Crossing the Pyrenees during the Late Glacial Maximum. The use of geochemistry to trace past human mobility

Journal of Anthropological Archaeology 56 (2019) 101105

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Crossing the Pyrenees during the Late Glacial Maximum. The use of geochemistry to trace past human mobility

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Marta Sánchez de la Torrea,b, , Xavier Mangadob, Mathieu Langlaisb,c, François Xavier Le Bourdonnecd, Bernard Gratuzee, Josep Maria Fullolab a

IUCA-PPVE, Universidad de Zaragoza, 12 Pedro Cerbuna St., 50009 Zaragoza, Spain SERP, Universitat de Barcelona, 6-8 Montalegre St., 08001 Barcelona, Spain c PACEA (UMR 5199), Allée Geoffroy Saint-Hilaire, CS 50 023, 33615 Pessac, France d IRAMAT-CRP2A (UMR 5060), Maison de l’Archéologie, Esplanade des Antilles, 33607 Pessac Cedex, France e IRAMAT-CEB (UMR 5060), 3D rue de la Férollerie, 45071 Orléans Cedex 2, France b

A R T I C LE I N FO

A B S T R A C T

Keywords: Chert ED-XRF LA-ICP-MS Lithic procurement Upper Palaeolithic Pyrenees

Chert was one of the most used lithic raw materials by Palaeolithic groups to make their tools. Their characterisation is essential for determining their provenance and inferring mobility patterns and lithic procurement strategies. The Pyrenees -a mountain range traditionally viewed as a natural boundary between the Iberian Peninsula and the rest of the continental Europe- are the location of a number of Palaeolithic human occupations dating to the Late Glacial Maximum (LGM). One example is the open-air site of Montlleó (Prats i Sansor, Catalonia, Spain), located at more than 1000 m asl, whose excavation has demonstrated that the ice retreat in this area was earlier than believed and humans took advantage of this new environment as evidenced by the variety of raw materials in the community’s lithic assemblage. Energy-dispersive X-ray fluorescence (ED-XRF) and laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) are applied to a representative sample of chert tools from Montlleó as well as six geological formations from different areas of the Pyrenean region. The aim was to identify potential raw material sources using major, minor and trace elements. Results suggest that the Pyrenees were not a barrier to human mobility at that time.

1. Introduction Until the 1980s, there was an animated discussion among specialists concerning the environmental conditions that allowed human settlement on both sides of the Pyrenean axial zone during the Upper Pleistocene. While the northern side was believed to have suffered harsher glacial conditions, the southern slopes were viewed as having warmer conditions due to a combined diminished influence of the northern glaciers and the influence of the Mediterranean’s temperate climate. Several studies undertaken by Quaternary geologists (Bordonau et al., 1992) on the southern slope in the last decades established a Pyrenean Glacial Maximum at about 50,000 cal BP, followed by a relatively fast glacial retreat. The chronology of the Pyrenean Last Glacial Maximum (LGM) is thus somewhat out of synchronisation with the global LGM (Gillespie and Molnar, 1995); such chrono-climatic regional divergences have since been noted elsewhere (Bordonau et al., 1992; Bordonau et al., 1993; Delmas, 2015;

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Jalut and Turu, 2009; Pallàs et al., 2006). This climatic context related to the physical characteristics of the Pyrenean mountain range would have brought about two main biogeographic periods. The first was between 30,000 and 16,900 cal BP, with a typically glacial environment, having an open landscape of steppe vegetation. The second was between 16,900 and 11,700 cal BP, known as the “Last termination”, environmentally characterised by the alternation of cold and temperate phases, the latter allowing the development of a more grassy steppe and a progressive establishment of tree species (Jalut and Turu, 2009). This proposal, defined in a broad regional framework, is characteristic of the southern slopes of the Eastern Pyrenees, where the open-air site of Montlleó is located, at more than 1000 m asl, in one of the largest highattitude valleys in the Pyrenean region (Fig. 1). Environmental studies demonstrated that ice retreat in the Pyrenees was earlier than expected, making human occupation of this mountain range feasible during the Upper Palaeolithic. The discovery of the archaeological site of Montlleó and its excavation has proven that the

Corresponding author. E-mail addresses: [email protected] (M. Sánchez de la Torre), [email protected] (X. Mangado), [email protected] (M. Langlais), [email protected] (F.X. Le Bourdonnec), [email protected] (B. Gratuze), [email protected] (J.M. Fullola). https://doi.org/10.1016/j.jaa.2019.101105 Received 4 September 2018; Received in revised form 20 July 2019 0278-4165/ © 2019 Elsevier Inc. All rights reserved.

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Fig. 1. Montlleó open-air site location (top), archaeological grid (bottom left) and excavation detail area (bottom right).

interpreted as representing two distinct phases of human occupation. The typology of the lithic industry as well as several radiocarbon dates indicate that the most recent activity at Montlleó occurred during the Lower Magdalenian (20,666–22,486 cal BP, 19,134–18,525 cal BP and 18,873–18,538 cal BP), with a lithic technology based mainly on bladelets and blade debitage. The earliest occupation at the site was during the Badegoulian (22,960–22,486 cal BP), as characterised by the abundance of scaled flakes, raclettes. Moreover, the presence of some Solutrean shouldered points could indicate an even earlier phase of activity (Fullola et al., 2019) (Fig. 2). The characterisation of lithic raw materials at Montlleó would allow defining the territory frequented by Palaeolithic groups. The valley where the site is located –the Cerdanya Valley- provides a range of locally available siliceous materials suitable for knapping (including rhyolites, quartz, quartzite and lydites) that were used by the Montlleó hunter-gatherers (Sánchez de la Torre and Mangado, 2016), but the dominant raw material for tool production was chert, a resource that does not naturally appear in the valley. It thus follows that these cherts were being procured from other regions. The Montlleó lithic industry is presently comprised of more than 20,000 pieces, of which 2265 constitute finished tools and cores; it is this material that has been studied in detail for the initial raw material characterisation. Two periods of human occupation have been recognised until now. Nevertheless, differentiating between levels is not easy, as erosion processes affect the sediment. For this reason, the analysis of lithic raw materials is presented as a whole. The study takes into account several scales of analysis. After a first macroscopic and petrographic study to determine the texture and the micropalaeontological and inclusions content, geochemical methods (energy dispersive X-ray fluorescence and laser-ablation inductively coupled plasma mass spectrometry) were applied to precisely determine the origin of the exploited cherts. Firstly, a visual and micropalaeontological description was undertaken. This macroscopic characterisation was carried out using a binocular microscope Olympus SZ61 (from 6.7 to 45× magnification).

