Why is sedimentation important



 

Sedimentation or. sedimentation (Drop, to lat. sedimentum "Sediment") is the depositing / settling of particles from liquids or gases under the influence of gravity and other forces, such as the centrifugal force in a centrifuge. If a layer of suspended matter forms at the bottom, this is also called this Sediment, sediment or (to avoid confusion with sedimentary rock) Loose sediment.

Basics

Sediments can be divided into three main groups:

  • the clastic sediments (particles transported by water or wind and thus mechanically formed, e.g. sand)
  • chemical sediments (excreted by chemical processes from aqueous solutions through precipitation, e.g. carbonates)
  • biogenic sediments (Deposits from organisms or from organism remains, e.g. coral reefs), whereby the biogenic sediments are also classified as a subgroup of the chemical sediments.

During sedimentation, the deposited particles are layered due to their different sedimentation speed (sinking speed) according to their density and size. The particles with the greatest sedimentation speed are deposited first, that is, they are at the bottom. Since the sedimentation speed is essentially determined by the density, different substances can be deposited separately in layers, which can also be used to separate the different substances of a mixture (see decanting). If only one material is deposited or materials of similar density, large particles deposit more quickly and lie under test, while small particles lie on top. In the case of foamed material, for example eruptive pumice stones, an inverse gradation can occur, small particles then have a higher density and are stored below, while large particles are above.

In the case of rivers, sediments are mainly brought in by the erosion of the cross-section. Another effect is the sediment entry. Sediments (and other solids) from the catchment area are brought in here.

Natural sediments

In the case of natural sedimentation, the suspended solids are usually brought in by erosion processes and, in particular, by fluvial transport, which in turn is usually preceded by weathering of the parent rock. The grain size distribution of the particles entrained in the water shows significant differences depending on the distance to the ablation site and the consequently increasingly lower flow velocity. Here, the grain size of the particles decreases with distance and with a decreasing flow velocity, since the largest or heaviest particles (debris) sediment first and the flow is often no longer able to stir them up from the bottom of the water.

Particularly in stagnant waters, these suspended matter form sediment layers (varves) through gravitational deposition, some of which are used to determine the age (stratigraphy). This is mainly due to the fact that, in contrast to rivers, there is no longer a current and therefore very small particles can also be deposited. In addition, depending on the climate system, the sedimentation often shows a different pattern in the course of the year, as the finer particles settle in a frozen body of water, for example. Thus, similar to the annual rings in trees, coarser and finer layers develop each year, which are known as varves. These often include living beings or their traces, which can develop into fossils in the course of fossilization. The formation conditions (paleoclimate) of the individual layers are also often documented in these, which is why sediments represent important climate archives. Marine, shallow marine and sea deposits in particular have a high informative value in this regard, which is why they also represent the main goal of climatological research boreholes.

While advancing sedimentation increases the thickness of the sediments, the increasing pressure in the deeper layers in particular can trigger further geological processes. The diagenesis forms the sedimentary rocks from the loose sediments. Snow represents a special case, which can also be layered and compressed to ice under the influence of pressure. If this effect lasts for several years, it can lead to the formation of a glacier.

application

In split systems, this effect is used for the preparative separation of particles. See also sedimentation velocity

In the mill laboratory a Sedimentation test carried out in which the volume of the sediment of a flour-water suspension is a measure of the swelling capacity of the proteins in the flour. In soil science, sedimentation experiments are used to determine the grain size distribution of a soil.

See also

literature

  • Maurice E. Tucker: Introduction to sediment petrology. Spectrum Academic Publishing House., 1985, ISBN 3-8274-1290-0.
  • Andreas Schäfer: Clastic Sediments - Facies and Sequence Stratigraphy. Spectrum Academic Publishing House., 2004, ISBN 3-8274-1351-6.

Category: Separation Process