The Naturita Formation is a classification used in western

Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of t ...

and eastern

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...

for a

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 sedimentary

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 exp ...

. This name was "applied to the upper or carbonaceous part of

Dakota Group 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 ...

" by R.G. Young in 1960, naming it for

Naturita, Colorado Naturita is a statutory town in Montrose County, Colorado, United States. The population was 485 at the 2020 census, down from 546 in 2010. A post office called Naturita has been in operation since 1882. Naturita is a name derived from Spanis ...

.Young, R.G., 1960, Dakota Group of Colorado Plateau: Bulletin of the American Association of Petroleum Geologists, v. 44, no. 2, p. 156-194. The name is not used by

U.S. Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and ...

authors, but has found growing acceptance by the Utah Geological Survey

History of the name

The formation in Utah and western Colorado overlies the Cedar Mountain and Burro Canyon Formations, and underlies the

Mancos Shale The Mancos Shale or Mancos Group is a Late Cretaceous (Upper Cretaceous) geologic formation of the Western United States. The Mancos Shale was first described by Cross and Purington in 1899 and was named for exposures near the town of Mancos, ...

formation, thus occupying a similar position of sedimentary strata that have widely been called

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 ...

in Iowa, Kansas and Nebraska. Witzke, B.J., and Ludvigson, G.A., 1994, The Dakota Formation in Iowa and the type area, in Shurr, G.W., Ludvigson, G.A., and Hammond, R.H, editors, Perspectives on the eastern margin of the Cretaceous Western Interior Basin: Geological Society of America Special Paper, v. 287, p. 43-78. The use of the name "Dakota" in western states was the result of early geological mapping by F.V. Hayden beginning in the 1850. For convenience, he maintained the same terminology developed during the early mapping along the Missouri River as he began mapping farther west in the 1860s even while acknowledging "There are very few points of resemblance between these beds and those which form the Dakota group, as seen in Kansas and Nebraska. All the evidence therefore that I have had to guide me in regard to these beds along the margin of the mountain ranges has been their position." (p. 114). Despite this doubt by Hayden, the name Dakota Formation became entrenched in many western states, but has been renamed as the Lakota Formation in South Dakota, the

Cloverly Formation The Cloverly Formation is a geological formation of Early and Late Cretaceous age (Valanginian to Cenomanian stage) that is present in parts of Montana, Wyoming, Colorado and Utah in the western United States. It was named for a post office on t ...

in Wyoming and Montana (in part), and the

South Platte Formation The South Platte Formation is a Mesozoic geologic formation found in the U.S. state of Colorado. Fossil ankylosaur tracks have been reported from the formation.Weishampel, et al. (2004). "Dinosaur distribution." Pp. 517-607. See also * List o ...

in eastern Colorado, but not on the northern half of the

Colorado Plateau The Colorado Plateau, also known as the Colorado Plateau Province, is a physiographic and desert region of the Intermontane Plateaus, roughly centered on the Four Corners region of the southwestern United States. This province covers an area of ...

where the name "Dakota Formation" continued to be used. In 1960, Young who was investigating uranium ore deposits on the Colorado Plateau for the U.S. Atomic Energy Commission, proposed the name Naturita Formation for the town of

. Although he described the general character of the formation, he did not designate a type section until five years later. The proposed name change was ignored by most geologists, probably because Young did not elaborate why he was proposing a name change. Years later, Witzke and Ludvigson independently noted a problem with the use of the name "Dakota Formation" in western states, writing "Usage of the term 'Dakota' for western-derived sedimentary sequences in the Rocky Mountain area is discouraged.". This, too was largely ignored until Carpenter made a detailed case for accepting "Naturita Formation" on the Colorado Plateau.Carpenter, K., 2014. Where the sea meets the land—the unresolved Dakota problem in Utah. ''Utah Geological Association Publication'', ''43'', pp.357-372. After a detailed review of the history of the problem, Carpenter argued 1) that during their deposition, the Dakota Formation and the Naturita Formation were separated by the Western Interior Cretaceous Seaway, 2) stream depositing the Dakota and Naturita Formations were flowing towards each other on opposite sides of the Seaway, but the formations did not connect one side of the seaway to the other, and 3) sediments of the Dakota Formation on the east side of the Seaway were derived from the North American Craton, whereas sediments of the Naturita Formation were derived from the Sevier uplift along the Nevada-Utah border. Thus, the two formations were derived independent of each other.

