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Results for speleothem:

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speleothem

SYNONYMS OR RELATED TERMS: cave deposit
CATEGORY: geology
DEFINITION: Mineral deposits that form in a cave after the creation of the cave itself. These deposits are generally composed of calcium carbonate dissolved from the surrounding limestone by groundwater. Carbon dioxide carried in the water is released as the water encounters the cave air; this reduces the water's capacity to hold calcite in solution and causes the calcite to be deposited. These deposits may accumulate to form stalactites, stalagmites, flowstone, cave pearls, and many other formations. Speleothem growth can be dated by the uranium series dating method. Speleothems can potentially bury earlier archaeological deposits.

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oxygen isotope analysis

SYNONYMS OR RELATED TERMS: oxygen isotope examination
CATEGORY: technique
DEFINITION: Isotope analysis looking at the O18/O16 ratio in materials. The method can be used to classify glass types and to analyze mollusk shells in order to try and reconstruct their original environment and thus the source. It is also used to interpret deep sea cores. The basis for this technique is the fact that the ratio of two of the stable isotopes of oxygen varies according to the material in which it is found. The oxygen is released from the sample, and is converted to carbon dioxide; the oxygen isotopic ratio is determined after ionization in a mass spectrometer. Variations in the isotopic ratios for the raw materials can lead to a classification of types and even, in some cases, the suggestion of a source for the raw materials. The technique is also used to analyze mollusk shells in an attempt to reconstruct the original aquatic environment. Because temperature variations are correlated with changes in atmospheric O18/O16 ratios, oxygen isotope analysis has also been used to identify seasonal changes in ice cores, interpret temperature variations during speleothem precipitation, and examine isotopic variations in tree ring climates. Foraminifera sampled from deep sea cores have revealed fluctuations in the O18/O16 ratio. These present evidence for glacial-interglacial cycles in the form of continental ice volume change.

uranium dating

SYNONYMS OR RELATED TERMS: uranium series dating, uranium series disequilibrium dating
CATEGORY: technique
DEFINITION: A method of dating based on measuring the rate of radioactive decay of uranium isotopes in bone and other organic remains to the stable isotope of lead. It has proved particularly useful for the period before 50,000 years ago, which lies outside the time range of radiocarbon dating. Each of the isotopes decays through a series of radioactive daughter isotopes until a stable isotope of lead is reached. Three daughter isotopes are created and decay with half-lives useful for dating: ionium, proactinium, and radium. Several uranium dating methods exist and material datable by these methods includes: aragonitic coral, speleothem, travertine, mollusk shell, marl, bone, teeth, caliche, calcretes, peat, wood, and detrital sediment.