The Coconino Sandstone is a geologic formation composed of light-colored

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

arenite of eolian origin. It erodes to form conspicuous, sheer cliffs in the upper walls of

Grand Canyon The Grand Canyon is a steep-sided canyon carved by the Colorado River in Arizona, United States. The Grand Canyon is long, up to wide and attains a depth of over a mile (). The canyon and adjacent rim are contained within Grand Canyon Nati ...

, as part of the

Mogollon Rim The Mogollon Rim ( or or ) is a topography, topographical and geological feature cutting across Northern Arizona, the northern half of the U.S. state of Arizona. It extends approximately , starting in northern Yavapai County, Arizona, Yavapa ...

to the south and east, and in many other parts of the

Colorado Plateau The Colorado Plateau is a physiographic and desert region of the Intermontane Plateaus, roughly centered on the Four Corners region of the Southwestern United States. This plateau covers an area of 336,700 km2 (130,000 mi2) within w ...

region. The Coconino Sandstone is well known for its

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

trackway Historic roads (or historic trails in the US and Canada) are paths or routes that have historical importance due to their use over a period of time. Examples exist from prehistoric times until the early 20th century. They include ancient track ...

s of terrestrial

invertebrates Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordate subphylum ...

and

vertebrates Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

and large-scale cross-stratification.Middleton, L.T., D.K. Elliott, and M. Morales (2002) ''Coconino Sandstone,'' in S.S. Beus and M. Morales, eds., ''Grand Canyon Geology.'' Oxford University Press, New York. Eastward of a north–south line from Monument Creek to Fossil Creek, the Coconino Sandstone overlies and interfingers with and grades into the Schnebly Hill Formation, which is equivalent in part to the De Chelly Sandstone in

Utah Utah is a landlocked state in the Mountain states, Mountain West subregion of the Western United States. It is one of the Four Corners states, sharing a border with Arizona, Colorado, and New Mexico. It also borders Wyoming to the northea ...

. In this area, it underlies the Kaibab Limestone. Further eastward, the Coconino Sandstone likely correlates with and is contemporaneous with the Glorieta Sandstone of

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

. Westward of this line, the upper part of Coconino Sandstone is known as 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 Utah and the Cave Springs Member in Arizona. It interfingers and merges westward into the

Toroweap Formation The Toroweap Formation outcrops as a distinct layer of generally darker, interbedded slope- and cliff-forming strata lying between the brighter colored cliffs of the Kaibab Limestone above, and Coconino Sandstone below. It outcrops in Grand Can ...

. The remaining lower part of the Coconino Formation is known as the Harding Point Member and underlies the Toroweap Formation and uncomfortablyy overlies the Hermit Formation. Between the Toroweap and Hermit formations, the Harding Point Member thins westward until it disappears.Blakey, R.C., and Knepp, R., 1989. ''Pennsylvanian and Permian geology of Arizona'', in: Jenney, J.P., and Reynolds S.J., eds., ''Geologic Evolution of Arizona'', ''Arizona Geological Society Digest'', 17. pp. 313-347.

