Grand Canyon Supergroup

Sub-unitsChuar Group
Nankoweap Formation
Unkar Group^[1]

UnderliesTonto Group, which is separated from it by the Great Unconformity

Grand Canyon Supergroup
Stratigraphic range: Meso- and Neo-Proterozoic, between 1,250 to 650–700 Ma Pha. Proterozoic Archean Had. ^[1]
Type	Supergroup
Sub-units	Chuar Group Nankoweap Formation Unkar Group^[1]
Underlies	Tonto Group, which is separated from it by the Great Unconformity
Overlies	Vishnu Basement Rocks
Thickness	11,500 ft (3,500 m) to 13,100 ft (4,000 m)
Location
Region	Southwestern United States
Country	United States
Type section
Named for	Grand Canyon
Named by	(Walcott, 1883, 1894)^[2]^[3]

The Grand Canyon Supergroup is a Mesoproterozoic to a Neoproterozoic sequence of sedimentary strata, partially exposed in the eastern Grand Canyon of Arizona. This group comprises 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.

Fossils

The Grand Canyon Supergroup uncomformably overlies the Vishnu Basement Rocks but was never subjected to metamorphism. The units of the Supergroup were faulted and then tilted from 10 to 15 degrees.^[4]

A section of the Unkar Group members is visible north of Grand Canyon Village, on the South Rim; specifically at the intersection of the Bright Angel Fault and the Grandview–Phantom Fault (which cuts through Phantom Creek), on the North Rim (at the north side of Granite Gorge).

The majority of the Grand Canyon Supergroup geologic members are found in the south and southwest stretch of the Colorado River starting from Marble Canyon, traverses the southeast perimeter of the Kaibab Plateau, and flows northeasterly entering Granite Gorge and regions of the Vishnu Basement Rocks. Here, the river leaves the last of the Unkar Group's lower-unit members behind. Other sections of the Unkar Group reappear downstream due to the general faulting of the Grand Canyon.

Geologic Sequence of the Super Group

The units of the Grand Canyon Supergroup in increasing age:^[1]

Chuar Group

Kwagunt Formation
Galeros Formation
Nankoweap Formation

Unkar Group

Cardenas Basalt, youngest, Meso-Proterozoic 1070 ± 70 million years
Dox Formation
Shinumo Quartzite
Diabase dikes and sills–(dikes and sills, lateral 25 feet (7.6 m) thickness max; associated with Cardenas Basalt)
Hakatai Shale
Bass Formation, (begins at ~1250 Ma)

The Chuar Group of the Grand Canyon Supergroup has yielded a few Neoproterozoic fossils. Its dolomite beds contain at least six different types of stromatolites. In some of the gray and black mudrocks, paleontologists have found an abundance of organic microfossils, including vase-shaped microfossils (VSMs) likely presentative of arcellinid testate amoebae,^[5] acritarchs, "Sphaerocongregus variabilis", and organic chemicals characteristic of dinoflagellates. Finally, the enigmatic circular fossils of Chuaria circularis are found at various levels within the Chuar Group.^[6]^[7]

The Unkar Group of the Grand Canyon Supergroup also contains fossil stromatolites. stromatolites have been found in the dolomite beds of Bass Formation; in the transitional zone between the Hakatai Shale and Bass Formation; and from the he Comanche Point Member of the Dox Formation.^[8]

Specific locales

Various creeks, canyons, or landforms give clues to unit locales of the Grand Canyon Supergroup members.

Isis Temple and "Cheops Pyramid"

The Isis Temple and Cheops Pyramid formation is a part of the Shinumo Quartzite 'island' and made up of the bottom three Unkar Group members. They were overlain at the Great Unconformity, onto Tapeats Sandstone (named for the bottom unit of the marine transgression series consisting of sandstone–(conglomerates)–shale–limestone laid down by the Tapeats Sea), and are evident along the Colorado River on the Tonto Platform. The three units of the Tonto Group are Muav Limestone, upon Bright Angle Shale, upon Tapeats Sandstone. The Tapeats is a thin cliff-former unit found along Granite Gorge and its side canyons forming a flat surface in locales not dramatically affected by faulting, up-warping (domes), or down-warping.

The Isis Temple with Cheops Pyramid formation contains the bottom three members, a virtual quartzite 'mountain island' in the Tapeats Sea. (Tapeats Sandstone was deposited only around Shinumo Quartzite monadnocks.) The formation is a fault-block section located north of Granite Gorge and the intersection of Phantom Creek with the Bright Angel Canyon (which is also the intersection of the Bright Angel and Grandview–Phantom faults). The dimensions of this block are approximately 3.5 mi by 2.0 mi,^[9] with slopes of multi-colored Hakatai Shale and Bass Formation (shown as reddish, yellowish, and lavender).

Apollo Temple

The Apollo Temple formation occurs^[10] at the southeast of the Kaibab Plateau (Walhalla Plateau). The base of the largely flat-topped Redwall Limestone monolith sits upon cliffs of Muav Limestone, then Bright Angel Shale, and Tapeats Sandstone. The Nankoweap Formation is near the monolith's center of the base. The northeast side of the base merges into the overlying unit above the Nankoweap, the Chuar Group slopes.

Northeast Grand Canyon

In the northeast Grand Canyon, the Tapeats is still the defining cliff unit at the Great Unconformity between the paleozoic Tapeats Sandstone and the basement geology below. However, the entire east of the Kaibab Plateau is an uplifted side of the East Kaibab Monocline.^[11] The down-dropped east side of the Kaibab Plateau is defined by the south-flowing Colorado River.

