Siltstone in the context of Porphyroblast


Siltstone in the context of Porphyroblast

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⭐ Core Definition: Siltstone

Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.

Although its permeability and porosity is relatively low, siltstone is sometimes a tight gas reservoir rock, an unconventional reservoir for methane gas that requires hydraulic fracturing for economic gas production.

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👉 Siltstone in the context of Porphyroblast

A porphyroblast is a large mineral crystal in a metamorphic rock which has grown within the finer grained matrix. Porphyroblasts are commonly euhedral crystals, but can also be partly to completely irregular in shape.

The most common porphyroblasts in metapelites (metamorphosed mudstones and siltstones) are garnets and staurolites, which stand out in well-foliated metapelites (such as schists) against the platy mica matrix.

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Siltstone in the context of Sediment

Sediment is a solid material made of loose particles that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand and silt can be carried in suspension in river water and on reaching the sea bed deposited by sedimentation; if buried, they may eventually become sandstone and siltstone (sedimentary rocks) through lithification.

Sediments are most often transported by water (fluvial processes), but also wind (aeolian processes) and glaciers. Beach sands and river channel deposits are examples of fluvial transport and deposition, though sediment also often settles out of slow-moving or standing water in lakes and oceans. Desert sand dunes and loess are examples of aeolian transport and deposition. Glacial moraine deposits and till are ice-transported sediments.

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Siltstone in the context of Cosmetic palette

Cosmetic palettes are archaeological artifacts, originally used in predynastic Egypt to grind and apply ingredients for facial or body cosmetics. The decorative palettes of the late 4th millennium BCE appear to have lost this function and became commemorative, ornamental, and possibly ceremonial. They were made almost exclusively out of siltstone with a few exceptions. The siltstone originated from quarries in the Wadi Hammamat.

Many of the palettes were found at Hierakonpolis, a centre of power in pre-dynastic Upper Egypt. After the unification of the country, the palettes ceased to be included in tomb assemblages.

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Siltstone in the context of Hermopolis

Hermopolis (or Hermopolis Magna) was a major city in antiquity, located near the boundary between Lower and Upper Egypt. Its Egyptian name Khemenu derives from the eight deities (the Ogdoad) said to reside in the city.

A provincial capital since the Old Kingdom of Egypt, Hermopolis developed into a major city of Roman Egypt, and an early Christian center from the third century. It was abandoned after the Muslim conquest of Egypt but was restored as both a Latin Catholic (meanwhile suppressed) and a Coptic Orthodox titular see.

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Siltstone in the context of Mudrock

Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. The varying types of mudrocks include siltstone, claystone, mudstone and shale. Most of the particles of which the stone is composed are less than 116 mm (0.0625 mm; 0.00246 in) and are too small to study readily in the field. At first sight, the rock types appear quite similar; however, there are important differences in composition and nomenclature.

There has been a great deal of disagreement involving the classification of mudrocks. A few important hurdles to their classification include the following:

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Siltstone in the context of Morrison Formation

The Morrison Formation is a distinctive sequence of Upper Jurassic sedimentary rock found in the western United States which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone, and limestone and is light gray, greenish gray, or red. Most of the fossils occur in the green siltstone beds and lower sandstones, relics of the rivers and floodplains of the Jurassic period.

It is centered in Wyoming and Colorado, with outcrops in Montana, North Dakota, South Dakota, Nebraska, Kansas, the panhandles of Oklahoma and Texas, New Mexico, Arizona, Utah, and Idaho. Equivalent rocks under different names are found in Canada. It covers an area of 1.5 million square kilometers (600,000 square miles), although only a tiny fraction is exposed and accessible to geologists and paleontologists. Over 75% is still buried under the prairie to the east, and much of its western paleogeographic extent was eroded during exhumation of the Rocky Mountains.

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Siltstone in the context of Red beds

Red beds (or redbeds) are sedimentary rocks, typically consisting of sandstone, siltstone, and shale, that are predominantly red in color due to the presence of ferric oxides. Frequently, these red-colored sedimentary strata locally contain thin beds of conglomerate, marl, limestone, or some combination of these sedimentary rocks. The ferric oxides, which are responsible for the red color of red beds, typically occur as a coating on the grains of sediments comprising red beds. Classic examples of red beds are the Permian and Triassic strata of the western United States and the Devonian Old Red Sandstone facies of Europe.

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Siltstone in the context of Lutite

Lutite is old terminology, which is not widely used, by Earth scientists in field descriptions for fine-grained, sedimentary rocks, which are composed of silt-size sediment, clay-size sediment, or a mixture of both. When mixed with water lutites often disintegrate into mud. Because this is a field term, there is a lack of any precise definition for it based upon specific grain-size characteristics. Lutites include a variety of fine-grained sedimentary rocks, including calcisiltite, calcilutite, claystone, mudstone, shale, and siltstone. It is equivalent to the term mudstone and the Greek-derived term pelite. Lutite was first used in 1904 by Grabau, who derived it from lutum, the Latin word for mud. He also proposed a number of prefixes to be used with and attached to "lutite" in order to designate various types of lutites. None of these prefixes are used by Earth scientists nowadays.

