Editing Varve (section)

== History of varve research ==
[[File:Parque Geologico do Varvito - Paredao.jpg|thumb|upright=1.35|Varves in a [[Geopark|geological park]] in [[Itu, São Paulo|Itu]], [[Brazil]]]]
Although the term varve was not introduced until the late nineteenth century, the concept of an annual rhythm of deposition is at least two centuries old. In the 1840s, [[Edward Hitchcock]] suspected laminated sediment in North America could be seasonal, and in 1884 [[Warren Upham]] postulated that light-dark laminated couplets represented a single year's deposition. Despite these earlier forays, the chief pioneer and populariser of varve research was Gerard De Geer. While working for the Geological Survey of Sweden, De Geer noticed a close visual similarity between the laminated sediments he was mapping, and [[dendrochronology|tree-rings]]. This prompted him to suggest the coarse-fine couplets frequently found in the sediments of glacial lakes were annual layers.

The first varve [[chronology]] was constructed by De Geer in [[Stockholm]] in the late 19th century. Further work soon followed, and a network of sites along the east coast of Sweden was established. The varved sediments exposed in these sites had formed in glaciolacustrine and glacimarine conditions in the Baltic basin as the last ice sheet retreated northwards. By 1914, De Geer had discovered that it was possible to compare varve sequences across long distances by matching variations in varve thickness, and distinct marker laminae. However, this discovery led De Geer and many of his co-workers into making incorrect correlations, which they called 'teleconnections', between continents, a process criticised by other varve pioneers like [[Ernst Antevs]].

In 1924, the Geochronological Institute, a special laboratory dedicated to varve research was established. De Geer and his co-workers and students made trips to other countries and continents to investigate varved sediments. Ernst Antevs studied sites from [[Long Island]], U.S.A. to [[Lake Timiskaming]] and [[Hudson Bay]], Canada, and created a North American varve chronology. [[Carl Caldenius]] visited [[Patagonia]] and [[Tierra del Fuego]], and Erik Norin visited central [[Asia]]. By this stage, other geologists were investigating varve sequences, including Matti Sauramo who constructed a varve chronology of the last deglaciation in [[Finland]].

1940 saw the publication of a now classic scientific paper by De Geer, the ''Geochronologia Suecica'', in which he presented the Swedish Time Scale, a floating varve chronology for ice recession from [[Skåne]] to [[Indalsälven]]. Ragnar Lidén made the first attempts to link this time scale with the present day. Since then, there have been revisions as new sites are discovered, and old ones reassessed. At present, the Swedish varve chronology is based on thousands of sites, and covers 13,200 varve years.

In 2008, although varves were considered likely to give similar information to [[dendrochronology]], they were considered "too uncertain" for use on a long-term timescale.<ref>{{cite journal | doi = 10.1111/j.1475-4754.2008.00394.x| author = Ramsey | pages = 249–275 | first = C. B. | issue = 2 | year = 2008 | title = Radiocarbon dating: revolutions in understanding | journal = [[Archaeometry (journal)|Archaeometry]] | volume = 50}}</ref> However, by 2012, “missing” varves in the [[Lake Suigetsu]] sequence were identified in the Lake Suigetsu 2006 Project by overlapping multiple cores and improved varve counting techniques, extending the timescale to 52,800 years.<ref>
{{cite journal|last=Reimer|first=P.J.|year=2009|title=IntCal09 and Marine09 Radiocarbon Age Calibration Curves, 0–50,000 Years cal BP|url=http://researchcommons.waikato.ac.nz/bitstream/10289/3622/1/Hogg%20Intcal09%20and%20Marine09.pdf|journal=Radiocarbon|volume=51|issue=4|pages=1111–1150|doi=10.1017/S0033822200034202|s2cid=12608574|display-authors=etal}}
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{{cite web|url=http://www.eurekalert.org/pub_releases/2012-10/aaft-jlr101212.php|title=Japanese lake record improves radiocarbon dating|publisher=AAAS|date=18 Oct 2012|access-date=18 Oct 2012}}
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