Chinle-Formation

The Chinle Formation is a lithostratigraphic rock unit of sedimentary origin, during the Upper Triassic period around 228-200 million years ago in the U.S. states of Arizona (north), Colorado ( west), Nevada, New Mexico ( west) and Utah to deposit came. Geologically, it is part of the Colorado Plateau, the Basin and Range and the southern sector of the Interior Plains.

4.1 sauropods
4.2 theropods

Stratigraphy

History

The Chinle Formation has no type locality. It was named in 1917 by Gregory after the Chinle Valley in Apache County, Arizona ( although he had two years earlier been used the same name, but at that time not yet expressed interest in a scientific recognition ). Layer members (Member) were for the first time in 1956 by Robeck and separated from Stewart in 1957. Poole and Stewart started in 1964 an overview. Sikich led in 1965 by revising the formation and different at the same time other members of. The geographical expansion was auskartiert by Wilson and Stewart 1967. Stewart et al attended prior to 1972 changes to the geographic expansion and published in the same year a revision. Kelley introduced in 1972 another layer limbs and revised the lineup. This was repeated by Lucas and Hayden 1989. Dubiel led the 1989 Rock Point Members.

1993 brought Lucas the formation of the group and thus were members of laminated formations. He also integrated the Dockum Group of eastern New Mexico and western Texas to the newly Chinle Group. His approach is controversial, and many geologists and also the USGS continue to hold firmly to the concept of formation and differ continue the Dockum Group. The Dockum Group was first described in 1890, long before the Chinle formation. Under current practice stratigraphischem the Chinle Group should therefore be actually incorporated into the Dockum Group and not vice versa.

General overviews were from Dubiel et al in 1992 and written by Hintze and Axen in 1995.

General overview

After the decay of the Sonoma orogeny, the Sonoma Mountains were lifted on the border of California and cordoned off a shallow sea basin to the west. The former West Coast went into north-south direction through Zentralnevada. However, deposited in the east adjoining flat hinterland Chinle Formation is purely continental origin ( red beds ), it consists mainly of sandstones, shales and occasional Frischwasserkalken. The sediments were either deposited in rivers with the associated floodplains and flood plains or in lakes, marshes and deltas. The lowest layer member Shinarump member, filled with gravel and coarse sandstones huge paleo- river valleys, which had cut deep into the overlying Moenkopi Formation below. It formed a dehydrating to the northwest river system, the so-called Chinle River. He probably had its origin in the Amarillo - Wichita Uplift in northwestern Texas. In northern New Mexico, he flowed through a barrier from the Pedernal Uplift in the south and the Uncompahgre Uplift to the north, and to finally culminate in northern Nevada in the sea basin. This mighty river system is likely to have passed almost to the end of the Chinle formation.

Switched to the largely fluvial sediments, there are also volcanic deposits, mostly ash but also pebbles. Area of origin of the volcanic component were probably located south of the Mogollon Rim and the magmatic island arc at the southwest edge of the American continent. For these volcanics easily herauszulösendes silicon for example, was responsible for the silicification of tree trunks in Petrified Forest Member, and thus their unique preservation.

The climatic conditions are due to the situation at that time in North America near the equator as tropical and humid. Towards the end of the Chinle time the climate became drier and it arose pronounced dry seasons to see the occasional low-tide marshes of the Petrified Forest Member. At the same time, there was a gradual withdrawal of the Absaroka - Sea to the west.

Structure

The Chinle formation usually superimposed unconformably the top layer members of the Moenkopi Formation, only in southwestern Colorado she reaches down even to the Cutler formation. The layer gap formed approximately represents a period of 20 to 25 million years ( the minimum value). The Chinle Formation is in turn unconformably covered by the Moenave lineup or from the Wingate Sandstone of the Glen Canyon Group.

