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3-D Experimental Modeling of Megaflaps Developed During Differential Loading: Application to the Gulf of Mexico


Megaflaps are characterized by rotated steeply dipping stratal panels corresponding to original thinned roofs of inflated salt structures flanking the margins of diapirs or their equivalent welds. They represent wide zones of drape folding close to the diapir flanks with high structural reliefs being characterized by near vertical to totally overturned strata. Megaflaps have been identified in different geological scenarios being an important impact on trap and reservoir definition. Nevertheless, in most cases the seismic images of these structures are very poor, thereby hindering their interpretation. Using an experimental approach based on sand-box models, this research focuses on how megaflaps develop by differential loading. Whereas salt was simulated with a silicone polymer, dry silica sand was used as analogue of brittle rocks. Among the main parameters tested in the experiments there are the pre-downbuilding overburden thickness, the overburden strength and different sedimentation rates between adjacent minibasins. Oblique and top time-lapse photographs; scanned of the experiments surface; 3D voxel models and 3D seismic obtained from serial sections were the different techniques used in the analysis of the physical models. The experimental results show that the main factor controlling megaflap development is the pressure gradient produced by the different sedimentary loads between two adjacent minibasins. Polymer withdrawal from beneath the minibasins depocenters took place during the first stages of the experiments developing an inflated area pierced later by a passive wall. The thinner prekinematic roof rotated up to 900 and extended only a short distance up the flanks during the early stages of passive diapirism. In contrast, a higher sedimentation rate in one basin resulted in two evolutionary stages: 1) an initial one with polymer withdrawal from beneath the thicker depocenter and polymer inflation in all other areas, and 2) a second stage starting after the development of a primary weld below the subsiding minibasin characterized by the collapse of the thinner basin located above the previously inflated polymer. The interplay between minibasin subsidence and diapiric rise enhanced the development of a tall, overturned megaflap in the diapir flank facing the second-stage basin. The kinematic evolution of the experiments is compared with some interpreted megaflaps developed by differential loading in the deepwater Gulf of Mexico.