Any form of repetitive sedimentary rock stratification that was deposited within a year. This annual deposit usually consists of paired contrasting layers (varves) of alternately finer (darker) and coarser (lighter) silt or clay, reflecting seasonal variations in sedimentation (winter and summer) within the year. Varved deposits are most commonly found in glacial lakes, but they can also be found in nonglacial lakes and marine settings.
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The word 'varve' is derived from the Swedish word varv whose meanings and connotations include 'revolution', 'in layers', and 'circle'. The term first appeared as Hvarfig lera (varved clay) on the first map produced by the Geological Survey of Sweden in 1862. Initially, varve was used to describe the separate components of annual layers in glacial lake sediments, but at the 1910 Geological Congress, the Swedish geologist Gerard De Geer (1858-1943) proposed a new formal definition where varve described the whole of any annual sedimentary layer. More recently introduced terms such as 'annually laminated' are synonymous with varve.
Of the many rhythmites found in the geological record, varves are one of the most important and illuminating to studies of past climate change. Varves are amongst the smallest-scale events recognised in stratigraphy.
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 to making incorrect correlations, which they called 'teleconnections', between continents, a process criticised by other varve pioneers like Ernst Antevs.
In 1924 a special laboratory dedicated to varve research - the Geochronological Institute - 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. 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.
The classic varve archetype is a light / dark coloured couplet deposited in a glacial lake. The light layer usually comprises a coarser laminaset of silt and fine sand deposited under higher energy conditions when meltwater introduces sediment load into the lake water. During winter months, when meltwater and associated suspended sediment input is reduced, and often when the lake surface freezes, fine clay-size sediment is deposited forming a dark coloured laminaset.
A well-known marine example of varve sediments are those found in the Santa Barbara basin, off California.
Identification of coherent links between interannual sedimentary structures and daily meteorological observations in Arctic proglacial lacustrine varves: potentials and limitations (1).(Report)
Jan 01, 2008; Abstract: Proglacial lacustrine sediments from High Arctic Lake R (76[degrees]17.9'N, 90[degrees]59.3'W, unofficial name) are...
Extreme sediment delivery events recorded in the contemporary sediment record of a montane lake, southern Coast Mountains, British Columbia.
Dec 01, 2006; Abstract: The extreme sediment delivery regime of a montane catchment was examined through the analysis of recent lacustrine...