Metagenesis

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metagenesis

[¦med·ə′jen·ə·səs]
(biology)
The phenomenon in which one generation of certain plants and animals reproduces asexually, followed by a sexually reproducing generation. Also known as alternation of generations.

Metagenesis

 

in animals, a form of alternation of generations in which a generation developed by sexual means is followed by one or more that reproduce asexually. Metagenesis is found in coelenterates, a number of worms, and certain lower chordates (salpa).


Metagenesis

 

(geology), the natural processes in the trans-formation of sedimentary rocks when they are buried in deeper horizons of the lithosphere under conditions of steadily increasing pressure and temperature. Scientists do not agree upon the meaning of the term “metagenesis.” The Soviet geologist N. B. Vassoevich, who first proposed the term in 1957, considers it a synonym of regional metamorphism of rocks. At virtually the same time Academician N. M. Strakhov began to use the term “metagenesis” for one of the stages in the transformation of sedimentary rocks, coming after diagenesis and continuing until they are converted into metamorphic rocks. Unlike catagenesis, which changes only certain components of the rock, metagenesis involves the entire mineral mass. For example, clay minerals are transformed into mica, hydroxides of aluminum are converted to corundum, and hydrogoethites are converted to hematite. At the same time the intergrowth of mineral grains is intensified, but the stratified structure of the rocks often persists.

REFERENCES

Vassoevich, N. B. “Eshche o terminakh dlia oboznacheniia stadii i etapov litogeneza.” Tr. Vsevoiuznogo neftianogo nauchno-issledovatel’skogo geologorazvedochnogo in-ta, 1962, fasc. 190.
Diagenez i katagenez osadochnykh obrazovanii. Moscow, 1971. (Translated from English.)

N. B. VASSOEVICH