Physico-chemical characterisation of a one hundred thousand year old ochre processing toolkit from Blombos Cave, South Africa

A Masters Dissertation submitted to the faculty of Science, University of the Witwatersrand in fulfillment of the requirements for the Masters` degree. Johannesburg 2016.The Middle Stone Age (MSA) levels (c. 100 – 72 ka) (thousand years) at Blombos Cave, South Africa, contain buried remnants of human existence and their activities (these include ochre-stained shell beads, processed ochre pieces, bone tools, stone tools, and ochre processing toolkits). A preliminary study on the occupation layers at Blombos Cave was done in order to chemically and physically characterise the sediment deposits. The interpretation of the information preserved in these sediments, as a result of human activities, was achieved by using the following characterisation techniques: FT-IR, ICP-OES/MS, CHNS analysis as well as pH and EC measurements. Fluctuations in the bio-essential trace elements (K, P, Mg, Ca, S, Fe, Al, Cr, Na, Cu and C) and in the markers of in situ burning (P, K, C, Ca and Mg) through the MSA levels suggested a non-contiunous anthropogenic occupation of the cave. Further, the dark coloured layers were indicative of periods when heavy human activities, such as fire use, were encoutered. These layers were characterised by high levels of P, K, C, Ca and Mg, also elevated pH and EC levels were observed. The calcite origin for these sediment deposits was confirmed to be pyrogenic. The layers found to contain large bone, ochre and shell densities (with no evidence of fire use) had high levels of Fe, P high Ca and low EC. The calcite origin for these sediment deposits was geogenic. Biogenic calcite was only observed in the more recent CA and CC layers. Substantial amounts of ochre assemblages were recovered from the MSA levels at Blombos Cave. Among these was an ochre processing toolkit recovered from the CP layer (c.100 ka). Ochre is abundant in African archaeological sites after 165 ka and is likely to have played a symbolic role in the lives of prehistoric people. It contains an iron-oxide mineral as well as accessory minerals. When mixed with a binder (such as fat or water) ochre can be used as a pigment. A large number of fragmented bone remains were found in the M1 and M2 levels. It is suggested that the majority of the fragmentation occurred while the bones were in a fresh state; implying marrow extraction by the site occupants. The exploitation of bone marrow was crucial in order to extract the fat and use it as a binder during the pigment production. Some of the broken and marrow-extracted bones were heated and used as fuel during seasons when wood was scarce while the other bones were deliberately engraved for symbolic intent. The characterisation of the ochre processing toolkit was achieved by mineralogical analysis and elemental fingerprinting. FT-IR analysis revealed that the general matrix of the ochre samples comprised of hematite (Fe2O3) or goethite (α-FeO(OH)) as the main chromophores and clay minerals (such as kaolinite (Al2Si2O5(OH)4), muscovite [(KF)2(Al2O3)3(SiO2)6(H2O)] and illite [K(Al4Si2O9(OH)3)]), calcite (CaCO3) and quartz (SiO2) as the main accessory minerals. PXRD analysis confirmed Fe2O3, Al2Si2O5 (OH)4, [K(Al4Si2O9(OH)3)] and SiO2 to be the predominant mineral phases in the ochre, implying this specific type of ochre was preferred during the production of the pigment. Fe2O3 contributed the red hue and the aluminosilicates their clayey properties making them good extenders of the pigment. Multivariate statistics and Fe ratios made it possible to identify elements important for differentiating the ochre recovered from the CP layer. Analysis of variance (ANOVA one-way) showed a statistically significant difference between the ochre residues in terms of trace elemental profiling. The variance suggested different geological origins for the ochre. FT-IR was used as a screening technique for any organic residues associated with the toolkit and GC-MS was used to identify the preserved organic residues. These were mostly lipids and terpenes. The identified bio-molecular markers; stearic acid and dehydroabietic acid were exploited to give insight on the origin of the residues. Stearic acid suggested the use of animal fat while dehydroabietic acid implied the use of a resin (potentially as a binder in the pigment). The characterisation investigations revealed that the prehistoric populations at Blombos Cave specifically sourced hematite and aluminosilicate- containing ochre pigments in order to fulfil their social and cultural demands. The MSA site occupants’ chemical understanding of these materials suggested they were technologically advanced. Keywords: Blombos Cave, MSA levels, ochre, mineralogical analysis and elemental fingerprinting.LG201