First use of the Awatubi Member of the Kwagunt Formation of the Chuar Group. Is dominantly argillaceous, with shales and mudstones of varying color diversified only by thin ferruginous siltstones. At the bottom of the 1128 ft, however, is a massive stromatolite layer, 12 ft thick. This consists of biohermal domes, each 8 to 10 ft in height and width, and made up of a radiate complex of columns 2 to 3 in. in diameter, alternating with confluent domes. The columns show nearly flat laminae, and are generally parallel-sided with few branches Dolomitization has destroyed most of the internal detail, but a clearly defined wall is present, indicative of the form BOXONIA Koroljuk. The matrix between columns is generally crystalline dolomite; that between bioherms is coarsely granular dolomite of a highly porous nature. Flat-pebble conglomerate can be seen at the nucleus of some bioherms. Some 30 ft from the top of the unit, black finely fissile shales yielded abundant CHUARIA CIRCULARIS on both eastern and western slopes of Nankoweap Butte, and the former is thought to be Walcott's type locality. Other beds with CHUARIA were found scattered through the upper part of the member. Age is late Precambrian.

Source: GNU records (USGS DDS-6; Menlo GNULEX).

Named as middle member of Kwagunt Formation (new) of Chuar Group for exposures in upper reaches of Awatubi Canyon, its type section, west side Colorado River, Coconino Co, AZ in the Southern Rocky Mountain region. Corresponds to Divisions 10 and 11 of Walcott (1899) and Division 7 of Hinds (1935). Overlies Carbon Butte Member (new) of Kwagunt. A conspicuous stromatolitic limestone 12 ft thick marks base of member. The stromatolites are 8 to 12 ft thick in height and diameter and as a result the upper surface of the bed is undulose. Each bioherm consists of radiating to subparallel columns of BOXONIA (of late Riphean age) 2 or 3 inches in diameter sometimes interrupted by undulating laminae. Both columns and laminae are fine-grained dolomitized limestone. Coarsely crystalline dolomite forms the matrix. Many stromatolites weather out as discrete units. Limestone overlain by greenish shale with spheroidal marcasite nodules and above that varicolored shale. Black shale beds with CHUARIA occur at several intervals especially at top. Overlain by Walcott Member (new) of Kwagunt. Is 1,128 ft thick on south slope Nankoweap Butte. Of late Precambrian age. Geologic map.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Awatubi Member of the Kwagunt Formation of the Chuar Group of the Grand Canyon Supergroup is adopted. Age is late Precambrian.

Source: GNU records (USGS DDS-6; Menlo GNULEX).

Age of the Awatubi Member of the Kwagunt Formation is modified from late Precambrian to: Proterozoic Y.

Source: GNU records (USGS DDS-6; Menlo GNULEX).

Is the middle member of the Kwagunt Formation of Chuar Group of Grand Canyon Supergroup. Is predominately shale. A ledge-forming biohermal (stromatolite) reef marks the base. Age designation of Proterozoic Y changed to Late Proterozoic, the age term applied to rocks younger than 900 Ma and older than 570 Ma. Change in age designation made to Kwagunt and its Carbon Butte (base), Awatubi, and Walcott (listed in ascending order) Members in northern AZ, Southern Rocky Mountain region. Base of Kwagunt shown at about 850 (estimated) and top of Kwagunt is shown at more than 825 Ma. Columnar section. Is 297 m thick.

Source: GNU records (USGS DDS-6; Denver GNULEX).