Muav Limestone

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Muav Limestone
Stratigraphic range: Middle Cambrian
502–499  Ma
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C
P
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Redwall, Temple Butte and Muav formations in Grand Canyon.jpg
representative sequence of Redwall Limestone, Temple Butte Formation, and Muav Limestone, in Grand Canyon
Type Geological formation
Unit of Tonto Group [2]
Underlieseither the Frenchman Mountain Dolostone (Cambrian) or Redwall Limestone (Mississippian). Locally underlies Temple Butte Formation (Devonian) that fills narrow paleovalleys cut into the Muav Limestone.
Overlies Bright Angel Shale
Thickness830 feet (250 m), at maximum
Lithology
Primary limestone and dolomite
Other shale and intraformational conglomerate.
Location
RegionNorthern Arizona (Grand Canyon), central Arizona, southeast California, southern Nevada, and southeast Utah
Country United States of America
Type section
Named forMuav Canyon, north side of Colorado River [3]
Named byNoble (1914) [3]

The Muav Limestone is a Cambrian geologic formation within the 5-member Tonto Group. It is a thin-bedded, gray, medium to fine-grained, mottled dolomite; coarse- to medium-grained, grayish-white, sandy dolomite and grayish-white, mottled, fine-grained limestone. It also contains beds of shale and intraformational conglomerate. The beds of the Muav Limestone are either structureless or exhibit horizontally laminations and cross-stratification. The Muav Limestone forms cliffs or small ledges that weather a dark gray or rusty-orange color. These cliffs or small ledges directly overlie the sloping surfaces of the Bright Angel Shale. The thickness of this formation decreases eastward from 250 feet (76 m) in the western Grand Canyon to 45 feet (14 m) in the eastern Grand Canyon. To the west in southern Nevada, its thickness increases to 830 feet (250 m) in the Frenchman Mountain region. [2] [4]

Contents

Beyond the Grand Canyon area, the Muav Limestone is recognized in southern Utah, southern Nevada and southern California. [5] In parts of California, it is known and mapped as the Muav Marble. [6]

Nomenclature

In 1875, G. K. Gilbert [7] mapped the Tonto Group within the lower part of the Grand Canyon. At that time, Gilbert subdivided it, from oldest to youngest, into the Tonto Group into the Tonto sandstone, Tonto sandstone, and Marbled limestone.

In 1914, L F. Noble [3] renamed Gilbert's three subdivisions of the Tonto Group. Noble renamed Tonto sandstone as the Tapeats Sandstone; the Tonto shale as the Bright Angel Shale; and the Marbled limestone as the Muav Limestone. As defined by Noble in 1914, his Muav Limestone consisted of "...the predominantly calcareous part of the Tonto group. lying between the underlying Bright Angel Shale and either discontinuous lenses of overlying Devonian beds or base of the Redwall Limestone.

In 1922, L F. Noble [8] subdivided the Muav Limestone into four informal subdivisions. From top to bottom, his subdivisions are subdivision A, bluff massive dolomite; subdivision B, gray cross-bedded sandstone; subdivision C, thin-bedded mottled limestone; and subdivision D, basal thin-bedded mottle limestone.

Later in 1945, E. D. McKee and C. E. Resser [9] removed subdivision A of L F. Noble from both the Muav Limestone and the Tonto Group and assigned it to an informal geologic unit called the Cambrian undifferentiated dolomites. This created an informal geologic unit that is composed entirely of dolomite overlying the Muav Limestone that is composed largely of limestone. [9] Finally, S. M. Rowland and others [1] [10] formally named the Cambrian undifferentiated dolomites as the Frenchman Mountain Dolostone and restored it to the Tonto Group. [2]

