Past thermal history of goethite and hematite fragments from Qafzeh Cave deduced from thermal activation characteristics of the 110°C TL peak of enclosed quartz grains
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Abstract
The first direct evidence for high temperature firing of ochre as early as 100 ka ago is presented. The thermal activation properties of three ochre fragments from archaeological levels at Qafzeh Cave, Israel, and a natural ochre from a geological source near Qiryat Shemona, Israel, were studied. The occupation of Qafzeh Cave is dated to -100 ka ago. Under some conditions, the past thermal history of quartz can be deduced on the basis of the thermal activation characteristic (TAC) of its 110°C thermoluminescence (TL) peak. The TAC of quartz grains extracted from as-recovered ochres showed wide differences in the onset of sensitization. Annealing the grains in the laboratory for 600 seconds at 390°C shifted the onset of sensitization up by 200° in the geological ochre and the archaeological ochre QS-2, but not at all in the archaeological ochre QS-1 and only by 30° in the archaeological ochre QS-4. This constitutes proof that QS-1 had indeed been heated in antiquity to a temperature in excess of our anneal, while QS-4 had been heated to a temperature equivalent to only slightly less than what we had chosen. We thus conclude that very early modern humans may have utilised deliberate heat treatment for the production of a variety of ochre colours. We also demonstrate that the direct luminescence dating of heated ochre fragments from archaeological sites is feasible, provided that TAC analysis confirms that they had been heat treated in antiquity to a sufficiently high temperature to have reset the TL clock, and that information essential to annual dose rate reconstruction is collected at time of excavation.
