Salt dome

Stratigraphically, salt basins developed periodically from the Proterozoic to the Neogene. The formation of a salt dome begins with the deposition of salt in a restricted basin. In these basins, the outflow of water exceeds inflow. Specifically, the basin loses water through evaporation, resulting in the precipitation and deposition of salt. While the rate of sedimentation of salt is significantly larger than the rate of sedimentation of clastics, it is recognized that a single evaporation event is rarely enough to produce the vast quantities of salt needed to form a layer thick enough for the formation of salt diapirs, indicating that a sustained period of episodic flooding and evaporation of the basin must occur. ^[1]

Over time, the layer of salt is covered with deposited sediment, becoming buried under an increasingly large overburden. Previously, researchers believed that the compaction of overlying sediment and subsequent decrease in buoyancy led to salt rising and intruding into the overburden due to its ductility, thereby creating a salt diapir. However, after the 1980s, the primary force that drives the flow of salt is considered to be differential loading. ^[2]

Some salt domes can be seen from Earth's surface. They can also be located by finding unique surface structures and surrounding phenomena. For instance, salt domes can contain or be near sulfur springs and natural gas vents.^[4] Some salt domes have salt sheets that extrude from the top of the dome; these are referred to as salt plugs. These plugs can coalesce to form salt canopies, which can then be remobilized by roof sedimentation, with the most prominent example in the northern Gulf of Mexico basin. Another structure that can form from salt domes are salt welds. These occur when the growth of a dome is prevented by an exhausted supply of salt, and the top and bottom contacts merge.^[2]

Salt domes have also been located using

The caprock above the salt domes can contain deposits of native sulfur (recovered by the Frasch process). They can also contain deposits of metals, sodium salts, nitrates, and other substances, which can be used in products such as table salt and chemical de-icers.^[6]

Occurrence

Salt domes occur in many parts of the world where there is a sufficiently thick layer of rock salt developed.

Hormuz Formation

In the Middle East, the upper Neoproterozoic salt of the Hormuz Formation is associated with widespread salt dome formation in most parts of the Persian Gulf and onshore in Iran, Iraq, United Arab Emirates and Oman. The thicker salt is found in a series of basins, the Western Gulf, Southern Gulf and Oman salt basins.^[7]

Paradox Basin

Pennsylvanian age salt of the Paradox Formation forms salt domes throughout the Paradox Basin in the US, which extends from eastern Utah, through southwestern Colorado into northwestern New Mexico.

An example of an emergent salt dome is at Onion Creek, Utah / Fisher Towers near Moab, Utah. A Paradox Formation salt body that has risen as a ridge through several hundred meters of overburden, predominantly sandstone. As the salt body rose, the overburden formed an anticline (arching upward along its center line) which fractured and eroded to expose the salt body.^[8]

Barents Sea

Offshore northern Norway in the southwestern

The Gulf Coast is home to over 500 salt domes formed from Middle Jurassic Louann Salt.^[4] This region is home to most of the US Strategic Petroleum Reserve. Avery Island was formed by a salt dome.^[9]

South Atlantic salt basins

During the break-up of the south Atlantic, Aptian (Lower Cretaceous) age salt was deposited within the area of thinned crust on both the Brazilian and conjugate Angola/Gabon margins forming many salt domes.

Messinian salt

During the Messinian salinity crisis (Late Miocene), thick salt layers were formed as the Mediterranean Sea dried out. Later deposition, once the sea refilled, triggered the formation of salt domes.

See also

• Plasticity (physics)
• Salt glacier
• Underground hydrogen storage
• Gorleben salt dome

References

External links

• Salt Dome Cutaway - Louisiana State Exhibit Museum

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