The Rock Point Formation is a

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 ...

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe, New Mexico, Santa Fe , LargestCity = Albuquerque, New Mexico, Albuquerque , LargestMetro = Albuquerque metropolitan area, Tiguex , Offi ...

Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a U.S. state, state in the Southwestern United States. It is the list of U.S. states and territories by area, 6th largest and the list of U.S. states and territories by population, 14 ...

, and

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 its ...

. It preserves

fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

dating back to the

late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch ...

Description

The formation is up to 70 m thick and is mostly reddish-brown and grayish-red massive

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, ...

and fine

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

beds. It is the uppermost portion of the

Chinle Group 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 Ne ...

wherever it is exposed. In the Chama basin, its base is placed at the first persistent sandstone bed above the mudstones of the

Petrified Forest Formation The Petrified Forest Member is a stratigraphic unit of the Chinle Formation in Arizona, Colorado, New Mexico, Nevada, and Utah. It preserves fossils dating back to the Triassic period. Subunits Beds (are in alphabetical order, asterisks ...

. Its contact with the overlying

Entrada Sandstone The Entrada Sandstone is a formation in the San Rafael Group found in the U.S. states of Wyoming, Colorado, northwest New Mexico, northeast Arizona, and southeast Utah. Part of the Colorado Plateau, this formation was deposited during the Jurass ...

is sharp.

Fossils

The Whitaker quarry of

Ghost Ranch Ghost Ranch is a retreat and education center located close to the village of Abiquiú in Rio Arriba County in north central New Mexico, United States. It was the home and studio of Georgia O'Keeffe, as well as the subject of many of her pain ...

, New Mexico is believed to be located in the Rock Point Formation, although these beds have also controversially been assigned to the Owl Rock Formation. This quarry has also been referred to as the ''

Coelophysis ''Coelophysis'' ( traditionally; or , as heard more commonly in recent decades) is an extinct genus of coelophysid theropod dinosaur that lived approximately 228 to 201.3 million years ago during the latter part of the Triassic Period fr ...

'' quarry due to preserving a large number of specimens of the early

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

''Coelophysis bauri''.

History of investigation

The unit was first named by J.W. Harshbarger, C.A. Repenning, and J.H. Irwin in 1957, who assigned

Herbert E. Gregory Herbert Ernest Gregory (October 15, 1869 – January 23, 1952) was a Yale University geologist well known for his early 20th-century explorations of the Colorado Plateau in Arizona and Utah. One of his most important works is ''Colorado Plateau Reg ...

's (1917) "A" division of the

Chinle Formation 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 ...

to the

Wingate Formation The Wingate Sandstone is a geologic formation in the Glen Canyon Group of the Colorado Plateau province of the United States which crops out in northern Arizona, northwest Colorado, Nevada, and Utah. Geology Wingate Sandstone is particular ...

as the Rock Point Member. It was named for Rock Point School, located near the type exposures at Little Round Rock. J.H. Stewart and coinvestigators argued in 1972 that the unit has more affinity with the Chinle, and R.F. Dubiel assigned the Rock Point to the Chinle in 1989. The unit has created an unusual amount of controversy, but

Spencer G. Lucas Spencer George Lucas is an American paleontologist and stratigrapher, and curator of paleontology at the New Mexico Museum of Natural History and Science. His main areas of study are late Paleozoic, Mesozoic and early Cenozoic vertebrate fo ...

and coinvestigators raised it to formation rank within the Chinle Group in 2005. File:Rock point concretions.jpg, Bed of concretions in the Rock Point Formation near Youngsville, New Mexico File:Redondasaurus bermani skull.jpg, left, Fossil from Rock Point Formation

Footnotes

References

* * * * * {{cite journal , last1=Stewart , first1=J.H. , last2=Poole , first2=F.G. , last3=Wilson , first3=R.F. , year=1972 , title=Stratigraphy and origin of the Chinle Formation and related Upper Triassic strata in the Colorado Plateau region, with sections on sedimentary petrology by R.A. Cadigan and conglomerate studies by William Thordarson and H.F. Albee , journal=U.S. Geological Survey Professional Paper , volume=690 , doi=10.3133/pp690, doi-access=free Triassic Arizona Triassic geology of Utah Triassic formations of New Mexico

Description

Fossils

History of investigation

See also

Footnotes

References