Chinle Formation
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The Chinle Formation is an
Upper Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...
continental
geological 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 ...
of
fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviog ...
,
lacustrine A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...
, and
palustrine Palustrine wetlands include any inland wetland that contains ocean-derived salts in concentrations of less than 0.5 parts per thousand, and is non-tidal. The word ''palustrine'' comes from the Latin word ''palus'' or marsh. Wetlands within this ca ...
to eolian deposits spread across the U.S. states of
Nevada Nevada ( ; ) is a U.S. state, state in the Western United States, Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. N ...
,
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 it ...
, northern
Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...
, western
New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Tiguex , OfficialLang = None , Languages = English, Spanish ( New Mexican), Navajo, Ker ...
, and western
Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of t ...
. 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 The Dockum is a Late Triassic (approximately late Carnian through Rhaetian, or 223–200 Ma) geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Colora ...
of eastern Colorado and New Mexico, western
Texas Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...
, the
Oklahoma Oklahoma (; Choctaw language, Choctaw: ; chr, ᎣᎧᎳᎰᎹ, ''Okalahoma'' ) is a U.S. state, state in the South Central United States, South Central region of the United States, bordered by Texas on the south and west, Kansas on the nor ...
panhandle, and southwestern
Kansas Kansas () is a state in the Midwestern United States. Its capital is Topeka, and its largest city is Wichita. Kansas is a landlocked state bordered by Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to the ...
. The Chinle Formation is part of the
Colorado Plateau The Colorado Plateau, also known as the Colorado Plateau Province, is a physiographic and desert region of the Intermontane Plateaus, roughly centered on the Four Corners region of the southwestern United States. This province covers an area of ...
,
Basin and Range Basin and range topography is characterized by alternating parallel mountain ranges and valleys. It is a result of crustal extension due to mantle upwelling, gravitational collapse, crustal thickening, or relaxation of confining stresses. The e ...
, and the southern section of the
Interior Plains The Interior Plains is a vast Physiographic province, physiographic region that spreads across the Laurentia, Laurentian craton of central North America, extending along the east flank of the Rocky Mountains from the Gulf Coast region to the Arcti ...
.GEOLEX database entry for Chinle
USGS (viewed 19 March 2006)
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 An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...
on the
Moenkopi Formation The Moenkopi Formation is a geological formation that is spread across the U.S. states of New Mexico, northern Arizona, Nevada, southeastern California, eastern Utah and western Colorado. This unit is considered to be a group in Arizona. Part ...
. 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.


History of investigation

While colorful Triassic sediments of the
Colorado Plateau The Colorado Plateau, also known as the Colorado Plateau Province, is a physiographic and desert region of the Intermontane Plateaus, roughly centered on the Four Corners region of the southwestern United States. This province covers an area of ...
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 Apache County is in the northeast corner of the U.S. state of Arizona. Shaped in a long rectangle running north to south, as of the 2020 census, its population was 66,021. The county seat is St. Johns. Most of the county is occupied by part ...
, land which is largely within the
Navajo Nation The Navajo Nation ( nv, Naabeehó Bináhásdzo), also known as Navajoland, is a Native American reservation in the United States. It occupies portions of northeastern Arizona, northwestern New Mexico, and southeastern Utah; at roughly , the ...
. 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 Edwin Eugene Howell (March 12, 1845 – April 16, 1911) was an American geologist and cartographer, who produced some of the most detailed raised-relief maps of his time, for which he was regarded by geologist Grove Karl Gilbert, G. K. Gilbert as " ...
in 1875), which he considered a separate formation.
United States Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...
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 The San Rafael Swell is a large geologic feature located in south-central Utah, United States about west of Green River. The San Rafael Swell, measuring approximately , consists of a giant dome-shaped anticline of sandstone, shale, and limesto ...
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 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 fossils ...
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 The Dockum is a Late Triassic (approximately late Carnian through Rhaetian, or 223–200 Ma) geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Colora ...
of eastern
New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Tiguex , OfficialLang = None , Languages = English, Spanish ( New Mexican), Navajo, Ker ...
and west
Texas Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...
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 is a Late Triassic (approximately late Carnian through Rhaetian, or 223–200 Ma) geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Colora ...
. 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).GEOLEX database bibliographic references for Chinle
(viewed 19 March 2006)


Paleobiota

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 Petrified Forest National Park is an American national park in Navajo County, Arizona, Navajo and Apache County, Arizona, Apache counties in northeastern Arizona. Named for its large deposits of petrified wood, the park covers about , encompassin ...
in
Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...
.


