Three-dimensional evolution of salt-controlled minibasins: Interactions, folding, and megaflap development

A megaflap, or an overturned, folded, sedimentary-basin edge, is a classic feature of salt-controlled basins, formed during the inception of salt allochthony. To illustrate the relative importance of the balance between salt and sediment inputs, basin rheology, and tectonism resulting from basin interactions in the development of megaflaps, a set of analog experiments were performed in a computed tomography scanner. Sediments are modeled using both granular material and a mix of granular and viscous material and salt as purely viscous material. Uneven sedimentary loading and associated salt flow localize primary minibasins, which then migrate and expand laterally until sufficient thickness is reached to pin the downbuilding phase. The encasement of minibasins into the mother-salt layer is followed by secondary minibasin development above the canopy, the inception and localization of which appear to be more locally controlled by the primary salt feeders, salt glaciers, and canopies. Enhanced salt extrusion along basin edges is responsible for (1) classic halokinetic sequences, (2) major wedging and basin-edge erosion, and (3) basin-edge backfolding onto the basin centers, forming megaflaps. Basin interactions during differential subsidence and secondary minibasin development above the allochthonous salt canopy result in the formation of salt welds and tectonic deformation at basin boundaries, including broken and transported basin edges. The major controlling factor in megaflap development is salt allochthony, which allows the local salt extrusion rate to be higher than the sedimentation rate. Enhanced allochthony is the result of enhanced pressure related to local salt stock squeezing, regional shortening, or basin tilting.