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Sedimentary Rocks

The world around us has so many dynamic forms of sediments and sedimentary rocks. It’s a very fundamental understanding of our Earth system which takes into account the environment around us for the surface characterization. 

The idea of natural resources, industrial, chemical, metallic, water and energy resources also helps in understanding where and how the sediments help in preserving these natural facts.

The various attributes of a sedimentary rock combines to give us the idea of facies which is basically the product of a particular deposit in that given environment. Facies identification and analysis of such features reflect the longer term and long term deposition which are primarily relative to sea level changes in tectonic, sediment supply, sediment production and climate in general.

There are several sedimentary rocks aspects to consider in the field and hence should be cross checked in detail. These are as follows:

• The texture of sediments refers the features and arrangements of the grains in such sediments. 

• The most important of such examination is to check the sediment grain size and variation. 

• The lithology of sediments such as the composition and mineral deposition of the sediment also is taken into account. 

• The sediments structure which are present in rock beds and under surfaces or even within the bed layers helps in recording the palaeocurents which has deposited in these rocks. 

• The colours of sediments are also big indicators as far as sedimentary study is considered. 

• The sediments geometry and beds or rocks relationship along with the lateral and vertical changes in thickness and composition gives us a detailed study of sedimentary rocks.

• The nature of fossils deposition, the type of deposition and how well the deposits are preserved also gives a big idea of sedimentary rocks.



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In one word the rocks which are formed from sediments of clay, sand, soil that settled in water or semi fluid zones and something which got compressed due to high pressure and temperature turned into sediment rock layers. Due to such huge pressure and high temperature the nature of the sediments got converted into the rocks but in specific layers as these mineral specific layers settle down according to their specific gravity and hence there are layers of matter found in cross section with different texture and colour.

How are Sedimentary Rocks Formed?

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The formation of sedimentary rocks begins with either other sedimentary rocks or igneous form and even metamorphic rocks. These when undergo millions of years of physical changes compliance with weathering, deposition and erosion we get to see layers of sedimentary rocks.

Weathering is a process by which all rock forms breaks into smaller forms and pieces and sediments due to the physical dynamics like rainfall, wind, ice formation and water accumulation and slowly the original form give way to newer forms of sedimentary layers.

Deposition is another physical process by which we might get to see a sedimentary layer forming. The deposits are either carried by wind, flowing water or even gravitational force. As the natural forces slowly loses their energy the matter carried by them settle down in a particular spot the layers of sediments are formed. These matters settle down according to the specific gravity of the matters involved. The larger and heavier forms settle at the bottom followed by other lighter particles. 

Erosion is another form of sediment formation in which the combined of forces of Earth gravitational force, tectonic movements and other natural forces work on these sediments or igneous rock forms helping in forming settling the sediment matter.  

Lithification is another physical process where a layer is slowly converted into rock forms. This process involves two different methods and they are compaction and cementation.

Types of Sedimentary Rock

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• The sedimentary rocks are mainly classified into three different forms of rock forms. They are either organic sedimentary rock, Clastic sedimentary and finally chemical sedimentary forms

• The Organic sedimentary forms mainly comprise of coal and lime stones which are formed due to deposition and accumulation of dead plants and animals in rock layers. 

• The chemical sediment layers are formed when chemical reactions between minerals present in rock forms settle down as precipitate and converts to rock forms over a period of time.

• The Clastic sediments are formed when rock layers are formed due to mechanical weathering of rock forms. 

How are Sedimentary Rocks Classified?

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Sedimentary rocks are classified mainly by cross checking the origin of these rock forms. They are either Organic deposition, mechanically weathered by natural processes or chemically reacted with minerals present in other forms of rocks and finally settling down as sediments after compaction. Classification is done mainly to help segregate these rock forms into their right order. 

Layers of Sedimentary Rock

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The different layers of sediments are Palaeozoic strata, Mesozoic strata, and Cainozoic strata. 

Due to huge horizontal pressure the rock layers are folded in many waves like forms or patterns which results in anticlines and synclines. The constant forces of erosion could help in reducing the size and appearance of the mountains by the wear and tear away the surface layers and remove the layers of rocks. 

Characteristics of Sedimentary Rocks

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• Sedimentary rocks are deposited on the Earth’s surface by various physical processes like wind, flowing water, moving glacier, or even biochemical process.

• The sedimentary rocks are deposited in layers one after another when the surface slowly cools down. 

• The sedimentary layers settle down according to the size of the particles with the largest particles first at the bottom followed by smaller particles.

Examples of sedimentary rocks

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• The sedimentary rocks are mainly classified and segregated according to the either various composition of minerals that helps in precipitation of these into rock layers or by different physical process like weathering, deposition and compaction.  Based on the type of formation method we have some main sediment rocks. 

• Breccia rocks are a form of clastic sediment, Chert a chemically precipitated rock form comprise of mainly SiO2, dolomite form are magnesium rich ground water washed with limestone  and Coal is an organic sediment rock form which forms mainly due to deposition and compaction of plants and animals parts long ago. 

• Other examples are conglomerate, flint and iron ore etc.
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