Type Geologic group Named for Tonto Creek Unit of Sauk sequence | Thickness 381 m Underlies Redwall Limestone | |
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Sub-units 3)-Muav Limestone, 2)-Bright Angel Shale, 1)-Tapeats Sandstone Overlies Vishnu Basement Rocks, and 8)-Sixtymile Formation, 7)-Chuar Group, 6)-Nankoweap Formation, 5–1)-Unkar Group,
(or Vishnu Basement Rocks and members of the Grand Canyon Supergroup, units 8-1) Other calcareous mudstone and glauconitic sandstone Region northern Arizona and southern Nevada Country United States of America Primary Sandstone, Conglomerate, Siltstone, Slate, Limestone | ||
Xmas party miaoli 2010 the ultimate tonto group
The Cambrian Tonto Group is the three-member sequence of geologic formations that represent the basal section of Paleozoic rocks in the Grand Canyon. The group is about 1,250 feet (381 m) thick. The base unit, the Cambrian Tapeats Sandstone was deposited upon the erosion surface of the Vishnu Basement Rocks, which is found in Granite Gorge (the Inner Gorge). The erosion resistant Tapeats Sandstone forms the platform, called Tonto Platform, that the two less erosion resistant upper layers, the Bright Angel Shale and Muav Limestone, rest on.
Contents
The Tonto Trail is a mostly horizontal trail on the south side of Granite Gorge. The horizontal Tonto Group units are laid upon the Vishnu Basement Rocks above an angular unconformity as the Vishnu Basement Rocks have a dip of about 15 degrees. This erosion unconformity prior to the deposition of the Tapeats upon the tilted Vishnu Basement Rocks is about 1,000 million years (1.0 billion years), and is called the Great Unconformity.
Geologic sequence
The units of the Tonto Group: (~544-505 Mya)