Nomenclature

In 1910, Darton named and mapped the ''Coconino sandstone'' as a member of the now abandoned ''Aubrey group'' for its widespread distribution in the Coconino Plateau. He named the Coconino sandstone for the cross-bedded gray to white sandstones that form a conspicuous sheer cliff in walls of Grand Canyon and underlies entire Coconino Plateau and the extensive Colorado Plateau north of the Grand Canyon. As defined at that time, it lay between the overlying ''Kaibab (Aubre) limestone'' and the underlying ''Supai formation''. The Kaibab limestone was later divided onto the Kaibab Limestone and Toroweap Formation and the Supai formation was later subdivided into the Hermit Formation and Supai Group.Noble, L.F., 1922
''A section of the Paleozoic formations of the Grand Canyon at the Bass Trail.''
''U.S. Geological Survey Bulletin.'' 131-B, pp. B23-B73. Later, the Coconino Sandstone was recognized and mapped in the San Rafael Swell in the Emery County, Utah, region.Gilluly, J., and Reeside, J.B., Jr., 1928, ''Sedimentary rocks of the San Rafael Swell and some adjacent areas in eastern Utah''. in ''Shorter contributions to general geology, 1927'', ''U.S. Geological Survey Professional Paper'', 150-D, p. D61-D110. In 1982, Hamilton recognized the fine-grained vitreous quartzites exposed in the Salton basin as the metamorphosed equivalent of Coconino Sandstone in the Big Maria Mountains of southeast California. Because of change in lithology, named and mapped these fine-grained quartzite as the Coconino Quartzite. In the Big Maria Mountains exposures, the Coconino Quartzite lies between the Hermit Schist and Kaibab Marble.Hamilton, W. H., 1982, ''Structural evolution of the Big Maria Mountains, northeastern Riverside County, southeastern California.'' in E. G. Frost and D. L. Martin, eds., pp. 1–27, ''Mesozoic-Cenozoic tectonic evolution of the Colorado River region, California, Arizona, and Nevada.'' Cordilleran Publishers, San Diego, California, United States. 608 pp. GrandNP4

Description

The Coconino Sandstone consists predominately of buff to white, well-sorted, uniformly fine grained , nearly pure

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...

held together by siliceous cement. It contains a few scattered potassium feldspar grains and traces of heavy minerals. Many of the sand grains are frosted or pitted and nearly all of them are rounded to subangular. Typically, iron oxide staining and cements are commonly absent, which is reflect in its pale, white to buff color. However, locally, the Coconino Sandstone is iron-stained and, as a result, is either a brownish color, as in Marble Canyon, or bright red, as near

Flagstaff, Arizona Flagstaff ( ), known locally as Flag, is the county seat of Coconino County, Arizona, in the southwestern United States. As of the 2020 United States census, the city's population was 76,831. Flagstaff is the principal city of the Coconino Cou ...

.McKee, E.D., 1934. ''The Coconino sandstone--its history and origin, in Papers concerning the Palaeontology of California, Arizona, and Idaho''. ''Carnegie Institution of Washington Publication'', 440, pp. 77-115.McKee, E.D. (1979
''A study of global sand seas.''
''Professional Paper'' 1052. U.S. Geological Survey, Reston, Virginia. 429 pp. The Coconino Sandstone exhibits a number of primary

sedimentary structure Sedimentary structures include all kinds of features in sediments and sedimentary rocks, formed at the time of deposition. Sediments and sedimentary rocks are characterized by bedding, which occurs when layers of sediment, with different parti ...

s. The most conspicuous of these is ubiquitous large-scale, wedge-planar, cross-stratification. It consists of long sweeping layers that often are long and as much as long as . The cross-stratification dip mostly at 25°- 30° with few at a maximum of about 34°. Their dip is generally unimodal southward, but with a spread of readings ranging between southwest and southeast. Truncated by overlying beds, they form large, irregular wedges. In addition to the wedge-planar, cross-stratification, the Coconino Sandstone exhibits rare, large-scale, low-angle, less than 15°, cross-stratification that dip in the opposite direction. They are only found in limited numbers in a few localities within in exposures of this sandstone. The basal of the Coconino Sandstone at many outcrops exhibits horizontal laminae. A distinctive characteristic of this sandstone is that the cross-stratification readily splits into thin plates. Although

ripple mark In geology, ripple marks are sedimentary structures (i.e., bedforms of the lower flow regime) and indicate agitation by water (Ocean current, current or wind wave, waves) or directly by wind. Defining ripple cross-laminae and asymmetric ripples ...

