The Supai Group is a slope-forming sequence of mixed red beds and limestones that outcrop in the Colorado Plateau. The group was laid down during the Pennsylvanian to Lower Permian. Cliff-forming interbeds of sandstone are noticeable throughout the group. The Supai Group is quite well exposed throughout the Grand Canyon in northwest Arizona, as well as local regions of southwest Utah, such as the Virgin River valley region. Known as the Supai Formation, it occurs in Arizona at Chino Point, Sycamore Canyon, and famously at Sedona as parts of Oak Creek Canyon. In the Sedona region, it is overlain by the Hermit Formation, and the colorful Schnebly Hill Formation.Jenney, J.P., and Reynolds, S. J., Pennsylvanian and Permian geology of Arizona. Tucson, Arizona Geological Society Digest, 17, pp. 313~347.Blakey, R.C., 2003. Supai Group and Hermit Formation in: Beus, S.S., Morales, M., eds., pp. 136–162, Grand Canyon Geology, 2nd. Oxford University Press, New York. 448 pp. The Supai Group has been traced westward into the Great Basin in Nevada and California.Hewett, D.F., 1923. Geology and mineral resources of the Ivanpah quadrangle, California and Nevada. U.S. Geological Professional Paper. 275, 172 pp. and recognized in Paleozoic metamorphic strata exposed in the Big Maria Mountains, northeastern Riverside County, southeastern California.Hamilton, W. H., 1982, Structural evolution of the Big Maria Mountains, northeastern Riverside County, southeastern California. in E. G. Frost and D. L. Martin, eds., pp. 1–27, Mesozoic-Cenozoic tectonic evolution of the Colorado River region, California, Arizona, and Nevada. Cordilleran Publishers, San Diego, California, United States. 608 pp.
Nomenclature The Supai Group was originally designated as the Supai Formation by Darton in 1910 for exposures at Supai, Arizona. Darton assigned the lower beds of G.K. Gilbert's (since abandonedMcKee, E.D., 1982. Chapter C Stratigraphy and lithology. In McKee, E.D., ed., pp. 29-50, The Supai Group of Grand Canyon. U.S. Geological Survey, Professional Paper, 1173, 504 pp.) Aubrey Group to the Supai Formation, at the same time assigning the overlying gray sandstone beds to the Coconino Sandstone. In 1922, Noble separated the uppermost fine-grained, slope-forming strata of the original Supai Group into the Hermit Shale, based on the disconformity between the two.Noble, L.F., 1922. A section of the Paleozoic formations of the Grand Canyon at the Bass Trail. U.S. Geological Survey Bulletin. 131-B, pp. B23-B73. doi:10.3133/PP131B. ISSN 0096-0446. Noble also established the lower boundary of the Supai Group based on a noticeable disconformity separating Mississippian strata from Pennsylvanian strata. He transferred of alternating red beds and compact limestones from the Redwall Limestone to the Supai Group partly on the basis that the red beds resembled more closely the strata of the Supai Group instead of the massive limestone beds of the Redwall Formation. Later, McKee raised its stratigraphic rank in 1975 from Supai Formation to Supai Group.McKee, E. D., 1975. The Supai Group—subdivision and nomenclature. U.S. Geological Survey Bulletin, 1395-J 11 pp. McKee also divided the Supai Group into four formations; the Watahomigi Formation, Manakacha Formation, Wescogame Formation and Esplanade Sandstone, in the Grand Canyon region. The Supai Group remains at formation rank at other locations where its subunits are difficult to distinguish.Blakey, R.C., 1990. Stratigraphy and geologic history of Pennsylvanian and Permian rocks, Mogollon Rim region, central Arizona and vicinity. Geological Society of America Bulletin, 102, pp. 1189–1217,
Description The Supai Group consists of alternatingly interbedded soft, reddish shales and sandy; hard, buff or pinkish buff sandstones; and, in its lower part, hard, gray limestones. Most the sandstone consist of thick, massive beds that erode as prominent, vertical cliffs. The limestones also erode to form prominent, vertical cliffs. The beds of shale and laminated sandstone weather as slopes. The alternation of hard and soft beds form a distinct step-like profile, which consists of alternating cliffs and slopes. The Supai Group overlies either the Redwall Limestone or Surprise canyon Formation and underlies the Hermit Formation.
This topographic profile of the Supai Group is consistent enough that it was initially divided into five subdivisions based upon the cliff versus its slope-forming character and, thus, indirectly on associated lithology within the Grand Canyon region. They are the (1.) Upper cliff unit, locally includes a receding ledge unit (Esplanade cliff); (2.) Upper slope unit; (3.) Middle cliff unit; (4.) Middle slope unit; (5.) Lower cliff and slope unit. These units can be traced throughout the Grand Canyon as they differ remarkably little from one end to the other. However, westward, the slope units do become less conspicuous. In particular, the middle slope unit becomes so weakly developed in the western Grand Cayon region, that the lower and middle cliff units seem to merge such that lower and middle cliff units appear to merge.
In 1975, McKee incorporated specific key beds, fauna zones, and erosion surfaces into the above topographic units to define the Watahomigi formation, Manakacha formation, Wescogame Formations and Esplanade Sandstone. Most important to defining and mapping these formations are three key beds, in addition to the basal conglomerate underlying the Redwall Limestone and Surprise canyon Formation, consisting of widespread, lithologically distinct, conglomerates. Two of these of conglomerates are associated with marked erosional surfaces and, thus, likely represent regional unconformities. Marine fossils that occur above and below. these conglomerates also indicate that represent significant periods of nondeposition and erosion.
