The Niobrara Formation , also called the Niobrara Chalk, is a
geologic formation
A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...
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
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 ...
. 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, and
pterosaurs as well as several primitive aquatic
bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...
s. The
type locality for the Niobrara Chalk is the
Niobrara River in
Knox County in northeastern
Nebraska
Nebraska () is a state in the Midwestern region of the United States. It is bordered by South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Kansas to the south; Colorado to the sout ...
. The formation gives its name to the Niobrara cycle of the Western Interior Seaway.
History of exploration
The Niobrara Chalk was recorded (1857) and named (1862) by
Meek, F.B., and
Hayden, F.V.[ It was first studied during an expedition led by ]Othniel Charles Marsh
Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of Paleontology in Yale College and President of the National Academy of Sciences. He was one of the preeminent scientists in the field of paleontology. Among ...
of Yale University
Yale University is a private research university in New Haven, Connecticut. Established in 1701 as the Collegiate School, it is the third-oldest institution of higher education in the United States and among the most prestigious in the w ...
in 1870. This and following expeditions to the area in 1871 and 1872 yielded the first of many fossil vertebrate remains commonly attributed with the formation. Excavations continued through the following years up to 1879 under the direction of professional fossil collectors such as B. F. Mudge and S. W. Williston appointed by Marsh.
The Niobrara Chalk has been continuously explored ever since, with specimens being found by H. T. Martin of the University of Kansas and George F. Sternberg
George Fryer Sternberg (1883–1969) was a paleontologist best known for his discovery in Gove County, Kansas of the "fish-within-a-fish" of ''Xiphactinus audax'' with a recently eaten ''Gillicus arcuatus'' within its stomach. Sternberg was bo ...
, the son of the famous fossil collector Charles H. Sternberg
Charles Hazelius Sternberg (June 15, 1850 – July 20, 1943) was an American fossil collector and paleontologist. He was active in both fields from 1876 to 1928, and collected fossils for Edward Drinker Cope and Othniel C. Marsh, and for the ...
. Much of the best material from the formation is on display at the Sternberg Museum of Natural History
Fort Hays State University (FHSU) is a public university in Hays, Kansas. It is the fourth-largest of the six state universities governed by the Kansas Board of Regents, with a total enrollment of approximately 15,100 students.
History
FHSU w ...
in Hays, Kansas
Kansas () is a U.S. state, state in the Midwestern United States, Midwestern United States. Its Capital city, capital is Topeka, Kansas, Topeka, and its largest city is Wichita, Kansas, Wichita. Kansas is a landlocked state bordered by Nebras ...
.
Stratigraphy
The Smoky Hill Chalk Member of the Niobrara Chalk contains the majority of the fossils found in the formation, and is subdivided into 23 marker beds. Most vertebrates are present from the upper half of the member. Most of the vertebrate remains were collected and described before the stratigraphy of the Niobrara Chalk was fully understood. Specimens were described as being from layers referred to as being either of gray-blue shale or yellow chalk
Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor. C ...
. This dichotomy is not indicative of different stratigraphic units as was previously thought, but rather is seen as a weathering phenomenon that can be found at varying points in the same outcrop.
The Fort Hays Limestone Member consists of somewhat harder, massive limestone beds.
The Niobrara Formation is overlain by the marine Pierre Shale and is underlain by the Carlile Shale or Benton Shale.
Flora and fauna
During the time of the deposition of the Niobrara Chalk, much life inhabited the seas of the Western Interior Seaway. By this time in the Late Cretaceous many new lifeforms appeared such as mosasaurs, which were to be some of the last of the aquatic lifeforms to evolve before the end of the Mesozoic. Life of the Niobrara Chalk is comparable to that of the 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 Wester ...
, although the Dakota Formation, which was deposited during the Cenomanian, predates the chalk by about 10 million years.
Mineral resources
Various exposures of Niobrara Chalk were covered and partially silicified as the Ogallala sediments covered the Neogene plains. Re-exposed during the Quaternary, these cherty materials, known as Smoky Hill Jasper and Smoky Hill silicified chalk, or more recently as Niobrara Jasper or Niobrarite, became source material for stone tools from the earliest human habitation of the High Plains.
In some regions, the Niobrara is a commercial hydrocarbon reservoir. Natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbon d ...
is produced from the Niobrara in the eastern Denver Basin
The Denver Basin, variously referred to as the Julesburg Basin, Denver-Julesburg Basin (after Julesburg, Colorado), or the D-J Basin, is a geologic structural basin centered in eastern Colorado in the United States, but extending into southeast ...
. Oil is produced from the Niobrara in the North Park Basin, and new fracturing methods are allowing much larger areas to be tapped for oil.
The Fort Hays member was historically quarried on the High Plains High Plains refers to one of two distinct land regions:
* High Plains (United States), land region of the western Great Plains
*High Plains (Australia)
The High Plains of south-eastern Australia are a sub-region, or more strictly a string of adja ...
for the manufacture of Portland cement
Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in the early 19t ...
at Superior, Nebraska and Yocemento, Kansas, as well as along the Dakota Hogback
: North terminus:
: South terminus:
The Dakota Hogback is a long hogback ridge at the eastern fringe of the Rocky Mountains that extends north-south from southern Wyoming through Colorado and into northern New Mexico in the United ...
in Colorado from Lyons to Boulder, and around Pueblo and Florence
Florence ( ; it, Firenze ) is a city in Central Italy and the capital city of the Tuscany region. It is the most populated city in Tuscany, with 383,083 inhabitants in 2016, and over 1,520,000 in its metropolitan area.Bilancio demografico ...
. Along the Dakota Hogback north of Laporte, Colorado
Laporte (originally spelled La Porte and alternatively spelled LaPorte) is an unincorporated town, a post office, and a census-designated place (CDP) located in and governed by Larimer County, Colorado, United States. The CDP is a part of the F ...
, the Fort Hays Limestone formed a secondary hogback, which was extensively quarried for manufacture of up to 450,000 tons of cement a year. The full depth of the Niobrara was quarried by the Western Portland Cement Company at Yankton, South Dakota, which supplied cement to the Panama Canal project.
References
Further reading
AAPG Datapages: "Stratigraphy of the Upper Carlile Shale and Lower Niobrara Formation (Upper Cretaceous), Fremont and Pueblo Counties, Colorado"
* Bennett, S. C. 2000. Inferring Stratigraphic Position of Fossil Vertebrates from the Niobrara Chalk of Western Kansas. College of Chiropractic, University of Bridgeport, Bridgeport, CT 06601-2449.
{{Chronostratigraphy of Colorado, Mesozoic state=expanded
Geologic formations of Colorado
Geologic formations of Kansas
Geologic formations of Nebraska
Geologic formations of North Dakota
Geologic formations of South Dakota
Geologic formations of Wyoming
Cretaceous Colorado
Cretaceous Kansas
Cretaceous geology of Nebraska
Cretaceous formations of New Mexico
Cretaceous geology of North Dakota
Cretaceous geology of South Dakota
Cretaceous geology of Wyoming
Upper Cretaceous Series of North America
Coniacian Stage
Santonian Stage
Campanian Stage
Chalk
Shale formations of the United States
Shallow marine deposits
Reservoir rock formations
Fossiliferous stratigraphic units of North America
Paleontology in Colorado
Paleontology in Kansas
Paleontology in Nebraska
Paleontology in New Mexico
Paleontology in North Dakota
Paleontology in South Dakota
Paleontology in Wyoming