Grand Canyon Supergroup

Grand Canyon Supergroup Stratigraphic range: Meso- and Neo-Proterozoic, between 1,250 and 650 to 700 Ma
Type	Geological formation
Sub-units	Unkar Group, Nankoweap Formation, Chuar Group and Sixtymile Formation
Underlies	Tonto Group, which is separated from it by the Great Unconformity
Overlies	Vishnu Basement Rocks
Thickness	11,500 feet (3,500 m) to 13,100 feet (4,000 m)
Location
Country	United States of America
Type section
Named for	Grand Canyon
Named by	(Walcott, 1883, 1894)

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.

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

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 south-southwest stretch of the Colorado River as it issues 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 lower-unit members behind. Other sections of the Unkar Group reappear downstream, due to the general faulting of the Grand Canyon.

The units of the Grand Canyon Supergroup (1250 Ma to 700 Ma):

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

The Isis Temple and "Cheops Pyramid" formation is a part of the Shinumo Quartzite 'island,' and is made up of the bottom three Unkar Group members (containing Unkar units 1–3, see above). 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 3-Muav Limestone, upon 2-Bright Angle Shale, upon 1-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.

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