Evaporite

Last updated • 7 min readFrom Wikipedia, The Free Encyclopedia
A cobble encrusted with halite evaporated from the Dead Sea, Israel (with Israeli NS1 coin [diameter 18mm] for scale) HaliteEncrustedCobbleDeadSea.JPG
A cobble encrusted with halite evaporated from the Dead Sea, Israel (with Israeli ₪1 coin [diameter 18mm] for scale)

An evaporite ( /ɪˈvæpəˌrt/ ) is a water-soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. [1] There are two types of evaporite deposits: marine, which can also be described as ocean deposits, and non-marine, which are found in standing bodies of water such as lakes. Evaporites are considered sedimentary rocks and are formed by chemical sediments.

Contents

Formation

Although all water bodies on the surface and in aquifers contain dissolved salts, the water must evaporate into the atmosphere for the minerals to precipitate. For this to happen, the water body must enter a restricted environment where water input into this environment remains below the net rate of evaporation. This is usually an arid environment with a small drainage basin fed by a limited input of water. When evaporation occurs, the remaining water is enriched in salts, and they precipitate when the water becomes supersaturated.

Depositional environments

Marine

Anhydrite Anhydrite HMNH1.jpg
Anhydrite

Marine evaporites tend to have thicker deposits and are usually the focus of more extensive research. [2] When scientists evaporate ocean water in a laboratory, the minerals are deposited in a defined order that was first demonstrated by Usiglio in 1884. [2] The first phase of precipitation begins when about 50% of the original water depth remains. At this point, minor carbonates begin to form. [2] The next phase in the sequence comes when the experiment is left with about 20% of its original level. At this point, the mineral gypsum begins to form, which is then followed by halite at 10%, [2] excluding carbonate minerals that tend not to be evaporites. The most common marine evaporites are calcite, gypsum and anhydrite, halite, sylvite, carnallite, langbeinite, polyhalite, and kainite. Kieserite (MgSO4) may also be included, which often will make up less than four percent of the overall content. [2] However, there are approximately 80 different minerals that have been reported found in evaporite deposits, [3] [4] though only about a dozen are common enough to be considered important rock formers. [2]

Non-marine

Non-marine evaporites are usually composed of minerals that are not common in marine environments because in general the water from which non-marine evaporite precipitates has proportions of chemical elements different from those found in the marine environments. [2] Common minerals that are found in these deposits include blödite, borax, epsomite, gaylussite, glauberite, mirabilite, thenardite and trona. Non-marine deposits may also contain halite, gypsum, and anhydrite, and may in some cases even be dominated by these minerals, although they did not come from ocean deposits. This, however, does not make non-marine deposits any less important; these deposits often help to paint a picture into past Earth climates. Some particular deposits even show important tectonic and climatic changes. These deposits also may contain important minerals that help in today's economy. [5] Thick non-marine deposits that accumulate tend to form where evaporation rates will exceed the inflow rate, and where there is sufficient soluble supplies. The inflow also has to occur in a closed basin, or one with restricted outflow, so that the sediment has time to pool and form in a lake or other standing body of water. [5] Primary examples of this are called "saline lake deposits". [5] Saline lakes includes things such as perennial lakes, which are lakes that are there year-round, playa lakes, which are lakes that appear only during certain seasons, or any other terms that are used to define places that hold standing bodies of water intermittently or year-round. Examples of modern non-marine depositional environments include the Great Salt Lake in Utah and the Dead Sea, which lies between Jordan and Israel.

Evaporite depositional environments that meet the above conditions include:

The most significant known evaporite depositions happened during the Messinian salinity crisis in the basin of the Mediterranean.

