Bright Angel Shale: Difference between revisions
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The units of the Tonto Group:<ref name="KarlstromOther2020a"/> |
The units of the Tonto Group:<ref name="KarlstromOther2020a"/> |
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* 5 – Frenchman Mountain |
* 5 – Frenchman Mountain Dolostone |
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* 4 – Muav Limestone |
* 4 – Muav Limestone |
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* 3 – Bright Angel Shale |
* 3 – Bright Angel Shale |
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Revision as of 03:00, 12 April 2022
| Bright Angel Shale | |
|---|---|
| Stratigraphic range: Middle Cambrian[1][2] | |
 Muav Limestone – (dk or lt gray, brown, or orange-red subcliff at base of Redwall Limestone cliff) and Bright Angel Shale (greenish slope-former), resting on Tapeats Sandstone (short, dp brown vertical cliff) (Tapeats forms the "Tonto Platform"), inner canyon, Granite Gorge. (The 3 units – Muav, Bright Angel, and Tapeats, are easily seen below the red-stained Redwall Limestone (550 ft thick)) | |
| Type | Geological formation |
| Unit of | Tonto Group[3] |
| Underlies | Muav Limestone |
| Overlies | Tapeats Sandstone |
| Thickness | 500 feet (150 m) at its maximum |
| Lithology | |
| Primary | micaceous siltstone and shale |
| Other | sandstone and glauconitic sandstone |
| Location | |
| Region | northern Arizona, southeast California, southern Nevada, and southcentral Utah |
| Country | United States of America |
| Type section | |
| Named for | Bright Angel Canyon, Bright Angel quadrangle, Coconino Co., Arizona[4] |
| Named by | Noble (1914)[4] |
The Cambrian Bright Angel Shale is the middle layer of the three member Tonto Group geologic feature. The 3-rock Tonto section famously sits upon the Great Unconformity because of the highly resistant cliffs of the base layer, vertical Tapeats Sandstone cliffs.
The Bright Angel Shale is easily identified for two reasons. Its soft-greenish color stands out against the browns, reds, and whites of neighboring rock units. And secondly for its slope-forming character against mostly cliff-forming resistant rocks.
The Bright Angel Shale is about 500 feet (152 m) thick at its maximum. It is a nonresistant slope-forming unit. The Bright Angel Shale consists of green and purple-red, siltstone and shale which is interbedded with red-brown to brown sandstone that is similar in lithology to the underlying Tapeats Sandstone.[3] The Bright Angel Shale underlies and interfingers with Muav Limestone. The Bright Angel Shale is located in the lower elevations of the Grand Canyon, Arizona.[5]
The units of the Tonto Group and the colorful Bright Angel Shale are easily identified as a geological sequence beneath the tall cliffs of the Redwall Limestone (the Redwall sits upon a short resistant cliff of Muav Limestone); the Tonto Group is also easily seen beside Granite Gorge of the Colorado River and the Vishnu Basement Rocks
The units of the Tonto Group:[5]
- 5 – Frenchman Mountain Dolostone
- 4 – Muav Limestone
- 3 – Bright Angel Shale
- 2 – Tapeats Sandstone (start of transgression series)
- 1 – Sixtymile Formation
See also
- Geology of the Grand Canyon area
- List of fossiliferous stratigraphic units in Arizona
- Paleontology in Arizona
References
- ^ Rose, E (2006) "Nonmarine aspects of the Cambrian Tonto Group of the Grand Canyon, USA, and broader implications." Palaeoworld. 15:223–241.
- ^ Rose, E (2011) Modification of the nomenclature and a revised deposition model for the Cambrian Tonto Group of the Grand Canyon, Arizona. in JS Hollingsworth, FA Sundberg, and JR Foster, eds., pp. 77–98, Cambrian Stratigraphy and Paleontology of Northern Arizona and Southern Nevada: Museum of Northern Arizona Bulletin 67, 321 p.
- ^ a b Connors, T.B., Tweet, J.S., and Santucci, V.L., 2020. Stratigraphy of Grand Canyon National Park. In: Santucci, V.L., Tweet, J.S., ed., pp. 54–74, Grand Canyon National Park: Centennial Paleontological Resource Inventory (Non-sensitive Version) . Natural Resource Report NPS/GRCA/NRR—2020/2103. National Park Service, Fort Collins, Colorado, 603 pp.
- ^ a b L. F. Noble (1914). "The Shinumo quadrangle, Grand Canyon district, Arizona" (PDF). U.S. Geological Survey Bulletin. 549. doi:10.3133/B549. ISSN 8755-531X. Wikidata Q57659039.
- ^ a b Karlstrom, K.E., Mohr, M.T., Schmitz, M.D., Sundberg, F.A., Rowland, S.M., Blakey, R., Foster, J.R., Crossey, L.J., Dehler, C.M. and Hagadorn, J.W., 2020. Redefining the Tonto Group of Grand Canyon and recalibrating the Cambrian time scale. Geology, 48(5), pp. 425–430.
Further reading
- Blakey, Ron and Wayne Ranney, Ancient Landscapes of the Colorado Plateau, Grand Canyon Association (publisher), 2008, 176 pages, ISBN 978-1934656037
- Brandriss, M. (2004) Angular unconformity between Proterozoic and Cambrian rocks, Grand Canyon, Arizona. GeoDIL, A Geoscience Digital Image Library, University of North Dakota, Grand Forks, North Dakota.
- Lucchitta, Ivo, Hiking Arizona's Geology, 2001, Mountaineers's Books, ISBN 0-89886-730-4
- Mathis, A., and C. Bowman (2007) The Grand Age of Rocks: The Numeric Ages for Rocks Exposed within Grand Canyon, Grand Canyon National Park, Arizona, National Park Service, Grand Canyon National Park, Arizona.
- Share, J. (2102a) The Great Unconformity of the Grand Canyon and the Late Proterozoic-Cambrian Time Interval: Part I – Defining It.
- Share, J. (2102a) The Great Unconformity and the Late Proterozoic-Cambrian Time Interval: Part II - The Rifting of Rodinia and the "Snowball Earth" Glaciations That Followed.
- Timmons, M. K. Karlstrom, and C. Dehler (1999) Grand Canyon Supergroup Six Unconformities Make One Great Unconformity A Record of Supercontinent Assembly and Disassembly. Boatman's Quarterly Review. vol. 12, no. 1, pp. 29–32.
- Timmons, S. S. (2003) Learning to Read the Pages of a Book (Grand Canyon Geology Training Manual), National Park Service, Grand Canyon National Park, Arizona.