A Raman micro-spectroscopy study of 77,000 to 71,000 year old ochre processing tools from Sibudu, KwaZulu-Natal, South Africa

• Main Authors: Marine Wojcieszak, Lyn Wadley
• Format: Article
• Language: English
• Published: SpringerOpen 2019-05-01
• Series: Heritage Science
• Subjects: Residues; Grindstones; Ochre; Middle Stone Age; Raman micro-spectroscopy
• Online Access: http://link.springer.com/article/10.1186/s40494-019-0267-9

Abstract Many Middle Stone Age sites in South Africa yielded hundreds, even thousands, of ochre pieces sometimes showing use traces. Less attention has been paid to the tools used for their processing. Here, seven tools excavated from the oldest layers (71,000 to 77,000 years ago) of Sibudu rock shelter were studied non-invasively to identify the micro-residues on them. The tools were first examined with optical microscopy to detect areas of interest. Then, Raman micro-spectroscopy was performed on the residues present, as well as on random areas of tool surfaces. These Raman signatures were compared to those obtained from the sediments and ochre samples recovered from the same layers. All tools exhibited red, orange and brown stains on their surfaces and these comprised iron oxides (haematite and maghemite) and oxyhydroxide (goethite). The other compounds detected include amorphous carbon, quartz, anatase and manganese oxides. All of these can occur within ochre, but they may alternatively be natural components of other rocks and sediments, formed secondarily by decay processes. However, the large and thick residues present on the surfaces of the artefacts imply their use for ochre processing (microscopic observations and chemical analyses of the sediments and the local rocks showed that they contain only traces of haematite). Ochre seems to have been the only material processed with these old Sibudu artefacts whereas in younger occupations, items such as bone were also processed with grindstones. The grinding tools are morphologically varied and the ochre pieces are both morphologically and chemically diverse.