Passive-margin salt basins tend to be much more deformed than their nonsalt equivalents, but they are by no means all the same. We used seismic data to study the Salina del Bravo region, northeast Mexico, to investigate the ways in which margin configuration and postsalt uplift history can influence passive-margin salt tectonics.
The Salina del Bravo area contains four main structural systems, all of which trend NNE across the entire region. These structures are the Bravo trough, Sigsbee salt canopy, Perdido fold-and-thrust belt, and BAHA high. Gravity-driven deformation did not begin until more than 130 m.y. after salt deposition, because of buttressing against the BAHA high. We suggest that deformation was ultimately triggered in the Cenozoic by Cordilleran uplift that tilted the margin seaward and created a major sediment source terrane. Sediments shed from the uplift expelled salt seaward to form the Sigsbee canopy. At the same time, tilted and loaded sediments were translated seaward on the Louann salt until they were buttressed against the BAHA high, forming the Perdido fold-and-thrust belt. A physical model was built to test this hypothesis. The model was able to reproduce most of the major structures in the region, suggesting that the hypothesis is reasonable.
The Salina del Bravo region shows how a downdip buttress can inhibit gravity-driven salt deformation in passive-margin salt basins. Furthermore, the area also shows the importance of postsalt uplift, which can destabilize a margin through a combination of tilting and sedimentation.