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sediment,mineral or organic particles that are deposited by the action of wind, water, or glacial ice. These sediments can eventually form sedimentary rocks (see rockrock,
aggregation of solid matter composed of one or more of the minerals forming the earth's crust. The scientific study of rocks is called petrology. Rocks are commonly divided, according to their origin, into three major classes—igneous, sedimentary, and metamorphic.
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Classification of Sediments
Sediments are commonly subdivided into three major groups—mechanical, chemical, and organic.
Mechanical, or clastic, sediments are derived from the erosion of earlier formed rocks on the earth's surface or in the oceans. These are then carried by streams, winds, or glaciers to the site where they are deposited. Streams deposit sediment in floodplainsfloodplain,
level land along the course of a river formed by the deposition of sediment during periodic floods. Floodplains contain such features as levees, backswamps, delta plains, and oxbow lakes.
..... Click the link for more information. or carry these particles to the ocean, where they may be deposited as a deltadelta
[from triangular shape of the Nile delta, like the Greek letter delta], a deposit of clay, silt, and sand formed at the mouth of a river where the stream loses velocity and drops part of its sediment load.
..... Click the link for more information. . Ocean sediments, especially in the form of turbidites, are usually deposited at the foot of continental slopes (see oceansocean,
interconnected mass of saltwater covering 70.78% of the surface of the earth, often called the world ocean. It is subdivided into four (or five) major units that are separated from each other in most cases by the continental masses. See also oceanography.
..... Click the link for more information. ). Glaciers carry sediment frozen within the mass of the ice and are capable of carrying even huge boulders (erratics).
Chemical sediments are formed by chemical reactions in seawater that result in the precipitation of minute mineral crystals, which settle to the floor of the sea and ultimately form a more or less chemically pure layer of sediment. For example, evaporation in shallow basins results in a sequence of evaporite sediments, which include gypsum and rock salt.
Organic sediments are formed as a result of plant or animal actions; for example, peat and coal form by the incomplete decay of vegetation and its later compaction. Deep-ocean sediment known as pelagic ooze consists largely of the remains of microscope organisms (mostly foraminifera and diatoms) from the overlying waters as well as minor amounts of windblown volcanic and continental dust. Limestones are commonly formed by the aggregation of calcite shells of animals.
Formation of Sedimentary Rock
Sediments form sedimentary rock by compaction and cementation of the particles. Thus, coarse sediments become conglomeratesconglomerate,
in geology, sedimentary rock composed largely of pebbles or other rounded particles whose diameter is larger than 2 mm (.08 in.). Essentially a cemented gravel, conglomerates are formed along beaches, as glacial drift, and in river deposits.
..... Click the link for more information. ; sands become sandstonesandstone,
sedimentary rock formed by the cementing together of grains of sand. The usual cementing material in sandstone is calcium carbonate, iron oxides, or silica, and the hardness of sandstone varies according to the character of the cementing material; quartz sandstones
..... Click the link for more information. ; and muds become shaleshale,
sedimentary rock formed by the consolidation of mud or clay, having the property of splitting into thin layers parallel to its bedding planes. Shale tends to be fissile, i.e., it tends to split along planar surfaces between the layers of stratified rock.
..... Click the link for more information. . Sedimentary rocks make up only about 5% of all rocks of the earth's crust, yet they cover 75% of the land area in a veneer that averages 2.26 km (1.4 mi) in thickness, ranging from 0 to 12.9 km (0–8 mi).