human occupation was not only feasible but real. The site is located in one of the most suitable ways to cross the eastern Pyrenees, and it has been demonstrated that contacts between both slopes were frequent from the late Upper Palaeolithic onward. The aim of this paper is to characterise lithic raw materials from Montlleó as a means of tracing the mobility patterns and territoriality of hunter-gatherer groups across the Pyrenees. Lithic raw material characterisations were incorporated into archaeological research projects some decades ago and are essential for understanding the relationship that hunter-gatherer groups had with their environment. Concerning the Pyrenean region, studies have mostly focused on the analysis of textural and petrographic characteristics (Briois, 2005; Foucher, 2004; Grégoire, 2000; Mangado, 2005; Normand, 2002; Ortega, 2002; Terradas, 2001) and only a few attempts to geochemically characterise chert artefacts have been made until now. Most of them have been dedicated to mineralogical determination (Roy-Sunyer, 2016), our recent analyses in the Central Eastern Pyrenees being the first attempts to analyse chert artefacts in the Pyrenean region based on macroscopic analysis and on geochemistry (Sánchez de la Torre et al., 2017b). Thus, this study was initiated to characterise chert raw materials with the aim of matching their petrographic and geochemical profiles with those of known source materials in order to provenance the Montlleó cherts as a means of determining the mobility of these groups as well as their most frequently used areas of raw material procurement. 2. Materials and methods 2.1. Montlleó lithic raw materials: the site, samples and first analyses Montlleó is located in the Eastern Pyrenees, at 1144 m asl, in one of the largest high-attitude valleys, the Cerdanya Valley, a natural pathway to cross the mountains following the axes of the Segre River to the south and the Têt River to the north. The site was discovered in the late 1990s and has been excavated since 2000 (Fullola et al., 2012; Mangado et al., 2015). Thus far the stratigraphic sequence is 2

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Fig. 2. Materials dispersion with the two archaeological levels and their representative lithic industry (top) and radiocarbon dates with calibration after OxCal v.4.3.2 (Ramsey, 2017) with IntCal13 atmospheric curve (Reimer et al., 2013) (bottom). Table 1 Outcrops selected for the study with the number of samples analysed. Name

Site

Formation

Age

ED-XRF

LA-ICP-MS

PC ED1 ED2 ED3 PM1 PM2A PM2B CDF ALF PERAL ALB1 ALB2 ZURI MENT

Puente Candasnos Étang du Doul 1 Étang du Doul 2 Étang du Doul 3 Port Mahon 1 Port Mahon 2A Port Mahon 2B Castelló de Farfanya Alfarràs Peraltilla Alberola 1 Alberola 2 Zurita Mentirosa

Aragonian limestones Lacustrine deposits (g3-m1) Lacustrine deposits (g3-m1) Lacustrine deposits (g3-m1) Lacustrine deposits (g3-m1) Lacustrine deposits (g3-m1) Lacustrine deposits (g3-m1) Castelltallat Fm Castelltallat Fm Castelltallat Fm Tartareu-Alberola Tartareu-Alberola Tremp Fm Tremp Fm

Miocene Oligocene-Aquitanian Oligocene-Aquitanian Oligocene-Aquitanian Oligocene-Aquitanian Oligocene-Aquitanian Oligocene-Aquitanian Oligocene Oligocene Oligocene Oligocene Oligocene Maastrichtian Maastrichtian

23 15 15 15 15 15 15 51 8 23 20 16 18 6

20 15 15 14 13 10 12 49 6 20 20 17 13 0*

2.2. Geological samples: surveys and first analyses

Images were taken using a coupled Olympus SC30 camera. As the aim of this study was to analyse both geological and archaeological samples, non-destructive techniques were prioritised. Nevertheless, we did undertake petrographic analyses on a selection of samples, selecting, when possible, at least two samples per type of chert. For the petrographic description, thin sections with thicknesses between 25 and 30 μm were prepared at the Servei de Làmina Prima laboratory of the University of Barcelona. Cherts in thin sections were analysed using a petrographic Olympus BX41 model microscope (from 40 to 400× magnification). The second stage of the study involved geochemical analyses to quantify major, minor and trace components so as to be able to compare the raw materials of the stone tools with those from known geological outcrops. For this part of the study we analysed 170 of the Montlleó chert artefacts by energy-dispersive X-ray fluorescence (ED-XRF). Forty of which were also analysed with laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS).

With the aim of comparing results obtained after the analysis of archaeological tools, geological formations with cherts having similar characteristics to those of the artefacts from Montlleó were surveyed and studied. This comprised all the lacustrine cherts from the CentralEastern Pyrenees and the Bages-Sigean basin (six geological formations in total), because the macroscopic analysis performed on the archaeological specimens suggested that they may have been the main chert sources used by these hunter-gatherers. To test that possibility, we undertook survey work at each location to systematically collect geological samples representative of the source’s internal variability. Two of the studied formations were located in the Bages-Sigean basin-, in the southeast of France, while the other four were situated in the southern Pyrenees and the Ebro basin, in northeast Iberia. Thus, after macroscopic observations and petrographic characterisations, a total of 255 samples from 14 different primary outcrops were selected for geochemical analyses (Table 1). Due to machine restrictions (samples too 3

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do not present evident marks of erosion, so a procurement in primary outcrops have to be supposed. With the aim of improving analysis time and to avoid surface alterations, geological samples were prepared in squares of 5 × 5 mm, removing cortex.

