Grand Canyon Supergroup Hakatai Shale with Basalt Dike

The Hakatai Shale is a

Mesoproterozoic The Mesoproterozoic Era is a geologic era that occurred from . The Mesoproterozoic was the first era of Earth's history for which a fairly definitive geological record survives. Continents existed during the preceding era (the Paleoproterozoic), ...

rock formation with important exposures in the Grand Canyon,

Coconino County, Arizona Coconino County is a county in the north-central part of the U.S. state of Arizona. Its population was 145,101 at the 2020 census. The county seat is Flagstaff. The county takes its name from ''Cohonino'', a name applied to the Havasupai p ...

. It consists of colorful strata that exhibit colors varying from purple to red to brilliant orange. These colors are the result of the

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...

of iron-bearing minerals in the Hakatai Shale. It consists of lower and middle members that consist of bright-red, slope-forming, highly fractured, argillaceous mudstones and shale and an upper member composed of purple and red, cliff-forming, medium-grained

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 ...

. Its thickness, which apparently increases eastwards, varies from . In general, the Hakatai Shale and associated strata of the

Unkar Group The Unkar Group is a sequence of strata of Proterozoic age that are subdivided into five geologic formations and exposed within the Grand Canyon, Arizona, Southwestern United States. The 5-unit Unkar Group is the basal member of the 8-member Gr ...

rocks dip northeast (10–30°) toward normal faults that dip 60° or more toward the southwest. This can be seen at the Palisades fault in the eastern part of the main Unkar Group outcrop area (below East Rim). In addition, thick, prominent, and dark-colored

basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...

ic sills and

dikes Dyke (UK) or dike (US) may refer to: General uses * Dyke (slang), a slang word meaning "lesbian" * Dike (geology), a subvertical sheet-like intrusion of magma or sediment * Dike (mythology), ''Dikē'', the Greek goddess of moral justice * Dikes ...

cut across the purple to red to brilliant orange strata of the Hakatai Shale.Hendricks, JD, and GM Stevenson (2003) ''Grand Canyon Supergroup: Unkar Group.'' In SS Beus and M Morales, eds., pp. 39–52, Grand Canyon Geology, 2nd ed. Oxford University Press, New York.Billingsley, GH (2000) ''Geologic Map of the Grand Canyon 30 × 60 Quadrangle, Coconino and Mohave Counties, Northwestern Arizona, Pamphlet to accompany Geologic Investigations Series I–2688 Version 1.0.''U.S. Geological Survey, Reston, Virginia. 15 pp.Beus, SS, RR Rawson, RO Dalton, GM Stevenson, VS Reed, and TM Daneker (1974) ''Preliminary report on the Unkar Group (Precambrian) in Grand Canyon, Arizona.'' In TNV Karlstrom, GA Swann, and RL Eastwood, ed., pp. 34–53, Geology of northern Arizona, with notes on archaeology and paleoclimate; Part 1, Regional studies. Geological Society of America, Rocky Mountain Section, Boulder, Colorado. 407 pp. The bright orange-red slopes of the Hakatai Shale contrasts sharply against the grayish outcrops of the Bass Formation. The outcrop of the Hakatai Shale also contrasts greatly with the steep cliffs formed by Shinumo Quartzite as seen at the base of Isis Temple. In the central Grand Canyon north of Grand Canyon Village and viewed from the south at the South Rim, the bright orange-red unit can be seen below the Isis Temple and Cheops Pyramid landforms at the intersection of Bright Angel Canyon and Granite Gorge; the Bright Angel Trail from the South Rim traverses through the geographic region to the north, the North Kaibab Trail in Bright Angel Canyon. The Hakatai Shale is part of a conformable sequence of sedimentary strata that comprise the

. The Unkar Group is about thick and composed, in ascending order, of the Bass Formation, Hakatai Shale, Shinumo Quartzite, Dox Formation, and Cardenas Basalt. In ascending order, the Unkar Group is overlain by the Nankoweap Formation, about thick; the Chuar Group, about thick; and the Sixtymile Formation, about thick. The Grand Canyon Supergroup, of which the Unkar Group is the lowermost part, overlies deeply eroded

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies under ...

gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures a ...

es, pegmatites, and

schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes ...

s that comprise

Vishnu Basement Rocks The Vishnu Basement Rocks is the name recommended for all Early Proterozoic crystalline rocks (metamorphic and igneous) exposed in the Grand Canyon region. They form the crystalline basement rocks that underlie the Bass Limestone of the Unkar ...