Stratigraphy

The formation members and their thicknesses are highly variable across the Chinle.


Arizona and western New Mexico

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 Conglomerate is a geologic formation found in the Four Corners region of the United States. It was deposited in the early part of the Late Triassic period. Description The Shinarump Conglomerate is a highly resistant coarse-grained ...
. The Shinarump includes braided-river system channel-deposit
facies In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with specified characteristics, which can be any observable attribute of rocks (such as their overall appearance, composition, or condition of formatio ...
. The Shinarump interfingers with a finer-grained subunit, the Mesa Redondo Member, one of the oldest widespread units in the badlands of the Painted Desert area. In western New Mexico (particularly the
Zuni Mountains Zuni may refer to: Peoples and languages * Zuni people, an indigenous people of the United States * Zuni language, their language Places * Zuni, Virginia, an unincorporated town in Virginia in the United States * Zuni Pueblo, New Mexico, a ce ...
area), the Mesa Redondo Member may be replaced by another sandy unit known as the
Zuni Mountains Formation The Shinarump Conglomerate is a geologic formation found in the Four Corners region of the United States. It was deposited in the early part of the Late Triassic period. Description The Shinarump Conglomerate is a highly resistant coarse-grained ...
. Sediments from this time interval are followed by a geological unit called the
Bluewater Creek Formation The Bluewater Creek Formation is a geologic formation in west-central New Mexico. It preserves fossils dating back to the late Triassic period. Description The formation consists of red sandstones and mudstones and has a total thickness in exce ...
. Most Chinle outcrops in the Painted Desert have traditionally been placed within the following
Petrified Forest Member 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 (*) in ...
, a segment of Triassic sediments which are so diverse and extensive that it is sometimes raised to its own formation, subdivided further, or redefined more narrowly. In its widest definition, the Petrified Forest Member (or Formation) is split into three sections: the muddy Lower Petrified Forest and Upper Petrified Forest, and the sandy Sonsela Sandstone bed, which separates them. The Lower "Petrified Forest Member" is generally known as the
Blue Mesa Member The Blue Mesa Member is a member of the Chinle Formation. It is located in the Petrified Forest National Park of northeast Arizona. Geology The colorful bands of mudstone and sandstone were laid down during the Triassic, when the area was part of ...
. In
Petrified Forest National Park Petrified Forest National Park is an American national park in Navajo County, Arizona, Navajo and Apache County, Arizona, Apache counties in northeastern Arizona. Named for its large deposits of petrified wood, the park covers about , encompassin ...
(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 Sonsela Sandstone is a collection of braided-stream channel facies. 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 Petrified Forest is predominately overbank deposits with thin lenses of channel-deposit facies and lacustrine deposits. The Petrified Forest Member grades into the Owl Rock Member, a marginal lacustrine to lacustrine facies possibly representing a large lake system. The Owl Rock Member is followed by the youngest and sandiest subunit of the Chinle, the Rock Point Member. The Rock Point is distinct enough that it was previously considered a unit of the
Wingate Sandstone 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 particularly ...
, a latest Triassic - early Jurassic aeolian formation which overlies the Chinle in many areas.


