Validity of Radiocarbon Dates on Terrestrial Snail Shells

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Abstract
Radiocarbon dating of terrestrial snail shells is examined. Three groups of samples, two from archaeological sites of Venezuela and one from the state of Texas, were taken as examples. The true ages were determined from radiocarbon dates on associated charcoal, and measurements on the snail shells allowed the errors to be determined. The groups showed completely different characteristics: 15 samples from Texas all had ages falsely old, 12 specimens of one Venezuelan group produced all correct dates, and another Venezuelan type with five samples gave dates all too recent. This study defines the directions and extents of errors for each group of snail shells, permitting them to be used as relatively reliable datable objectives in excavations where better materials are not available.The possibility of correcting the radiocarbon dates using carbon-13 concentrations is considered, and 24 measurements are presented. It is concluded that more than one factor can influence the stable isotope concentrations in each case, and, therefore, carbon-13 is not useful for the improvement of the accuracy of snail shell dates.