Trade Networks in the Neighbouring Roman Provinces of Aquitania-Tarraconensis on the Bay of Biscay: Evidence from Petrographic and Chemical Analyses of Common Coarse Ware Pottery
Abstract
This research was funded by Fundación José Miguel de Barandiaran Fundazioa, grant number 2004, and the Basque Country government, grant number IT1442-22. The APC was funded by the Basque Country government, grant number IT1442-22.
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Citation: Alonso-Olazabal, A.; Zuluaga, M.C.; Martínez-Salcedo, A.; Esteban-Delgado, M.; Izquierdo-Marculeta, M.T.; Rechin, F.; Ortega, L.Á. Trade Networks in the Neighbouring Roman Provinces of Aquitania-Tarraconensis on the Bay of Biscay: Evidence from Petrographic and Chemical Analyses of Common Coarse Ware Pottery. Minerals 2023,13, 887. https:// doi.org/10.3390/min13070887 Academic Editor: Alberto De Bonis Received: 14 April 2023 Revised: 27 June 2023 Accepted: 27 June 2023 Published: 29 June 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). minerals Article Trade Networks in the Neighbouring Roman Provinces of Aquitania-Tarraconensis on the Bay of Biscay: Evidence from Petrographic and Chemical Analyses of Common Coarse Ware Pottery Ainhoa Alonso-Olazabal 1,*, Maria Cruz Zuluaga 1, Ana Martínez-Salcedo 2, Milagros Esteban-Delgado 3, Maria Teresa Izquierdo-Marculeta 4, François Rechin 5and Luis Ángel Ortega 1,* 1Department of Geology, University of the Basque Country (UPV/EHU), Sarriena s/n, 48940 Leioa, Spain; [email protected] 2Sociedad para el Estudio de la Cerámica Antigua en Hispania (SECAH), P.O. Box 33, 28086 Madrid, Spain; [email protected] 3Faculty of Social and Human Sciences, University of Deusto, Mundaiz Kalea 50, 20012 Donostia, Spain; [email protected] 4Basque Cultural Heritage Centre, Basque Government, Donostia-San Sebastian Kalea 1, 01010 Vitoria-Gasteiz, Spain; [email protected] 5ITEM (UR 3002), Universitéde Pau et des Pays de l’Adour, Av. du Doyen Poplawski, 64000 Pau, France; [email protected] *Correspondence: [email protected] (A.A.-O.); [email protected] (L.Á.O.) Abstract: Common non-wheel-thrown Roman pottery from the southern Aquitania and north-eastern of Tarraconensis provinces (CNT-AQTA) of the Early and Later Roman Empire (1st to 5th centuries AD) has been studied. Petrological, mineralogical, and chemical analyses were conducted to contrast with the archaeological study of the pottery. The chemical composition of many pottery samples displays different patterns of burial chemical modification, limiting their use for provenance and diffusion studies. Particular emphasis has been paid to the petrographic features of the fabrics, as they do not change during burial, reflecting the nature of the raw material and making it possible to identify the provenance areas of the raw materials. Around the Bay of Biscay, the same pottery tradition continued in the neighbouring provinces during Roman times. Petrographic studies make it possible to determine the distribution of pottery and the changes in trade networks during the Roman period across the area of the Bay of Biscay being studied. Keywords: coarse pottery; burial chemical modifications; provenance areas; trade networks; Bay of Biscay; Roman Empire 1. Introduction Pottery is an important source for the reconstruction of the socio-economic framework of different periods and cultures since it provides clues not only about technological skills, but also about cultural and trade networks [ 1 – 3 ]. The Roman period is a particularly good example of how the analysis of pottery distribution reveals patterns of exchange and interaction between different areas or societies. At Roman sites in the Mediterranean and Atlantic regions, both fine and coarse wares are profuse, revealing trade between the Mediterranean Sea and Atlantic Ocean and evidencing not only long-distance movements but also cross-border trade relations. The Roman occupation of the neighbouring areas of the northern Iberian Peninsula and southern France is well documented by numerous archaeological excavations carried out in this geographic area [ 4 – 12 ]. The communication network, by both terrestrial and maritime routes, linking the Cantabrian coast to the rest of the Roman world, is well Minerals 2023,13, 887. https://doi.org/10.3390/min13070887 https://www.mdpi.com/journal/minerals
Minerals 2023,13, 887 2 of 21 known [ 13 – 19 ]. The connection between the Cantabrian coast and the coasts of Aquitaine and Brittany was mentioned by Caesar (CAES. Gal.3.26.6), Strabo (STR. 3.4.18) and Orosius (OROS. Hist.6.21.4) in de Soto [ 20 ]. Important harbours such as Oiasso (Irun), Lapurdum (Bayonne) and Burdigala (Bordeaux) as well as secondary harbours in rivers and estuaries (e.g., Portus Amanum-Flaviobriga in Castro Urdiales, Forua in Gernika, Zarautz, Donostia and Hondarribia) have been identified for the trade of goods (e.g., wine, fish products, lard, broad beans and mineral resources). All of them articulated a network of ports that guaranteed maritime communications around the Bay of Biscay [ 21 – 26 ]. The maritime route was active together with the main continental roads of Ab Asturica-Burdigalam and secondary routes crossing the Pyrenees, Tarraco-Oiasso and Pisoraca VI-Portu Amamus. Maritime, waterway, and continental routes constitute the main trading communication network operating in the eastern Cantabrian region, linking the Roman provinces of Aquitania and Tarraconensis. In this way, the northeast of Hispania was fully integrated into the framework of Roman trade across the Cantabrian Sea. The most frequent type of pottery found at Roman sites on the Bay of Biscay ( Sinus Aquitanicus ) was the common non-wheel-thrown pottery, known as “cerámica común no torneada Aquitano-Tarraconensis” (CNT-AQTA) [ 27 ]. This type of pottery occurs at all sites on the Cantabrian coast, in Aquitaine and in the middle and upper Ebro valleys [ 4 , 27 , 28 ]. Very few studies about this coarse pottery have been carried out due to its rough appearance and lack of aesthetic appeal. However, in recent decades, interest in this type of pottery has increased due to its multiple uses in everyday activities, allowing coarse pottery to be used as a tool for assessing the way of life in Roman settlements. The studied pottery was collected from sites in the neighbouring