.Elton, DP, and EH McKee (1982) ''Age and correlation of the late Proterozoic Grand Canyon disturbance, northern Arizona.'' Geological Society of America Bulletin. 93(8): 681–99.Karlstrom, KE, BR Ilg, Bradley, D Hawkins, ML Williams, G Dumond, KK. Mahan, and SA Bowring, Samuel (2012) ''Vishnu Basement Rocks of the Upper Granite Gorge: Continent formation 1.84 to 1.66 billion years ago.'' In JM Timmons and KE Karlstrom, eds., pp. 7–24, Grand Canyon geology: Two billion years of earth's history. Special Paper no 294, Geological Society of America, Boulder, Colorado.

Description

Typically, the Hakatai Shale is subdivided into three informal members. In ascending order they are the Hance Rapids (lower), Cheops Pyramid (middle), and Stone Creek (upper) members. The total thickness of the Hakatai Shale varies from at Hance Rapids to nearly at the

type section A stratotype or type section in geology is the physical location or outcrop of a particular reference exposure of a stratigraphic sequence or stratigraphic boundary. If the stratigraphic unit is layered, it is called a stratotype, whereas the stan ...

in Hakatai Canyon in the Shinumo Creek area.Timmons, JM, KE Karlstrom, MT Heizler, SA Bowring, GE Gehrels, and LJ Crossey, (2005) ''Tectonic inferences from the ca. 1254–1100 Ma Unkar Group and Nankoweap Formation, Grand Canyon: Intracratonic deformation and basin formation during protracted Grenville orogenesis.'' Geological Society of America Bulletin. 117(11–12): 1573–95. First, the Hance Rapids (lower) member consists of purple to reddish-purple mudstone, interbedded

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

y siltstone, and rare occurrences of thin-bedded sub arkose- to

quartz arenite A quartz arenite or quartzarenite is a sandstone composed of greater than 90% detrital quartz. Quartz arenites are the most mature sedimentary rocks possible, and are often referred to as ultra- or super-mature, and are usually cemented by sili ...

. Beds of the lower member of the Hakatai Shale grade upward into the fine-grained middle member, with a boundary drawn at or very near their color change. Second, the Cheops Pyramid (middle) member consists of mudstone, siltstone, and subordinate sandy siltstone that exhibit a striking reddish-orange color. These distinctively red-colored strata are commonly mottled with small to large (up to 10 cm and more across), non-red, spherical to spheroidal reduction spots. These mottles have dark-gray to greenish-gray central nuclei that contain very dark gray to black central cores. Finally, the Stone Creek (upper) member of the Hakatai Shale consists of pale purple or lavender, fine- to coarse-grained, crossbedded coarse arkose.Reed VS (1976) ''Stratigraphy and depositional environment of the Hakatai Shale, Grand Canyon, Arizona.'' Unpublished Master's Thesis, Northern Arizona University, Flagstaff, Arizona. 163 pp.Elston, DP (1989) ''Middle and late Proterozoic Grand Canyon Supergroup, Arizona.'' In DP Elston, GH Billingsley, and RA Young, RA., eds., pp. 94–105, Geology of the Grand Canyon, Northern Arizona (with Colorado River Guides). American Geophysical Union Fieldtrip Guidebook T115/315 for International Geologic Congress, 28th. American Geophysical Union, Washington DC. 239 pp. Basaltic sills and dikes intrude all of the Unkar Group below the Cardenas Basalt. Sills intruded only the Bass Formation and Hakatai Shale. Dikes intrude the Hakatai Shale, Shinumo Quartzite, and Dox Formation. The sills range in thickness from at Hance Rapids, eastern Grand Canyon, to in Hakatai Canyon in the Shinumo Creek area. The feeder dikes to these sills are not exposed. However, the feeder dikes for the Cardenas Basalt can be traced, discontinuously, to within a few meters of its base. Adjacent to the sills, the Hatakai Shale has been altered to knotted