Evaporitic formations

Hopper crystal cast of halite in a Jurassic rock, Carmel Formation, southwestern Utah SaltCrystalCasts.JPG
Hopper crystal cast of halite in a Jurassic rock, Carmel Formation, southwestern Utah

Evaporite formations need not be composed entirely of halite salt. In fact, most evaporite formations do not contain more than a few percent of evaporite minerals, the remainder being composed of the more typical detrital clastic rocks and carbonates. Examples of evaporite formations include occurrences of evaporite sulfur in Eastern Europe and West Asia. [6]

For a formation to be recognised as evaporitic it may simply require recognition of halite pseudomorphs, sequences composed of some proportion of evaporite minerals, and recognition of mud crack textures or other textures.

Economic importance

Evaporites are important economically because of their mineralogy, their physical properties in-situ, and their behaviour within the subsurface.

Evaporite minerals, especially nitrate minerals, are economically important in Peru and Chile. Nitrate minerals are often mined for use in the production on fertilizer and explosives.

Thick halite deposits are expected to become an important location for the disposal of nuclear waste because of their geologic stability, predictable engineering and physical behaviour, and imperviousness to groundwater.

Halite formations are famous for their ability to form diapirs, which produce ideal locations for trapping petroleum deposits.

Halite deposits are often mined for use as salt.

Major groups of evaporite minerals

Calcite Calcite-k270c.jpg
Calcite

This is a chart that shows minerals that form the marine evaporite rocks. They are usually the most common minerals that appear in this kind of deposit.

Mineral ClassMineral nameChemical Composition
ChloridesHaliteNaCl
SylviteKCl
CarnalliteKMgCl3· 6 H2O
KainiteKMg(SO4)Cl · 3 H2O
SulfatesAnhydriteCaSO4
GypsumCaSO4· 2 H2O
KieseriteMgSO4· H2O
LangbeiniteK2Mg2(SO4)3
PolyhaliteK2Ca2Mg(SO4)6· H2O
CarbonatesDolomiteCaMg(CO3)2
CalciteCaCO3
MagnesiteMgCO3
Hanksite,
Na22K(SO4)9(CO3)2Cl, one of the few minerals that is both a carbonate and a sulfate Hanksite.JPG
Hanksite, Na22K(SO4)9(CO3)2Cl, one of the few minerals that is both a carbonate and a sulfate

Evaporite minerals start to precipitate when their concentration in water reaches such a level that they can no longer exist as solutes.

The minerals precipitate out of solution in the reverse order of their solubilities, such that the order of precipitation from sea water is:

  1. Calcite (CaCO3) and dolomite (CaMg(CO3)2)
  2. Gypsum (CaSO4· 2 H2O ) and anhydrite (CaSO4).
  3. Halite (i.e. common salt, NaCl)
  4. Potassium and magnesium salts

The abundance of rocks formed by seawater precipitation is in the same order as the precipitation given above. Thus, limestone (dolomite are more common than gypsum, which is more common than halite, which is more common than potassium and magnesium salts.

Evaporites can also be easily recrystallized in laboratories in order to investigate the conditions and characteristics of their formation.

Possible evaporites on Titan

Recent evidence from satellite observations [7] and laboratory experiments [8] suggest evaporites are likely present on the surface of Titan, Saturn's largest moon. Instead of water oceans, Titan hosts lakes and seas of liquid hydrocarbons (mainly methane) with many soluble hydrocarbons, such as acetylene, [9] that can evaporate out of solution. Evaporite deposits cover large regions of Titan's surface, mainly along the coastlines of lakes or in isolated basins (Lacunae) that are equivalent to salt pans on Earth. [10]

See also

Related Research Articles

<span class="mw-page-title-main">Sedimentary rock</span> Rock formed by the deposition and cementation of particles

Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles to settle in place. The particles that form a sedimentary rock are called sediment, and may be composed of geological detritus (minerals) or biological detritus. The geological detritus originated from weathering and erosion of existing rocks, or from the solidification of molten lava blobs erupted by volcanoes. The geological detritus is transported to the place of deposition by water, wind, ice or mass movement, which are called agents of denudation. Biological detritus was formed by bodies and parts of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on the floor of water bodies. Sedimentation may also occur as dissolved minerals precipitate from water solution.