imperial provinces of Tarraconensis and Aquitania, in different administrative districts, but within the organisational framework of the Roman state. Some sites were associated with productive activities (Arbiun) or funerary activities (Santa Elena). Other sites correspond to different settlement models: urban centres (Iruña/Veleia), civitas Aqvensium (Dax) or Lapurdum (Bayonne), rural settlements or villae (Aloria, Lalonquette and Pardies). Small temporary settlements (Moliets) and coastal enclaves with industrial and maritime activities (Forua, Santa María la Real and Zarautz-Jauregia) were also considered. Finally, the Santiagomendi site represents the transition from the pre-Roman way of life to the new Roman socio-economic, political and cultural patterns [29,30]. Mineralogical, petrographic, and chemical analyses were conducted to support the archaeological study based on the examination of ware shape, style, colour, decoration, and the overall fabric of the pottery. Petrographic, mineralogical, and chemical characterisation can provide significant information on raw material provenance and potentially the technology involved in the manufacturing process. The aim of this study is to assess the petro-mineralogical and geochemical composition to determine differences in the composition and provenance of Roman coarse pottery, to define an accurate distribution pattern and to establish connections with different Roman period productions (1st–5th AD centuries) to trace the evolution of trade networks around the Bay of Biscay. 2. Geological Background The structure and geology of the studied region are highly complex as a result of the convergence of the Iberian and Eurasian plates during the Cretaceous-Miocene. The Bay of Biscay and the western Pyrenean domains represent a strongly structured region as a consequence of consecutive extensive and compressive tectonic cycles that started in the early Palaeozoic. The Palaeozoic basement complex, known in the studied area as the Palaeozoic Basque Massifs: Aldudes, Cinco-Villas and Ursuya massifs, is formed by Ordovician to Carboniferous sedimentary rocks, limestones, sandstones and shales where Permian Aya granite and andesite dykes intruded, and the Ursuya massif consists of high-grade granulites, paragneisses and migmatites. During the Permian-Early Triassic, a red detrital unit was deposited in extensional conditions with abundant volcanic materials. Later Triassic to Jurassic rift events developed the formation of intracontinental
Minerals 2023,13, 887 3 of 21 basins filled by thick sequences of siliciclastics, carbonates, and evaporites with associated mantle-derived intrusions, ophites. The latest Triassic and Jurassic marine transgression resulted in marls and limestone deposits. During the early Cretaceous, extension led to the development of several troughs that consist of limestones, sandstones and marls that are surrounded by continental and platform domains covered by thick fluvial to deltaic sandstones and marls, and shallow marine limestones. Extreme crustal thinning in the Bay of Biscay led to the exhumation of the subcontinental mantle and resulted in continental breakup and seafloor spreading initiation. This event was recorded by the deposition of deep marine sediments and was accompanied by alkaline magmatism, both intrusive and volcanic, from the late Aptian to the early Santonian. The beginning of compressional deformation is marked by a regional unconformity in Santonian sediments. The transition from post-rift to syn-orogenic evolution is recorded by the deposition of siliciclastic turbidites dated from the Cenomanian to the Eocene, topped by Oligocene sandstones, conglomerates and evaporites. The major collision phase was reached during the Eocene and continued until the end of the Oligocene with the generalised uplift of the chain and the formation of foreland basins. Between the late Miocene and the early Pleistocene, in the north Pyrenean foothills, the last main fluvial depositional stage occurred with siliciclastic fan deposits fed by the erosion of the Pyrenees and the Massif Central. During the Pleistocene, foothills underwent strong incisions on stage, developing alluvial sheets, some of them controlled by glacial pulses. The climatic alternations, oscillations in sea level and a succession of episodes of excavation and filling in the hydrographic network promoted the tiering of alluvial terraces along the rivers, and the north-westerly winds developed dune deposits along the Atlantic edge [31–33]. 3. Materials and Methods 3.1. Materials The pottery included in the present study corresponds to Roman non-wheel-thrown pottery productions from different archaeological sites in the eastern Cantabrian region (Spain) and southern Aquitaine (south France) on the Bay of Biscay (Figure 1). The pottery analysed corresponds to rough, handmade domestic pottery, mainly used for everyday activities (cooking, table and storage ware). This unsophisticated pottery, coarse and essentially functional, lacks major changes in form and stylistic evolution over the course of the centuries. The selected samples correspond to the most representative and profusely common non-wheel-thrown pottery productions at the studied sites. The macroscopic analysis based on the abundance and grain-size of inclusions, firing conditions, hardness, fracture, compaction, and finishing allowed us to classify the potteries into three main groups, named G1, G2 and G3 productions [ 4 , 28 , 29 , 34 ]. G1 production (86 potsherds) is composed of grey (7.5R 6/0, 7.5R 5/0), with some superficial patches of reddish-yellow (5YR 5/8) and light red (2.5YR 6/8). This production shows medium sand grains with well-sorted white, grey, black, reddish, golden and silver rounded inclusions (0.5–2 mm). The fabric is hard and rough, with a smooth fracture. The G2 production (45 sherds) is composed of various grey (7.5R 4/0; 7.5R 5/0), grey-pink (7.5YR 6/2) and yellow-reddish (5Y 6/6) bodies with scarce voids. This medium-coarse sand-grained (0.5–3 mm) fabric is characterised by poorly sorted white, grey, brownish, blackish, reddish, and silver inclusions. The fabric is hard and rough, with a smooth fracture. The G3 group (55 potsherds) is reddish-orangish (5YR 5/6; 2.5YR 5/8) coloured at the external borders and grey (7.5R 6/0; 7.5R 5/0) coloured in fresh cuts or the internal body. Medium-coarse sand-grained (0.5–3 mm) fabric is characterised by poorly sorted white, grey, silver, and golden inclusions with voids. The inclusions are different in type, abundance, and size. The fabric is hard and rough, with smooth fractures. The studied G1, G2 and G3 groups correspond to the G3, G1 and G2 pottery groups described by Martínez-Salcedo [ 34 ]. A total of 186 potsherds were selected for the archaeometric analyses from eight Tarraconensis archaeological sites and eight Aquitania
