How do evaporites occur

Skip to main content Skip to table of contents. This service is more advanced with JavaScript available. Beaches and Coastal Geology Edition. Contents Search. Authors Authors and affiliations Alan B. Reference work entry First Online: 08 July How to cite. Marine evaporites precipitate in a succession of mineral species whose broad outlines were first made known by Usiglio summarized by Stewart, The Usiglio succession is shown in figure 1.

The complex of potash-rich salts that forms as seawater approaches dryness is of great economic importance and has been intensively studies. Yet the details of the formation of these bittern salts are still incompletely known see Borchert and Muir, , for discussion.

Open image in new window. This is a preview of subscription content, log in to check access. Adams, J. In Reading, H. Oxford: Blackwell, pp. Krijgsman, W. Chronology, causes and progression of the Messinian salinity crisis. Nature , , — Lowenstein, T. Paleoclimate record from death valley salt core.

Geology , 27 , 3—6. Oscillations in Phanerozoic seawater chemistry: evidence from fluid inclusions. Science , , — Murray, R. Origin and diagenesis of gypsum and anhydrite. Nijman, W. Precambrian Res. Schreiber, B. Subaqueous evaporite deposition. Evaporites and Hydrocarbons. New York: Columbia University Press, pp. This evaporation may occur in either shallow basins on land or in the sea. Material salts is eroded from land surfaces and is then carried to the sea by rivers. When seawater evaporates, the salts precipitate and settle to the bottom.

Arid lagoons In hot, dry climates the loss of water by evaporation from the surface of a lagoon is high. If it is not balanced by influx of fresh water from the land or exchange of water with the ocean the salinity of the lagoon will rise and it will become hypersaline, more concentrated in salts than normal seawater. An area of hypersaline shallow water that precipitates evaporite minerals is known as a saltern.

In the restricted circulation of a lagoon conditions are right for large crystals of selenitic gypsum to form by growing upwards from the lagoon bed. Coorong saline lagoons, Australia. Arid sabkha flats Arid shorelines are found today in places such as the Arabian Gulf, where they are sites of evaporate formation within the coastal sediments.

These arid coasts are called sabkhas; they typically have a very low relief and there is not always a well-defined beach. The coastal plain of a sabkha is occasionally wetted by seawater during very high tides or during onshore storm winds, but more important is also a supply of water through groundwater seepage from the sea.

Gypsum and anhydrite grow within the sediment while a crust of halite forms at the surface. In general, anhydrite forms in the hotter, drier sabkhas and gypsum where the temperatures are lower or where there is a supply of fresh, continental water to the sabkha.

The gypsum and anhydrite grow by displacement within the sediment, with the gypsum in clusters and the anhydrite forming amorphous coalesced nodules with little original sediment in between. These layers of anhydrite with remnants of other sediment have a characteristic chicken-wire structure. Halite crusts are rarely preserved because they are removed by any surface water flows.

Nodular anhydrite. Dukan sabkha chicken-wire structure in anhydrite Nonmarine Evaporites Evaporite deposition in the nonmarine environment occurs in closed lake, those without outlet, in arid and semiarid regions.

Such lakes form in closed interior basins or shallow depressions on land where drainage is internal and runoff does not reach the sea.