| Shinumo Quartzite | |
|---|---|
| Stratigraphic range: Meso-Proterozoic: between | |
 (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 |
| Underlies | Dox Formation |
| Overlies | Hakatai Shale |
| Thickness | 350 to 410 m (1,150 to 1,350 ft) |
| 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 |
| Country |  United States |
| Type section | |
| Named for | Shinumo Canyon |
| Named by | Noble |
| Year defined | 1914[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]
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]
- ^ Noble, LF (1914) The Shinumo Quadrangle, Grand Canyon District, Arizona. Bulletin. no. 549. US Geological Survey, Reston, Virginia. 100 pp.
- ^ a b 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.
- ^ 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.
- ^ 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.