Minerals 2023,13, 887 4 of 21 sites. The main distinguishing features are summarised in Figure 2and correspond to various types of wares, mainly pots, plates, jars and bowls (Table S1). Minerals2023,13,8874of22 Figure1.Geographiclocationofthearchaeologicalsiteswheresampleswereanalysedaroundthe BayofBiscay:sitesofAloria(Amurrio,Araba);Iruña‐Veleia(IruñadeOca,Araba);Forua‐PeñaFo‐ rua(Forua,Bizkaia);Getaria‐ZarautzJauregia(Getaria,Gipuzkoa);SantaMariaLaReal(Zarautz, Gipuzkoa);Arbium(Zarautz,Gipuzkoa);SantaElena(Irun,Gipuzkoa);Santiagomendi(Astigar‐ raga,Gipuzkoa)inTarraconensianprovince,Spain.SitesofSaint‐Paul‐en‐Born(Landes,Nouvelle‐ Aquitaine);Moliets‐et‐Maa(Landes);Bayonne(Nouvelle‐Aquitaine);Dax(Landes,Nouvelle‐Aqui‐ taine);Lalonquette(Pyrénées‐Atlantiques,Nouvelle‐Aquitaine);Pardies(Peyrehorade,Landes); Sorde‐l’Abbaye(Landes,Nouvelle‐Aquitaine);Lescar(Pau,Nouvelle‐Aquitaine)inAquitanian province,France. Theselectedsamplescorrespondtothemostrepresentativeandprofuselycommon non‐wheel‐thrownpotteryproductionsatthestudiedsites.Themacroscopicanalysis basedontheabundanceandgrain‐sizeofinclusions,firingconditions,hardness,fracture, compaction,andfinishingallowedustoclassifythepotteriesintothreemaingroups, namedG1,G2andG3productions[4,28,29,34].G1production(86potsherds)iscomposed ofgrey(7.5R6/0,7.5R5/0),withsomesuperficialpatchesofreddish‐yellow(5YR5/8)and lightred(2.5YR6/8).Thisproductionshowsmediumsandgrainswithwell‐sortedwhite, grey,black,reddish,goldenandsilverroundedinclusions(0.5–2mm).Thefabricishard andrough,withasmoothfracture.TheG2production(45sherds)iscomposedofvarious grey(7.5R4/0;7.5R5/0),grey‐pink(7.5YR6/2)andyellow‐reddish(5Y6/6)bodieswith scarcevoids.Thismedium‐coarsesand‐grained(0.5–3mm)fabricischaracterisedby poorlysortedwhite,grey,brownish,blackish,reddish,andsilverinclusions.Thefabricis hardandrough,withasmoothfracture.TheG3group(55potsherds)isreddish‐orangish (5YR5/6;2.5YR5/8)colouredattheexternalbordersandgrey(7.5R6/0;7.5R5/0)coloured infreshcutsortheinternalbody.Medium‐coarsesand‐grained(0.5–3mm)fabricischar‐ acterisedbypoorlysortedwhite,grey,silver,andgoldeninclusionswithvoids.Thein‐ clusionsaredifferentintype,abundance,andsize.Thefabricishardandrough,with smoothfractures.ThestudiedG1,G2andG3groupscorrespondtotheG3,G1andG2 potterygroupsdescribedbyMartínez‐Salcedo[34].Atotalof186potsherdswereselected forthearchaeometricanalysesfromeightTarraconensisarchaeologicalsitesandeight Aquitaniasites.ThemaindistinguishingfeaturesaresummarisedinFigure2andcorre‐ spondtovarioustypesofwares,mainlypots,plates,jarsandbowls(TableS1). Figure 1. Geographic location of the archaeological sites where samples were analysed around the Bay of Biscay: sites of Aloria (Amurrio, Araba); Iruña-Veleia (Iruña de Oca, Araba); ForuaPeña Forua (Forua, Bizkaia); Getaria-Zarautz Jauregia (Getaria, Gipuzkoa); Santa Maria La Real (Zarautz, Gipuzkoa); Arbium (Zarautz, Gipuzkoa); Santa Elena (Irun, Gipuzkoa); Santiagomendi (Astigarraga, Gipuzkoa) in Tarraconensian province, Spain. Sites of Saint-Paul-en-Born (Landes, Nouvelle-Aquitaine); Moliets-et-Maa (Landes); Bayonne (Nouvelle-Aquitaine); Dax (Landes, Nouvelle-Aquitaine); Lalonquette (Pyrénées-Atlantiques, Nouvelle-Aquitaine); Pardies (Peyrehorade, Landes); Sorde-l’Abbaye (Landes, Nouvelle-Aquitaine); Lescar (Pau, Nouvelle-Aquitaine) in Aquitanian province, France. Minerals2023,13,8875of22 Figure2.Synopticsketchofmacroscopicandmicroscopicfeaturesofthethreemainpotterypro‐ ductions.Freshsamplephotographs:diametercorrespondsto1cm.Photomicrographs:widthof fieldcorrespondsto2.4mm.Geometricsymbolsinthesynopticsketchcorrespondtoinclusionsof differentcompositions. 3.2.Methods ThepetrographicstudywasperformedonthinsectionsusingaNikonEclipse LV100polpolarisedlightmicroscopeequippedwithaDSF‐11digitalcameraandDSL‐2 controlunitattheLaboratoryoftheDepartmentofGeology,UniversityoftheBasque Country(UPV/EHU).Eachthinsectionwasanalysedunderplaneandcross‐polarised transmittedlighttoevaluatethemineralogyandclaymatrixcharacteristicsaccordingto [35,36],withspecialattentiontosomeaspectsdescribedin[37–39]. Chemicalcompositionanalysisofmineralinclusionswascarriedoutonpolishedcar‐ bon‐coatedthinsectionsusingaJEOLJSM‐6400ScanningElectronMicroscope(SEM) (JEOL,Tokyo,Japan)equippedwithanINCAEDXdetectorX‐sightSeriesSi(Li)Oxford pentaFETmicroanalysissystem. PotterymineralogicalcompositionwasanalysedbyX‐raydiffraction(XRD)usinga PhilipsX’Pertdiffractometer(MalvernPANalytical,Almelo,TheNetherlands)equipped withgraphitemonochromatoradjustedtoCu‐kα1X‐radiationoperatingat40kVand20 mA.Thedatacollectionwasperformedinacontinuousscanrangingfrom5to70°2θat acquisitionrateof0.02°2θpersecond.Themineralphaseidentificationandsemi‐quanti‐ tativedeterminationswereperformedusingX’PertHighScorePlus3.0software(Malvern PANalytical,Almelo,TheNetherlands).Semiquantitativeanalysesofthemineralphase wereobtainedusingtheexperimentalreferenceintensityratio(RIR)foreachmineralin thesample. Themajorandtraceelementanalysisforpotterysherdswascarriedoutusinga ThermoX‐Series2quadrupoleICP‐MS(ThermoFisherScientific,Bremen,Germany),af‐ terfusionof250mgoffinelygroundsamplewith500mghigh‐puritygradeLiBO2(anal‐ ysisgradepure,CorporationScientifiqueClaisse)inPt‐Aucrucibles,followedbynitric aciddissolutionofthemelt.Thesamplepreparationandconditionsofmeasurements wereperformedfollowingtheprocedureofGarcíadeMadinabeitiaetal.[40].Allthe analyseswerecarriedoutattheAdvancedResearchFacilities(SGIker)oftheUniversity oftheBasqueCountry(UPV/EHU). Figure 2. Synoptic sketch of macroscopic and microscopic features of the three main pottery productions. Fresh sample photographs: diameter corresponds to 1 cm. Photomicrographs: width of field corresponds to 2.4 mm. Geometric symbols in the synoptic sketch correspond to inclusions of different compositions.
