# Sourcing and nuclear magnetic resonance: new applications for old materials

Isabelle Pianet, Anna Gutiérrez Garcia-Moreno, Marie-Claire Savin, Pilar Lapuente Mercadal, Marta Sánchez de La Torre, François-Xavier Le Bourdonnec

► To cite this version:

Isabelle Pianet, Anna Gutiérrez Garcia-Moreno, Marie-Claire Savin, Pilar Lapuente Mercadal, Marta Sánchez de La Torre, et al.. Sourcing and nuclear magnetic resonance: new applications for old materials. STAR: Science & Technology of Archaeological Research, 2019, International Symposium on Archaeometry 2018 (Merida, Mexico): Proceedings, 5 (2), pp.20-28. 10.1080/20548923.2019.1643549. hal-02963543

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# Sourcing and nuclear magnetic resonance: new applications for old materials

Isabelle Pianet ID a, Anna Gutiérrez Garcia-M. b, Marie-Claire Savin a,c, Pilar Lapuente Mercadal ID c, Marta Sánchez de la Torre d and François-Xavier Le Bourdonnec ID a

aIRAMAT-CRP2A, Université Bordeaux-Montaigne, CNRS, Maison de l'archéologie, Pessac, France; bICAC, Tarragona, Spain; cDepartamento de Ciencias de la Tierra, Area de Petrología y Geoquímica, Facultad de Ciencias, Universidad de Zaragoza, Zaragoza, Spain; dDepartamento de Ciencias de la Antigüedad (PPVE), Universidad de Zaragoza, Zaragoza, Spain

## ABSTRACT

Solid-state nuclear magnetic resonance, which enables the characterization of structures of a variety of materials whatever their crystallinity/amorphous state, is used in the present work to determine the provenance of two raw materials, namely marbles and cherts. Regarding marbles, the ¹³C NMR signal of the carbonate function contains information about both the Fe content in its area and the presence of calcium substitutions in the calcite crystal in its linewidth. Regarding cherts, discriminant information is provided by both ²⁹Si and ²⁷Al NMR: the ²⁹Si area signal depends on the paramagnetic ion content of the material, and the ²⁷Al spectra give information both on the aluminosilicate content and its distribution in tecto- and layer-lattice aluminosilicates. As an application, we use the differences observed from one source to another to determine the provenance of archaeological finds.

## ARTICLE HISTORY

Received 19 April 2019

Accepted 10 July 2019

## KEYWORDS

Cherts; marbles; solid state

NMR; provenance

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## Introduction

Determining the geographical origin of the raw materials used for precious artefacts such as prehistoric tools and ancient monuments/statues is a challenge that allows to get an essential insight to historical aspects of past societies. The analyst looks for some clues, up to traces of some minerals, crystalline phases, fossils while applying more and more statistical tools to analyse the data collected. The aim of the present work was to identify the provenance of two kinds of stone used at very different periods for different purposes: chert tools from the Magdalenian, and marbles, symbols of power and luxury whose prestige reached its apogee during the reign of the emperor Augustus (63 BC–14 AC). In this goal, we used a methodological approach combining traditional analysis methods with Nuclear

Magnetic Resonance (NMR). NMR has many advantages for the study of archaeomaterials: it is a non-destructive and versatile technique since it allows to probe the raw material without any previous preparation. While some NMR applications are able to be used in a non-invasive way without any sampling, using portable NMR instruments (mobile NMR), they are currently limited to detect the most sensitive nucleus, ¹H, in a liquid state (Baias and Blümich 2018). Alternatively, Solid State NMR spectroscopy permits to obtain detailed structural information of inorganic materials down to a few milligrams of powder, in a non-destructive way since the radiation used for this kind of spectroscopy is non-ionising (Stebbins and Xue 2014) making the collected samples available for further analyses. It also provides invaluable chemical information which cannot be obtained with other techniques since
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all nuclei of the periodic table having at least one NMR-active isotope can be analysed, their respective sensitivities being linked to both the natural abundance of the isotope chosen and its frequency resonance.

