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Kayenta Formation
Kayenta Formation
Kayenta Formation
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Kayenta Formation west of Tuba City, Arizona.

Key Information

The Kayenta Formation is a geological formation in the Glen Canyon Group that is spread across the Colorado Plateau area of the United States, including northern Arizona, northwest Colorado, Nevada, and Utah. Originally suggested as being Sinemurian-Pliensbachian, but more recent dating of detrital zircons has yielded a depositional age of 183.7 ± 2.7 Ma, thus a Pliensbachian-Toarcian age is more likely.[2] A previous depth work recovered a solid "Carixian" (Lower-Middle Pliensbachian) age from measurements done in the Tenney Canyon.[3] More recent works have provided varied datations for the layers, with samples from Colorado and Arizona suggesting 197.0±1.5-195.2±5.5 Ma (Middle Sinemurian), while the topmost section is likely Toarcian or close in age, maybe even recovering terrestrial deposits coeval with the Toarcian Oceanic Anoxic Event.[4] This last age assignation also correlated the Toarcian Vulcanism on the west Cordilleran Magmatic Arc, as the number of grains from this event correlate with the silt content in the sandstones of the upper layers.[4]

This rock formation is particularly prominent in southeastern Utah, where it is seen in the main attractions of a number of national parks and monuments. These include Zion National Park, Capitol Reef National Park, the San Rafael Swell, and Canyonlands National Park.

The Kayenta Formation frequently appears as a thinner dark broken layer below Navajo Sandstone and above Wingate Sandstone (all three formations are in the same group). Together, these three formations can result in immense vertical cliffs of 600 metres (2,000 ft) or more. Kayenta layers are typically red to brown in color, forming broken ledges.

Kayenta Formation in Utah

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Southeast Utah

[edit]
Redbeds including the Kayenta Formation and the Navajo Sandstone in Kolob Canyons, Zion National Park, Utah, USA
The Permian through Jurassic stratigraphy of the Colorado Plateau area of southeastern Utah that makes up much of the famous prominent rock formations in protected areas such as Capitol Reef National Park and Canyonlands National Park. From top to bottom: Rounded tan domes of the Navajo Sandstone, layered red Kayenta Formation, cliff-forming, vertically jointed, red Wingate Sandstone, slope-forming, purplish Chinle Formation, layered, lighter-red Moenkopi Formation, and white, layered Cutler Formation sandstone. Picture from Glen Canyon National Recreation Area, Utah.

In most sections that include all three geologic formations of the Glen Canyon group the Kayenta is easily recognized. Even at a distance it appears as a dark-red, maroon, or lavender band of thin-bedded material between two thick, massive, cross bedded strata of buff, tan, or light-red color. Its position is also generally marked by a topographic break. Its weak beds form a bench or platform developed by stripping the Navajo sandstone back from the face of the Wingate cliffs. The Kayenta is made up of beds of sandstone, shale, and limestone, all lenticular, uneven at their tops, and discontinuous within short distances. They suggest deposits made by shifting streams of fluctuating volume. The sandstone beds, from less than 25 millimetres (1 in) to more than 3 metres (10 ft) thick, are composed of relatively coarse, well-rounded quartz grains cemented by lime and iron. The thicker beds are indefinitely cross bedded. The shales are essentially fine-grained, very thin sandstones that include lime concretions and balls of consolidated mud. The limestone appears as solid gray-blue beds, a few inches to a few feet thick, and as lenses of limestone conglomerate. Most of the limestone lenses are less than 8 metres (25 ft) long, but two were traced for nearly 150 metres (500 ft) and one for 500 metres (1,650 ft).

Viewed as a whole, the Kayenta is readily distinguished from the geologic formations above and below it. It is unlike them in composition, color, manner of bedding, and sedimentary history. Obviously the conditions of sedimentation changed in passing from the Wingate Sandstone formation to the Kayenta and from the Kayenta to the Navajo sandstone, but the nature and regional significance of the changes have not been determined. In some measured sections the transition from Wingate to Kayenta is gradual; the material in the basal Kayenta, beds seems to have been derived from the Wingate immediately below and redeposited with only the discordance characteristic of fluviatile sediments. But in many sections the contact between the two formations is unconformable; the basal Kayenta consists of conglomerate and lenticular sandstone that fills depressions eroded in the underlying beds. In Moqui Canyon near Red Cone Spring nearly 3 metres (10 ft) of Kayenta limestone conglomerate rests in a long meandering valley cut in Wingate. Likewise, the contact between the Kayenta and the Navajo in places seems to be gradational, but generally a thin jumbled mass of sandstone and shales, chunks of shale and limestone, mud balls, and concretions of lime and iron, lies at the base of the fine-grained, cross bedded Navajo. Mud cracks, a few ripple marks, and incipient drainage channels were observed in the topmost bed of the Kayenta on Red Rock Plateau; and in west Glen Canyon, wide sand-filled cracks appear at the horizon. These features indicate that, in places at least, the Wingate and Kayenta were exposed to erosion before their overlying geologic formations were deposited, are it may be that the range in thickness of the Kayenta thus in part (is) accounted for.

Southwest Utah

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The red and mauve Kayenta siltstones and sandstones that form the slopes at base of the Navajo Sandstone cliffs record the record of low to moderate energy streams. Poole (1997) has shown that the streams still flowed toward the east depositing from 150 to 210 m (500 to 700 ft) of sediment here. The sedimentary structures showing the channel and flood plain deposits of streams are well exposed on switchbacks below the tunnel in Pine Creek Canyon.

In the southeastern part of Zion National Park a stratum of cross bedded sandstone is found roughly halfway between the top and bottom of the Kayenta Formation. It is a "tongue" of sandstone that merges with the Navajo formation east of Kanab, and it shows that desert conditions occurred briefly in this area during Kayenta time. This tongue is the ledge that shades the lower portion of the Emerald Pool Trail, and it is properly called Navajo, not Kayenta.

Fossil mudcracks attest to occasional seasonal climate, and thin limestones and fossilized trails of aquatic snails or worms mark the existence of ponds and lakes. The most interesting fossils, however, are the dinosaur tracks that are relatively common in Kayenta mudstone.

These vary in size, but all seem to be the tracks of three-toed reptiles that walked upright, leaving their tracks in the muds on the flood plains. Unfortunately, so far no bone materials have been found in Washington County that would enable more specific identification.

Apparently during Kayenta time Zion was situated in a climatic belt like that of Senegal with rainy summers and dry winters at the southern edge of a great desert. The influence of the desert was about to predominate, however, as North America drifted northward into the arid desert belt.

Glen Canyon

[edit]

The Kayenta Formation is approximately 120 metres (400 ft) thick and consists of a fine-grained sandstone interbedded with layers of siltstone. The alternation of these units generally produces a series of ledges and slopes between the cliffs of the Navajo and Moenave formation. Dinosaur tracks are fairly common in the siltstone, and fresh water mussels and snails occur but are rare. The Kayenta Formation is colored pale red and adds to the splendor of the Vermilion Cliffs. It accumulated as deposits of rivers.

Fossils

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Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Invertebrates

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Genus Species Location Stratigraphic position Material Notes Images

Darwinula[5]

  • D. magna
  • D.sarytirmensis
  • Gold Spring Quarry 1

Base of the "typical facies"

Valves

A freshwater (lacustrine or fluvial) ostracod, type member of the family Darwinulidae. Kayenta specimens have a distinctive columnar calcitic layer. The Kayenta fauna is similar to the Sinemurian faunas of the Toutunhe Formation of Xinjiang, China.

