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Sediments

A sedi­ment comes into exis­tence when pie­ces of rock are depo­si­ted at the sur­face of the Earth – be it on dry land or in the water. Wind may blow a sand dune tog­e­ther, gra­vel is depo­si­ted by a river, fine mud is depo­si­ted in a lake, a gla­cier car­ri­es lar­ge bould­ers tog­e­ther to form a morai­ne: in each case, bits and pie­ces of rocks are brought tog­e­ther. The­re are count­less types of sedi­ment with dif­fe­rent pro­per­ties: they have dif­fe­rent colour, abili­ty to resist ero­si­on or to store water, gas or oil etc. Sedi­ments often have a cle­ar­ly visi­ble laye­ring, which is usual­ly hori­zon­tal unless they have later been defor­med. The lowest lay­ers are the oldest ones.

Sand- and Siltstone in original, approximately horizontal position

Sand- and Silts­tone in ori­gi­nal, appro­xi­m­ate­ly hori­zon­tal posi­ti­on

The abo­ve examp­les are all ‘cla­s­tic’ sedi­ments. In all cases, pie­ces of rock (‘clasts’) have been ero­ded some­whe­re and brought tog­e­ther some­whe­re else. The­re are still other types of sedi­ment: bio­ge­nic and che­mi­cal ones.

An important bio­ge­nic sedi­ment is lime­s­tone in most of its many varia­ti­ons. It can ori­gi­na­te from a coral reef or by slow depo­si­ti­on from cal­care­ous shells from mus­sels or algae. Ano­ther important bio­ge­nic sedi­ment is coal, which is deri­ved from vege­ta­ti­on over various stages such as peat and brown coal.

Examp­les for che­mi­cal sedi­ments are gypsym and hali­te (salt). Both come into exis­tance, when lagoons eva­po­ra­te and the water is not being repla­ced suf­fi­ci­ent­ly. Also, some varia­ti­ons of lime­s­tone may ori­gi­na­te from anor­ga­nic pro­ces­ses, wit­hout invol­ving orga­nisms.

All sedi­ments have in com­mon that they come into exis­tance at the sur­face of the Earth (inclu­ding the sea flo­or).

Once this sand­stone lay­er was straight, it has later been defor­med by com­pres­si­ve tec­to­nic move­ments (size ca. 15 cm. Ant­ar­c­tic Pen­in­su­la).

Once this sandstone layer was straight, it has later been deformed by compressive tectonic movements

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last modification: 2013-10-12 · copyright: Rolf Stange
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