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Figures 1-8
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modified on 2019-09-08, 22:22
Figure 1: Context of Boling Point and Babine Lake Rock Art. (a) Sketch drawings of section of Boling Point pictograph, adapted from Corner (1968); (b) area of rock art panel shown in photographs and where sample was taken; (c-d) photograph of Boling Point rock art panel in color (c) and digitally enhanced with D-Stretch (d), Babine Lake (courtesy of G. Keddie, Royal BC Museum); (e) map of British Columbia, highlighting area of study; (f) extracted fragment of Boling Point pictograph from Mohs and Mohs (1976) survey, from the Royal British Columbia Museum archive (Vancouver, Canada).
Figure 2: Structure and morphology of a L. ochracea microcolony cluster on a sediment particle. Scanning electron micrographs using secondary electrons illustrating freshly collected and untreated L. ochracea, collected by D. Emerson. (a) Large cluster of sheaths on a sediment particle. Scale = 10 µm. (b) Cluster of L. ochracea growth. Scale = 5 µm. (c) Detail of L. ochracea cluster showing unidirectional growth pattern. Note the relatively smooth surface texture. Scale = 2.5 µm. (d) Detail of broken L. ochracea sheath. Scale = 0.25 µm.
Figure 3: Selected micrographs from SEM examination of targeted red pigment particle in GcSi-1 rock art sample. (a) Concentration of broken and randomly oriented L. ochracea sheaths. Note the fractured diatom fragment in the upper right corner, and hematite and silicate microspheres distributed throughout. Scale = 2.5 µm. (b) Detail of L. ochracea sheath showing advanced degradation (holes) in the sidewall of a sheath body. Scale = 2.5 µm. (c) Detail of a small, intact cluster of L. ochracea bodies. This was the sole identifiable example of a coherent cluster in the sample. Note the warped shapes of the tube openings. Scale = 2.5 µm. (d and e) Concentrations of L. ochracea sheaths displaying fractured ends and globular, porous sheath exterior walls. Note the clusters of hematite and silicate microspheres and blocky octahedral and tetrahedral hematite polymorphs distributed through the pigment matrix. Scale = 2.5 µm. (f) Rare example of a relatively intact L. ochracea sheath. Scale = 1.25 µm (g – i) Details of broken sheath ends. Note the globular surface texture indicating localized melt and recrystallization of iron and silica. Specimens shown in (g) and (i) have double-walled inner rings, indicating maturity at the time of death. Scales = 0.5 µm.
Figure 4: SEM-EDS Hyperspectral Map of GcSi-1. (a) Cross section EDS detail of a red pigment particle embedded in the calcite layer. Scale = 25 µm. (b) EDS map detail of pigment particle showing concentrations of iron and phosphorus.
Figure 5: HRTEM Analysis of GcSi-1. (a) HRTEM image showing magnetite particle coated with hematite phase on the exterior surface of a L. ochracea sheath body. (b) Hematite and magnetite phases highlighted in color. Details on phase identification and image processing can be found in SI Fig. 2b. Scales = 5 nm.
Figure 6: Thermally-induced Color Change of L. ochracea Control Samples. A series of digital micrographs illustrating thermally-induced color change of L. Ochracea control samples. Samples were heated in oxidizing atmosphere in a muffle furnace, held for 3 h each. Munsell scores are provided. (a) Untreated (2.5YR 2.5/2), (b) 200°C (2.5YR 2.5/3), (c) 400°C (2.5YR 3/4), (d) 600°C, (2.5YR 3/6), (e) 800°C (2.5YR 3/6), (f) 1,000°C (10R 2.5/1). Scale 1 = mm.
Figure 7: SEM Micrographs of Incrementally Heat-Treated L. ochracea Control Samples. (a) Untreated FeOB. Note the smooth exterior texture. Scale = 10 µm (b) 200°C, note the absence of structural changes. Scale = 0.25 µm (c) 400°C, note the absence of structural changes and smooth sheath exterior. Scale = 1.25 µm (d) 600°C, showing structural changes including globular deposits and fraying of sheath exteriors. Scale = 0.75 µm. (e) 800°C, note melt features on sheath exterior surfaces and nucleation of hematite microspheres. Scale = 1.0 µm (f) 1,000°C, note the complete phase transformation to magnetite and hematite polymorphs. Scale = 1.25 µm.
Figure 8: SQUID magnetometry and associated L. ochracea sheath transformation. Hysteresis loops for GcSi-1 and L. ochracea control samples (center). SEM micrographs (left and right) showing the morphological transitions of L. ochracea sheaths corresponding each thermal gradient. Scale = 1.0 µm.
