Amino acid racemisation and radiocarbon dating of a contact period midden, Greenglade rockshelter, New South Wales

The extent of racemisation of one of the fastest racemising amino acids, aspartic acid, in the marine gastropod Turbo undulatus from Greenglade rockshelter, southern New South Wales, is examined in an attempt to resolve time within the last few hundred years, an interval that is difficult to date by radiocarbon. Aspartic acid racemisation, in conjunction with radiocarbon dating and stratigraphic evidence, indicates that Greenglade rockshelter was occupied episodically since AD 1300. The variation in the amino acid results obtained in this study help to define the limitations of applying the amino acid racemisation (AAR) method to middens of recent origin. Comparison of AAR analyses on shell of equivalent age and known not to have been burnt, suggests that some of the shells within the middens have been reworked and/or heated during multiple episodes of rockshelter occupation. Cultural evidence indicates that the rockshelter was used until historically‐recent times, well after British colonisation and possibly as late as the middle twentieth century. The difficulties of dating this interval are also considered in the context of the contact period in Australia. It is concluded that dating midden materials of recent age, known to have been heated by camp fires, is a particularly difficult task by the AAR method, but that meaningful results may be obtained if the technique is used with caution.