2.3. Geochemical analyses: ED-XRF and LA-ICP-MS To analyse major and minor elements, energy-dispersive X-ray Fluorescence (ED-XRF) was employed. Analyses were done at the Research Centre for Applied Physics in Archaeology, IRAMAT, Bordeaux, France. Nine element concentrations were quantified (Na, Mg, Al, Si, P, K, Ca, Ti, Fe) using an X-ray fluorescence spectrometer SEIKO SEA 6000 VX (Orange et al., 2016), using fundamental parameters corrected by the granodiorite GSP2 from the US Geological Survey (USGS) international standard (Wilson, 1998). A 3 × 3 mm collimator was prioritized, and analysis time was set to 400 s for each measurement condition (3 conditions with air or He environment and Cr or Pb filter were established). To check instrument calibration and accuracy, JCh-1 chert standard from the Geological Survey of Japan (GSJ) was employed (Imai et al., 1996). To prove and validate the formula which was used and to check instrument accuracy, a measurement with the JCh-1 chert standard was established, with the standard deviation obtained always being lower than 0.08 w%, validating the accuracy of the formula used (Sánchez de la Torre et al., 2017b). To analyse trace elements, we used laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) at the Ernest Babelon laboratory, IRAMAT, Orleans, France. Elements were quantified using a Thermo Fisher Scientific Element XR mass spectrometer associated with a Resonetics RESOlution M50e ablation device. This spectrometer has the advantage of being equipped with a dual mode (counting and analogue modes) secondary electron multiplier (SEM) with a linear dynamic range of over nine orders of magnitude, associated with a single Faraday collector which allows an increase in the linear dynamic range by an additional three orders of magnitude. This feature is particularly important for laser ablation analysis of lithic samples, as it is possible to analyse major, minor and trace elements in a single run regardless of their concentrations and their isotopic abundance. The ablation device is an excimer laser (ArF, 193 nm), which was operated at 7–8 mJ and 20 Hz and only if saturation was observed were conditions reduced to 10 Hz. A dual gas system with helium (0.65 l/min) released at the base of the chamber, and argon at the head of the chamber (1.1 l/min) carried the ablated material to the plasma torch. Ablation time was set to 40 s: 10 s pre-ablation to let the ablated material reach the spectrometer and 30 s collection time. Laser spot size was set to 100 μm, and only reduced to 80 or 50 μm if saturation was detected, and line mode acquisition was chosen to enhance sensitivity. Background measurements were run every 10–20 samples. Fresh fractures were analysed on geological samples to reduce potential contamination. Priority was given to characterising large samples; thus, only one ablation line was carried out per specimen. However, if element spikes due to the presence of inclusions or heterogeneities were observed during analysis, results were discarded and a new ablation location was selected. Calibration was performed using standard reference glass NIST610 which was run periodically (every 10–20 samples) to correct for drift. NIST610 was used to calculate the response coefficient (k) of each element (Gratuze, 1999, 2014), and the measured values of each element were normalised against 28Si, the internal standard, to produce a final percentage. Glass Standard NIST612 was analysed independently of calibration to provide comparative data. After doing some tests with 56 elements, a total of 29 elements were quantified (Li, Be, B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Ga, As, Rb, Sr, Y, Zr, Nb, Cs, Ba, La, Ce, Pr, Nd, Sm, W, Bi, Th, U).

Fig. 3. Types of chert identified at Montlleó based on the macroscopic and petrographic study.

big), samples from la Mentirosa could not be analysed by LA-ICP-MS. Only primary and subprimary outcrops were considered for this study as no secondary outcrop of lacustrine chert was identified in the areas studied. Moreover, when present in the archaeological record, cortices 4

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Fig. 4. Location of the archaeological site of Montlleó and the main outcrops that could had been exploited by past human groups (type 1 outcrops are not presented as they are analysed separately).

3. Results

and probably organic matter inclusions. Charophyte algae and gastrops constitute the main micropalaeontological content. At the petrographic level, microquartz mosaic fabric constitutes the main texture, with cementations of length-fast chalcedony and macroquartz. These cherts originated in a lacustrine sedimentary environment; six geological formations of chert with identical macroscopic and petrographic characteristics are known from the north and the south of the Eastern Pyrenees. Type 2 is comprised of 375 artefacts (21.4% of the sample), the raw material being characterised by the absence of bioclastic content, as they originated in a hypersaline sedimentation environment. The texture is quite smooth, with only a few inclusions of metal oxides and lenticular gypsum pseudomorphs identified. Microscopically, microquartz fabric is the main texture, but cementations of length-fast and length-slow chalcedony and macroquartz are also observed. Metal oxides and evaporitic evidence is abundant. Parallels can be drawn between this raw material, with Palaeocene cherts outcropping in the northern Pyrenean slopes (Petites Pyrénées), and sources from the Tremp formation, in the southern Pyrenees. Type 3 is represented by 209 artefacts (11.9% of the sample), the chert being macroscopically characterised by a homogeneous texture composed of abundant metal oxides and detrital quartz crystals. The main micropalaeontological content is composed of sponge spicules and, in some cases, macroforaminifera are identified, probably Omphalocyclus macroporus and Siderolites. Under the petrographic microscope, a microquartz mosaic fabric is the main texture, with the occasional appearance of length-fast chalcedony. This type of chert can

