Fig 1.
Map of the excavated area at KDS and site stratigraphy with OSL dates (illustration credit: Magnus M. Haaland, university of Bergen).
Table 1.
Sample numbers and descriptions of the artifacts analyzed destructively and by IR spectroscopy.
Fig 2.
Comparison between fracture surfaces from before and after heat treatment.
(a, b, c) = before heat treatment, (d, e, f) = after heat treatment. SK-13-03C before (a) and after (d) heat treatment; SK-13-04C before (b) and after (e) heat treatment; SK-13-03B before (c) and after (f) heat treatment. Note that, regardless of the initial roughness of the silcrete type, heat treatment results in smoother fracture patterns but pre-heating fracture scars on fine-grained silcrete (a) may be smoother than post-heating scars on coarser silcrete types (f). All fracture surfaces were photographed at identical magnification and in similar raking light conditions.
Fig 3.
Map of the KDS area showing the six sampling locations for our reference collection (illustration credit: Gauthier Devilder, PACEA/CNRS-university of Bordeaux).
The black spots correspond to primary silcrete and ferricrete outcrops georeferenced by Roberts (2003). The red x of source 5 indicates that this outcrop was not georeferenced by Roberts.
Fig 4.
Micrographs of archaeological samples and geological samples with similar petrographic textures.
(a, c, e) = Archaeological samples and (b, d, f) = geological samples. Cross polarized light. (a) K2782 and (b) its geological counterpart SK-13-01A, (c) K2714 and (d) its geological counterpart SK-13-03B, (e) K576 and (f) its geological counterpart SK-13-04C.
Fig 5.
A: pre-heating scar distinguishable by the contrast between relatively rough and smooth surfaces, B: heat-induced non-conchoidal (HINC) fracture, characterized here by a non-conchoidal fracture plane with scalar features, C: post-heating scars, D: potlid fractures.
Table 2.
Comparative frequencies of the heated vs unheated or non-diagnostic component and of the heating proxies for the basic technological type-products.
Fig 6.
Heated blades and tools on blades from KDS, layer PBD.
1–16: silcrete blades showing their diversity in terms of size attributes and visual transformations after heating, 17–19: backed tools including one fragment of backed tool (17), one bi-truncated tool (18), one segment (19); 20,21: notched blades; 22,23: blades with slight continuous retouch on one lateral edge.
Fig 7.
Heated blade cores from layer PBD, KDS.
Caption for drawings: 1. knapping platform preparation, 2. convexity preparation, 3. blade removal without initiation, 4. blade removal with initiation, 5. indeterminate removal, 6. cortex, 7. pre-heating surface, 8. heat-induced non-conchoidal fracture (HINC), 9. post-heating removal. Note that all three cores (A, B, C) show a sequence of core exploitation (preparation and blade production) that follows a heat treatment which has resulted for A and C in heat-induced fractures, and which was preceded for A and B by a first stage of core exploitation.
Fig 8.
Heated blade cores from layer PBD, KDS.
Caption for drawings: 1. knapping platform preparation, 2. convexity preparation, 3. blade removal without initiation, 4. blade removal with initiation, 5. indeterminate removal, 6. cortex, 7. pre-heating surface, 8. heat-induced non-conchoidal fracture (HINC), 9. post-heating removal, 10. patina. Note that all three cores present heat-induced non-conchoidal fractures; the heat-induced fracture visible on core B produced two refitted fragments, the biggest fragment was exploited as a core whereas the smallest was discarded. Core C shows a pre-heating knapping stage that includes core preparation and blade production. The initial blanks of cores B and C are flakes (V = ventral face, D = dorsal face).
Fig 9.
Size distribution of the cores and of the heated/unheated blades from KDS, layer PBD.
A, B: length/width and length/thickness distribution of the cores showing heat-induced fractures compared with the cores showing only pre- and post-heating surfaces, C, D: length/width and length/thickness distribution of the heated blades compared with the unheated or non-diagnostic ones.
Fig 10.
Micro-ATR infrared spectra and reflection photo-micrographs of KDS tempering-residue.
Left: infrared spectra in the CH-stretching region: (a) K2782, (b) KB421, (c) K2840, (d) KDS-5. Spectra vertically offset for clarity. Right: reflection micrographs of a section of tempering residue on KB421. Note the low reflectance value of the residue (appearing as grey), indicating that it is formed by tar, and the pores close to the silcrete surface, indicate melt degassing during the formation of the tar as a hot liquid. Reflected white light and oil immersion.