Geology: What´s a Sediment?

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In geology, a sediment is defined as an assemblage of particles, loose or indurated materials that form on the Earth’s surface (Selley 2000, 41). The study of sediment includes its provenance and the processes that result in their deposition of the weathered and eroded products of its older material. The purpose of sedimentology is to provide a deeper understanding about the Earth’s history.
In a sediment, maturity is described as the degree of how much a sediment changed due to weathering, transport and reworked toward its ultimate end product, quartz sand (Nichols 2009, 26). Sediment maturity can be measured in terms of its texture and composition.
Texture in a sedimentary rock refers to its grain sizes, grain shapes, sorting and rounding.
Textural maturity is defined by the sorting and its roundness of sediment whereas composition maturity is a reflection to its quartz content. The maturity of a sediment or a sedimentary rock can be represented as shown in Figure 1.
There are four types of textural maturity; immature, submature, mature and supermature.
Texturally immature sediments are those which comprise of mostly matrix and contains little amount of grains in the rock. The grains are usually poorly sorted and are angular (Tucker 2001, 20). A rock which composed of mud, silt and sand sized materials such as the greywacke is considered to be texturally immature. An indication of a texturally immature sediment is that the distance of its transport may be short.
A sediment is considered to be submature when sorting is moderate to poor. Submature grains are usually smaller and appears to be slightly more rounded than immature sediments.
Texturally mature sediments are those where there is little matrix and have a range of moderate to good sorting and subrounded to rounded grains. Mature grains usually often more rounded and have higher sphericity compare to immature and submature grains.
Texturally supermature sediments are those with no matrix, have very good sorting and consists of well-rounded grains. As quartz is hard and lacks cleavage, it is commonly the ultimate survivor and is durable to changes in a turbulent environment (Skinner, Porter and Park 2004, 178). A rock which consists of well-rounded quartz grains of a restricted grain size would be very mature.
The determination of the textural maturity of a sediment is independent to its composition as it is influenced largely to its depositional processes, although it can be altered by diagenetic processes (Tucker 2001, 11).
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