Arenite

Arenite (Latin: Arena, "sand") is a sedimentary clastic rock with sand grain size between 0.0625 mm (0.00246 in) and 2 mm (0.08 in) and contain less than 15% matrix.[1] The related adjective is arenaceous. The equivalent Greek-derived term is psammite, though this is more commonly used for metamorphosed sediments.

Since it refers to grain size rather than chemical composition, the term is used for example in the classification of clastic carbonatic limestones, as the granulometrically equivalent term sandstone is not appropriate for limestone. Other arenites include sandstones, arkoses, greensands, and greywackes.

Arenites mainly form by erosion of other rocks or turbiditic re-deposition of sands. Some arenites contain a varying amount of carbonatic components and thus belong to the rock-category of carbonatic sandstones or silicatic limestones. Arenites often appear as massive or bedded medium-grained rocks with a middling- to wide-spaced preferred lamination and often develop a pronounced cleavage.

Pettijohn[2] gives the following descriptive terms based on grain size, avoiding the use of terms such as "clay" or "argillaceous" which carry an implication of chemical composition:

Descriptive size terms
Texture Common Greek Latin
Coarse gravel(ly) psephite (psephitic) rudite (rudaceous)
Medium sand(y) psammite (psammitic) arenite (arenaceous)
Fine clay(ey) pelite (pelitic) lutite (lutaceous)
Arenito2
Arenite

References

  1. ^ Britannica definition of arenite. Accessed on January 1, 2008
  2. ^ Pettijohn, Francis J. (1975). Sedimentary Rocks. Harper & Row. ISBN 0-06-045191-2.
Ardvreck Group

The Ardvreck Group is a stratigraphic group of early Cambrian age found in the Northwest Highlands of Scotland. It lies unconformably on gneisses of the Lewisian complex or sandstones of the Torridonian Supergroup. It consists of two formations, the basal quartzites and quartz arenites of the Eriboll Formation and the overlying dolomitic siltstones and sandstones and quartz arenites of the An-t-Sron Formation. It is overlain conformably by the Ghrudaidh Formation of the Durness Group. The Ardvreck Group was at one time known as the "Eriboll Group".

Arenite Ridge

Arenite Ridge (69°41′S 69°32′W) is a steep-sided rock and snow ridge in northern Alexander Island, extending 15 nautical miles (28 km) in a north-south direction lying immediately west of the Douglas Range and forming the eastern wall of Toynbee Glacier. The ridge includes Mount Tyrrell (which has two summits) and Mount Tilley. It was named by the UK Antarctic Place-Names Committee in 1977 from the sandstone-type rocks (arenite) that form this feature.

Caballos Formation

The Caballos Formation (Spanish: Formación Caballos, KI) is a geological formation of the Upper Magdalena Valley (VSM), Caguán-Putumayo Basin, Central and Eastern Ranges of the Colombian Andes. The sandstone and shale formation dates to the Middle Cretaceous period; Aptian to Albian epochs and has a maximum thickness of 411 metres (1,348 ft).

Calcicole

A calcicole, calciphyte or calciphile is a plant that thrives in lime rich soil. The word is derived from the Latin 'to dwell on chalk'. Under acidic conditions, aluminium becomes more soluble and phosphate less. As a consequence, calcicoles grown on acidic soils often develop the symptoms of aluminium toxicity, i.e. necrosis, and phosphate deficiency, i.e. anthocyanosis (reddening of the leaves) and stunting.

A plant that thrives in acid soils is known as a calcifuge.

A plant thriving on sand (which may be acidic or calcic) is termed psammophilic or arenaceous (see also arenite).