3.1. Macroscopic and petrographic characterizations: chert types and related formations Over three-quarters of the 2265 finished tools and cores from Montlleó were made of chert (1752, 77%). Rhyolites made up 14% of the assemblage, with quartz and quartzite accounting for 3% and 2% of the dataset respectively. The remaining 4% is composed of other rocks. The macroscopic and petrographic observation of the Montlleó chert has allowed us to determine seven different types (Fig. 3). Two types (1 and 2) appear to be the preferred raw materials –comprising c. 30% and 20% of the chert assemblage respectively. Types 3 and 4 appear regularly in the stratigraphic sequence (with averages between 7 and 12%), while types 5, 6 and 7 are the least frequently documented cherts (always less than 20 artefacts per type), suggesting that these raw materials were only occasionally being procured. In some cases, it was possible to establish a connection between archaeological raw materials and specific chert outcrops on the basis of macroscopic and petrographic analyses alone, specifically with regard to types 3, 4, 6 and 7 (Fig. 4). In other cases –specifically types 1 and 2-, the geological materials displayed identical macroscopic and petrographic characteristics, whereby geochemical analyses were required to discriminate the sources. Type 1 is the dominant group, represented by 535 artefacts (30.5% of the sample). Macroscopically this chert possess a heterogeneous texture with metal oxides, micritic residues, grains of detrital quartz 5

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carbonate residues and probably organic matter. Charophyte algae, gastropods and ostracods form the micropalaeontological content. At a microscopic scale, a microquartz mosaic fabric is the main texture. Length-fast chalcedony was identified filling pores, as well as macroquartz. Subangular detrital quartz rarely appears. The Castelltallat formation (Rupelian, Oligocene) largely outcrops in Serra Llarga (IGME, 1998), a mountain range located between the towns of Castelló de Farfanya and Alfarràs (Lleida, Spain), in the contact between the Pre-Pyrenees and the Central Depression (Anadón et al., 1989). Nodular cherts appear within the stratified limestone, more than 40 primary outcrops having been identified along the Serra Llarga (Mangado, 2005). The presence of chert nodules from the Castelltallat formation was also noticed near the village of Peraltilla (Huesca, Spain), several kilometres to the west of Serra Llarga and close to the Cinca River (Sáez, 1987). Cherts from the Castelltallat formation are quite homogeneous, possessing similar textural, micropalaeontological and petrographic features in nodules collected within Serra Llarga outcrops (CDF) and the Peraltilla outcrop (PERAL). A macroscopic heterogeneous texture, with metal oxides, carbonate remains, detrital quartz and probable organic matter was observed during the textural characterisation. Charophyte algae and lacustrine gastropods are the representative micropalaeontological content. Concerning the petrographic description, the primary silica texture is a microquartz mosaic fabric, length-fast chalcedony appearing in some cases. That said, a variability was detected in cherts outcropping near the town of Alfarràs (ALF), possessing an inhomogeneous texture and orange to reddish colours though the micropalaeontological content and the petrographic characteristics were mostly similar to the samples collected at other outcrops. The Tartareu-Alberola cherts (Rupelian, Oligocene) appear within the lacustrine stratified limestones outcropping in the San Miquel mountain range, a Pre-Pyrenean mountain chain located to the north of Serra Llarga and being limited by the Noguera Ribagorzana River to the west and the Farfanya River to the east, a tributary from the Segre River (IGC, 2008). Two primary outcrops were identified during the surveys. This chert possesses macroscopic heterogeneous textures with metal oxides and micritic remains. The micropalaeontological content is formed of Charophyte algae and gastropod sections. A microquartz mosaic fabric is the main texture at the petrographic scale, with some vestiges of length-fast chalcedony. The Aragonian limestone formation containing chert nodules (Aquitanian-Vindobondian, Miocene) outcrops near Candasnos, in the Central Depression of the Middle Ebro Basin (IGME, e.p.). This chert possesses irregular nodular morphologies with homogeneous textures with metal oxides, carbonate remains, probably organic matter and detrital quartz crystals. Charophyte algae and gastropod sections make up the micropalaeontological content. At the microscopic scale, a microquartz mosaic fabric is the main texture, with some length-fast chalcedony and macroquartz cementations. Two different groups of outcrops of lacustrine deposits (g3-m1) with chert nodules (Oligocene-Aquitanian) occur in the Bages-Sigean Basin, in SE France (Gregoire et al., 2009). The first one is constituted by Port Mahon cherts (close to Sigean), with three different outcrops (PM1, PM2A & PM2B), while the Étang du Doul group, near Peyriac-deMer, has three different outcrops (ED1, ED2 & ED3). The cherts from the studied outcrops all possess similar macroscopic and petrographic characteristics. There are cherts with nodular morphologies and homogeneous textures with metal oxides, carbonate remains and probably organic matter. Charophyte algae and gastropod sections are the main micropalaeontological content. At the microscopic scale, a microquartz mosaic is the main texture, with some length-fast chalcedony and some macroquartz cementations.

