Shinumo Quartzite

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Shinumo Quartzite
Stratigraphic range:
Meso-Proterozoic: between
1,170 and 1,150 Ma
USA 09855 Grand Canyon Luca Galuzzi 2007.jpg
(photo bottom)-Isis Temple-monadnock—Medium tannish vertical cliffs of Shinumo Quartzite-(at angular dip) below drab-greenish slopes of Bright Angel Shale
Type Geological formation
Unit of Unkar Group-(5 subunits)
Underlies Dox Formation-(unit 4)
Overlies Hakatai Shale-(unit 2)
Thickness1,150 to 1,345 feet (351 to 410 m)
Lithology
Primary quartzite
Other conglomeratic sandstone,
quartzitic sandstone,
arkosic sandstone,
mudstone
Location
Region Arizona, Grand Canyon, Isis Temple region,
southwest Bright Angel Canyon, at north side, Granite Gorge, and along Colorado River and tributary canyons
CountryFlag of the United States.svg  United States
Type section
Named forShinumo Canyon
Named byNoble
Year defined1914 [1]

The Shinumo Quartzite also known as the Shinumo Sandstone, is a Mesoproterozoic rock formation, which outcrops in the eastern Grand Canyon, Coconino County, Arizona, (Northern Arizona). It is the 3rd member of the 5-unit Unkar Group. The Shinumo Quartzite consists of a series of massive, cliff-forming sandstones and sedimentary quartzites. Its cliffs contrast sharply with the stair-stepped topography of typically brightly-colored (orange, red, yellow, etc) strata of the underlying slope-forming Hakatai Shale. Overlying the Shinumo, dark green to black, fissile, slope-forming shales of the Dox Formation create a well-defined notch. It and other formations of the Unkar Group occur as isolated fault-bound remnants along the main stem of the Colorado River and its tributaries in Grand Canyon.

Typically, the Shinumo Quartzite and associated strata of the Unkar Group dip northeast (10°-30°) toward normal faults that dip 60+° 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). [2]

Contents

The Shinumo Quartzite is a middle member of the Unkar Group. The Unkar Group is about 1,600 to 2,200 m (5,200 to 7,200 ft) thick and composed of, in ascending order, the Bass Formation, Hakatai Shale, Shinumo Quartzite, Dox Formation, and Cardenas Basalt.

The Unkar Group consists of a sequence of sedimentary rocks that accumulated in a variety of environments ranging from fluvial to shallow-marine. Overall, the strata within it are conformable with the exception of a significant disconformity between the Hakatai Shale and Shinumo Quartzite. The Unkar Group is overlain in ascending order by the Nankoweap Formation, about 113 to 150 m (371 to 492 ft) thick; the Chuar Group, about 1,900 m (6,200 ft) thick; and the Sixtymile Formation, about 60 m (200 ft) thick. The Unkar Group, as the base section of the Grand Canyon Supergroup, overlies deeply eroded granites, gneisses, pegmatites, and schists that comprise Vishnu Basement Rocks. [2] [3] [4]

Description

In sharp contrast to argillaceous strata above and below it, the Shinumo Quartzite consists predominately of beds of red, brown or purple sedimentary quartzites that are firmly, to extremely well cemented by silica, and characterized by poorly developed bedding. It also contains beds of massive white, red or purple sandstone and conglomeratic sandstone. One conglomeratic sandstone layer that lies about 21 m (69 ft) above the base of the Shinumo Quartzite near the South Kaibab trail contains jasper pebbles. [2] [5] [6]

Typically, the Shinumo Quartzite has been subdivided into four poorly defined, unnamed members. First, the basal lower member consisting of purplish arkosic conglomeratic sandstone. Unlike the rest of the Shinumo Quartzite, it contains quartzite and granite gravels up to 5 cm (2.0 in) in diameter. As in the case of the Hotauta Conglomerate, the quartzite gravel of the lower member lacks any known equivalents in the Grand Canyon region.

Second, the lower-middle member is composed of purple cross-bedded quartzite, sometimes is subdivided into two units, and overlies the lower member. The purple quartzites of the lower-middle member exhibit crisp, well-defined reduction spots. Third, the upper-middle member is composed of "rusty red" quartzite and overlies the lower-middle member. The "rusty-red" quartzite of the upper-middle member grades downward into the lower-middle member through an interval of interbedded purple and red-brown quartzite. Their colors and cementation appear to be the result of ground or connate water alteration after their deposition.