Liratina[5]

  • L. sp.
  • Gold Spring Quarry 1

Base of the "typical facies"

Single shell

A freshwater (lacustrine or fluvial) snail, incertae sedis inside Mesogastropoda. Differs considerably from the species from the Upper Jurassic Morrison Formation, Liratina jurassicum

Lymnaea[6]

  • L. hopii
  • Colorado Plateau

Base of the "typical facies"

Shells

A freshwater (lacustrine or fluvial) snail, member of the family Lymnaeidae.

Scabriculocypris[5]

S. n. sp

  • Gold Spring Quarry 1

Base of the "typical facies"

Valves

A freshwater (lacustrine or fluvial) ostracod, incertae sedis inside Cypridacea. Differs from all other described species of the genus in being more elongate and from most in being spinose.

Unio[7]

  • U. dumblei
  • U. dockumensis
  • U. iridoides
  • South of Moab

Base of the "typical facies"

Shells

A freshwater (lacustrine or fluvial) Bivalve, member of the family Unionidae.

Valvata[6]

  • V. gregorii
  • Colorado Plateau

Base of the "typical facies"

Shells

A freshwater (lacustrine or fluvial) snail, member of the family Valvatidae.

Fishes

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The "Kayenta Fish Fauna" is the last one recovered from the Glen Canyon Group sequence and it is delimited mostly to the silty facies of the Lower-Middle Part of the formation.[8] This Fauna is rather scarce and delimited to several concrete locations with proper lacustrine or fluvial deposition, and are also scarce due to preservation bias.[8] Another aspect that can explain the lack of fish fossils found is the use of different research techniques than used on the Chinle Formation.[8]

Chondrichthyes

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Taxon Species Location Stratigraphic position Material Notes Images

Hybodontoidea[9]

Indeterminate

  • Shonto Trading Post, Segi Canyon
  • Ward Terrace

Base of the "typical facies"

UCMP 136104, 136105 + ten uncatalogued specimens, teeth

A freshwater (lacustrine or fluvial) non-neoselachian shark, incertae sedis inside Hybodontoidea. The remains of sharks are rather rare on the formation and limited to several locations with typical lacustrine or fluvial floodplain deposition.

Toarcibatidae (= "Archaeobatidae")[10]

Indeterminate

Gold Spring Quarry 1

Base of the "typical facies"

Isolated Tooth

A freshwater (lacustrine or fluvial) toarcibatid. Related originally with Micropristis or Libanopristis, and stated to be reworked from younger Cretaceous deposits, was found due to its asymmetrical cusp to fit within the definition of Toarcibatis, being more likely to be native of the formation.[10]

Actinopterygii

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Taxon Species Location Stratigraphic position Material Notes Images

Lophionotus[11]

L. kanabensis

  • Washington Dome
  • Ward Terrace
  • Warner Valley
  • Zion National Park

Base of the "typical facies"

  • Fragmentary Specimens, Isolated Teeth and Scales

A freshwater (lacustrine or fluvial) semionotid semionotiform.

"Palaeoniscidae"[8][12][13]

Indeterminate

  • Utah Route 7 near St.George
  • Warner Valley

Base of the "typical facies"

  • Isolated Ganoid Scales& Teeth

A freshwater (lacustrine or fluvial) palaeoniscid palaeonisciform.

Semionotidae[8][12][13]

Indeterminate

  • Utah Route 7 near St.George
  • Downtown Moab
  • Warner Valley
  • Washington Dome
  • Ward Terrace
  • Warner Valley
  • Zion National Park
  • Desert Tortoise tracksite 1

Base of the "typical facies"

  • Large (1 m) Complete specimen; Isolated Ganoid Scales & Teeth

A freshwater (lacustrine or fluvial) semionotid semionotiform, probably related to the genus Semionotus. Semionotiformes are the only properly identified bony fishes from the formation, including a large specimen exposed at the Dan O'Laurie Museum.[8]

Semionotus is probably related to the Kayenta Seminotiformes

Sarcopterygii

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Genus / Taxon Species Location Stratigraphic position Material Notes Images

Ceratodus[8][14]

C. stewarti

  • Goblin Valley State Park

Middle "Silty Facies"

  • OMNH 69332, left pterygopalatine plate

A freshwater (lacustrine or fluvial) ceratodontid dipnomorph (lungfish).

Ceratodus

Coelacanthidae[14][12]

Indeterminate

  • Tsegi Canyon
  • Warner Valley

Base of the "typical facies"

  • Isolated remains & Scales

A freshwater (lacustrine or fluvial) coelacanthid Coelacanthiform. Coelacanths are quoted from this zone, but their remains have not been studied.

Potamoceratodus[15]

P. guentheri

  • Tsegi Canyon?
  • Little Colorado River Valley on Ward Terrace

Middle "Silty Facies"

  • Single dipnoan tooth plate (MCZ 13865)

A freshwater (lacustrine or fluvial) ceratodontid dipnomorph (lungfish). Was described as C. felchi, know from the Upper Jurassic Morrison Formation. Other dipnoan specimens have been cited but never described.[14]

Amphibia

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Genus / Taxon Species Location Stratigraphic position Material Notes Images

Anura[9]

Indeterminate

Gold Spring Quarry 1

Silty Facies Member

  • MCZ 9019, distal humerus
  • MCZ 9020–24, ilia

An early frog, incertae sedis relationships

Eocaecilia[16]

E. micropodia

Gold Spring Quarry 1

Silty Facies Member

  • MNA V8066 (type), Nearly complete skull and lower jaw
  • Isolated multiple specimens, cranial and postcranial: MNA V8053, 8054, 8055...

A genus whose relationships are controversial, being considered one of the earliest gymnophionans as a close relative of caecilians

Eocaecilia

Lissamphibia[9]

Indeterminate

Gold Spring Quarry 1

Silty Facies Member

  • MCZ 9025–9028, jaws; MCZ 9031, 9032, vertebrae
  • MCZ 9035, atlas vertebra; MCZ 9034 + 4 uncatalogued specimens, proximal femora
  • MCZ 9066, 9067, proximal humeri
  • MCZ 9068–9072, proximal limb bones, possibly humeri

Incertae sedis relationships

Prosalirus[17]

P. bitis

Gold Spring Quarry 1

Silty Facies Member

MNA V 8725, associated disarticulated remains of 2 individuals; referred MCZ 9324 A & MCZ 9323 A

An early frog, probably related to Notobatrachidae

Prosalirus

Urodela[9]

Indeterminate

Gold Spring Quarry 1

Silty Facies Member

MCZ 9017, 9018, atlas vertebrae

A possible stem-salamander, incertae sedis inside Urodela. The oldest record of an urodelan from North America

Reptilia

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Rhynchocephalia

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Taxon Species Location Stratigraphic position Material Notes Images

Navajosphenodon[18]

N. sani

  • Gold Springs Quarry
  • Silty Facies Main Quarry
  • Adeii Eechii Cliffs

Silty Facies

  • MNA.V.12442, a fully articulated skeleton, including the skull, mandibles, axial and appendicular skeleton
  • Referred multiple specimens MCZ VP 9098, MCZ VP 101562, MCZ VP 9099, MCZ VP 101564, MCZ VP 101575, MCZ VP 9094, MCZ VP 9102, MCZ VP 9103, MCZ VP 101569, MCZ VP 101563, MNA.V.8726, MNA.V.8727

