Sedimentary rock

Sediments and sedimentary rocks, and sedimentary rocks or rock layer, caused by sedimentation, ie the deposition of material on land and in the sea ( terrestrial and marine sediments ). Be distinguished of which the igneous rocks, although also form on the surface, but emerge from the rapid cooling of molten rock.

Sediments and sedimentary rocks are divided into the main groups Clastic sediments ( clastics, Debris rocks ), Chemical sediments, biogenic sediments ( organogenic sediments ) and Residualgesteine ​​:

• Clastic sediments caused by erosion and the subsequent transport of a pre-existing rock,
• Biogenic sediments resulting from the organic or inorganic substance of organisms and their skeletons,
• Chemical sediments caused by the direct precipitation in solution befindlicher substances.
• Residue Rocks ( Residualgesteine ​​) remain as residue after the decomposition of a rock

The process of sedimentation takes place on land (terrestrial ), in rivers ( fluvial ) or in lakes ( limnic ) and oceans (marine ).

To distinguish unconsolidated sediments unconsolidated sediment or loose rock are called, while solidified sediments are called sedimentary rocks.

Formation of sedimentary rocks from unconsolidated sediments

Sedimentary rocks go through diagenesis ( Lithifizierung, Lithogenesis ) from unconsolidated sediments ( unconsolidated sediments ) out. In the diagenesis occurs due to the increased confining pressure as a result of further interference with sediment progresses sedimentation for dewatering and compression of a sediment layer, the pressure solution in the contact of mineral grains and the precipitation of cement, resulting in the conversion of sedimentary loose rock in a hard rock. A special case of diagenesis is the coalification, in which are deposited volatile organic components of a rock under the action of pressure and temperature, optionally escape or that they be converted into low-volatility, largely aromatic hydrocarbons.

Basic Properties

Characteristic of sediments is going back to material change stratification. A layer surface, the interface between two directly superposed layers, it is often synonymous with the former sediment surface, which, depending on the depositional environment, the earth, the sea floor or the bottom of a river or lake may have been. However, stratification does not necessarily have come through the actual deposition processes about. You can also later, during diagenesis occur (so-called pseudo- stratification ).

Furthermore, the only sedimentary rocks that may contain fossils. The effect of high pressure or high temperature in sedimentary rocks throughout their geological history was not given (otherwise one speaks, depending on the degree of exposure and the associated change of the rock metasediments or orthogneisses ).

The sediment- forming processes are influenced by the effects of Earth's atmosphere, the hydrosphere and the biosphere on the surface of the solid earth system. The sediment is thereby influenced by the conditions under which it arose. All environmental conditions which cause or influence the formation of a sediment are summarized under the term milieu, and the resulting sediment properties (eg grain size, grain minerals, color, fossil content ) is called the sedimentary facies. Environment and facies are characteristic of different depositional areas and in practice, the term facies is often equated with a specific depositional environment (eg Tiefseefazies or fluvial facies ).

Classification

After the deposition chamber or the deposition mechanism

The geology classified the process of sedimentation of the origin of the sediments, the corresponding branch of science is called sedimentology.

It differs sediments after their formation as

• Marines sediment: from the land by rivers, glaciers, landslides or wind into the sea verfrachtetes rock material deposited on the sea floor in the Wadden Sea, on the shelf or the continental slope and at the bottom of the deep sea from or is formed by the activity of living marine organisms (eg, corals, foraminifera, diatoms ).
• Fluviatile sediments: riverine store the carried crushed rock material from depending on the flow velocity in the form of clay, silt, sand or gravel.
• Glacial sediment: transported by glacial ice rock material is deposited in the form of moraines or boulder clay; Single blocks remain as boulders. Fluvioglaziales sediment: meltwater transported rock debris and runoff water from the glacier and deposited it in broad outwash plains before starting.

After the grain sizes

The sediments are referred to as the grain sizes simply as clay, silt (or silt ), sand or gravel. Loose sediments with a predominant proportion of coarse grain sizes, such as gravel, stones and boulders, called particles with rounded boulders and angular material debris.

Depending on the grain size, the following thin clastic hard rocks:

• Conglomerate or breccia with particle sizes greater than 2 mm. Conglomerates consist of rounded, breccia of angular rock debris.
• Sandstone consists mainly of quartz grains of the grain size from 0.063 to 2 mm.
• Siltstone (or siltstone ) consists mainly of quartz grains that are 0.002 to 0.063 mm.
• Mudstone contains predominantly particles that are smaller than 0.002 mm (2 microns ).

