varved

Varved describes sediments that form in standing, often glacially influenced lakes and display regular annual laminations. A varve is typically a pair of layers representing one year: a lighter, coarser summer layer formed from meltwater carrying silt and sand, overlain by a darker, finer winter layer rich in clay and organic matter deposited under ice-covered, slower-moving conditions. Over many years, these couplets accumulate to create a laminated sediment sequence.

The thickness and composition of varves reflect past environmental conditions, including summer melt rates, sediment supply, and winter oxygen levels. Because the layers correspond to consecutive years, varved sediments can be counted to establish a chronology with annual resolution. When preserved well, they provide detailed records of past climate, hydrology, and glacier activity, contributing to paleoclimatology, Quaternary science, and regional stratigraphy. Varves are especially common in high-latitude or high-altitude lakes and in basins directly influenced by glacier melt, including regions in Scandinavia, North America, and other glaciated areas.

Limitations and complexities exist. Varve preservation can be interrupted by bioturbation, erosion, or post-depositional alteration. Not every year deposits material in a way that produces a distinct layer, leading to gaps or ambiguous counts. Different lakes may exhibit variations in layer color and composition, and local environmental changes can complicate long-term interpretation.

The term varve derives from the Swedish varv, meaning a layer, and was adopted to describe these annual sediment laminations.