s are not abundant within the Coconino Sandstone, they are distinctive and locally numerous. They consist typically of low, wide, and asymmetrical ripples with ripple indexes, the ratio of wavelength to amplitude, greater than 17 with most considerably higher. Typically, the ripple crests and troughs lie parallel to the direction of dip of the foreset slopes. The ripple crest are rounded and generally had the concentration of coarser sand grains on or about their crests. The crests and troughs of these ripple are straight and parallel and, where exposed, exhibit little change in direction for distances of or more. They are less common in the Coconino Sandstone than in modern sand dunes because of the general lack of preservation of both the windward-side deposits of sand dunes and of ripple marks formed in dry sand without special circumstances.McKee, E.D. (1945
"Small-scale structures in the Coconino Sandstone of northern Arizona"
"The Journal of Geology". 53(5):313–325. On the bedding planes of Coconino Sandstone, the small, crater-like pits of raindrop impressions are recognized at several outcrops. They are oriented in respect to the sloping surface of laminations such that these circular pits tend to face upward, or vertically, with a raised downslope rim. Rain pits have been reproduced in the laboratory on sloping surfaces of fine dry sand to provide positive evidence of subaerial formation by brief rain showers. Slump marks from mass movement or avalanching when lee-side slopes of dunes near the angle of repose are oversteepened are also found in the Coconino Sandstone. The slump marks range from those resulting from "successive discontinuous jerks with miniature landslides" to series of variable and irregular lines that are roughly parallel to the lee side's slope and mark the edge of a slumped sand mass, ''miniature terrace-and-cliff structures'', and other types of dry-sand slump marks. The Coconino Sandstone uncommonly exhibits deformed bedding in the form of penecontemporaneously deformed cross-strata. In the few outcrops in which they are found, they can be quite abundant as near Doney Crater northeast of Flagstaff, Arizona. Typically, they consist of dipping foresets within a bed that for many feet in length have been folded locally, while the cross-strata above and below them are undisturbed. The thickness of the Coconino Sandstone varies due to regional structural features. In the Grand Canyon area, it is only thick in the west, thickens to over in the middle and then thins to in the east.

Fossils

The only known fossils found in the Coconino Sandstone are

trace fossils A trace fossil, also called an ichnofossil (; ), is a fossil record of biological activity by lifeforms, but not the preserved remains of the organism itself. Trace fossils contrast with body fossils, which are the fossilized remains of part ...

. Plant fossils have yet to be reported from the Coconino Sandstone. The body fossils of

