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South American Radiocarbon Dates

Published online by Cambridge University Press:  27 June 2018

Junius Bird
Junius Bird*
Affiliation:
American Museum of Natural History, New York City
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Extract

The Stratigraphic data on some of the Peruvian samples provide a fairly good basis for evaluating the radiocarbon date measurements in relation to each other. The accompanying chart (Fig. 1) was prepared to clarify what is bound to be tedious reading. On it the plotting of the radiocarbon dates is obvious. The insertion with them of sectional profiles of midden excavations may be confusing, but does show where the tested material was found. In one instance (382), although the tested sample did not come from this midden, it belongs chronologically at the level indicated. Knowledge of the nature of the structure between the various layers gives us further means of assessing the results. Thus it is possible to compare the date blocks, as we might call the total plus and minus time span, and to point out which portions cannot be reconciled and are therefore impossible and which portions are improbable. The remaining segments mark the periods within which the actual dates are most likely to fall.

Type
Research Article
Information
Memoirs of the Society for American Archaeology , Volume 8: Radiocarbon Dating: A Report on the Program to Aid in the Development of the Method of Dating , 1951 , pp. 37 - 49
Copyright
Copyright © Society for American Archaeology 1951

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References

* Sample 318a (wood and twigs). The result in this case does not conform at all to the other figures. If these are even approximately correct, then we must grade all of the 313 result as impossible. This would be quite disturbing except for the fact that in this sample there was a greater possibility for contamination than with any of the other material from the Huaca Prieta site. Among the 243 grams of wood and twigs forming the sample was one piece of hard, dense, partially charred wood, probably “huarango.” Because of the possibility that this might have been part of an artifact or might retain tool marks, its surface, while still caked with salt hardened dirt, was lightly, coated with a thick solution of alovar or ambroid. At that time our supply of the solvent acetone could not be renewed so such specimens were not soaked or drenched and the solution was more viscous than usually used. Actually a brushed-on coating proved to be of little or no value for the salt-impregnated specimens from this deposit. In this instance penetration was so slight that most of the film had separated from the object by the time it was unwrapped and the rest lay on it as a loose scale.

In the belief that all traces of this could be eliminated, all of the surface was ground down with an electric powered steel wire buffer used for cleaning fossil bones. Checks and cracks were further cleared with dental tools and as none of these were deep I believed that the piece had been freed of all contaminated material.

In view of the results, however, some doubt as to its value will always remain. There seems no alternative but to refrain from using the figures derived from it and not to let them influence our thinking regarding the value of radiocarbon age determination. The error in judgment in this case is entirely mine.

** Several measurements were made of sample 322, and also 271, 521, 460. The variation of these measurements is shown in Fig. 1 by appropriately numbered interlocking boxes. The average of these measurements is indicated.