Studies of Non-Marine Mollusks for the Selection of Shell Samples for Radiocarbon Dating

Abstract

14 C dating of shells from terrestrial and freshwater mollusks is prone to distortion by post-depositional diagenesis as well as incorporation of material depleted in 14 C while the mollusk was alive. Three types of diagenetic change can result: etching, the development of surface crusts, and replacement of aragonite by calcite. Inspection under the light microscope, x-ray diffraction, and scanning electron microscope make it possible to assess the relative importance of the changes. When they are confined to the surface, mechanical cleaning combined with judicious leaching can reduce them to <1% of the total sample. The corresponding errors, which can now be specified, are often no greater than those associated with the statistics of counting.