Cerros Negros de Jama

Cerros Negros de Jama is a monogenetic volcanic group in the Andes, Jujuy Province, Argentina. The group is formed by about four well preserved scoria cones (between 100–150 metres (330–490 ft) high and 450–800 metres (1,480–2,620 ft) wide at the basis, subcircular to elliptic) with lava fields and one isolated lava field, constructed on Ordovician marine sediments and dacitic lavas from the adjacent Cerro Bayo de Archibarca (7.2 million years old) volcano. These cones are aligned submeridionally with a fault system in the ground. The lavas and associated dykes have porphyritic appearance and variable morphology. The lavas show no evidence of ponding in crustal magma chambers, suggesting that the large volatile content of the magma was sufficient to quickly transport it through the crust. Magma temperatures have been estimated at higher than 1,000 °C (1,830 °F).The cones are constructed by reddish lapilli and lava bombs up to 1 metre (3 ft 3 in) wide with subordinate amounts of ash-like material, concentrated in the talus deposits that have been formed by erosion at the basis of the cones. Arenite of sedimentary origin and dacite are found as xenoliths. The cones were presumably built by Strombolian activity with occasional Hawaiian episodes.Usually less than 1 metre (3 ft 3 in) thick folded lava flows of gray colour are found in the field, containing xenoliths and scoriaceous material from the cones. In two of the cones were erupted at the base of the cones by dykes. In the northernmost cone, two northeastern lava flows were erupted above each other. The lower flow (900 by 3,000 metres (3,000 ft × 9,800 ft) wide and long) is thinner and contains pyroxene phenocrysts, the upper one has a smaller extent (1,200 metres (3,900 ft) long) and is dominated by olivine. On its western margin, it borders a lineament that cuts through the cones. The eastern cone has no less than four lava flows dominated by olivine, one of which is 2.5 kilometres (1.6 mi) long.Two other lava fields are also present. Two lava flows at Cerro El Chileno extend 2 kilometres (1.2 mi) southeastward and are associated with pyroclastic mounds (2 by 1 metre (6 ft 7 in × 3 ft 3 in)), suggesting some explosive activity, but no cone. The cone may be buried beneath the lava or might have been eroded away. 3.15 kilometres (1.96 mi) north of Cerro El Chileno lies an isolated lava flow with a circular shape (230 by 220 metres (750 ft × 720 ft)) that may be linked to a cone 2 kilometres (1.2 mi) north.The volcanic field is located in the Puna-Altiplano highland, a region with strong tectonic and volcanic activity since the Oligocene. Changes in subduction style of the Nazca plate have produced changes in the nature and amount of volcanic activity, with the latest change being a westward shift of volcanic activity to the main belt of the Central Volcanic Zone. In the region, mafic volcanism has been active since the Oligocene. Most volcanism in the area is of silicic nature however.

Enticho Sandstone

The Enticho Sandstone is a geological formation in north Ethiopia. It forms the lowermost sedimentary rock formation in the region and lies directly on the basement rocks. Enticho Sandstone consists of arenite that is rich in quartz. The formation has a maximum thickness of 200 metres. Locally, its upper part is coeval with the Edaga Arbi Glacials. The Enticho Sandstone has been deposited during the Ordovician (485–443 million years), as evidenced by impressions of organisms.

Geology of Skye

The geology of Skye in Scotland is highly varied and the island's landscape reflects changes in the underlying nature of the rocks. A wide range of rock types are exposed on the island, sedimentary, metamorphic and igneous, ranging in age from the Archaean through to the Quaternary.

Geology of Sweden

The geology of Sweden is the regional study of rocks, minerals, tectonics, natural resources and groundwater in the country. The oldest rocks in Sweden date to more than 2.5 billion years ago in the Precambrian. Complex orogeny mountain building events and other tectonic occurrences built up extensive metamorphic crystalline basement rock that often contains valuable metal deposits throughout much of the country. Metamorphism continued into the Paleozoic after the Snowball Earth glaciation as the continent Baltica collided with an island arc and then the continent Laurentia. Sedimentary rocks are most common in southern Sweden with thick sequences from the last 250 million years underlying Malmö and older marine sedimentary rocks forming the surface of Gotland.

Kittatinny Formation

The Ordovician Kittatinny Formation or Kittatinny Limestone is a dolomitic limestone formation in New Jersey. The Kittatinny Limestones are located primarily in the Kittatinny Valley where it lies above the Ordovician Martinsburg Formation within the long valley running from Picatinny Arsenal in Rockaway Township, southwest toward Chester Township. It overlies the Cambrian Hardyston Quartzite.The Kittatinny is now usually considered a Supergroup, rather than a Formation, as it includes several other Groups and Formations. Drake and Lyttle made this revision in 1980. The Supergroup includes the Leithsville Formation, Allentown Dolomite, and Beekmantown Group (which in turn includes the Stonehenge Limestone, Rickenbach Dolomite, Epler Formation, and Ontelaunee Formation). Richard Dalton wrote a more recent review of the stratigraphy of the Kittatinny.

The Kittatinny Limestone in New Jersey locally contains hydrocarbons and numerous accessory minerals including fluorite, sphalerite, arsenopyrite, galena, quartz, albite, and others. The Kittatiny is an exception to the general rule that Paleozoic rocks in this area are generally poor aquifers, since wells drilled into it produce relatively large flows of water.The Kittatinny Formation is named for the Kittatinny Valley in which it is located. The formation is not connected to or associated with the geology of Kittatinny Mountain, the easternmost ridge of the Appalachians in New Jersey, which is composed of Shawangunk Formation, a silica-cemented combination of quartz arenite and quartz-pebble conglomerate; and the Bloomsburg Formation (known as the "Bloomsburg Red Beds"), consisting of red shale, siltstone, and sandstone.

List of caves in Brazil

This is the List of caves in Brasil with links displayed alphabetically.

Lithic sandstone

Lithic sandstones, or lithic arenites, or litharenites, are sandstones with a significant (>5%) component of lithic fragments, though quartz and feldspar are usually present as well, along with some clayey matrix. Lithic sandstones can have a speckled (salt and pepper) or gray color, and are usually associated with one specific type of lithic fragment (i.e., igneous, sedimentary, or metamorphic).Tectonically, lithic sandstones often form in a wide variety sedimentary depositional environments (including fluvial, deltaic, and alluvial sediments) associated with active margins. This tectonic setting provides the source of the lithic fragments, either through arc volcanism, thin-skinned faulting, continental collisions, unroofing, and subduction roll-back.

