The Organ Rock Formation or Organ Rock Shale is a formation within the
late Pennsylvanian
The Pennsylvanian ( , also known as Upper Carboniferous or Late Carboniferous) is, in the ICS geologic timescale, the younger of two subperiods (or upper of two subsystems) of the Carboniferous Period. It lasted from roughly . As with most oth ...
to
early Permian 01 or '01 may refer to:
* The year 2001, or any year ending with 01
* The month of January
* 1 (number)
Music
* '01 (Richard Müller album), 01'' (Richard Müller album), 2001
* 01 (Son of Dave album), ''01'' (Son of Dave album), 2000
* 01 (Urban ...
Cutler Group
The Cutler Formation or Cutler Group is a rock unit that is exposed across the U.S. states of Arizona, northwest New Mexico, southeast Utah and southwest Colorado. It was laid down in the Early Permian during the Wolfcampian epoch.
Descri ...
and is deposited across southeastern Utah, northwestern New Mexico, and northeastern Arizona. This formation notably outcrops around
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 ...
,
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 ...
, and
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 ...
of northeast Arizona, southern Utah. The age of the Organ Rock is constrained to the latter half of the
Cisuralian
The Cisuralian is the first Series (stratigraphy), series/Epoch (geology), epoch of the Permian. The Cisuralian was preceded by the Pennsylvanian (geology), Pennsylvanian and followed by the Guadalupian. The Cisuralian Epoch is named after the w ...
epoch by age dates from overlying and underlying formations. Important early terrestrial vertebrate fossils have been recovered from this formation in northern Arizona, southern Utah, and northern New Mexico. These include the iconic Permian terrestrial fauna: ''
Seymouria
''Seymouria'' is an extinct genus of seymouriamorph from the Early Permian of North America and Europe. Although they were amphibians (in a biological sense), ''Seymouria'' were well-adapted to life on land, with many reptilian features—so ...
'', ''
Diadectes
''Diadectes'' (meaning ''crosswise-biter'') is an extinct genus of large reptiliomorphs or synapsids that lived during the early Permian period (Artinskian-Kungurian stages of the Cisuralian epoch, between 290 and 272 million years ago). ''Diade ...
'', ''
Ophiacodon
''Ophiacodon'' (meaning "snake tooth") is an extinct genus of synapsid belonging to the family Ophiacodontidae that lived from the Late Carboniferous to the Early Permian in North America and Europe. The genus was named along with its type spec ...
'', and ''
Dimetrodon
''Dimetrodon'' ( or ,) meaning "two measures of teeth,” is an extinct genus of non-mammalian synapsid that lived during the Cisuralian (Early Permian), around 295–272 million years ago (Mya). It is a member of the family Sphenacodontid ...
''. The fossil assemblage present suggests arid environmental conditions. This is corroborated with
paleoclimate
Paleoclimatology (British spelling, palaeoclimatology) is the study of climates for which direct measurements were not taken. As instrumental records only span a tiny part of Earth's history, the reconstruction of ancient climate is important to ...
data indicative of global drying throughout the early Permian.
Geographic extent
The Organ Rock Formation is present across southeastern Utah, U.S.A. It outcrops around
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 ...
,
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 ...
, and
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 ...
.
In these areas the Organ Rock typically outcrops as a dark-red/brown
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, p ...
to
mudstone
Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...
gently dipping towards the southeast. Within Canyonlands N.P. it forms towers which are meters to tens of meters tall. These are protected by caps of the
White Rim Sandstone
The White Rim Sandstone is a sandstone geologic formation located in southeastern Utah. It is the last member of the Permian Cutler Group, and overlies the major Organ Rock Formation and Cedar Mesa Sandstone; and again overlies thinner units of ...
. In general, the Organ Rock Formation records the evolution of terminal
fluvial fan
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 fluvio ...
s, which dry up into sections of overlying formations.
Animals living during the time of the Organ Rock's deposition had the capacity to travel across most of earth's landmass, as at the time, land was all concentrated into the supercontinent
Pangea
Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million y ...
.
Stratigraphy and age
The Organ Rock Formation is
conformably
Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology.
In general, strata are primarily igne ...
underlain by the
Cedar Mesa Sandstone
Cedar Mesa Sandstone (also known as the Cedar Mesa Formation) is a sandstone memberThe Cutler Formation is sometimes classified as the Cutler Group, in which case Cedar Mesa Sandstone is classified as a formation rather than a member. of the Cutle ...
.
