Fig 1.
Flow diagram outlining the basic structure of the ‘fiReproxies’ computer simulation employed in this study.
Fig 2.
Diagrams depicting the layouts of the hypothetical cave and occupation layers utilized in the simulations.
The grid cells delimit the extents of Layer 1 (left: 40 m2 in 80–50-cm2 units) and Layer 2 (right: 80 m2 or 160–50-cm2 units). The red, orange and yellow grid cells indicate the relative distribution of lithic fragments within individual lithic scatters, the numbers expressing the percentage of lithic artefacts deposited in each grid cell. Lithic artefacts are absent in green grid cells. The dashed lines delineate the stratigraphic cross-section of the cave deposits (center), with the shaded portions corresponding to Layer 1 (lower) and Layer 2 (upper).
Fig 3.
Diagrams showing the logic behind thermal buffering (TB) in our model.
This is the rate at which extant lithic scatters are potentially heated in subsequent occupations. a) Assuming the 250°C isotherm of a 50-cm-wide hearth is able to penetrate 6 cm into the substrate, 100% of lithic fragments lying within the hearth’s footprint at the surface would be thermally altered, while <35% of the same lithic scatter would be thermally altered if buried 4 cm below the hearth due to the reduction in surface area exposed to the heat. b) The ‘δ Total %’ value per unit of depth change increases as the depth of penetration of the 250°C isotherm becomes more shallow and/or the unit of depth (corresponding in our model to the amount of sediment deposited between occupations) is increased. For simplicity, we use the average δ Total % value, rounded to the nearest whole value, as the TB value in our model. See S3 Table for TB value calculator based on these diagrams. (Note: Figures are not to scale. d = diameter, SA = surface area, H = height of the spherical cap).
Fig 4.
Chart comparing occupation surface size and various fire and lithic scatter placement scenarios.
Parameters: 1 fire, fire size 1, 4 lithic scatters, 30 occupations, 1% introduced lithics. Given the near identical results obtained for simulations using the FNP/LR and FNP/LU settings (blue), as well as for all simulations using the FR setting (green), for the sake of clarity these are shown here as single curves. FNP = Fire near previous, FR = Fires random, LSNF = Lithic scatters near fire, LSR = Lithics scatters random, LR = Lithics random, LU = Lithics uniform, TB = Thermal buffering.
Fig 5.
Chart comparing same-sized occupation surfaces of different shapes (i.e. degree of elongation) and different hearth and lithic placement scenarios.
Parameters: 1 fire, fire size 1, 4 lithic scatters, 30 occupations, 0–100% TB, 1% introduced lithics. FNP = Fire near previous, FR = Fires random, LSNF = Lithic scatters near fire, LSR = Lithics scatters random, TB = Thermal buffering.
Fig 6.
Charts comparing fire and lithic scatter placement scenarios between Layer 1 and Layer 2.
Parameters: 1 fire, fire size 1, 4 lithic scatters, 30 occupations, 0–100% TB, 1% introduced lithics. The heated lithic percentages and curves for the FR/LR and FR/LU settings are virtually identical to those seen in the FR/LSNF and FR/SLR charts, while the plots using the FNP/LR and FNP/LU settings are nearly identical to those seen in the FNP/LSR chart, so these were not included here but were included in S1 Fig in the Supporting Information. FNP = Fire near previous, FR = Fires random, LSNF = Lithic scatters near fire, LSR = Lithic scatters random, LR = Lithics random, LU = Lithics uniform, TB = Thermal buffering.
Fig 7.
Charts demonstrating how the number of occupations per layer impacts heated lithic percentages for Layer 1 and Layer 2.
Parameters: Fires Random/Lithic Scatters Random (FR/LSR), 1 fire, fire size 1. 4 lithic scatters, 0% and 5% TB, 1% introduced lithics.
Fig 8.
Chart demonstrating the effects of fire size on the percentage of heated lithics.
Parameters: Fires Random/Lithic Scatters Random (FR/LSR), 1 fire, 4 lithic scatters, 0–100% TB, 1% introduced lithics. While a 1 m-wide fire (fire size 4) is effectively a cluster of four 50 cm-wide hearths (fire size 1) in our model, note the slightly lower relative percentages compared to four individually placed 50 cm-wide hearths in Fig 9.
Fig 9.
Chart demonstrating the effects of increasing the number of fires per occupation on fire proxy production for Layer 1 and Layer 2.
Parameters: Fires Random/Lithic Scatters Random (FR/LSR), fire size 1, 4 lithic scatters, 30 occupations, 0% and 30% TB, 1% introduced lithics.
Fig 10.
Chart showing how the number of lithic scatters per occupation influences heated lithic percentages for Layer 1 and Layer 2.
Parameters: Fires Random/Lithic Scatters Random (FR/LSR), 1 fire, fire size 1, 30 occupations, 0% and 10% TB, 1% introduced lithics.
Fig 11.
Chart demonstrating the effects of placing occupation layers without fires between fire-bearing occupation layers.
Parameters: 30 total occupations, Fires Random/Lithic Scatters Random (FR/LSR), 1 fire, fire size 1, 4 lithic scatters, 0–100% TB, 1% introduced lithics.
Fig 12.
Chart comparing a layer with hearths every third occupation (30 occupations total) with a layer with 10 occupations and fire in every occupation.
Parameters: Fires Random/Lithic Scatters Random (FR/LSR), 1 fire, fire size 1, 4 lithic scatters, 0–100% TB, 1% introduced lithics.
Fig 13.
Chart demonstrating the effects of increasing the number of lithic artefacts introduced directly into a hearth (i.e. introduced lithics, see Section 2.1) from 1% to 3%.
Parameters: Fires Random/Lithic Scatters Random (FR/LSR), 1 fire, fire size 1, 4 lithic scatters, 5% TB. Changing this percentage only appears to affect the final percentages by around the same number.
Fig 14.
Rose plots providing visual representations of the Layer 1 and Layer 2 occupation scenarios described in section 4.2.
The red arrows and associated red numbers indicate the resultant percentages of heated lithics produced in each scenario, while the values of other parameters are depicted as blue arrows. Note the different scales for heated lithics between Layer 1 and Layer 2. FNP = Fire near previous, FR = Fires random, LSNF = Lithic scatters near fire.