Redwall Limestone
| Redwall Limestone | |
|---|---|
| Stratigraphic range: Early and early Late Mississippian[1][2] | |
 Redwall Limestone cliff, and upper platform of cliff extension (resting on very short Muav Limestone cliff), from Tower of Set, central Grand Canyon, adjacent Granite Gorge. The bottom of Redwall cliffs typically rest on sections of Temple Butte Formation-(locally), or attached sections of Muav Limestone cliffs (regionally exposed in Grand Canyon, elsewhere in Arizona, not always with surface exposure). | |
| Type | Geological formation |
| Underlies | Supai Group and locally Surprise Canyon Formation. The Surprise Canyon Formation fills local paleovalleys, caves, and collapse structures cut into the underlying Redwall Limestone. |
| Overlies | Muav Limestone and Temple Butte Formation |
| Thickness | 800 feet (240 m), at maximum |
| Lithology | |
| Primary | fossiliferous limestone |
| Other | dolomite and chert |
| Location | |
| Region | Northern Arizona, southeast California, New Mexico, and southern Utah, Nevada |
| Country | United States of America |
| Type section | |
| Named for | the red appearance of its escarpment on either side of the Grand Canyon[3] |
| Named by | Gilbert (1875)[3] |
The Redwall Limestone is an erosion-resistant, Mississippian age, cliff-forming geological formation that forms prominent, red-stained cliffs in the Grand Canyon. these cliffs range in height from 500 feet (150 m) to 800 feet (240 m).[1][2]
Nomenclature[edit]
In 1875, Gilbert[3] recognized and named the Redwall Limestone for the red coloration of its escarpment on either side of Grand Canyon. As originally defined by him, it included some strata younger and older than as it is currently defined. Later in 1910, Darton[4] selected a canyon that he named the Redwall Canyon in the Shinumo drainage basin, on north side of the Grand Canyon, as the type section of the Redwall Limestone. At this location, it consists mostly of the usual heavily bedded massive limestone and is circa 800 ft (240 m) thick. Noble[5] subsequently redefined the Redwall Limestone in its present definition, which includes all strata of Mississippian age. As a result of studies in Yavapai County, Arizona, Gutschick[6] recognized four informal members within the Redwall Limestone and McKee[7] later formally named them. The most comprehensive study of the Redwall Limestone is the History of the Redwall Limestone of northern Arizona by McKee and Gutschick.[2]
Description[edit]
Redwall Limestone consists predominantly of light-olive-gray to light-gray, fine- to coarse-grained, thin- to thick-bedded, often cherty, limestone. Its lower part consists of brownish-gray, interbedded with finely crystalline dolomite and fine- to coarse-grained limestone with layers of white chert lenses and yellowish-gray and brownish-gray, cliff-forming, thick-bedded, fine-grained dolomite.[1][2]
In ascending order, the Redwall Limestone is divided into the Whitmore Wash, Thunder Springs, Mooney Falls, and Horseshoe Mesa members. All four member have their type locality in the Grand Canyon or its tributaries. They are recognized throughout the Grand Canyon area, northen Arizona, and southern Utah. They are all Mississippian in age.[1][2]
The Whitmore Wash Member is the basal, oldest, member of the Redwall Limestone. It typically forms a high, resistant cliff standing on a narrow bench or series of ledges typical of underlying strata. This member consists of nearly pure limestone and dolomite, which contains less than 2 percent insoluble gypsum and iron oxides. This member is predominately composed of thick-bedded, ranging from 2 to 4 ft (0.61 to 1.22 m) and locally thicker, limestone in western Grand Canyon and changes to mostly very thick-bedded 4 to 15 ft (1.2 to 4.6 m), fine-grained dolomite in central and eastern Grand Canyon. The limestones are composed mostly of pelletal, skeletal or oolitic wackestones and packstones. In a few places, this member exhibits conspicuous medium-scale crossbedding. In the Grand Canyon, the Whitmore Wash Member varies in thickness from about 100 ft (30 m) in the eastern Grand Canyon to nearly 100 ft (30 m) at Iceberg Ridge, 5 mi (8.0 km) beyond the western end of Grand Canyon. The overlying Thunder Springs Member lies comfortably on Whitmore Wash Member and its base is easily recognized by the lowest appearance of thin, dark, chert beds alternating with thin beds of lighter gray limestone or dolomite.[1][7]
The Thunder Springs Member is the most distinctive member of the Redwall Limestone, because it forms cliffs that exhibit prominent black and light-brown banding. Its light and dark banded appearance is imparted by thin beds of either light gray limestone or light gray dolomite alternating with thin beds of dark reddish brown or dark gray beds or lenses of chert. Most of the limestone is fine to very coarse, thin-bedded, crinoidal grainstone or packstone. The carbonate beds vary from being predominately limestone in the western Grand Canyon and to predominately dolomite in the eastern Grand Canyon. The thin chert beds in this member consist of silicified bryozoan wackestones and lime mudstones. The Thunder Springs Member gradually increases in thickness from 100 ft (30 m) in eastern Grand Canyon to about 150 ft (46 m) in the western Grand Canyon. The contact of the overlying Mooney Falls Member with the underlying Thunder Springs Member is disconformable except in the extreme western end of Grand Canyon. Locally, this contact is a low-angle unconformity. This is indicative of a period of emergence, minor tectonic activity, and erosion between the deposition of the Thunder Springs and Mooney Falls members.[1][7]