Finally, the upper member of the Shinumo Quartzite is composed of reddish brown and locally purple sandstone and an overlying well-cemented gray quartzite. The Shinumo Quartzite is characterized as a quartzite, but the gray quartzite within the upper member of the Shinumo Quartzite contains mudstone-rich intervals. In addition, the gray quartzite was subjected to cementation by silica and bleaching that removed its original reddish brown and purple hematite pigments, after its deposition. [2] [5] [6]

Basaltic sills and dikes intrude all formations of the Unkar Group below the Cardenas Lava. The Hakatai Shale, Shinumo Quartzite, and Dox Formation are intruded by these dikes. They can be traced, discontinuously, to within a few meters of the base of the Cardenas Lava. [2] [5] [6]

Sedimentary structures

The Shinumo Quartzite exhibits a variety of sedimentary structures. The sandstones of the lower and lower-middle members exhibit centimeter- to meter-scale planar tabular cross-stratification and trough cross-beds. These cross beds record north-directed paleocurrents along with subordinate bidirectional paleocurrents. The upper-middle member exhibits abundant cross beds, clay galls, and mudcracks. The sandstones of the upper member exhibit trough cross-beds, suggesting a more northerly transport direction. The sandstone and quartzite beds of the upper member exhibit an abundance of complexly contorted, gnarly bedded, fluid expulsion structures and dramatic convolute bedding. The beds that exhibit these soft-sediment deformation structures are meters- to tens-of-meters thick. They are cited as evidence for frequent earthquake activity and fluid migration during the deposition of the Shinumo Quartzite. These deformed beds can be seen at river level in the vicinity of Nevilles Rapid, (List of Colorado River rapids), at river mile 75. [2] [5] [6]

Thickness

The Shinumo Quartzite ranges in thickness from 330 m (1,080 ft) in the Bright Angel Canyon area to 345 m (1,132 ft) at Papago Creek and 405 m (1,329 ft) in the Shinumo Creek area. In the Bright Angel Canyon area, the upper member is about 18 m (59 ft) thick, the upper middle member is about 80 m (260 ft) thick, and the lower middle member is about 130 m (430 ft) thick. [2] [5] [6]

Contacts

The contact of the Shinumo Quartzite with the Hakatai Shale is the only documented unconformity that has been found within the Unkar Group. This unconformity truncates across beds and channel deposits of the Hakatai Shale. The relief at this unconformity is small, being about 10 m (33 ft). The Shinumo Quartzite overlying this unconformity consists of arkosic conglomeratic sandstone that contains quartzite and granite pebbles. [6] [7]

Within the Unkar Group, the upper contact of the Shinumo Quartzite with the Dox Formation appears to be gradational and is marked by a change in topographic expression and color. The basal 12 m (39 ft) of the Dox Formation directly overlying Shinumo Quartzite consists of predominantly dark green to black, fissile, slope-forming shale that contains thin sandstone beds. This shale makes a distinct notch between the resistant cliff-forming quartzites of the Shinumo Quartzite underlying them and resistant cliff-forming arkosic sandstones of the Dox Formation overlying them. The change in topographic expression, color, and the facies change, from quartz arenite, to mudstone and fine-grained arkose – is gradational. [2] [8]

Between the three-member Tonto Group (above) and the Shinumo Quartzite, and the rest of the folded and faulted Unkar Group, is a prominent angular unconformity, which is part of the Great Unconformity. Though this surface is typically a plane, differential erosion (also areal erosion) of the tilted strata of the Unkar Group left resistant beds of the Cardenas Basalt and Shinumo Quartzite as ancient hills, called monadnocks, that are up to 240 m (790 ft) tall. Thin drapes of Tapeats Sandstone of the Tonto Group now cover most of these ancient monadnocks. However, a few of these monadnocks protrude further up into the Bright Angel Shale (Isis Temple prominence example). These monadnocks served locally as sources of coarse-grained sediments that accumulated during the marine transgression to form the Tonto Group. [2] [9]

Fossils

No fossils have been reported from the Shinumo Quartzite. [2] [5] [6]

