alluvium


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alluvium

a fine-grained fertile soil consisting of mud, silt, and sand deposited by flowing water on flood plains, in river beds, and in estuaries

Alluvium

 

or alluvial deposits. (1) Deposits of fluvial water courses—rivers, streams—forming floodplains and terraces of river valleys. They play a very important role in the structure of most continental sedimentary formations. The alluvium of plains rivers (see Figure 1) usually combines fluvial alluvium deposited in the migrating bed (obliquely laminated sands and gravel), floodplain alluvium which accumulates on the fluvial during floods (mainly loams and sandy loams), and oxbow-lake alluvium which settles in the oxbow-lakes (mainly sandy loams and loams which are rich in organic matter).

Figure 1. Diagram of structure of alluvium from plain river: (1) fluvial alluvium, (2) floodplain alluvium, (3) oxbow-lake alluvium, (4) bedrock from slopes and bottom of river valley, (5) water level during flooding.

The composition and structure of the alluvium differ substantially depending on the size and hydraulic regime of the flow, the relief of the drainage system, and the rock composing it. For example, in the alluvium of mountain rivers, there is a predominance of boulder and pebble fluvial alluvium; streams which flow through ravines and gullies deposit poorly graded alluvium in which it is difficult to distinguish the fluvial, floodplain, and other types of alluvium. In ancient sedimentary beds, the alluvium is usually cemented together and composed of hard fragmented rock such as conglomerates, sandstones, argillites, and so forth. The fluvial alluvium may contain placers of gold, platinum, and other useful minerals in addition to deposits of construction sands and gravel.

(2) In foreign literature, alluvium is the name often given to any deposits of running waters, including proluvium and deluvium.

(3) The obsolete name of all recent continental deposits formed in the postglacial age (Holocene); the term “alluvium” is sometimes used in this sense only in German literature.

REFERENCES

Shantser, E. V. Alluvii ravninnykh rek umerennogo poiasa i ego znachenie dlia poznaniia zakonomernostei stroeniia i for-mirovaniia alliuvial’nykh svit. Moscow, 1951.
Shantser, E. V. Ocherki ucheniia o geneticheskikh tipakh. kontinental’nykh osadochnykh obrazovanii. Moscow, 1966.

E. V. SHANTSER

alluvium

[ə′lüv·ē·əm]
(geology)
The detrital materials that are eroded, transported, and deposited by streams; an important constituent of shelf deposits. Also known as alluvial deposit; alluvion.

alluvium

Gravel, sand, silt, soil, or other material that is deposited by running water.
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