Minerals 2023,13, 887 5 of 21 3.2. Methods The petrographic study was performed on thin sections using a Nikon Eclipse LV100pol polarised light microscope equipped with a DSF-11 digital camera and DSL-2 control unit at the Laboratory of the Department of Geology, University of the Basque Country (UPV/EHU). Each thin section was analysed under plane and cross-polarised transmitted light to evaluate the mineralogy and clay matrix characteristics according to [ 35 , 36 ], with special attention to some aspects described in [37–39]. Chemical composition analysis of mineral inclusions was carried out on polished carbon-coated thin sections using a JEOL JSM-6400 Scanning Electron Microscope (SEM) (JEOL, Tokyo, Japan) equipped with an INCA EDX detector X-sight Series Si (Li) Oxford pentaFET microanalysis system. Pottery mineralogical composition was analysed by X-ray diffraction (XRD) using a Philips X’Pert diffractometer (Malvern PANalytical, Almelo, The Netherlands) equipped with graphite monochromator adjusted to Cu-k α1 X-radiation operating at 40 kV and 20 mA. The data collection was performed in a continuous scan ranging from 5 to 70 ◦ 2 θ at acquisition rate of 0.02 ◦ 2 θ per second. The mineral phase identification and semiquantitative determinations were performed using X’Pert HighScore Plus 3.0 software (Malvern PANalytical, Almelo, The Netherlands). Semiquantitative analyses of the mineral phase were obtained using the experimental reference intensity ratio (RIR) for each mineral in the sample. The major and trace element analysis for pottery sherds was carried out using a Thermo X-Series 2 quadrupole ICP-MS (Thermo Fisher Scientific, Bremen, Germany), after fusion of 250 mg of finely ground sample with 500 mg high-purity grade LiBO2 (analysis grade pure, Corporation Scientifique Claisse) in Pt-Au crucibles, followed by nitric acid dissolution of the melt. The sample preparation and conditions of measurements were performed following the procedure of García de Madinabeitia et al. [ 40 ]. All the analyses were carried out at the Advanced Research Facilities (SGIker) of the University of the Basque Country (UPV/EHU). 4. Results 4.1. Petrographic Analysis The microstructure characteristics, considering amount, grain-size, sorting, roundness and sharpness, as well as the nature of components, allowed the identification of different petrographic fabrics within the three main pottery productions. The abundance and distribution of the petrographic types at the archaeological sites are shown in Figure 3. Minerals2023,13,8876of22 4.Results 4.1.PetrographicAnalysis Themicrostructurecharacteristics,consideringamount,grain‐size,sorting,round‐ nessandsharpness,aswellasthenatureofcomponents,allowedtheidentificationof differentpetrographicfabricswithinthethreemainpotteryproductions.Theabundance anddistributionofthepetrographictypesatthearchaeologicalsitesareshowninFigure 3. Figure3.Distributionofpetrographicfabricsatthestudysites.Eachpointrepresentsonesample. Right:locationofthesites.Eachsymbolrepresentadifferentpetrographicfabric. TheG1fabricgroupisformedbytwopetrographicfabrics,TP1.1andTP1.2.The fabricTP1.1ishighlyabundant,comprising95%oftheG1groupofwares(82samplesof n=86intheG1assemblage).Thefabricshowsaveryhomogeneousmatrix/inclusions ratio.Thegroundismainlyclayey.Porespresentasingle‐spacedrelateddistributionand areorientedparalleltothemargins.Thenonplasticinclusions(35%–45%)presentaclosed tosingle‐spacedrelateddistributionandarecommonlyorientedparalleltothemargins. Thesubangular‐subroundedinclusionsdisplaytypicallyaunimodalgrainsizedistribu‐ tion,arewellsorted,andhavegrainsizesrangingbetween0.25and0.50mm.Theinclu‐ sionscorrespondtoawidevarietyofrockandmineralfragments.Therockfragments includesedimentaryrocks(greywackes,ferruginoussandstones),metamorphicrocks (schistsandslates,sometimeswithcrenulationschistosity,gneisses,high‐grademetamor‐ phicrockswithepidoteandoccasionalmylonites),plutonicandvolcanicrocks(diorites, basaltsanddiabaseswithophitic/subophitictexture).Withinmineralfragments,mono‐ andpolycrystallinequartz,idiomorphicevaporiticquartz,epidote,plagioclase,perthitic potassiumfeldspar,amphibole,sparitecalcitenodules,micriticnodules,spathiccalcite, blackishinclusionsandrarebiotitelaths,pyroxenes,garnets,etc.havebeenrecognised (Figure4a–c).Somegrogfragmentsarealsoobserved.ThefabricTP1.2showssimilar featurestoTP1.1,althoughitisdistinguishedbytheoccurrenceofhigh‐sphericityquartz inclusionswithahomogeneousgrainsize(Figure4d). Figure 3. Distribution of petrographic fabrics at the study sites. Each point represents one sample. Right: location of the sites. Each symbol represent a different petrographic fabric.
Minerals 2023,13, 887 6 of 21 The G1 fabric group is formed by two petrographic fabrics, TP 1.1 and TP 1.2. The fabric TP 1.1 is highly abundant, comprising 95% of the G1 group of wares (82 samples of n= 86 in the G1 assemblage). The fabric shows a very homogeneous matrix/inclusions ratio. The ground is mainly clayey. Pores present a single-spaced related distribution and are oriented parallel to the margins. The nonplastic inclusions (35%–45%) present a closed to single-spaced related distribution and are commonly oriented parallel to the margins. The subangular-subrounded inclusions display typically a unimodal grain size distribution, are well sorted, and have grain sizes ranging between 0.25 and 0.50 mm. The inclusions correspond to a wide variety of rock and mineral fragments. The rock fragments include sedimentary rocks (greywackes, ferruginous sandstones), metamorphic rocks (schists and slates, sometimes with crenulation schistosity, gneisses, high-grade metamorphic rocks with epidote and occasional mylonites), plutonic and volcanic rocks (diorites, basalts and diabases with ophitic/subophitic texture). Within mineral fragments, monoand polycrystalline quartz, idiomorphic evaporitic quartz, epidote, plagioclase, perthitic potassium feldspar, amphibole, sparite calcite nodules, micritic nodules, spathic calcite, blackish inclusions and rare biotite laths, pyroxenes, garnets, etc. have been recognised (Figure 4a–c). Some grog fragments are also observed. The fabric TP 1.2 shows similar features to TP 1.1, although it is distinguished by the occurrence of high-sphericity quartz inclusions with a homogeneous grain size (Figure 4d). Minerals2023,13,8877of22 Figure4.RepresentativethinsectionphotomicrographsoftheG1fabricceramicfromdifferentsites. (a):FabricTP1.1fromArbiumsite(sampleARBI‐10,PPL).(b):Inclusionsofcalcitespar,carbonate fragmentsandepidoteincludedinTP1.1fabricfromBayonnesite(sampleBAY‐36,PPL).