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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.
As currently defined Tonto Group consists of the Sixtymile Formation, Tapeats Sandstone, Bright Angel Shale, Muav Limestone, and Frenchman Mountain Dolostone. [1] [2] The Sixtymile Formation is a very thin accumulation of sandstone, siltstone, and breccia underlying the Tapeats Sandstone. It is exposed only atop Nankoweap Butte and within ...
This exposure is frequently illustrated in popular and educational publications, and is often part of geological fieldtrips. There is a gap of about 1.2 billion years where 550 million year old strata of the Tapeats Sandstone rests on 1.7 billion (1700 million) year old Vishnu Basement Rocks. [8] [9] [10]
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.
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 ...
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 ...
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.
The Sixtymile Formation is a very thin accumulation of sandstone, siltstone, and breccia underlying the Tapeats Sandstone that is exposed in only four places in the Chuar Valley. These exposures occur atop Nankoweap Butte and within Awatubi and Sixtymile Canyons in the eastern Grand Canyon, Arizona.