Central New Mexico

Unambiguous exposures of the Chinle Formation extend into central New Mexico, beyond the eastern edge of the Colorado Plateau. Most of these are found in the
Chama Basin The Chama Basin is a geologic structural basin located in northern New Mexico. The basin closely corresponds to the drainage basin of the Rio Chama and is located between the eastern margin of the San Juan Basin and the western margin of the R ...
of north-central New Mexico, particularly several famed paleontological sites at
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 painti ...
near Abiquiu. Minor exposures also occur in the Lucero Uplift west of
Albuquerque Albuquerque ( ; ), ; kee, Arawageeki; tow, Vakêêke; zun, Alo:ke:k'ya; apj, Gołgéeki'yé. abbreviated ABQ, is the most populous city in the U.S. state of New Mexico. Its nicknames, The Duke City and Burque, both reference its founding in ...
, as well as other areas along the
Rio Grande Rift The Rio Grande rift is a north-trending continental rift zone. It separates the Colorado Plateau in the west from the interior of the North American craton on the east. The rift extends from central Colorado in the north to the state of Chihua ...
.As in the Colorado Plateau, the lowest major unit in north-central New Mexico is a sandstone-rich member. This layer, the
Agua Zarca Sandstone The Shinarump Conglomerate is a geologic formation found in the Four Corners region of the United States. It was deposited in the early part of the Late Triassic period. Description The Shinarump Conglomerate is a highly resistant coarse-grained ...
, is often synonymized with the Shinarump Conglomerate, though it may be derived from a different erosional source. It is often preceded by a very thin layer of silty mottled strata. This mottled strata is sometimes termed the Zuni Mountains Formation, though the application of this term beyond the Zuni Mountains is questionable. In the Chama Basin at least, the mottled strata is derived from the eroded and pedogenically modified surface of the Moenkopi Formation. The coarse lower unit grades into the fine-grained
Salitral Formation The Salitral Formation is a Late Triassic geologic formation found in north-central New Mexico, primarily the northwestern Jemez Mountains. It is an older subunit of the Chinle Group (or formation), overlying the Shinarump Conglomerate and underl ...
, which is equivalent to the Blue Mesa Member and Bluewater Creek Formation. In south-central New Mexico, it may instead grade into the San Pedro Arroyo Formation, a similar heterolithic unit. Coarse sandstone returns along a sharp contact with the following
Poleo Formation The Poleo Formation is a geologic formation in northern New Mexico. Its stratigraphic position corresponds to the late Triassic epoch. Description The Poleo Formation is a cliff-forming formation composed mostly of yellowish-gray fine to medium ...
, an equivalent of the Sonsela Member. The Poleo Formation grades into the thick colorful sediments of the Petrified Forest Member. Authors which raise this member to a formation subdivide it into the lower Mesa Montosa Member and the upper Painted Desert Member. The Petrified Forest Member is fossiliferous in the Chama Basin, with major sites including the Hayden, Canjilon, and Snyder quarries of Ghost Ranch. 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 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 c ...
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 ''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 fro ...
''. The “siltstone member” may be equivalent to the Rock Point Member, and some authors refer to it as such.


