Alluvium (from Latinalluvius, from alluere'to wash against') is looseclay,silt,sand, orgravel that has been deposited by running water in a stream bed, on afloodplain, in analluvial fan orbeach, or in similar settings.[1][2][3] Alluvium is also sometimes calledalluvial deposit.[4][5] Alluvium is typically geologically young and is notconsolidated into solid rock.Sediments deposited underwater, in seas,estuaries, lakes, or ponds, are not described as alluvium.[1]Floodplain alluvium can be highly fertile, and supported some of the earliest human civilizations.[6]
The presentconsensus is that "alluvium" refers to loosesediments of all types deposited by running water infloodplains or inalluvial fans or relatedlandforms.[1][7][8] However, the meaning of the term has varied considerably since it was first defined in the French dictionary ofAntoine Furetière, posthumously published in 1690. Drawing upon concepts fromRoman law, Furetière definedalluvion (the French term for alluvium) as new land formed by deposition of sediments along rivers and seas.[8]
By the 19th century, the term had come to mean recent sediments deposited by rivers on top of olderdiluvium, which was similar in character but interpreted as sediments deposited byNoah's flood. With the rejection by geologists of the concept of a primordial universal flood, the term "diluvium" fell into disfavor and was replaced with "older alluvium". At the same time, the term "alluvium" came to mean all sediment deposits due to running water on plains. The definition gradually expanded to include deposits in estuaries, coasts, and young rock of marine andfluvial origin.[8]
Alluvium and diluvium were grouped ascolluvium in the late 19th century. "Colluvium" is now generally understood as sediments produced by gravity-driven transport on steep slopes. At the same time, the definition of "alluvium" has switched back to an emphasis on sediments deposited by river action. There continues to be disagreement over what other sediment deposits should be included under the term "alluvium".[8]
Most alluvium isQuaternary in age and is often referred to as "cover" because these sediments obscure the underlyingbedrock. Most sedimentary material that fills abasin ("basin fill") that is notlithified is typically lumped together as "alluvial".[9] Alluvium ofPliocene age occurs, for example, in parts of Idaho.[10] Alluvium of lateMiocene age occurs, for example, in the valley of theSan Joaquin River, California.[11]
^Jackson, Julia A., ed. (1997). "alluvial deposit".Glossary of geology (Fourth ed.). Alexandria, Virginia: American Geological Institute.ISBN0922152349.
^Allaby, Michael (2013). "alluvium".A dictionary of geology and earth sciences (Fourth ed.). Oxford: Oxford University Press.ISBN9780199653065.
^Kidder, Tristram; Liu, Haiwang; Xu, Qinghai; Li, Minglin (July 2012). "The Alluvial Geoarchaeology of the Sanyangzhuang Site on the Yellow River Floodplain, Henan Province, China: THE YELLOW RIVER FLOODPLAIN, HENAN PROVINCE".Geoarchaeology.27 (4):324–343.doi:10.1002/gea.21411.S2CID140587757.
