Sedimentary rock

The sedimentary rocks are the Roche S which result from the accumulation and the compaction of remains of origin Minéral E (degradation of other rocks), Organique (remainders of plants or animals, fossils), or of chemical precipitation.

In fact exogenic rocks, i.e. are formed on the surface of the Ground. The sedimentary rocks level on 75% of the surface of the continents, but by considering the whole of the Earth's crust (from surface up to 35 km of depth under a flat relief), they constitute nothing any more but 5% of its total volume.

Classification

According to their mode of formation

the detrital rocks terrigenous (ex: silicoclastic): they come from the erosion of continental preexistent rocks, like the sandstone, the Sable, the silt, the Lœss, the Argile or the Schiste. The components (sediments) of these rocks were initially transported by the rivers to the seas and oceans of which they paper then the bottom.

organogenic rocks or biogenes (ex: carbonaceous, siliceous): they are related to the activity of the living organisms. The organizations form mineral-bearing skeletons which could be fragmented to form bioclastes (remains of skeleton of organization). There can be transport but there exist also organizations manufacturers which build themselves the rock, like the coral reefs. Examples: the coal, the Oil, the Calcareous , the Chalk;

chemical rocks (ex: carbonated, évaporites): they come from the precipitation of a chemical solution:

the evaporitic rocks : the salt or the Gypsum;
the residual rocks of which laterites (ex: allumino-ferruginous, magnesiferous, phosphatic): they are formed by concentration in a given place of “insoluble” solution quasi. They are formed during a very strong chemical weathering of a preexistent rock, the majority of the components are solubilized but there remains a phase far from soluble which precipitates in situ.

According to their nature

the siliceous rocks
the carbonated rocks
the argillaceous rocks
the saltworks or évaporites
the carbonaceous rocks
the phosphatic rocks
the iron-bearing rocks

Because of their formation, the sedimentary rocks are presented generally impure and in several layers.

Evolution of the sedimentary rocks

The sedimentary rocks are carried on the surface within the framework of the great movements Tectonique S which affect the Earth's crust. The shock of the continental plates involved the emergence of sea-beds, which appear, today, in the form of basin S or of formations of altitude.

At the time of these tectonic movements, these rocks could be subjected, locally, with very strong pressures and very high heats. It is resulted from it a transformation from these rocks into metamorphic rocks. Limestones are métamorphisent in Marbre S and clays in Schiste S, even in Gneiss.

The sedimentary areas are rich in mineral resources, in particular in coal, Pétrole and Fer. Coal and oil were formed themselves at the bottom of the seas, respectively by decomposition of forests or sea lives buried, trapped generally between layers of nimble or limestones.

See too

Déodat Gratet de Dolomieu

Simple: Sedimentary rock'n'roll

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