(c):Cal‐ cite,epidote,andpyroxeneinclusionsoftheTP1.1fabricfromZarautzsite,(SNR‐18,PPL).(d): TextureoftheTP1.2petrographicfabricfromDax,(DAX‐79‐19,XPL),PPL:parallel‐polarisedlight, XPL:cross‐polarisedlight. TheG2fabricgroupiscomposedofthreepetrographicfabrics.Thepetrographicfab‐ ricTP2.1isthemostabundant,accountingfor80%(36/45)oftheG2wares.Theseceramics arecharacterisedbyafine‐grainedgroundmassvaryingfromclayeytosandyinnature, withangulartosubroundedcoarseinclusionsrangingfrom0.5to6mminsize.Thepores presentasingle‐ todouble‐spacedrelateddistributionandareorientedparalleltothe vesselmargin.Thenumberofinclusionsrangesbetween15%and25%andtheirorienta‐ tionismainlyparalleltothemargins,showingpoorsortingwithabimodalgrainsize distribution.Thecoarsefractionincludesrockfragmentsmainlyofquartz‐feldspaticig‐ neous‐felsicnature,frequentmetamorphicrockswithsillimaniteandafewsandstones. Inaddition,mineralfragmentssuchasmono‐andpolycrystallinequartzwithundulose extinction,potassiumfeldsparandblackishinclusionsarefrequent,whilemuscovite,bi‐ otitelathsandamphiboleareveryfew.Twoendsubgroups,orsubfabrics,canbedistin‐ guisheddependingontheclayeyorsandynatureofthegroundmass.Thesandymatrix constitutesoneoftheendsubgroupscharacterisedbyabimodalgrainsizedistribution (modesrangingbetween0.125–0.25mmand0.5–2.0mm)ofmainlysubangularquartz‐ feldspathicinclusions(Figure5a,b). ThefabricTP2.2wasonlyidentifiedattwosites,accountingfor13%(6/45)oftheG2 groupwares.Dependingonthesitelocationofthesamples,thegroundmassvariesbe‐ tweenclayey(Molietssite)andsandy(Bayonnesite),withporespresentingasingle‐or double‐spacedrelateddistributionandapreferredorientationparalleltothevesselmar‐ gins.Asarule,theinclusions(15%–20%)showabimodalgrainsizedistributionwith commonpoorlysorted,subroundedtosubangularfinetocoarseinclusionsoffrequent quartzgrainsandstronglyalteredfeldspars(0.125–0.5mm),especiallyidiomorphicpla‐ gioclase,thelatterbeingdistinctiveofthispetrographictype.Abundantroundedtoan‐ gularquartz‐feldsparandraremicainclusionsareobservedwithinthefine‐grained groundmass.Additionally,raremuscovite‐bearinggraniticrockfragments,scarcegran‐ odioriticaswellassedimentaryrockfragmentsarealsoobserved(Figure5c). Figure 4. Representative thin section photomicrographs of the G1 fabric ceramic from different sites. ( a ): Fabric TP 1.1 from Arbium site (sample ARBI-10, PPL). ( b ): Inclusions of calcite spar, carbonate fragments and epidote included in TP 1.1 fabric from Bayonne site (sample BAY-36, PPL). ( c ): Calcite, epidote, and pyroxene inclusions of the TP 1.1 fabric from Zarautz site, (SNR-18, PPL). ( d ): Texture of the TP 1.2 petrographic fabric from Dax, (DAX-79-19, XPL), PPL: parallel-polarised light, XPL: cross-polarised light. The G2 fabric group is composed of three petrographic fabrics. The petrographic fabric TP 2.1 is the most abundant, accounting for 80% (36/45) of the G2 wares. These ceramics are characterised by a fine-grained groundmass varying from clayey to sandy in nature, with angular to subrounded coarse inclusions ranging from 0.5 to 6 mm in size. The pores present a singleto double-spaced related distribution and are oriented parallel to the vessel margin. The number of inclusions ranges between 15% and 25% and their orientation is mainly parallel to the margins, showing poor sorting with a bimodal
Minerals 2023,13, 887 7 of 21 grain size distribution. The coarse fraction includes rock fragments mainly of quartzfeldspatic igneous-felsic nature, frequent metamorphic rocks with sillimanite and a few sandstones. In addition, mineral fragments such as monoand polycrystalline quartz with undulose extinction, potassium feldspar and blackish inclusions are frequent, while muscovite, biotite laths and amphibole are very few. Two end subgroups, or subfabrics, can be distinguished depending on the clayey or sandy nature of the groundmass. The sandy matrix constitutes one of the end subgroups characterised by a bimodal grain size distribution (modes ranging between 0.125–0.25 mm and 0.5–2.0 mm) of mainly subangular quartz-feldspathic inclusions (Figure 5a,b). Minerals2023,13,8878of22 Figure5.PhotomicrographsshowingpetrographicfeaturesoftheG2fabricgroup.(a):Sandymatrix endsubgroupshowingbimodaldistributionsofangularinclusionsdistinctiveofTP2.1fabric(sam‐ pleSNR‐33,XPL).Notesillimanite‐bearingrockfragmentatthecentre.(b):Theclayeymatrixend subgroupshowscoarseangularinclusionsofTP2.1fabric(sampleF‐55,XPL).(c):Representative TP2.2fabricshowingsub‐roundedtosub‐angularquartzwithidiomorphicplagioclaseinclusions (sampleBAY‐39,XPL).(d):PolygeniccharacteroftheTP2.3fabric;notetheelongatedslatefragment (sampleGEA‐8,PPL);PPL:parallel‐polarisedlight,XPL:cross‐polarisedlight. OnlythreesamplesconstitutetheTP2.3petrographicfabric.Thisfabricisnotably polygenic,includingafine‐grained(<0.1mm)quartz‐feldspathicandmuscovitesandy groundmass,andamedium‐coarsefraction(0.25–1.25mm)including,mainlysubangu‐ lar‐subrounded,poorlysortedinclusionsofdifferentcomposition.Thecoarseinclusions (30%–40%)displayaclose‐spacedtodouble‐spacedrelateddistributionandapreferred orientationparalleltothevesselmargins.Thecoarsefractionconsistsofcommonmono‐ andpolycrystallinequartz,potassiumfeldspar,alteredplagioclaseandafewbiotite,py‐ roxene,andcalciteaggregates.Additionally,rarerockfragmentsofdifferentoriginsare included:slatefragmentsintheGetaria‐ZarautzJauregiasample,subvolcanicrocksdis‐ playingophitictextureintheArbiunsampleandhigh‐grademetamorphicrockswithsil‐ limanitefragmentsintheLalonquetesample(Figure5d). TheG3fabricgroupistheleastcommonatthesitesandthemostheterogeneous basedonpetrographiccriteria,includingsixpetrographicfabrics.Theoccurrenceofeach petrographicfabricismainlyrestrictedtoasinglearchaeologicalsite.TheTP3.1fabric includes11samplesfromtheDaxandSantaElenasites.Theoccurrenceofchessboard subgrainpatternsinquartzisthedistinctivefeatureofthisfabric(Figure6a).Thefabricis characterisedbyaveryfineclayeymatrixwithafeworientedporesparalleltovessel margins.Themoderatelysortedcoarsefraction(20%–25%)ismainlycomposedofquartz inclusionsofhighroundnessandsphericityandquartzinclusionsofvariablegrainsize (0.25–1.25mm),insomecaseswithbimodaldistribution.Inadditiontoperthiticpotas‐ siumfeldspar,thereisacommonoccurrenceofplagioclasereplacedbyepidoteand brownbiotite.Morerarely,two‐micagranitefragmentsoccur. PetrographicfabricTP3.2isthemostnumerousandwidelydistributedfabricinthe G3groupandincludes25samplesfromForua‐PeñaForua,Santiagomendi,SantaElena, Saint‐Paul‐en‐Born,PardiesandDax.Thedistinctivefeatureofthisfabricisthepresence