Shinumo Quartzite

Shinumo Quartzite Stratigraphic range: Meso-Proterozoic, between 1,170 and 1,150 Ma
(photo bottom)-Isis Temple-monadnock—Cliffs of Shinumo Quartzite-(at angular dip) below drab-greenish slopes of Bright Angel Shale
Type	Geological formation
Unit of	Unkar Group
Underlies	Dox Formation
Overlies	Hakatai Shale
Thickness	1,150 to 1,345 feet (351 to 410 m)
Lithology
Primary	quartzite
Other	conglomeratic sandstone, quartzitic sandstone, arkosic sandstone, mudstone
Location
Region	Arizona, Grand Canyon Isis Temple region, southwest Bright Angel Canyon, at north side, Granite Gorge, and along Colorado River
Country	United States of America
Type section
Named for	Shinumo Canyon
Named by	Noble (1914)

The Shinumo Quartzite also known as the Shinumo Sandstone, is a Mesoproterozoic rock formation, which outcrops in the eastern Grand Canyon, Coconino County, Arizona. The Shinumo Quartzite consists of a series of massive, cliff-forming sandstones and sedimentary quartzites. Its cliffs contrast sharply with the stair-stepped topography of the underlying Hakatai Shale. Overlying it, dark green to black, fissile, slope-forming shales of the Dox Formation create a well-defined notch. It and other formations of the Unkar Group occur as isolated fault-bound remnants along the main stem of the Colorado River and its tributaries in Grand Canyon. Typically, the Shinumo Quartzite and associated strata of the Unkar Group dip northeast (10°-30°) toward normal faults that dip 60+° toward the southwest. This can be seen at the Palisades fault in the eastern part of the main Unkar Group outcrop area (below East Rim).

The Shinumo Quartzite is a middle member of the Unkar Group. The Unkar Group is about 1,600 to 2,200 m (5,200 to 7,200 ft) thick and composed of, in ascending order, the Bass Formation, Hakatai Shale, Shinumo Quartzite, Dox Formation, and Cardenas Basalt. The Unkar Group consists of a sequence of sedimentary rocks that accumulated in a variety of environments ranging from fluvial to shallow-marine. Overall, the strata within it are conformable with the exception of a significant disconformity between the Hakatai Shale and Shinumo Quartzite. The Unkar Group is overlain in ascending order by the Nankoweap Formation, about 113 to 150 m (371 to 492 ft) thick; the Chuar Group, about 1,900 m (6,200 ft) thick; and the Sixtymile Formation, about 60 m (200 ft) thick. The Unkar Group, as the base section of the Grand Canyon Supergroup, overlies deeply eroded granites, gneisses, pegmatites, and schists that comprise Vishnu Basement Rocks.