The first applications of NMR in the field of Cultural Heritage started less than 10 years ago, and were described in a review (Capitani, Di Tullio, and Proietti 2012), special issue (Capitani and Proietti 2015) and even book chapter (Webb 2018), showing that NMR is a very promising technology capable of investigating liquid, solid or even swollen samples by following isotopes with a non-zero nuclear spin of many different elements (Abragam 1961). Thus, NMR offers a very wide array of techniques for studying the structure and dynamics of organic or inorganic materials. For example, spectra of minerals were recorded soon after NMR development in the late 1940s, and the progress observed for this technique has advantageously contributed to the Earth Sciences domain (Mackenzie and Smith 2002). Probably more than other spectroscopic methods, NMR gives information on the immediate structural surrounding through the chemical shift values of the resonances observed in the spectrum, on the number of atoms involved in the different resonances through the signal area when the relaxation conditions are respected and the presence of defects in the component observed thanks to the breadth at half-height of the resonance (Engelhardt 1989). At last, the spin-lattice T1 relaxation process can vary in proportion of the paramagnetic impurities content present in natural materials (Goldman 2001) and can be estimated when spectra are recorded under saturation conditions.

Regarding marbles, the target was their major component, calcium carbonate, whose NMR signal response depends on its local environment, such as the presence of secondary elements (Gutiérrez et al. 2019), and its crystallisation state (dolomite vs. calcite) (Pianet et al. 2018). The Carbon nuclide ¹³C, which is the NMR detectable isotope present at 1% naturally, was targeted. Its signal contains information about both the Fe content in its area and the presence of calcium substitution in the calcite crystal in its linewidth. In a previous work, we successfully used ¹³C solid-state NMR for white marble provenance, and we were able to distinguish between fine-grained white marbles coming from quarries located in six different countries (France, Italy, Spain, Portugal, Turkey and Greece) and to use the NMR spectrum profile to identify the origin of some archaeologic items (Gutiérrez et al. 2019). In the present work, we focus our analysis on marbles from the district of Saint-Béat (Région Occitanie, Département Haute-Garonne, Pyrénées, France) and try to localize the origin of the marble used for two archaeological items from the Musée d'Aquitaine collection (Bordeaux, Région Aquitaine, Département de la Gironde, France).

Cherts are mainly composed of silicate, and to a lesser extent of aluminosilicate. Thus, the nuclides

commonly amenable to NMR measurements for this kind of mineral are ²⁹Si (natural abundance, 4%) and ²⁷Al NMR (natural abundance 100%) (Jakobsen, Jakobsen, and Lindgreen 1988). In the present work, solid-state NMR is used to get information in chert chemical structure, and to see if differences are observed depending on their geographic location. For this purpose, chert was collected from three different deposits of the Pyrénées (France), Montgaillard, Montsaunès and Buala (Sànchez de la Torre, Le Bourdonnec, and Gratuze 2019) and their ²⁹Si and ²⁷Al spectra compared with two archaeologic artefacts found in two different places (Montlléo -Prats i Sansor, Cerdanya, Spain- and Cova del Parco -Alòs de Balaguer, La Noguera, Spain) (Sànchez de la Torre 2015), and their provenances were successfully confirmed.

For the two kinds of lithic materials, marbles and cherts, studied herein, NMR spectroscopy has been successfully used as a tool for supporting decision-making for provenance identification.

# Materials and methods

## Samples

For marbles, white marbles were collected from four different quarries in the district of Saint-Béat: Boutx, Marignac, Saint-Béat Lavigne and Saint-Béat Château (see Figure 1 for their location). Samples were taken off two artefacts from the Musée d'Aquitaine collection for analyses purposes: a togatus (inventory number 60.2.19) and an altar dedicated to the Tutela Augusta (inventory number 60.1.20, ILA 17), both of them found at Bordeaux (Roman *Burdigala*).