An Advanced Sphenodont, member of Sphenodontinae. The skeleton of N. sani shows a large number of similarities with the modern tuatara S. punctatus, clustering them closely together in the morphospace of sphenodontians and early lepidosaurs.[18]

Navajosphenodon

Rhynchocephalia[19]

Indeterminate

Airhead West

Silty Facies

Uncertain Fragments

Rhynchocephalians of uncertain assignment

Sphenodontia[9]

Indeterminate

Gold Spring Quarry 1

Silty Facies

MCZ 9036 through 9040, jaw fragments

An indeterminate sphenodont

Testudinatans

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Genus / taxon Species Location Stratigraphic position Material Notes Images

Cryptodira[9]

Indeterminate

Red Knob

Silty Facies

Uncertain fragments

Cryptodirans of uncertain assignment

Kayentachelys[20]

  • K. aprix
  • K. spp.
  • Gold Spring Quarry 1
  • Gold Spring South
  • Gold Spring General
  • Gold Spring Wash
  • Hummingbird Canyon
  • Ted's Turtle Town
  • Gerald's Turtle

Silty Facies Member

  • MNA V1558, complete skull only lacking the right temporal arch and mandible
  • Referred multiple cranial and postcranial material: MNAV2664, TMM 436701–3, TMM 43656-1...

A mesochelydian

Kayentachelys

Testudinata[9][19]

Indeterminate

  • Airhead West
  • Gold Spring General
  • Moenkopi Point
  • Valley of the Buttes
  • Paiute Canyon General
  • East Paiute Valley

Silty Facies

Uncertain fragments

Testudinatans of uncertain assignment

Crocodylomorphs

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Genus / Taxon Species Location Stratigraphic position Material Notes Images

Calsoyasuchus[21]

C. valliceps

Adeii Eechii Cliffs, Navajo Nation

Silty Facies

TMM 43631-1 (holotype), partial skull

A terrestrial member of the Hsisosuchidae. Alternatively can be a relative of Thalattosuchia

Crocodylomorpha[9][13]

  • "Undescribed new genus"
  • Indeterminate
  • Utah Route 7 near St.George
  • Airhead West
  • Moenkopi Point, Pumpkin Patch
  • Blue layer, Silty Facies
  • Gold Spring Quarry 1

Silty Facies

  • Teeth (+30)
  • UCMP 97639, 97640
  • MCZ 9044, dermal armor fragment
  • MCZ 9199, fragment of pseudosuchian dermal scute
  • MCZ 9200, dermal scute, probably Eopneumatosuchus
  • UCMP 136102, fragment of lower jaw

Indeterminate crocodylomorphs. Includes a new taxon with skull similar to Orthosuchus stormbergi.

Eopneumatosuchus[22]

E. colberti

Blue layer, Silty Facies

Silty Facies

  • MNA P1.2460, partial skull
  • Isolated Jaw

An early terrestrial or semiterrestrial protosuchid crocodylomorph

Kayentasuchus[23][12]

K. walkeri

  • Warner Valley
  • Willow Springs 13

Silty Facies

  • UCMP 131830, nearly complete skeleton
  • UMNH VP 21923

An early terrestrial or semiterrestrial crocodylomorph

Kayentasuchus, preserved bones in white

Protosuchidae[9][24]

  • "Gomphosuchus wellesi"
  • "Edentosuchus-like taxon"
  • Moenkopi Point, Pumpkin Patch
  • Blue layer, Silty Facies

Silty Facies

  • MCZ 8816, mandible
  • UCMP 97638, A skull and articulated mandible
  • UCMP 125395: A cranium.
  • UCMP 125871: Skull with mandibles and one epibranchial lacking the dorsal part of the braincase, articulated with the atlas, axis, and 2 cervical vertebrae.
  • UCMP 125358
  • UCMP 125359: An eroded compressed braincase.
  • UCMP 125872: A right jugal and maxilla in articulation in a large block of unprepared material.
  • UCMP 125870: A very well-preserved braincase
  • UCMP 130082

Early terrestrial or semi-terrestrial herbivorous Crocodylomorphs. Includes two taxa similar to the Cretaceous Edentosuchus tienshanensis, one that has been referred to informally as "Gomphosuchus" (including UCMP 97638 and UCMP 125871) and another unnamed taxon (including UCMP 130082).[25] Previously considered one taxon (the 'Kayenta form') in older literature.[26]

Dinosaurs

[edit]

Indeterminate ornithischian remains located in Arizona, USA.[27] Ornithischian tracks located in Arizona, USA.[27] Indeterminate theropod remains located in Arizona, US.[27] Theropod tracks located in Arizona and Utah, US.[27] Possible theropod tracks located in Arizona, Colorado, and Utah, US.[27]

Ornithischians
[edit]
Genus / Taxon Species Location Stratigraphic position Material Notes Images

Heterodontosauridae[28][29]

Indeterminate

Gold Springs

Silty Facies

  • MCZ 9092, complete upper and lower dentitions, many other portions of the skull, vertebrae from all portions of the axial column, and portions of fore and hind girdles and limbs[28]

A heterodontosaurid of uncertain placement. Appears to have been an insectivore downsized to a degree not seen before among early dinosaurs.

Ornithischia[30][13][31]

  • Utah Route 7 near St.George
  • Gold Spring Quarry

Silty Facies

  • MNA.V.109, a large left femur
  • Isolated Teeth (+20)

A uncertain placement large ornithischian and teeth from diverse type of genera. The femur was assigned to Dilophosaurus wetherilli.[30] The femur resembles that of the early neornithischian Lesothosaurus.[31]

Scelidosaurus[32][33]

S. sp. (S. "arizonensis")

Valley of the Buttes

Silty Facies

UCMP 130056, scutes

A controversial thyreophoran, resembles the osteoderms of S. harrisonii.

Scutellosaurus[34][35][30]

S. lawleri

  • Paiute North
  • West Moenkopi Plateau
  • Paiute Canyon General
  • East Paiute Valley
  • Southwest Paiute Canyon
  • Rock Head
  • Willow Spring General
  • Gold Spring General
  • Gold Spring Quarry
  • Gold Spring South
  • Gerald's Turtle
  • Ted's Turtle Town
  • Hummingbird Canyon

Silty Facies

  • MNA P1.175, almost complete skeleton (holotype)
  • MNA P1.1752, partial skeleton (paratype)
  • Referred multiple specimens: TMM 43669-5/6, TMM 43661-1, TMM 43691-18, TMM 43691-20, TMM 43648-13, TMM 43663-1, TMM 43664-1, 2, TMM 47001-1, TMM 43690-6, TMM 43687-13, 117, 123...