Depositional environments

The sedimentary strata comprising the Shinumo Quartzite are inferred to have accumulated in a variety of environments. The lower member is regarded to have been deposited by ancient river systems and later, in coastal tidal flats. The lower-middle, and upper-middle members are argued to have accumulated in nearshore marine environments and coastal tidal and supratidal flats. The upper member is inferred to have accumulated in the delta plain, delta front, and mouth-bar of an ancient delta. The deformed strata of the upper member are interpreted as evidence of reoccurring earthshocks along regional fault and fold systems that were active during its deposition. The contact between the Shinumo Quartzite and Dox Formation indicates a shift from deposition in coastal deltas to fluvial deposition by a large river system. [2] [5] [6] [7]

Age

The age of the Shinumo Quartzite is approximately known. Based upon recent dates of volcanic ash layers, detrital zircon grains, and detrital mica flakes, geologists agree that the Unkar Group was deposited between about 1254 and 1100 Ma. The Hakatai Shale, Shinumo Quartzite, and Dox Formation samples yield clusters of zircon as young as 1170 Ma. Thus, these strata must be younger than 1170 Ma. The Dox Formation, which overlies the Shinumo Quartzite is estimated to have accumulated between 1150 and 1140 and 1100 Ma. Thus, the Shinumo Quartzite must date to between 1170 and 1150 to 1140 Ma. This would suggest that the disconformity at the base of the Shinumo Quartzite is a minor one. [7] [8]

See also

Related Research Articles

Geology of the Grand Canyon area

The geology of the Grand Canyon area includes one of the most complete and studied sequences of rock on Earth. The nearly 40 major sedimentary rock layers exposed in the Grand Canyon and in the Grand Canyon National Park area range in age from about 200 million to nearly 2 billion years old. Most were deposited in warm, shallow seas and near ancient, long-gone sea shores in western North America. Both marine and terrestrial sediments are represented, including lithified sand dunes from an extinct desert. There are at least 14 known unconformities in the geologic record found in the Grand Canyon.

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, or that observed by John Wesley Powell in the Grand Canyon in 1869. Both instances are exceptional examples of where the contacts between sedimentary strata and either sedimentary or crystalline strata of greatly different ages, origins, and structure represent periods of geologic time sufficiently long to raise great mountains and then erode them away.

Kaibab Limestone

The Kaibab Limestone is a resistant cliff-forming, Permian geologic formation that crops out across the U.S. states of northern Arizona, southern Utah, east central Nevada and southeast California. It is also known as the Kaibab Formation in Arizona, Nevada, and Utah. The Kaibab Limestone forms the rim of the Grand Canyon. In the Big Maria Mountains, California, the Kaibab Limestone is highly metamorphosed and known as the Kaibab Marble.

Tonto Group

The Cambrian Tonto Group is the three-member sequence of geologic formations that represent the basal section of Paleozoic rocks in the Grand Canyon. The group is about 1,250 feet (381 m) thick. The base unit, the Cambrian Tapeats Sandstone was deposited upon the erosion surface of the Vishnu Basement Rocks, which is found in Granite Gorge. The erosion resistant Tapeats Sandstone forms the platform, called Tonto Platform, that the two less erosion resistant upper layers, the Bright Angel Shale and Muav Limestone, rest upon.

Tapeats Sandstone

The Cambrian Tapeats Sandstone is the lower geologic unit, about 230 feet (70 m) thick, at its maximum, of the 3-member Tonto Group. It is famous for being the highly-resistant mostly-horizontal unit above the 1,000 my, Great Unconformity expressed areally in the Grand Canyon of Arizona; also in other areas of Arizona and adjacent Nevada.

Cardenas Basalt

The Cardenas Basalt, also known as either the Cardenas Lava or Cardenas Lavas, is a rock formation that outcrops over an area of about 310 km2 (120 mi2) in the eastern Grand Canyon, Coconino County, Arizona. The lower part of the Cardenas Basalt forms granular talus slopes. Its upper part forms nearly continuous low cliffs that are parallel to the general course of the Colorado River. The most complete, readily accessible, and easily studied exposure of the Cardenas Basalt lies in Basalt Canyon. This is also its type locality.

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 Grand Canyon Supergroup. The Unkar is about 1,600 to 2,200 m thick and composed, in ascending order, of the Bass Formation, Hakatai Shale, Shinumo Quartzite, Dox Formation, and Cardenas Basalt. Units 4 & 5 are found mostly in the eastern region of Grand Canyon. Units 1 through 3 are found in central Grand Canyon. The Unkar Group accumulated approximately between 1250 and 1104 Ma. In ascending order, the Unkar Group is overlain by the Nankoweap Formation, about 113 to 150 m thick; the Chuar Group, about 1,900 m (6,200 ft) thick; and the Sixtymile Formation, about 60 m (200 ft) thick. These are all of the units of the Grand Canyon Supergroup. The Unkar Group makes up approximately half of the thickness of the 8-unit Supergroup.

