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Point-Counting Technique for Fission-Track Dating of Tephra Glass Shards, and Its Relative Standard Error

Published online by Cambridge University Press:  20 January 2017

Giulio Bigazzi  and
Rex F. Galbraith
Giulio Bigazzi
Affiliation:
Istituto di Geocronologia e Geochimica Isotopica, CNR, Via Cardinale Maffi, 36, 56127, Pisa, Italy
Rex F. Galbraith
Affiliation:
Department of Statistical Science, University College London, Gower Street, London, WC1E 6BT, United Kingdom
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Abstract

Fission-track dating of glass is potentially an efficient technique for tephrochronological studies. However, most glasses from Quaternary tephra have very low spontaneous track densities and track counting is laborious. The point-counting technique is a simplified procedure for evaluating fission-track areal densities in a glass shard population that allows the analyst to count larger numbers of tracks in significantly shorter times. A field of view is coded as 1 if its center is on glass and is 0 otherwise, and the total area of glass is estimated by counting the number of 1's. Under simple assumptions, the binomial distribution appears to provide a reasonable evaluation of the additional experimental error in a fission-track density determination by this technique. Glass shard populations have been simulated, assuming that glass areas are random samples from distributions analogous to real ones. The effect of variation in glass area on the relative standard error of the estimated track density is found to be small. The point-counting technique significantly enhances the potential of fission-track dating, especially for very low track densities typical of most Quaternary tephra, as the additional error associated with its use is largely counterbalanced by the greater number of tracks that can be counted.

Keywords

point-counting techniquetephrochronologyglass shardsfission-track dating
Type
Original Articles
Information
Quaternary Research , Volume 51 , Issue 1 , January 1999 , pp. 67 - 73
Copyright
University of Washington

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