A basal thyreophoran, the most abundant dinosaur of the formation

Scutellosaurus
Sauropodomorphs
[edit]
Genus / Taxon Species Location Stratigraphic position Material Notes Images

Sarahsaurus[36][37]

S. aurifontanalis[27]

  • Gold Springs
  • Rock Head

Silty Facies

  • TMM 43646–2 partially articulated skeleton
  • TMM 43646–3, partial skeleton
  • MCZ 8893, articulated skull with fragmentary postcranial elements

A sauropodomorph, a member of the family Massospondylidae. Originally thought to be Massospondylus[27]

Sarahsaurus
Theropods
[edit]
Genus / Taxon Species Location Stratigraphic position Material Notes Images

Coelophysidae[38]

Unnamed, informally known as the "Shake-N-Bake" coelophysid

  • Rock Head (Bowl Area)
  • Shake-N-Bake

Silty Facies

  • MCZ 8817 dorsal, cervical, caudal vertebra, partial sacrum, partial pelvis, partial tooth, partial caudal centrum, proximal femur, distal tibiotarsus, distal fibula, partial astragalus, partial scapulocoracoid
  • MCZ 9442; sacrum, partial ilia, proximal pubes, proximal ischia
  • MCZ 9463; distal tibiotarsus
  • TMM 43689-4; proximal tarsometatarsus
  • MNA V3181; pubis

A coelophysid neotheropod.

Coelophysis[39][40]

C. kayentakatae

  • Rock Head (Bowl Area)
  • Gold Spring Wash
  • Shake-N-Bake

Silty Facies

  • MNI; MNA V2623
  • TMM 43669-3
  • MNA V100, V140

A coelophysid neotheropod. Referred to as Syntarsus by Weishampel et al.[27] Formerly known as Megapnosaurus.

Coelophysis kayentakatae

Dilophosaurus[41][42]

D. wetherilli
  • Tuba City, Silty Facies
  • Dilophosaurus Quarry
  • Gold Spring East
  • Gold Spring General
  • Rock Head (Bowl Area)
  • Moenkopi Point, Pumpkin Patch

Silty Facies

  • UCMP 37302 (holotype), nearly complete skeleton
  • UCMP 37303, partial skeleton; third skeleton eroded and not collected
  • MNA V3145, distal end of R femur
  • Referred TMM 43687-52; UCMP 77270; UCMP 130053; TMM 43646-0, 1; TMM 47006-1

An advanced neotheropod, type member of the family Dilophosauridae. Dilophosaurus is the main identified dinosaur from the formation, being both the most known and studied. It was among the largest theropods present locally, and very likely an active hunter, rather than a fisher.[42]

Dilophosaurus

Kayentavenator[43]

K. elysiae[43]

Willow Springs

Silty Facies

  • UCMP V128659, six proximal caudal centra, three centra, two partial neural arches, fragmentary ilium, proximal pubes, pubic shaft fragments, incomplete femora, proximal tibiae, proximal fibula, fragments

A neotheropod of uncertain relationships, probably a coelophysoid. Originally referred to M. kayentakatae by Rowe.

Kayentavenator

Theropoda[19][13][34]

Indeterminate

  • ARCH 71v, near the Garden of Eden
  • Utah Route 7 near St.George
  • Airhead West
  • Gold Spring General
  • Gold Spring Wash

Silty Facies

  • ARCH 4012, fragmentary skeletal[44]
  • Isolated Teeth (+50)
  • TMM 43669-10
  • TMM 43687-10, 58, 60, 71, 85, 91, 98, 102, 105, 119

Incertae sedis within Theropoda, probably Neotheropoda

Pterosauria

[edit]
Genus / Taxon Species Location Stratigraphic position Material Notes Images

Pterosauria[13]

Indeterminate

  • Utah Route 7 near St.George

Silty Facies

  • Teeth

Possible pterosaur teeth

Rhamphinion[19][45]

R. jenkinsi[45]

  • Airhead West
  • MCZ 23/78A, Foxtrot Mesa

Silty Facies, Ward Mesa

  • MNA V 4500 (holotype), skull fragments
  • UCMP 128227, left fourth wing metacarpal

A pterosaur, considered a member of the family Dimorphodontidae. Was originally classified as a "rhamphorhynchoid", represents the only major pterosaur identified from the formation and one of the oldest from North America.

Synapsida

[edit]
Genus / Taxon Species Location Stratigraphic position Material Notes Images

Dinnebitodon[46]

  • D. amarali[46]
  • D. spp.
  • Dinnebito Wash
  • Hummingbird Canyon
  • Gold Spring General

Silty Facies

  • MNA V3222 (Type, partial skull and associated postcrania)
  • Referred MNA V3223, partial skull and scapula; MCZ 8831 includes two left dentaries; MCZ 8830, Crushed snout; TMM 43647-3, 4, TMM 43687-7

A relatively large and common tritylodont

Dinnetherium[47]

D. nezorum

  • Gold Spring Quarry 1

Silty Facies

  • MNA V3221; MCZ 20870-20877

A mammaliaform, member of the family Megazostrodontidae

Haramiyidae[47]

Indeterminate

  • Gold Spring Quarry 1

Silty Facies

  • MCZ 20879

Incertae sedis, a possible haramiyid

Kayentatherium[48]

  • K. wellesi[48]
  • K. spp.
  • MCZ, The Landmark
  • Hummingbird Canyon
  • Gold Spring General
  • Gold Spring wash
  • Willow Spring General
  • Rock Head, general area

Silty Facies

  • MCZ 8812, well-preserved partial skeleton of a large individual
  • Referred TMM 43669-9; MCZ 8842; TMM 43647-9, 10; TMM 43687-111

A Large tritylodont, with a suggested semiaquatic mode of life. A specimen has been recovered with several associated perinates.[49]

Kayentatherium

Morganucodon[47]

M. sp.

  • Gold Spring Quarry 1

Silty Facies

  • MCZ 20878

A mammaliaform, member of the family Morganucodontidae

Morganucodon

Oligokyphus[50]

  • O. sp.
  • cf. O. sp.
  • Gold Spring General
  • Gold Spring Quarry 1

Silty Facies

  • TMM 43687-86
  • Referred > 42 specimens

A tritylodont, also present on coeval deposits from Asia and Europe.

Oligokyphus

Tritylodontidae[19][9]

Indeterminate

  • Airhead West
  • MCZ, The Landmark
  • Rock Head, general area
  • Willow springs
  • Gold Spring General
  • Gold Spring 1

Silty Facies

  • Teeth

Indeterminate tritylodontid remains

Ichnofossils

[edit]
Genus Species Location Material Type Origin Notes Images

Anomoepus[51][52][53]

  • A. scambus
  • A. shingi
  • A. moabensis
  • A. isp.
  • Moenkopi Wash
  • Lisbon Valley Oilfield tracksite
  • Hamblin tracksite
  • Warner Valley tracksite
  • Utah Route 7 near St.George
  • Poison Spider Mesa tracksite

Footprints

Moving Tracks

  • Ornithischians

Ornithischian Footprints of the ichnofamily Moyenisauropodidae.

Batrachopus[54][11]

  • B. isp.
  • Desert Tortoise tracksite

Tracks

Moving Tracks

  • Crocodylomorphs

Pseudosuchia Footprints of the ichnofamily Batrachopodidae.

Characichnos[13]

  • C. isp.
  • Utah Route 7 near St.George

Tracks

Moving Trails

  • Dinosaurs

Dinosaur Traces left while swimming

Dilophosauripus[55]

  • D. williamsi
  • D. isp.
  • Moenkopi Wash 4 tracksite
  • Moenave Road Tracksite
  • Goldtooth Spring tracksite
  • Cameron tracksite

Footprints

Moving Tracks

Theropod Footprints of the ichnofamily Grallatoridae.