The Mooney Falls Member forms a major part of the high, sheer escarpment for which the Redwall Limestone is named. It consists predominantly of pure limestone, except locally where it is dolomitized. It contains less than 0.5 percent insoluble residue. These limestones consist of oolites, pellets, and a variety of skeletal fragments dominated by crinoid plates. In its upper part near its contact with the overlying Horseshoe Mesa Member, one or two zones containing thin beds or lenses of chert occur. The Mooney Falls Member is normally thick-bedded and looks massive in outcrop. The upper third of this member at several localities in central and eastern Grand Canyon reportedly exhibits large-scale, tabular-planar cross-bedding. The Mooney Falls Member is the thickest member of the Redwall, ranging from about 200 ft (61 m) in eastern Grand Canyon to nearly 400 ft (120 m) at the western end. The overlying Horseshoe Mesa Member lies conformably on the Mooney Falls Member and its contact can be difficult to define in outcrops. Typically, the boundary is located at the change from vertical, cliff-forming, medium- and coarse-grained, and thick- or massive-bedded limestone to a receding-ledge-forming, fine-grained, and relatively thin-bedded, limestone.[1][7]
Horseshoe Mesa Member is the youngest, thinnest, and of the least areal extensive member of the Redwall Limestone. This member is normally composed of thin-bedded, light gray, fine-grained, limestone, typically a mudstone to wackestone that commonly contains encrusting and sediment-binding algal structures. It contains some chert lenses in its lower part. Also, crossbedding, ripple marks, and oolite beds occur locally. The Horseshoe Mesa Member typically forms weak receding ledges in contrast to the massive cliff that characterizes the Mooney Falls below. Within the Grand Canyon it varies from 45 to 125 ft (14 to 38 m). It normally thinnest in the eastern Grand Canyon. Because of erosion, this member wedges out 30 to 40 mi (48 to 64 km) south of the Grand Canyon. The Horseshoe Mesa Member is also absent from the Redwall Limestone in most of central Arizona.[1][7]
Contacts[edit]
The upper and lower contacts of the Redwall Limestone are both unconformities. Locally, the Redwall Limestone directly overlies the unconformity that forms its lower contact consisting of a basal conglomerate. This basal conglomerate is typically composed of gravel that is locally derived from either the underlying Temple Butte Formation or Muav Limestone. The Temple Butte Formation consists of a thin layer of Devonian strata that fills paleovalleys cut into the underlying Cambrian Muav Limestone. Outside of the paleovalleys, the Redwall Limestone overlies the Muav Limestone.[1]
The upper contact of the Redwall Limestone consists of a deeply eroded disconformity characterized by deeply incised paleovalleys and deep paleokarst depressions that are often filled by sediments of the Surprise Canyon Formation.[1][8]
See also[edit]
References[edit]
- ^ a b c d e f g h i j Beus, SS (2003) "Redwall Limestone and Surprise Canyon Formation." in: Beus, S.S., Morales, M., eds., pp. 115–134, Grand Canyon Geology, 2nd. Oxford University Press, New York.
- ^ a b c d e McKee, E.D., and Gutschick, R.C., eds., 1969. History of the Redwall Limestone of northern Arizona, [with] chapters on paleontology of the Redwall Limestone by B. Skipp, W.J. Sando, H. Duncan, E.L. Yochelson, W.M. Furnish, D.B. Macurda, Jr., and J.C. Brower. Geological Society of America Memoir. 114. Boulder, Colorado, Geological Society of America. 612 pp ISBN 978-08-137-1114-0
- ^ a b c Gilbert, G.K., 1875. Report upon the geology of portions of Nevada, Utah, California, and Arizona, Chapter 6. In Wheeler, G.M., ed., pp. 17-187, Report on the Geographical and Geological Explorations and Surveys West of the One Hundredth Meridian, vol. 3. U.S. Geological and Geographical Survey, Publication of the Wheeler Survey, Washington, D.C., 681 pp.
- ^ Darton, N. H., 1910. A reconnaissance of parts of northwestern New Mexico and northern Arizona. U.S. Geological Survey Bulletin. 435, 88p.
- ^ Noble, LF (1914) The Shinumo quadrangle, Grand Canyon district, Arizona. Bulletin no. 549, US Geological Survey, Reston, Virginia. 42 pp.
- ^ Gutschlck, R. C., 1943. The Redwall Limestone (Mississippian) of Yavapai County, Arizona. Plateau, 16(1), pp. 1-11.
- ^ a b c d e McKee, E. D., 1963. Nomenclature for lithologic subdivisions of the Redwall Limestone, Arizona. U.S. Geological Survey Professional Paper. 475-C, pp. C21-C23.
- ^ Kenny, R (2010) Continental paleoclimate estimates from the late Mississippian Redwall karst event: northern and north-central Arizona (USA). Carbonates Evaporites. 25(4):297–302
Further reading[edit]
- Blakey, Ron and Wayne Ranney, Ancient Landscapes of the Colorado Plateau, Grand Canyon Association (publisher), 2008, 176 pages, ISBN 978-1934656037
- Chronic, Halka. Roadside Geology of Arizona, Mountain Press Publishing Co., 1983, 23rd printing, pp. 229–232, ISBN 978-0-87842-147-3
- Lucchitta, Ivo, Hiking Arizona's Geology, 2001, Mountaineers's Books, ISBN 0-89886-730-4
External links[edit]
- Abbot, W, (2001) Revisiting the Grand Canyon – Through the Eyes of Seismic Sequence Stratigraphy. Search and Discovery Article # 40018, America Association of Petroleum Geologists, Tulsa, Oklahoma.
- Anonymous (nda) The Redwall Limestone Formation. Utah Geology.
- Mathis, A., and C. Bowman (2007) The Grand Age of Rocks: The Numeric Ages for Rocks Exposed within Grand Canyon, Grand Canyon National Park, Arizona, National Park Service, Grand Canyon National Park, Arizona.
- Shur, C., and D. Shur (2008) The Mississippi Redwall Limestone In Northern Arizona. Arizona Fossil Adventures.
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