[ It is conformably overlain by the ]De Chelly Sandstone
The Yeso Group is a group of geologic formations in New Mexico. It contains fossils characteristic of the Kungurian Age of the early Permian Period.
Description
The Yeso Group is lithologically complex, ranging from marine shelf carbon ...
around 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 ...
and by the White Rim Sandstone
The White Rim Sandstone is a sandstone geologic formation located in southeastern Utah. It is the last member of the Permian Cutler Group, and overlies the major Organ Rock Formation and Cedar Mesa Sandstone; and again overlies thinner units of ...
in the 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 ...
. In locations where the De Chelly and White Rim are absent, the Organ Rock is unconformably overlain by the Triassic
The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...
Moenkopi or 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 Ne ...
s by an erosional contact. Toward its eastern extent, the Organ Rock Formation grades into the Cutler Formation
The Cutler Formation or Cutler Group is a rock unit that is exposed across the U.S. states of Arizona, northwest New Mexico, southeast Utah and southwest Colorado. It was laid down in the Early Permian during the Wolfcampian epoch.
Descript ...
, undivided. This transition occurs to the southwest of Moab, UT
Moab () is the largest city and county seat of Grand County in eastern Utah in the western United States, known for its dramatic scenery. The population was 5,366 at the 2020 census. Moab attracts many tourists annually, mostly visitors to th ...
.
The age of the Organ Rock Formation is unconfirmed. The preceding Cedar Mesa Sandstone is dated to the Wolfcampian
The Cisuralian is the first Series (stratigraphy), series/Epoch (geology), epoch of the Permian. The Cisuralian was preceded by the Pennsylvanian (geology), Pennsylvanian and followed by the Guadalupian. The Cisuralian Epoch is named after the w ...
(ICS stage: Artinskian
In the geologic timescale, the Artinskian is an age or stage of the Permian. It is a subdivision of the Cisuralian Epoch or Series. The Artinskian likely lasted between and million years ago (Ma) according to the most recent revision of the ...
). The anteceding De Chelly and White Rim Sandstone
The White Rim Sandstone is a sandstone geologic formation located in southeastern Utah. It is the last member of the Permian Cutler Group, and overlies the major Organ Rock Formation and Cedar Mesa Sandstone; and again overlies thinner units of ...
s are dated to the Leonardian
In the geologic timescale, the Kungurian is an age or stage of the Permian. It is the latest or upper of four subdivisions of the Cisuralian Epoch or Series. The Kungurian lasted between and million years ago (Ma). It was preceded by the Artin ...
(ICS stage: Kungurian
In the geologic timescale, the Kungurian is an age or stage of the Permian. It is the latest or upper of four subdivisions of the Cisuralian Epoch or Series. The Kungurian lasted between and million years ago (Ma). It was preceded by the Artin ...
). These formations constrain the age of the Organ Rock Formation to the latter part of the Cisuralian
The Cisuralian is the first Series (stratigraphy), series/Epoch (geology), epoch of the Permian. The Cisuralian was preceded by the Pennsylvanian (geology), Pennsylvanian and followed by the Guadalupian. The Cisuralian Epoch is named after the w ...
Epoch, approximately 290.1 to 272.3 Ma. The Organ Rock Formation may contain the Artinskian
In the geologic timescale, the Artinskian is an age or stage of the Permian. It is a subdivision of the Cisuralian Epoch or Series. The Artinskian likely lasted between and million years ago (Ma) according to the most recent revision of the ...
/Kungurian
In the geologic timescale, the Kungurian is an age or stage of the Permian. It is the latest or upper of four subdivisions of the Cisuralian Epoch or Series. The Kungurian lasted between and million years ago (Ma). It was preceded by the Artin ...
boundary. This is during the early to mid-Permian, a time where synapsid
Synapsids + (, 'arch') > () "having a fused arch"; synonymous with ''theropsids'' (Greek, "beast-face") are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids, the group that includes reptil ...
s and temnospondyl
Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order (biology), order of small to giant tetrapods—often considered Labyrinthodontia, primitive amphi ...
amphibians are the dominant players in terrestrial ecosystems. These animals predate the advent of archosaur
Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avian d ...
reptiles which give rise to dinosaurs in the Triassic.
Depositional environments
The Organ Rock Formation is composed of 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) ...
s, 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, p ...
s, conglomerates, and mudstone
Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...
s.[ These rocks occur in two primary ]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 ...
: 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 channel, as well as eolian dunes and sand sheets.