<span class="mw-page-title-main">Halite</span> Mineral form of sodium chloride

Halite, commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride (NaCl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, pink, red, orange, yellow or gray depending on inclusion of other materials, impurities, and structural or isotopic abnormalities in the crystals. It commonly occurs with other evaporite deposit minerals such as several of the sulfates, halides, and borates. The name halite is derived from the Ancient Greek word for "salt", ἅλς (háls).

<span class="mw-page-title-main">Salt pan (geology)</span> Flat expanse of ground covered with salt and other minerals

Natural salt pans or salt flats are flat expanses of ground covered with salt and other minerals, usually shining white under the sun. They are found in deserts and are natural formations.

<span class="mw-page-title-main">Anhydrite</span> Mineral, anhydrous calcium sulfate

Anhydrite, or anhydrous calcium sulfate, is a mineral with the chemical formula CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium (baryte) and strontium (celestine) sulfates, as might be expected from the chemical formulas. Distinctly developed crystals are somewhat rare, the mineral usually presenting the form of cleavage masses. The Mohs hardness is 3.5, and the specific gravity is 2.9. The color is white, sometimes greyish, bluish, or purple. On the best developed of the three cleavages, the lustre is pearly; on other surfaces it is glassy. When exposed to water, anhydrite readily transforms to the more commonly occurring gypsum, (CaSO4·2H2O) by the absorption of water. This transformation is reversible, with gypsum or calcium sulfate hemihydrate forming anhydrite by heating to around 200 °C (400 °F) under normal atmospheric conditions. Anhydrite is commonly associated with calcite, halite, and sulfides such as galena, chalcopyrite, molybdenite, and pyrite in vein deposits.

<span class="mw-page-title-main">Carnallite</span> Evaporite mineral

Carnallite (also carnalite) is an evaporite mineral, a hydrated potassium magnesium chloride with formula KCl.MgCl2·6(H2O). It is variably colored yellow to white, reddish, and sometimes colorless or blue. It is usually massive to fibrous with rare pseudohexagonal orthorhombic crystals. The mineral is deliquescent (absorbs moisture from the surrounding air) and specimens must be stored in an airtight container.

<span class="mw-page-title-main">Glauberite</span>

Glauberite is a monoclinic sodium calcium sulfate mineral with the formula Na2Ca(SO4)2.

<span class="mw-page-title-main">Bristol Lake</span> Lake in United States of America

Bristol Lake is a dry lake in the Mojave Desert of San Bernardino County, California, 42 km (26 mi) northeast of Twentynine Palms.

<span class="mw-page-title-main">Sabkha</span> Salt lake above the tide line, where evaporite deposits accumulate

A sabkha is a coastal, supratidal mudflat or sandflat in which evaporite-saline minerals accumulate as the result of semiarid to arid climate. Sabkhas are gradational between land and intertidal zone within restricted coastal plains just above normal high-tide level. Within a sabkha, evaporite-saline minerals sediments typically accumulate below the surface of mudflats or sandflats. Evaporite-saline minerals, tidal-flood, and aeolian deposits characterize many sabkhas found along modern coastlines. The accepted type locality for a sabkha is at the southern coast of the Persian Gulf, in the United Arab Emirates. Evidence of clastic sabkhas are found in the geological record of many areas, including the UK and Ireland. Sabkha is a phonetic transliteration of the Arabic word used to describe any form of salt flat. A sabkha is also known as a sabkhah,sebkha, or coastal sabkha.

<span class="mw-page-title-main">Depositional environment</span> Processes associated with the deposition of a particular type of sediment

In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be formed after lithification, if the sediment is preserved in the rock record. In most cases, the environments associated with particular rock types or associations of rock types can be matched to existing analogues. However, the further back in geological time sediments were deposited, the more likely that direct modern analogues are not available.

