GEOLEX

Summary of Citation: Chuar

Publication:
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

Usage in Publication:
Chuar group*

Modifications:	Geologic Province:	Dominant Lithology:
First used	Southern Rocky Mountain region	Shale Sandstone Limestone

Summary:
First published use of name. Name attributed to Powell. No type locality designated. Considered a group above the Grand [Canyon] group of Early Cambrian age and beneath massive Tonto sandstones of Late Cambrian age. [Canyon spelled Canon with a tilde over the n in this report.] Consists of sandy and clay shales interbedded with sandstone and limestone. Ripple marks and mud cracks are present in many horizons. Few fossils identified--discinoid shell, Pteropod specimens. Separated from Tonto by a great unconformity. Is exposed in the inner canyon valleys between the Kaibab Plateau and the six great buttes forming the west wall of the lower part of Marble Canyon, Grand Canyon, AZ in the Southern Rocky Mountain region. Thickness not stated. Of Early Cambrian age. Thought to be equivalent in part to the Keweenawan series of WI. Columnar section shown on p. 484 illustrates relationship of Tonto to Chuar and Grand [Canyon] groups.

Summary of Citation: Chuar

Publication:
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

Usage in Publication:
Chuar terrane*

Modifications:	Geologic Province:	Dominant Lithology:
Revised Overview	Southern Rocky Mountain region

Summary:
Designated as the upper division of the Grand Canyon group (or series) above the newly named Unkar terrane of the Grand Canyon series and unconformably beneath the Tonto sandstone. Report area lies in northern AZ in the Southern Rocky Mountain region. Section 5,120 ft thick measured from summit of Nankoweap butte, on divide between Nankoweap and Kwagunt valleys, down the side of the butte to the base of the massive red-brown sandstone. Lower division of measured section consists of interbedded 1) shale that may be brown, gray, black, maroon, and green, argillaceous, sandy; 2) limestone that may be buff, gray shaly; 3) sandstone that may be buff, brown, gray, friable, coarse grained; and 4) gypsum as irregular masses. Some of the shale beds are ripple marked. Stromatopora in some limestone beds. Upper division consists of red brown sandstone, red-brown to black shale that may be sandy and argillaceous, and gray to buff limestone that has Stromatopora, oolitic and cherty bands. Algonkian age.

Summary of Citation: Chuar

Publication:
Ford, T.D. and Breed, W.J., 1973, Late Precambrian Chuar Group,
   Grand Canyon, Arizona: Geological Society of America Bulletin,
   v. 84, no. 4, p. 1243-1260

Usage in Publication:
Chuar Group

Modifications:	Geologic Province:	Dominant Lithology:
Revised	Southern Rocky Mountain region

Summary:
Is exposed in tributary canyons to the Colorado River over an area 15 mi long and 4 mi wide of northern AZ in the Southern Rocky Mountain region. Faulted against Paleozoic rocks by Butte fault to east and unconformably overlain by Tapeats Sandstone to west. Unconformably overlies Nankoweap Group. Is 6,610 ft thick. Divided into Galeros Formation (new, at base), Kwagunt Formation (new), and Sixty Mile Formation (new, at top). Galeros divided into Tanner (base), Jupiter, Carbon Canyon, and Duppa (top) Members, all new. Kwagunt divided into Carbon Butte (base), Awatubi, and Walcott (top) Members, all new. Stromatolitic limestones present in Jupiter, Carbon Canyon, and Awatubi Members. Of late Precambrian age. Geologic map.

Summary of Citation: Chuar

Publication:
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

Usage in Publication:
Chuar Group*

Modifications:	Geologic Province:	Dominant Lithology:
Revised	Southern Rocky Mountain region

Summary:
Assigned as the upper group (undivided on geologic maps) of the Precambrian Grand Canyon Supergroup (new rank; formerly Grand Canyon Series) in the Grand Canyon area of northern AZ in the Southern Rocky Mountain region. Lies unconformably above the Nankoweap Formation of the Grand Canyon Supergroup and unconformably below the Cambrian Tapeats Sandstone of the Tonto Group.