For cherts, experiments were performed on geologic samples from three distinct sources from the Pyrénées (Montgaillard, Montsaunès and Buala) and samples were taken from two archaeologic items found in the Palaeolithic sites of Montlleó and Cova del Parco.

## Solid state NMR experiments

NMR experiments were recorded on a Bruker Avance II 400 (magnetic field of 9.4 T) equipped with a 4 mm CP-MAS probe (CESAMO facilities, Bordeaux, France).

For marbles, ¹³C MAS NMR spectra were recorded on 200 mg powdered samples at 100.6 MHz (9.4 T) and a spinning rate of 8 kHz; Single pulse-MAS spectra were collected with a recycling delay of 300 s, 32 transients and 2 dummy scans for a total experimental time of 170 min per sample.

For cherts, around 170 mg of powdered samples were used to record (i) ²⁹Si at 79.51 MHz (9.4 T) and a rotation rate of 8 kHz, using a single pulse sequence with a recycling delay of 50 s and 256 transients for a total experiment time of 4 h, a Cross-Polarization
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<figure><img src="image_7.png" /><figcaption>**Figure 1.** Location of the marble quarries in the district of Saint-Béat (Département Haute Garonne, Région Occitanie, France). Left: the black insert localizes the district of interest; Right: expansion of the geographical area.</figcaption></figure>

pulse sequence using a contact time of 6 ms, a recycling delay of 5 s and 6000 transients for a total experiment time of 10 h and (ii) $^{27}$Al at 104.3 MHz (9.4 T) and a rotation rate of 10 kHz, or 3 kHz using a single pulse experiment with a recycling delay of 0.5 s and 5120 transients for a total experiment time of 45 min.

Spectra were analysed using the NMR solid state fitting process (sola) of the Topspin 3.5, pl7 software (Bruker™).

## Results

### Marbles

In a previous paper (Gutiérrez et al. 2019), we demonstrated how $^{13}$C NMR was useful to determine the

provenance of some archaeologic items: the target is the principal component of marble, calcite, whose $^{13}$C NMR signal presents a specific profile (area and full width at half maximum, $\Delta\nu_{1/2}$) depending on its provenance. In this previous work, we demonstrated that the area depends on the iron content, when the linewidth reflects defects in the calcite crystal in

<table><caption>**Table 1.** Area and full width at half maximum of the $^{13}$C resonance of marbles from different geographic origins.</caption><thead><tr><td>Origin</td><td>Area</td><td>Δν<sub>1/2</sub> (Hz)</td></tr></thead><tbody><tr><td>Boutx (n = 3)</td><td>1.1 ± 0.3</td><td>84 ± 5</td></tr><tr><td>CM-Château (n = 2)</td><td>2.5 ± 0.2</td><td>74 ± 5</td></tr><tr><td>Marignac (n = 2)</td><td>3.5 ± 0.4</td><td>95 ± 10</td></tr><tr><td>MR-Lavigne (n = 3)</td><td>3.4 ± 0.4</td><td>114 ± 8</td></tr><tr><td>Togatus (60.2.19)</td><td>2.7</td><td>68</td></tr><tr><td>Altar (60.1.20)</td><td>2.9</td><td>62</td></tr></tbody></table>

<figure><img src="image_8.png" /><figcaption>**Figure 2.** $^{13}$C NMR spectra of white marbles from different quarries in the district of Saint-Béat: quarry "Château" in the Cap de Mont (CM-Château, purple); quarry "Lavigne" in the Mont-Rié (MR-Lavigne, green); quarry "Marignac" (grey); quarry "Boutx" (black).</figcaption></figure>
<figure><img src="image_9.png" /></figure>

