Eureka Quartzite Stratigraphic range: Ordovician | |
---|---|
Type | Geologic formation |
Underlies | Hanson Creek Formation |
Overlies | Copenhagen Formation |
Thickness | 150 ft (46 m) (in southern Nevada) |
Lithology | |
Primary | Quartzite |
Location | |
Region | California, Nevada, Utah, Idaho British Columbia Alberta |
Country | United States Canada |
Extent | 2,200 km (1,400 mi) |
Type section | |
Named for | Eureka, Nevada |
Year defined | 1883 |
The Eureka Quartzite is an extensive Paleozoic marine sandstone deposit in western North America that is notable for its great extent, extreme purity, consistently fine grain size of Quartzite, and its tendency to form conspicuous white cliffs visible from afar.
The Eureka is commonly underlain and overlain by contrasting slope-forming limestone and dolomite strata, all of Ordovician age. It was named in 1883 for the Eureka mineral district in Nevada, [1] and that name is used almost exclusively in Nevada, but, in ensuing years, as extensions of the deposit were discovered in other areas, the same formation was given many other local names.
By whatever name, the Eureka can be traced, with gaps, from Nevada northward through Idaho into western Canada along the British Columbia-Alberta boundary, [2] [3] and southward to southeastern California, [2] [4] a north-south extent of about 2,200 kilometres (1,400 mi). An isolated exposure was identified in Sonora, Mexico 950 kilometres (590 mi) south of its most southerly exposure in California, but that occurrence probably was tectonically displaced there from California. [5] The Eureka and its correlatives are lenticular in cross-section: in Nevada and Utah the formation extends more than 300 kilometres (190 mi) east-west, thinning out in both directions from maxima along its axis of more than 150 metres (490 ft). In Canada the east-west extent is much less but there also, it thins out to both east and west. [3]
Cliff-forming quartzite, the principle part of the Eureka, is composed of more than 99 percent quartz, which includes both the sand grains and the cement that binds them. [6] The quartz cement accounts for its outstanding hardness and resistance to erosion. Minor constituents are grains of zircon and tourmaline and a trace of feldspar. [6] All of the constituents in Nevada and Utah are less than 1 mm (0.039 in) in diameter; those in Canada are slightly larger. Bioturbation is believed to account for the scarcity of internal bedding. [6]
Almost all of the constituent grains of the formation were deposited in a near-shore environment, mainly in shallow water, and to a much lesser extent on the beach as determined by the nature of bedding from place to place. [6] The surfaces of the quartz grains are almost universally "frosted" or abraded, indicating that they, at one time or another, occupied a subaerial environment. [6] Almost all of the constituent grains were determined to have originated in Canada, and were carried southward by currents along the eastern shore of the Paleozoic sea. [2] This concept is supported by several lines of evidence: (1) the only plausible source of such a large volume of sand is in Canada at about 56° north latitude where Cambrian sandstone was exposed extensively in Ordovician time; [7] (2) the base of the formation decreases in age from north to south as determined by marine fossils in subjacent beds; [2] [4] (3) the formation becomes finer grained from north to south apparently due to progressive abrasion of the grains along the way; [2] and (4) the radiometric age of constituent zircon grains points to a northern source. [8]
Wikimedia Commons has media related to Eureka Quartzite . |
Shale is a fine-grained, clastic sedimentary rock, composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. Shale is characterized by breaks along thin laminae or parallel layering or bedding less than one centimeter in thickness, called fissility. It is the most common sedimentary rock.
Quartzite is a hard, non-foliated metamorphic rock which was originally pure quartz sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to grey, though quartzites often occur in various shades of pink and red due to varying amounts of hematite. Other colors, such as yellow, green, blue and orange, are due to other minerals.
The Antler orogeny was a tectonic event that began in the early Late Devonian with widespread effects continuing into the Mississippian and early Pennsylvanian. Most of the evidence for this event is in Nevada but the limits of its reach are unknown. A great volume of conglomeratic deposits of mainly Mississippian age in Nevada and adjacent areas testifies to the existence of an important tectonic event, and implies nearby areas of uplift and erosion, but the nature and cause of that event are uncertain and in dispute. Although it is known as an orogeny, some of the classic features of orogeny as commonly defined such as metamorphism, and granitic intrusives have not been linked to it. In spite of this, the event is universally designated as an orogeny and that practice is continued here. This article outlines what is known and unknown about the Antler orogeny and describes three current theories regarding its nature and origin.
The Sonoma orogeny was a period of mountain building in western North America. The exact age and structure of the Sonoma orogeny is controversial. The orogeny is generally thought to have occurred during the Permian / Triassic transition, around 250 million years ago, following the Late Devonian Antler orogeny. The Sonoma orogeny was one of a sequence of accretionary events along the Cordilleran margin, possibly caused by the closure of the basin between the island arc of Sonomia and the North American continent. Evidence of this event has been reported throughout western North America, but most distinctly in northwest Nevada.
The Thiviers-Payzac Unit is a metasedimentary succession of late Neoproterozoic and Cambrian age outcropping in the southern Limousin in France. The unit geologically forms part of the Variscan basement of the northwestern Massif Central.
