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Sedimentary Rocks

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| Sedimentary Rocks | Sci. 245 Week 5 Assignment | | Bree Odion | 7/24/2011 |

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SEDIMENTARY ROCKS

Introduction to Sedimentary Rocks
The most common rock on Earth’s surface is sedimentary. Sandstone, limestone, and salt are all forms of sedimentary rocks to name a few. (National Atlas of the United States n.d.)
This paper will explore the origination of sedimentary rocks; categories associated with sedimentary rocks; and compare the distinguishing characteristics of the three. The discussion will also include how sedimentary rocks are formed and affect of plate tectonics on rocks.
Sedimentary rocks are our best records today of how our earth is changing everyday and the best to describe to us why it is changing. Not only can geologists tell based on the shape, and deposits made of sediment but we can tell by the fossils that are made within the sediment rock. This allows us to know things about our earth from billions of years ago that we may have not known if h had not been for sediment.

Where Sedimentary Rocks Originate
Sedimentary rocks originate from the weathering and erosion of pre-existing rocks. When sediment is deposits it lithifies to create new rocks. Sedimentary rocks occur when sediments, weathered fragments from older rocks as well as biological debris like leaves, trees, and dead animals, are deposited and stay in place long enough for rock to form. It is known that sedimentary rocks contain sandstones, shale’s, and coal seams. Sedimentary deposits are a many key in economic geology for they include coal seams and oil deposits. There are ways to tell how deposits were made according to the rock beds they lie in. There are many ways they could have been created such as streams, wind and ocean waves. Depending on the way the sediment was deposited in these rocks beds, geologists can tell how they got there by the markings they have left behind.
When sediment deposition builds up, the overload (or 'lithostatic') pressure squeezes the sediment into layered solids in a process known as lithification ('rock formation') and the original connate fluids are dispossessed. This would be how sediment rocks are actually formed by the tectonic pressure created by the earth. There are three categories of sedimentary rocks clastic, chemical, and biogenic. Chemical and biogenic sediments are not as strongly affected by plate tectonics as clastic sediment is because of the difference in the way they are formed. There is also a difference in the strength of the sediments that are created.
Clastic rocks range in many sizes beginning with boulder size down to particles smaller than flour. They are also categorized by shape, angularity, and size range of grain in the rock. There are also volcaniclastic sediments which are volcanic in origin. Clastic sediment consists of clasts that make up the sediment. Clasts can become rounded during transport by wind or water, but never seem to be affected by the transport of ice or glaciers. There are four basic classes of clastic sediment which are familiar to us all as gravel, sand, silt, and mud. This is also considered the most abundant sediment rock opposed to chemical and biogenic sediment.
Water that evaporates and turns into precipitation from seas or lakes is considered chemical sediments. There are many things that alter the chemical balance in water such as animals and deposits of matter. This therefore makes the chemical sediment. Things such as limestone are created through this process. Different rocks are formed from sea water opposed to just basic ground waters. Calcite, gypsum, and halite are just a few that are formed from sea water.
Biogenic sediments are created by plants and animals. The hard parts such as bones, teeth, and shells are what form the calcium in the biogenic sediments. Limestone is considered biogenic sediment as well as it is considered chemical sediment. Limestone is also considered the most abundant of the biogenic sediments.
There are many areas that are environments for sediment deposits such as the ocean, streams, and lakes. Streams are considered transporters of sediment and you can usually find outer markings on the sediment telling where it came from. Some of these markings may be mud cracks or ripples in the sediment. This also helps determine where the actual sediment was transported from. There are many distinguishable differences in sediment rocks, but there are similarities as well. They are all created by something that is transported whether it be evaporated or carried by stream. These rocks are very important to geology today in helping us understand things that have happened in the past through fossils and new formations that are being created every day.

References

Axia College. (2011). Visualizing Geology. Retrieved July 24th, 2011, from Axia College, Week Five, SCI 245.

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