Shinumo Quartzite
Shinumo Quartzite* of Unkar Group of Grand Canyon Supergroup
Shinumo Quartzite crops out in the Grand Canyon near Phantom Ranch. This view is from the Grand Canyon's Bright Angel Trail.
Precambrian*
Proterozoic, Middle*
Mesoproterozoic (1100 to 1200 million years old)
(age used by National Park Service; Mathis and Bowman, 2005)
Southern Rocky Mountain region*
AZ(n)*
Not designated. Named for Shinumo Creek, north side Colorado River, Shinumo quad, Coconino Co, AZ (Noble, 1914).
Shinumo Quartzite—Red-brown, purple, and gray, cliff-forming sandstone. Includes four undivided informal members as defined by Daneker (1975). In descending order, they are upper, upper middle, lower middle, and lower sandstone members. Upper member consists of red-brown and purple, fine- to coarse-grained, well-sorted, highly contorted, gnarly bedded sandstone capped by nondisrupted, flat-bedded, gray sandstone. Upper middle member consists of rusty-red, fine- to coarse-grained, highly contorted, gnarly bedded sandstone. Lower middle member consists of purple “freckled” (reduction spots), fine-grained, well-sorted, lowangle cross-bedded sandstone with local contorted beds in upper part. Lower member consists of purplish-red, coarse-grained, flat-bedded, arkosic conglomeratic sandstone. All members cemented with silica, making sandstone as hard as metamorphic quartzite, but unit is not metamorphosed. Angular unconformity separates cliff of red-brown Shinumo Quartzite from underlying slope of red Hakatai Shale, marked at truncated beds of the Hakatai. The Shinumo increases in thickness from 1,132 ft (345 m) at eastern edge of map area to 1,540 ft (470 m) at Shinumo Creek, central part of map area.
Named as a formation of Unkar Group of Grand Canyon Series (Noble, 1914). Assigned to Unkar Group of Grand Canyon Supergroup (Elston, Scott, 1976). Revised (Stevinson, Beus, 1982). Age modified (Elston, 1989b). Paleomagnetics (Elston, 1989b). Overview (Elston, 1989b).
References
Noble, L.F., 1914, The Shinumo quadrangle, Grand Canyon district, Arizona: U.S. Geological Survey Bulletin, 549, 100 p., (incl. geologic map, scale 1:48,000).
Elston, D.P. and Scott, G.R., 1976, Unconformity at the Cardenas-Nankoweap contact (Precambrian), Grand Canyon Supergroup, northern Arizona: Geological Society of America Bulletin, v. 87, no. 12, p. 1763-1772.
Stevenson, G.M. and Beus, S.S., 1982, Stratigraphy and depositional setting of the upper Precambrian Dox Formation in Grand Canyon: Geological Society of America Bulletin, v. 93, no. 2, p. 163-173.
Elston, D.P., 1989, Grand Canyon Supergroup, northern Arizona; stratigraphic
summary and preliminary paleomagnetic correlations with parts of other
North American Proterozoic successions, IN Jenney, J.P., and Reynolds,
S.J., editors, Geologic evolution of Arizona: Arizona Geological Society
Digest, v. 17, p. 259-272.
Billingsley, George H., 2000, Geologic Map of the Grand Canyon 30' by 60' Quadrangle, Coconino and Mohave Counties, Northwestern Arizona: U.S. Geological Survey Geologic Investigation Series I-2688, Available on-line at: http://pubs.usgs.gov/imap/i-2688/.).
Mathis, A. and Bowman, C., 2005, What's in a number? Numeric ages for rocks exposed within the Grand Canyon, Part 2: Nature Notes ( Grand Canyon National Park ), v. 21, no. 2, p. 1-5.