ofidiomorphicplagioclaseinclusions(Figure6b)scatteredinaclayey‐sandymatrix, sometimesrichinmicas.Thecoarsefractioninclusions(15%–20%)aresubangularto roundedinshape,withvariablegrainsizerangingfromveryfinetogravelsize(0.1–2.5 mm),poorlysortedandarrangedinabimodalgrainsizedistribution.Frequentinclusions Figure 5. Photomicrographs showing petrographic features of the G2 fabric group. ( a ): Sandy matrix end subgroup showing bimodal distributions of angular inclusions distinctive of TP 2.1 fabric (sample SNR-33, XPL). Note sillimanite-bearing rock fragment at the centre. ( b ): The clayey matrix end subgroup shows coarse angular inclusions of TP 2.1 fabric (sample F-55, XPL). ( c ): Representative TP 2.2 fabric showing sub-rounded to sub-angular quartz with idiomorphic plagioclase inclusions (sample BAY-39, XPL). ( d ): Polygenic character of the TP 2.3 fabric; note the elongated slate fragment (sample GEA-8, PPL); PPL: parallel-polarised light, XPL: cross-polarised light. The fabric TP 2.2 was only identified at two sites, accounting for 13% (6/45) of the G2 group wares. Depending on the site location of the samples, the groundmass varies between clayey (Moliets site) and sandy (Bayonne site), with pores presenting a singleor double-spaced related distribution and a preferred orientation parallel to the vessel margins. As a rule, the inclusions (15%–20%) show a bimodal grain size distribution with common poorly sorted, subrounded to subangular fine to coarse inclusions of frequent quartz grains and strongly altered feldspars (0.125–0.5 mm), especially idiomorphic plagioclase, the latter being distinctive of this petrographic type. Abundant rounded to angular quartz-feldspar and rare mica inclusions are observed within the fine-grained groundmass. Additionally, rare muscovite-bearing granitic rock fragments, scarce granodioritic as well as sedimentary rock fragments are also observed (Figure 5c). Only three samples constitute the TP 2.3 petrographic fabric. This fabric is notably polygenic, including a fine-grained (<0.1 mm) quartz-feldspathic and muscovite sandy groundmass, and a medium-coarse fraction (0.25–1.25 mm) including, mainly subangularsubrounded, poorly sorted inclusions of different composition. The coarse inclusions
Minerals 2023,13, 887 8 of 21 (30%–40%) display a close-spaced to double-spaced related distribution and a preferred orientation parallel to the vessel margins. The coarse fraction consists of common monoand polycrystalline quartz, potassium feldspar, altered plagioclase and a few biotite, pyroxene, and calcite aggregates. Additionally, rare rock fragments of different origins are included: slate fragments in the Getaria-Zarautz Jauregia sample, subvolcanic rocks displaying ophitic texture in the Arbiun sample and high-grade metamorphic rocks with sillimanite fragments in the Lalonquete sample (Figure 5d). The G3 fabric group is the least common at the sites and the most heterogeneous based on petrographic criteria, including six petrographic fabrics. The occurrence of each petrographic fabric is mainly restricted to a single archaeological site. The TP 3.1 fabric includes 11 samples from the Dax and Santa Elena sites. The occurrence of chessboard subgrain patterns in quartz is the distinctive feature of this fabric (Figure 6a). The fabric is characterised by a very fine clayey matrix with a few oriented pores parallel to vessel margins. The moderately sorted coarse fraction (20%–25%) is mainly composed of quartz inclusions of high roundness and sphericity and quartz inclusions of variable grain size (0.25–1.25 mm), in some cases with bimodal distribution. In addition to perthitic potassium feldspar, there is a common occurrence of plagioclase replaced by epidote and brown biotite. More rarely, two-mica granite fragments occur. Minerals2023,13,8879of22 werequartz(mono‐andpolycrystalline),zonedandpoorlyalteredplagioclase,common perthiticpotassiumfeldspar,granitefragmentsandveryfewbiotitelathsandamphibole. PetrographicfabricTP3.3comprisesonlythreesamplesandoccursatGetaria‐ ZarautzJauregiaandSantaElena.Themostdistinctivefeatureisthepresenceofcoarse (0.25–0.50mm)highlysphericalandroundedquartzandpotassiumfeldsparinclusions (30%–40%),spreadinaveryfineclayeymatrix.Theydisplayamoderatelysorted,bi‐ modalgrainsizedistribution.Frequentinclusionsaremono‐andpolycrystallinequartz withcommonalteredcoarseplagioclase(≤1.3mm),granitoidfragmentsorafewslates andferruginoussandstones(Figure6c). Figure6.PhotomicrographsshowingpetrographicfeaturesoftheG3fabricgroup.(a):Petrographic fabricTP3.1presentingroundedchessboardpatternquartz(sampleDAX‐79‐3,XPL).(b):Idiomor‐ phicplagioclasedistinctiveoftheTP3.2fabric(sampleF‐16,XPL).(c):Highlysphericalandrounded quartzgrainsembeddedinaveryfineclayeymatrixdistinctiveoftheTP3.3fabric(sampleGEA‐4, XPL).(d):TheTP3.4fabricincludespolygenicinclusionssuchasslatesandschists,biotitic‐amphi‐ bolegranodioritesandsandstones(sampleLescar‐10,PPL).(e):Clayeymatrixwithveryfinequartz grainswithrandomcoarsequartzfragmentsofTP3.5fabric(sampleSTGR‐17,XPL).(f):TP3.6 fabricshowingmoderatelysortedpolygenicinclusions(sampleDAX‐5,XPL).PPL:parallel‐polar‐ isedlight,XPL:cross‐polarisedlight. PetrographicfabricTP3.4includessixsamplesfromtheLescarsite.Waresofthis fabricshowafineclayeymatrix,withfewporesparalleltothevesselmargin.Thepoly‐ genicinclusions(25%–35%)displayabimodalgrainsizedistributionwithapoorlysorted coarsefraction(0.8–2mm)ofangulartosubroundedshapes.Thenatureoftheinclusions isdiverse,includingfrequentfragmentsofmetamorphicrocks(frequentslatesand schists,someofgravelsize>2mm),commonsubroundedigneousrockfragments(am‐ phibolegranodiorites,subvolcanicrockswithophitictextures)andveryfewsedimentary lithicfragments(sandstones)(Figure6d). Figure 6. Photomicrographs showing petrographic features of the G3 fabric group. ( a ): Petrographic fabric TP 3.1 presenting rounded chessboard pattern quartz (sample DAX-79-3, XPL). ( b ): Idiomorphic plagioclase distinctive of the TP 3.2 fabric (sample F-16, XPL). ( c ): Highly spherical and rounded quartz grains embedded in a very fine clayey matrix distinctive of the TP 3.3 fabric (sample GEA-4, XPL). ( d ): The TP 3.4 fabric includes polygenic inclusions such as slates and schists, biotitic-amphibole granodiorites and sandstones (sample Lescar-10, PPL). ( e ): Clayey matrix with very fine quartz grains with random coarse quartz fragments of TP 3.5 fabric (sample STGR-17, XPL). ( f ): TP 3.6 fabric showing moderately sorted polygenic inclusions (sample DAX-5, XPL). PPL: parallel-polarised light, XPL: cross-polarised light.