Salt Flat is a ghost town in northeastern Hudspeth County, Texas, United States. It lies along the concurrent U.S. Routes 62 and 180, north of the Census-designated place (CDP) of Sierra Blanca, the county seat of Hudspeth County. Its elevation is 3,730 feet (1,137 m). Although Salt Flat is unincorporated, it has a ZIP Code of 79847. The headquarters of the nearby Guadalupe Mountains National Park uses this ZIP Code, although it is located closer to Pine Springs, which has no post office.

The Muskeg Formation is a geologic formation of Middle Devonian (Givetian) age in the Western Canada Sedimentary Basin. It extends from the plains of northwestern Alberta to northeastern British Columbia, and includes important petroleum and natural gas reservoirs in the Zama lake and Rainbow Lake areas of northwestern Alberta.

<span class="mw-page-title-main">Elk Point Group</span> Stratigraphic unit in the Western Canada and Williston sedimentary basins

The Elk Point Group is a stratigraphic unit of Early to Middle Devonian age in the Western Canada and Williston sedimentary basins. It underlies a large area that extends from the southern boundary of the Northwest Territories in Canada to North Dakota in the United States. It has been subdivided into numerous formations, number of which host major petroleum and natural gas reservoirs.

<span class="mw-page-title-main">Paradox Formation</span>

In geology, the Paradox Formation Is a Pennsylvanian age formation which consists of abundant evaporites with lesser interbedded shale, sandstone, and limestone. The evaporites are largely composed of gypsum, anhydrite, and halite. The formation is found mostly in the subsurface, but there are scattered exposures in anticlines in eastern Utah and western Colorado. These surface exposures occur in the Black Mesa, San Juan and Paradox Basins and the formation is found in the subsurface in southwestern Colorado, southeastern Utah, northeastern Arizona and northeastern New Mexico.

<span class="mw-page-title-main">Shallow water marine environment</span>

Shallow water marine environment refers to the area between the shore and deeper water, such as a reef wall or a shelf break. This environment is characterized by oceanic, geological and biological conditions, as described below. The water in this environment is shallow and clear, allowing the formation of different sedimentary structures, carbonate rocks, coral reefs, and allowing certain organisms to survive and become fossils.

<span class="mw-page-title-main">Prairie Evaporite Formation</span> Geologic formation of Givetian age

The Prairie Evaporite Formation, also known as the Prairie Formation, is a geologic formation of Middle Devonian (Givetian) age that consists primarily of halite and other evaporite minerals. It is present beneath the plains of northern and eastern Alberta, southern Saskatchewan and southwestern Manitoba in Canada, and it extends into northwestern North Dakota and northeastern Montana in the United States.

<span class="mw-page-title-main">Geology of Senegal</span>

The geology of Senegal formed beginning more than two billion years ago. The Archean greenschist Birimian rocks common throughout West Africa are the oldest in the country, intruded by Proterozoic granites. Basins formed in the interior during the Paleozoic and filled with sedimentary rocks, including tillite from a glaciation. With the rifting apart of the supercontinent Pangaea in the Mesozoic, the large Senegal Basin filled with thick sequences of marine and terrestrial sediments. Sea levels declined in the Eocene forming large phosphate deposits. Senegal is blanketed in thick layers of terrestrial sediments formed in the Quaternary. The country has extensive natural resources, including gold, diamonds, and iron.

<span class="mw-page-title-main">Ephemeral acid saline lake</span>

An ephemeral acid saline lake is a lake that is relatively high in dissolved salts and has a low pH, usually within the range of <1 - 5 and does not have standing water year round. These types of lakes are identified by high concentrations of evaporite minerals, notably halite, gypsum, and various iron oxides allowing the lakes to become hypersaline. Low pH and evaporite minerals are positively correlated, allowing lakes with lower pH's to have visible evaporite mineral "crusts". Due to the highly unusual geochemistries present in these lake systems, they are considered extreme environments in nature.

