Varve dating method
The main factor controlling varve formation is climate variability; there must be large seasonal differences in both temperature and precipitation.This sets up the succession of biotic life and the physical and chemical structure of the lake necessary to form the contrasting layers.The rest of the year, dark clay sediments settle on the bottom.At the bottom of Lake Suigetsu, thin layers of microscopic algae have been piling up for many years.A single year’s deposit includes a light (summer) layer and a dark (winter) layer.Varves don’t form in all lakes, in fact they are found in very few.In some cases, if the right chemical composition is present in the lake, calcite will also deposit in the sediments.
This can prevent the organisms that can mix the sediment from becoming established (O’Sullivan, 1983).
In these cases a second independent approach is used, C dating, their use became less popular. Since the layers are annual segmented, it is known that the material wasn’t further mixed after deposition.
It wasn’t until more recently that varved sediments have seen a resurgence as a source of paleoecological data. This is a critical assumption of paleoecology termed superposition, sediment along with any material (e.g.
The alternating layers of dark and light count the years like tree rings.
The sedimentation or annual varve thickness is relatively uniform, typically 1.2 mm per yr for present conditions in Lake Suigetsu which is located near the coast of the Sea of Japan.
With varved sediments this can be observed, since the annual layers are visible, instead of assumed.