It used to be used for the classification, the terms Psephite for large grain sizes, Psammite for medium and pelitic rocks for small grain sizes. The latter term is still used today. Also related to the grain size, the terms are Lutit (less than 0.063 mm), arenite (greater than 2 mm ), which are mainly used in the classification of ( clastic ) limestones ( 0.063 to 2 mm) and Rudit.

After the development process

Clastic sedimentary rocks

As clastics ( gr klastó, down) broken (', Klan, (ab) break ') or clastic sedimentary rocks is referred to sedimentary rocks whose material originates from the mechanical destruction of other rocks. Another name is conglomerate. Clastic sediments are characterized in terms of the particle size spectrum, based on the material from which they are made and the basis of their genesis.

Material and binder

• Includes a sandstone significant amounts of other minerals as quartz (mainly feldspar ), one speaks of an arkose, with a wide range of minerals and other rock fragments and mica and clay minerals consisting of a matrix of a greywacke.
• Siliciclastic consist mainly of silicate minerals such as quartz or feldspar.
• A clastic sedimentary rock made ​​of different minerals and with a wide range of grain sizes that were deposited by a turbidity current is called a turbidite.

The mineral grains and rock fragments that make up the clastic sedimentary rocks hold together by means of a primary or secondary binder.

• The primary binder is referred to as a matrix, and is usually either of clay particles or microscopically small calcium carbonate particles, which are deposited together with the coarser components of the sediment. However, a binding effect develops, the matrix only after the sediment was dewatered to a certain extent.
• The secondary binder is formed after deposition of the sediment by means of chemical precipitation, and is referred to as a cement. It may be calcareous cement (calcium carbonate, CaCO3), " pebble " cement (silicon dioxide, SiO2 ) to act clay minerals or oxides and hydroxides of iron (eg, hematite, goethite ).

Chemical sedimentary rocks

Chemical sedimentary rocks and chemical sedimentary rocks are formed by the precipitation of solutes from supersaturated solutions. Through evaporation caused, for example, the evaporites (sulphates, such as gypsum or anhydrite, and halides such as halite or potassium salts ). The Zechstein series in Central Europe is an example of a sequence with powerful evaporite camps. Also carbonates can occur so. But they do not count as evaporites.

Another possibility for the precipitation of carbonates, is to increase the water temperature ( carbonate dissolves in contrast to for example halite better in cold water than in warm water ). In this way, travertine is formed at the outlets of sources.

The precipitation of carbonates can also be done indirectly by living organisms. Algal photosynthesis and carbon dioxide to escape the water. This has the consequence that the carbon dioxide forms compensation bicarbonate, which in turn responds, for example, with calcium sparingly soluble calcium ions.

Biogenic sedimentary rocks

Biogenic sedimentary rocks, also organogenic sedimentary or biogenic sedimentary rocks, living organisms through activities as well as from the remains of dead organisms are formed. This includes the active excretion of mineral substances (usually carbonate or phosphate skeletons ), which can accumulate to more or less powerful sediment packages, such as reef limestones, Mud Mounds or bone beds. The massive limestone deposits of the Cretaceous period often consist to a large part of extremely small calcium carbonate skeletons of algae (→ nannoplankton ). Even non-mineral remains of dead organisms can form larger sediment body, eg Peat or coal, caused by the accumulation and transformation of dead plant residues.

Residue rocks

Residue rocks, also Residualgesteine ​​, arise from the residues chemically processed rocks at the place of rock destruction ( weathering ) as laterite ( from almost all rocks ), bauxite ( from carbonate rocks → Kalkbauxit or silicate rock → silicate bauxite ) and kaolin ( granite, rhyolite, Arkose ) or routing of easily soluble rock components.

Importance of sedimentary rocks

Many sedimentary rocks are used commercially (eg limestone in the construction industry ). In sediments, oil and gas can occur (petroleum source rock ), which can then be pressed into a reservoir rock. Hard coal and brown coal are also sedimentary rocks of great economic importance.

Sedimentary rocks (notably limestone and dolomite) may contain large amounts of carbonate, for the formation of carbon dioxide is needed. Compared to the atmosphere as Venus or Mars, where these sediments not or hardly occur, the proportion of carbon dioxide in the atmosphere, therefore, is extremely low.

The study of sedimentary rocks made ​​possible with the structures, minerals and fossils contained in them the reconstruction of habitats that existed prior geological periods.