Monument Valley and southern Utah

The Chinle continues northwards into southern Utah and the Four Corners area, though it thins greatly to the northwest. A narrow band of undifferentiated purplish sediments from the lower part of the formation extend into vicinity of
St. George Saint George (Greek: Γεώργιος (Geórgios), Latin: Georgius, Arabic: القديس جرجس; died 23 April 303), also George of Lydda, was a Christian who is venerated as a saint in Christianity. According to tradition he was a soldier ...
. The formation thickens eastward into
Zion National Park Zion National Park is an American national park located in southwestern Utah near the town of Springdale. Located at the junction of the Colorado Plateau, Great Basin, and Mojave Desert regions, the park has a unique geography and a variety ...
and
Grand Staircase–Escalante National Monument The Grand Staircase–Escalante National Monument (GSENM) is a United States national monument protecting the Grand Staircase, the Kaiparowits Plateau, and the Canyons of the Escalante (Escalante River) in southern Utah. It was established in 199 ...
. The Chinle is a prominent component of badlands and outcrops in the various national parks, monuments, and recreation areas of southeast Utah, extending in a discontinuous patchwork up to the
San Rafael Swell The San Rafael Swell is a large geologic feature located in south-central Utah, United States about west of Green River. The San Rafael Swell, measuring approximately , consists of a giant dome-shaped anticline of sandstone, shale, and limesto ...
. The stratigraphic nomenclature used in southern Utah is also utilized in
Monument Valley Monument Valley ( nv, Tsé Biiʼ Ndzisgaii, , meaning ''valley of the rocks'') is a region of the Colorado Plateau characterized by a cluster of sandstone buttes, the largest reaching above the valley floor. It is located on the Utah-Arizona s ...
, where the coarse-grained lower members of the Chinle form a caprock for many famous buttes which characterize the valley. In this region, the stratigraphically lowest unit in the Chinle is usually the Shinarump Conglomerate (or Shinarump Member), which thins northward but is a reliable component of outcrops throughout the region. In several areas, a thin layer of mottled
paleosols In the geosciences, paleosol (''palaeosol'' in Great Britain and Australia) is an ancient soil that formed in the past. The precise definition of the term in geology and paleontology is slightly different from its use in soil science. In geol ...
, the
Temple Mountain Member 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 N ...
, may be superimposed onto the Shinarump and underlying Moenkopi Formation. 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. The facies of this interval have been interpreted as overbank (distal
floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...
) and
lacustrine A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...
deposits. At Zion National Park, the Monitor Butte Member is replaced by a thick time-equivalent unit, the Cameron Member, which is also found in the Navajo Nation near its namesake of
Cameron, Arizona Cameron ( nv, ) is a census-designated place (CDP) in Coconino County, Arizona, United States, on the Navajo Nation. The population was 885 at the 2010 census. Most of the town's economy is tourist food and craft stalls, restaurants, and other ...
. The Cameron Member is practically identical to the Blue Mesa Member, and likely represents the same depositional environment along the ancient river system responsible for the Chinle Formation. It is also distinct from the Monitor Butte Member, which has more evaporite deposits and fewer red sandy layers. The drab mudstone of the Monitor Butte and Cameron members are succeeded in a few areas by a thin section of massive conglomeratic sandstone, the
Moss Back Member 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 ...
. This member represents sandy river channel deposits and is likely equivalent to part of the Sonsela Member. Elsewhere, the Monitor Butte grades into the Petrified Forest Member, which in Utah includes the thin but geographically extensive Correo Sandstone Bed. The Petrified Forest Member is followed by the Owl Rock Member. A unit of drab interbedded coarse and fine sediments, the Kane Springs beds, develops in the Paradox Basin. The Kane Springs beds are river deposits which are likely equivalent to the Owl Rock Member and the upper part of the Petrified Forest Member. Finally, either the Rock Point Member or Church Rock Member overlie the Owl Rock. Some researchers feel that the Church Rock and Rock Point members may be synonymous. They are complex heterolithic units, representing variously braided-river facies, lacustrine, and overbank deposits.


Chronology


Tetrapod biostratigraphy

The Chinle Formation is entirely
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 ...
in age. Tetrapod biostratigraphy for the Chinle was first developed based on
phytosaurs Phytosaurs (Φυτόσαυροι in greek) are an extinct group of large, mostly semiaquatic Late Triassic archosauriform reptiles. Phytosaurs belong to the order Phytosauria. Phytosauria and Phytosauridae are often considered to be equivalen ...
and aetosaurs, which in 1998 were combined into global biozones in
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 fossils ...
's
Land Vertebrate Faunachron Land vertebrate faunachrons (LVFs) are biochronological units used to correlate and date terrestrial sediments and fossils based on their tetrapod faunas. First formulated on a global scale by Spencer G. Lucas in 1998, LVFs are primarily used withi ...
s system. Simplified
stratigraphy Stratigraphy is a branch of geology concerned with the study of rock (geology), rock layers (Stratum, strata) and layering (stratification). It is primarily used in the study of sedimentary rock, sedimentary and layered volcanic rocks. Stratigrap ...
based on Litwin. Note that age inferrences devised by Lucas do not necessarily align with other chronological methods used in the Chinle Formation. Other works on Chinle biostratigraphy, such as Martz & Parker (2017), are better integrated with magnetostratigraphy and radiometric dating, and are considered more accurate.