Nankoweap Formation

The Neoproterozoic Nankoweap Formation, is a thin sequence of distinctive red beds that consist of reddish brown and tan sandstones and subordinate siltstones and mudrocks that unconformably overlie basaltic lava flows of the Cardenas Basalt of the Unkar Group and underlie the sedimentary strata of the Galeros Formation of the Chuar Group. The Nankoweap Formation is slightly more than 100 m in thickness. It is informally subdivided into informal lower and upper members that are separated and enclosed by unconformities. Its lower (ferruginous) member is 0 to 15 m thick. The Grand Canyon Supergroup, of which the Nankoweap Formation is part, unconformably overlies deeply eroded granites, gneisses, pegmatites, and schists that comprise Vishnu Basement Rocks.

Isis Temple

Isis Temple, in the Grand Canyon, Arizona, USA, is a prominence below the North Rim, and adjacent to Granite Gorge. The prominence lies north of the north bank of the west-flowing Colorado River and is just north of Middle Granite Gorge. The Trinity Creek and canyon flow due-south at its west border; its north, and northeast border/flank is formed by Phantom Creek and canyon, a west tributary of Bright Angel Creek; the creeks intersect about 3 mi southeast, and 1 mi north of Granite Gorge. The peak of Isis Temple is only ~202 ft lower than Grand Canyon Village.

Grand Canyon Supergroup

The Grand Canyon Supergroup is a Mesoproterozoic to Neoproterozoic sequence of sedimentary strata, mostly exposed in the eastern Grand Canyon of Arizona. This group is composed of the Unkar Group, Nankoweap Formation, Chuar Group and the Sixtymile Formation, which overlie Vishnu Basement Rocks. Several notable landmarks of the Grand Canyon, such as the "Isis Temple and Cheops Pyramid" and the "Apollo Temple," are surface manifestations of the Grand Canyon Supergroup.

Tanner Graben

Located directly downstream of the Little Colorado River confluence with the Colorado River, the Tanner Graben, in the Grand Canyon, Arizona, USA is a prominence and cliffside rock formation below the East Rim. Tanner Graben is located riverside, on the Colorado River, on a north-northwest bank at Mile 68.5, and lies opposite Tanner Canyon. The Tanner Rapid, created by Tanner Creek lies at the riverside foot of the graben. The graben is a pronounced feature because of the black Cardenas Basalt that forms the middle section of the graben, presumably free of debris accumulation by its cliff face steepness, and winds, and airflow drainage that course through the Colorado River's canyons; unprotected side canyons of Cardenas Basalt show accumulations as a slope-forming geologic unit, with little showing of black basalt.

Hakatai Shale

The Hakatai Shale is a Mesoproterozoic rock formation that outcrops in the Grand Canyon, Coconino County, Arizona. It consists of colorful strata that exhibit colors that vary from purple to red to brilliant orange on outcrop. The colors are the result of the oxidation 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. Its thickness, which apparently increases eastwards, varies from 137 to 300 m. In general, the Hakatai Shale and associated strata of the Unkar Group 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. In addition, thick, prominent, and dark-colored basaltic sills and dikes cut across the purple to red to brilliant orange strata of the Hakatai Shale.

Surprise Canyon Formation Geologic formation in Arizona, United States

The Surprise Canyon Formation is a geologic formation that consists of clastic and calcareous sedimentary rocks that fill paleovalleys and paleokarst of Late Mississippian (Serpukhovian) age in Grand Canyon. These strata outcrop as isolated, lens-shaped exposures of rocks that fill erosional valleys and locally karsted topography and caves developed in the top of the Redwall Limestone. The Surprise Canyon Formation and associated unconformities represent a significant period of geologic time between the deposition of the Redwall Limestone and the overlying Supai Group.

Bass Formation

The Bass Formation, also known as the Bass Limestone, is a Mesoproterozoic rock formation that outcrops in the eastern Grand Canyon, Coconino County, Arizona. The Bass Formation erodes as either cliffs or stair-stepped cliffs. In the case of the stair-stepped topography, resistant dolomite layers form risers and argillite layers form steep treads. In general, the Bass Formation in the Grand Canyon region and associated strata of the Unkar Group-rocks dip northeast (10°-30°) toward normal faults that dip 60+° toward the southwest. This can be seen at the Palisades fault in the eastern part of the main Unkar Group outcrop area. In addition, thick, prominent, and dark-colored basaltic sills intrude across the Bass Formation.

