Naturita Formation
Encyclopedia
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)
Naturita, Colorado
Naturita is a Statutory Town in Montrose County, Colorado, United States. The population was 635 at the 2000 census.-Geography:Naturita is located at ....
.
Cedar Mountain Formation
The Cedar Mountain Formation is the name given to distinctive sedimentary rocks in eastern Utah that occur between the underlying Morrison Formation and overlying Naturita Formation . It is composed of non-marine sediments, that is, sediments deposited in rivers, lakes and on flood plains...
(sometimes called the Burro Canyon Formation in Colorado) and Mancos Shale
Mancos Shale
The Mancos Shale or Mancos Group is an Upper Cretaceous geologic formation of the Western United States dominated by mudrock that accumulated in offshore and marine environments of the Cretaceous North American Inland Sea. The Mancos was deposited during the Cenomanian through Campanian ages,...
, thus occupies the position for sedimentary strata that have historically been called the Dakota Formation
Dakota Formation
The Dakota Formation is a geologic formation composed of sedimentary rocks deposited on the western side of the Late Cretaceous Western Interior Seaway. F.B. Meek and F.V. Hayden named it for exposures along the Missouri River near Dakota City, Nebraska...
. 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.
Lignite
Lignite, often referred to as brown coal, or Rosebud coal by Northern Pacific Railroad,is a soft brown fuel with characteristics that put it somewhere between coal and peat...
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)