As a stratigraphically lowest unit, the Temple Mountain member is conducted, although it is still underlain in most areas of the Shinarump member. The Shinarump member consists of a river sediments Zopfstromfazies. It in turn is usually overlaid by the Monitor Butte member, a distal Auenfazies with intercalated lacustrine sediments. To the west of the fluvial depositional environment on the Moss Back Members follows. However, the Monitor Butte Members Usually gradually changes into the Petrified Forest Member. The Petrified Forest Member consists mainly of overflow sediments, in which thin lenses of riverbed and lake sediments occur. In Arizona and New Mexico, it is divided by the Sonsela - Sandstone member in a lower - Petrified Forest Member and an Upper - Petrified Forest Member. The Sonsela - Sandstone Members also consists Zopfstromablagerungen. The Petrified Forest Member shows a gradual transition to the Owl Rock Member - marginal lacustrine to lacustrine sediments full of a possibly very large inland lake. On the Owl Rock Members eventually follow either the Rock Point Members or the Church Rock Members. There is suspicion is expressed that the two layer elements are synonymous. These both are complex structure, plurifazielle sediment body ( Zopfstrom, sea and overflow sediments ).

Sequenzstratigraphisch can the Chinle Formation into three sequences, which can be separated from each other by unconformities. At the bottom are conglomerates and sandstones of eroding rivers. In follow clayey sediments of a floodplain with formation of paleosols. The third sequence consists of alternating siltstones and fine-grained sandstones; it is a trend towards increasingly aeolian conditions.

Age

On the basis of the fossil record of the Chinle Formation of the lower Carnium period can be assigned to Rhaetian, ie an absolute age of approximately 228 bis 200 million years BP.

Absolute ages are so far relatively rare. From the top member is a U / Pb age dates of 207 ± 2 MA BP from reclaimed tuffs. The Black Forest Bed, a tuffhaltige sandstone located in the Upper Petrified Forest Member revealed by U / Pb dating of 213 ± 1.7 MA BP.

The following biostratigraphic age correlations on the established Lucas land vertebrate biozones (English country vertebrate faunachron - LVF ) are based. These biozones are based on the initial or last occurrence of Phytosauriern. The somewhat simplified stratigraphy is based on Litwin.

To call at the same time in some rock units were the Newark supergroup with a very similar fauna in the eastern United States, the Santa Maria Formation and the Caturrita formation in Brazil and the Middle Keuper in Germany.

Cardinality

Their maximum thickness of about 520 meters reaches the Chinle Formation in the southern part of their Sedimentationsraumes. The individual layer members of the Chinle Formation are subject to this strong thickness changes.

Layer links

With group status ( in alphabetical order - is not recognized by the USGS)

Petrified Forest Formation ( AZ, UT, NM)
San Pedro Arroyo Formation ( NM)
Santa Rosa Formation ( NM)
Shinarump Formation ( NM).
Many more

With formation status ( in alphabetical order - Members without an asterisk (* ) are not recognized by the USGS)

Agua Zarca - Sandstone Member ( NM)
Bluewater Creek Member ( AZ, CO, NM)
Church Rock Member ( AZ *, CO *, UT *)
Correo - Sandstone Member ( NM)
Cuervo Sandstone Member ( NM)
Duffin - Sandstone Member ( UT)
Gartra Member ( CO *, UT *)
Mesa Redondo Member ( AZ *, NM *)
Monitor Butte Member ( AZ *, CO *, UT *)
Moss Back Member ( AZ *, CO *, UT *)
Newspaper Rock Sandstone Bed ( AZ)
Owl Rock Member ( AZ *, NM *, UT *)
Petrified Forest Member ( AZ *, CO *, NV *, NM *, UT *)
Poleo - Sandstone Lentil (NM )
Redonda Member ( NM)
Rock Point Member ( AZ *, NM *)
Salitral Shale Tongue (NM *),
Shinarump Member ( AZ *, NV *, NM *, UT *)
Silver Reef Sandstone Member ( UT)
Stanaker Members (UT )
Temple Mountain Member ( UT *)
Trail -Hill Sandstone Member ( UT)

Occurrence

The Chinle formation occurs in the following geological Sedimentationsräumen:

Black Mesa Basin
Great Basin
Geen River Basin
Las-Vegas-Becken/Raton-Becken
Orogrande Basin
Palo Duro Basin
Paradox Basin
Permian Basin
Piceance Basin
San Juan Basin
Sierra Grande Uplift
Uinta Basin
Uinta Uplift
Wasatch Uplift

Furthermore, in the following national parks and parks (incomplete listing):

Canyonlands National Park - see geology of the Canyonlands
Capitol Reef National Park - see geology of the Capitol Reef
Glen Canyon National Recreation Area - see geology of the Glen Canyon
Petrified Forest National Park - see geology of the Petrified Forest National Park
Zion National Park - see geology of the Zion National Park

The equivalence of the Chinle Formation to the Dockum Group in eastern Colorado, eastern New Mexico, southwestern Kansas, western Texas and the Oklahoma Panhandle is still controversial. In New Mexico and sometimes Texas in the Chinle Formation is something freely out as a formation within the Dockum Group.

