 a varve is an annual layer of sediment or sedimentary rock. 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 (1858â1943) proposed a new formal definition where varve described the whole of any annual sedimentary layer.de geer, g. (1912). a geochronology of the last 12,000 years. proceedings of the international geological congress stockholm (1910),1, 241â257. 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. an annual layer can be highly visible because the particles washed into the layer in the spring when there is greater flow strength are much coarser than those deposited later in the year. this forms a pair of layersâone coarse and one fineâfor each annual cycle. varves form only in fresh or brackish water, because the high levels of salt in normal sea water coagulates the clay into coarse grains. since the saline waters will leave coarse particles all year, it is nearly impossible to distinguish the individual layers in salt waters. indeed, clay flocculation occurs at high ionic strength due to the collapse of the clay electrical double layer (edl) which decreases the electrostatic repulsion between negatively charged clay particles. == history of varve research == 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, 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 s
Climatology Incremental_dating Sedimentary_rocks Sedimentology