<figure><img src="image_10.png" /><figcaption>**Figure 3.** $^{13}$C NMR spectra of the altar dedicated to the Tutele Augusta (left, 60.1.20) and of a togatus (right, 60.2.19) in black compared with a spectrum of saint-Béat, from the quarry Château, in grey.</figcaption></figure>

which the calcium is replaced by another atom such as
aluminium, strontium or magnesium. Thus, by com-
bining different geochemical methodologies such as
ICP-OES, XRD and NMR, with common petrological
techniques for the marbles considered (Gutiérrez
2011; Lapuente Mercadal 2014; Gutiérrez et al. 2016;
Royo Plumed 2016) we were able to distinguish the
marbles depending on their geological source. Also in
the present work, focused on the contribution of
solid-state NMR as a “decision-making” technique,
we extend this analysis to marbles coming from the
same region, the district of Saint-Béat (region Occita-
nie, France, Figure 1), for which further analyses are
still under investigation (notably ICP-OES and DRX).
Figure 2 presents $^{13}$C NMR spectra recorded for four
different quarries around the town of Saint Béat:
Boutx, Marignac, Lavigne (Saint-Béat, Mont Rié) and
Château (Saint-Béat, Cap du Mont). Table 1 displays

the area and linewidth measured for the white marbles
obtained in the previously mentioned quarries. Some
interesting differences can be outlined, and were used
to determine the geographic origin of the two artefacts
from the Musée d'Aquitaine of Bordeaux, whose petro-
graphic, cathodoluminescence and ¹³C/¹⁸O isotope sig-
nature features are characteristic of marbles coming
from this region of the Pyrénées (Royo Plumed et al.
2015; Royo Plumed et al. 2018).¹ The comparison of
the ¹³C spectrum of these artefacts with the different
marbles from the district of Saint-Béat permits to pro-
pose that they could be made of marble of the quarry
Saint-Béat Château (Figure 3).

Cherts

Considering the success of solid-state NMR for
decision-making purpose concerning marbles

<figure><img src="image_11.png" /><figcaption>**Figure 4.** $^{29}$Si MAS NMR spectra of Buala chert using a single pulse experiment (down) or a Cross-Polarization pulse sequence with a 6 ms contact time (top).</figcaption></figure>
<figure><img src="image_12.png" /><figcaption>**Table 2.** $^{29}$Si MAS NMR data obtained for three geologic cherts and two archaeologic items (Cova del Parco and Montlleó).</figcaption></figure>

<table><thead><tr><th></th><th>Total area</th><th>δ Q<sup>4</sup> (ppm)</th><th>Δν<sub>1/2</sub> Q<sup>4</sup> (Hz)</th><th>δ Q<sup>3</sup> (ppm)</th><th>Δν<sub>1/2</sub>Q<sup>3</sup> (Hz)*</th><th>Q<sup>3</sup>/Q<sup>4</sup></th></tr></thead><tbody><tr><td>Buala (n = 5)</td><td>2.0 ± 0.2</td><td>-104.5 ± 0.1</td><td>169 ± 15</td><td>-97.1 ± 0.4</td><td>383 ± 28</td><td>0.18 ± 0.05</td></tr><tr><td>Montsaunès (n = 6)</td><td>2.6 ± 0.2</td><td>-104.5 ± 0.1</td><td>189 ± 12</td><td>-97.0 ± 0.5</td><td>382 ± 15</td><td>0.18 ± 0.03</td></tr><tr><td>Montgaillard (n = 5)</td><td>1.1 ± 0.2</td><td>-104.5 ± 0.1</td><td>165 ± 16</td><td>-96.5 ± 1.5</td><td>402 ± 18</td><td>0.20 ± 0.02</td></tr><tr><td>Cova del Parco</td><td>1.9</td><td>-104.5</td><td>181</td><td>-97.1</td><td>436</td><td>0.22</td></tr><tr><td>Montlleó</td><td>2.8</td><td>-104.5</td><td>150</td><td>-96.8</td><td>413</td><td>0.24</td></tr></tbody></table>