Lithology

The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lithology may refer to either a detailed description of these characteristics, or a summary of the gross physical character of a rock. Lithology is the basis of subdividing rock sequences into individual lithostratigraphic units for the purposes of mapping and correlation between areas. In certain applications, such as site investigations, lithology is described using a standard terminology such as in the European geotechnical standard Eurocode 7.

Marlboro Mountains

The Marlboro Mountains, sometimes Marlborough Mountains, are a group of hogbacked mountains arranged in a 25-mile-long (40 km) ridge extending from Newburgh, New York to just south of Kingston, New York. Considered to be part of the Ridge and Valley Appalachians, the mountains, which reach elevations over 1,100 feet, form an imposing geologic barrier just west of the Hudson River. They subdivide the relatively flat Hudson River Valley (a section of the Great Appalachian Valley) to create the Wallkill Valley further west. Rising abruptly on their eastern flanks, the Marlboro Mountains are known for their sweeping views of the region.

Quartz arenite

A quartz arenite or quartzarenite is a sandstone composed of greater than 90% detrital quartz, with limited amounts of other framework grains (feldspar, lithic fragments, etc.) and matrix. It can have higher-than-average amounts of resistant grains, like chert and minerals in the ZTR index.

The term 'quartz arenite' is derived from the main component (quartz) and arenite, a Latin term for a rock with sand-sized grains. In some literature, these can be called orthoquartzites, a confusing term which usually refers to the metamorphic rock quartzite, though most metamorphic quartzites are diagentically fused from quartz arenites. The term "quartzose sandstone" can also be used for a quartz arenite.

Quartz arenites are the most mature sedimentary rocks possible, and are often referred to as ultra- or super-mature, and are usually cemented by silica. They often exhibit both textural and compositional maturity. The two primary sedimentary depositional environments that produce quartz arenites are beaches/upper shoreface and aeolian processes, due to their high residence time, high transport distance, and/or high energy of the environment. Most of the time, these sediments are reworked over and over, even being eroded out of a lithified rock and becoming a brand new sediment and rock. This is known as a multicycle sand.

Sandstone

Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) mineral particles or rock fragments.

Most sandstone is composed of quartz or feldspar (both silicates) because they are the most resistant minerals to weathering processes at the Earth's surface, as seen in the Goldich dissolution series. Like uncemented sand, sandstone may be any color due to impurities within the minerals, but the most common colors are tan, brown, yellow, red, grey, pink, white, and black. Since sandstone beds often form highly visible cliffs and other topographic features, certain colors of sandstone have been strongly identified with certain regions.

Rock formations that are primarily composed of sandstone usually allow the percolation of water and other fluids and are porous enough to store large quantities, making them valuable aquifers and petroleum reservoirs. Fine-grained aquifers, such as sandstones, are better able to filter out pollutants from the surface than are rocks with cracks and crevices, such as limestone or other rocks fractured by seismic activity.

Quartz-bearing sandstone can be changed into quartzite through metamorphism, usually related to tectonic compression within orogenic belts.

Serpentine Lakes

The Serpentine Lakes is a chain of salt lakes in the Great Victoria Desert of Australia. It runs for almost 100 km (62 mi) along the border between South Australia and Western Australia. When full, the lakes cover an area of 9,700 hectares (97 km2). Most of it is located in the Mamungari Conservation Park. The Anne Beadell Highway crosses the northernmost arm of the lake.

The Serpentine Lakes are considered an important wetlands area. They form part of a major palaeo-drainage system, a now-inactive drainage system from the Palaeozoic era. The surface of the lake normally consists of dry clay, silt and sand, and is covered with a salty crust. The sediment is mostly quartz arenite. The lakes form the main channel of the palaeo-drainage system. Other channels are covered by sand dunes and are not well defined. The surface elevation is 264 m (866 ft) above mean sea-level.Tektites high in magnesium have been found in these lakes.

Tepui

A tepui , or tepuy (Spanish: [teˈpui]), is a table-top mountain or mesa found in the Guiana Highlands of South America, especially in Venezuela and western Guyana. The word tepui means "house of the gods" in the native tongue of the Pemon, the indigenous people who inhabit the Gran Sabana.

Tepuis tend to be found as isolated entities rather than in connected ranges, which makes them the host of a unique array of endemic plant and animal species. Some of the most outstanding tepuis are Neblina, Autana, Auyantepui and Mount Roraima. They are typically composed of sheer blocks of Precambrian quartz arenite sandstone that rise abruptly from the jungle, giving rise to spectacular natural scenery. Auyantepui is the source of Angel Falls, the world's tallest waterfall.

Languages

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.