPWATER, WESTERN GULF OF MEXICO

New geometric models have been developed for detachment folds with a deformable lower layer that can accommodate massive thickness changes and flow laterally such that anticlines move positively up and synclines move positively down displacing sediments below them until they hit an undeformable horizon. In this case, the resulting anticlines grow rapidly due to the material being added from the subsiding synclines. In the geometric models, the displacement and material gained in the folds is known. In previous geometric models of detachment folds, the anticlines are shown to move positively up, but the base of the synclines does not move down in an absolute sense. Preliminary analyses of several compressional structures in the deep-water western Gulf of Mexico (GOM) show a plot of excess area versus depth to detachment from an arbitrary reference horizon that has influences of material movement from underneath synclines. In the natural detachment folds, the true detachment horizon is clearly recognizable in seismic profiles as the base of Jurassic Louann salt. The excess area curve should go to zero at the known detachment (the depth intercept), instead the excess area curve is displaced up from the depth axis by an area equal to the amount of salt added to the core of the anticline. In the new geometrical model, regional for the excess area calculations is positioned equal to that of flat lying, undeformed sediments directly adjacent to the fold structures, rather than being placed at the bottom of the synclines as in older models. By doing this, the anticlines and synclines can be interpreted independently and when plotted on the same graph, the lines intersect. The intersection shows 1) the approximate true depth to detachment, and 2) the excess area either lost or added in the deformation process. Our work improves on previous interpretations by showing positively downward moving synclines and positively upward moving anticlines as a result of detachment folding above a mobile salt substrate.