Muav Limestone

The Cambrian Muav Limestone is a geologic unit within the 5-member Tonto Group. It is about 650 feet (198 m) thick at its maximum. It is a resistant cliff-forming unit. The Muav consists of dark to light-gray, brown, and orange red limestone with dolomite and calcareous mudstone.[5][3] The Muav Limestone is overlain in the western Grand Canyon by the late Cambrian Frenchman Mountain Dolostone. Eastward, the Frenchman Mountain Dolostone pinches out and the Mississippian Redwall Limestone, which forms prominent vertical cliffs, directly lies upon the Muav Limestone. The Devonian Temple Butte Formation fill deep paleovalleys that have been cut through the Frenchman Mountain Dolostone and into the Muav Limestone.[3]

Muav Limestone
Stratigraphic range: Middle Cambrian[1][2]
representative sequence of Redwall Limestone, Temple Butte Formation, and Muav Limestone, in Grand Canyon
TypeGeological formation
Unit ofTonto Group[3]
Underlieseither the Frenchman Mountain Dolostone (Cambrian) or Redwall Limestone (Mississippian). Locally underlies Temple Butte Formation (Devonian) that fills narrow paleovalleys cut into the Muav Limestone.
OverliesBright Angel Shale
Thickness650 feet (200 m), at maximum
Lithology
Primarylimestone and dolomite
Othercalcareous mudstone
Location
RegionNorthern Arizona (Grand Canyon), central Arizona, southeast California, southern Nevada, and southeast Utah
CountryUnited States of America
Type section
Named forMuav Canyon, north side of Colorado River[4]
Named byNoble (1914)[4]

The Muav is in part younger than, and in-part grades into, the Bright Angel Shale, which is less erosion resistant and is categorized as a slope-forming unit. The Muav is about 350 feet thick in the east and reaches about 600 feet thick in the western part of its exposure area in the Grand Canyon.[6] The two units lie above the erosion-resistant cliff-forming Tapeats Sandstone.

In the eastern canyon, the Tapeats Sandstone creates the extremely horizontal Tonto Platform. In west Grand Canyon, the north-south Toroweap Fault is the west perimeter of the Tonto Platform, and west Grand Canyon is dominated by the erosion resistant unit of the Esplanade Sandstone. The Tonto Trail is a mostly horizontal trail on the south side of Granite Gorge, on the Tonto Platform.

The Tonto Group units were deposited on an ancient erosion surface (angular unconformity) on the Vishnu Basement Rocks. The Vishnu sequence has a dip of about 45 degrees. As this long-timeframe unconformity represents about 1,000 million years (1.0 billion years) of non–deposition, tectonic activity and erosion, on the Vishnu Basement Rocks, is called the Great Unconformity.

Beyond the Grand Canyon area the Muav occurs in southern Utah, southern Nevada and southern California. In the California occurrence it is known as the Muav Marble.[6]

Geologic sequence

The units of the Tonto Group:[3]

  • 5 – Frenchman Mountain Dolostone
  • 4 – Muav Limestone
  • 3 – Bright Angel Shale
  • 2 – Tapeats Sandstone (start of transgression series)
  • 1 – Sixtymile Formation
  • Muav Limestone cliff example, below Redwall Limestone cliff, on the North Kaibab Trail (closeup photos, often show purple erosion debris)(expandable photo)
    Muav Limestone cliff example, below Redwall Limestone cliff, on the North Kaibab Trail (closeup photos, often show purple erosion debris)(expandable photo)
  • (view due-north, northeast, from Bright Angel Trail, (South Rim section) – View of south-draining Bright Angel Canyon, containing in its lowest section with the Tapeats Sandstone, upon the Granite Gorge, the cliffs of gray-brown Muav Limestone (25% at base of Redwall Limestone), laid upon the slope-forming & greenish Bright Angel Shale. (The trail also descends/ascends through units on the South Rim, at near photo view.)
    (view due-north, northeast, from Bright Angel Trail, (South Rim section) – View of south-draining Bright Angel Canyon, containing in its lowest section with the Tapeats Sandstone, upon the Granite Gorge, the cliffs of gray-brown Muav Limestone (25% at base of Redwall Limestone), laid upon the slope-forming & greenish Bright Angel Shale. (The trail also descends/ascends through units on the South Rim, at near photo view.)
  • View to Sumner Butte, Redwall Limestone peak & vertical cliff, sitting on Muav Limestone
    View to Sumner Butte, Redwall Limestone peak & vertical cliff, sitting on Muav Limestone

See also

References
  1. Rose, E. (2006) "Nonmarine aspects of the Cambrian Tonto Group of the Grand Canyon, USA, and broader implications". Palaeoworld. 15:223–241.
  2. 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.
  3. 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.
  4. Noble, LF (1914). "The Shinumo quadrangle, Grand Canyon district, Arizona" (PDF). U.S. Geological Survey Bulletin. 549. doi:10.3133/B549. ISSN 8755-531X. Wikidata Q57659039.
  5. 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.
  6. Anonymous (2006d) Muav Limestone Archived 2015-11-22 at the Wayback Machine, Stratigraphy of the Parks of the Colorado Plateau Archived 2010-12-24 at the Wayback Machine. U.S. Geological Survey, Reston, Virginia.

Further reading
  • Blakey, and Ranney, 2008. Ancient Landscapes of the Colorado Plateau, Ron Blakey, Wayne Ranney, c 2008, Grand Canyon Association (publisher), 176 pages, with Appendix, Glossary, Index. Contains approximately 75 shaded topographic maps, for geology, etc., with 54 (23 pairs, (46)) for Colorado Plateau specifically; others are global, or North American.
  • Arizona Geological Society, Arizona Geological Survey, c. 1998 (etc.) Geologic Highway Map of Arizona. Contains geologic map, Arizona Shaded Relief Map, Geologic Cross Sections, Shaded Relief Map of Arizona, Geologic Map of the Grand Canyon in the Vicinity of the South Rim Visitor Center, etc.
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