Bright Angel Shale: Difference between revisions
m added link |
m →Nomenclature: aded links |
||
| Line 28: | Line 28: | ||
== Nomenclature == |
== Nomenclature == |
||
In 1875, G. K. Gilbert<ref name="Gilbert1875a">Gilbert, G.K., 1875. ''Report upon the geology of portions of Nevada, Utah, California, and Arizona, Chapter 6.'' In Wheeler, G.M., ed., pp. 17–187, ''Report on the Geographical and Geological Explorations and Surveys West of the One Hundredth Meridian'', vol. 3. U.S. Geological and Geographical Survey, Publication of the Wheeler Survey, Washington, D.C., 681 pp.</ref> recognized that strata exposed near the bottom of parts of the Grand Canyon are similar to those known elsewhere in Arizona as the ''Tonto Group''. Based upon this similarity, he assigned the strata that form the lowermost part of the Phanerozoic strata in the Grand Canyon to the ''Tonto Group''. Without designating formal [[Type locality (geology)|type localities]], he also subdivided the Tonto Group into three subdivisions, from youngest to oldest, the ''Marbled limestone'', the ''Tonto shale'', and the ''Tonto sandstone''.<ref name="Gilbert1875a"/> |
In 1875, G. K. Gilbert<ref name="Gilbert1875a">Gilbert, G.K., 1875. ''Report upon the geology of portions of Nevada, Utah, California, and Arizona, Chapter 6.'' In Wheeler, G.M., ed., pp. 17–187, ''Report on the Geographical and Geological Explorations and Surveys West of the One Hundredth Meridian'', vol. 3. U.S. Geological and Geographical Survey, Publication of the Wheeler Survey, Washington, D.C., 681 pp.</ref> recognized that strata exposed near the bottom of parts of the Grand Canyon are similar to those known elsewhere in Arizona as the ''Tonto Group''. Based upon this similarity, he assigned the strata that form the lowermost part of the [[Phanerozoic]] [[strata]] in the Grand Canyon to the ''Tonto Group''. Without designating formal [[Type locality (geology)|type localities]], he also subdivided the Tonto Group into three subdivisions, from youngest to oldest, the ''Marbled limestone'', the ''Tonto shale'', and the ''Tonto sandstone''.<ref name="Gilbert1875a"/> |
||
In 1914, L F. Noble<ref name="Noble1914a"/> renamed Gilbert's subdivisions of the Tonto Group. He renamed the Tonto sandstone as the ''Tapeats Sandstone'' and the Tonto shale as the ''Bright Angel Shale''. He named the Bright Angel Shale after Bright Angel Canyon because in the walls of this canyon, this formation is well exposed.<ref name="Noble1914a"/> |
In 1914, L F. Noble<ref name="Noble1914a"/> renamed Gilbert's subdivisions of the Tonto Group. He renamed the Tonto sandstone as the ''Tapeats Sandstone'' and the Tonto shale as the ''Bright Angel Shale''. He named the Bright Angel Shale after Bright Angel Canyon because in the walls of this canyon, this formation is well exposed.<ref name="Noble1914a"/> |
||
Revision as of 16:04, 7 June 2023
| Bright Angel Shale | |
|---|---|
| Stratigraphic range: Middle Cambrian[1] | |
 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 feet (170 m) thick) | |
| Type | Geological formation |
| Unit of | Tonto Group[2] |
| Underlies | Muav Limestone |
| Overlies | Tapeats Sandstone |
| Thickness | 450 feet (140 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[3] |
| Named by | Noble (1914)[3] |
The Bright Angel Shale is one of five geological formations that comprise the Cambrian Tonto Group. It and the other formations of the Tonto Group outcrop in the Grand Canyon, Arizona, and parts of northern Arizona, central Arizona, southeast California, southern Nevada, and southeast Utah. The Bright Angel Shale consists of locally fossiliferous, green and red-brown, micaceous, fissile shale (mudstone) and siltstone with local, thicker beds of brown to tan sandstone and dolomite. It ranges in thickness from 57 to 450 feet (17 to 137 m). Typically, its thin-bedded shales and sandstones are interbedded in cm-scale cycles. They also exhibit abundant sedimentary structures that include current, oscillation, and interference ripples. The Bright Angel Shale also gradually grades downward into the underlying Tapeats Sandstone. It also complexly interfingers with the overlying Muav Limestone. These chracters make defining the upper and lower contacts of the Bright Angel Shale often difficult to define. Typically, its thin-bedded shales and sandstones erode into green and red-brown slopes that rise from the Tonto Platform up to cliffs formed by limestones of the overlying Muav Limestone and dolomites of the Frenchman Mountain Dolostone.[2][4]