Dinosauropedida[56][57]

Indeterminate
  • North Creek tracksite
  • Parunuweap-West Temple tracksite
  • Tenmile Canyon tracksite

Footprints

Moving Tracks

  • Dinosaurs

Possible Dinosaur Footprints, non assigned to any concrete ichnogenus

Example of Indeterminate Dinosaur Footprint from the Kayenta Formation

Eubrontes[51][58][54][53][59][60]

  • E. giganteus
  • E. isp.
  • Washington City Water Tank tracksite 1
  • Flat Iron Mesa tracksite
  • Trout Water Canyon tracksite
  • Grapevine Pass Wash Tracksite
  • Warner Valley tracksite
  • Desert Tortoise tracksite
  • Flag Point I tracksite
  • Rainbow Bridge tracksite
  • Explorer's Canyon tracksite
  • Mike's Mesa tracksite (Kayenta)
  • Utah Route 7 near St.George
  • Cactus Park track site

Footprints

Moving Tracks

Theropod Footprints of the ichnofamily Grallatoridae. This type of tracks match with Dilophosaurus pes

Grallator[51][58][54][53]

  • G. tenuis
  • G. isp.
  • Lisbon Valley Oilfield tracksite
  • Washington City Water Tank tracksite 1
  • Exit 13 North tracksite
  • Exit 13 South tracksite
  • Desert Tortoise site
  • Warner Valley tracksite
  • Desert Tortoise tracksite
  • Flag Point II tracksite
  • Utah Route 7 near St.George
  • Flat Iron Mesa tracksite
  • Cactus Park track site

Footprints

Moving Tracks

  • Theropods (Coelophysoids?)

Theropod Footprints of the ichnofamily Grallatoridae. Likely from smaller local theropods

Kayentapus[51][54][61]

  • K. hopii[55]
  • K. soltykovensis
  • K. isp.
  • Moenkopi Wash
  • Trout Water Canyon tracksite
  • Desert Tortoise tracksite
  • Flag Point I tracksite
  • Flag Point II tracksite
  • Flat Iron Mesa tracksite

Footprints

Moving Tracks

  • Theropods

Theropod Footprints of the ichnofamily Grallatoridae.

Limulidae[51]

Indeterminate
  • Lisbon Valley Oilfield tracksite

Trackways

Moving Tracks

  • Limuloids
  • Insects?

Saltwater/Blackish-linked tracks with resemblance with extant Xiphosuran traces

Moyenisauropus[13]

  • M. isp.
  • Utah Route 7 near St.George

Footprints

Moving Tracks

  • Thyreophorans

Ornithischian Footprints of the ichnofamily Moyenisauropodidae.

Otozoum[62][63]

  • O. isp.
  • Flat Iron Mesa tracksite
  • Poison Spider Mesa tracksite

Footprints

Moving Tracks

  • Sauropodomorphs

Theropod Footprints of the ichnofamily Otozoidae. Includes tracks referable to bipedal Sauropodomorphs

Planolites[64]

  • P. isp.
  • Near St. George, Washington County

Cylindrical burrows

Pascichnia

  • Annelids

Burrow-like ichnofossils. It is referred to vermiform deposit-feeders. It is controversial, since is considered a strictly a junior synonym of Palaeophycus.[65]

Example of Planolites fossil

Skolithos[64]

  • S. isp.
  • Near St. George, Washington County

Cylindrical to subcylindrical Burrows

Domichnia

  • Annelids
  • Crustaceans
  • Fishes

Burrow-like ichnofossils. Ichnofossils done by organisms advancing along the bottom surface. Very narrow, vertical or subvertical, slightly winding unlined shafts filled with mud. Interpreted as dwelling structures of vermiform animals, more concretely the Domichnion of a suspension-feeding Worm or Phoronidan, with certain Skolithos representing entrance shafts to more complicated burrows.

Skolithos ichnofosil reconstruction, with possible fauna associated

Synapsidipedia[51]

Indeterminate
  • Lisbon Valley Oilfield tracksite

Tracks

Moving Tracks

  • Mammaliformes
  • Tritylodonts

Possible Synapsid Footprints, non assigned to any concrete ichnogenus

Taenidium[64]

  • T. isp
  • Near St. George, Washington County

Unlined meniscate burrows

Fodinichnia

Saltwater/Blackish burrow-like ichnofossils. Taenidium is a meniscate backfill structure, usually considered to be produced by an animal progressing axially through the sediment and depositing alternating packets of differently constituted sediment behind it as it moves forward.

Theropodipedia[51][52][58]

Indeterminate
  • Lisbon Valley Oilfield tracksite
  • Hamblin tracksite
  • South Gate tracksite
  • Long Canyon tracksite
  • Washington City Water Tank tracksite 2
  • Lion's Back tracksite

Footprints

Moving Tracks

  • Theropods

Possible Theropod Footprints, non assigned to any concrete ichnogenus

Example of Indeterminate Theropod Footprint from the Kayenta Formation

Undichna[13]

  • U. isp.
  • Utah Route 7 near St.George

Trails

Moving Trails

  • Bony Fishes

Fish-swimming fossil trail left as a fossil impression on a substrate

Plants

[edit]
Genus Species Stratigraphic position Material Notes Images

Clathropteris[13]

  • C. sp.
  • Utah Route 7 near St.George
  • Leaflets

Affinities with Dipteridaceae inside Polypodiales.

Example of Clathropteris meniscioides specimen

Cycadidae[13]

Indeterminate
  • Utah Route 7 near St.George
  • Leaflets

Affinities with Cycadidae inside Cycadopsida.

Example of extant cycad, Encephalartos longifolius

Otozamites[13]

  • O. sp.
  • Utah Route 7 near St.George
  • Leaflets

Affinities with Williamsoniaceae inside Bennettitales.

Pinopsida[13]

Indeterminate
  • Utah Route 7 near St.George
  • Leave Compressions
  • Isolated Cones

Affinities with Pinopsida inside Pinaceae.

Zamites[13]

  • Z. powellii
  • Utah Route 7 near St.George
  • Leaflets

A member of Williamsoniaceae inside Bennettitales. It has been interpreted as a cycad in the family Cycadaceae or a Bennettitalean plant, and also a late surviving member of Noeggerathiales.

Example of Zamites mandelslohi specimen

See also

[edit]

Footnotes

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Kayenta Formation

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The Kayenta Formation is an geological formation primarily exposed across the in the , consisting of interbedded reddish-brown sandstones, varicolored mudstones, and siltstones that represent fluvial and deposits in an arid . As a key member of the Glen Canyon Group—alongside the underlying Wingate Sandstone (or Moenave Formation in some areas) and overlying —it spans parts of , , , and , with its type locality near the town of Kayenta in . Dating to approximately 195 to 180 million years ago ( to stages), the formation records fluvial deposits transitioning from braided streams to more distal meandering river systems and floodplains, evidenced by cross-bedded channel sandstones and finer-grained overbank sediments. Notable for preserving dinosaur tracks and fossils, such as those of theropod and sauropodomorph dinosaurs, it forms prominent slopes and ledges in landscapes like and Canyonlands National Parks, and serves as a vital in regions including the Moab area of . The formation's thickness varies from about 100 to 300 meters, intertonguing laterally with the Navajo Sandstone in some areas, reflecting dynamic sediment transport during a period of regional tectonic stability.