Contacts

The Muav is in part younger than, and in-part grades into, the underlying Bright Angel Shale. To the west, the underlying Bright Angel Shale interfingers complexly with the overlying Muav Limestone. Its upper contact with the overlying Frenchman Mountain Dolostone is a well-defined disconformity. The Muav Limestone is overlain in the western Grand Canyon by the Cambrian Frenchman Mountain Dolostone. Eastward, the Frenchman Mountain Dolostone pinches out and the Mississippian Redwall Limestone, which forms prominent vertical cliffs, directly lies upon the Muav Limestone. Discontinuous lenses of Devonian Temple Butte Formation fill deep paleovalleys that have been cut into and occasionally through the Frenchman Mountain Dolostone and into the Muav Limestone. [2] [4]

Fossils

The body fossils of invertebrates found in the Muav Limestone are infrequent and often poorly preserved. They include sponges, brachiopods, hyoliths, helcionelloids, trilobites, eocrinoids, and enigmatic invertebrates. The types of body fossils reported from the Muav Limestone are not as diverse as those reported from the Bright Angel Shale. The invertebrate body fossils are dominated by ptychopariid and corynexochid trilobites. The Muav Limestone is likely not substantially younger than the Bright Angel Shale, as it contains trilobites of the same age as trilobites found in the Bright Angel Shale of eastern Grand Canyon region. In addition, to trilobites, the Muav Limestone contains enigmatic body fossils such as hyoliths; the single-shelled, mollusk Helcionella; Scenella hermitensis; and Chancelloria. [2] [11]

Although trace fossils are common in the Muav Limestone, they are less abundant than those found in the underlying Bright Angel Shale. They consist of invertebrate burrows and trails and Girvanella -like structures (oncolites). [12] Pervasive bioturbation of the calcareous sediment is responsible for the mottled appearance of most of the Muav Limestone. [13]

Depositional Environment

It is currently accepted that that Muav Limestone accumulated in an offshore marine environment during a series of at least five transgressive and regressive events. These events are reflected the in five members into which the Muav Limestone has been subdivided and the step-like pattern in which the Muav Limestone interfingers with the underlying Bright Angel Shale and diagonally crosses time planes. Presumably, these transgressions are the result of rapid, periodic, rises in relative sea level, interrupted by at least four drops in relative sea level that caused regressions of lesser extent. The interfingering of shales and sandstones of the Bright Angel Shake into the limestones of the Muav Limestone are the result of such transgressive and regressive events. [9] [12]

See also

Related Research Articles

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<span class="mw-page-title-main">Tonto Group</span> Cambrian geologic unit in the Grand Canyon region, Arizona

The Tonto Group is a name for an assemblage of related sedimentary strata, collectively known by geologists as a Group, that comprises the basal sequence Paleozoic strata exposed in the sides of the Grand Canyon. As currently defined, the Tonto groups consists of the Sixtymile Formation, Tapeats Sandstone, Bright Angel Shale, Muav Limestone, and Frenchman Mountain Dolostone. Historically, it included only the Tapeats Sandstone, Bright Angel Shale, and Muav Limestone. Because these units are defined by lithology and three of them interfinger and intergrade laterally, they lack the simple layer cake geology as they are typically portrayed as having and geological mapping of them is complicated.

<span class="mw-page-title-main">Tapeats Sandstone</span> Cambrian geologic formation found in the Southwestern United States

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<span class="mw-page-title-main">Isis Temple</span> Landform in the Grand Canyon, Arizona

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<span class="mw-page-title-main">Bright Angel Shale</span> Cambrian geologic formation found in the Southwestern United States

The Bright Angel Shale is one of five geological formations that comprise the Cambrian Tonto Group. It and the other formations of the Tonto Group outcrop in the Grand Canyon, Arizona, and parts of northern Arizona, central Arizona, southeast California, southern Nevada, and southeast Utah. The Bright Angel Shale consists of locally fossiliferous, green and red-brown, micaceous, fissile shale (mudstone) and siltstone with local, thicker beds of brown to tan sandstone and limestone. It ranges in thickness from 57 to 450 feet. Typically, its thin-bedded shales and sandstones are interbedded in cm-scale cycles. They also exhibit abundant sedimentary structures that include current, oscillation, and interference ripples. The Bright Angel Shale also gradually grades downward into the underlying Tapeats Sandstone. It also complexly interfingers with the overlying Muav Limestone. These characters make the upper and lower contacts of the Bright Angel Shale often difficult to define. Typically, its thin-bedded shales and sandstones erode into green and red-brown slopes that rise from the Tonto Platform up to cliffs formed by limestones of the overlying Muav Limestone and dolomites of the Frenchman Mountain Dolostone.

