The Eureka Quartzite is an extensive

Paleozoic The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...

marine

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

deposit in western North America that is notable for its great extent, extreme purity, consistently fine grain size of

Quartzite Quartzite is a hard, non- foliated metamorphic rock that was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tecton ...

, and its tendency to form conspicuous white cliffs visible from afar. The Eureka is commonly underlain and overlain by contrasting slope-forming

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

and dolomite

strata In geology and related fields, a stratum (: strata) is a layer of Rock (geology), rock or sediment characterized by certain Lithology, lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by v ...

, all of

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

age. It was named in 1883 for the

Eureka Eureka often refers to: * Eureka (word), a famous exclamation attributed to Archimedes * Eureka effect, the sudden, unexpected realization of the solution to a problem Eureka or Ureka may also refer to: History * Eureka Rebellion, an 1854 g ...

mineral district in

Nevada Nevada ( ; ) is a landlocked state in the Western United States. It borders Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the seventh-most extensive, th ...

, 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.

Description

Extent

By whatever name, the Eureka can be traced, with gaps, from

northward through

Idaho Idaho ( ) is a landlocked U.S. state, state in the Pacific Northwest and Mountain states, Mountain West subregions of the Western United States. It borders Montana and Wyoming to the east, Nevada and Utah to the south, and Washington (state), ...

into western Canada along the

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

Alberta Alberta is a Provinces and territories of Canada, province in Canada. It is a part of Western Canada and is one of the three Canadian Prairies, prairie provinces. Alberta is bordered by British Columbia to its west, Saskatchewan to its east, t ...

boundary, and southward to southeastern

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

,Ketner, Keith B. (1968). ''Origin of Ordovician quartzite in the Cordilleran miogeosyncline''. U.S. Geological Survey, Professional Paper 600-B. pp. 169–177.Ross, R.J., Jr. (1964a). ''Middle and Lower Ordovician formations in southernmost Nevada and adjacent California''. U.S. Geological Survey, Bulletin 1180-C. pp. C1–C101. a north-south extent of about . An isolated exposure was identified in

Sonora Sonora (), officially Estado Libre y Soberano de Sonora (), is one of the 31 states which, along with Mexico City, comprise the Administrative divisions of Mexico, Federal Entities of Mexico. The state is divided into Municipalities of Sonora, 72 ...

, Mexico south of its most southerly exposure in California, but that occurrence probably was tectonically displaced there from

. The Eureka and its correlatives are lenticular in cross-section: in

and

Utah Utah is a landlocked state in the Mountain states, Mountain West subregion of the Western United States. It is one of the Four Corners states, sharing a border with Arizona, Colorado, and New Mexico. It also borders Wyoming to the northea ...

the formation extends more than east-west, thinning out in both directions from maxima along its axis of more than . In Canada the east-west extent is much less but there also, it thins out to both east and west.Norford, B.S. (1966). ''Ordovician-Silurian of the Cordillera in Geological History of Western Canada''. Alberta Society of Petroleum Geologists, Canadian Sedimentary Basins Symposium, Chapter 4, part 2. pp. 42–48.

Composition

Cliff-forming quartzite, the principle part of the Eureka, is composed of more than 99 percent

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

, which includes both the sand grains and the cement that binds them. The quartz cement accounts for its outstanding hardness and resistance to erosion. Minor constituents are grains of

zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of th ...

and

tourmaline Tourmaline ( ) is a crystalline silicate mineral, silicate mineral group in which boron is chemical compound, compounded with chemical element, elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. This gemstone comes in a ...

and a trace of

feldspar Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagiocl ...

.McBride, E.F. (2012). ''Petrology of the Eureka Quartzite (Middle and Late Ordovician) Utah and Nevada U.S.A.'' Rocky Mountain Geology 47: 81–111 All of the constituents in Nevada and

are less than 1 mm (0.039 in) in diameter; those in Canada are slightly larger.

Bioturbation Bioturbation is defined as the reworking of soils and sediments by animals or plants. It includes burrowing, ingestion, and defecation of sediment grains. Bioturbating activities have a profound effect on the environment and are thought to be a ...

is believed to account for the scarcity of internal bedding.

Origin

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. The surfaces of the quartz grains are almost universally "frosted" or abraded, indicating that they, at one time or another, occupied a subaerial environment. 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. 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 The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

sandstone was exposed extensively in Ordovician time;deMille, George (1958). ''Pre-Mississippian History of the Peace River Arch,'' in Scott, J.C., ed., ''Symposium on the Peace River Arch''. Alberta Society of Petroleum Geologists Journal 6: 61–68. (2) the base of the formation decreases in age from north to south as determined by marine fossils in subjacent beds; (3) the formation becomes finer grained from north to south apparently due to progressive abrasion of the grains along the way; and (4) the radiometric age of constituent zircon grains points to a northern source.Gehrels, G.E., Dickinson, W.R., Riley, B.C.D., Finney, S.C., and Smith, M.T. (2000). Detrital zircon geochronology of the Roberts Mountains allochthon, Nevada, in Soreghan, M.J. and Gehrels, G.E., eds., ''Paleozoic and Triassic paleogeography and tectonics of western Nevada and northern California,'' Special Paper 347. Boulder, Colorado: Geological Society of America. pp. 19–42.

References

{{Reflist Geologic formations of Alberta Geologic formations of British Columbia Geologic formations of California Geologic formations of Idaho Geologic formations of Nevada Geologic formations of Utah Ordovician System of North America Ordovician Alberta Ordovician British Columbia Ordovician California Ordovician Idaho Ordovician geology of Nevada Ordovician geology of Utah Ordovician southern paleotropical deposits Quartzite formations Shallow marine deposits

Description

Extent

Composition

Origin

See also

References