<figure><img src="image_13.png" /><figcaption>**Figure 5.** Left. $^{29}$Si NMR spectra permitting the assignment of the provenance of two archaeologic cherts: one found at Cova del Parco (Blue) coming from Buala (Green) and the second one found at Montlleó (Red) coming from Montsaunès (Orange). Right. Map showing the location of the different geological and archaeological samples described in this work.</figcaption></figure>

provenance, we use a similar strategy for cherts. In the present case, $^{29}$Si and $^{27}$Al magic-angle-spinning (MAS) NMR experiments are used for the identification of the silicate minerals within cherts. The $^{29}$Si NMR spectrum (Figure 4) shows two components assigned to the Q$^4$ framework tetrahedral units – quartz- at –104.5 ppm and the Q$^3$ silanol units around –97 ppm, whose attribution is consistent with the enhancement of its resonance observed under the Cross-Polarization experiment (Adams, Hawkes, and Curzon 1991). The Q$^3$/Q$^4$ ratio is close to 0.2 whatever the sample, highlighting, as expected, the dominance of SiO$_4$ species. The line broadening observed for Q$^3$ and Q$^4$ species (Δν$_{1/2}$, Table 2) mainly reflects overlapping of different silicate structures of varying degrees of polymerization since spectra were recorded at Magic Angle spinning -MAS- with sufficient speed to cancel both dipole-dipole interactions and chemical shift anisotropy (Mackenzie and Smith 2002). Few differences can be observed on the Q$^4$ resonance notably concerning the Montsaunès sample whose line width is slightly higher than for Buala or Montgaillard. However, the most significant difference observed from one to another geologic chert samples is the signal area: it evolves from 1.1 for the Montgaillard sample to 2.6

for the one of Montsaunès (Table 2, Figure 5). This difference is not the consequence of a variable SiO$_2$ content –that is constant and close to 99.2 ± 0.2% as measured using XRF for each sample – but should be due instead to magnetic susceptibility arising from the presence of magnetic impurities (Oldfield et al. 1983), whose content plays a role in the transversal relaxation T1 of the NMR signal, as for marbles. Their measures were performed for each geological source and were estimated close to 270 s for Montsaunès, 440 s for Buala and 720 s for Montgaillard, confirming the role of T1 in the signal area.

$^{29}$Si spectra were also recorded for two archaeologic items found in different sites in the south Pyrenean Region (Figure 5). The comparison of their $^{29}$Si spectra with those performed for three different deposits permits to propose the following provenances, Buala for the chert coming from Cova del Parco and Montsaunès for the chert found at Montlleó (Figure 5, Table 2).

$^{27}$Al MAS-NMR experiments were also conducted on the different cherts samples. Despite the low aluminum abundance in cherts (less than 1% Sànchez de la Torre et al. 2017a), $^{27}$Al is a nucleus easy to observe by NMR, its natural abundance being of 100%, its gyromagnetic ratio comparable to one of

<footnote>*Measured from CP-AV experiments.</footnote>
<figure><img src="image_14.png" /></figure>

<figure><img src="image_15.png" /><figcaption>**Figure 6.** $^{27}$Al MAS-NMR spectra of MontSaunes Chert recorded at a 10KHz (bottom) or 3KHz (top) spinning rate. (*) represents the rotation side bands.</figcaption></figure>

$^{13}$C and short relaxation times. Due to these favourable properties, $^{27}$Al MAS-NMR spectra were obtained in a reasonable time (close to 1 h, Figure 6). Interestingly, two resonances are observed: the main one ($\delta_{iso}$ 52–54 ppm, see Table 3) assigned to a 4-coordinated Aluminosilicate (Al$^{IV}$), such as AlO$_4$ connected to SiO$_4$ tetrahedra of Q$^4$(4Si) type, and a minor resonance assigned to a 6-coordinated Al (Al$^{VI}$) occurring at 4–5 ppm such as AlO$_6$ (Guarino et al. 1997). The ability to distinguish octahedral and tetrahedral Al in inorganic compounds make possible the semi-quantitative estimate of their amount as shown in Table 3. The quadripolar nature of $^{27}$Al nuclei (spin 5/2) also requires the determination of the Chemical Shift Anisotropy (CSA) and the asymmetry parameter ($\eta$) that permit the determination of $\delta_{iso}$. To ensure a better estimation of these parameters, spectra were also recorded at a spin rate of 3000 Hz (Figure 6, top). All these values are reported in Table 3. First of all, the total area observed is representative of the content already measured for each sample using XRF as previously reported (Sànchez de la Torre et al. 2017b) (0.55% for Buala, vs. 0.35% for Montgaillard and Montsaunès). Another interesting measure is the Al$^{IV}$/Al$^{VI}$ ratio that appears to be different in the Montsaunès sample (7.3) compared to the one observed for Buala or Montgaillard (1.7 and 1.8, respectively).

