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01-Feb-2015 05:24

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Patterns in tree-ring growth can be used to establish the age of old wood samples, and also give some hints to local climatic conditions.This technique is useful to about 9,000 years ago for samples from the western United States using overlapping tree-ring series from living and dead wood.These ages will result in a calibration that is too old and often well outside the uncertainties associated with the precision of C measurement.In some cases, errors may become obvious as they are sometimes on the order of 10 kyr or more (Miller and Thompson, 1979).A varve sequence might also have events in it of known calendar age, such as beds from flood events or volcanic ash layers that have historic records associated with them.The more usual case is when numerical ages (estimates of true calendar ages) based on radiometric or other techniques are applied to varves.Storage on land, prior to transport and later deposition, may not cause an error in the age of the fossil, but there will be a potential mismatch or lag between the age of the fossil and the younger varve in which the fossil was eventually deposited.Lag times in glacial or periglacial environments may be significant because of the ability of cold environments to protect plant fossils on land from decay for long periods of time.

An important preliminary requirement for an accurate calibration is that the varves being studied should be exactly matched to a varve chronology or they should be measured and have there own numbering system.

Laboratory procedures may not be fully able to remove the contaminants.

Perhaps the most vexing problem in some outcrop studies are pervasive tiny rootlets from modern plants.

C ages from terrestrial plants avoid some problems with other materials.

Bulk sediment samples and samples of aquatic plants or animals such as the carbonate shells of clams, snails, and ostracodes may yield ages that are too old because of how carbon was fixed by the organism and the potential for the incorporation of “old” carbon from a water body.

Many water bodies are not in equilibrium with the atmosphere or have non-atmospheric or recycled sources of carbon in their water columns.