Tephrochronology: Difference between revisions

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[[image:Icelandic tephra.JPG|250px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at the height of the [[volcanologists]] hands is [[rhyolitic]] [[tephra]] from [[Hekla]].]]
 
[[Image:tephrochronology_icelandtephrochronology iceland.JPG|thumb|right|250px|Geologist explaining the importance of tephochronology to students on field in [[Iceland]].]]
'''Tephrochronology''' is a [[Geochronology|geochronological]] technique that uses discrete layers of [[tephra]]—volcanic ash from a single eruption—to create a chronological framework in which [[Paleoenviroment|paleoenvironmental]] or [[Archaeology|archaeological]] records can be placed. Such an established event provides a "tephra horizon". The premise of the technique is that each volcanic event produces ash with a unique chemical "fingerprint" that allows the deposit to be identified across the area affected by fallout. Thus, once the volcanic event has been independently dated, the tephra horizon will act as time marker.
 
 
A pioneer in the use of tephra layers as [[marker horizon]]s to establish chronology was [[Sigurdur Thorarinsson]], who began by studying the layers he found in his native Iceland.<ref>Alloway et al. (2007)</ref> Since the late 1990s, techniques developed by Chris S. M. Turney ([[QUB]], Belfast; now [[University of Exeter]]) and others for extracting tephra horizons invisible to the naked eye ("cryptotephra")<ref>Turney et al. (1997)</ref> have revolutionised the application of tephrochronology. This technique relies upon the difference between the specific gravity of the microtephra shards and the host sediment matrix. It has led to the first discovery of the Vedde ash on the mainland of Britain, in Sweden, in [[the Netherlands]], in the Swiss Lake [[Soppensee]] and in two sites on the [[Karelian Isthmus]] of Baltic Russia.
It has also revealed previously undetected ash layers, such as the Borrobol Tephra first discovered in northern [[Scotland]], dated to ca. 14.4 cal. ka BP,<ref>Turney et al. (1997)</ref> the microtephra horizons of equivalent geochemistry from southern [[Sweden]], dated at 13,900 Cariaco varve yrs BP<ref>Davies (2004)</ref> and from northwest Scotland, dated at 13.6 cal. ka BP.<ref>Ranner et al. (2005)</ref>
 
==Notes==
{{reflist}}
 
== Sources ==
*Alloway B.V., Larsen G., Lowe D.J., Shane P.A.R., Westgate J.A. (2007). "Tephrochronology", ''Encyclopedia of Quaternary Science'' (editor&mdash;Elias S.A.) 2869–2869 (Elsevier).
*{{Cite journal | last1 = Davies | first1 = S.M., | last2 = Wastegård | first2 = S., | last3 = Wohlfarth | first3 = B. (| year = 2003). "| title = Extending the limits of the Borrobol Tephra to Scandinavia and detection of new early Holocene tephras", ''| url = | journal = Quaternary Research'', | volume = 59: | issue = | pages = 345–352. }}
*{{Cite journal | last1 = Davies, | first1 = S. M., | last2 = Wohlfarth, | first2 = B., | last3 = Wastegård, | first3 = S., | last4 = Andersson, | first4 = M., | last5 = Blockley, | first5 = S., &| last6 = Possnert, | first6 = G.,( | year = 2004). "| title = Were there two Borrobol Tephras during the early Late-glacial period: implications for tephrochronology?", ''| url = | journal = Quaternary Science Reviews'', | volume = 23, | issue = | pages = 581–589. }}
*Dugmore A., Buckland P.C. (1991). "Tephrochronology and Late Holocene soil erosion in South Iceland", ''Environmental Change in Iceland: Past and Present'' (eds. J.K. Maizels and C. Caseldine) 147–159 (Dordrecht: Kluwer Academic Publishers).
*Keenan D.J. (2003). "[http://www.informath.org/pubs/G%5E303a.pdf Volcanic ash retrieved from the GRIP ice core is not from Thera]", ''Geochemistry, Geophysics, Geosystems'', 4, doi: 10.1029/2003GC000608.
*{{Cite journal | last1 = Pearce | first1 = N.J.G., | last2 = Eastwood | first2 = W.J., | last3 = Westgate | first3 = J.A., | last4 = Perkins | first4 = W.T. (| year = 2002). | title = "Trace-element composition of single glass shards in distal Minoan tephra from SW Turkey", ''| url = | journal = Journal of the Geological Society, London'', | volume = 159: | issue = | pages = 545–556. | doi: = 10.1029/2003GC000672 }}
*{{Cite journal | last1 = Pollard | first1 = A.M., | last2 = Blockley | first2 = S.P.E., | last3 = Ward | first3 = K.R. (| year = 2003). "| title = Chemical alteration of tephra in the depositional environment", ''| url = | journal = Journal of Quaternary Science'', | volume = 18: | issue = | pages = 385–394. | doi: = 10.1002/jqs.760 }}
*{{Cite journal | last1 = Ranner, | first1 = P. H., | last2 = Allen, | first2 = J. R. M. &| last3 = Huntley, | first3 = B. (| year = 2005). | title = A new early Holocene cryptotephra from northwest Scotland. ''| url = | journal = Journal of Quaternary Science'', | volume = 20, | issue = | pages = 201–208. }}
*{{Cite journal | last1 = Smith | first1 = D.G.W., | last2 = Westgate | first2 = J.A. (| year = 1969). "| title = Electron probe technique for characterizing pyroclastic deposits", ''| url = | journal = Earth and Planetary Science Letters'', | volume = 5: | issue = | pages = 313–319. }}
*[[Sigurður Þórarinsson|Þórarinsson S.]] (1970). "Tephrochronology in medieval Iceland", ''Scientific Methods in Medieval Archaeology'' (ed. R. Berger) 295–328 (Berkeley: University of California Press).
*{{Cite journal | last1 = Turney | first1 = C.S.M., | last2 = Harkness | first2 = D.D., | last3 = Lowe | first3 = J.J. (| year = 1997). "| title = The use of microtephra horizons to correlate late-glacial lake sediment successions in Scotland", ''| url = | journal = Journal of Quaternary Science'', | volume = 12: | issue = | pages = 525–531. }}
 
== External links ==