The Inyan Kara Group is a geologic group classification applied in

South Dakota South Dakota (; Sioux language, Sioux: , ) is a U.S. state in the West North Central states, North Central region of the United States. It is also part of the Great Plains. South Dakota is named after the Lakota people, Lakota and Dakota peo ...

and adopted in portions of

Wyoming Wyoming () is a U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the south ...

and

Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columbi ...

. It preserves

fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...

of the mid-

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

. Of late

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0.9 M ...

age, this classification correlates with the lower

Dakota Formation The Dakota is a sedimentary geologic unit name of formation and group rank in Midwestern North America. The Dakota units are generally composed of sandstones, mudstones, clays, and shales deposited in the Mid-Cretaceous opening of the Western Int ...

(Nishnabotna member) known in the southwest corner of the State. The South Dakota Geological Survey has also extended the

Graneros Graneros is a Chilean Communes of Chile, commune and List of cities in Chile, city in Cachapoal Province, O'Higgins Region. Deportes Graneros se conoce como unas de las candidatas a ganar la copa de la región Libertador Bernardo Ohiggins Tiene s ...

to group other formations into a unit that correlates with the upper Dakota Formation ''(Note: This definition is widely different than the generally consistent definitions of Graneros/

Belle Fourche Belle Fourche (; ) is a city in and the county seat of Butte County, South Dakota, United States. Its population was 5,617 at the 2020 census. It is near the geographic center of the United States, which moved some 550 miles northwest from the g ...

.'''')''. These state definitions of the Inyan Kara and Graneros Groups thereby cover the first two sequences of the Western Interior Seaway recorded by the Dakota Formation.

North Dakota North Dakota () is a U.S. state in the Upper Midwest, named after the Native Americans in the United States, indigenous Dakota people, Dakota Sioux. North Dakota is bordered by the Canadian provinces of Saskatchewan and Manitoba to the north a ...

also classifies the same strata as Inyan Kara, but only of formation rank without recognizing further formal subdivision, and assigns this Inyan Kara Formation as the lowest member of the Dakota Group.''North Dakota Stratigraphic Column''
North Dakota Geological Survey, 2009.

References

Geologic groups of South Dakota Cretaceous System of North America {{Cretaceous-stub

See also

References