Varves, in geological formations, are regular, alternating layers caused by annual seasonal variation. In other words, they are traces, in any geological deposit, that reflect a yearly cycle. Each varve is laid down in a year and is normally composed of two distinct types of sediments, one forms during cold months, and another during the warm season.
For example, during the spring and summer months, while ice is melting, strong currents in lakes and rivers favor the deposition of coarse material. But the cold months, when currents are slack, favor deposition of fine silt. The result is annual, alternating layering. Seasonal winds can also produce deposits with annual layering. Such traces are used in estimating the absolute and relative ages of geological formations.
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Outcrop containing Pleistocene age varves.
Scarboro Cliffs, Toronto, Ontario, Canada.
Credit: Bruce F. Molnia, USGS
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