Minerals 2023,13, 887 9 of 21 Petrographic fabric TP 3.2 is the most numerous and widely distributed fabric in the G3 group and includes 25 samples from Forua-Peña Forua, Santiagomendi, Santa Elena, Saint-Paul-en-Born, Pardies and Dax. The distinctive feature of this fabric is the presence of idiomorphic plagioclase inclusions (Figure 6b) scattered in a clayey-sandy matrix, sometimes rich in micas. The coarse fraction inclusions (15–20%) are subangular to rounded in shape, with variable grain size ranging from very fine to gravel size ( 0.1–2.5 mm ), poorly sorted and arranged in a bimodal grain size distribution. Frequent inclusions were quartz (monoand polycrystalline), zoned and poorly altered plagioclase, common perthitic potassium feldspar, granite fragments and very few biotite laths and amphibole. Petrographic fabric TP 3.3 comprises only three samples and occurs at Getaria-Zarautz Jauregia and Santa Elena. The most distinctive feature is the presence of coarse ( 0.25–0.50 mm ) highly spherical and rounded quartz and potassium feldspar inclusions (30–40%), spread in a very fine clayey matrix. They display a moderately sorted, bimodal grain size distribution. Frequent inclusions are monoand polycrystalline quartz with common altered coarse plagioclase ( ≤ 1.3 mm), granitoid fragments or a few slates and ferruginous sandstones (Figure 6c). Petrographic fabric TP 3.4 includes six samples from the Lescar site. Wares of this fabric show a fine clayey matrix, with few pores parallel to the vessel margin. The polygenic inclusions (25–35%) display a bimodal grain size distribution with a poorly sorted coarse fraction (0.8–2 mm) of angular to subrounded shapes. The nature of the inclusions is diverse, including frequent fragments of metamorphic rocks (frequent slates and schists, some of gravel size > 2 mm), common subrounded igneous rock fragments (amphibole granodiorites, subvolcanic rocks with ophitic textures) and very few sedimentary lithic fragments (sandstones) (Figure 6d). Only two samples from the Santiagomendi site define the TP 3.5 petrographic fabric. These samples are characterised by a mainly clayey matrix with pores in an open-spaced, related distribution. The nonplastic inclusions (<10%) display an open-spaced related distribution, medium grain size (0.25–0.80 mm) and variable subrounded to subangular shapes, thus defining a poorly sorted fabric with a bimodal grain size distribution. Fragments of granitic rocks and fragments of potassium feldspar, plagioclase and quartz are common (Figure 6e). Petrographic fabric TP 3.6 includes five samples from the Dax site. This fabric shows petrographic similarities to the TP 1.1 fabric regarding the heterogeneous composition of inclusions. The coarse-grained (0.25–0.5 mm) inclusions (35–45%) reflect a bimodal grain size distribution with poorly to moderately sorted fabric. The angular to subrounded inclusions present a closedto double-spaced related distribution and correspond to various types of sedimentary, igneous, and metamorphic fragments (Figure 6f). 4.2. X-ray Powder Diffraction X-ray powder diffraction results agree with the data obtained by mineralogical and petrographic observations. Figure 7shows a representative diffractogram per pottery fabric group. The samples are composed of quartz, phyllosilicates, feldspars (both plagioclase and potassium feldspar) and minor amounts of calcite and titanium oxides. Quartz is the most abundant mineral in the three fabric groups, with an average content of 50%. The most homogeneous contents in quartz are found in the G2 group samples, while contents below 30% are observed in some G1 group samples and above 60% in some G3 group samples. Phyllosilicates are the second most abundant minerals, with average values of approximately 40%. Phyllosilicates vary inversely with quartz content, although in some cases variations are related to feldspar and carbonate content. The most significant mineralogical difference between the three fabric groups is related to the minor minerals such as feldspar and calcite. Feldspar content (plagioclase and potassium feldspar) is by far the highest in the G3 fabric samples. The samples from the Moliets, Pardies, Bayonne and Dax sites show above-average feldspar contents. In fact, Moliets samples contain up to 30% plagioclase and up to 10% potassium feldspar. With
Minerals 2023,13, 887 16 of 21 Roman Empire (1st–2nd century), although some samples have been found in later Roman archaeological contexts at the geographically very close sites of Arbiun, Getaria-Zarautz Jauregia and Santa Maria la Real [29]. The G2 fabric group was geographically distributed in both provinces in the early Roman period. Petrographically, it is more homogeneous than the G1 group. Thus, the petrographic fabric TP 2.1 occurs at Tarraconensis sites, whereas the fabric TP 2.2 occurs at Aquitania sites, although recent unpublished studies recognise the occurrence of TP 2.1 fabric at several Aquitanian sites. In addition, some wares of TP 2.1 fabric show graffiti attributed to the potter [ 34 , 71 ]. As with the previous G1 pottery, the petrographic fabric of the G2 group indicates that the raw materials must be linked to the areas where plutonic and high-grade metamorphic rocks occur; thus, the sediments used as raw materials originated from the Axial Zone or central Pyrenees. The Palaeozoic Ursuya Massif in the westernmost Pyrenees, which includes diorite plutonic and high-grade metamorphic rocks [ 72 ] and is drained by the Nive River and its tributaries, may be the most likely source area for the raw material. In addition, the grain size heterogeneity and high angularity of the inclusions indicate a provenance area from the middle-upper Nive River basin (Figure 12; Table S2). Although the provenance area of the raw material can be attributed to the Nive River basin, the regional geographical distribution of the petrographic fabrics suggests several production centres with different supply areas. The production centres for these ceramics must therefore be located in southern Aquitania. The pottery of the G3 fabric group is the most heterogeneous, as shown by the wide variety of petrographic fabrics, and has been found in both Aquitania and Tarraconensis provinces. Chronologically, it corresponds to the early Roman period (1st–2nd century) at the sites of Lescar, Pardies (Aquitania) and Santa Elena, Santiagomendi sites (Tarraconensis), and to the Late Roman period (4th–5th century) for most of the pottery at the Dax site. In most cases, each of the petrographic fabrics has been found at a single archaeological site, suggesting a local provenance of the raw material for each site (Figure 12; Table S2). Most of the TP 3.1 wares were found at the Dax site and are characterised by polycrystalline chessboard-patterned quartz inclusions. These microstructures were described for Lys and Néouvielle pluton lithologies within the axial zone of the Pyrenees at the headwaters of the Adour River [ 31 , 32 ]. The Adour River then transported the sediments formed by the weathering and erosion of these materials to the middle or lower reaches of the river, where the raw material supply area was located. The TP 3.2 petrographic fabric is the most common and is found at sites on both sides of the Pyrenees. The occurrence of idiomorphic plagioclase indicates that the sediments were formed close to the plutonic areas. Therefore, the raw material supply area can probably be located in the western Pyrenees within the