directly be related to two chert formations outcropping in the northern slopes of the Central Pyrenees, namely the Montgaillard flysch cherts (Turonian-Santonian) and the Montsaunès-Buala cherts from the Nankin formation (Middle Maastrichtian). Type 4 is composed of 131 artefacts (7.5% of the sample). Macroscopically this type of chert is constituted by inclusions of metal oxides, abundant detrital quartz crystals, calcite or dolomite rhombohedral crystals and probably organic material as impurities. Sponge spicules and small foraminifera (globigerinids) comprise the micropalaeontological content. Under the petrographic microscope a microquartz mosaic fabric is observed as the main texture, being the only silica texture identified. Type 4 can directly be related to cherts from the Agua-Salenz Formation (Conacian), outcropping in the southern slopes of the Central Pyrenees, near the Turbón Massif. Type 5 is represented by 10 artefacts (0.6% of the sample), the chert having a heterogeneous texture with metal oxide inclusions and some macroforaminifera as Alveolinidae. Due to the limited number of artefacts made of this type of chert, we were not able to prepare thin sections for petrographic analyses. Concerning its macroscopic features, this raw material cannot be linked to any of the Pyrenean geological materials included in this study. This suggests that this raw material and tools made of this chert were procured from regions at greater distance, potentially the product of exchanges between Palaeolithic groups. Type 6 is composed of 18 artefacts (1% of the sample). Macroscopically this chert type is comprised of some metal oxides and abundant rhombohedral crystals of calcite or dolomite in the process of dissolution. As with type 5, the rarity of tools made of this raw material meant that we were unable to conduct petrographic analyses. Nevertheless, the macroscopic characteristics allow us to directly relate this raw material type to cherts from the Corones Formation, outcropping near the Cerdanya Valley, in the southern slopes of the Cadí mountain range. Finally, type 7 is represented by only one tool (0.1% of the sample). This artefact possesses a homogeneous texture characterised by the presence of a few metal oxides, micritic residues and an abundance of macroforaminifera, such as Lepidorbitoides and Siderolites as well as Bryozoaires. This chert type, despite being represented by only one sample, possesses a characteristic micropalaeontological content that allows us to directly relate this raw material to the Chalosse cherts that outcrops in southwest France. Moreover, the association between some macroforaminifera observed in the artefact from Montlleó allows us to relate this artefact’s raw material more specifically with the Maastrichtian cherts outcropping in Audignon, where the association between Lepidorbitoides, Siderolites and Bryozoaires has been documented. The presence of type 7 chert in the Montlleó lithic assemblage thus constitutes clear evidence for long distance interactions. 3.2. Lacustrine cherts: main geological formations As detailed in the previous section, the macroscopic and petrographic analysis of the Montlleó chert artefacts allowed us to connect some of the raw materials with specific geological formations. This was not, however, the case with the assemblage’s dominant raw material, the type 1 chert, whose macroscopic and petrographic characteristics were perceived to be identical to those of specimens from a number of geological outcrops (Figs. 5 and 6). An initial description of these formations is presented in the next section. The Tremp formation (Maastrichtian, Upper Cretaceous) possesses a level of laminated micritic limestones with Charophyte algae and gastropod moulds filled with sparite (IGME, e.p.). This formation, which also contains a nodular chert level, outcrops in the Carrodilla mountain range, a Pre-Pyrenean foothill located between the Cinca River Basin to the west and the Noguera Ribagorzana River to the east. The outcrops identified (MENT & ZURI) possess chert with a macroscopic heterogeneous texture with impurities of mineral oxides,

3.3. Geochemical analyses: ED-XRF results ED-XRF analyses were undertaken to quantify major and minor 6

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Fig. 5. Visual, macroscopic and petrographic views of the six main geological lacustrine cherts. A: Tremp Formation cherts (Zurita); B: Castelltallat Formation cherts (Peraltilla); C: Tartareu-Alberola cherts (Alberola 1); D: Aragonian cherts (Candasnos); E: Oligocene cherts (Port Mahon); F: Oligocene cherts (Étang du Doul).

northwest corner of the boxplot, also outside the dispersion of the archaeological cherts. These are located in the southwest corner, and very close to the cherts from the Tremp Fm (ZURI & MENT), the Aragonian limestones (PC) and those from the Aquitanian-Oligocene outcrops near Peyriac-de-Mer (ED1, ED2 and ED3), plus the cherts from the Castelltallat formation (CDF, ALF & PERAL). A scatterplot that only takes into account those elements with higher values (SiO2, CaO and Al2O3) is shown in Fig. 8, presented in the form of Ln Al2O3/SiO2 vs Ln CaO/SiO2. This represents all the geological and archaeological cherts from Montlleó, and produces similar results to those obtained by the PCA. Thus, taking into consideration the dispersion of the archaeological cherts, it is possible to highlight that cherts from the Castelltallat formation (CDF, ALF & PERAL) and cherts from the Bages-Sigean basin outcropping near Peyriac-de-Mer (ED1, ED2 & ED3) are the raw materials that best fit the data generated from the Montlleó cherts. In turn, the geological cherts from the Tartareu-Alberola (ALB 1 & ALB 2) and Port Mahon (PM1, PM2A & PM2B)

elements. While nine oxides were targeted (Na2O, MgO, Al2O3, SiO2, P2O5, K2O, CaO, TiO2 and Fe2O3), data relating to Na2O and P2O5 were limited, as their values were almost always below the instrument’s detection limits. With the obtained data, median values were calculated for each group (Table 2) and a Principal Component Analysis (PCA) was run to see if quantified distinctions were visible at the major and minor elemental levels. Principal Component Analysis (PCA) was calculated using XLSTAT software (Addinsoft, 2017). PCA of the nine elements measured by ED-XRF with the median of each outcrop shows that some differences can indeed be observed immediately between formations using this technique (Fig. 7). 81.36% of the total variance - F1 (57.14%) and F2 (24.22%) is represented in the PCA. Cherts from the Tartareu-Alberola (ALB 1 & ALB 2) are located in the southeast corner of the biplot, far away from the median value of the archaeological cherts of Montlleó. Moreover, cherts from the lacustrine deposits (g3-m1) of the Aquitanian-Oligocene, outcropping near Port Mahon (PM1, PM2A & PM2B) are located in the 7

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Fig. 6. Location of the archaeological site of Montlleó and the main outcrops containing lacustrine cherts (type 1). Table 2 Median value by group with the 9 elements quantified by ED-XRF. Variable

Al2O3

CaO

Fe2O3

K2O

MgO

Na2O

P2O5

SiO2

TiO2

Alberola 1 Alberola 2 Alfarràs Castelló de Farfanya Mentirosa Montlleó Peraltilla Port Mahon 1 Port Mahon 2A Port Mahon 2B Puente Candasnos Zurita Étang du Doul 1 Étang du Doul 2 Étang du Doul 3

0,971 0,750 0,558 0,605 0,312 0,754 0,416 0,041 0,036 0,215 0,377 0,430 0,300 0,477 0,351

3,015 2,879 0,360 2,165 0,178 0,252 2,753 3,166 2,090 1,613 0,282 0,282 0,152 0,699 0,182

0,274 0,209 0,183 0,099 0,013 0,046 0,088 0,051 0,041 0,037 0,015 0,017 0,009 0,029 0,019

0,163 0,124 0,050 0,033 0,010 0,041 0,047 0,035 0,025 0,026 0,023 0,017 0,011 0,021 0,013

