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Alluvium (from the
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic, it became the ...
''alluvius'', from ''alluere'', "to wash against") is loose, unconsolidated (not cemented together into a solid rock)
soil Soil (often stylized as SOiL) is an American rock band that was formed in Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive maps of Chicago , coordinates = , coo ...
or
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently sediment transport, transported by the action of wind, water, or ice or by the force of gravity acting on the particles. Fo ...
that has been
eroded
eroded
, reshaped by water in some form, and redeposited in a non- marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and
clay Clay is a type of fine-grained natural soil material containing clay minerals. Clays develop plasticity (physics), plasticity when wet, due to a molecular film of water surrounding the clay particles, but become hard, brittle and non–plastic ...

clay
and larger particles of sand and gravel. When this loose alluvial material is deposited or cemented into a lithological unit, or lithified, it is called an alluvial deposit.Chisholm, 1911


Definitions

The term "alluvium" is not typically used in situations where the formation of the sediment can clearly be attributed to another geologic process that is well described. This includes (but is not limited to): lake sediments ( lacustrine), river sediments (
fluvial In geography and geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, an ...
), or glacially-derived sediments (
glacial till image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is di ...
). Sediments that are formed or deposited in a perennial stream or
river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases a river flows into the ground and becomes dry at the end of its course without reaching another body of water. Sm ...
are typically not referred to as alluvial.


Age

Most alluvium is geologically
Quaternary Quaternary ( ) is the current and most recent of the three Period (geology), periods of the Cenozoic Era (geology), Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from ...
in age and is often referred to as "cover" because these sediments obscure the underlying
bedrock Bedrock in geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, and ...
. Most sedimentary material that fills a basin ("basin fill") that is not lithified is typically lumped together as "alluvial". On basis of their ages it is divided into two types: *Bhangar (Old alluvium) *Khadar (New alluvium) Alluvium of
Pliocene The Pliocene ( ; also Pleiocene) Epoch is the epoch in the geologic timescale that extends from 5.333 million to 2.58 How To Research a Report, Essay or Topic

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