- Paleosol
In
soil science , paleosols ("palaeosols" inGreat Britain andAustralia ) can have two meanings. The first meaning, is simply that of a "former soil" preserved by burial underneath eithersediment s (alluvium orloess ) or volcanic deposits (Volcanic ash), which in case of older deposits, have lithified into rock. InQuaternary geology,sedimentology ,paleoclimatology , andgeology in general, it is the typical and accepted practice to use the term "paleosol" to designate such "fossil" soils found buried within eithersedimentary or volcanic deposits exposed in all continents as illustrated by Rettallack (2001), Kraus (1999), and innumerable other published papers and books.More generally in
soil science , paleosols are soils formed long periods ago that have no relationship in their chemical and physical characteristics to the present-day climate or vegetation. Such soils form on extremely old continentalcraton s and as small scattered localities in outliers of ancient rock. Because of the changes in the Earth's climate over the last fifty million years, soils formed undertropical rainforest (or evensavanna ) have become exposed to increasinglyarid climates which cause formerOxisols ,Ultisols or evenAlfisols to dry out in such a manner that a very hard crust is formed. This process has occurred so extensively in most parts of Australia as to restrict soil development - the former soil is effectively the parent material for a new soil, but it is so unweatherable that only a very poorly developed soil can exist in present dry climates, especially when they have become much drier during glacial periods in theQuaternary .In other parts of Australia, and in many parts of
Africa , drying out of former soils has not been so severe. This has led to large areas of relictpodsol s in quite dry climates in the far southern inland of Australia (wheretemperate rainforest was formerly dominant) and to the formation of Torrox soils insouthern Africa . Here, present climates allow, effectively, the maintenance of the old soils under climates which they could not actually form if one were to start with the parent material on which they developed in theMesozoic andPaleocene .Paleosols in this sense are always "exceedingly infertile
soils ", containing availablephosphorus levels orders of magnitude lower than in temperate regions with younger soils. Ecological studies have shown that this has forced highly specialised evolution amongst Australian flora (Tim F. Flannery, "The Future Eaters: An Ecological History of the Australian Lands and People"; published 1994 by George Braziller) to obtain "minimal"nutrient supplies. The fact that soil formation is "simply not occurring" makes ecologically sustainable management even more difficult. However, paleosols often contain the most exceptionalbiodiversity due to the absence of competition (David Tilman; "Resource Competition And Community Structure"; published 1982 by Princeton University Press).References
Retallack, G.J., 2001, "Soils of the Past", 2nd ed. New York, Blackwell Science. ISBN 0-632-05376-3
Kraus, M.J., 1999, "Paleosols in clastic sedimentary rocks: their geologic applications", Earth Science Review 47:41-70.
ee also
*
Paleopedology
*Paleopedological record
*Pedogenesis
*Pedology (soil study)
*Korshov External links
[http://fadr.msu.ru/inqua/ Commission on Paleopedology of the International Union of Soil Science, Subcommission on Paleopedology of the International Union for Quaternary Research]
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