0,094 0,082 0,148 0,018 0,000 0,040 0,000 0,415 0,436 0,107 0,007 0,000 0,010 0,012 0,005

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0,002 0 0 0 0,013 0 0 0 0 0

95,440 95,924 98,689 97,068 99,483 98,858 96,681 96,289 97,369 97,986 99,294 99,253 99,519 98,759 99,425

0,043 0,034 0,011 0,013 0 0,007 0,016 0,001 0 0,001 0,003 0 0 0,003 0,001

3.4. Geochemical analyses: LA-ICP-MS results

outcrops are once again seen as not matching the general data dispersal of the archaeological raw materials. Finally, cherts from the Aragonian limestones (PC) and the Tremp formation (ZURI & MENT), while not exactly matching the dispersion area of the Montlleó data, are not that far away, and as such we cannot exclude them as potential raw material sources used by these prehistoric groups. Our PCA and scatterplot analyses thus demonstrate that after the quantification of major and minor elements by ED-XRF we can eliminate two of the six geological formations as sources of the raw materials used to make the Montlleó stone tools (Tartareu-Aberola [ALB 1 & ALB 2] and Port Mahon [PM1, PM2A & PM2B].

In order to refine the information that could help link geological sources to Montlleó, we also conducted LA-ICP-MS analysis to quantify a wider assay of trace elements (n = 29). The data, when investigated using PCA, revealed similar results as those obtained by ED-XRF (Fig. 9, Table 3). The boxplot (Fig. 9) accounts for 73.75% of the total variance after the PCA – F1 (57.66%) and F2 (16.09%) - and reveals that archaeological samples from Montlleó had chemical profiles that closely matched those from the Castelltallat formation cherts (Castelló de

8

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Fig. 7. Results of Principal Component Analysis (PCA) of the 9 elements quantified by ED-XRF with the median of each outcrop accounting for the 81.36% of the total variance.

Fig. 8. Scatterplot concerning Ln Al2O3/SiO2 vs Ln CaO/SiO2 and representing all the geological outcrops (squares in colours) and the archaeological samples from Montlleó (black points). 9

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Fig. 9. Results of Principal Component Analysis (PCA) of the 29 elements quantified by LA-ICP-MS with the median of each outcrop accounting for 73.75% of the total variance.

can see that the data from the artefacts fits well with those generated from the geological cherts of the Castelltallat formation from the Castelló de Farfanya outcrop (in brown). In contrast, the geological samples from the two other outcrops of the Castelltallat formation –Alfarràs and Peraltilla- are not represented on the scatterplot, as they do not fit within the main dispersion of the Montlleó artefact data and so can thus be discounted as raw material sources for the occupations of this site. The scatterplot further indicates that the geological cherts from all the geological outcrops and archaeological samples from Montlleó are

Farfanya, Alfarràs, Peraltilla), the Aragonian limestone cherts (Puente Candasnos), the Tremp formation cherts (Zurita) and the OligoceneAquitanian cherts from Étang du Doul (1, 2 and 3). Once again, the Tartareu-Alberola cherts (Alberola 1 and 2) as well as the Port Mahon cherts (Port Mahon 1, 2A and 2B) can clearly be seen as different from the archaeological raw materials. With the aim of further discriminating between the more suitable chert outcrops following the ED-XRF results, we produced a scatterplot (Fig. 10) showing Ln W/U vs Ln As/U. In the upper part of the chart one

Table 3 Median value by group with the 29 elements measured by LA-ICP-MS. Variable

Li

Be

B

Mg

Al

Si

Ca

Ti

V

Cr

Fe

Ga

As

Rb

ALB 1 ALB 2 ALF CDF Montlleó PERAL PM 1 PM 2a PM 2b PC ZURI ED 1 ED 2 ED 3

20,67 18,72 9,40 13,48 10,54 15,46 7,21 13,36 13,12 7,13 2,44 1,85 7,41 8,25

0,51 0,40 0,28 0,16 0,13 0,16 0,05 0,04 0,07 0,23 0,07 0,04 0,07 0,04

41,97 39,49 39,17 56,48 47,82 62,91 16,55 18,11 26,95 43,78 31,32 51,09 23,05 22,34

2571 2819 1150 550 195 1347 11,500 25,671 4342 173 238 146 324 186

9713 7722 3008 2237 1223 3300 1703 898 3248 965 470 160 267 328

406,164 417,379 455,427 450,453 460,072 421,341 383,870 388,694 435,055 461,256 456,861 460,713 456,742 460,654

71,674 58,013 7906 20,437 8297 61,376 109,748 86,296 35,125 7146 14,378 9213 14,618 8540

519,14 504,68 160,83 172,98 90,00 246,92 106,01 57,09 183,53 153,24 94,46 27,33 30,63 52,82

19,39 14,38 9,17 4,76 7,23 8,44 6,13 5,07 10,36 2,33 2,80 1,74 2,54 2,32

13,44 11,42 6,00 4,73 3,16 7,48 10,54 8,68 19,31 4,65 3,91 2,80 3,00 2,63

4522 3501 4176 1299 754 2009 1245 1162 2949 372 625 430 691 741

28,72 24,59 23,34 13,13 9,54 32,84 21,86 18,98 77,76 2,75 3,67 8,04 31,98 58,95

11,22 4,01 29,13 8,13 3,51 12,50 0,96 1,46 1,18 2,10 4,15 2,92 0,61 3,42

16,61 13,66 4,93 3,47 1,93 6,00 3,98 2,31 9,78 1,99 1,18 0,17 0,39 0,38

Variable

Sr

Y

Zr

Nb

Cs

Ba

La

Ce

Pr

Nd

Sm

W

Bi

Th

U

ALB 1 ALB 2 ALF CDF Montlleó PERAL PM 1 PM 2a PM 2b PC ZURI ED 1 ED 2 ED 3

293,51 326,29 52,00 63,10 25,74 399,93 654,42 1242,04 1452,57 16,26 25,63 68,03 39,47 44,17