hornfel Hornfels is the group name for a set of contact metamorphic rocks that have been baked and hardened by the heat of intrusive igneous masses and have been rendered massive, hard, splintery, and in some cases exceedingly tough and durable. These pro ...

s containing

porphyroblasts A porphyroblast is a large mineral crystal in a metamorphic rock which has grown within the finer grained matrix. Porphyroblasts are commonly euhedral crystals, but can also be partly to completely irregular in shape. The most common porphyrobl ...

andalusite Andalusite is an aluminium nesosilicate mineral with the chemical formula Al2SiO5. This mineral was called andalousite by Delamétehrie, who thought it came from Andalusia, Spain. It soon became clear that it was a locality error, and that the spe ...

and

cordierite Cordierite (mineralogy) or iolite (gemology) is a magnesium iron aluminium cyclosilicate. Iron is almost always present and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: to . A high-temperat ...

that have been replaced by

muscovite Muscovite (also known as common mica, isinglass, or potash mica) is a hydrated phyllosilicate mineral of aluminium and potassium with formula K Al2(Al Si3 O10)( F,O H)2, or ( KF)2( Al2O3)3( SiO2)6( H2O). It has a highly perfect basal cleavag ...

and green chlorite, respectively.

Contacts

In the eastern part of the Grand Canyon, the contact between the Hatakai Shale with underlying Bass Formation is typically gradational over an interval of a meter or so. For example, in Red Canyon, the contact consists of an interval in which stromatolitic

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

of the Bass Formation is intimately interbedded with coarse deposits of the overlying Hakatai Shale. In the eastern part of the Grand Canyon, the contact is sharp, but conformable. The contact between the Hatakai Shale and the overlying Shinumo Quartzite is a distinct, significant

disconformity An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...

. This disconformity is sharp and locally truncates cross-beds, and channel forms, within the sandstones of the underlying Hatakai Shale. Within the lower subarkose of the Shinumo Sandstone, a basal lag of conglomerate, which contains basement clasts up to across, lies on the eroded surface that forms this disconformity. This basal conglomerate contains

quartzite Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tec ...

clasts that lack any known equivalents in the Grand Canyon region. As documented by the dating of detrital

zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of t ...

s, this disconformity is estimated to represent a period of about 75 million years. The contact between the

Tapeats Sandstone Except where underlain by the Sixtymile Formation, Cambrian Tapeats Sandstone is typically the lowest geologic unit, about thick, at its maximum, of the 5-member Tonto Group. It is famous for being the highly-resistant mostly-horizontal unit ...

and Hatakai Shale and the rest of the folded and faulted Unkar Group is a prominent

angular unconformity An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...

, which is part of the

Great Unconformity Of the many unconformities (gaps) observed in geological strata, the term Great Unconformity is frequently applied to either the unconformity observed by James Hutton in 1787 at Siccar Point in Scotland,Rance, H (1999''Historical Geology: The ...

. The differential

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is dis ...

of the Unkar Group left resistant beds of the Cardenas Basalt and Shinumo Quartzite as topographic highs, ancient monadnocks, that are now buried by sandstones, shales, and conglomerates of the Tapeats Sandstone. These monadnocks served locally as sources of coarse-grained sediments during the

marine transgression A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, which results in flooding. Transgressions can be caused by the land sinking or by the ocean basins filling ...

that deposited the Tapeats Sandstone and other members of the Tonto Group. The contact between the Hatakai Shale and the Tapeats Sandstone forms part of a relatively flat surface that lies between the monadnocks.