Geological Overview

Location and Extent

The Kayenta Formation is primarily exposed across the , with its main outcrops in , southeastern , northwestern , and southern , where it forms part of the Group. This distribution reflects a broad depositional basin during the , spanning multiple geologic provinces including the Black Mesa basin, basin, and Plateau sedimentary province. The formation's exposures are particularly prominent in areas like the in and the canyonlands of , contributing to the region's dramatic landscapes. The type locality of the Kayenta Formation is located along Comb Ridge, approximately 1 mile northeast of Kayenta in , within the northwest corner of the Kayenta East 7.5-minute quadrangle. Here, the formation is well-exposed and represents a classic section for , originally described in . Mapping efforts by the U.S. Geological Survey have delineated its boundaries across these states, highlighting its continuity within the Group, which it occupies as the middle unit below the . In terms of thickness, the Kayenta Formation generally measures 100–120 meters across much of its extent, though it varies regionally due to depositional patterns and erosion. In southwestern Utah, it reaches up to approximately 270 meters, reflecting thicker accumulation in fluvial channels and floodplains. Outcrops often form distinctive benches and slopes, particularly in Glen Canyon, where the formation creates recessed, ledge-forming terrain between the cliff-dominated units above and below, aiding in the area's geomorphic expression and trail networks.

Age and Stratigraphic Position

The Kayenta Formation is assigned to the epoch, specifically spanning the to stages, corresponding to an approximate temporal range of 199 to 183 million years ago (Ma). More refined geochronological constraints from detrital uranium-lead (U-Pb) indicate a depositional age of 183.7 ± 2.7 Ma, placing the formation within the to stages. This maximum depositional age was determined through laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) analysis of grains extracted from silty in , yielding a cluster of youngest zircons that establish the upper limit for . Stratigraphically, the Kayenta Formation occupies a middle position within the Glen Canyon Group of the , conformably overlying the Wingate Sandstone and conformably underlying the . The contact with the underlying Wingate Sandstone marks a transition from eolian-dominated deposits of the Norian-Rhaetian stages to fluvial and lacustrine sediments, while the upper boundary with the reflects a shift to widespread eolian dune accumulation. This vertical stacking positions the Kayenta as a key interval bridging and strata in the region. Biostratigraphic correlations align the Kayenta Formation with European Early Jurassic stages, particularly through shared tetrapod assemblages including theropod dinosaurs like and thyreophorans akin to from the Sinemurian-Pliensbachian of . Within , it correlates with units in the broader Navajo Group succession and with formations in the , based on shared Early Jurassic palynomorph and vertebrate faunal assemblages that confirm the Sinemurian-Pliensbachian timeframe. Additional age constraints from a 2018 detrital study on fossil-bearing horizons further support these correlations, with maximum depositional ages consistent with late deposition in specific localities.

Stratigraphy and Lithology

General Characteristics

The Kayenta Formation consists predominantly of reddish-brown, fine- to medium-grained sandstones interbedded with siltstones, mudstones, shales, and minor limestones, forming a sequence of thinly bedded layers that weather into ledges and slopes. The sandstones are typically pale red-purple to pale reddish-brown in color, while the mudstones and shales exhibit grayish-red to moderate-reddish-brown hues, reflecting staining characteristic of the unit. These lithologies indicate a mixed fluvial depositional , with sandstones representing channel and bar deposits and finer units derived from overbank environments. Sedimentary structures within the formation include trough-type cross-bedding at small- to medium-scales with low angles, lenticular , flat , , mud cracks, and contorted heterolithic interpreted as evidence of bank collapses or seismic influences. The beds are generally thin, ranging from laminated to 2-4 feet thick, contributing to the formation's characteristic bench-forming topography across its exposures. Mineralogically, the sandstones are quartz-rich, composed mainly of subrounded to subangular grains with minor , lithic fragments, chert, and heavy minerals such as and ; clay flakes are common in the matrix. Diagenetic features include cementation that binds the grains, with some units showing siliceous cement, leaching spots, and variable cementation from poorly to well-consolidated. The formation attains an average thickness of 100–120 m (330–394 ft), though it varies regionally, and demonstrates lateral continuity across the , intertonguing with adjacent units like the while pinching out eastward.

Regional Variations in Utah

In , the Kayenta Formation displays notable regional variations in thickness, , and depositional , reflecting its fluvial origin within a dynamic landscape. These differences are particularly evident between the southeast and southwest subregions, where provenance, stream gradients, and proximity to depositional basins influenced the rock record. The formation generally consists of red to brown sandstones and shales, but local highlight transitions from proximal braided systems to distal meandering rivers. In southeast , the Kayenta Formation reaches a thickness of approximately 100 m and is characterized by red to brown thin-bedded sandstones interbedded with shales and minor limestones, forming prominent bench-like layers that cap underlying Wingate Sandstone cliffs. These lithologies represent fluvial channel deposits with associated overbank fines, including mud-pellet conglomerates at channel bases, indicative of moderate-energy stream environments. Key exposures occur along Comb Ridge and Indian Creek, where irregularly bedded gray to red-brown sandstones dominate, and near , where lenticular cross-bedded sandstones up to 107 m thick are well preserved. In contrast, the southwest portion of the formation is thicker, ranging from 150 to 210 m, and features more conglomeratic bases with coarse-grained s and shales derived from east-flowing streams. The basal Springdale Sandstone Member, a distinctive tongue, interfingers laterally with the underlying Moenave Formation, marking a transitional zone where fluvial sands encroached on lacustrine or playa deposits. Exposures near exemplify these characteristics, with crumbly red siltstones and s forming steep slopes up to 210 m thick, often showing evidence of waning fluvial energy. Facies transitions across progress from systems in the southeast, with high channel amalgamation and minimal overbank deposits (less than 5-35% mudstones), to meandering fluvial systems in the southwest, where isolated channels comprise only 13% of the section amid increased overbank fines (36-44%) and finer-grained sands. This downstream evolution reflects decreasing gradient and energy, with braided macroforms giving way to lateral-accretion sets in more distal settings.

Regional Variations in Arizona and Colorado

In the area of , the Kayenta Formation reaches thicknesses of approximately 76 to 100 meters, consisting primarily of fine-grained sandstones interbedded with siltstones and shales that weather into slopes and ledges. The type section is located along Comb Ridge, about 1 mile northeast of Kayenta in Navajo County, where the formation measures around 44 meters thick and exhibits thin-bedded, reddish sandstones with minor shale interbeds. The upper portion intertongues with the overlying , creating transitional of cross-bedded sandstones that reflect lateral shifts in depositional styles. Further north in , particularly in regions like the Grand Canyon and , the formation attains thicknesses of 30 to 70 meters and is dominated by fluvial sandstones with subordinate lenses indicative of localized quiet-water deposits. These exposures form prominent benches and cliff bases, with grayish-red to pale-red sandstones that are thinner-bedded than adjacent units, contrasting with the thicker, more uniformly fluvial sections observed in . In northwest , such as in the Davis Mesa and areas, the Kayenta Formation is thinner, ranging from 24 to 73 meters, and shows increased influence from at its margins, including minor cross-bedded dune sands interfingering with fluvial deposits. It conformably overlies the Wingate Sandstone and underlies the , with correlations to the Entrada Sandstone in broader sequences where the Group thins eastward. Current understanding of the formation's extent remains limited, particularly regarding detailed mapping of its minor extensions into , where exposures are sparse and correlations are tentative.

