Seismically Determined Multiple Deep Salt Layers beneath Shelf/Shelfbreak Argue for Multiple Sigsbee Salt Wedge-Type Events along Northern Gulf of Mexico

Reviews of state-of-the-art, deep-dip seismic reflection data of the continental shelf–upper slope suggest the occurrence of two salt layers. The deepest salt is a layer with top and bottom marked by strong double reflectors. Where existent, the layer thickness is generally uniform and is interrupted by “basement highs” of irregular and discontinuous reflectors. Above the deepest salt, there is a “salt weld” characterized by a single reflector couplet. Basinward seismic data suggests a termination. Extensions of normal faults within the overlying sediment wedge terminate at salt wedge reflector with few extending to the deeper salt.

Seismically indicated occurrence of two salt layers, one over another, is a phenomenon not reported before. Deposition of the Sigsbee Salt Layer (SSL) over the Gulf of Mexico rifting is at shelf water depths. This salt remains continuous until rifting emerges, as does basement within the Afar Triangle today. More basin subsidence equals sediment encroachment. Sediment accumulates, “forcing” semi-plastic salt basinward. Buoyant salt and regional tectonics, including earthquakes, may cause salt to rise within overlying sediments. This rising/migrating salt then advances over original salt deposited on basement, creating two salts that are migrating basinward. The upper salt becomes a lubricating horizon as sediment subsides and rotates basinward. Sediment motion “forces” salt to evacuate and migrate basinward, leaving a weld. As sediment progrades, several proto-SSL could appear, each for a period, ending when salt supply ends. The present SSL exists because of a continuing salt source.