<span class="mw-page-title-main">Redwall Limestone</span> Geologic formation in Arizona, USA

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<span class="mw-page-title-main">Temple Butte Formation</span> Landform in the Grand Canyon, Arizona

The Devonian Temple Butte Formation, also called Temple Butte Limestone, outcrops through most of the Grand Canyon of Arizona, USA; it also occurs in southeast Nevada. Within the eastern Grand Canyon, it consists of thin, discontinuous and relatively inconspicuous lenses that fill paleovalleys cut into the underlying Muav Limestone. Within these paleovalleys, it at most, is only about 100 feet (30 m) thick at its maximum. Within the central and western Grand Canyon, the exposures are continuous. However, they tend to merge with cliffs of the much thicker and overlying Redwall Limestone.

The geology of Arizona began to form in the Precambrian. Igneous and metamorphic crystalline basement rock may have been much older, but was overwritten during the Yavapai and Mazatzal orogenies in the Proterozoic. The Grenville orogeny to the east caused Arizona to fill with sediments, shedding into a shallow sea. Limestone formed in the sea was metamorphosed by mafic intrusions. The Great Unconformity is a famous gap in the stratigraphic record, as Arizona experienced 900 million years of terrestrial conditions, except in isolated basins. The region oscillated between terrestrial and shallow ocean conditions during the Paleozoic as multi-cellular life became common and three major orogenies to the east shed sediments before North America became part of the supercontinent Pangaea. The breakup of Pangaea was accompanied by the subduction of the Farallon Plate, which drove volcanism during the Nevadan orogeny and the Sevier orogeny in the Mesozoic, which covered much of Arizona in volcanic debris and sediments. The Mid-Tertiary ignimbrite flare-up created smaller mountain ranges with extensive ash and lava in the Cenozoic, followed by the sinking of the Farallon slab in the mantle throughout the past 14 million years, which has created the Basin and Range Province. Arizona has extensive mineralization in veins, due to hydrothermal fluids and is notable for copper-gold porphyry, lead, zinc, rare minerals formed from copper enrichment and evaporites among other resources.

The geology of Utah, in the western United States, includes rocks formed at the edge of the proto-North American continent during the Precambrian. A shallow marine sedimentary environment covered the region for much of the Paleozoic and Mesozoic, followed by dryland conditions, volcanism, and the formation of the basin and range terrain in the Cenozoic.

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<span class="mw-page-title-main">Sheba Temple</span> Landform in the Grand Canyon, Arizona

Sheba Temple is a 4,990-foot (1,520 m)-elevation summit located in the eastern Grand Canyon, in Coconino County of northern Arizona, United States. The landform is 1.0 mile (1.6 km) west of Solomon Temple, 1.0 mile south of Rama Shrine, and about one mile north-northeast of the west-flowing Colorado River. The west of Sheba Temple's drainage is the short Asbestos Canyon which drains Krishna Shrine, northwest, Vishnu Temple, northwesterly, and Rama Shrine, north; the east side of Sheba Temple's drainage are short north drainages to the Colorado.

