Tapeats Sandstone

Tapeats Sandstone
Stratigraphic range: Early to Middle Cambrian[1][2]

Muav Limestone-(greenish, slope-forming) and Bright Angel Shale, resting on Tapeats and the Tonto Platform, inner canyon, Granite Gorge (the two units are easily seen below the red-stained Redwall Limestone) (550 ft thick)
Type Geological formation
Unit of Tonto Group
Underlies Bright Angel Shale
Overlies Vishnu Basement Rocks, Unkar Group, Nankoweap Formation, Chuar Group, and Sixtymile Formation
Thickness 230 feet (70 m)
Lithology
Primary sandstone and conglomerate
Other conglomeratic sandstone
Location
Region northern Arizona (Grand Canyon), central Arizona, southeast California, southern Nevada, and southeast Utah
Country United States of America
Type section
Named for Tapeats Creek[3]
Named by Noble (1914)[3]
Tapeats Sandstone ledges in Salt Creek, Grand Canyon National Park

The Cambrian Tapeats Sandstone is the lower geologic unit, about 230 feet (70 m) thick,[4] at its maximum, of the 3-member Tonto Group.

The Tapeats Sandstone is the highly erosion-resistant unit laid upon the Vishnu Basement Rocks in the central, parts of east, and parts of west Grand Canyon, Arizona. The unit comprises the 'base horizontal unit' of the platform around Granite Gorge (Inner Gorge) on the Colorado River, and because of its hardness, creates the Tonto Platform upon which the two slope-forming, highly erodable units, the Muav Limestone, and Bright Angel Shale lie.

The Tapeats Sandstone and the Tonto Platform follow the Colorado River, and surrounding tributary canyons, creeks, watercourses, or washes, in a dendritic fashion, much like the branches of a tree.

The Tapeats unit is the bottom member of the Tonto Group, a typical marine transgression series of sandstone-(conglomerate)-shale-limestone, all part of a paleo sea, initially adjacent to land, the source of the Tapeats rocks-(conglomerates) and sand; (a regressing sequence has the reverse order). The Tapeats Sea at the early Devonian ceased to deposit more Muav Limestone, and a period of erosion ensued, a deposition unconformity.

The Tapeats Sandstone was laid upon the Vishnu Basement Rocks, after an unconformity of erosion, the Great Unconformity, of 1,000 million years (1.0 billion). Besides the erosion unconformity, the Unkar Group of the basement rocks are also at an angular unconformity, being an 8-member sequence tilted at 45 degrees.

The horizontal Tonto Platform has hiking trails that cross it from the South Rim to North Rim, Grand Canyon for instance. The extensive Tonto Trail lies on parts of the Tapeats Sandstone, and the platform on the south side of Granite Gorge.


Geologic sequence

The units of the Tonto Group:

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. 1 2 Noble, LF (1914) The Shinumo quadrangle, Grand Canyon district, Arizona. Bulletin no. 549, US Geological Survey, Reston, Virginia.
  4. ↑ Chronic, H (1983) Roadside Geology of Arizona. The Mountaineers Books, Seattle, Washington. (softcover, ISBN 978-0-87842-147-3) p. 179.

Gallery--Tapeats Sandstone

Wikimedia Commons has media related to Tapeats Sandstone.

Examples of the deposition unconformity of time (550-800 million yrs), the Great Unconformity. The Tapeats approximately 200 ft thick.

  • View of Tonto Group, in descending order: Muav Limestone, Bright Angel Shale, and Tapeats Sandstone, overlying the Great Unconformity cut into Vishnu Basement Rocks in Granite Gorge region.
  • Another view of Tonto Group, in descending order: Muav Limestone, Bright Angel Shale, and Tapeats Sandstone, overlying the Great Unconformity cut into Vishnu Basement Rocks in Granite Gorge region.

Gallery—Great Unconformity and angular unconformity

Examples of the angular unconformity below the Tapeats Sandstone, (approx. 15 degrees).

  • view opposite Lipan Point, (at Desert View (Grand Canyon), East Rim), showing the banded Nankoweap Formation, (horizontal Tapeats at left, extending at base of prominence, in two fingers of rock)
This article is issued from Wikipedia - version of the 11/4/2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.