Prairie Evaporite Formation
| Prairie Evaporite Formation Stratigraphic range: Middle Devonian (Givetian) |
|
|---|---|
| Type | Geological formation |
| Unit of | Elk Point Group |
| Sub-units | Up to 6 members |
| Underlies | Watt Mountain Formation and Dawson Bay Formation |
| Overlies | Keg River Formation and Winnipegosis Formation |
| Thickness | Up to 300 metres (980 ft) |
| Lithology | |
| Primary | Halite, anhydrite |
| Other | Dolostone, mudstone |
| Location | |
| Region |
 Alberta  Saskatchewan Manitoba  North Dakota Montana
|
| Country |
 Canada  United States
|
| Type section | |
| Named by | A.D. Baillie (1953) |
The Prairie Evaporite Formation, also known as the Prairie Formation, is a geologic formation of Middle Devonian (Givetian) age that consists primarily of halite (rock salt) 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.
The formation is a major source of potash, most of which is used for fertilizer production.Salt is also produced from the formation, and solution caverns are created in its thick salt beds for natural gas storage.
The Prairie Evaporite Formation consists thick beds of halite, with interbeds of anhydrite, dolostone, dolomitic mudstone and claystone. In southern Saskatchewan and northern North Dakota it includes major deposits of sylvite and carnallite that are mined for their potassium content.Gypsum is present in areas where anhydrite has been altered by reaction with groundwater.
The Prairie Evaporite Formation was deposited in an embayment called the Elk Point Basin. It extended from an open ocean in the present-day Northwest Territories in Canada to northern North Dakota in the United States, covering an area roughly 30% to 40% as large as that covered by today's Mediterranean Sea. An extensive reef complex called the Presqu'ile Barrier developed across the mouth of the embayment, blocking it from the open ocean and restricting the inflow of sea water. Low water levels and excessive evaporation resulted in the deposition of halite and other evaporite minerals in sabkha, supratidal flat and coastal lagoon environments, ultimately leading to the accumulation of potash minerals in the southern part of the area. These events can be compared to the drying of the Mediterranean Sea that occurred during late Miocene time. That event, called the Messinian salinity crisis, resulted in the deposition of sequences of evaporite minerals up to 1,600 metres (5,250 ft) thick.
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