Varve Dating

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A technique for producing chronometric dates based on the annual formation of layers of sediment on lake and river beds in glacial regions. Seasonal fluctuations in particle size and speed of sedimentation take place. During the winter, ice melting is very slow, melt-water streams do not contain much water, and they flow slowly, carrying little material. During the summer, melting accelerates, melt-water streams flow faster and carry more material. The supply of sediment to the ice-marginal lake varies with the season. A varve chronology, similar to a tree-ring chronology may be set up. But as with tree rings (see dendrochronology) the varves will vary from year to year, depending on the rapidity of the thaw, quantity of summer rain, winter snow, etc., the variations showing some correlation with the sunspot cycle. Such varve chronologies have been built up for Scandinavia and are used to date the retreat of the Weichselian ice-sheet. Varve dating has a greater significance than just for local dating, since frequently there is enough organic material to allow radiocarbon dates to be calculated. There is therefore the possibility of using the calendrical varve chronology to calibrate radiocarbon dates. Its use for archaeological dating is rather limited in that sites have to be related to the geological changes (the ice-sheet moraines or changing Baltic sea-levels) before their dates can be determined. Swedish pioneer Baron Gerard de Geer discovered in the late 19th century that these could be counted and correlated or linked over long distances, which gave him a timescale of 12,000 years and fixed the end of the Ice Age at about 10,000 years ago.

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