Radiometric dating

Since 2011, widespread
radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares t ...
has helped to refine precise age data for part of the Chinle Formation, particularly in areas with a more complete stratigraphic record such as Petrified Forest National Park (PEFO). Volcanism further southwest along the Cordilleran magmatic arc supplies
zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of the r ...
crystals to the Chinle system, allowing for U-Pb dating of layers which host zircon grains. Eroded sediments from the
Ancestral Rocky Mountains The geology of the Rocky Mountains is that of a discontinuous series of mountain ranges with distinct geological origins. Collectively these make up the Rocky Mountains, a mountain system that stretches from Northern British Columbia through cen ...
,
Ouachita Mountains The Ouachita Mountains (), simply referred to as the Ouachitas, are a mountain range in western Arkansas and southeastern Oklahoma. They are formed by a thick succession of highly deformed Paleozoic strata constituting the Ouachita Fold and Thru ...
and Mogollon Highlands also supply older reworked zircon to the basin. Chinle radiometric dating is complicated by lithological quirks of zircon deposition. Taken at face value, U-Pb dates from coarse-grained layers are often several million years older than expected based on magnetostratigraphy, while mud-dominated layers are generally more accurate despite a lower sample size. This is likely because sandy rivers receive a higher proportion of recycled zircon grains from distant eroded rocks, while muddy plains are supplied with fresh zircon-rich ash from contemporary volcanic eruptions. While zircons from sandstone-rich layers are less useful for inferring direct depositional ages, they can be very useful for inferring sediment sources: each igneous or metamorphic sediment source has its own set of old (usually Precambrian) zircon ages, which can be traced in Triassic sediments. Outcrops of the Mesa Redondo Member at PEFO have been dated to ~225 Ma (2011) or ~228 Ma (2013), though these may be influenced by recycled grains. Later estimates from a major core drilling project support a more recent depositional age of 223-222 Ma (2020). This firmly suggests that practically all of the Chinle Formation was deposited in the
Norian The Norian is a division of the Triassic Period. It has the rank of an age (geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian. Stratigraphic defi ...
stage; According to the consensus "long Norian" hypothesis and radiometric assessments of marine strata, the Carnian-Norian boundary is tentatively set to ~227 Ma. At PEFO, U-Pb estimates from the
Blue Mesa Member The Blue Mesa Member is a member of the Chinle Formation. It is located in the Petrified Forest National Park of northeast Arizona. Geology The colorful bands of mudstone and sandstone were laid down during the Triassic, when the area was part of ...
include 223 Ma (2011), 222 Ma (2020), and 221-218 Ma (2020). Dated outcrops of drab mudstone near
St. Johns, Arizona Saint Johns ( nv, , )Wilson, A. ''Navajo Place Names'' Audio Forum 1995 is the county seat of Apache County, Arizona, United States. It is located along U.S. Route 180, mostly west of where that highway intersects with U.S. Route 191. As of t ...
fit this general time period as well. The fossiliferous ''Placerias'' quarry, previously regarded as belonging to an older subunit, is likely part of the Blue Mesa Member based on an age date of 219.4 Ma (2014). At Six Mile Canyon near
Fort Wingate, New Mexico Fort Wingate was a military installation near Gallup, New Mexico. There were two other locations in New Mexico called Fort Wingate: Seboyeta, New Mexico (1849–1862) and San Rafael, New Mexico (1862–1868). The most recent Fort Wingate (186 ...
, the base of the Blue Mesa Member (or its local equivalent) is defined by a distinct sandstone bed, which has been dated to 221-219 Ma (2009) or 218 Ma (2011). The underlying
Bluewater Creek Formation The Bluewater Creek Formation is a geologic formation in west-central New Mexico. It preserves fossils dating back to the late Triassic period. Description The formation consists of red sandstones and mudstones and has a total thickness in exce ...
has also been dated to 221-219 Ma (2014), suggesting that it overlaps in time with the Arizonan Blue Mesa Member and possibly part of the Sonsela Member. Radiometric dates are well-recorded for the Sonsela Member, though a high concentration of reworked zircons must be accounted for when inferring an accurate age of deposition. The true duration of the Sonsela Member is likely from around 218 Ma to 213 Ma (2020), though older estimates place its base at 220-219 Ma (2011, 2013). A prominant biological turnover is found at the Adamanian-Revueltian boundary in the middle of the Sonsela Member, around 214 Ma. It may correspond to a local extinction, or simply represents a time period which is truncated by slow deposition or a geological hiatus. The thin Sonsela Sandstone bed, the namesake of its corresponding member, has been dated to 216.6 Ma (2019) at its type locality at Sonsela Buttes in Arizona. The first Chinle U-Pb age data to be published referred to the Black Forest Bed, a sandstone layer near the top of the
Petrified Forest Member 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 (*) in ...
in PEFO. U-Pb estimates for this layer include ~213 Ma (2003 maximum), ~211 Ma (2009), and ~210 Ma (2011, 2020). A presumably older exposure of the Petrified Forest Member, the Hayden Quarry at Ghost Ranch, is dated to 212 Ma (2011). A similar age was found for the middle part of the member in PEFO. The end of the Petrified Forest Member was probably close to 208 Ma, meaning that overlying strata is presumably latest Norian-Rhaetian in age.