Floodplain and channel
In these deposits, mixed reddish-brown sands and silts dominate with minor mudstones and conglomerates interspersed.[ Interpreted channel deposits grade from laterally accreting coarse sands – into conglomerates of pebble-sized ]carbonate
A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...
clast
Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks ...
s. Channels are 0.5 meter to 7 meters thick and may extend laterally for a few hundred meters. Fine-grained silt to mudstone deposits are proximal to interpreted channels. These deposits are interpreted as meandering streams with associated floodplains.
Eolian dune and sand sheet
Deposits are characterized by pale red fine- to medium-grained sandstones.[ These units are cross-bedded. Each cross-bed is composed of thin, consistently spaced laminations. These strata are interpreted as those made by migrating ]dune
A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, f ...
s. This facies is marked by a sharp contact at the top of the preceding floodplain and channel facies. Mud cracks found at the top of the facies are filled by fine-grained sand from the overlying dune facies. This facies is most common at the western extent of the Organ Rock Formation.
Plant fossils
Plant fossils include ''Supaia
''Supaia'' is an extinct genus of fern-like plants, possibly seed ferns. Species belonging to the genus lived during the Permian
The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the ...
'', '' Walchi'' and '' Yakia'' which lived in semi-arid conditions.
Vertebrate fossils
Fossil vertebrates represent the majority of the faunal assemblage present in the Organ Rock Formation.[Sumida, Stuart S., Lombard, B. Eric, Berman, David S., Henrici, Amy C., 1999b, Late Paleozoic amniotes and their near relatives from Utah and northeastern Arizona, with comments on the Permian – Pennsylvanian boundary in Utah and northern Arizona: Miscellaneous Publication- Utah Geological Survey, v. 99(1), p. 21 – 30.] Animal remains are most commonly preserved within ancient stream channels of the floodplain and channel facies. Within this facies, fossilized bone occurs proximal to conglomeratic lenses. Taxa recovered include: freshwater actinopterygian
Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species.
The ray-finned fishes are so called because their fins are webs of skin supported by bony or ho ...
fishes, temnospondyl
Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order (biology), order of small to giant tetrapods—often considered Labyrinthodontia, primitive amphi ...
amphibians, diadectomorph
Diadectomorpha is a clade of large tetrapods that lived in Euramerica during the Carboniferous and Early Permian periods and in Asia during Late Permian (Wuchiapingian), They have typically been classified as advanced reptiliomorphs (transitional ...
s, seymouriamorph
Seymouriamorpha were a small but widespread group of limbed vertebrates (tetrapods). They have long been considered reptiliomorphs, and most paleontologists may still accept this point of view, but some analyses suggest that seymouriamorphs are s ...
s, and early synapsid
Synapsids + (, 'arch') > () "having a fused arch"; synonymous with ''theropsids'' (Greek, "beast-face") are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids, the group that includes reptil ...
s.
Freshwater Actinopterygian fishes
Fossil fish material, either bone or scale, is infrequent within the Organ Rock Formation.[ Scales from the extinct group of fishes Palaeoniscoidea are present. These scales, however, are only found preserved in fossilized feces (]coprolite
A coprolite (also known as a coprolith) is fossilized feces. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour (in this case, diet) rather than morphology. The name is de ...
s). Some coprolites are interpreted to be from fish; others from indeterminate terrestrial vertebrates.
Temnospondyls
Temnospondyl
Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order (biology), order of small to giant tetrapods—often considered Labyrinthodontia, primitive amphi ...
amphibian remains are present within the Organ Rock Formation.[ Three taxa have been reported. These include: '']Trimerorhachis
''Trimerorhachis'' is an extinct genus of dvinosaurian temnospondyl within the family Trimerorhachidae. It is known from the Early Permian of the southwestern United States, with most fossil specimens having been found in the Texas Red Beds. Th ...
'', ''Eryops
''Eryops'' (; from Greek , , 'drawn-out' + , , 'face', because most of its skull was in front of its eyes) is a genus of extinct, amphibious temnospondyls. It contains the single species , the fossils of which are found mainly in early Permian (a ...
'', and '' Zatrachys''. Of these three taxa, fragments of Eryops are the most commonly recovered. Remains of this animal are very common in other formations of the Cutler Group
The Cutler Formation or Cutler Group is a rock unit that is exposed across the U.S. states of Arizona, northwest New Mexico, southeast Utah and southwest Colorado. It was laid down in the Early Permian during the Wolfcampian epoch.
Descri ...
and in general during the Early Permian of southwestern North America.