Fossils

Stromatolite Stromatolites () or stromatoliths () are layered sedimentary formations ( microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). T ...

s have been found within spectacular exposures of the Hatakai Shale in Rodgers Canyon. At this outcrop, they occur in the transitional zone between it and the Bass Formation where stromatolitic carbonate beds are intimately interbedded with coarse deposits of the Hakatai Shale. The base of these deposits contains stromatolite onchaloids, small

algal Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mi ...

mounds, that are built upon coarse clasts of sandstone-conglomerate.Timmons, JM, J Bloch,K Fletcher, KE Karlstrom, M Heizler, and LJ Crossey (2012) ''The Grand Canyon Unkar Group: Mesoproterozoic basin formation in the continental interior during supercontinent assembly.'' In JM Timmons and KE Karlstrom, eds., pp. 24–47, Grand Canyon Geology: Two Billion Years of Earth's History. Special Paper no. 489, Geological Society of America, Boulder, Colorado. In addition, the dark gray to black central cores of the reduction mottles found in the Cheops Pyramid (middle) member is possible of organic (stromatolitic?) origin. A number of spurious and discredited reports about other types of

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 preserved ...

s found in the Hatakai Shale have been made. In one case, apparent trails of

metazoan Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...

s were reported from the Hatakai Shale.Glaessner, MF (1965) ''Pre-Cambrian life – Problems and perspectives'' Geological Society of London Proceedings. 1626: 165–69. However, these reported

trace fossil A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...

s are now regarded to be nonbiogenic pseudofossils.Cloud, P (1973) ''Pseudofossils: A Plea for Caution.'' Geology. 1(3): 123–27.

Depositional environments

The strata comprising the Hance Rapids (lower) member is interpreted to have accumulated beneath shallow, low-energy waters. The change from Bass Formation to the lower member likely represent the waning stages of marine deposition during which the Bass Formation accumulated. The Cheops Pyramid (middle) member is regarded to have accumulated either in a shallow, near-shore marine environment or in coastal plain mudflats, or

deltas A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more rarel ...

. The greenish gray reduction mottles are similar in nature to reduction mottles observed in the lower middle and upper members of the Dox Formation, which are regarded as having accumulated in nonmarine environments. The Stone Creek (upper) member is of probable marine deltaic origin.

Age

The Hatakai Shale is between 1,253 and 1,104 million years old. It is younger than a layer of

volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to refer ...

in the underlying Bass Formation that has been dated at 1,253 million years. In addition, the ⁴⁰Ar/³⁹Ar dating of detrital

from the basal, Escalante Creek Member of the overlying Dox Formation indicates that it is younger than 1,140 million years. The overlying Dox Formation is older than the age of the Cardenas Basalt, which is 1,104 million years.Heizler, MT., KE Karlstrom, and MJ Timmons (1999) ''Where have all the old micas gone?'' New Mexico Geology. 21(2):34.Timmons, JM, KE Karlstrom, CM Dehler, JW Geissman, and MT Heizler (2001) ''Proterozoic multistage (ca. 1.1 and 0.8 Ga) extension recorded in the Grand Canyon Supergroup and establishment of northwest- and north-trending tectonic grains in the southwestern United States.'' Geological Society of America Bulletin. 113(2):163– 180.

Isis Temple-Cheops Pyramid horst

Isis Temple-Cheops Pyramid is a small horst, located close to the geographic center of the Grand Canyon. It is bordered on the east by the Bright Angel Fault and on the south by Granite Gorge; the Bright Angel Fault continues to the south-southwest across Granite Gorge and up Garden Creek, up the

Bright Angel Trail The Bright Angel Trail is a hiking trail located in Grand Canyon National Park in the U.S. state of Arizona. Description The trail originates at Grand Canyon Village on the south rim of the Grand Canyon, descending 4380 feet to the Colorad ...

to the South Rim. The north side of Isis Temple-Cheops Pyramid is bordered by the approximate east-west, Grandview Fault.

Description

Contacts

Fossils

Depositional environments

Age

Isis Temple-Cheops Pyramid horst

See also

References

Further reading