Dox Formation

The Dox Formation, also known as the Dox Sandstone, is a Mesoproterozoic rock formation that outcrops in the eastern Grand Canyon, Coconino County, Arizona. The strata of the Dox Formation, except for some more resistant sandstone beds, are relatively susceptible to erosion and weathering. The lower member of the Dox Formation consists of silty-sandstone and sandstone, and some interbedded argillaceous beds, that form stair-stepped, cliff-slope topography. The bulk of the Dox Formation typically forms rounded and sloping hill topography that occupies an unusually broad section of the canyon.

Vishnu Basement Rocks

The Vishnu Basement Rocks is the name recommended for all Early Proterozoic crystalline rocks exposed in the Grand Canyon region. They form the crystalline basement rocks that underlie the Bass Limestone of the Unkar Group of the Grand Canyon Supergroup and the Tapeats Sandstone of the Tonto Group. These basement rocks have also been called either the Vishnu Complex or Vishnu Metamorphic Complex. These Early Proterozoic crystalline rocks consist of metamorphic rocks that are collectively known as the Granite Gorge Metamorphic Suite; sections of the Vishnu Basement Rocks contain Early Paleoproterozoic granite, granitic pegmatite, aplite, and granodiorite that have intruded these metamorphic rocks, and also, intrusive Early Paleoproterozoic ultramafic rocks.

Bright Angel Shale

The Cambrian Bright Angel Shale is the middle layer of the three member Tonto Group geologic feature. The 3-rock Tonto section famously sits upon the Great Unconformity because of the highly resistant cliffs of the base layer, vertical Tapeats Sandstone cliffs.

The Neoproterozoic Chuar Group consists of 5,250 feet (1,600 m) of fossiliferous, unmetamorphosed sedimentary strata that is composed of about 85% mudrock. The Group is the approximate upper half of the Grand Canyon Supergroup, overlain by the thin, in comparison, Sixtymile Formation, the top member of the multi-membered Grand Canyon Supergroup.

Sixtymile Formation

The Sixtymile Formation is a very thin accumulation of sandstone, siltstone, and breccia underlying the Tapeats Sandstone that is exposed in only four places in the Chuar Valley. These exposures occur atop Nankoweap Butte and within Awatubi and Sixtymile Canyons in the eastern Grand Canyon, Arizona. The maximum preserved thickness of the Sixtymile Formation is about 60 meters (200 ft). The actual depositional thickness of the Sixtymile Formation is unknown owing to erosion prior to deposition of the Tapeats Sandstone.

Holy Grail Temple

Holy Grail Temple is a 6,711-foot-elevation (2,046 meter) summit located in the Grand Canyon, in Coconino County of northern Arizona, USA. It is situated seven miles north-northeast of Havasupai Point, and two miles west-northwest of King Arthur Castle, within the Shinumo Amphitheater. Topographic relief is significant as it rises over 4,500 feet (1,370 meters) above the Colorado River in three miles. According to the Köppen climate classification system, Holy Grail Temple is located in a Cold semi-arid climate zone, with precipitation runoff draining south to Shinumo Creek, which flows west to the Colorado River.

References

  1. ↑ Noble, LF (1914) The Shinumo Quadrangle, Grand Canyon District, Arizona. Bulletin. no. 549. US Geological Survey, Reston, Virginia. 100 pp.
  2. 1 2 3 4 5 6 7 8 9 10 11 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.
  3. ↑ 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):681–699.
  4. ↑ 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.
  5. 1 2 3 4 5 6 7 Daneker, TM (1974) Sedimentology of the Precambrian Shinumo Sandstome, Grand Canyon, Arizona. Unpublished Master’s thesis, Northern Arizona University : Flagstaff, Arizona. 390 pp.
  6. 1 2 3 4 5 6 7 8 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.
  7. 1 2 3 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.
  8. 1 2 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):1573–1595.
  9. ↑ Sharp, RP (1940) Ep-Archean and Ep-Algonkian erosion surfaces, Grand Canyon, Arizona. Geological Society of America Bulletin. 51(8):1235–1270.

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