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What is sedimentary rock? How They are formed? What is the role plays by process of weathering, erosion, transportation and deposition?

 As we know that the rocks are changing or transformed with time due to the action of atmospheric agencies (including temperature, pressure, water, wind, etc.).The cyclic process through which, rocks are transformed from one category to another one such process is called the Rock cycle.

    On the earth, there are three types of rocks are exist-

1)      Igneous rocks (also known as primary rocks)

2)      Sedimentary rocks (also known as secondary rocks)

3)      Metamorphic rocks (also known as secondary rocks)

Sedimentary rocks are formed by the consolidation and cementation of sediments deposits underwater. Sedimentary rocks also include the rocks formed by the accumulation of chemically precipitated or organically derived material. The formation of sedimentary rocks takes place in three stages:


 


       Weathering and Erosion: Sedimentary rocks are secondary rocks, which are constituted of sediments (broken rock fragments of pre-existing rocks formed by weathering). The sediments are formed by mechanical or chemical activity of the natural agencies like running water, blowing wind, percolating water (underground), glaciers, etc., which causes disintegration as well as decomposition of the pre-existing rocks. The products of decay (sediments) are transported to some depositional sites by natural agencies. During transportation, the sediments are roughly sorted and deposited according to size. Bigger rock fragments, such as gravel, settle first, sands are next in order and clay particles are deposited in the last.



b)      Sedimentation: The process of accumulation of sediments at a site of deposition is called “sedimentation”.

 


Lithification and Diagenesis: Lithification is a process by which loose and soft sediments are converted into hard and firm rocks. This process is also called “consolidation”. During this process many physical and chemical changes take place within the sediments. Such changes are called the diagenetic changes and the process is described as “diagenesis”. The diagenesis includes three processes-

·         Compaction: Compaction occurs when the weight of overlying layers compresses the sediments below. As the grains of sediments are pressed closer and closer together, there is a considerable reduction in pore space and volume. Fine-grained sediments, such as clays are consolidated more effectively by this process. 

·         Cementation: When water circulates through the pores of coarse-grained sediments, dissolved minerals matter is precipitated between the gains which cause cementation. The most common cementing materials are silica, calcium carbonate, iron oxide, and clay minerals.

·         Recrystallization: Although most sedimentary rocks are lithified by compaction, cementation, or a combination of both, some are consolidated chiefly by the recrystallization of their constituents. Chemically formed rocks, such as limestone, dolomites, salt, and gypsum are example of the rocks consolidated by recrystallization.  

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