SEDIMENTATION PROCESS

 

                                        SEDIMENTATION PROCESS

                                       FIGURE 1.1 SEDIMENTARY ROCK

 Rivers, oceans, winds, and rain runoff all have the ability to carry the particles washed off of eroding rocks. Such material is called as detritus, consists of fragments of rocks and minerals. When the energy of the transporting current is not strong enough to carry these particles, the particles drop out in the process of sedimentation. This type of sedimentary deposition is referred to as clastic sedimentation. Another type of sedimentary deposition occurs when material is dissolved in water, and chemically precipitates from the water. This type of sedimentation is referred to as chemical sedimentation. A third process can occur, where in living organisms extractions dissolved in water to make such things as shells and bones. This type of sedimentation is called biochemical sedimentation. The accumulation of plant matter, such as at the bottom of a swamp, is referred to as organic sedimentation. 

 

 There are 4 major types of sedimentary rocks:

1.     Clastic Sedimentary Rocks, 

2.     Chemical Sedimentary Rocks,

3.     Bio-chemical Sedimentary rocks, and 

4.     Organic Sedimentary rocks. 

The formation of clastic sediment and sedimentary rocks involves five processes:

1. Weathering :-

                                           FIGURE 1.2 WEATHERED ROCKS 

The physical and chemical condition of rocks are altered when they are exposed to the atmosphere such an altered product is known as weathered material and the process involved is said as weathering , in which the larger particle of rock breaks up into smaller particle and transported by geological agents .

2. Erosion :-

                                          FIGURE 1.3 ERODED ROCK 

 Erosion is actually many processes which act together to lower the surface of the earth. In terms of producing sediment, erosion begins the transportation process by moving the weathered products from their original location. This can take place by gravity (mass movement events like landslides or rock falls), by running water, blowing wind, or by moving ice. Erosion overlaps with transportation.

3. Transportation :-

Sediment can be transported by sliding down slopes, being picked up by the wind, or by being carried by running water in streams, rivers, or ocean currents. The distance the sediment is transported and the energy of the transporting medium all leave clues in the final sediment that tell us something about the mode of transportation.

4. Deposition :-

 Sediment is deposited when the energy of the transporting medium becomes too low to continue the transport process. In other words, if the velocity of the transporting medium becomes too low to transport sediment, the sediment will fall out and become deposited. The final sediment thus reflects the energy of the transporting medium.

5. Lithification (Diagenesis) :-

 Lithification is the process that turns sediment into rock. The first stage of the process is compaction. Compaction occurs as the weight of the overlying material increases. Compaction forces the grains closer together, reducing pore space and eliminating some of the contained water. Some of this water may carry mineral components in solution, and these constituents may later precipitate as new minerals in the pore spaces. This causes cementation, which will then start to bind the individual particles together.

 

Classification - Clastic sedimentary particles and sedimentary rocks are classified in terms of grain size, shape and also by other factors.

 

Name of Particle	Size Range	Loose Sediment	Consolidated Rock
Boulder	>256 mm	Gravel	Conglomerate or Breccia      (depends on Cobble 64 - 256 mm Gravel rounding)
Cobble	64 - 256 mm	Gravel
Pebble	2 - 64 mm	Gravel
Sand	1/16 - 2mm	Sand	Sandstone
Silt	1/256 - 1/16mm	Silt	Siltstone
Clay	<1/256 mm	Clay	Clay stone, mudstone, and shale