In northwestern Colorado and northeastern Utah the Chinle Formation occupies a separate detached sedimentation.

Paleosols

In the Chinle Formation, the diverse growth stages and types of paleosols are observed. To form came Calcisole, Gleye, clayey tropical soil, calcareous desert soils and Luvisols.

Calcareous desert soils: Church Rock Members
Calcisole: Owl Rock, and Church Rock Members
Loamy tropical soil: Monitor Butte and Petrified Forest Members
Luvisols: Monitor Butte and Petrified Forest Members
Gleye: Shinarump Members

The retrieved soil types reflect an unambiguous way the increasing aridity in the upper layer links.

Fossil content

The Chinle Formation has a very rich vertebrate fauna. It is the oldest formation in North America, the real dinosaur walks (eg Coelophysis ). In addition to numerous theropods and sauropods also contains Ornithischia ( Krzyzanowskisaurus ). Available also are Aetosaurier, amphibians, Archisauriformes, archosaurs, Dicynodontier, primitive crocodiles and numerous Phytosauria. Also remains of real bone fish, lungfish ( Arganodus ) and freshwater sharks ( Lissodus and Xenacanthus ) are to be found.

Vertebrates

Aetosaurier Acaenosuchus geoffreyi
Calyptosuchus wellesi
Desmatosuchus smalli
Desmatosuchus spurensis
Heliocanthus chamaensis
Paratypothorax
Rioarribasuchus chamaensis
Stagonolepis
Typothorax

Apachesaurus
Koskinodon
Metoposaurus fraasi

Acallosuchus Rectori
Vancleavea campi

Chatterjeea
Poposaurus gracilis
Postosuchus
Revueltosaurus callenderi
Shuvosaurus
Trilophosaurus dornorum

Placerias

Hesperosuchus agilis
Parrishia mccreai
Sphenosuchus

Leptosuchus adamanensis
Leptosuchus crosbiensis
Pseudopalatus Buceros
Pseudopalatus jablonskiae
Pseudopalatus macauleyi
Pseudopalatus pristinus
Rutiodon
Smilosuchus gregorii

Noteworthy is the Petrified Forest Member with its huge silicified conifer tree trunks ( Araucarioxylon arizonicum ), reaching up to 60 meters, as well as the reference Ghost Ranch in northern New Mexico, were swept along in the thousands of Coelophysis.

In the Chinle Formation is also found very many trace fossils. Among the tracks of large amphibians, of various archosaurs such as Anchisauripus sillimani and Rhynchosauroides, from small primitive dinosaurs (caused by Coelophysis ) of prosauropods and mammal-like reptiles. The Grallatorfährten (small dinosaurs) are in the top layers of the Chinle Formation and more frequently. Also coprolites occur.

To call on invertebrates are gastropods, bivalves and ostracods.

The Chinle Formation also contains numerous tracks and buildings of invertebrates such as annelids, crayfish, insects ( Hymenoptera ), beetles, millipedes and even termites ( first appearance in the fossil record ).

Examples of buildings are:

Archeoentomoichnos - termites
Camborygma - crayfish
Cylindricum -
Scoyenia - insect larvae

The plant remains are very diverse, so can the Chinle Formation has over 70 different plant taxa. Available include Bärlapppflanzen such as Chinlea and Seleginella anasazia, tree ferns as Itopsidema, Bennettiteen as Zamites powellii, ferns as Cladophlebis, Cynepteris lasiophora and Phlebopteris smithii, ginkgo as Baiera arizonica and Ginkgoites, conifers, such as Araucariaxylon arizonicum, Arboramosa semicircumtrachea, Brachyphyllum, Dechellyia gormanii, Dinophyton, Masculostrobus clathratus, Pagiophyllum, Schilderia adam anica and Woodworthia arizonica, cycads as Charmorgia, Eoginkgoites davidsonii and Zamites powellii and horsetails as Neocalamites.

Pollen and spores impress with an enormous biodiversity.

Also worth mentioning is the occurrence of amber (oldest amber Fund of North America ), unfortunately so far without fossil content.