Bright Angel Shale facts for kids

Quick facts for kids Bright Angel Shale Stratigraphic range: Middle Cambrian
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
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
Named by	Noble (1914)

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. 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. The Bright Angel Shale preserves fossils dating back to the Cambrian Period.

Bright Angel Shale sites

Relative long distance photo of Isis Temple (adjacent prominence is Tiyo Point, of the North Rim)

The entire Tonto Group 3-unit sequence is visible above the Colorado River (side intersecting canyon to Granite Gorge)

(From Komo Point)-Sloping Supai Group redbeds upon Redwall Limestone cliffs and horizontal platforms on the Muav Limestone on greenish Bright Angel Shale

The three 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:

• Redwall Limestone
• Temple Butte Formation, Devonian – (409–363 Ma), channel deposits upon Muav Limestone
• Tonto Group (~544–505 Ma)
  • Muav Limestone
  • Bright Angel Shale
  • Tapeats Sandstone