The Bass Formation, also known as the Bass Limestone, is a Mesoproterozoic rock formation that outcrops in the eastern Grand Canyon, Coconino County, Arizona. The Bass Formation erodes as either cliffs or stair-stepped cliffs. In the case of the stair-stepped topography, resistant dolomite layers form risers and argillite layers form steep treads. In general, the Bass Formation in the Grand Canyon region and associated strata of the Unkar Group-rocks 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. In addition, thick, prominent, and dark-colored basaltic sills intrude across the Bass Formation.
The Shinumo Quartzite also known as the Shinumo Sandstone, is a Mesoproterozoic rock formation, which outcrops in the eastern Grand Canyon, Coconino County, Arizona,. It is the 3rd member of the 5-unit Unkar Group. 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 typically brightly-colored strata of the underlying slope-forming Hakatai Shale. Overlying the Shinumo, 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.
The Dox Formation, also known as the Dox Sandstone, is a Mesoproterozoic rock formation that outcrops in the eastern Grand Canyon, Coconino County, Arizona. The strata of the Dox Formation, except for some more resistant sandstone beds, are relatively susceptible to erosion and weathering. The lower member of the Dox Formation consists of silty-sandstone and sandstone, and some interbedded argillaceous beds, that form stair-stepped, cliff-slope topography. The bulk of the Dox Formation typically forms rounded and sloping hill topography that occupies an unusually broad section of the canyon.
The Burro Canyon Formation is an Early Cretaceous Period sedimentary geologic formation, found in western Colorado, the Chama Basin and eastern San Juan Basin of northern New Mexico, and in eastern Utah, US.
The Fish Haven Dolomite is an Ordovician period geologic formation in southern Idaho, northeastern Nevada, and northwestern Utah.
The Ely Springs Dolomite is an Ordovician period geologic formation in the Southwestern United States.
The Crystal Peak Dolomite is a geologic formation in the Wah Wah Mountains of western Utah. It preserves fossils dating to the Middle Ordovician period.
The Vinini Formation is a marine, deep-water, sedimentary deposit of Ordovician to Early Silurian age in Nevada, U.S.A. It is notable for its highly varied, mainly siliceous composition, its mineral deposits, and controversies surrounding both its depositional environment and structural history. The formation was named by Merriam and Anderson for an occurrence along Vinini Creek in the Roberts Mountains of central Nevada and that name is now used extensively in the State.
The Tunnel Mountain Formation is a geologic formation that is present on the western edge of the Western Canada Sedimentary Basin in the Canadian Rockies of western Alberta. Named after Tunnel Mountain near Banff, it was deposited during the Early Pennsylvanian sub-period of the Carboniferous period.
The Skoki Formation is a stratigraphic unit of Early to Middle Ordovician age that is present on the western edge of the Western Canada Sedimentary Basin in the Canadian Rockies of Alberta and British Columbia. It was named for Skoki Mountain near Lake Louise in Banff National Park by Charles Doolittle Walcott in 1928. The Skoki Formation is fossiliferous and includes remains of brachiopods and other marine invertebrates, as well as conodonts and oncolites.
The geology of Germany is heavily influenced by several phases of orogeny in the Paleozoic and the Cenozoic, by sedimentation in shelf seas and epicontinental seas and on plains in the Permian and Mesozoic as well as by the Quaternary glaciations.
Detrital zircon geochronology is the science of analyzing the age of zircons deposited within a specific sedimentary unit by examining their inherent radioisotopes, most commonly the uranium–lead ratio. The chemical name of zircon is zirconium silicate and its corresponding chemical formula is Zr SiO4. Zircon is a common accessory or trace mineral constituent of most granite and felsic igneous rocks. Due to its hardness, durability and chemical inertness, zircon persists in sedimentary deposits and is a common constituent of most sands. Zircons contain trace amounts of uranium and thorium and can be dated using several modern analytical techniques. It has become increasingly popular in geological studies from the 2000s mainly due to the advancement in radiometric dating techniques. Detrital zircon age data can be used to constrain the maximum depositional age, determine provenance, and reconstruct the tectonic setting on a regional scale.
The Precordillera terrane of western Argentina is a large mountain range located southeast of the main Andes mountain range. The evolution of the Precordillera is noted for its unique formation history compared to the region nearby. The Cambrian-Ordovian sedimentology in the Precordillera terrane has its source neither from old Andes nor nearby country rock, but shares similar characteristics with the Grenville orogeny of eastern North America. This indicates a rift-drift history of the Precordillera in the early Paleozoic. The Precordillera is a moving micro-continent which started from the southeast part of the ancient continent Laurentia. The separation of the Precordillera started around the early Cambrian. The mass collided with Gondwana around Late Ordovician period. Different models and thinking of rift-drift process and the time of occurrence have been proposed. This page focuses on the evidence of drifting found in the stratigraphical record of the Precordillera, as well as exhibiting models of how the Precordillera drifted to Gondwana.
One of the major depositional strata in the Himalaya is the Lesser Himalayan Strata from the Paleozoic to Mesozoic eras. It had a quite different marine succession during the Paleozoic, as most parts of it are sparsely fossiliferous or even devoid of any well-defined fossils. Moreover, it consists of many varied lithofacies, making correlation work more difficult. This article describes the major formations of the Paleozoic – Mesozoic Lesser Himalayan Strata, including the Tal Formation, Gondwana Strata, Singtali Formation and Subathu Formation.
The geology of Utah 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. Utah is a state in the western United States.