Salt dome

Salt dome

A salt dome is a type of structural dome formed when a thick bed of evaporite minerals (mainly salt, or halite) found at depth intrudes vertically into surrounding rock strata, forming a diapir.

The salt that forms these domes was deposited within restricted marine basins. Due to restricted flow of water into a basin, evaporation occurs resulting in the precipitation of salts from solution, depositing evaporites. It is recognised that a single evaporation event is rarely enough to produce the vast quantities of salt found in evaporite deposits indicating that a sustained period of episodic flooding and evaporation of the basin must occur, as can be seen from the example of the Mediterranean Messinian salinity crisis. At the present day, evaporite deposits can be seen accumulating in basins that merely have restricted access but do not completely dry out; they provide an analogue to some deposits recognised in the Geological record, such as the Garabogazköl basin in Turkmenistan.

Over time, the salt is covered with sediment and becomes buried. Since the density of salt is generally less than that of surrounding material, it has a tendency to move upward toward the surface, forming large bulbous domes, diapirs , sheets, pillars and other structures as it rises. If the rising salt diapir breaches the surface, it can become a flowing salt glacier. In cross section, these large domes may be anywhere from 1 to 10 kilometers across and extend as far down as 6.5 kilometers.

One example of an island formed by a salt dome is Avery Island in Louisiana. At present ocean levels it is no longer surrounded by the sea but it is surrounded by bayous on all sides.

Another example of an emergent salt dome is at Onion Creek / Fisher Towers near Moab, UT, U.S. These two images show a Cretaceous age salt body that has risen as a ridge through several hundred meters of overburden, predominately sandstone. As the salt body rose, the overburden formed an anticline (arching upward along its centerline) which fractured and eroded to expose the salt body.

The term "salt dome" is also sometimes inaccurately used to refer to dome-shaped silos used to store rock salt for melting snow on highways. These domes are actually called monolithic domes and are used to store a variety of bulk goods.

Commercial uses

The rock salt that is found in salt domes is mostly impermeable. As the salt moves up towards the surface, it can penetrate and/or bend strata of existing rock with it. As these strata are penetrated, they are generally bent slightly upwards at the point of contact with the dome, and can form pockets where petroleum and natural gas can collect between impermeable strata of rock and the salt. The strata immediately above the dome that are not penetrated are pushed upward, creating a dome-like reservoir above the salt where petroleum can also gather. These oil pools can eventually be extracted, and indeed form a major source of the petroleum produced along the coast of the Gulf of Mexico.

Other uses include storing oil, gas, or even hazardous waste in large caverns formed after salt mining, as well as excavating the domes themselves for uses in everything from table salt to the granular material used to prevent roadways from icing over.

See also

* Salt tectonics
* Strategic Petroleum Reserve

External links

* [ Salt dome] at Schlumberger's Oilfield Glossary
* [ Hattiesburg Mississippi Salt Domes] interactive map of domes use to store LPG and other gas

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Look at other dictionaries:

  • salt dome — salt′ dome n. gel a domal geologic structure formed by upward movement of a salt mass: associated with pools of oil and gas • Etymology: 1905–10 …   From formal English to slang

  • salt dome — ☆ salt dome n. a domelike structure produced in stratified rocks by the intrusion of a mass of salt in a plastic state and frequently containing oil, gas, etc …   English World dictionary

  • salt dome — Geol. a domelike rock structure that is formed beneath the earth s surface by the upward movement of a mass of salt, may reach thousands of feet in vertical extent, and is more or less circular in plan: often associated with oil and gas pools. Cf …   Universalium

  • salt dome — noun : a domical anticline in sedimentary rocks having a mass of rock salt as its core and being forced up in plastic form by earth stresses from an underlying bed of salt * * * Geol. a domelike rock structure that is formed beneath the earth s… …   Useful english dictionary

  • salt dome —    A dome like intrusion of a mobile salt core into sedimentary rock [16] …   Lexicon of Cave and Karst Terminology

  • salt dome — noun a dome shaped structure in sedimentary rocks, formed where a large mass of salt has been forced upwards …   English new terms dictionary

  • salt dome — /ˈsɒlt doʊm/ (say solt dohm) noun (in sedimentary rocks) a domelike anticline having a core of rock salt which was forced upwards from an underlying bed of salt when in the plastic state under pressure. Also, salt plug …   Australian English dictionary

  • salt dome — noun Date: 1908 a domical anticline in sedimentary rock that has a mass of rock salt as its core …   New Collegiate Dictionary

  • salt dome — noun An upwelling of crystalline rock salt and its aureole of deformed sediments …   Wiktionary

  • Salt dome —   A domical arch (anticline) of sedimentary rock beneath the earth s surface in which the layers bend downward in opposite directions from the crest and that has a mass of rock salt as its core.   U.S. Dept. of Energy, Energy Information… …   Energy terms

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