Grand Canyon Supergroup
Grand Canyon Supergroup*
View of the Unkar Group of the Grand Canyon Supergroup in the Grand Canyon near Phantom Ranch. The trail to Platform Point on the Tapeats Sandstone (above the Great Unconformity) is in the foreground. Above the Vishnu Basement Rocks of the Inner Gorge are the Bass Formation, Hakatai Shale, and Shinumo Quartzite of the Grand Canyon Supergroup.
Precambrian*
Proterozoic, Middle*
Proterozoic, Late*
Southern Rocky Mountain region*
AZ(n)*
Not designated (Walcott, 1883).
Unit Name History:
First used as Grand Canyon Group (Walcott, 1883). Divided into Unkar and
Chuar terranes; Overview (Walcott, 1894). Redesignated Grand Canyon Supergroup,
divided into Unkar Group, Nankoweap Formation, Chuar Group (Elston and
Scott, 1976). Revised to Dox Formation, divided into named members (Stevenson
and Beus, 1982). Sixtymile Formation removed from Chuar and retained as
upper formation of supergroup (Elston and McKee, 1982). Overview; Age
modified; Paleomagnetics (Elston, 1989). Paleomagnetics (Elston and Clough,
1993). Overview (Elston, 1993).
Grand Canyon Supergroup—As mapped by J.W. Sears (Huntoon and others, 1996).
Unkar Group (Middle Proterozoic)—Includes, in descending order, unnamed diabase sills and dikes, Cardenas Basalt, Dox Formation, Shinumo Quartzite, Hakatai Shale, and Bass Formation. The Cardenas and upper part of the Dox are not exposed in map area, but complete sections are present about 6 mi (9.5 km) east of map area. There, the Cardenas is about 900 ft (300 m) thick and the Dox is about 1,280 ft (390 m) thick.
Unnamed diabase sills and dikes—Black, medium- to coarse-grained, olivine-rich diabase. Contains plagioclase, olivine, clinopyroxene, magnetite-ilmenite, and biotite. Diabase sills and dikes intrude all rocks within Unkar Group below Cardenas Basalt. Chemical variation diagrams indicate a potential common parentage between dikes and sills and the overlying Cardenas, but direct physical connection has not been observed, although isochron ages are basically identical at 1,070±70 Ma (Hendricks and Stevenson, 1990). Sills range in thickness from about 65 ft (20 m) in Clear Creek at eastern edge of map area to more than 655 ft (200 m) near Bass Rapids in central part of map area. Dike widths range from 3 to 12 ft (1 to 4 m).
Dox Formation—Includes, in descending order, Ochoa Point, Comanche Point, Solomon Temple, and Escalante Creek Members as defined by Stevenson and Beus (1982). Of these, only part of the Escalante Creek is exposed in map area. Upper two-thirds or more of the Dox is removed by erosion and subsequently covered by Paleozoic rocks. The Escalante Creek is exposed in upper Bright Angel Creek and Shinumo Creek, eastern quarter of map area.
Escalante Creek Member—Gray, light-brown to dark-brown, cliff-forming, fine- to medium-grained sandstone and interbedded dark-brown to green, slopeforming shale and mudstone. Includes gray contorted sandstone beds in lower part similar to those in underlying Shinumo Quartzite and small-scale, tabularplanar cross-bedded and graded-bedding sets. Conformable contact with the underlying Shinumo marked at lowest shaley slope of the Dox. Incomplete exposure due to erosion of upper part. Exposed thickness about 200 ft (60 m).
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.
Hakatai Shale—Orange-red, purple, and red mudstone, shale, and sandstone. Forms an upper cliff unit, a middle slope unit, and a lower slope unit. Upper cliff unit consists of pale-purple or lavender, fine- to coarse-grained, thin- to mediumbedded, cross-bedded sandstone. Forms gradational contact with underlying middle slope unit at distinct color change from purple to bright red. Middle slope unit is the most distinctive red-bed unit in the Grand Canyon, consisting of reddish-orange, thin-bedded, fine-grained mudstone, siltstone and sandy siltstone; includes nonred, spherical reduction spots (“freckles”) less than 10 cm in diameter. Gradational contact with underlying lower slope unit arbitrarily placed at red to purple color change. Lower slope unit consists of purple to reddish-purple, thin-bedded to laminated, fine-grained mudstone, siltstone, and sandy siltstone. Mudcracks, ripple marks, and tabular-planar cross-bedding are common in all units. Gradational contact with underlying Bass Formation in eastern part of map area; sharp but conformable contact in central part of map area. Overall thickness varies from about 445 ft (135 m) in eastern part of map area to nearly 985 ft (300 m) in Hakatai Canyon, central part of map area.
Bass Formation—Red-brown and reddish-gray, ledge-forming dolomite, silty sandstone, and conglomerate. Includes basal Hotauta Conglomerate Member as defined by Dalton (1972). Consists of fine- to coarse-grained, thin- to mediumbedded dolomite, fine- to coarse-grained, thin-bedded sandstone, silty sandstone, conglomerate, and breccia. Dolomite is most common lithology in Shinumo Creek area (central part of map area), becoming mostly sandstone, siltstone, and conglomerate in Bright Angel Canyon and eastern part of map area. Dolomite beds contain biscuit-shaped biohermal stromatolite fossils and red chert; sandstone beds contain ripple marks, desiccation cracks, and intraformational breccia and conglomerate. The Hotauta is considered part of the Bass in most map areas because of its lensing characteristics. The Bass, including the Hotauta, gradually thickens from southeast to northwest across map area from about 260 to 300 ft (80 to 91 m).
