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Except where underlain by the Sixtymile Formation, the Tapeats Sandstone is the Cambrian geologic formation that is the basal geologic unit of the Tonto Group.Typically, it is also the basal geologic formation of the Phanerozoic strata exposed in the Grand Canyon, Arizona, and parts of northern Arizona, central Arizona, southeast California, southern Nevada, and southeast Utah.
In the Grand Canyon, the Tapeats Sandstone is a medium- to coarse-grained, thin-bedded, cliff-forming conglomeratic sandstone that weathers to a tan or reddish-brown. Its thickness varies from very thin or absent where deposited over prominent paleotopographic highs, as much as to 90 m (300 ft) high.
The three units of the Tonto Group are Muav Limestone, upon Bright Angle Shale, upon Tapeats Sandstone. The Tapeats is a thin cliff-former unit found along Granite Gorge and its side canyons forming a flat surface in locales not dramatically affected by faulting, up-warping (domes), or down-warping.
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.
Thin drapes of Tapeats Sandstone of the Tonto Group either cover or drape onto most of these ancient monadnocks. However, the summits of the highest monadnocks protrude up through the base layer Tapeats Sandstone and are blanketed by overlying Bright Angel Shale as can be seen at Isis Temple. Lava Butte is a partially exhumed prehistoric ...
Tapeats Sandstone averages 525 million years old and is made of medium- to coarse-grained sand and conglomerate that was deposited on an ancient shore (see 3a in figure 1). [11] Ripple marks are common in the upper members of this dark brown thin-bedded layer. Fossils and imprint trails of trilobites and brachiopods have also been found in the ...
At the base of this sequence, the Great Unconformity, with the Tapeats Sandstone of the Tonto Group overlying the Vishnu Basement Rocks, is well exposed in a manner that is atypical and scientifically significant in its combination of extent and accessibility. This exposure is frequently illustrated in popular and educational publications, and ...
They form the crystalline basement rocks that underlie the Bass Limestone of the Unkar Group of the Grand Canyon Supergroup and the Tapeats Sandstone of the Tonto Group. These basement rocks have also been called the Vishnu Complex and Vishnu Metamorphic Complex .