Nomenclature
In 1875, G. K. Gilbert[5] recognized that strata exposed near the bottom of parts of the Grand Canyon are similar to those known elsewhere in Arizona as the Tonto Group. Based upon this similarity, he assigned the strata that form the lowermost part of the Phanerozoic strata in the Grand Canyon to the Tonto Group. Without designating formal type localities, he also subdivided the Tonto Group into three subdivisions, from youngest to oldest, the Marbled limestone, the Tonto shale, and the Tonto sandstone.[5]
In 1914, L F. Noble[3] renamed Gilbert's subdivisions of the Tonto Group. He renamed the Tonto sandstone as the Tapeats Sandstone and the Tonto shale as the Bright Angel Shale. He named the Bright Angel Shale after Bright Angel Canyon because in the walls of this canyon, this formation is well exposed.[3]
Later in 1922,[6] the Marbled limestone was redefined and renamed as the Muav Limestone by L. F. Noble. According to Noble's definition, the Muav Limestone consisted of an upper set of dolomite beds and a lower set of limestone beds.[6] Nobles's lower set of limestone beds is now defined as the Muav Limestone and the Frenchman Mountain Dolostone is now defined as Nobles's upper set of dolomite beds.[4]
E. D. McKee and C. E. Resser[7] largely retained Noble's nomenclature. However, they did subdivide the Bright Angel Shale into a number of subdivisions, members, based upon prominent beds of limestone and sandstone within it. However, these members have found to be confusing and unhelpful in understanding the stratigraphy of the Bright Angel Shale and are typically ignored and rarely used in the published literature.[8][9]
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
See also
- Geology of the Grand Canyon area
- List of fossiliferous stratigraphic units in Arizona
- Paleontology in Arizona
References
- ^ 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.
- ^ a b Middleton, L.T. and Elliott, D.K., 2003. Tonto Group, in Beus, S. S., and Morales, M., eds. Grand Canyon geology Museum of Northern Arizona Press, Flagstaff, Arizona. pp. 90–106.
- ^ a b c d 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 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 Gilbert, G.K., 1875. Report upon the geology of portions of Nevada, Utah, California, and Arizona, Chapter 6. In Wheeler, G.M., ed., pp. 17–187, Report on the Geographical and Geological Explorations and Surveys West of the One Hundredth Meridian, vol. 3. U.S. Geological and Geographical Survey, Publication of the Wheeler Survey, Washington, D.C., 681 pp.
- ^ a b Noble, L.F., 1922. A section of the Paleozoic formations of the Grand Canyon at the Bass Trail. U.S. Geological Survey Bulletin. 131-B, pp. 23–73
- ^ McKee, E.D., and Resser, C.E., 1945, Cambrian history of the Grand Canyon region. Carnegie Institution of Washington Publication 563, 168 pp.
- ^ Huntoon, P.W., 1977. Cambrian stratigraphic nomenclature and ground‐water prospecting failures on the Hualapai Plateau, Arizona. Groundwater, 15(6), pp.426-433.
- ^ Huntoon, P. W. (1989). Cambrian stratigraphic nomenclature, Grand Canyon, Arizona: Mappers nightmare, in Elston, D.P., Billingsley, G.H., and Young, R.A., eds. Geology of Grand Canyon, northern Arizona (with Colorado River guides): Lees Ferry to Pierce Ferry, Arizona. Field trips for the 28th international geological congress. Museum of Northern Arizona Press, Flagstaff, Arizona. pp. 128–129. doi:10.1029/FT115p0128
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.
- 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.