Paleoenvironment

Depositional Environments

The Kayenta Formation primarily records deposition in low- to moderate-energy fluvial systems, characterized by braided and ephemeral streams that transported sediments across a broad . Evidence for these riverine environments includes channel scours, scour-and-fill structures, and fining-upward sequences consisting of coarse-grained sandstones grading into siltstones and mudstones, indicative of channel migration, overbank flooding, and accumulation. In the Springdale Sandstone Member, particularly prominent in southwestern , braided-stream channels dominate with trough and minor conglomerate lenses reflecting higher-energy flow conditions. Lacustrine elements are subordinate but present, particularly in the lower silty and during episodes of increased , where shallow ponds and lakes formed in topographic lows. These are represented by thin limestones, dolomitic shales, and fine-grained mudstones with ripple cross-bedding and mudcracks, suggesting fluctuating water levels in playa-like or marginal lacustrine settings. Minor playa deposits occur in distal fluvial areas, with evaporitic mudstones and siltstones indicating periodic drying. Sediments were primarily sourced from erosion of the Ancestral and the Uncompahgre uplift to the east, with paleocurrent indicators such as azimuths revealing predominantly westward transport directions in . In other regions, such as northeastern , flows trended southeast to northwest along structural features like the Zuni Sag. Over time, the fluvial systems evolved in response to climatic cyclicity, shifting from braided, ephemeral rivers in drier phases to more perennial, locally meandering styles during wetter intervals, as evidenced by changes in channel morphology and increased lacustrine development in sequence sets.

Paleoclimate and Geography

The Kayenta Formation was deposited under a semi-arid to arid climate characterized by seasonal rainfall, as evidenced by the presence of pedogenic calcretes, evaporite minerals such as gypsum, and well-developed soil horizons indicative of periodic wetting and drying cycles. These features suggest an environment with limited but episodic precipitation, promoting evaporative concentration in floodplain settings and the formation of carbonate-rich paleosols. This climatic regime is analogous to that of modern northern Senegal, where braided river systems and dune fields develop under a regime of wet summers and prolonged dry winters. During the Early Jurassic, the depositional area of the Kayenta Formation lay at a paleolatitude of approximately 10–15°N, positioning it within a subtropical high-pressure belt conducive to dry conditions punctuated by monsoonal influences from the Pangaean megamonsoon system. This location, slightly north of the paleoequator on the western margin of Laurentia, facilitated the development of ephemeral fluvial systems responsive to seasonal moisture influxes. The tectonic setting was one of relative stability along the cratonic margin of western , with minor extensional rifting associated with the ongoing breakup of Pangea following the emplacement of the around the Triassic- boundary. This stable platform experienced limited , allowing for the accumulation of continental sediments without significant marine incursion until later Jurassic times. Paleogeographic reconstructions depict the Kayenta Formation as part of broad alluvial plains dominated by meandering and braided rivers that drained northward toward the emerging embayment in the . These fluvial systems transported sediments across a vast, low-relief landscape flanked by eolian dunes to the south and southwest.

Fossil Record

Plants and Invertebrates

The fossil record of in the Kayenta Formation is sparse, consisting primarily of indeterminate stems and obscure remains preserved in fluvial and lacustrine deposits. Notable among these are impressions of leaves assigned to Clathropteris sp., discovered in mudrock horizons near highway construction sites in , indicating a low-diversity adapted to moist, shoreline environments. Horsetail ( sp.) stems and possible cycad-like fragments (Podozamites sp.) have also been reported from similar contexts, suggesting riparian vegetation dominated by early gymnosperms and pteridophytes in floodplain settings. remains, including cone scales of Araucarites sp. and branch fragments of undetermined genera, further attest to the presence of wooded habitats along ancient streams and lakes. A particularly significant plant fossil is Sanmiguelia lewisi, represented by a large stem with attached palm-like leaves embedded in fine-grained sandstone at the boundary of the Springdale Sandstone Member in , . This specimen, with leaves up to 25 cm long and pleated without visible veins, marks the first post-Triassic occurrence of the genus, extending its stratigraphic range into the and highlighting transitional floral elements in the formation. Palynomorphs, such as and spores indicative of riparian assemblages, are absent from the Kayenta Formation, underscoring the rarity of dispersed organic remains compared to body fossils. Invertebrate fossils in the Kayenta Formation are predominantly freshwater taxa preserved in limnic sediments, reflecting permanent water bodies within a fluvial-lacustrine . Ostracods form a low-diversity assemblage, including Darwinula magna, Darwinula sarytirmensis, and Scabriculocypris n. sp., recovered from northeastern localities; these seed shrimps exhibit wedge-shaped carapaces and suggest correlations with faunas from Asia. Gastropods, represented by Liratina sp., and unionid bivalves occur alongside ostracods in siltstones and mudstones, indicating stable, low-energy aquatic habitats with minimal marine influence. Conchostracans (clam shrimps) are also present, contributing to the overall picture of a supporting small, benthic . Taphonomic evidence points to preservation primarily in lake beds and overbank floodplains, where fine-grained silty facilitated the burial of delicate plant impressions and shells before decay or transport. The diversity of these non-vertebrate fossils, though limited, reflects habitats with periodic fluvial input, as seen in the association of ostracod-rich layers with paleosols and root traces near vertebrate-bearing sites. Recent studies, including the 2014 of Sanmiguelia lewisi, have refined understandings of floral preservation in these deposits, emphasizing rapid in proximal lake margins.

Vertebrates

The vertebrate fauna of the Kayenta Formation documents an important phase of post-end- mass extinction recovery during the (Sinemurian-Pliensbachian), featuring a mix of holdover lineages and emerging clades in a fluvial-dominated environment. This assemblage, one of the most diverse known from the North American , includes over a dozen taxa, with body fossils primarily from and deposits in and southern . Key localities such as Dinosaur Canyon in the have yielded multiple skeletons, highlighting the formation's role in preserving early Jurassic terrestrial ecosystems. Fish remains are scarce in the Kayenta Formation, reflecting the predominantly non-lacustrine depositional settings that limited preservation of aquatic vertebrates. Known taxa include chondrichthyans such as indeterminate hybodont sharks, actinopterygians like semionotids, and sarcopterygians represented by (e.g., or Potamoceratodus species). Amphibians are rare but notable, with the formation preserving early records of lissamphibian diversification. Fossils include the Eocaecilia micropodia, a limbed stem-gymnophione providing insights into the origins of modern amphibians, and the salientian Prosalirus bitis, the oldest known . Reptiles form the bulk of the Kayenta's vertebrate diversity, encompassing several archosauromorph and testudinate lineages. Crocodylomorphs are represented by basal forms such as Kayentasuchus walkeri, a sphenosuchian known from a partial skeleton, alongside Calsoyasuchus valliceps and Eopneumatosuchus colberti. Turtles include the primitive Kayentachelys aprix, one of the earliest North American records of the group. Rhynchocephalians are documented by Navajosphenodon sani, a 2022-described sphenodontian from Gold Spring Quarry, extending the group's fossil record back to approximately 190 million years ago. Dinosaurs are prominent, with theropods like Dilophosaurus wetherilli (from Dinosaur Canyon) and Sarahsaurus aurifontanalis (a basal sauropodomorph), and ornithischians such as the thyreophoran Scutellosaurus lawleri. In 2024, postcranial body fossils of a saurischian dinosaur, likely a theropod, including vertebrae, a radius, femur, fibula, and metatarsals, were described from the Kayenta Formation in , —the first such remains from the typical in the state. Pterosaurs are known from Rhamphinion jenkinsi, an early record in the based on limb elements. Synapsids in the Kayenta Formation primarily consist of non-mammalian cynodonts, underscoring the transition toward mammalian characteristics. Tritylodontids, herbivorous relatives, include Kayentatherium wellesi, Dinnebitodon amarali, and Oligokyphus species, known from cranial and postcranial remains. Early mammal relatives among morganucodontans are represented by Dinnetherium nezorum and a species, with indicating insectivorous diets. In 2023, a rare bonebed containing bones and teeth of tritylodontid mammaliaforms was discovered near in , , marking the first such assemblage from the Kayenta Formation in the state and illuminating the diversification of herbivorous relatives approximately 180 million years ago.

