Niobrara Formation

Niobrara Formation
Stratigraphic range: Coniacian–Campanian
The Smoky Hill Chalk badlands are in the Niobrara Formation, in Kansas.
TypeFormation
Sub-unitsSmoky Hill Chalk Member
Fort Hays Limestone Member
UnderliesPierre Shale
OverliesCarlile Formation
Or Benton Shale where the Carlile or Greenhorn Formations are not developed
Lithology
PrimaryChalk
OtherShale
Location
Coordinates42°44′49″N 98°02′24″W / 42.747°N 98.040°W / 42.747; -98.040
RegionNorth America
Country
 United States
Type section
Named forNiobrara River, Knox Co., Nebraska[1]
Named byMeek, F.B., and Hayden, F.V.
Year defined1862
Niobrara Formation is located in the United States
Niobrara Formation
Niobrara Formation (the United States)
Niobrara Formation is located in Nebraska
Niobrara Formation
Niobrara Formation (Nebraska)
Monument Rocks, Smoky Hill Chalk[clarification needed]
Cremnoceramus deformis is an index fossil of the Fort Hays Limestone Member.
Niobrara Chalk was weathered and opalized in the Valentine phase of the Ogallala Formation.

The Niobrara Formation /ˌn.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.

  1. ^ "Geologic Unit: Niobrara". National Geologic Database. Geolex — Significant Publications. United States Geological Survey. Retrieved June 5, 2020.