As previously shown, some discriminant elements can be exploited to determine the geographic origin of archaeologic cherts such as the area signal of $^{29}$Si or even $^{27}$Al spectra combined with the Al$^{IV}$/Al$^{VI}$ ratio. Using these different data, we are able to assign the chert found at Cova del Parco to the Buala deposit when the Montlleó one appears to come from the Montsaunès place.

## Discussion

In the present work, we apply solid-state MAS-NMR spectroscopy for arch-aeometric purposes, notably to identify the provenance of archaeologic artefacts through two examples, Marbles and Cherts. The thread is the same, it consists of looking at the major component of the stone and inspecting the NMR response, which can be extremely sensitive to the chemical environment of the studied nucleus.

For marbles, the target was the calcite CaCO$_3$, and the nucleus tracked the carbon $^{13}$C. In a previous work (Gutiérrez et al. 2019), we demonstrate how the $^{13}$C nuclide was sensitive to the presence of paramagnetic species such as Fe$_2$O$_3$, by the intensity of the calcite signal and to the defects of the calcite crystals in which calcium could be replaced by another atom. This property, which was applied to marbles coming

<table><caption>**Table 3.** $^{27}$Al NMR quantities. $\delta_{iso}$, CSA and $\Delta\nu$ were obtained by fitting the Al$^{IV}$ resonance using the software TOPSPIN 3.5 (Bruker).</caption><thead><tr><th></th><th>Total Area</th><th>Al<sup>IV</sup></th><th>Al<sup>VI</sup></th><th>Al<sup>IV</sup>/Al<sup>VI</sup></th><th>δ<sub>iso</sub> (ppm)</th><th>η</th><th>CSA</th><th>Δν (Hz)</th></tr></thead><tbody><tr><td>Buala (n = 4)</td><td>160 ± 20</td><td>157 ± 20</td><td>3 ± 1</td><td>1.7 ± 0.7</td><td>53.4 ± 0.4</td><td>0.4 ± 0.1</td><td>37 ± 4</td><td>1050 ± 50</td></tr><tr><td>Montsaunès (n = 6)</td><td>128 ± 18</td><td>119 ± 18</td><td>8 ± 1</td><td>7.3 ± 1.3</td><td>53.3 ± 0.6</td><td>0.3 ± 0.2</td><td>34 ± 18</td><td>960 ± 100</td></tr><tr><td>Montgaillard (n = 5)</td><td>121 ± 22</td><td>117 ± 23</td><td>2 ± 1</td><td>1.8 ± 1.1</td><td>53.2 ± 0.9</td><td>0.8 ± 0.2</td><td>41 ± 28</td><td>1030 ± 140</td></tr><tr><td>Cova del Parco</td><td>169</td><td>167.5</td><td>2.5</td><td>1.5</td><td>52.1</td><td>0.3</td><td>30</td><td>1300</td></tr><tr><td>Montlleó</td><td>120</td><td>112</td><td>8</td><td>7.1</td><td>52.5</td><td>0.3</td><td>30</td><td>1200</td></tr></tbody></table>
<figure><img src="image_16.png" /></figure>