Trace Fossils

The Kayenta Formation preserves a diverse assemblage of trace fossils, primarily in its fluvial and lacustrine deposits, providing insights into the behavior, locomotion, and ecological interactions of vertebrates and invertebrates across the . Ichnofossils include well-preserved trackways, burrows, and trails that reflect a dynamic paleoenvironment with episodic flooding and drying, allowing for the documentation of gregarious movement and substrate exploitation. These traces are concentrated in and layers, often in association with microbial mats that enhanced preservation. Dinosaur tracks dominate the ichnofauna, with theropod prints being the most abundant and indicative of predatory and scavenging behaviors. Large tridactyl tracks assigned to (footprints exceeding 30 cm in length) represent bipedal theropods similar in size to , while smaller -like tracks (under 20 cm) suggest juveniles or smaller carnivores; intermediate forms such as Kayentapus show wider digit divarication and gracile morphology. Dilophosauripus tracks, characterized by robust digits and a narrow pace angulation, are attributed to theropods akin to and occur in floodplain mudstones. Sauropodomorph traces, including Otozoum-like quadrupedal prints with manus impressions, are rarer but document early long-necked herbivores navigating riverine settings. Ornithischian tracks, such as Anomoepus, feature narrow-gauge quadrupedal patterns with short claws, pointing to basal armored or bipedal plant-eaters. Other ichnofossils expand the behavioral record beyond dinosaurs. Crocodylomorph tracks assigned to Batrachopus consist of small, quadrupedal pes-manus sets (20-60 mm long) with outwardly rotated manus prints, preserved in coarse sandstones near body fossil sites of Protosuchus; these indicate semi-aquatic reptiles traversing floodplains. burrows and trails, including vertical Skolithos (worm tubes), sinuous Planolites (feeding trails), and branched Taenidium (dwelling structures), reflect detritivores and burrowers in moist sediments, often alongside rhizoliths from vegetation. Key sites highlight the density and interpretive value of these traces, particularly in southern Utah and . The site in , yields over 370 theropod tracks across 70 trackways in the Springdale Sandstone Member, with parallel orientations (e.g., five aligned paths) suggesting gregarious herding along paleochannels. Nearby Moenave Formation trackways, transitional to the Kayenta, feature extensive theropod assemblages implying social behavior in arid intervals. These sites, along with exposures in , preserve multimodal orientations (northeast-southwest to southwest) that record migratory or foraging patterns. Trace fossils in the Kayenta Formation hold significant biostratigraphic utility, aiding correlation across the Group and with contemporaneous units like the . Theropod tracks, such as and Dilophosauripus, align temporally with body fossils of from mid-formation horizons, supporting a Hettangian-Sinemurian age (~201-190 Ma) and regional faunal continuity. Recent analyses in the , including reassessments of assemblages, have refined ichnoassemblage diversity through swim traces and multiproxy dating, enhancing correlations with global events like the Triassic-Jurassic extinction recovery.

History of Research

Discovery and Early Studies

The geological reconnaissance of the Navajo Country conducted by Herbert E. Gregory in 1917 provided some of the earliest detailed mapping of the region's strata, though the layers now recognized as the Kayenta Formation were not yet distinguished as a separate unit and were grouped with the underlying Wingate Sandstone and overlying . This work laid foundational observations on the and distribution of these sandstones across parts of , , and , highlighting their role in the broader sequence. In 1936, Arthur A. Baker formally named the Kayenta Formation in a U.S. Geological Survey bulletin, designating its type locality approximately one mile north of , and defining it as the middle formation of the Group based on its distinctive cross-bedded sandstones, siltstones, and mudstones that contrasted with the purer eolian deposits of the adjacent units. This naming clarified the stratigraphic distinctions, resolving earlier ambiguities in correlating the formation across and southeastern . Paleontological interest in the Kayenta Formation emerged in the 1940s with the discovery of theropod dinosaur remains near , initially reported by Navajo herder Jesse Williams in 1940 and subsequently excavated in 1942 by paleontologists Charles L. Camp and Samuel P. Welles of the Museum of Paleontology. These specimens, representing early theropods such as , marked the first significant vertebrate fossils from the formation and spurred targeted field surveys in the region. Stratigraphic studies advanced in the 1980s through Patricia R. Luttrell's basin analysis, which interpreted the Kayenta Formation's sediments as fluvial deposits from low- to moderately sinuous streams draining westward from source areas in the Mogollon highlands, integrating paleocurrent data and provenance analysis to reconstruct the depositional system. This work, building on earlier mappings, emphasized the formation's role in a setting during the .

Recent Developments and Key Discoveries

In the past decade, paleontological research in the Kayenta Formation has intensified, particularly through surveys in national parks and protected lands, leading to significant new fossil discoveries that enhance understanding of terrestrial ecosystems. A notable advancement came in 2021 with a comprehensive anatomical and histological study of Scutellosaurus lawleri, the earliest known , based on over 70 specimens from the formation's silty in . This work detailed the dinosaur's bipedal locomotion, distribution, and growth patterns, revealing a lower compared to later ornithischians and supporting its position as a basal member of outside more derived groups like and . Further progress occurred in 2023 when paleontologists discovered a rare bonebed of tritylodontid iaforms in the Kayenta Formation near , , within . This assemblage, consisting of bones and teeth from these extinct mammal relatives, represents one of the few concentrated deposits of such synapsids in the formation and was exposed temporarily due to fluctuating reservoir levels, allowing collection of several hundred pounds of encasing rock. The find provides critical evidence of post-Triassic extinction recovery among non-mammalian cynodonts in fluvial environments approximately 180 million years ago, with specimens now under study at institutions like the . A landmark in 2024 described the first postcranial body fossils of a —likely a theropod—from the typical red-bed of the Kayenta Formation in , recovered during a 2011 survey at . The partial skeleton, including elements such as a caudal , , , , and metatarsals, indicates a small-bodied predator comparable in size to early coelophysoids like . Cataloged as ARCH 4012, this discovery underscores the underrepresentation of vertebrate remains in the formation's mudstone-dominated layers and highlights the value of systematic surveys in federally managed areas for uncovering new . These developments reflect broader trends in Kayenta Formation research, including refined and taphonomic analyses that contextualize preservation in its varied depositional settings. For instance, U-Pb efforts have narrowed the formation's age to the Sinemurian-Pliensbachian stages (approximately 199–183 million years ago), aiding correlations with global faunas. Ongoing collaborations between the , Utah Geological Survey, and academic institutions continue to yield insights into the formation's role as a key archive of early dinosaurian diversification.

References

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