• AMS Dating of a Late Quaternary Tephra at Graham's Terrace, New Zealand

      Gillespie, Richard; Hammond, A. P.; Goh, K. M.; Tonkin, P. J.; Lowe, D. C.; Sparks, R. J.; Wallace, Gavin (Department of Geosciences, The University of Arizona, 1992-01-01)
      The radiocarbon dating of volcanic ash (tephra) deposits in New Zealand has been difficult on sites remote from the eruption, which contain either little carbon or degraded and contaminated charcoal. Although many studies of contamination removal from macroscopic charcoals from tephra sequences have been made, little attention has been paid to those containing no visible charcoal, because of the difficulty of obtaining sufficient carbon for radiometric dating. We report here experiments using accelerator mass spectrometry to establish a reliable method for dating a low-carbon aeolian and peat deposit containing a tephra horizon. Results so far demonstrate that improvements to existing chemical pretreatment methods are possible, and that dates obtained on oxidized fine-grained residues can approach the maximum age determined on good quality chaffed wood samples.
    • AMS Dating of Alluvial Sediments on the Southern Tablelands of New South Wales, Australia

      Gillespie, Richard; Prosser, I. P.; Dlugokencky, Edward; Sparks, R. J.; Wallace, Gavin; Chappell, J. A. (Department of Geosciences, The University of Arizona, 1992-01-01)
      The dating of alluvial deposits is frequently hampered by a lack of good-quality charcoal or other material for radiocarbon samples. We have dated two sites in southeastern Australia using traditional radiometric methods with minimal pretreatment. Results yielded an inconsistent chronology, affected by contamination with younger humic materials. A more consistent and older chronology was achieved using AMS dating of rigorously pretreated samples of fine-grained charcoal. The results have important implications for the radiocarbon dating of many Late Quaternary stratigraphic sequences with low charcoal abundance.