from different quarries of the Mediterranean basin (Turkish, Greek, Italian, Spanish and French quarries), is presently extended to neighbouring quarries from the district of Saint-Béat. Four of them were chosen due to their location regarding the Garonne river: Marignac and the quarry of Lavigne are on the left bank, in the Mont Rié while Boutx and Château on the right bank, in the Cap du Mont (see Figure 1). The ¹³C NMR spectra recorded are significantly different and thus, they can be used as a help to discriminate between marbles coming from this same district, which is usually very difficult to achieve through the usual archaeometric methods applied to the study of marbles. The two archaeologic items tested were probably made of the same marble, and the comparison of their spectra with those of marbles from studied quarries suggests that they were coming from that of Saint-Béat Château.

Concerning cherts, we target both the main component SiO₂ quartz-like structure – which represents up to 99% of the mineral content – using ²⁹Si NMR and their aluminosilicate contents – less than 1% – using ²⁷Al NMR, since this nuclide is recognized to be easy to observe, and permits the determination of Al(IV)/Al(VI) ratios (Jakobsen, Jakobsen, and Lindgreen 1988; Smith 1993). The ²⁹Si spectra of the three geologic Pyrenean deposits studied in this work present significant differences notably in the peak area of the major component Q⁴, that should be used as a discriminant element for provenance purpose. This phenomenon is the consequence of differences in “spin-lattice” or T1 relaxation from one sample to another attributed to different contents of magnetic impurities such as transition metals or rare earth cations. ²⁷Al spectra also present discriminant profiles: the total signal area, which reflects the aluminium-containing minerals and does not depend on the relaxation time since this nuclide is known to have short T1 and the distribution of the signal between two species Al (IV) and Al(VI). These discriminant NMR profiles served previous analyses for decision-making about the provenance of two archaeologic items, found in two different Pyrenean sites, Cova del Parco and Montleó. In fact, previous studies demonstrated that the Cr, Sr and Th trace elements levels permit to discriminate the Montgaillard flysch and the Montsaunes cherts (Sànchez de la Torre et al. 2017b), however the comparative petrographic and geochemical characterization of the archaeological sample from Cova del Parco does not fit with one or the other geologic site. The discovery of another geological outcrop near Montgaillard, Buala (Sànchez de la Torre, Le Bourdonnec, and Gratuze 2019), and the analysis of these artefacts and the Buala site by Micro-PIXE (Sànchez de la Torre et al. 2019) to determine major, minor and trace elements in cherts demonstrated that this latter site can be distinguished using PCA graphs. However,

some uncertainties still remain to attribute the provenance for the archaeologic chert tools. At this stage, ²⁷Al and ²⁹Si solid-state NMR can help to take a decision: with regards to the spectra profiles, we can propose that the artefact coming from Cova del Parco is made of Buala chert when the one of Montlléo, of Montsaunès demonstrating trans-Pyrenean human circulation on long distance associated to procurement strategies since the Magdalenian (13,700–18,800 BP).

In conclusion, solid-state NMR that is known to be useful for material characterization purpose can be also successfully used for provenance purposes. It supports the approaches commonly used, and helps for decision-making when the identification of the provenance could not be achieved by using them alone. Indeed, the different methods used to give information on the structure of the material under investigation according to different point of view: if NMR probes the ensemble of local environments around the nucleus observed in the material (C for marbles, Si or Al for cherts) whether it is crystalline or amorphous, powder X-ray Diffraction data will inform about the different crystalline components present and elementary analysis will track the content of secondary or trace elements. All these analyses combined with others (notably the isotopic ratio for marbles for which numerous data still exist (Gorgoni et al. 2002)) permit step by step to propose a provenance with confidence.