Watahomigi Formation
The Watahomigi Formation, which is named for Watahomigi Point on the west side of Havasu Canyon, consists chiefly of red mudstone and siltstone, gray limestone and dolomite, and two conglomerate beds. Typically, one conglomerate bed occurs at or near its base. The other, the Atokan conglomerate, occurs locally about two-thirds up its thickness. The basal conglomerate is interbedded with purple siltstone and gray limestone and fills small erosion channels cut into either the Surprise Canyon Formation or Redwall Limestone. The upper and lower thirds of it consist of slope-forming redbeds, The middle third of the formation is composed mostly of limestone beds containing red chert lenses and nodules. These limestone beds form a massive cliff. The Watahomigi Formation conformably underlies the Manakacha Formation. The Watahomigi Formation is a broad, slightly westward-thickening sheet. It ranges from thick in eastern Grand Canyon to thick in western Grand Canyon and along the Grand Wash Cliffs.
Manakacha Formation The Manakacha Formation is named from Manakacha Point on the east side of Havasu Canyon and directly above Supai village. It consists of quartz sandstone, calcareous sandstone, dark-red siltstone, and gray limestone. The sandstone exhibits sets of trough, planar, and compound cross-bedding that ranges from to in thickness. The Manakacha Formation rests conformably on the Watahomigi Formation. Its upper contact is an unconformity consisting of an erosional surface. The basal conglomerate of the Wescogame Formation overlies this erosional surface. The Manakacha Formation is broad, sheetlike deposit across northwestern and central Arizona that averages about thick in Grand Canyon and 150 feet (45 m) thick across the Verde and Chino valleys.
Wescogame Formation
The Wescogame Formation is named from Wescogame Point on the west side of Havasu Canyon and directly above Hualapai Canyon. Its lower part consists of cliff-forming, light-red to gray, high-angle, large- and medium-scale, tabular-planar, cross-bedded sandstone and calcareous sandstone as much as thick Its upper part consists mainly of slope-forming, dark-red, fine-grained siltstone and mudstone interbedded with light-red, coarse-grained, calcareous sandstone and dolomitic sandstone, siltstone, mudstone, and a basal conglomerate. the basal conglomerate unconformably overlies the Manakacha Formation. The unconformable contact with underlying Manakacha Formation consists of paleovalleys as much as deep in the western Grand Canyon area and less than deep in the eastern Grand Canyon area. Conglomerates composed of either limestone, chert, or both commonly fill the paleovalleys. The Wescogame Formation lies unconformably beneath the Esplanade Sandstone. The Wescogame Formation consists of a sheet that ranges from thick across the Grand Canyon and the western Mogollon Rim region.
Esplanade Sandstone The Esplanade Sandstone is named for the Esplanade platform that is a prominent bench in the walls of the Grand Canyon. It consists mainly of beds generally thick beds of cross-stratified sandstone. The sandstone beds are typically separated by either thin, red mudstone; fine-grained limestones or dolomite; or prominent, irregular-bedding planes. Most cross-bedded sandstone exhibit climbing translatent strata. In western Grand Canyon, the Esplanade Sandstone contains some extensive beds of gypsum. As previously noted, it unconformably overlies the Wescogame Formation. The Hermit Formation unconformably overlies the Esplanade Sandstone and is and separated from it in many places by an erosional surface exhibiting numerous paleovalleys. The Esplanade Sandstone is a steadily northwestward-thickening wedge. This wedge ranges from over in the western Grand Canyon and along the Grand Wash Cliffs to thick in the eastern Grand Canyon and western Mogollon Rim region. In the western Grand Canyon region grades into the Pakoon Limestone, which is included in its thickness.
Contacts
The contact between the base of the Supai Group and the underlying Redwall Limestone and Surprise Canyon Formation is a regional unconformity. It consists of an eroded surface, which covered by either a thin widespread, but locally discontinuous, limestone and chert pebble conglomerate or purplish red calcareous siltstones and mudstones.Billingsley, G.H., and Beus, S.S., 1985, The Surprise Canyon Formation—an upper Mississippian and Lower Pennsylvanian (?) rock unit in the Grand Canyon, Arizona. Stratigraphic Notes, 1984. U. S. Geological Survey Bulletin, no. 1605-A, pp. 27–33.
The top of the Redwall Limestone represents a period of subaerial erosion during the Late Mississippian period during which rivers entrenched deep paleovalleys, as much as deep, into the Redwall Limestone. Also, during this period an extensive karst plain formed on the surface of the Redwall Limestone. Later with rising sea levels, the strata of the Surprise Canyon Formation accumulated within the paleovalleys before it and extensive karst plain were buried by the accumulation of the Watahomigi Formation.McKee, E.D., 1982. Chapter H. Erosion surfaces. In McKee, E.D., ed., pp. 155-177, The Supai Group of Grand Canyon. U.S. Geological Survey, Professional Paper, 1173, 504 pp.
The contact between the top of the Supai Group and the overlying Esplanade Sandstone is a regional unconformity marked by an erosion surface. Where it is beautifully exposed in the walls of Hermit Canyon, this unconformity consists of numerous paleovalleys cut down into what were massive sands, but now sandstones. Shaly mudstone and siltstones fill these paleovalleys, which range in depth from and have rounded sides and flat bottoms. Residual mesas with relief of and above this unconformity's normally flat surface can be found in National Canyon and along the Apache Trail in Havasu Canyon. Conglomerates are absent from this erosion surface.
Fossils