UOPX Wk 5 SCI 245 Assignment Sedimentary Rock

7/29/2019 UOPX Wk 5 SCI 245 Assignment Sedimentary Rock

1/5

Sedimentary Rock

Evonia Hogan

SCI - 245 Physical Geology

Axia of University of Phoenix

May 30, 2009


2/5

Sediment originates from the erosion of pre-existing rocks that have been

broken down through weathering.

Sedimentary rock is formed by individual particles that are bound together into a

cohesive unit. After a layer of sediment is buried, either by the accumulation of more

sediment or by tectonic processes, it is placed under higher pressure, leading to

compaction. Sedimentary rock can be made up of particles derived from the

weathering and erosion of igneous rock as well. Sedimentary rock is one of the most

abundant rock on the planet. They cover over 60% of the continental surface and most

of the ocean floor.

Sedimentary rocks are composed nearly entirely (>95%) of three types of rocks,

mudstones, sandstones, and carbonates. Of these groups, the mudstones are the

most abundant, followed by sandstones and then carbonates. The remaining

sedimentary rocks are composed of evaporites, bedded chert, bedded phosphate, and

bedded iron ore. These rocks make up less than 5% of the sedimentary rocks.

(http://www.suite101.com/article.cfm/everyday_geology/89686)

Sedimentary rocks are formed thru a process called lithification. Lithification

can be accomplished by one of three methods. These methods consist of compaction,

cementation and re-crystallization. Lithification can be the result of all or some of these

methods.

Compaction is the reduction of pore space in sediment as a result of the weight

of overlying sediments. Compactionis the first step in lithification.


3/5

Cementation is the process in which substances dissolved in pore water

precipitate out and form a matrix in which grains of sediment are joined together.

Re-crystallization is the formation of new crystalline mineral grains from old

ones.This is the layered arrangement of strata in a body of sediment or sedimentary

rock. In the process of re-crystallizing, crystals that were separate can grow together.

There are three main types of sedimentary rocks, Clastic, Biogenic and

Chemical sediment.

Clastic rocks are made up of individual particles or clasts. They differ in size

and shape and are derived from eroded rock debris. Sediment formed from

fragmented rock and mineral debris produced by weathering and erosion. Clasts may

become rounded and sorted during transport by water and wind, but they typically

remain unsorted during transport by glaciers or as a result of mass wasting.

They are classified by sizes that can be boulder, pebble, cobble, sand, silt or

clay. Boulder is the size of a baseball or larger. Its size is 256mm or more in

measurement.

Cobble is the size of a chickens egg. Its size is 64 and 256mm in

measurement.

Pebble is the size of a pea. Its size is between 2 and 64mm in measurement.

Sand is the size of the head on a pin. Its size is 1/6 to 2mm in measurement.


4/5

The silt is around the size of salt. Its size is 1/256mm to 1/16 in measurement.

The clay is the size of a grain of flour which can form shale rock. Its size is less

than 1/256mm in measurement

Chemical sediment is formed by the precipitation of minerals dissolved in lake,

river, or sea water. All surface water and groundwater contains dissolved chemicals

that eventually find their way to a lake or sea. Most chemical sedimentary rocks

contain only one important mineral, such as calcite, dolomite, gypsum, or halite

Biogenic sediment, that is primarily composed of plant and animal remains, or

precipitates as a result of biologic processes. This includes the hard parts of large

animals, such as shells, bones, and teeth, as well as fragments of plant matter, such

as wood, roots, and leaves. Limestone is the most abundant biogenic sedimentary

rock.

Volcaniclastic sediments are another kind of clastic sediment. This is where all

of the clasts are made from a volcanic origin.

Basically, all sedimentary rock is created by the deposition of sediment that has

been laid down in layers over many years. The pressure from the many layers of

sediment compresses itself into a rock that may be formed from many types of

sediment.

The individual layers can be analyzed by geologist to determine what was

happening in the environment during certain time frames in our past. Each layer holds


5/5

the secret to what the worlds terrain might have been experiencing. It also helps us to

understand what types of life forms may have been here and when they were here.

References

Sedimentary rock. (2008, May 4). In Wikipedia, The Free Encyclopedia. Retrieved08:38, May 30, 2009, fromhttp://en.wikipedia.org/w/index.php?title=Sedimentary_rock&oldid=294342710

Introduction to Sedimentary Rocks, (2002, February 25). Retrieved 7:45, May 31, 2009,fromhttp://www.suite101.com/article.cfm/everyday_geology/89686
http://en.wikipedia.org/w/index.php?title=Sedimentary_rock&oldid=294342710http://en.wikipedia.org/w/index.php?title=Sedimentary_rock&oldid=294342710http://www.suite101.com/article.cfm/everyday_geology/89686http://www.suite101.com/article.cfm/everyday_geology/89686http://www.suite101.com/article.cfm/everyday_geology/89686http://www.suite101.com/article.cfm/everyday_geology/89686http://en.wikipedia.org/w/index.php?title=Sedimentary_rock&oldid=294342710

Documents

UOPX Wk 5 SCI 245 Assignment Sedimentary Rock