Australia: The Land Where Time Began

A biography of the Australian continent 

Optical Dating of Grave-Infill of Human Burials, Lake Mungo, Australia

Age constraints on Mungo I and III, the oldest human remains found in Australia to date, from Lake Mungo, western New South Wales, were based on the optical dating of sand from the same stratigraphic units as those which the remains had been inserted into, 42±3 ka, and the overlying sand, 38±2 ka, gave the age of burial as 40±2 ka. As the original site where the burials were found had been eroded away it was necessary to date the burials by this indirect method. When Mungo III was originally excavated blocks of grave infill sediment were collected for sediment fabric analysis which entailed impregnating the blocks of sediment with polyester resin, after which the blocks were sectioned for analysis, the remaining blocks being stored in a cupboard for the next 30 years. In this study the authors¹ optically dated single quartz grains they extracted from the centre of one of the bocks of sediment and these grains were found to display a wide distribution of equivalent doses ranging from 0.0±0.3 to 43.7±8.3 Gy, indicating that light has not been excluded from all grains following excavation. According to the authors¹ their study has shown that the population of grains with the maximum equivalent doses indicate an age consistent with that of the previous study, which indicates that at least some of the grains have remained light-safe. The authors¹ used linearly modulated optically stimulated luminescence to identify single grains that had remained light-safe, and these were found to have an age of 41±4 ka, representing a direct optical age for the grave-infill, consistent with the ages arrived by the previous study of the same stratigraphic unit as that contained the burial. The authors¹ suggest these results demonstrate the potential of the application of optical dating of archived samples of sediment that were not stored in a light-safe environment.

Sources & Further reading

1. Olley, Jon M., Richard G. Roberts, Hiroyuki Yoshida, and James M. Bowler. "Single-Grain Optical Dating of Grave-Infill Associated with Human Burials at Lake Mungo, Australia." Quaternary Science Reviews 25, no. 19–20 (10// 2006): 2469-74.