1,32 2,17 0,48 0,47 0,42 0,58 0,52 0,50 0,67 0,15 0,12 0,06 0,13 0,12

10,62 8,81 2,38 2,80 2,02 2,87 3,28 3,76 4,92 0,84 1,06 0,68 1,34 1,72

1,58 1,48 0,42 0,49 0,34 0,62 0,87 0,41 2,24 0,39 0,29 0,15 0,35 0,47

1,04 0,87 0,32 0,19 0,11 0,83 0,47 0,28 1,10 0,10 0,13 0,03 0,03 0,03

138,56 117,61 109,71 58,20 33,27 158,78 58,96 69,33 238,37 8,09 15,98 23,80 148,31 236,25

3,82 2,70 0,71 0,62 0,78 1,20 0,79 0,57 2,17 0,27 0,18 0,10 0,18 0,24

7,66 5,88 2,14 1,33 1,17 2,43 1,83 1,50 3,75 0,57 0,40 0,23 0,36 0,48

0,78 0,61 0,18 0,16 0,16 0,25 0,19 0,15 0,38 0,06 0,10 0,03 0,04 0,06

2,91 2,37 0,68 0,53 0,54 1,07 0,75 0,59 1,29 0,22 0,15 0,09 0,12 0,17

0,50 0,49 0,14 0,13 0,13 0,19 0,15 0,15 0,22 0,04 0,06 0,09 0,04 0,05

0,40 0,26 9,44 0,58 0,06 2,20 0,29 0,08 0,25 2,53 2,49 0,12 0,14 0,18

0,14 0,09 0,14 0,11 0,12 0,20 0,05 0,05 0,07 0,11 0,68 0,69 0,09 0,19

1,42 1,21 0,36 0,36 0,21 0,51 0,24 0,23 0,48 0,13 0,10 0,04 0,07 0,09

11,13 4,43 320,46 52,99 7,77 4,54 3,33 2,79 1,79 113,84 3,87 1,36 2,02 1,93

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Fig. 10. Scatterplot for Ln W/U vs Ln As/U and representing all the geological outcrops (squares in colours) and the archaeological samples of Montlleó (black points): on the top, the suitable outcrops fitting with the dispersion of Montlleó and on the bottom, the rejected outcrops.

material groups within the archaeological record. Macroscopic and microscopic analyses are not always sufficient when it comes to determining the exact source of raw material acquisition, or discriminating between geo-spatially distinct outcrops that possess identical features at these scales of analysis. This was the case with regard to the type 1 cherts from Montlleó. As the six geological formations potentially exploited by past human groups possessed identical features from a macroscopic and petrographic point of view, the determination of the source area was not possible. For this reason, geochemical analyses were undertaken to define the specific geochemical signature of each chert type. The aim was to establish differences between formations and thus to discriminate between the various geological raw materials and ultimately connecting the products of specific outcrops with the archaeological cherts. Through quantifying major and minor elements by ED-XRF, then employing PCA and a SiO2, CaO and Al2O3 scatterplot, it was then possible to discard two of the six potential sources. Finally, by employing LAICP-MS analyses to generate a wider array of trace elemental data (then employing a scatterplot using W, U and As values), it was then possible to match the chemical signatures of the Montlleó type 1 cherts with those of the geological cherts outcropping in Castelló de Farfanya (Castelltallat formation) and near Peyriac-de-Mer (Étang du Doul). Such a combination of analytical techniques has thus enabled us to produce robust new data concerning prehistoric lithic procurement at Montlleó (Fig. 11). As noted from the outset, a range of locally available

represented. On the top is presented the scatterplot with the archaeological samples and the geological cherts from Étang du Doul outcrops (1, 2 and 3, in green colour), which also matched well with the main dispersion of the artefact data. The PCA plots of both the ED-XRF and LA-ICP-MS data suggested that the geological cherts from the Tremp formation (Zurita) and the Aragonian limestones (Candasnos) were potentially represented at Montlleó. However, the lower scatterplot in Fig. 10, employing W, U and As, now enables us to discard these sources as they do not fit with the general dispersion of the archaeological data. In this way, LA-ICPMS analyses have provided greater discriminatory power for our studies, particularly when employing certain trace elements not available to us through ED-XRF, specifically W, U and As. These elements allow us to directly connect the archaeological cherts from Montlleó with geological sources outcropping in Castelló de Farfanya (Castelltallat formation) and near Peyriac-de-Mer (Étang du Doul). 4. Discussion The textural and micropalaeontological analysis of cores and tools recovered at Montlleó allowed us to determine the presence of several lithic raw materials exploited by these Late Pleistocene hunter-gatherers. The combination of macroscopic analysis with petrographic characterisation forms the basis of any archaeopetrological study, as these techniques allow us to define the existence of different raw 11

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Fig. 11. Location of the archaeological sites of Montlleó, Cova Alonsé and Forcas I Shelter and the connected outcrops for Montlleó chert tools after the archaeopetrological study.

nearly 200 km to the southwest, and can be accessible by following the Segre River. The archaeopetrological analysis of the lithic tools from Montlleó thus indicates: (1) that the Cerdanya Valley represented an important territory for these hunter-gatherers – indicated by their use of local siliceous resources – rather than simply a route across the Pyrenees; (2) that direct connections were probably established with the BagesSigean Basin, in the northern Pyrenees, maybe following the Têt River axis; (3) that direct relation was also established with the southern PrePyrenees and the Ebro Basin, probably via the Segre River; (4) that these groups’ territory included both the Pyrenean slopes and further into the Central Pyrenees –as attested by the presence of cherts from the Agua-Salenz formation and the Montgaillard-Montsaunès types; (5) that the presence of Maastrichtian cherts demonstrates these groups’ interaction with intermediary populations via exchange, rather than longdistance direct procurement. Data recovered during this archaeopetrological study can also be related to those produced by similar studies from sites located in northeast Iberia and the south of France, not least the recently published studies of lithic raw materials procurement at Cova Alonsé and Forcas I Shelter (Huesca, Spain) (Sánchez de la Torre, 2014; Sánchez de la Torre et al., 2017b; Sánchez de la Torre and Mangado, 2013). Both sites are located on the southern slope of the Central Pre-Pyrenees, in the Cinca River axis, and were also frequented during the first phases of the Magdalenian. The archaeopetrological and geochemical analyses of these artefacts has shown that groups at both sites also exploited lacustrine cherts from the Castelltallat formation (Sánchez de la Torre et al., 2017a). Additionally, the Forcas I Shelter also produced evidence of marine cherts from the Montgaillard and Montsaunès-Buala groups, of the Pyrenees’ northern slope. If we take the results of these studies

