TheWilliston Basin is a largeintracratonicsedimentary basin in easternMontana, westernNorth Dakota,South Dakota, southernSaskatchewan, and south-westernManitoba that is known for its rich deposits ofpetroleum andpotash. The basin is a geologicstructural basin but not atopographic depression; it is transected by theMissouri River. The oval-shaped depression extends approximately 475 miles (764 km) north-south and 300 miles (480 km) east-west.
The Williston Basin lies above an ancientPrecambriangeologic basement feature, theTrans-Hudson Orogenic Belt that developed in this area about 1.8-1.9 billion years ago, and that created a weak zone that later led to sagging to produce the basin.[1] The Precambrian basement rocks in the center of the basin beneath the city ofWilliston, North Dakota lie about 16,000 feet (4,900 m) below the surface.
Deposition of sediments began in the Williston area duringCambrian time, but subsidence and basin filling were most intense during theOrdovician,Silurian, andDevonian Periods, when thick accumulations of limestone and dolomite, with lesser thicknesses of sandstones, siltstones, shales, andevaporites were laid down. Subsidence continued on a reduced scale into theMississippian and was largely ended byPennsylvanian time. Regional subsidence returned during theMesozoic Era, although total sediment thicknesses were much less than during thePaleozoic. Near the end of theCretaceous, tectonic activity during theLaramide Orogeny rejuvenated several basement structures in the Williston Basin to produce anticlines that serve as oil traps today.[2]
The long history of sedimentary deposition in the Williston Basin included deposition of rocks well suited to serve as hydrocarbonsource andreservoir rocks. The basin's oil and gas fields are found in a wide range of geologic ages, as indicated by the generalized stratigraphic column.[4]
In 1913, shallow gas was discovered in anUpper Cretaceoussandstone on the Cedar CreekAnticline, and oil was discovered on the same anticline in 1936.[5] The basin did not become a major oil province until the 1950s when large fields were discovered in North Dakota.Amerada Corporation began the search in 1946. After four years of testing and mapping they started drilling at a promising lease 30 miles north-east ofWilliston, North Dakota, and on April 4, 1951, discovered oil on the Nesson Anticline, with the Amerada Hess Corporation Clarence Iverson #1 well.[6] Otheroil firms rushed in to buy up leases on farm land to explore for oil and by 1954 80% of the possible oil producing areas were under lease. Royal Dutch Shell at that time had leases on over 8 million acres. Many local farmers and area speculators became instant millionaires, leasing land at an average of $25 an acre and then selling those leases back at a much higher cost per acre.[7]
Production peaked in 1986, and tehn decreased. In the early 2000s significant increases in production began because ofhorizontal drilling techniques (fracking), especially in theBakken Formation.[8]
Cumulative basin production totals about 3.8 billion barrels (600,000,000 m3) of oil[9] and 470 billion cubic feet (1.3×1010 m3) of natural gas.[10] The largest oil fields are listed in the following table, showing estimated ultimate recoveries.[4]
| Field Name | Discovery Year | Est. ult. oil (million barrels) | Est. ult. gas (billion cubic feet) | Est. ult. nat. gas liquids (million barrels) |
|---|---|---|---|---|
| Elm Coulee, Richland Co., MT[11] | 2000 | 270 | ||
| Beaver Lodge, N. Dak. | 1951 | 130 | 115 | 47 |
| Pine, Mont. | 1952 | 127 | 20 | |
| Pennel, Mont. | 1955 | 115 | ||
| Cabin Creek, Mont. | 1953 | 115 | ||
| Little Knife, N. Dak. | 1977 | 96 | 120 | 15 |
| Tioga, N. Dak. | 1952 | 77 | 43 | 17 |
| Blue Buttes, N. Dak. | 1955 | 53 | 36 | 5 |
| Charlson, N. Dak. | 1952 | 52 | 100 | 11 |
Potash produced from the Williston Basin makes Canada the world's leading producer of that commodity.[12] The deposits occur in theMiddle DevonianPrairie Formation.[13] Major potash-producing companies includeNutrien and Mosaic.
The Williston Basin holds large coal deposits, primarily in theFort Union Formation of mostlyPaleogene age, and were first noted during theLewis and Clark Expedition. Mining of the coal began in 1873 nearSims, North Dakota, but was soon abandoned. TheNorthern Pacific Railway took over the mine and developed thelignite beds as the Northern Pacific Coal Company. Other mines followed nearMinot, North Dakota andDickinson, North Dakota, and the period from 1900 to 1920 saw a large-scale increase in the lignite industry.Strip-mining was common from 1920 until 1940, and 320 mines were in operation by 1940. However, production peaked in 1951, and by 1965, only 38 mines were in operation, while by 1999, only 4.[14]
In 1952,helium concentrations were discovered in southwestern Saskatchewan. Production from four wells took place from 1963 to 1977, and resumed again in 2014. The Deadwood Formation, and other LowerPaleozoic formations, had the highest concentration. The helium originated through naturalradioactive decay ofuranium andthorium inPrecambriangraniticbasement rocks, or Lower Paleozoicshales.[15][16]
TheUpper CambrianDeadwood Formation wastransgressively deposited on the low-reliefPrecambrian surface. The Deadwood is characterized byshallow marine andcoastal plain sediments, with abundantglauconite giving the formation a distinctive green color. The basin startedsubsiding due tostrike-slip movement along northeast–southwest trendingfaults, resulting in the deposition of the Winnipeg Group, which liesunconformably on the Deadwood. The Winnipeg consists of shallow marine sandstone, shale and shalycarbonate. TheRed River Formation lies unconformably on the Winnipeg, and consists of shallow marine carbonate,anhydrite, andsaltsedimentation. Conformably overlying the Red River is theOrdovicianStony Mountain Formation andStonewall Formation, followed by theSilurianInterlake Group. During theDevonian, the Williston Basin became the southeastern corner of the Elk Point Basin when theElk Point Group,Manitoba Group, andSaskatchewan Group were deposited. TheBakken Formation, anorganic-rich marine shale, was deposited in the Late Devonian. TheLodgepole Limestone was deposited during theMississippian, followed by theMadison Group and theBig Snowy Group. The Tyler Formation was deposited in thePennsylvanian, and consists ofinterbedded sandstone,siltstone, shale, andlimestone. The overlyingMinnelusa Formation is characterized by deposition inalluvial plains,progradingriver delta, andbarrier island environments. TheMinnekahta Formation was deposited during thePermian, followed by theSpearfish Formation and the Nesson Formation. ThePierre Shale was deposited curing theCretaceous, followed by theHell Creek Formation, and theTertiaryFort Union Formation.[17]
Several confirmedimpact craters are located in Williston Basin such asViewfield,Red Wing Creek, andEagle Butte while the Dumas and Hartney craters are still unconfirmed.
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