Varve

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.

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.

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.

Ernst Antevs studied sites from Long Island, U.S.A. to Lake Timiskaming and Hudson Bay, Canada, and created a North American varve chronology.

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.

[4][5] Varves form in a variety of marine and lacustrine depositional environments from seasonal variation in clastic, biological, and chemical sedimentary processes.

This is the consequence of dead phytoplankton, and other micro-organisms that create their skeletons or shells out of silica or calcium carbonate, falling to the lake bottom.

This process of the precipitation and deposition of dead micro-organisms out of the water column is restricted to warm months when productivity (ecology) is high.

The corresponding dark colored layers are composed of organic matter and fine sediment particles transported and deposited during spring freshets as a result of winter snowmelt.