siliceous raw materials were exploited for tool production by the hunter-gatherers of Montlleó, including quartz, quartzite, rhyolites and lydites. These rocks outcrop in primary and secondary positions in the Cerdanya Valley, where the site is located, and are easily accessible 2–15 km from the site. The use of local rocks indicate that the site was not just a short-term occupation for those traversing the Pyrenees. The presence of non-local cherts within the assemblage provides valuable data concerning these prehistoric peoples’ larger territory and/or web of social connections (depending on whether the raw materials were produced directly or indirectly). In this way, the discovery of cherts from the northern slopes of the Pyrenees (cherts from Étang du Doul, cherts from Montgaillard and Montsaunès-Buala types and also Maastrichtian cherts) bring to light the direct connection with the northern slope of the Pyrenees. While type 3 (marine cherts from Montgaillard and Montsaunès-Buala) appears regularly but scarcely, lacustrine cherts from type 1 from the Bages-Sigean basin (Étang du Doul cherts), at some 100 km away, are the main chert used throughout both occupation phases. Moreover, the presence of some Maastrichtian chert tools, whose outcrops are more than 300 km distant, suggest long distance procurement strategies. Furthermore, our study has demonstrated the presence of cherts from the southern slope of the Pyrenees, with the regular but low-level procurement of raw materials from the Agua-Salenz marine formation and the lacustrine cherts from the Castelltallat formation. Cherts from the Agua-Salenz formation are located near the Turbón Massif, in the Central Pre-Pyrenees, at more than 150 km west of Montlleó, a journey that would necessarily involve having to cross several mountain chains to reach the outcrops. Concerning the Castelltallat formation cherts, and taking into account that this type was the most exploited chert at Montlleó, the distance between the site and the closest outcrops is 12

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from the Spanish Government and SGR2017-11 from the Catalan Government. This research program has also been financially supported by the ANR (no. ANR-10-LABX-52) and Région Nouvelle Aquitaine. Authors are indebted to Tristan Carter and Otis Crandell for the English revision of the manuscript and to the anonymous reviewers for their comments, helping to increase the quality of the paper.

together, then it can be argued convincingly that during the Upper Palaeolithic the groups occupying the area today defined as northeast Iberia and the south of France operated within a large territory that comprised both Pyrenean slopes, having lithic raw materials which circulated by direct or indirect acquisition systems over hundreds of kilometres. Consequently, the study presented here indicates that the Pyrenees were not a barrier during the Upper Palaeolithic. This statement, believed to be true until the mid-decades of the past century, was based on the fact that the ice retreat started later than expected. During the last decades of the past century, environmental analyses of the Pyrenean region increased, demonstrating that the ice retreat in this mountain chain occurred earlier than expected, such that large areas of the Pyrenean mountain range were free of ice during most of the Upper Palaeolithic period. Thus, archaeological research in the Pyrenean region increased in recent years, with interesting results indicating past human settlements since the Upper Palaeolithic, and maybe the Middle Palaeolithic (Mangado et al., 2010; Utrilla et al., 2010). Nevertheless, while the settlement of human groups in the Pyrenees was already documented by recent archaeological works and new data about ice retreat suggested more suitable environmental conditions, the existence of contacts between both Pyrenean slopes was not recognized.

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5. Conclusion In this paper we presented a complete and detailed archaeopetrological study aimed at characterising the types of chert used to make stone tools at the LGM site of Montlleó, as a means of determining the raw materials’ geological sources, and by extent the location and scale of these hunter-gatherers’ territories. This involved the first nondestructive analysis of c. 500 geological chert samples from both Pyrenean slopes. The results from such a large-scale sample have confirmed the value of geochemistry in such chert sourcing studies, and more specifically the analytical utility of ED-XRF and LA-ICP-MS techniques. By using data from the ED-XRF analysis of major and minor elements we were able to immediately achieve a certain level of source discrimination amongst the most geologically pertinent outcrops. Subsequent determination of trace elements using LA-ICP-MS allowed us to achieve further distinctions between sources, eventually enabling us to match the major chert raw materials employed at the site with two specific geological outcrops. The determination of the chert procurement areas for the groups that settled the open-air site of Montlleó, has provided invaluable information concerning human mobility strategies in northeast Iberia at the end of the Upper Palaeolithic. For the first time it has been demonstrated that the most popular raw materials at Montlleó had their origins in chert sources to both the north and south of the Pyrenees. The questions we now need to ask are whether it was the same group that alternatively procured cherts from both sides of the mountain, or was the site a place where groups gathered from several different regions? Forthcoming analysis of other archaeological assemblages from both Pyrenean slopes will hopefully increase our knowledge about huntergatherer populations, their economic behaviour concerning lithic raw materials procurement and their mobility patterns. Acknowledgements The research leading to these results has received funding by a postdoctoral fellow from the Ministry of Economy, Industry and Competitiveness through the Juan de la Cierva post-doctoral program (grant agreement n. FJCI-2016-27911) and the People Program (Marie Curie Actions) of the European Union’s Seventh Framework through the PRESTIGE program (grant agreement n. PCOFUND-GA-2013-609102), both held by M. Sánchez de la Torre. Archaeological works have been supported by “Middle and Upper Segre Valley during Prehistory” project, funded by the Catalan Government and projects HAR 2017-86509 13

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