Places found

Geologic Province: Parklands: *
Arches National Park Arches National Park is a national park in eastern Utah, United States. The park is adjacent to the Colorado River, north of Moab, Utah. More than 2,000 natural sandstone arches are located in the park, including the well-known Delicate Arch, ...
*
Canyonlands National Park Canyonlands National Park is an American national park located in southeastern Utah near the town of Moab. The park preserves a colorful landscape eroded into numerous canyons, mesas, and buttes by the Colorado River, the Green River, and their r ...
– see
geology of the Canyonlands area The exposed geology of the Canyonlands area is complex and diverse; 12 formations are exposed in Canyonlands National Park that range in age from Pennsylvanian to Cretaceous. The oldest and perhaps most interesting was created from evaporites ...
*
Capitol Reef National Park Capitol Reef National Park is an American national park in south-central Utah. The park is approximately long on its northsouth axis and just wide on average. The park was established in 1971 to preserve of desert landscape and is open all ye ...
– see
geology of the Capitol Reef area The exposed geology of the Capitol Reef area presents a record of mostly Mesozoic-aged sedimentation in an area of North America in and around Capitol Reef National Park, on the Colorado Plateau in southeastern Utah. Nearly 10,000 feet (3, ...
*
Colorado National Monument Colorado National Monument is a National Park Service unit near the city of Grand Junction, Colorado. Sheer-walled canyons cut deep into sandstone and granite–gneiss–schist rock formations. This is an area of desert land high on the Colorad ...
*
Dinosaur National Monument Dinosaur National Monument is an American national monument located on the southeast flank of the Uinta Mountains on the border between Colorado and Utah at the confluence of the Green and Yampa rivers. Although most of the monument area is in ...
*
Flaming Gorge National Recreation Area Flaming Gorge National Recreation Area is a United States national recreation area in Wyoming and Utah. Its centerpiece is the long Flaming Gorge Reservoir. History The area was given the name "Flaming Gorge" by John Wesley Powell during his ...
*
Glen Canyon National Recreation Area Glen Canyon National Recreation Area (shortened to Glen Canyon NRA or GCNRA) is a national recreation area and conservation unit of the United States National Park Service that encompasses the area around Lake Powell and lower Cataract Canyon i ...
* Gold Butte National Monument *
Grand Canyon National Park Grand Canyon National Park, located in northwestern Arizona, is the 15th site in the United States to have been named as a national park. The park's central feature is the Grand Canyon, a gorge of the Colorado River, which is often consider ...
– see
geology of the Grand Canyon The geology of the Grand Canyon area includes one of the most complete and studied sequences of rock (geology), rock on Earth. The nearly 40 major sedimentary rock layers exposed in the Grand Canyon and in the Grand Canyon National Park area rang ...
*
Grand Staircase–Escalante National Monument The Grand Staircase–Escalante National Monument (GSENM) is a United States national monument protecting the Grand Staircase, the Kaiparowits Plateau, and the Canyons of the Escalante (Escalante River) in southern Utah. It was established in 199 ...
*
