Lichenometry: Difference between revisions

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undo good-faith edit: it seemed to make more sense as it was (if radio-carbon dating was _more_ accurate for the last 500 years, then lichenometry would be _less_ useful for this period)
added ref to 2009 article by James Bell Benedict
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[[Image:Rhizocarpon geographicum on quartz.jpg|thumb|right|230px|The [[map lichen]] (''Rhizocarpon geographicum''), the lichen most used in lichenometry.]]
[[Image:Rhizocarpon geographicum on quartz.jpg|thumb|right|230px|The [[map lichen]] (''Rhizocarpon geographicum''), the lichen most used in lichenometry.]]
In [[archaeology]], [[palaeontology]], and [[geomorphology]], '''lichenometry''' is a geomorphic method of [[geochronologic]] dating that uses [[lichen]] growth to determine the [[Surface exposure dating|age of exposed rock]], based on a presumed specific rate of increase in radial size over time.<ref>Holocene climatic and glacial history of the central Sierra Nevada, California, R.R. Curry, pp. 1-47, 1969, Geological Society of America Special Paper, 123, S.A. Schumm and W.C. Bradley, eds., 1969</ref><ref name=LSN>Lichens in relation to management issues in the Sierra Nevada national parks, McCune, B., J. Grenon, and E. Martin, L. Mutch, Sierra Nevada Network, Cooperative agreement CA9088A0008. Oregon State University, Corvallis, Oregon, and Sequoia and Kings Canyon National Parks, Three Rivers, California, [http://openjournals.wsu.edu/index.php/pnwfungi/article/view/1031]</ref>{{rp|9}} Measuring the diameter of the largest lichen of a species on a rock surface can therefore be used to determine the length of time the rock has been exposed. Lichen can be preserved on old rock faces for up to{{cn|date=August 2014}} 10,000 years, providing the maximum age limit of the technique, though it is most accurate (within 10% error) when applied to surfaces that have been exposed for less than 1,000 years.<ref>Sowers, J.M., Noller, J.S., and Lettis, W.R., eds., 1997, Dating and Earthquakes: Review of Quaternary Geochronology and its Application to Paleoseismology. U.S. Nuclear Regulatory Commission, NUREG/CR 5562.</ref> Lichenometry is especially useful for dating surfaces less than 500 years old, as radiocarbon dating techniques are less accurate over this period.<ref name="innes">{{cite journal | author=John L. Innes | title=Lichenometry | journal=Progress in Physical Geography | volume=9 | issue=187 | url=http://ppg.sagepub.com/cgi/reprint/9/2/187 }}</ref> The lichens most commonly used for lichenometry are those of the genera ''[[Rhizocarpon]]'' (e.g. the species ''[[Rhizocarpon geographicum]]'') and ''[[Xanthoria]]''.
In [[archaeology]], [[palaeontology]], and [[geomorphology]], '''lichenometry''' is a geomorphic method of [[geochronologic]] dating that uses [[lichen]] growth to determine the [[Surface exposure dating|age of exposed rock]], based on a presumed specific rate of increase in radial size over time.<ref>Holocene climatic and glacial history of the central Sierra Nevada, California, R.R. Curry, pp. 1-47, 1969, Geological Society of America Special Paper, 123, S.A. Schumm and W.C. Bradley, eds., 1969</ref><ref name=LSN>Lichens in relation to management issues in the Sierra Nevada national parks, McCune, B., J. Grenon, and E. Martin, L. Mutch, Sierra Nevada Network, Cooperative agreement CA9088A0008. Oregon State University, Corvallis, Oregon, and Sequoia and Kings Canyon National Parks, Three Rivers, California, [http://openjournals.wsu.edu/index.php/pnwfungi/article/view/1031]</ref>{{rp|9}} Measuring the diameter of the largest lichen of a species on a rock surface can therefore be used to determine the length of time the rock has been exposed. Lichen can be preserved on old rock faces for up to{{cn|date=August 2014}} 10,000 years,<ref name=Benedict>{{cite journal|journal=[[American Antiquity]]|volume=74|issue=1|date=January 2009|pages=143–172|title=A Review of Lichenometric Dating and Its Applications to Archaeology
|author=Benedict, James B.|doi=10.1017/S0002731600047545}}</ref> providing the maximum age limit of the technique, though it is most accurate (within 10% error) when applied to surfaces that have been exposed for less than 1,000 years.<ref>Sowers, J.M., Noller, J.S., and Lettis, W.R., eds., 1997, Dating and Earthquakes: Review of Quaternary Geochronology and its Application to Paleoseismology. U.S. Nuclear Regulatory Commission, NUREG/CR 5562.</ref> (The practical limit of the technique might be 4,000 to 5,000 years.<ref name=Benedict/>) Lichenometry is especially useful for dating surfaces less than 500 years old, as radiocarbon dating techniques are less accurate over this period.<ref name="innes">{{cite journal | author=John L. Innes | title=Lichenometry | journal=Progress in Physical Geography | volume=9 | issue=187 | url=http://ppg.sagepub.com/cgi/reprint/9/2/187 }}</ref> The lichens most commonly used for lichenometry are those of the genera ''[[Rhizocarpon]]'' (e.g. the species ''[[Rhizocarpon geographicum]]'') and ''[[Xanthoria]]''.


