Radiocarbon dating of wood using different pretreatment procedures; application to the chronology of Rotoehu Ash, New Zealand.

Abstract

We compare radiocarbon accelerator mass spectrometry (AMS) ages of wood samples subjected to a conventional acid-base-acid pretreatment with stepped combustion (ABA-SC) with results from the same samples subjected to an acid-base-wet oxidation pretreatment with stepped combustion (ABOX-SC) and cellulose extraction with stepped combustion (CE-SC). The ABOX-SC procedure has been shown previously to lead to lower backgrounds for old charcoal samples. Analyses of relatively uncontaminated " (super 14) C-dead" samples of wood suggest that backgrounds of 0.11+ or -0.04 pMC are obtainable for both the ABOX-SC and ABA-SC procedures. Where wood is significantly contaminated the ABOX-SC technique provides significantly better decontamination than either the ABA-SC technique or cellulose extraction alone, although CE-SC can produce comparably low backgrounds to the ABOX-SC procedure. We also report the application of the ABOX-SC, ABA-SC and CE-SC procedures to wood samples associated with the chronologically controversial Rotoehu Ash eruption, New Zealand. New (super 14) C-AMS dates from wood sampled from below the Rotoehu Ash span an age range of 43-50 ka BP consistent with recently presented OSL dates of 42-44 ka obtained for palaeosols beneath the ash.