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, wherein living organisms extract ions 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. The formation of a clastic sediment and sedimentary rocks involves five processes:.
Classification - Clastic sedimentary particles and sedimentary rocks are classified in terms of grain size and shape, among other factors. In general, the coarser sediment gets left behind by the transportation process. Thus, coarse sediment is usually found closer to its source and fine grained sediment is found farther from the source. When sediment is transported and deposited, it leaves clues to the mode of transport and deposition.
For example, if the mode of transport is by sliding down a slope, the deposits that result are generally chaotic in nature, and show a wide variety of particle sizes. Grain size and the interrelationship between grains gives the resulting sediment texture. Thus, we can use the texture of the resulting deposits to give us clues to the mode of transport and deposition. Sorting - The degree of uniformity of grain size. Particles become sorted on the basis of density, because of the energy of the transporting medium.
High energy currents can carry larger fragments. As the energy decreases, heavier particles are deposited and lighter fragments continue to be transported. This results in sorting due to density. If the particles have the same density, then the heavier particles will also be larger, so the sorting will take place on the basis of size. We can classify this size sorting on a relative basis - well sorted to poorly sorted. Sorting gives clues to the energy conditions of the transporting medium from which the sediment was deposited.
Rounding - During the transportation process, grains may be reduced in size due to abrasion. Random abrasion results in the eventual rounding off of the sharp corners and edges of grains. Thus, rounding of grains gives us clues to the amount of time a sediment has been in the transportation cycle. Rounding is classified on relative terms as well. Sediment Maturity refers to the length of time that the sediment has been in the sedimentary cycle.
Texturally mature sediment is sediment that is well rounded, as rounding increases with transport distance and time and well sorted as sorting gets better as larger clasts are left behind and smaller clasts are carried away.
Because the weathering processes continues during sediment transport, mineral grains that are unstable near the surface become less common as the distance of transport or time in the cycle increases.
Thus compositionally mature sediment is composed of only the most stable minerals. For example a poorly sediment containing glassy angular volcanic fragments, olivine crystals and plagioclase is texturally immature because the fragments are angular, indicating they have not been transported very far and the sediment is poorly sorted, indicating that little time has been involved in separating larger fragments from smaller fragments.
It is compositionally immature because it contains unstable glass along with minerals that are not very stable near the surface - olivine and plagioclase. On the other hand a well sorted beach sand consisting mainly of well rounded quartz grains is texturally mature because the grains are rounded, indicating a long time in the transportation cycle, and the sediment is well sorted, also indicative of the long time required to separate the coarser grained material and finer grained material from the sand.
The beach sand is compositionally mature because it is made up only of quartz which is very stable at the earth's surface. Conglomerate and Breccia are rocks that contain an abundance of coarse grained clasts pebbles, cobbles, or boulders.
In a conglomerate, the coarse grained clasts are well rounded, indicating that they spent considerable time in the transportation process and were ultimately deposited in a high energy environment capable of carrying the large clasts. In a breccia, the coarse grained clasts are very angular, indicating the the clasts spent little time in the transportation cycle.
A Sandstone is made of sand-sized particles and forms in many different depositional settings. Texture and composition permit historic interpretation of the transport and depositional cycle and sometimes allows determination of the source. Quartz is, by far, the dominant mineral in sandstones. Still there are other varieties.
An Arkose contains abundant feldspar. In a lithic sandstone, the grains are mostly small rock fragments. Sandstones are one of the most common types of sedimentary rocks. Mudrocks are made of fine grained clasts silt and clay sized.
A siltstone is one variety that consists of silt-sized fragments. A shale is composed of clay sized particles and is a rock that tends to break into thin flat fragments See figure 7. A mudstone is similar to a shale, but does not break into thin flat fragments.
Organic-rich shales are the source of petroleum. Fine grained clastics are deposited in non-agitated water, calm water, where there is little energy to continue to transport the small grains. Thus mudrocks form in deep water ocean basins and lakes. Biochemical and Organic sediments and sedimentary rocks are those derived from living organisms.
When the organism dies, the remains can accumulate to become sediment or sedimentary rock. Among the types of rock produced by this process are:. Biochemical Limestone - calcite CaCO 3 is precipitated by organisms usually to form a shell or other skeletal structure.
Accumulation of these skeletal remains results in a limestone. Sometimes the fossilized remains of the organism are preserved in the rock, other times recrystallization during lithification has destroyed the remains.
Limestones are very common sedimentary rocks. Biochemical Chert - Tiny silica secreting planktonic organism like Radiolaria and Diatoms can accumulate on the sea floor and recrystallize during lithification to form biochemical chert.
The recrystallization results in a hard rock that is usually seen as thin beds see figure 7. Diatomite - When diatoms accumulate and do not undergo recrystallization, they form a white rock called diatomite as seen in the White Cliffs of Dover see figure 7. Coal - Coal is an organic rock made from organic carbon that is the remains of fossil plant matter.
It accumulates in lush tropical wetland settings and requires deposition in absence of Oxygen. It is high in carbon and can easily be burned to obtain energy. Dissolved ions released into water by the weathering process are carried in streams or groundwater. Eventually these dissolved ions end in up in the ocean, explaining why sea water is salty.
When water evaporates or the concentration of the ions get too high as a result of some other process, the ions recombine by chemical precipitation to form minerals that can accumulate to become chemical sediments and chemical sedimentary rocks.
Among these are:. Evaporites - formed by evaporation of sea water or lake water. One categor As a lea Please help Solve the equation using inverse operations. Check your solutions. In your final answer, include all of your work.
What is the weight in newtons of a bowling ball that has a mass of 3 kg? If there 21 green cars, how many cars are parked in the parking lot? More questions: Biology Another questions. Questions on the website: See results 0 The answer is not found? Log in Forgot your password? Join now Forgot your password? You are registered. Access to your account will be opened after verification and publication of the question. Ok Close. Add photo Send. Question sent to expert.
This is usually much less efficient than drilling rocks that will yield oil or gas directly into a well. The processes used for hydrocarbon extraction also produce emissions and waste products that cause significant environmental concerns. It typically breaks into thin flat pieces. Environments where large amounts of sand can accumulate include beaches, deserts, flood plains, and deltas.
The best way to learn about rocks is to have a collection of specimens to examine while you study. Seeing and handling the rocks will help you understand their composition and texture much better than reading about them on a website or in a book.
The Geology. Mineral collections and instructive books are also available. The specimen in the photo is about two inches five centimeters across. Article by: Hobart M. Find Other Topics on Geology. Maps Volcanoes World Maps. Rock, Mineral and Fossil Collections. Hardness Picks. Flint, Chert, and Jasper. Tumbled Stones. Fluorescent Minerals. Lapis Lazuli. Rocks: Galleries of igneous, sedimentary and metamorphic rock photos with descriptions.
Minerals: Information about ore minerals, gem materials and rock-forming minerals. Volcanoes: Articles about volcanoes, volcanic hazards and eruptions past and present. Gemstones: Colorful images and articles about diamonds and colored stones.
General Geology: Articles about geysers, maars, deltas, rifts, salt domes, water, and much more! Geology Store: Hammers, field bags, hand lenses, maps, books, hardness picks, gold pans.
Earth Science Records: Highest mountain, deepest lake, biggest tsunami and more. Diamonds: Learn about the properties of diamond, its many uses, and diamond discoveries.
0コメント