## Note

1. Unpublished data from the analysis undertaken within the framework of the ROMAE project (LaScArBx n°ANR-10-LAB-52).

## Acknowledgments

This project is part of (i) concerning marbles, the ROMAE project of the LaScArBx (programme funded by the ANR-N° ANR-10-LABX-52) and of a collaboration with the project HAR2015-65319-P (MINECO/FEDER) of the ICAC, Tarragona, Spain and (ii) concerning cherts, a Post-doctoral fellowship from the Initiative d'Excellence de l'Université de Bordeaux (M. Sánchez de la Torre). NMR analyses were performed at the CESAMO, ISM, Université de Bordeaux, Département Sciences et Technologie, and we want to thank the CESAMO team and especially Cybille Rossy for their help. We also want to thank A. Ziegle, curator of Roman antiquities at the Musée d'Aquitaine, for her precious help and Nathan McClenaghan for the English.

## Disclosure statement

No potential conflict of interest was reported by the authors.

## Funding

This research programme has been financially supported by the ANR (ANR-10-LABX-52) and the Université Bordeaux Montaigne PSE (Politique Scientifique d'Établissement).
<figure><img src="image_17.png" /></figure>

## Notes on contributors

**Dr Isabelle Pianet** received her Ph.D. in Biochemistry at the University of Bordeaux (1990) and entered at the CNRS as an Ingénieure de Recherche (1991). After 25 years at the Institut des Sciences Moléculaires in Bordeaux where she managed the analytical chemistry department CESAMO, she joined the IRAMAT-CRP2A laboratory. Her research focuses on the development of new tools such as NMR for sourcing purpose and for the characterisation of archaeological residues such as wine.

**Dr Anna Gutiérrez Garcia-M.** received her MA in Lithic and Ceramic Analysis for Archaeologists at the University of Southampton (2003) and her PhD in Archaeology at the Autonomous University of Barcelona (2007). She has developed her research at the Laboratory for the Study of Stones in Antiquity (LEMLA) at the UAB, the IRAMAT-CRP2A as Chaire Junior of the LaScArBx, and the Catalan Institute of Classical Archaeology (ICAC), where she is currently a Ramón y Cajal researcher and director of the Archaeometric Studies Unit.

**Marie Claire Savin** is currently preparing for his Ph.D. in Archaeometry between two Universities, Bordeaux Montaigne and Zaragoza. The theme of her research concerns the marble resources of the North of Spain, and their use/reuse during Antiquity and later.

**Dr Pilar Lapuente Mercadal** is a Lecturer in Petrology and Geochemistry at the University of Zaragoza, Department of Earth Sciences, where she received her Ph.D. in Geology in 1991. From October 1991 to December 1992, she got a postdoctoral fellowship to specialize in Archaeometry at diverse Institutions from U.K. In 1994, she received the award "young researchers of the Spanish Society of Mineralogy" for her contribution using TL (at the RLAHA of Oxford University), in the field of Mineralogy applied to architectural heritage. Her research is focused on Petrology and Geochemistry applied to Heritage and Archaeometry of lithic materials such as marbles, ceramics, pottery, building and decorative materials.

**Dr Marta Sánchez de la Torre** received her Ph.D. in Prehistory at the University of Barcelona (2015) and after this, she joined the IRAMAT-CRP2A as a postdoctoral researcher (funded by IdEx Bordeaux) between 2015 and 2017. In 2018 she joined the University of Zaragoza as a Juan de la Cierva postdoctoral researcher. Her research mostly focuses on the geochemical analysis of lithic raw materials from Palaeolithic periods. She is currently directing archaeological works at several Palaeolithic and Neolithic sites from the Pyrenean region as Parco Cave, Xicotó rockshelter and Montlleó open-air site.

**Dr François-Xavier Le Bourdonnec** is an Associate Professor in Archaeological Sciences at the Université Bordeaux Montaigne. Since 2002, his research has mainly focused on sourcing prehistoric lithic raw materials.

## ORCID

Isabelle Pianet http://orcid.org/0000-0002-2694-3133

Pilar Lapuente Mercadal http://orcid.org/0000-0002-8321-2396

François-Xavier Le Bourdonnec http://orcid.org/0000-0002-1051-5337

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<figure><img src="image_18.png" /></figure>

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