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varves
varves Varves represent rhythmic accumulations of fine sands, silts, or clays that are deposited annually in couplets. The relatively coarser-grained layers alternate with layers of finer-grained sediments. Deposition of varved sediment is always associated with cycles of annual deposition, usually (although not always) within ice-marginal lakes. Because varves are deposited annually, they have been used in Quaternary studies as a means of relative dating.
The annual deposition of varved sediment is believed to take place as a result of two distinct seasonal depositional processes. During winter, when the lake is covered in ice, the finest-grained sediment is deposited out of suspension on to the floor of the lake. During spring and summer, when there is no surface cover of ice and when glacial meltwaters enter the lake, coarser material is deposited on the lake floor, and this forms the annual sediment couplet. The use of varves as a dating technique was pioneered by the Swedish scientist de Geer, who first investigated late- and post-glacial Swedish varve deposits in the late nineteenth century. De Geer was the first scientist to present detailed measurements of annual varve sequences, and he was also the first to demonstrate spatial correlation between different varve sequences. He established a varve chronology for Scandinavia that extends back to approximately 13 000 years before the present. The deposition of varves need not always take place in ice-marginal lakes. In some areas, chemical precipitation of sediments can take place on the floors of lakes on an annual basis. In other lakes, seasonal changes in the deposition of organic detritus can result in the production of organic varves. Similarly, seasonal variations in the deposition of certain microfossils (e.g. diatoms) may result in the production of annually laminated sediments. Annual varves are also deposited in marine environment, although here the processes of sedimentation are complicated by clay flocculation. Alastair G. Dawson Bibliography De Geer, G. (1912) Geochronology of the last 12,000 years. XI International Geological Congress, Stockholm, 1, 241–53. |
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PAUL HANCOCK and BRIAN J. SKINNER. "varves." The Oxford Companion to the Earth. 2000. Encyclopedia.com. 10 Feb. 2012 <http://www.encyclopedia.com>. PAUL HANCOCK and BRIAN J. SKINNER. "varves." The Oxford Companion to the Earth. 2000. Encyclopedia.com. (February 10, 2012). http://www.encyclopedia.com/doc/1O112-varves.html PAUL HANCOCK and BRIAN J. SKINNER. "varves." The Oxford Companion to the Earth. 2000. Retrieved February 10, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O112-varves.html |
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varve dating
varve dating (geochronology) An absolute dating technique using thin sedimentary layers of clays called varves. The varves, which are particularly common in Scandinavia, have alternate light and dark bands corresponding to winter and summer deposition. Most of them are found in the Pleistocene series, where the edges of varve deposits can be correlated with the annual retreat of the ice sheet, although some varve formation is taking place in the present day. By counting varves it is possible to establish an absolute time scale for fossils up to about 20 000 years ago.
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"varve dating." A Dictionary of Biology. 2004. Encyclopedia.com. 10 Feb. 2012 <http://www.encyclopedia.com>. "varve dating." A Dictionary of Biology. 2004. Encyclopedia.com. (February 10, 2012). http://www.encyclopedia.com/doc/1O6-varvedating.html "varve dating." A Dictionary of Biology. 2004. Retrieved February 10, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O6-varvedating.html |
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varve
varve A banded layer of silt and sand deposited annually in lakes, especially near to ice sheets. The coarse, paler material is deposited in summer; the finer, darker material in winter. One varve consists of one light band and one dark band. Varves can be counted to calculate the age of glacial deposits (varve analysis, also called varve chronology or varve count). Since the pattern of thicknesses of successive varves is often distinctive, correlations can be made between widely separated deposits, using the same principle as that of dendrochronology.
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AILSA ALLABY and MICHAEL ALLABY. "varve." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 10 Feb. 2012 <http://www.encyclopedia.com>. AILSA ALLABY and MICHAEL ALLABY. "varve." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. (February 10, 2012). http://www.encyclopedia.com/doc/1O13-varve.html AILSA ALLABY and MICHAEL ALLABY. "varve." A Dictionary of Earth Sciences. 1999. Retrieved February 10, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O13-varve.html |
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varve
varve A banded layer of silt and sand deposited annually in lakes, especially near to ice sheets. The coarse, paler material is deposited in summer; the finer, darker material in winter. One varve consists of one light band and one dark band. Varves can be counted to calculate the age of glacial deposits (varve analysis, also called varve chronology or varve count). Since the pattern of thicknesses of successive varves is often distinctive, correlations can be made between widely separated deposits, using the same principle as that of dendrochronology.
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MICHAEL ALLABY. "varve." A Dictionary of Ecology. 2004. Encyclopedia.com. 10 Feb. 2012 <http://www.encyclopedia.com>. MICHAEL ALLABY. "varve." A Dictionary of Ecology. 2004. Encyclopedia.com. (February 10, 2012). http://www.encyclopedia.com/doc/1O14-varve.html MICHAEL ALLABY. "varve." A Dictionary of Ecology. 2004. Retrieved February 10, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O14-varve.html |
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varve
varve in geology, pair of thin sedimentary layers formed annually by seasonal climatic changes. Usually found in glacial lake deposits, varves consist of a coarse-grained, light-colored summer deposit and a finer-grained, dark-colored winter deposit formed when fine sediment settles out from the water under the ice cover. Varves, and the pollen they contain, are useful for interpreting recent climatic history. |
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"varve." The Columbia Encyclopedia, 6th ed.. 2008. Encyclopedia.com. 10 Feb. 2012 <http://www.encyclopedia.com>. "varve." The Columbia Encyclopedia, 6th ed.. 2008. Encyclopedia.com. (February 10, 2012). http://www.encyclopedia.com/doc/1E1-varve.html "varve." The Columbia Encyclopedia, 6th ed.. 2008. Retrieved February 10, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1E1-varve.html |
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