Naturita Formation

The Naturita Formation was named by Robert G. Young (1960, 1965) for Cretaceous sedimentary rocks exposed near Naturita, Colorado.

Naturita Formation exposed above the town of Naturita Colorado.

The formation lies between the Cedar Mountain Formation (sometimes called the Burro Canyon Formation in Colorado) and Mancos Shale, thus occupies the position for sedimentary strata that have historically been called the Dakota Formation. However, as Witzke and Ludvigson (1994) noted, the term cannot be used for Cretaceous strata that were deposited on the western side of the Cretaceous Seaway.

Naturita Formation exposed in a roadcut in eastern Utah. A coal seam is visible below the sandstone bed. A thin volcanic ash (white layer) occurs in the upper portion of the coal.

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 sea. 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.

Fossils from the Naturita including dinosaur bone fragments of ceratopsians, a possible primitive tyrannosaurid, nodosaurid ankylosaurs, and a brachiosaurid sauropod (Carpenter 2006). Abundant fossil plants are also known from the coal-rich layers (Rushforth 1971)

References

• 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

• 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.

• 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.

• Young, R.G. 1960. Dakota Group of Colorado Plateau. Bulletin of the American Association of Petroleum Geologists 44:156-194.

• Young, R.G. 1965. Type section of the Naturita Formation. Bulletin of the American Association of Petroleum Geologists 49:1512-1516.