Pettijohn 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:

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Siltstone in the context of Sisquoc Formation

The Sisquoc Formation is a sedimentary geologic unit widespread in Southern California, both on the coast and in mountains near the coast. Overlying the Monterey Formation, it is of upper Miocene and lower Pliocene age (from about 4 to 6 million years old). The formation consists of claystone, mudstone, siltstone, shale, diatomite, and conglomerates, with considerable regional variation, and was deposited in a moderately deep marine environment at a depth of approximately 500–5,000 feet (150–1,520 m). Since some of its diatomites, along with those of the underlying Monterey Formation, are of unusual purity and extent, they can be mined as diatomaceous earth. France-based Imerys operates a mine in the Sisquoc and Monterey Formations in the hills south of Lompoc, California, the largest such operation in the world.

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Siltstone in the context of Interbedded

In geology, interbedding occurs when beds (layers of rock) of a particular lithology lie between or alternate with beds of a different lithology. For example, sedimentary rocks may be interbedded if there were sea level variations in their sedimentary depositional environment.

Intercalation is a special case of interbedding where a layer is variably inserted into an already existing sequence; or where two separate depositional environments in close spatial proximity migrate alternately across the contact.

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Siltstone in the context of MacGillycuddy's Reeks

MacGillycuddy's Reeks (Irish: Na Cruacha Dubha, meaning 'the black stacks') is a sandstone and siltstone mountain range in the Iveragh Peninsula in County Kerry, Ireland. Stretching 19 kilometres (12 miles), from the Gap of Dunloe in the east, to Glencar in the west, the Reeks is Ireland's highest mountain range, and includes most of the highest peaks and sharpest ridges in Ireland, and the only peaks on the island over 1,000 metres (3,300 feet) in height.

Near the centre of the range is Carrauntoohil, Ireland's highest mountain at 1,038.6 metres (3,407 ft). The range was heavily glaciated which carved out deep corries (e.g. the Eagle's Nest), U-shaped valleys (e.g. Lough Coomloughra), and sharp arêtes and ridges (e.g. the Beenkeragh Ridge).

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Siltstone in the context of Pelite

A pelite (from Ancient Greek πηλός (pēlós) 'clay, earth') or metapelite is a metamorphosed fine-grained sedimentary rock, i.e. mudstone or siltstone. The term was earlier used by geologists to describe a clay-rich, fine-grained clastic sediment or sedimentary rock, i.e. mud or a mudstone, the metamorphosed version of which would technically have been a metapelite. It was equivalent to the now little-used Latin-derived term lutite. A semipelite is defined in part as having similar chemical composition but being of a crystalloblastic nature.

Pettijohn (1975) 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. The Ancient Greek terms are more commonly used for metamorphosed rocks, and the Latin for unmetamorphosed:

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Siltstone in the context of Tendaguru Formation

The Tendaguru Formation, or Tendaguru Beds are a highly fossiliferous formation and Lagerstätte located in the Lindi Region of southeastern Tanzania. The formation represents the oldest sedimentary unit of the Mandawa Basin, overlying Neoproterozoic basement, separated by a long hiatus and unconformity. It reaches a total sedimentary thickness of more than 110 metres (360 ft). The formation ranges in age from the late Middle Jurassic to the Early Cretaceous, Oxfordian to Hauterivian stages, with the base of the formation possibly extending into the Callovian.

The Tendaguru Formation is subdivided into six members; these are from oldest to youngest the Lower Dinosaur Member, the Nerinella Member, the Middle Dinosaur Member, the Indotrigonia africana Member, the Upper Dinosaur Member, and the Rutitrigonia bornhardti-schwarzi member. The succession comprises a sequence of sandstones, shales, siltstones, conglomerates with minor oolitic limestones, deposited in an overall shallow marine to coastal plain environment, characterized by tidal, fluvial and lacustrine influence with a tsunami deposit occurring in the Indotrigonia africana member. The climate of the Late Jurassic and Early Cretaceous was semi-arid with seasonal rainfall and the eustatic sea level was rising in the Late Jurassic from low levels in the Middle Jurassic. Paleogeographical reconstructions show the Tendaguru area was located in the subtropical southern hemisphere during the Late Jurassic.

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Siltstone in the context of Devon Island

Devon Island (Inuktitut: ᑕᓪᓗᕈᑎᑦ, Tallurutit) is an island in Canada and the largest uninhabited island (no permanent residents) in the world. It is located in Baffin Bay, Qikiqtaaluk Region, Nunavut, Canada. It is one of the largest members of the Arctic Archipelago, the second-largest of the Queen Elizabeth Islands, Canada's sixth-largest island, and the 27th-largest island in the world. It has an area of 55,247 km (21,331 sq mi) (slightly smaller than Croatia). The bedrock is Precambrian gneiss and Paleozoic siltstones and shales. The highest point is the Devon Ice Cap at 1,920 m (6,300 ft) which is part of the Arctic Cordillera. Devon Island contains several small mountain ranges, such as the Treuter Mountains, Haddington Range and the Cunningham Mountains, as well as the Haughton impact crater. The notable similarity of its surface to that of Mars has attracted interest from scientists.

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