Diadectomorphs
Diadectomorph
Diadectomorpha is a clade of large tetrapods that lived in Euramerica during the Carboniferous and Early Permian periods and in Asia during Late Permian (Wuchiapingian), They have typically been classified as advanced reptiliomorphs (transitional ...
s are medium to large (2–3 meters), heavily-built reptiliomorph
Reptiliomorpha (meaning reptile-shaped; in PhyloCode known as ''Pan-Amniota'') is a clade containing the amniotes and those tetrapods that share a more recent common ancestor with amniotes than with living amphibians ( lissamphibians). It was de ...
s with robust limbs. These animals are thought to be the closest outgroup to the clade Amniota
Amniotes are a clade of tetrapod vertebrates that comprises sauropsids (including all reptiles and birds, and extinct parareptiles and non-avian dinosaurs) and synapsids (including pelycosaurs and therapsids such as mammals). They are distingu ...
. Two taxa are present within the Organ Rock Formation: ''Diadectes
''Diadectes'' (meaning ''crosswise-biter'') is an extinct genus of large reptiliomorphs or synapsids that lived during the early Permian period (Artinskian-Kungurian stages of the Cisuralian epoch, between 290 and 272 million years ago). ''Diade ...
'', and '' Tseajaia campi''.
''Diadectes'' is more abundant in the Organ Rock than the other formations of the Cutler Group. Fragments of the animal are most commonly reported. The most complete two specimens include pectoral girdles and limbs. These were collected in San Juan County, Utah. ''Diadectes'' is an important animal as it is the first terrestrial vertebrate to demonstrate characteristics necessary for obligatory herbivory
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
. These include: peg-shaped teeth in the front of the mouth, as well as broad blunt teeth used to more effectively process vegetation.
'' Tseajaia campi'' is a very rare taxon known from one nearly complete specimen recovered from the Organ Rock. Originally described by Vaughn,[ this animal was first assigned to the group ]Seymouriamorpha
Seymouriamorpha were a small but widespread group of limbed vertebrates (tetrapods). They have long been considered reptiliomorphs, and most paleontologists may still accept this point of view, but some analyses suggest that seymouriamorphs are ...
, however, upon reassessment of the holotype it was demonstrated to have a closer affinity to Diadectomorpha.
Seymouriamorphs
Seymouriamorph
Seymouriamorpha were a small but widespread group of limbed vertebrates (tetrapods). They have long been considered reptiliomorphs, and most paleontologists may still accept this point of view, but some analyses suggest that seymouriamorphs are s ...
s are small- to medium- sized (0.5 to 1.5 meters), reptiliomorphs. These animals have a generalized early amphibian body plan with a large “u”-shaped head and a sprawling lizard-like posture. The taxon '' Seymouria sanjuanensis'' is the only seymouriamorph found in the Organ Rock Formation.
''Seymouria sanjuanensis'' is a unique taxon because of its extensive geographic range. This particular animal was first described by Vaughn (1966)[ from the Organ Rock Formation. Since this initial find, a number of these individuals have been recovered from localities as distant as Germany.][Benton, Michael J., 2015, Vertebrate Palaeontology: Wiley-Blackwell, Oxford, 4th edition.]
Early Synapsids
Four early synapsid taxa are present within the Organ Rock Formation. These include ''Ophiacodon
''Ophiacodon'' (meaning "snake tooth") is an extinct genus of synapsid belonging to the family Ophiacodontidae that lived from the Late Carboniferous to the Early Permian in North America and Europe. The genus was named along with its type spec ...
'', as well as three sphenacodontid
Sphenacodontidae (Greek: "wedge point tooth family") is an extinct family (biology), family of small to large, advanced, carnivore, carnivorous, Late Pennsylvanian to Guadalupian, middle Permian pelycosaurs. The most recent one, ''Dimetrodon ang ...
s: ''Ctenospondylus
''Ctenospondylus'' ("comb vertebra") is an extinct genus of sphenacodontid synapsid
Species were about three meters (ten feet) long. The genus is known only from the 'Seymouran' Land Vertebrate Faunachron, which is equivalent to the upper part ...
'', ''Dimetrodon
''Dimetrodon'' ( or ,) meaning "two measures of teeth,” is an extinct genus of non-mammalian synapsid that lived during the Cisuralian (Early Permian), around 295–272 million years ago (Mya). It is a member of the family Sphenacodontid ...
'', and '' Sphenacodon ferocior''. Most taxa are known from fragmentary material.
Early synapsids were dominant members of the terrestrial Permian ecosystem. Some early synapsids adapted an herbivorous diet, however, the Organ Rock Formation only preserves carnivorous animals; these were likely the apex predator
An apex predator, also known as a top predator, is a predator at the top of a food chain, without natural predators of its own.
Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the highest trophic lev ...
s of this ecosystem. The three sphenacodontid
Sphenacodontidae (Greek: "wedge point tooth family") is an extinct family (biology), family of small to large, advanced, carnivore, carnivorous, Late Pennsylvanian to Guadalupian, middle Permian pelycosaurs. The most recent one, ''Dimetrodon ang ...
s were terrestrial predators consuming other tetrapods, while ''Ophiacodon'' likely hunted fishes and other aquatic animals.
Coprolites
Coprolite
A coprolite (also known as a coprolith) is fossilized feces. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour (in this case, diet) rather than morphology. The name is de ...
s associated with a labyrinthodont
"Labyrinthodontia" (Greek, 'maze-toothed') is an informal grouping of extinct predatory amphibians which were major components of ecosystems in the late Paleozoic and early Mesozoic eras (about 390 to 150 million years ago). Traditionally consid ...
tooth as well as “Pelycosaur
Pelycosaur ( ) is an older term for basal or primitive Late Paleozoic synapsids, excluding the therapsids and their descendants. Previously, the term ''mammal-like reptile'' had been used, and pelycosaur was considered an order, but this is no ...
” and didectid remains have been recovered from this formation.
Paleoecological significance
The vertebrate faunal assemblage found in the Organ Rock Formation is diverse with respect to taxonomic groups, body plans, and diets. This material represents a decent cross-section of what terrestrial vertebrate life was like during the early Permian
The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...
. It is noteworthy that no diapsid
Diapsids ("two arches") are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The group first appeared about three hundred million years ago ...
material has been definitively recovered from this formation.
As one moves younger in time through the Organ Rock Formation, temnospondyl
Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order (biology), order of small to giant tetrapods—often considered Labyrinthodontia, primitive amphi ...
s become less abundant with respect to other major groups such as diadectomorph
Diadectomorpha is a clade of large tetrapods that lived in Euramerica during the Carboniferous and Early Permian periods and in Asia during Late Permian (Wuchiapingian), They have typically been classified as advanced reptiliomorphs (transitional ...
s and early synapsid
Synapsids + (, 'arch') > () "having a fused arch"; synonymous with ''theropsids'' (Greek, "beast-face") are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids, the group that includes reptil ...
s.[ This could track the general trend of ]aridification
Aridification is the process of a region becoming increasingly arid, or dry. It refers to long term change, rather than seasonal variation.
It is often measured as the reduction of average soil moisture content.
It can be caused by reduced precip ...
as indicated by sedimentology of the formation. This trend is globally recognized during the Early Permian, supported by many lines of geologic evidence including significant deposits of calcrete
Caliche () is a sedimentary rock, a hardened natural cement of calcium carbonate that binds other materials—such as gravel, sand, clay, and silt. It occurs worldwide, in aridisol and mollisol soil orders—generally in arid or semiarid regions, ...
s, eolianite
Eolianite or aeolianite is any rock formed by the lithification of sediment deposited by aeolian processes; that is, the wind. In common use, however, the term refers specifically to the most common form of eolianite: coastal limestone consisting ...
s, and evaporite
An evaporite () is a water-soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as ocea ...
s.[Tabor, Neil J., and Poulsen, Christopher J., 2008, Palaeoclimate across the Late Pennsylvanian _ early Permian tropical palaeolatitudes: A review of climate indicators, their distribution, and relation to palaeophysiographic climate factors: Palaeogeography, Palaeoclimatology, Palaeoecology, 268, p. 293 – 310.]
External links and Gallery
File:Monument Valley (15).jpg, Typical Organ Rock angled skirts,
below De Chelly Sandstone
The Yeso Group is a group of geologic formations in New Mexico. It contains fossils characteristic of the Kungurian Age of the early Permian Period.
Description
The Yeso Group is lithologically complex, ranging from marine shelf carbon ...
,
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 ...
File:Monument Valley Navajo Tribal Park. The Three Sisters (2).jpg, Angled skirts of Organ Rock,
at base of De Chelly Sandstone
The Yeso Group is a group of geologic formations in New Mexico. It contains fossils characteristic of the Kungurian Age of the early Permian Period.
Description
The Yeso Group is lithologically complex, ranging from marine shelf carbon ...
vertical massive cliffs
References
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Permian Arizona
Geologic formations of Utah
Permian formations of New Mexico
Geologic formations of Arizona
Canyonlands National Park
Cutler Formation