Geology of North Dakota
Extensive deposition of sedimentary rocks began 515 million years ago, when the Canadian Shield and North Dakota flooded during a marine transgression forming the Sauk Sequence.
A renewed marine transgression began the Tippecanoe Sequence, including Winnipeg Group sandstone and shale, overlain by Red River, Stony Mountain, Stonewall and Interlake Formation carbonates.
Percolating groundwater eroded limestone into caves and hollows typical of a karst topography during a mid-Paleozoic dry period, before a return to a shallow sea in the Ordovician.
The ancestral Rocky Mountains began to rise around this time, bringing the Otter Formation shales and then draining the sea and uplifting the land.
Rivers and streams moving across the eroded Jurassic landscape deposited the sandstone and siltstone Inyan Kara Formation.
Thick layers of shale, such as the Pierre Formation, formed in the Western Interior Seaway during a major global marine transgression in the Cretaceous.
Even as Bullion Creek sediments were being deposited in the center of the state, swamps to the west were filling and covering them over with Sentinel Butte material.
During the Eocene, mammals and grasses diversified in the area as North Dakota transitioned from a warm temperate to subtropical climate.
The Tejas Sequence began to form in the Oligocene, starting off with conglomerate, siltstone, clay, volcanic ash, freshwater limestone and sands of the White River Group.
Evidence of the erosion is found in the Turtle Mountains, which were originally part of a continuous plateau before up to 600 feet of sandstone and shale eroded between the two features prior to glaciation.
The lignite and sandstone of the Fort Union Group in the west is the top groundwater unit and a common source of water for farms and ranches.
Very few wells were drilled in the aquifer before 1900, although one at Elledale in 1886 went down 1087 feet and produced up to 700 gallons a minute with a pressure reaching 176 pounds per square inch.
Between the north of the Little Missouri River and the Burke County line is the Nesson Anticline, one of the largest geologic features in the state.
Limestone to the northeast and east of the anticline in Bottineau, Burke and Renville counties, oil and gas is trapped by anhydrite infilling or shale and siltstone cap rock in the Triassic Spearfish Formation, over an unconformity.
In one unusual case, the oil-bearing Red Wing Structure in McKenzie County contains Mississippian strata uplifted 3000 feet higher than neighboring sediments of the same age due to a meteorite impact.
Western North Dakota is notable for widespread clinker—clay, shale and sandstone baked into a material like natural brick by burning coal.
Peat, concentrated in areas like the Souris River in McHenry County is used in gardens, but not widely produced, and the state has up to 100,000 tons of reserves.
Both sand and gravel are most common in the formerly glaciated parts of the state northeast of the Missouri River where beach deposits formed after the ice sheets melted.
Only a few hundred tons were ever extracted and ended in 1967 due to difficulty milling lignite compared with sandstone deposits in the Colorado Plateau.