Colorado sits below the East Rim, where the Little Colorado River enters from the east-southeast. Other sub-faults intersect it north and south of Little Colorado. Even further to the extreme northeast, at the Marble Canyon (Marble Platform), four parallel faults (2 sets of 2 – including the Eminence Fault), run parallel to the side of the Paria Plateau, striking northeasterly, resulting in the Colorado River's sharp turn to the southwest. The river then turns due-south – running down the East Kaibab Monocline.

References

1 2 3 Connors, T.B., Tweet, J.S., and Santucci, V.L., 2020. Stratigraphy of Grand Canyon National Park. In: Santucci, V.L., Tweet, J.S., ed., pp. 54–74, 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.
↑ Walcott, CD (1883) Pre-Carboniferous strata in the Grand Canyon of the Colorado, Arizona. American Journal of Science, 3d ser., vol. 26, pp. 437–42, 484.
↑ Walcott, CD (1894) Precambrian igneous rocks of the Unkar terrane, Grand Canyon of the Colorado. 14th Annual Report for 1892/3, part 2, pp. 492–519, United States Geological Survey, Reston, Virginia.
↑ Timmons, M, KE Karlstrom, and C Dehler (1998) Grand Canyon Supergroup Six Unconformities Make One Great Unconformity A Record of Supercontinent Assembly and Disassembly Archived 2013-07-13 at the Wayback Machine. Boatman's Quarterly Review. vol. 12, no. 1 Archived 2013-09-28 at the Wayback Machine, pp. 29–32. online: accessed April 2014
↑ Lahr, Daniel J.G.; Kosakyan, Anush; Lara, Enrique; Mitchell, Edward A.D.; Morais, Luana; Porfirio-Sousa, Alfredo L.; Ribeiro, Giulia M.; Tice, Alexander K.; Pánek, Tomáš; Kang, Seungho; Brown, Matthew W. (2019-03-18). "Phylogenomics and Morphological Reconstruction of Arcellinida Testate Amoebae Highlight Diversity of Microbial Eukaryotes in the Neoproterozoic". Current Biology. 29 (6): 991–1001.e3. doi:10.1016/j.cub.2019.01.078. hdl:10261/240246. ISSN 0960-9822. PMID 30827918. S2CID 72333352.
↑ Ford, TD, and CM Dehler (2003) "Grand Canyon Supergroup: Nankoweap Formation, Chuar Group, and Sixtymile Formation." in: Beus, S.S., Morales, M., eds., pp. 49–72, Grand Canyon Geology. Oxford University Press, New York.
↑ Dehler, CM, SM Porter, and JM Timmons (2012) "The Neoproterozoic Earth system revealed from the Chuar Group of Grand Canyon", in JM Timmons and KE Karlstrom, eds., pp. 49–72, Grand Canyon Geology: Two Billion Years of Earth's History. Special Paper no. 489, Geological Society of America, Boulder, Colorado.
↑ 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.
↑ Arizona Road & Recreation Atlas, Benchmark Maps, pp. 12–13.
↑ Note: The Apollo Temple formation is at mile 72 from Lee's Ferry
↑ Chronic, Halka. Roadside Geology of Arizona, from Section: "Grand Canyon National Park", pp. 279–87. Graphic, Faults of eastern Grand Canyon show an NW-SE trend superimposed on a NE-SW trend inherited from Precambrian time. In Grand Canyon, these faults can be studied in three-dimensional detail. (about 35 faults shown), p. 286.

v t e Grand Canyon
Facilities	Black Suspension Bridge Bridge Canyon Dam Grand Canyon National Park Grand Canyon West Grand Canyon Skywalk Grand Canyon Village, Arizona Kolb Studio Marble Canyon Dam Maswik Lodge Phantom Ranch
Geology	Agave phillipsiana Apollo Temple Bat Cave mine Cardenas Basalt Dox Formation Ericameria arizonica Esplanade Sandstone Grand Canyon Caverns Grand Canyon Forest Reserve Grand Canyon–Parashant National Monument Grand Canyon Supergroup Chuar Group Nankoweap Formation Sixtymile Formation Unkar Group Bass Formation Shinumo Quartzite Grand Staircase Freya Castle Hakatai Shale Hermit Formation Hyaloclastite Dam Isis Temple Kanab Plateau Newton Butte Ochoa Point Prospect Dam Redwall Limestone Tanner Graben Temple Butte Tonto Group Bright Angel Shale Toroweap Fault Uinkaret volcanic field Vasey's Paradise Venus Temple Vishnu Temple Vulcan's Throne
Bodies of water	Colorado River Deer Creek Havasu Creek Havasu Falls Kanab Creek Little Colorado River Bright Angel Creek
People	Harvey Butchart Colin Fletcher Kenton Grua John Hance
Tribes	Havasupai Hualapai
Events	Powell Geographic Expedition of 1869 1956 Grand Canyon mid-air collision Grand Canyon Airlines Flight 6
Related	Grand Canyon Backcountry Camping List of trails in Grand Canyon National Park National Register of Historic Places listings in Grand Canyon National Park Grand Canyon Conservancy Grand Canyon Suite Desert Wonderland Grand Canyon (1958 film) A Bigger Grand Canyon (1998 painting) Grand Canyon (2017 children's book) The Man Who Walked Through Time Grand Canyon: The Hidden Secrets Grand Canyon: A Different View Grand Canyon Escalade