It was first employed by [[Knut Fægri]] in 1933, though the first exclusively lichenometric paper was not published until 1950, by Austrian [[Roland Beschel]]<ref>Beschel R. (1950). "Flechten als Altersmasstab rezenter Moränen". ''Zeitschrift für Gletscherkunde und Glazialgeologie'' '''1''': 152–161.</ref> (1928-1971),<ref>http://pubs.aina.ucalgary.ca/arctic/Arctic24-4-316.pdf</ref> in a paper concerning the European [[Alps]].<ref>{{cite web|url=http://mc2.vicnet.net.au/home/date/web/lich.html |title=Archived copy |accessdate=2009-02-25 |deadurl=yes |archiveurl=https://web.archive.org/web/20080823052446/http://mc2.vicnet.net.au/home/date/web/lich.html |archivedate=2008-08-23 |df= }}</ref>
It was first employed by [[Knut Fægri]] in 1933, though the first exclusively lichenometric paper was not published until 1950, by Austrian [[Roland Beschel]]<ref>Beschel R. (1950). "Flechten als Altersmasstab rezenter Moränen". ''Zeitschrift für Gletscherkunde und Glazialgeologie'' '''1''': 152–161.</ref> (1928-1971),<ref>http://pubs.aina.ucalgary.ca/arctic/Arctic24-4-316.pdf</ref> in a paper concerning the European [[Alps]].<ref>{{cite web|url=http://mc2.vicnet.net.au/home/date/web/lich.html |title=Archived copy |accessdate=2009-02-25 |deadurl=yes |archiveurl=https://web.archive.org/web/20080823052446/http://mc2.vicnet.net.au/home/date/web/lich.html |archivedate=2008-08-23 |df= }}</ref>

Revision as of 00:16, 12 May 2018

The map lichen (Rhizocarpon geographicum), the lichen most used in lichenometry.

In archaeology, palaeontology, and geomorphology, lichenometry is a geomorphic method of geochronologic dating that uses lichen growth to determine the age of exposed rock, based on a presumed specific rate of increase in radial size over time.[1][2]: 9  Measuring the diameter of the largest lichen of a species on a rock surface can therefore be used to determine the length of time the rock has been exposed. Lichen can be preserved on old rock faces for up to[citation needed] 10,000 years,[3] providing the maximum age limit of the technique, though it is most accurate (within 10% error) when applied to surfaces that have been exposed for less than 1,000 years.[4] (The practical limit of the technique might be 4,000 to 5,000 years.[3]) Lichenometry is especially useful for dating surfaces less than 500 years old, as radiocarbon dating techniques are less accurate over this period.[5] The lichens most commonly used for lichenometry are those of the genera Rhizocarpon (e.g. the species Rhizocarpon geographicum) and Xanthoria.

It was first employed by Knut Fægri in 1933, though the first exclusively lichenometric paper was not published until 1950, by Austrian Roland Beschel[6] (1928-1971),[7] in a paper concerning the European Alps.[8]

Lichenometry can provide dates for glacial deposits in tundra environments, lake level changes, glacial moraines, trim lines, palaeofloods,[9] rockfalls, seismic events associated with the rockfalls,[2] talus (scree) stabilization and former extent of permafrost or very persistent snow cover.[10] It has also been explored as a tool in assessing the speed of glacier retreat due to climate change.[11]

Among the potential problems of the technique are the difficulty of correctly identifying the species, delay between exposure and colonization, varying growth rates from region to region as well as the fact that growth rates are not always constant over time, dependence of the rate of growth upon substrate texture and composition, climate, and determining which lichen is the largest.[5]

Methods

Xanthoria elegans was one of the first lichens used for lichenometry.