Adour River basin, although the Oiartzun or Bidasoa River basins cannot be excluded [ 31 ]. The petrographic fabrics TP 3.3 and TP 3.5 occur only at Tarraconensis sites. The high sphericity and high roundness of the quartz grains occurring in TP 3.3 indicate that the raw material supply can be the coastal dune deposits consistent with the Landes region bordering the Bay of Biscay in the Aquitania Basin. The decanted fabric without the temper of the TP 3.5 makes tracing the provenance difficult. The fabric TP 3.4 occurs only at the Lescar site in Aquitania. The large grain size, high angularity and polygenic nature of the inclusions of this fabric suggest a source of raw material close to the river headwaters. The local sediments formed in the upper basin of the Gave de Pau (tributary of the Adour) can be considered a raw material source for this pottery. The fabric TP 3.6 was restricted to the Dax site. As in the previous case, the low frequency and limited distribution of the vessels and the fabric characteristics suggest the use of local clays compatible with the Adour deposits that dominate this area. The studied pottery appears at sites associated with maritime, land or fluvial communication routes, both coastal and terrestrial. The production of G1 pottery was widespread in the studied region around the Bay of Biscay, with the greatest production and diffusion during the Later Empire times. Although G1 pottery production started in the Early Empire, it was not until the Later Empire that it became regionally widespread. The homogeneity
Minerals 2023,13, 887 17 of 21 of this type of fabric indicates careful processing of the raw materials, suggesting a pottery workshop complex located in southern Aquitania. The good quality of the pottery and the development of robust trade networks favoured its widespread distribution, as evidenced by the profuse occurrence of these wares around the Bay of Biscay from Galicia to Bordeaux, and by the inland trade along the Ebro River as far as Saragossa [28,67,73–75]. The production of the G2 pottery group occurred mainly in the Early Empire period, although some samples were found in Later Empire contexts. The slight textural variability suggests a common technological tradition with small variations in the pottery’s manufacture and slight differences in the provenance of raw materials from the western Pyrenees, in southern Aquitania during the early Roman period. Furthermore, the restricted distribution of this production on coastal sites suggests a preferential geographical distribution over inland areas. The G3 pottery group occurs in two periods, during the Early Empire and at the end of the Later Empire. This production displays a limited and heterogeneous distribution network, occurring mainly in the Aquitania sites and in some of the easternmost sites of the Tarraconensis province. Local raw material provenance indicates local pottery production using similar technological patterns. Local productions suggest systems of trade networks that were not yet consolidated in the Early Empire, while in the Later Empire there was a weakening of the trade networks, coinciding with the crisis at the end of the empire, leading to their deconstruction and a re-localisation of pottery production. 6. Conclusions The use of chemical composition in pottery provenance and diffusion studies should be taken with caution, as the composition may have undergone modifications either by the use of the pottery or by burial processes. The present study of pottery from several sites displays different patterns of chemical modification, limiting their use as a tool for studying their provenance and diffusion. Nevertheless, the mineralogical and microstructural composition of the fabrics does not change during burial, reflecting the original features of the raw materials and allowing the identification of provenance areas and trade networks. The petrography study has also been applied to the common non-wheel thrown pottery from the Roman Aquitania-Tarraconensis provinces (CNT-AQTA), enabling the establishment of diffusion and trade patterns during Roman times around the Bay of Biscay. Technological persistence in pottery production traditions was observed throughout the Roman Empire. Variations in both the distribution patterns and the provenance areas of pottery during Roman times have also been identified. The chronology of the manufacture and spread of CNT-AQTA pottery begins locally in Aquitania. Then, during the Early Empire, pottery of the G2 group was manufactured in several production centres in southern Aquitania following the same technological tradition. This ware production was the most widespread but restricted to coastal sites, suggesting a well-consolidated distribution network but limited to maritime traffic around the Bay of Biscay. During the Later Empire period, G1 pottery production was predominant and widely distributed both along the coast and in inland territories in the provinces of Aquitania and Tarraconensis. These wares were manufactured in the centres of production in southern Aquitania and/or a broader region surrounding the Pyrenees and widely distributed through a well-established trade network. Finally, during the final period of the later Roman Empire, locally manufactured G3 pottery was produced, preserving the technological tradition but with a reduced distribution and commercial capacity, closer to the Aquitania region and the easternmost Tarraconensis sites, reflecting the deterioration of the trade networks. Supplementary Materials: The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/min13070887/s1, Table S1: Archaeological site, pottery group, petrographic fabric, vessel typology and epoch of the studied samples, Table S2: Lithologies outcropping in the surroundings of the studied archaeological sites.
Minerals 2023,13, 887 18 of 21 Author Contributions: Conceptualization, L.Á.O., A.A.-O., M.C.Z. and A.M.-S.; methodology, L.Á.O., A.A.-O. and M.C.Z.; investigation, A.A.-O., L.Á.O., M.C.Z. and A.M.-S.; resources, A.A.-O., L.Á.O., M.C.Z., A.M.-S., M.T.I.-M., M.E.-D. and F.R.; writing—original draft preparation, L.Á.O., M.C.Z. and A.A.-O.; writing—review and editing, L.Á.O. and M.C.Z.; funding acquisition, A.A.-O., L.Á.O., M.C.Z., A.M.-S., M.T.I.-M., M.E.-D. and F.R. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by Fundación JoséMiguel de Barandiaran Fundazioa, grant number 2004, and the Basque Country government, grant number IT1442-22. The APC was funded by the Basque Country government, grant number IT1442-22. Data Availability Statement: Not applicable. Acknowledgments: We would like to thank the Archaeological Museum of Bilbao (Bizkaia), the Gipuzkoa Heritage Collection Centre, the Archaeological Museum of Alava and the Pyrenees Atlantiques Archaeological Deposit Centre (Hasparren, France) for the provision of material for this study. We highly appreciate reviewers’ insightful corrections and comments on improving the paper. We are also grateful to Peter Smith for the language assistance. Conflicts of Interest: The authors declare no conflict of interest. References 1. Costin, C.L. Production and Exchange of Ceramics. In Empire and Domestic Economy; D’Altroy, T.N., Hastorf, C.A., Eds.; Springer: Boston, MA, USA, 2002; pp. 203–242. 2. Sillar, B. Reputable pots and disreputable potters: Individual and community choice in present-day pottery production and exchange in the Andes. 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