Summary of Citation: Chuar

Publication:
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

Usage in Publication:
Chuar Group*

Modifications:	Geologic Province:	Dominant Lithology:
Revised	Southern Rocky Mountain region

Summary:
Is a Proterozoic unit and part of the Grand Canyon Supergroup in northern AZ, Southern Rocky Mountain region, that is restricted to only the lower two formations--the Galeros and Kwagunt. The Sixtymile Formation is removed from the Chuar because of its different lithology and environment of deposition. Galeros and Kwagunt are predominantly dark-gray, marine shale, locally stromatolite-bearing carbonates and subordinate redbeds. Sixtymile is a very fine to coarse grained, landslide- and breccia-bearing redbed deposit of continental origin. Three horizons of algal stromatolitic limestone and CHUARIA found within shale units of the Chuar. Microflora and chitinozoan-like microfossils found in the Kwagunt. Galeros and Kwagunt are 1,900 m thick. Columnar section.

Summary of Citation: Chuar

Publication:
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., eds., Geologic evolution
   of Arizona: Arizona Geological Society Digest, v. 17, p.
   259-272

Usage in Publication:
Chuar Group*

Modifications:	Geologic Province:	Dominant Lithology:
Age modified Overview	Southern Rocky Mountain region

Summary:
A group in the Grand Canyon Supergroup of northern AZ in the Southern Rocky Mountain region whose age is changed from Proterozoic Y to Late Proterozoic, the age term applied to rocks younger than 900 Ma and older than 570 Ma. Shown as spanning the interval between 900 Ma (est) and older than 825 Ma (est). Predominately finely laminated dark shale sequence with widely spaced dolomite beds that provide a means for separating the sequence. Is a shallow-water lacustrine deposit with stromatolites of tidal flat origin, and red beds that have sedimentary structures indicating intermittent flooding. Divided into Galeros Formation and its Tanner (base), Jupiter, Carbon Canyon, and Duppa Members and the overlying Kwagunt Formation and its Carbon Butte (base), Awatubi, and Walcott Members. Unconformably overlies Nankoweap Formation. Unconformably underlies Sixtymile Formation. Is 1,632 m thick. Has a variety of micro- and planktonic fossils. Acritarch fossils indicate Late Proterozoic age. Microbiota identical to those found in Uinta Mountain Group. Predates Windermere Supergroup of CN. Probably correlates with Mackenzie Mountains Supergroup of CN. Columnar section. Little polar motion occurred during Chuar time.

Summary of Citation: Chuar

Publication:
Elston, D.P., Link, P.K., Winston, Don and Horodyski, R.J.,
   1993, Correlations of Middle and Late Proterozoic successions,
   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, eds., Precambrian; conterminous U.S.: Geological
   Society of America, The Geology of North America, The Decade
   of North American Geology (DNAG), v. C-2, p. 468-487

Usage in Publication:
Chuar Group*

Modifications:	Geologic Province:	Dominant Lithology:
Overview	Southern Rocky Mountain region

Summary:
Chuar Group of Grand Canyon Supergroup of northern AZ in the Southern Rocky Mountain region correlates with Uinta Mountain Group. CHUARIA-bearing acritarchs and vase-shaped chitinozoan-like microfossils have been reported from the Kwagunt Formation and from a sandstone in the Uinta Mountain Group beneath the Red Pine Shale. Strata bearing these fossils predate the Windermere Supergroup. Paleontologic correlation between these two groups is supported by the coincidence of their paleomagmetic poles. They have normal polarity in the lower part and they have a westward polar shift of some reversely polarized rocks in the upper part. Uinta Mountain thought to have been deposited at the north margin of the shallow Chuar sea or saline Chuar lake. Stratigraphic chart. Correlation chart. Late Proterozoic age.

Summary of Citation: Chuar

Publication:
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, eds.,
   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

Usage in Publication:
Chuar Group*

Modifications:	Geologic Province:	Dominant Lithology:
Overview	Southern Rocky Mountain region

Summary:
In northern AZ, Southern Rocky Mountain region, Middle-Late Proterozoic boundary is at unconformity between Chuar and underlying Nankoweap Formation, both of Grand Canyon Supergroup. Although boundary is placed at unconformity, no appreciable structural disturbance is recognized in Grand Canyon rocks. Nominal age of boundary is 900 Ma. Boundary separates Middle Proterozoic redbed rocks from overlying early Late Proterozoic rocks that record a time of flourishing of plankters and a general suppression of redbeds. Middle-Late Proterozoic boundary previously (Elston, 1979, USGS Prof. Paper 1092; Elston, McKee, 1982) drawn to correspond with Grand Canyon-Mackenzie Mountains orogeny at top of Grand Canyon Supergroup to which nominal age of 800 Ma was assigned. Late Proterozoic age.