A04_03

MIS-3 megafauna radiocarbon ages and blank control practices at ANSTO

Levchenko V¹,  Bertuch F¹, Smith A¹, Jenkinson A¹, Hua Q¹, Williams A¹, Kumar S¹, Yang B¹

¹ANSTO, Kirrawee DC, Australia

Reliable radiocarbon age determinations close to the limit of the method are dependent on effective pre-treatment and correction for extraneous carbon added during processing. At ANSTO this is controlled by processing continuous stream of various representative blanks to characterise major pre-treatment protocols – ABA, cellulose purification, collagen extraction, also combustion-graphitisation and hydrolysis-graphitisation procedures.

Special collections of materials with ages beyond the radiocarbon limit are used – charcoal from a million-year-old tree, MIS-5 bones from permafrost, subfossil wood, IAEA-C1 marble, and Ceylonese and commercial graphite. For graphitisation blank, the cylinder with geological CO₂ is used. Blanks ranging from ten of μg to several mg of carbon are processed for every AMS radiocarbon run. For each material and procedure, a mass dependence function for blank pMC values is constructed on the subset including the most recent few-month determinations. This allows building a representative statistic for blank variability and flags any significant blank level increases prompting a review of relevant laboratory activity.

As an example, we present the dating of Diprotodon remains from Lake Callabonna in South Australia. Diprotodons became extinct around 70-50 ka BP, period also noted by the arrival of humans to Australia. To better understand the extinction causes, a reliable determination of the species extinction time is required. To date, all diprotodon remains returned infinite ages beyond the radiocarbon limit. Our studied specimen after a set of determinations produced a finite age of 51,900+/-1200 radiocarbon years, bringing the species survival time to the times of human presence in Australia.