spitzbergen-3
fb  de  en  
Marker

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

Back

last modification: 2013-10-12 · copyright: Rolf Stange
css.php