Several methods exist for dating surfaces with help of lichenometry; the most simple relies on a single largest lichen while other methods use more. There are also differences in the way the lichen is measured; while some suggest that the largest diameter should be measured, other scientists prefer the diameter of the largest inscribed circle. A problem in dating lichens is the fact that several thalli can fuse together, making several minor lichens appears as a larger one of older age.[12] Lichenometrist Tom Bradwell has listed the following five method families as the principal ones into which most other methods can be classified:

  • Largest lichen (LL): When the single largest lichen of a species is used it means that the lichen that is oldest or grows in most favorable conditions is used to date the minimum age of the exposed surface. This was the original lichenometric from which others then developed or used as reference. Despite relying upon a single lichen this technique is praised for its simplicity and allows obtaining an image of the age of rock exposure while still in the field.[13]
  • Largest five lichens (5LL): This method is a development of the LL and was developed in the 1970s to avoid reliance on one single potentially anomalous lichen. It has been proved that neither accuracy nor precision improves significantly by having more than five lichens.[13]
  • Fixed-area largest lichen (FALL): This technique was initially specially designed for dating rockfalls and talus cones with no uniform age of deposition. The largest thallus in a unit area is measured. The sample areas are usually boulders with surfaces of about 1 m².[13]
  • Size-frequency approach (SF): The analysis of size and frequency of lichens was initially done in order to study lichen populations and preexisting thalli growing on surfaces, but has since been used as an effective absolute and relative dating method.[13]
  • Lichen cover approach (LC): This method works with the premise of that the area covered by a single species will increase over time, and by measuring the total area percentage covered by a certain lichen species the age of exposure can be inferred.[13]

References

  1. ^ Holocene climatic and glacial history of the central Sierra Nevada, California, R.R. Curry, pp. 1-47, 1969, Geological Society of America Special Paper, 123, S.A. Schumm and W.C. Bradley, eds., 1969
  2. ^ a b Lichens in relation to management issues in the Sierra Nevada national parks, McCune, B., J. Grenon, and E. Martin, L. Mutch, Sierra Nevada Network, Cooperative agreement CA9088A0008. Oregon State University, Corvallis, Oregon, and Sequoia and Kings Canyon National Parks, Three Rivers, California, [1]
  3. ^ a b Benedict, James B. (January 2009). "A Review of Lichenometric Dating and Its Applications to Archaeology". American Antiquity. 74 (1): 143–172. doi:10.1017/S0002731600047545.
  4. ^ Sowers, J.M., Noller, J.S., and Lettis, W.R., eds., 1997, Dating and Earthquakes: Review of Quaternary Geochronology and its Application to Paleoseismology. U.S. Nuclear Regulatory Commission, NUREG/CR 5562.
  5. ^ a b John L. Innes. "Lichenometry". Progress in Physical Geography. 9 (187).
  6. ^ Beschel R. (1950). "Flechten als Altersmasstab rezenter Moränen". Zeitschrift für Gletscherkunde und Glazialgeologie 1: 152–161.
  7. ^ http://pubs.aina.ucalgary.ca/arctic/Arctic24-4-316.pdf
  8. ^ "Archived copy". Archived from the original on 2008-08-23. Retrieved 2009-02-25. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)CS1 maint: archived copy as title (link)
  9. ^ William Allen (2013) https://www.scribd.com/doc/156523915/A-Lichenometric-Study-of-Palaeofloods-in-the-Brecon-Beacons
  10. ^ Olga Solomina, Mikhail Ivanov, Tom Bradwell. Lichenometric studies on moraines in the Polar Urals.
  11. ^ Richard Armstrong (September 2004). "Lichens, Lichenometry, and Global Warming" (PDF). Microbiologist: 32–35. Archived from the original (PDF) on 2009-02-25. {{cite journal}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  12. ^ Lichen, Lichenometry and Global Warming Archived 2011-07-08 at the Wayback Machine
  13. ^ a b c d e Bradwell, Tom 2009. Lichenometric Dating: A commentary in the light of some recent statistical studies. Geografiska Annaler.
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