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

s and

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

s are also lacking. However, it is a common occurrence, especially in continental desert deposits, that trace fossils provide the only available paleontologic and palaeobotanic information for paleoenvironmental reconstructions.Miller, A.E., Marchetti, L., Francischini, H., and Lucas, S.G., 2020. ''Chapter 8. Paleozoic invertebrate ichnology of Grand Canyon national Park''. In: Santucci, V.L., Tweet, J.S., ed., pp. 277–331
''Grand Canyon National Park: Centennial Paleontological Resource Inventory (Non-sensitive Version)''
Natural Resource Report NPS/GRCA/NRR—2020/2103. National Park Service, Fort Collins, Colorado, 603 pp.Spamer, E.E., 1984. ''Paleontology in the Grand Canyon of Arizona: 125 years of lessons and enigmas from the late Precambrian to the present.'' ''The Mosasaur.'' 2, pp. 45–128. The invertebrate trace fossils are known from the Coconino Sandstone include possible producers, such as worms, millipedes, isopods, spiders, scorpions. ''Paleohelcura'', a possible scorpion track, is the most common invertebrate trace fossil. Other arthropod tracks, meniscate horizontal burrows, and conical pits have also been documented in the Coconino Sandstone. Many of the invertebrate trace specimens been collected from it include long, complete, and beautifully preserved trackways and burrows. Typically, these trace fossils are reported from the lower half of the Coconino Sandstone. They are commonly preserved on the surfaces of foreset laminae of eolian sand dunes. The invertebrate tracks were likely made on dry sand that was then moistened and covered by sand before the surface dried out, or on dunes dampened by dew. Because of the preservation of so much extramorphological variation, the effects of the trackmaker's travels across inclined sand, foreset beds can be recognized and studied. The number of valid ichnotaxa known from the Coconino Sandstone is low and consists of only 6 ichnogenera: '' Diplichnites'', ''Diplopodichnus'', '' Lithographus'', '' Octopodichnus'', ''Palaeohelcura'', and ''Taenidium''. One fossil specimen from the Mogollon Rim area consists of two trackways, one composed of two parallel rows of tracks, ''Lithographus isp'' (possibly insect such as blattoids). The insect trackway ends abruptly after a change its path in at a tetrapod trackway trending transverse to it at a quite high pace. This association of insect and tetrapod trackways is interpreted as predation behavior by the tetrapod relative to an insect prey.Kramer, J.M., Erickson, B.R. Lockley, M.G. Hunt, A.P., and Braddy, S., 1995. ''Pelycosaur predation in the Permian: Evidence from Laoporus trackways from the Coconino Sandstone with description of a new species of Permichnium.'' ''New Mexico Museum of Natural History and Science Bulletin.'' 6, pp. 245–249. This interpretation has been questioned, although predation cannot be excluded.Marchetti, L., Francischini, H., Lucas, S. G., Voigt, S., Hunt, A. P., and Santucci, V.L., ''Chapter 9. Paleozoic Vertebrate Ichnology of Grand Canyon National Park'' In: Santucci, V.L., Tweet, J.S., ed., pp. 333-379
''Grand Canyon National Park: Centennial Paleontological Resource Inventory (Non-sensitive Version)''
. Natural Resource Report NPS/GRCA/NRR—2020/2103. National Park Service, Fort Collins, Colorado, 603 pp. Because of its abundant and well-preserved vertebrate tracks and trackways, the Coconino Sandstone is one of the most famous track-bearing formation of the Grand Canyon and a standard for the description of tetrapod tracks from Paleozoic eolian strata. Fossil tracks were first reported from the Coconino Sandstone by LullLull, R.S., 1918. ''Fossil footprints from the Grand Canyon of the Colorado.'' ''American Journal of Science (4th series)'' 45, pp. 337–346. in 1918 from material collected by Schuchert in 1915 along the Hermit Trail. This was followed large-scale excavations along the Hermit Trail by John C. Merriam in 1924. In 1926 and later years, GilmoreGilmore, C.W., 1926. ''Fossil footprints from the Grand Canyon.'' ''Smithsonian Miscellaneous Collections'', 77(9), 55 pp.Gilmore, C. W. 1928. ''Fossil footprints from the Grand Canyon: Third contribution.'' ''Smithsonian Miscellaneous Collections'' 80(8), 22 pp. described a number of ichnotaxa using the material excavated by Merriam. Gilmore was followed by subsequent studies of Coconino Sandstone vertebrate trace fossils, have focused on ichnotaxonomy, locomotion and paleoecology that included new material Mogollon Rim area from the middle part of the Coconino Sandstone and through comparisons with modern equivalents. The new Mogollon Rim trace fossils included specimens from the Ash Fork site. This site is well known for the presence of very long trackways, including the longest known Paleozoic trackway for number of tracks. Controversy occurred over the interpretation of some trackways as alternatively as subaerial tetrapod upslope movement on sand dunes or subaqueous current-driven lateral progression.Brand, L.R., and Tang, T., 1991. ''Fossil vertebrate footprints in the Coconino Sandstone (Permian) of northern Arizona: Evidence for underwater origin.'' ''Geology'', 19(12), pp. 1201–1204. The latter hypothesis has been since rejected by mainstream paleontologists.Helble, T., 2024. ''Flood Geology and Conventional Geology Face Off over the Coconino Sandstone.'' ''Perspectives on Science & Christian Faith'', 76(2), 86-106. Since then, trace fossils from the Coconino Sandstone have been widely used to model tetrapod locomotion in eolian paleoenvironments and distinguish variability induced in track morphology by upslope versus downslope progression and differences in the transverse component of motion. Before their recognition, these variations in track morphology caused an overestimation of footprint diversity in older works and underestimation of footprint diversity in more recent works. The six vertebrate ichnotaxa, which are regarded as valid, from the Coconino Sandstone are ''cf. Amphisauropus isp.'' (

anamniotes The anamniotes are an informal group of craniates comprising all fish and amphibians, which lay their eggs in aquatic environments. They are distinguished from the amniotes (reptiles, birds and mammals), which can reproduce on dry land either ...

