Naturita Formation

The Naturita Formation is a Cretaceous Period sedimentary geologic formation, found in western Colorado and eastern Utah.

Naturita Formation
Stratigraphic range: Cenomanian
~99–94 Ma
↓
Naturita Formation above Naturita, Colorado
TypeGeological formation
Sub-unitsCulver Coal Zone member
UnderliesMancos Shale
OverliesCedar Mountain & Burro Canyon Formations
Lithology
PrimaryMudstone
OtherShale, sandstone
Location
Coordinates37.6°N 112.9°W / 37.6; -112.9
Approximate paleocoordinates39.4°N 75.5°W / 39.4; -75.5
RegionColorado, Utah
Country United States
Type section
Named forNaturita, Colorado
Naturita Formation (the United States)
Naturita Formation (Utah)

It was named for a rock outcrop of the formation located near Naturita, Colorado.[1]

Geology
Naturita Formation exposed in a roadcut in eastern Utah.
A coal seam is visible below its sandstone bed, with a thin volcanic ash (white) layer in its upper portion.

The formation overlies the Cedar Mountain Formation, and underlies the Mancos Shale formation, thus occupying the position of sedimentary strata that have historically been called the Dakota Formation. That term is no longer used for Cretaceous strata that were deposited on the western side of the Cretaceous Seaway.[2][3]

In most areas, the Naturita Formation is composed of a lower unit of conglomeratic sandstone, a middle part of lignitic mudstones and coal, and fine- to medium-grained sandstones in the upper part. The Naturita is not uniform in thickness and in many places is very thin or missing so that the Mancos Formation is in direct contact with the Cedar Mountain Formation.

Where missing, a lag of conglomerate may be present to indicate winnowing of sediments, which occurred by advancing Cretaceous seas. In other places, deposition of Naturita sediments did not occur, and these areas may have been quiet lagoons.

Coastal coal swamps also formed in low areas as the encroaching sea raised the base level of rivers and the water table.

Fossil content

Fossils from the Naturita include dinosaur bone fragments of ceratopsians, a possible primitive tyrannosaurid, nodosaurid ankylosaurs, a brachiosaurid sauropod, and the bothremyid turtle Paiutemys.[4][5]

Abundant mammals as well as fossil plants are also known from the coal-rich layers.[6]

Mammals

See also

References
  1. Young, R.G. 1965. Type section of the Naturita Formation. Bulletin of the American Association of Petroleum Geologists 49:1512-1516.
  2. Witzke, B.J., and Ludvigson, G.A. 1994. The Dakota Formation in Iowa and its type area. In Shurr, G.W., Ludvigson, G.A., and Hammond, R.H. (eds). Perspectives on the eastern margin of the Cretaceous Western Interior Basin. Geological Society of America, Special Paper 287:43 78.
  3. Young, R.G. 1960. Dakota Group of Colorado Plateau. Bulletin of the American Association of Petroleum Geologists 44:156-194.
  4. Carpenter, K. 2006. Assessing dinosaur faunal turnover in the Cedar Mountain Formation (Lower Cretaceous) of eastern Utah, USA. Ninth International Symposium on Mesozoic Terrestrial Ecosystems and Biota, Abstract and Proceedings Volume, p. 21-25
  5. Joyce WG, Lyson TR, Kirkland JI. (2016) An early bothremydid (Testudines, Pleurodira) from the Late Cretaceous (Cenomanian) of Utah, North America. PeerJ 4:e2502 https://doi.org/10.7717/peerj.2502
  6. Rushforth, S.R. 1971. A flora from the Dakota Sandstone Formation (Cenomanian) near Westwater, Grand County, Utah. Brigham Young University Science Bulletin 14(3):1-44.
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