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Conditions Involved in Dating Terrestrial Shells

Published online by Cambridge University Press:  18 July 2016

Jacques Evin ,
Joëlle Marechal ,
Christiane Pachiaudi  and
J J Puissegur
Jacques Evin
Affiliation:
Centre de Datations et d'Analyses Isotopiques, Université, Claude-Bernard, Lyon, France
Joëlle Marechal
Affiliation:
Centre de Datations et d'Analyses Isotopiques, Université, Claude-Bernard, Lyon, France
Christiane Pachiaudi
Affiliation:
Centre de Datations et d'Analyses Isotopiques, Université, Claude-Bernard, Lyon, France
J J Puissegur
Affiliation:
Département de Géologie, Université de Dijon, France
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Abstract

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Mollusks living only on ground surface can be expected to give the most reliable results in 14C dating from carbonates of continental origin. One may assume they have a homogeneous biotope and are not affected by any hard-water effect. In order to verify these assumptions and to test shells as routine dating material, results from terrestrial gastropods are compared with other 14C dates from classic biologic material, such as peat, charcoal, or bone, collected in the same archaeologic or geologic levels in miscellaneous places. Two sites were selected for which other chronologic data, such as prehistoric industries or malacologic diagrams were available.

All results indicate older values for 14C shell dates. The discrepancy between “normal” and snail dates amounts to 300 to 1200 14C years and remains the same whatever the absolute age of the sample. All 13C values of perfectly cleaned shells are between —5 to —10%, versus PDB. The initial 14C content of shells that is too low may be different according to species, as suggested by 13C variations.

Although fairly constant, this deviation of 14C ages generally makes such samples unreliable for most archaeologic studies, which often need more precise results. However, some measurements were performed on microfauna shells from several Würmian loess to show that dating of shells may be useful in fairly ancient geologic sediments for lack of better carbonaceous samples. Good agreement of some snail dates with expected sediment ages point to the importance of proper sample selection and pretreatment that might be checked by 13C measurements.

Type
Dating Various Materials
Information
Radiocarbon , Volume 22 , Issue 2 , 1980 , pp. 545 - 555
Copyright
Copyright © The American Journal of Science 

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