Формация Чинле: Геологическое строение западных США.

Geological formation in the western US

The Chinle Formation is an Upper Triassic continental geological formation of fluvial, lacustrine, and palustrine to eolian deposits spread across the U. S. states of Nevada, Utah, northern Arizona, western New Mexico, and western Colorado. In New Mexico, it is often raised to the status of a geological group, the Chinle Group. Some authors have controversially considered the Chinle to be synonymous to the Dockum Group of eastern Colorado and New Mexico, western Texas, the Oklahoma panhandle, and southwestern Kansas. The Chinle Formation is part of the Colorado Plateau, Basin and Range, and the southern section of the Interior Plains. A probable separate depositional basin within the Chinle is found in northwestern Colorado and northeastern Utah. The southern portion of the Chinle reaches a maximum thickness of a little over Typically, the Chinle rests unconformably on the Moenkopi Formation. The Chinle Formation was probably mostly deposited in the Norian stage, according to a plethora of chronological techniques. It is a thick and fossiliferous formation with numerous named members (subunits) throughout its area of deposition.

While colorful Triassic sediments of the Colorado Plateau have been investigated since the 19th century, the Chinle Formation was only formally named and described by Herbert E. Gregory in 1917. It was named for Chinle Valley in Apache County, Arizona, land which is largely within the Navajo Nation. Gregory did not designate a type locality. He split the Chinle into four subunits, labelled A (youngest) to D (oldest). This did not include the underlying Shinarump Conglomerate (named by G. K. Gilbert and Edwin E. Howell in 1875), which he considered a separate formation. United States Geological Survey geologists and paleontologists continued to map out the Chinle Formation through the 20th century, revising the unnamed subunits of Gregory. A basic stratigraphy of the formation was developed for north central New Mexico by Wood and Northrop (1946), and stratigraphy in the Four Corners Region was established by the late 1950s. In 1956, Economic geologist Raymond C. Robeck identified and named the Temple Mountain member as the basal most unit in the area of the San Rafael Swell of Utah. In 1957, John H. Stewart revised the Shinarump Conglomerate and renamed it the Shinarump member of the Chinle formation. Study of the formation expanded northwards into northern Utah and Colorado, facilitated through papers by Forrest G. Poole and Stewart (1964) and Steve W. Sikich (1965), who named informal local members equivalent to those of Arizona and New Mexico. The complete areal extent of the unit was mapped by R. F. Wilson and Stewart in 1967. Stewart and his colleagues created an expansive overview and revision of the formation in 1972, summarizing previous knowledge on Chinle stratigraphy. V. C. Kelley assigned more members and revised the unit in 1972. Spencer G. Lucas and S. N. Hayden did the same thing in 1989. The Rock Point Member was assigned by R. F. Dubiel in 1989. The Chinle was raised to group rank by Lucas in 1993, thus also raising many of the members to formation status. He also included the formations of the Dockum Group of eastern New Mexico and west Texas within the "Chinle Group". This modified nomenclature is controversial; many still retain the Chinle as a formation and separate out the Dockum Group. The Dockum was named in 1890, before the Chinle. Lucas also advocated abandoning the name Dolores Formation as a parochial synonym for the Chinle Group. Overviews of the Chinle were created by Dubiel and others (1992) and Hintze and Axen (1995).

The Chinle Formation is fossiliferous, with a diverse array of extinct reptile, fish, and plant fossils, including early dinosaurs and the famous petrified wood of Petrified Forest National Park in Arizona.

Some of the most extensive deposits of the Chinle Formation are found in the southern Colorado Plateau, including Arizona and the western portion of New Mexico. In this region, the oldest and stratigraphically lowest portion of the Chinle is the Shinarump Conglomerate. The Shinarump includes braided river system channel deposit facies. one of the oldest widespread units in the badlands of the Painted Desert area. In western New Mexico (particularly the Zuni Mountains area), the Mesa Redondo Member may be replaced by another sandy unit known as the Zuni Mountains Formation. Sediments from this time interval are followed by a geological unit called the Bluewater Creek Formation. In Petrified Forest National Park (PEFO) and its vicinities, the Sonsela Sandstone is thick enough that it can be resolved into several distinct sandstone rich layers. It is renamed as the Sonsela Member in this situation. The Upper "Petrified Forest Member" is sometimes called the Painted Desert Member, or simply referred to as the Petrified Forest Member in a more restricted definition of the term. The stratigraphically highest unit in north central New Mexico is the informally named “siltstone member”. This unit is best exposed at Ghost Ranch, where it has produced the famous Whitaker Quarry, also known as the Coelophysis quarry due to a high concentration of fossils belonging to the theropod dinosaur Coelophysis bauri. The "siltstone member" may be equivalent to the Rock Point Member, and some authors refer to it as such. The stratigraphic nomenclature used in southern Utah is also utilized in Monument Valley, where the coarse grained lower members of the Chinle form a caprock for many famous buttes which characterize the valley. The Monitor Butte Member overlies the Shinarump and Temple Mountain members in southeast Utah and Monument Valley. This unit comprises drab and generally fine grained sediments, equivalent to the Blue Mesa Member and Bluewater Creek Formation found further south. They are complex heterolithic units, representing variously braided river facies, lacustrine, and overbank deposits.