Hotauta Conglomerate Member—Red-brown and gray conglomerate of well-rounded to subangular pebbles and boulders of granite, gneiss, and schist derived from underlying Early Proterozoic igneous and metamorphic rocks. Clasts are cemented in red-brown, coarse-grained, gravelly sandstone matrix. Unconformable contact with underlying Early Proterozoic rocks called the “Greatest Angular Unconformity” (Noble, 1922), a hiatus lasting about 450 million years (Hendricks and Stevenson, 1990). Unit does not include diabase sills. Variable thickness 0–30 ft (0–10 m).
Walcott, C.D., 1883, Pre-Carboniferous strata in the Grand [Canyon] of the Colorado, Arizona: American Journal of Science, 3rd series, v. 26, p. 437-442.
Walcott, C.D., 1894, Pre-Cambrian igneous rocks of the Unkar terrane, Grand Canyon of the Colorado, Arizona: U.S. Geological Survey Annual Report, 14, pt. 2, p. 503-519.
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.
Elston, D.P. and McKee, E.H., 1982, Age and correlation of the late Proterozoic Grand Canyon disturbance, northern Arizona: Geological Society of America Bulletin, v. 93, no. 8, p. 681-699.
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.
Elston, D.P. and Clough, G.A., 1993, Paleomagnetic poles from the Middle Proterozoic Hazel Formation, Van Horn area, West Texas; rotations of a Grenville-deformed terrane and correlations with Keweenawan events on craton [abs.]: Geological Society of America Abstracts with Programs, v. 25, no. 1, South-Central Section, 27th Annual Meeting, Fort Worth, TX, March 15-16, 1993, p. 9.
Elston, D.P., 1993, Middle and early Late Proterozoic Grand Canyon Supergroup,
northern Arizona, IN Link, P.K., ed., Middle and Late Proterozoic stratified
rocks of the western U.S. Cordillera, Colorado Plateau, and Basin and
Range province, Chapter 6, OF Reed, J.C., Jr., and others, editors, Precambrian;
conterminous U.S.: Geological Society of America, The Geology of North
America, The Decade of North American Geology (DNAG), v. C-2, p. 521-529.
Huntoon, P.W., Billingsley, G.H., Sears, J.W., Ilg, B.R., Karlstrom, K.E., Williams, M.L., and Hawkins, David, 1996, Geologic map of the eastern part of the Grand Canyon National Park, Arizona: Grand Canyon, Ariz., Grand Canyon Association, and Flagstaff , Ariz. , Museum of Northern Arizona , scale 1:62,500.
Sears, J.W., 1973, Structural geology of the Precambrian Grand Canyon Series: Laramie , Wyo. , University of Wyoming M.S. thesis, 100 p.
Timmons, J. Michael., Karlstrom, Karl E., Heizler, Matthew T., Bowring, Samuel A., 2001, A synthesis from the Unkar Group of Grand Canyon, and inferences on late Mesoproterozoic intracratonic sedimentation and deformation in the Western U.S.: Geological Society of America, Abstracts with Programs, v. 33, no. 5, p. 20.
Timmons, J Michael., Karlstrom, Karl E., Dehler, Carol M., Geissman, John W., Heizler, Matthew T., 2001, Proterozoic multistage (ca. 1.1 and 0.8 Ga) extension recorded in the Grand Canyon Supergroup and establishment of northwest- and north-trending tectonic grains in the Southwestern United States: Geological Society of America Bulletin, v. 113, no. 2, p. 163-180.
Schwab, Fred L., 2000, The Neoproterozoic breakup of Rodinia., sedimentary and stratigraphic constraints form the western edge of Laurentia: Geological Society of America, Abstracts with Programs, v. 32, no. 7, pp. 319.
Price, L. Greer, 1999, An introduction to Grand Canyon geology: The Grand Canyon Association, 64 p.
Weil, Arlo B., Van der Voo, Rob., Geissman, John., Karlstrom, Karl, 1999, Preliminary paleomagnetic results from the Neoproterozoic Chuar Group, Grand Canyon Supergroup, Arizona: Geological Society of America, Abstracts with Programs, v. 31, no. 7, p. 317.
Hendricks, J.D., Stevenson, G.M., 1990, Grand Canyon Supergroup: Unkar Group. In: Beus, S.S., Morales, M., editors, Grand Canyon Geology, Oxford University Press, New York, p. 29-47.
Ford, T.D., 1990, Grand Canyon Supergroup: Nankoweap Formation, Chuar Group, And Sixtymile Formation. In: Beus, S.S., Morales, M., editors, Grand Canyon Geology, Oxford University Press, New York, p. 49-70.
Bickford, M E., Soegaard, Kristian., Nielsen, K. C.,1997, A transform
southern Laurentian margin during the Mesoproterozoic., evidence from
rift-related deposits: Geological Society of America, Abstracts with Programs,
v. 29, no. 6, p.433.
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.