), ''cf. Dromopus isp.'' (

reptile Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...

), ''Erpetopus isp.'' (reptile), '' Ichniotherium sphaerodactylum'' (

synapsid Synapsida is a diverse group of tetrapod vertebrates that includes all mammals and their extinct relatives. It is one of the two major clades of the group Amniota, the other being the more diverse group Sauropsida (which includes all extant rept ...

), ''cf. Tambachichnium isp.'' (synapsid), and ''Varanopus curvidactylus'' (reptile). The presence of ''Ichniotherium'' and ''Erpetopus'' together in the Coconino Sandstone suggests a late

Artinskian In the geologic timescale, the Artinskian is an age (geology), age or stage (stratigraphy), stage of the Permian. It is a subdivision of the Cisuralian Epoch (geology), Epoch or series (stratigraphy), Series. The Artinskian likely lasted between ...

–

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 Arti ...

age for the Coconino Sandstone. Because of its stratigraphic position, Kungurian age is more likely.

Depositional environments

It consists primarily of fine, well-sorted sand deposited by eolian processes (wind-deposited) approximately 275 million years ago. Primary sedimentary structures such as large-scale cross-stratification, ripple marks, rain impressions, slump marks, and fossil tracks are well preserved within it and contribute evidence of its eolian origin. Its composition, along with its well-sorted, uniformly fine grained sand and stratigraphic relationships, are also consistent with an eolian origin

Meteor crater

Lechatelierite Lechatelierite is silica glass, amorphous SiO2, non-crystalline mineraloid. It is named for Henry Louis Le Chatelier. Structure Lechatelierite is a mineraloid as it does not have a crystal structure. Although not a true mineral, it is often clas ...

(silica glass), as well as

coesite Coesite () is a form (polymorphism (materials science), polymorph) of silicon dioxide (silicon, Sioxide, O2) that is formed when very high pressure (2–3 gigapascals), and moderately high temperature (), are applied to quartz. Coesite was first ...

and

stishovite Stishovite is an extremely hard, dense tetragonal form ( polymorph) of silicon dioxide. It is very rare on the Earth's surface; however, it may be a predominant form of silicon dioxide in the Earth, especially in the lower mantle. Stishovite w ...

(high pressure forms of SiO₂) were formed during the impact of a

meteorite A meteorite is a rock (geology), rock that originated in outer space and has fallen to the surface of a planet or Natural satellite, moon. When the original object enters the atmosphere, various factors such as friction, pressure, and chemical ...

into the Coconino Sandstone at Barringer Crater in

Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

.Kieffer, S.W. (1971
''Shock metamorphism of the Coconino sandstone at Meteor Crater.''
Arizona, Journal of Geophysical Research. 76(23):5449-5473.Kieffer, S.W. (1971
''I, Shock Metamorphism of the Coconino Sandstone at Meteor Crater, Arizona; II, The Specific Heat of Solids of Geophysical Interest.''Unpublished PhD. dissertation.
Department of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California. 253 pp.

References

External links

* Anonymous (nd
Coconino Formation
West Coast Regional Carbon Sequestration Partnership (WESTCARB). * U.S. Geological Survey (2011

U.S. Department of the Interior, Denver, Colorado. {{Authority control Sandstone formations of the United States Natural history of the Grand Canyon Geologic formations of Arizona Geologic formations of Colorado Geologic formations of Nevada Geologic formations of Utah Geography of Coconino County, Arizona Permian Arizona Permian Colorado Permian geology of Nevada Permian geology of Utah Permian System of North America