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Alluvium

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Section of alluvium at the Blue Ribbon Mine in Alaska

Alluvium deposits in the Gamtoos Valley in South Africa

Alluvium (from the Latin, alluvius, from alluere, "to wash against") is loose, unconsolidated (not cemented together into a solid rock), soil or sediments, eroded, deposited, and reshaped by water in some form in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel. When this loose alluvial material is deposited or cemented into a lithological unit, or lithified, it would be called an alluvial deposit.

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), or glacially-derived sediments (glacial till). Sediments that are formed and/or deposited in a perennial stream or river are typically not referred to as alluvial.

Most, if not all, alluvium is very young (Quaternary in age), and is often referred to as "cover" because of the fact that these sediments obscure the underlying bedrock. Most sedimentary material that fills a basin ("basin fill") that is not lithified is typically lumped together in the term alluvial.

Alluvium can contain valuable ores such as gold and platinum and a wide variety of gemstones. Such concentrations of valuable ores is termed a placer deposit.

See also

• Alluvial desert
• Alluvial fan
• Alluvial plain
• Alluvion
• Colluvium
• Eluvium
• Fluvial
• Illuvium

References

External links

Wikimedia Commons has media related to: Alluvium

•  "Alluvium". Encyclopædia Britannica (11th ed.). 1911.