Geology of South Dakota
The geology of South Dakota began to form more than 2.5 billion years ago in the Archean eon of the Precambrian. Igneous crystalline basement rock continued to emplace through the Proterozoic, interspersed with sediments and volcanic materials. Large limestone and shale deposits formed during the Paleozoic, during prevalent shallow marine conditions, followed by red beds during terrestrial conditions in the Triassic. The Western Interior Seaway flooded the region, creating vast shale, chalk and coal beds in the Cretaceous as the Laramide orogeny began to form the Rocky Mountains. The Black Hills were uplifted in the early Cenozoic, followed by long-running periods of erosion, sediment deposition and volcanic ash fall, forming the Badlands and storing marine and mammal fossils. Much of the state's landscape was reworked during several phases of glaciation in the Pleistocene.[1] South Dakota has extensive mineral resources in the Black Hills and some oil and gas extraction in the Williston Basin. The Homestake Mine, active until 2002, was a major gold mine that reached up to 8000 feet underground and is now used for dark matter and neutrino research.
Stratigraphy, tectonics and geologic history
The oldest rocks in South Dakota date to the
Paleozoic (541–251 million years ago)
In the
The Deadwood Formation is beach sand and gravel at its base, but as the ancient shoreline moved eastward, thin layers of mudstone and limestone formed in the west, in deeper waters. The formation contains trilobite fossils and tracks left by worms, exposed at low tide. Intraformational conglomerate is also common, resulting from fragments of limestone broken up in waves The
Sea levels receded in the Permian, marked by erosion in the east and continued marine deposition in the west.[2]
Mesozoic (251–66 million years)
Red beds formed throughout the west, during the Triassic, at the start of the Mesozoic. The region returned to terrestrial conditions in the Jurassic, with extensive erosion, and then returned to a shallow marine environment in the Cretaceous, depositing thick sequences of black Pierre shale—the thickest and most widespread sedimentary unit in the state. Originally, the shale ranged between 2500 feet thick at the Wyoming line and only tens of feet thick in the east, although erosion stripped it away in the Black Hills. The Laramide orogeny began the uplift of the Rocky Mountains during the Cretaceous.
West of the Missouri River, the Niobrara chalk formed in the inland sea during the Cretaceous, which contains mosasaur and plesiosaur bones. Tepee buttes form as small, conical hills in the Pierre shale landscape, from lenses of more erosion resistant limestone. Beach sand coal sequences left behind as the up to 200 feet thick Fox Hills Formation after the Western Interior Seaway began to recede, 15 million years after the Pierre shale first started to form. Low permeability shale yielded a poorly drained landscape, cut streams and rivers, which brought in large amounts of sediment—clay, silt and sand up to 500 feet thick—which deposited as the Hell Creek Formation. The formation contains thin lignite beds, triceratops and tyrannosaurus bones.
Like many other locations around the world, South Dakota preserves the inch thick boundary clay, left by the asteroid impact of the
Cenozoic (66 million years ago-present)
Following the retreat of the Cretaceous inland sea, the
In the northwest, the Ludlow, Cannonball and Tongue River formations are categorized as the Fort Union Group, with thick sandstone layers sourced from the Rocky Mountains.
Throughout the Eocene, the Black Hills eroded, shedding debris into the east, during a period with sub-tropical temperatures. Iron pyrite in shales oxidized, becoming bright red and yellow iron oxides. Sediments did not accumulate in the region until the end of the Eocene, as large streams carried material away to the ocean. Volcanic rocks from the Eocene preserve petrified trees.
The Oligocene brought a shift in the climate to arid conditions, transforming the region into a vast alluvial desert plain. Up to 600 feet of sands and clays, buried the Black Hills within 2000 feet of their crests in western South Dakota, forming the White River Formation, while some erosion occurred in the east. Gravel deposits containing crocodile bones and land snails, tortoises and hackberry seeds are also common in the fossil record. Bird bones and even fossil duck eggs have been found in association with clams, snails and the remains of algal mats in temporary ponds.
Since the 1800s, geologists have debated how to subdivide the White River Formation. The
Smaller volumes of light-colored sand and clay deposited in the Miocene, but the period came with a return to warm and wet conditions. Revitalized streams carried away large amounts of sediments, wiping out much of the White River Formation. Hundreds of feet of younger sediment cover the White River group in southwest South Dakota. Miocene sandstones, which often form cliffs, often overlay the White River Formation.
A period of erosion occurred in South Dakota during the
Natural resource geology
The Black Hills were extensively explored and periodically mined for silver, gold, mica, tungsten, feldspar, bentonite, beryl, lead, zinc, uranium, lithium and sand, as well as oil, beginning in the 1870s.[8] The Homestake Mining Company, which managed the Homestake Mine until its closure in 2002, merged the Deadwood, Golden Terra, Father DeSmet and Caledonia gold mines around 1900. Its employees used emerging pneumatic drill technology and cyanide processing, creating the Ross Shaft and Yates Shaft—both 5000 feet deep—by 1941. Mine activity was suspended during World War II and resumed. By the mine's centennial in 1976, it was 8000 feet deep and had produced 31 million ounces of gold, seven million ounces of silver and 115 million tons of milled ore.
After its closure, the location was deemed a Superfund site, although the shafts are now reused for the Sanford Underground Research Facility, the largest underground laboratory in the US, used for dark matter and neutrino research. Southwest of Lead, South Dakota, there is still an active open pit gold mine, run by Goldcorp.[9]
South Dakota has oil and gas production in the Williston Basin in the northwest, although it produces only one percent of the US total, primarily from traditional vertical wells. One hundred wells produce 1.6 million gallons of oil annually. Almost all production is centered in a 400 square mile area within Harding County, relying on the Red River Formation.[10]
References
- ^ Gries 1996.
- ^ Gries 1996, p. 205–210.
- ^ Gries 1996, p. 93–96.
- ^ Gries 1996, p. 191–197.
- ^ Gries 1996, p. 3.
- ^ Gries 1996, p. 17.
- ^ Driscoll et al. 1990.
- ^ Driscoll et al. 1990, p. 2.
- ^ "South Dakota Mining History". www.mininghistoryassociation.org. Retrieved 7 July 2018.
- ^ "Industry Facts - South Dakota Oil and Gas Association". sdoil.org. Retrieved 7 July 2018.
Bibliography
- Driscoll, Daniel G.; Carter, Janet M.; Williamson, Joyce E.; Putnam, Larry D. (1990). "Hydrology of the Black Hills Area, South Dakota" (PDF). USGS.
- Gries, John Paul (1996). Roadside geology of South Dakota. Mountain Press Publishing Company.