Heritage Cases

Established chronometers do not fully meet the needs of archaeologists and paleoanthropologists conducting MSA research. While single-grain quartz optically-stimulated luminescence (SGQ-OSL) dating has become one of the principal chronological techniques applied to >50 ka MSA-bearing strata, it is desirable to assess the chronologies of archaeological sites by using a second, independent technique. Since comprehensive single-grain quartz OSL dating has already been applied at Klipdrift Shelter, we propose to conduct U-Th dating of OES at this site to provide a detailed comparison between OSL and U-Th dates, thereby assessing the accuracy of both techniques. (Western Cape Province) U-Th burial dating of a pilot set of OES from layers spanning the vertical extent of excavation at Blombos has produced self-consistent results and the ages preserve stratigraphic order. Some ages agree with SGQ-OSL ages from the same layers and some do not. At Klipdrift, our pilot samples were insufficient in number to test internal consistency and chronostratigraphic principles, but generally our ages disagree with SGQ-OSL ages. In collaboration with Drs. C. S. Henshilwood and K. L. van Niekerk, we propose to expand the application of U-Th dating of ostrich eggshell (OES) at Klipdrift Shelter to test both the internal consistency of U-Th burial dating and preservation of chronostratigraphic principles at Klipdrift, and to further assess the relationship between U-Th burial ages and SGQ-OSL ages. Accordingly, we request permission to export a suite of OES samples for U-Th isotopic dating via analysis by ICP-MS (inductively coupled plasma mass spectrometry). Analyses will include: (1) profiling the uranium concentrations across eggshells by laser ablation ICP-MS, (2) analyzing U and Th isotopic compositions at selected positions along the uranium concentration gradients by ICP-MS analyses in solution mode, and (3) determining U-Th burial ages for the eggshells from the analytical data. These analyses will be conducted by E. Niespolo and W. Sharp at the Berkeley Geochronology Center (BGC), Berkeley, CA, U.S.A. These analyses cannot be done in South Africa because the instrumentation and facilities required to perform such work are not available in the country. Furthermore, the Niespolo and Sharp are developing a novel approach to U-Th dating of OES using analytical protocols and data analysis techniques developed by them at the BGC. Hence, the BGC and the proposal authors are uniquely suited to performing these analyses. Specifically, we request permission to export 23 OES pieces from Klipdrift Shelter in order to carry out systematic dating throughout the sequence excavated in 2018 via U-Th on eggshells. The OES pieces are taken from horizons with existing OSL ages or those that are currently being dated by OSL by Dr. Simon Armitage (Royal Holloway U. and Sapiens Centre of Excellence, U. of Bergen). The requested OES from Klipdrift Shelter will allow us to rigorously test the reproducibility of U-Th burial ages within individual layers and preservation of stratigraphic order among layers, and to compare with OSL dates in close stratigraphic association. The 23 OES pieces have been examined by E. Niespolo to ensure that they have the best potential for dating compared to other OES in the sequence. We expect to complete the analyses within 1 year of receiving the OES at our laboratory. The dating process is destructive but any unused portions of the OES can be returned. Prior to any destructive analyses, all samples will be photo-documented. The results of the study will be reported to Prof. C. S. Henshilwood and Dr. K. L. van Niekerk and in collaboration with them will be published in a referred journal. The U-Th ages on eggshells will help to provide reliable, precise ages for the archaeological record at Klipdrift shelter and will also likely strengthen future dating of other Middle Stone Age archaeological sequences in South Africa.