[1] Sedimentary rocks

Sedimentary rocks are constantly developing at the surface of the Earth. Their formation is often due to the following process :

1 - Alteration and erosion : gravity, wind, glaciers, rain and chemical attack all degrade rocks. This results in a release of material.

2 - Transport : this material is removed by running water. Wind bears away the smallest particles.

3 - Sedimentation : when water and wind are not strong enough to remove the particles, they form a deposit, usually in an aquatic environment (sea, lakes, rivers, …).

4 - Diagenesis : this is the process by which sediments are transformed into rocks. After the initial deposition of sediments, the organic matter they contain is damaged by micro-organisms. The pressure due to overloading causes water to be ejected ; “compaction” occurs, followed by “cementation” of the grains. Water is released as the geothermal gradient increases (about 30° per kilometer) thus causing crystallization of grains, eg. sands become sandstones, and muds - depending on their nature - are transformed into limestone, clay, etc…