The role of rock properties in stone tool production in the Middle Stone Age at Sibudu

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2016

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Kempson, Helen

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Abstract

This study is within the context of the Howiesons Poort Industry of the Middle Stone Age. This is a dynamic period of increasing behavioural and material complexity. In the lithic assembles, this can be seen in a strong bias towards the selection of high-quality fine-grained rocks. This has often been interpreted as evidence for long distance travel, reciprocal exchange, or even increased mobility. This study aims to determine what influence the mechanical properties of rock types exerted on the Middle Stone Age assemblages at Sibudu. This requires a consideration of the distribution of rock types across the landscape surrounding Sibudu Cave. The study was limited to hornfels and dolerite as these rock types dominate the Sibudu assemblage, and quartz and quartzite that were sometimes used at the site are exceedingly difficult to collect in large enough sample sizes to conduct experiments. It was important to carry out tests on the mechanical properties of hornfels and dolerite and to characterise them. Hardness, roughness, elasticity and brittleness dictate the ease of knapping as well as the durability of flaked tools and these rock properties can be measured by the mechanical tests described here. To understand how these properties affect the assemblage in practice, dolerite and hornfels flakes were produced and used experimentally for cutting and scraping leather. The edge damage produced was compared. Finally, preliminary analysis was undertaken of square C4, layer PGS, which forms part of the oldest Howiesons Poort layer at Sibudu. The information and insights gained from the mechanical tests and experimental work were used to interpret the role of mechanical properties for the archaeological sample of PGS. The results show that all rocks used at Sibudu are local, and do not support any models of long distance travel/trade, reciprocal exchange, or models of increased mobility. Dolerite and hornfels form the bulk of the assemblage at all times (except briefly in the post-Howiesons Poort), and there is a bias towards the selection of fine-grained rocks during the Howiesons Poort. Dolerite can be characterised as hard, tough, elastic, and rough, while hornfels is hard, brittle, and fine-grained. These properties affect knapping and the qualities of a tool’s edge. The properties of hornfels allow for knapping accuracy and predictability, and it is better suited to blade production and cutting. However, tool edges are not robust. Dolerite is not as easy to knap, but produces tools with a robust edge that are particularly suited to scraping. Each rock type appears to have fulfilled a different function at Sibudu. Most rock studies geochemically source rocks, establish models of rock procurement or show trends in rock selection for artefact classes. Mechanical studies of rocks have typically formed part of heat treatment debates (Brown et al 2009; Domanski & Webb 1992, 1994; Webb & Domanski 2008). Through the combined approach of mechanical testing, experimental knapping and tool use, and lithic analysis, this research provides a context for possible rock procurement choices at a time in the past when many African sites reveal a changing pattern of rock selection.

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A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2016.

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Kempson, Helen (2016) The role of rock properties in stone tool production in the Middle Stone Age at Sibudu, University of Witwatersrand, Johannesburg, <http://wiredspace.wits.ac.za/handle/10539/21730>

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