Lake Mead National Recreation Area Lake Mead National Recreation Area is a U.S. national recreation area in southeastern Nevada and northwestern Arizona. Operated by the National Park Service, Lake Mead NRA follows the Colorado River corridor from the westernmost boundary of Gran ...
*
Natural Bridges National Monument Natural Bridges National Monument is a U.S. National Monument located about northwest of the Four Corners boundary of southeast Utah, in the western United States, at the junction of White Canyon and Armstrong Canyon, part of the Colorado ...
*
Petrified Forest National Park Petrified Forest National Park is an American national park in Navajo County, Arizona, Navajo and Apache County, Arizona, Apache counties in northeastern Arizona. Named for its large deposits of petrified wood, the park covers about , encompassin ...
*
Red Fleet State Park Red Fleet State Park is a state park of Utah, United States, featuring a reservoir and a fossil trackway of dinosaur footprints. The park is located north of Vernal. Geography Red Fleet State Park lies at an elevation of in northeastern Ut ...
*
Wupatki National Monument The Wupatki National Monument is a United States National Monument located in north-central Arizona, near Flagstaff. Rich in Native American archaeological sites, the monument is administered by the National Park Service in close conjunction w ...
*
Zion National Park Zion National Park is an American national park located in southwestern Utah near the town of Springdale. Located at the junction of the Colorado Plateau, Great Basin, and Mojave Desert regions, the park has a unique geography and a variety ...
– see
geology of the Zion and Kolob canyons area The geology of the Zion and Kolob canyons area includes nine known exposed formations, all visible in Zion National Park in the U.S. state of Utah. Together, these formations represent about 150 million years of mostly Mesozoic-aged sediment ...
*
Red Rock Canyon National Conservation Area The Red Rock Canyon National Conservation Area in Clark County, Nevada, is an area managed by the Bureau of Land Management as part of its National Landscape Conservation System, and protected as a National Conservation Area. It is about west ...
Other: *
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 painti ...


See also

*
List of dinosaur-bearing rock formations This list of dinosaur-bearing rock formations is a list of geologic formations in which dinosaur fossils have been documented. Containing body fossils * List of stratigraphic units with dinosaur body fossils ** List of stratigraphic units with ...
*
Paleobiota of the Chinle Formation The Chinle Formation is an extensive geological unit in the southwestern United States, preserving a very diverse fauna of Late Triassic (primarily Norian-age) animals and plants. This is a list of fossilized organisms recovered from the formation. ...
*
Triassic land vertebrate faunachrons Land vertebrate faunachrons (LVFs) are biochronological units used to correlate and date terrestrial sediments and fossils based on their tetrapod faunas. First formulated on a global scale by Spencer G. Lucas in 1998, LVFs are primarily used withi ...


References


Further reading

* Lucas, S.G. (1998). "Global Triassic tetrapod biostratigraphy and biochronology". ''Palaeogeography, Palaeoclimatology, and Palaeoecology'', v. 143, pp. 347–384.


External links


Spatial distribution of Chinle in Macrostrat


{{Chronostratigraphy of Colorado, Mesozoic state=expanded Geologic formations of Nevada Triassic formations of New Mexico Triassic Colorado Geologic formations of Utah Triassic Arizona