Fig 1.
From the meter (landscape and archaeological site) to the micrometer (charcoal particle) scale.
A—Location of the sample collection area in South America. B—Archaeological site Bibocas II. The area marked with the red box indicates the excavated site. C—Stratigraphy of the archaeological site with the dating. The black box indicates the location of the thin section samples. D—Micromorphology thin section. The black boxes indicate the locations in which the carbon particles in the transect were analyzed. E—Larger particle of charcoal observed with an optical microscope with transmitted light. F—Smaller particle of charcoal observed with an optical microscope with incident light. G—Example of a Raman spectrum, still untreated, of the smaller-sized charcoal particle (image F).
Table 1.
Samples used in this work.
Fig 2.
Example of the fitting performed in the samples used in this work.
Table 2.
General information on the bands used in this work.
Fig 3.
Width of the base of the peak to half-height in 2Ɵ for the hkl planes (002), (004), and (100).
Fig 4.
(A) Raman spectra of the charcoal samples obtained from the eucalyptus bark burned at temperatures from 400 to 1000 °C; (B) FWHM for the G-band as a function of the firing temperature; and (C) frequency of the G-band as a function of the charred temperature.
Fig 5.
Schematic profile of the stratigraphy of the archaeological site Bibocas II by Déborah Duarte and Luis Felipe Bassi (A). Raman spectra of charcoal superimposed according to stratigraphy (B).
Fig 6.
Characteristics of the Raman spectrum distributed along the stratigraphic profile in the following sequence: (A)—frequency of G (cm-1); (B)—intensity ratio of ID/IG; and (C)—intensity ratio of ID4/ID1.
Fig 7.
Analysis of the grouping of the samples produced in the muffle oven and collected from the archaeological site: 400, 500 and 700 °C; Sup—surface; I—layer I—610 years BP; III—layer III, 1170 years BP; IVs–layer IV-upper; IVm–layer IV-middle; IV- layer IV-lower; Vm–layer V- middle (8500 years BP); VI–V lower; VIs–layer VI upper.
Fig 8.
Structural disorder and size of the crystal from the periphery towards the center; A and B, ID/IG and La of charcoal at 1.5 mm; C and D, ID/IG and La of charcoal at 600 μm.
Fig 9.
Scanning electron microscopy of particles of charcoal from a soil thin section collected between Layers II and III of the Bibocas II archaeological site.
The red points indicate the EDS microanalysis data shown in Table 3. Images A and B show the charcoal particles within a soil microaggregate. Image C shows a clay coating over the charcoal particles. Image D illustrates the quasi-coating formed by clay minerals and nano-charcoal particles, which is suggested by the high content of carbon in the clay matrix.
Table 3.
Microanalysis points observed by EDS and indicated in Fig 9A, 9B, 9C and 9D.