Naturita Formation

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

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)