Radiocarbon dating marine sediments
Varves form only in fresh or brackish water, because the high levels of salt in normal sea water coagulate the clay into coarse grains.
Since the saline waters leave coarse particles all year, it is nearly impossible to distinguish the individual layers in salt waters.
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 layers—one coarse and one fine—for each annual cycle.
While working for the Geological Survey of Sweden, De Geer noticed a close visual similarity between the laminated sediments he was mapping, and tree-rings.
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.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.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. to Lake Timiskaming and Hudson Bay, Canada, and created a North American varve chronology.In 1924, the Geochronological Institute, a special laboratory dedicated to varve research was established. Carl Caldenius visited Patagonia and Tierra del Fuego, and Erik Norin visited central Asia.