Niobrara Formation

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Niobrara Formation
Stratigraphic range: Coniacian–Campanian PreꞒ Ꞓ O S D C P T J K Pg N
The Smoky Hill Chalk badlands are in the Niobrara Formation, in Kansas.
Type	Formation
Sub-units	Smoky Hill Chalk Member Fort Hays Limestone Member
Underlies	Pierre Shale
Overlies	Carlile Formation Or Benton Shale where the Carlile or Greenhorn Formations are not developed
Lithology
Primary	Chalk
Other	Shale
Location
Coordinates	42°44′49″N 98°02′24″W / 42.747°N 98.040°W / 42.747; -98.040
Region	North America
Country	United States
Type section
Named for	Niobrara River, Knox Co., Nebraska[1]
Named by	Meek, F.B., and Hayden, F.V.
Year defined	1862
Niobrara Formation (the United States) Show map of the United States Niobrara Formation (Nebraska) Show map of Nebraska

The Niobrara Formation /ˌnaɪ.əˈbrærə/, also called the Niobrara Chalk, is a geologic formation in North America that was deposited between 87 and 82 million years ago during the Coniacian, Santonian, and Campanian stages of the Late Cretaceous. It is composed of two structural units, the Smoky Hill Chalk Member overlying the Fort Hays Limestone Member. The chalk formed from the accumulation of coccoliths from microorganisms living in what was once the Western Interior Seaway, an inland sea that divided the continent of North America during much of the Cretaceous. It underlies much of the Great Plains of the US and Canada. Evidence of vertebrate life is common throughout the formation and includes specimens of plesiosaurs, mosasaurs, pterosaurs, and several primitive aquatic birds. The type locality for the Niobrara Chalk is the Niobrara River in Knox County in northeastern Nebraska. The formation gives its name to the Niobrara cycle of the Western Interior Seaway.