GeologyRocks

A thin layer of fine-grained sediment deposited in still waters which occur in rhythmic bands. Varves form in a variety of marine and lacustrine depositional environments from seasonal variation in clastic, biological, and chemical sedimentary processes. The classic varve is a light to dark coloured couplet deposited in a glacial lake melting of the ice carrying sediment into the lake. The light layer usually deposited in summer. During winter months, when sediment input is reduced, fine clay-size sediment is deposited forming a dark coloured layers. In addition to seasonal variation of sedimentary processes and deposition, varve formation requires the absence of bioturbation. In other areas, e.g. arid environments, other types of varves occur, such as evaporites in summer and clastic deposition in winter.

The word 'Varve' is derived from the Swedish word varv whose meanings and connotations include revolution, in layers, and circle.

Varved intervals (thin, striped) beds and flood (thick, massive) beds in the composite Manila Creek section of the Sanpoil River Valley. Courtesy United States Geological Survey

Varves in the Lissan Formation, Masada, Israel. The layers consist of light evaporite rich layers from the summers and darker silty layers from the winters. Counting the layers between major 'seismite' slumped horizons allows the time between major earthquakes to be determined. Courtesy of Hypocentre.