Geology

The formation is described as having a lower section that is dark-brown to black, carbonaceous claystone, gray shale, and siltstone, and some beds of gray-orange to white coarse-grained sandstone which may form ledges; a middle section of mostly thin, but locally thick coal beds; and an upper section that is gray-orange to light brown, moderately erosion resistant, locally fossiliferous sandstone that is interbedded with light-olive-gray shale. Locally, a channel conglomerate is present at the base. Where missing, a lag of conglomerate may be present indicating 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 because oyster shells are often present in great abundance. The lower portion of the Naturita Formation represents river channel and floodplain deposits, whereas the upper part represent a complex of estuarine, lagoonal, and swamp environments of a coastal plain. Ludvigson and Witzke, correlated the Dakota Formation in Iowa with the "Dakota" along the Colorado

Front Range The Front Range is a mountain range of the Southern Rocky Mountains of North America located in the central portion of the U.S. State of Colorado, and southeastern portion of the U.S. State of Wyoming. It is the first mountain range encountere ...

based on

palynostratigraphy Palynology is the "study of dust" (from grc-gre, παλύνω, palynō, "strew, sprinkle" and ''-logy'') or of "particles that are strewn". A classic palynologist analyses particulate samples collected from the air, from water, or from deposits ...

and recognized those palynostratigraphic sequences throughout the Western Interior. In 2012, the Dakota/Naturita Formation sequence and fossil pollen species in Utah were correlated with the Ludvigson and Witzke report on the Dakota at the Nebraska type location. Radiometric dates and fossil invertebrates show that the Naturita Formation becomes progressively younger southwards and westwards across Utah, thus recording the advancing Western Interior Seaway.

Fossil content

Plants

A low diversity flora assemblage has been described from Utah consisting of horsetails, ferns and angiosperms. Many of the identifications are dated and a new study may increase the diversity. ''Equisetum'' ''Asplenium'' ''Coniopteris'' ''Hausmannia'' ''Gleichenia'' ''Matonidium'' ''Astralopteris'' ''Cladophlebis'' ''Ilex'' ''Magnolia'' ''Ficus'' ''Eucalyptus'' ''Platanus'' ''Salix''

Vertebrates

Fossi vetebrates include dinosaur bone fragments of

ceratopsian Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. ...

s, a possible primitive

tyrannosaurid Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family of coelurosaurian theropod dinosaurs that comprises two subfamilies containing up to thirteen genera, including the eponymous ''Tyrannosaurus''. The exact number of genera ...

, nodosaurid

ankylosaur Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. ...

s, a brachiosaurid

sauropod Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their bo ...

, the bothremyid turtle '' Paiutemys''.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 and fossil mammals

= Mammals

= * '' Cedaromys minimus'' * '' Cimolodon cf. similis'' * '' Dakotadens morrowi'' * '' Dakotamys malcolmi'' * '' Eoalphadon clemensi'' * '' E. lillegraveni'' * '' E. woodburnei'' * '' Paracimexomys cf. robisoni'' * '' Pariadens kirklandi'' * '' Varalphadon janetae'' * '' Alphadon sp.'' * '' Bryceomys sp.'' * '' Dakotadens sp.'' * '' Eoalphadon sp.'' * '' Paracimexomys sp.'' * '' Protalphadon sp.''

References

{{Reflist Geologic formations of Colorado Geologic formations of Utah Lower Cretaceous Series of North America Cretaceous Colorado Cretaceous geology of Utah Cenomanian Stage Mudstone formations Fluvial deposits Shallow marine deposits Paleontology in Utah