<span class="mw-page-title-main">La Saline Natural Area</span> Nature preserve in Canada

La Saline Natural Area in the boreal forest of northeastern Alberta, Canada, preserves Saline Lake, a saline oxbow lake adjacent to the Athabasca River north of Fort McMurray. The lake is an important stop for waterfowl and other birds that migrate along the Athabasca River. Large deposits of tufa have accumulated around the salt springs on the lake's southeastern shore.

<span class="mw-page-title-main">Teepee structure</span> Sedimentary structures

Teepee structures are sedimentary structures interpreted to represent formation in peritidal environments. Teepees are largely the result of evaporation of water and subsequent precipitation of minerals within sediment, resulting in expansion and buckling to form a teepee-like shape. Their name originates from geologists working in the Guadalupe Mountains, who noted their appearance in cross-section resembles that of a Native American teepee.

Douglas James Shearman was a British geologist and sedimentologist, who made significant contributions to the study of evaporites and other sediments and sedimentary rocks in desert climates. His research on evaporites is important for understanding the entrapment and migration of petroleum.

References

  1. Jackson, Julia A. (1997). Glossary of Geology (4th ed.). Alexandria, Virginia: American Geological Institute.
  2. 1 2 3 4 5 6 7 Boggs, Sam (2006). Principles of sedimentology and stratigraphy (4th ed.). Upper Saddle River, N.J.: Pearson Prentice Hall. ISBN   0131547283.
  3. Stewart, F.H. (1963). "Marine evaporites". U.S. Geological Society Professional Paper. 440-Y. doi: 10.3133/pp440Y .
  4. Warren, John (1999). Evaporites : their evolution and economics. Oxford: Blackwell Science. ISBN   978-0632053018.
  5. 1 2 3 Melvin, John L., ed. (1991). Evaporites, petroleum and mineral resources. Amsterdam: Elsevier. ISBN   978-0444555762.
  6. C.Michael Hogan. 2011. Sulfur. Encyclopedia of Earth, eds. A.Jorgensen and C.J.Cleveland, National Council for Science and the environment, Washington DC Archived October 28, 2012, at the Wayback Machine
  7. Barnes, Jason W.; Bow, Jacob; Schwartz, Jacob; Brown, Robert H.; Soderblom, Jason M.; Hayes, Alexander G.; Vixie, Graham; Le Mouélic, Stéphane; Rodriguez, Sebastien; Sotin, Christophe; Jaumann, Ralf (2011-11-01). "Organic sedimentary deposits in Titan's dry lakebeds: Probable evaporite". Icarus. 216 (1): 136–140. Bibcode:2011Icar..216..136B. doi:10.1016/j.icarus.2011.08.022. ISSN   0019-1035.
  8. Czaplinski, Ellen C.; Gilbertson, Woodrow A.; Farnsworth, Kendra K.; Chevrier, Vincent F. (2019-10-17). "Experimental Study of Ethylene Evaporites under Titan Conditions". ACS Earth and Space Chemistry. 3 (10): 2353–2362. arXiv: 2002.04978 . Bibcode:2019ESC.....3.2353C. doi:10.1021/acsearthspacechem.9b00204. S2CID   202875048.
  9. Singh, S.; Combe, J. -Ph.; Cordier, D.; Wagner, A.; Chevrier, V. F.; McMahon, Z. (2017-07-01). "Experimental determination of acetylene and ethylene solubility in liquid methane and ethane: Implications to Titan's surface". Geochimica et Cosmochimica Acta. 208: 86–101. Bibcode:2017GeCoA.208...86S. doi:10.1016/j.gca.2017.03.007. ISSN   0016-7037.
  10. MacKenzie, S. M.; Barnes, Jason W. (2016-04-05). "Compositional Similarities and Distinctions Between Titan's Evaporitic Terrains". The Astrophysical Journal. 821 (1): 17. arXiv: 1601.03364 . Bibcode:2016ApJ...821...17M. doi: 10.3847/0004-637x/821/1/17 . ISSN   1538-4357.

Other reading