<span class="mw-page-title-main">Swilling Butte</span> Ridgeline summit in the Grand Canyon

Swilling Butte is a 6,785-foot (2,068 m)-elevation ridgeline summit located in the eastern Grand Canyon, in Coconino County of northern Arizona, United States. The landform is in a group of nearby summits, Colter Butte, west, and Hutton and Duppa Buttes, east. All four buttes are at the north of the east-flowing Kwagunt Creek and Canyon drainage to the Colorado River. Swilling Butte is 3.0 miles (4.8 km) northeast of Atoko Point, East Rim of the Walhalla Plateau, and 4.0 miles (6.4 km) west of the (north)-East Rim, Grand Canyon; the south-flowing Colorado River is west and adjacent to the East Rim. Swilling Butte is a triangular-platform summit of bright-red, tall Redwall Limestone. Being a cliff-former, the Redwall is also a platform-former. The upper platform of the Redwall Limestone supports a remainder-debris of the Supai Group. Of the two lower units, no. 2 is a cliff-former, hard rocks (cliffs), of the Manakacha Formation; the slope-former,, the Watahomigi Formation, forms most of the Supai debris upon the Redwall. Below the Redwall Limestone are members of the Cambrian Tonto Group, the Muav Limestone and the slopes of the Bright Angel Shale.

<span class="mw-page-title-main">The Battleship (Grand Canyon)</span> Landform in the Grand Canyon, Arizona

The Battleship is a 5,850-foot (1,780 m)-elevation summit located in central Grand Canyon, in Coconino County of northern Arizona, United States. The ridgeline, Battleship landform forms part of the western border of Garden Creek Canyon, which contains the Bright Angel Trail down to the Colorado River, and across it to Phantom Ranch. The east border of Garden Creek Canyon is the South Rim, with the overlooks of Grandeur Point and Yavapai Point. The Battleship is 1.5 miles (2.4 km) northwest of Yavapai Point, 1.5 miles due-north of Grand Canyon Village, and roughly 2.0 miles (3.2 km) southwest of the Colorado River.

<span class="mw-page-title-main">Cocopa Point</span> Landform in the Grand Canyon, Arizona

Cocopa Point is a 6,627 foot (2,020 m)-cliff-elevation Point located in the central,, Grand Canyon, Coconino County of northern Arizona, United States. Cocopa Point is 1.1 miles from its closest highest scenic viewpoint, Yuma Point (6,654 ft), located east at Eremita Mesa, at the northeast, overlooking Central Hermit Canyon.

Cocopa Point is in a region of points, at the headwaters of canyons, and landforms below the South Rim. Mimbreno Point lies ~1.7 miles west, and Hermit Canyon and Pima Point, at the west-terminus of West Rim Drive, are about 1.5 mi and 2.0 miles due-east. Cocopa Point is at the northwest of Eremita Mesa; Yuma Point is at the northeast; the mesa lies between Hermit Canyon, east, and Upper Boucher Canyon, west. Cocopa Point is a sheer-walled cliff, sitting at the northwest headwaters of short, Travertine Canyon. At the west of Lower Travertine Canyon, adjacent the Colorado River, sits Whites Butte, about 1.2 miles distant from Cocopa Point.

The Frenchman Mountain Dolostone is the uppermost and youngest of five Cambrian geologic formations that comprise the Tonto Group. It consists of beds of mottled white to gray dolomite often separated by thin seams of shale, especially in its lower part. In the Grand Canyon, this formation forms vertical cliffs that thicken westward between the top of the Muav Limestone and the base of either the Devonian Temple Butte Formation or Mississippian Redwall Limestone. Because of unidentified trace fossils and lack of datable body fossils, the Frenchman Mountain Dolostone exact age is uncertain. Within the Grand Canyon, it thickness varies between 200 to 450 feet. West into the Lake Mead region, it thickens considerably and is 1,217 feet (371 m) thick at Frenchman Mountain near Las Vegas, Nevada.

References

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  11. Lassiter, S.L., Tweet, J.S., Sundberg, F.A., Foster, J.R., and Bergman, P.J., 2020. Chapter 5. Paleozoic Invertebrate Paleontology of Grand Canyon National Park. In: Santucci, V.L., Tweet, J.S., ed., pp. 109-236, Grand Canyon National Park: Centennial Paleontological Resource Inventory (Non-sensitive Version) . Natural Resource Report NPS/GRCA/NRR—2020/2103. National Park Service, Fort Collins, Colorado, 603
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Further reading