white marbles, estremoz anticline marbles, almadÉn de la plata marbles augusta emerita

White marbles, estremoz anticline marbles,

almadén de la Plata marbles augusta emerita

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1. Introduction2. Archaeological setting3. Geological setting4. Studied samples 5. Methodology6. Results 6.1. Very fine grained marbles (Group A) 6.2. Fine grained marbles (Group B) 6.3. Medium grained marbles (Group C) 6.4. Medium to coarse grained marbles (Group D) 6.4. Coarse grained marbles (Group E)7. Updated characterization of the Estremoz Anticline vs. Almadén de la Plata marbles8. Discussion 8.1. Provenance of marble 8.1.1. Marble provenance of Group A 8.1.2. Marble provenance of Group B 8.1.3. Marble provenance of Group C 8.1.4. Marble provenance of Group D 8.1.5. Marble provenance of Group E 8.2. Considerations regarding the local and imported archaeological pieces9. Conclusions10. Acknowledgments11. References

Titles of TablesTable 1Table 2Table 3

Figures CaptionsFigures 1, 2, 3, 4, 5, 6a, 6b, 7a, 7b

Abstract:

This contribution reports the results of the archaeometric study of 51 marble sculptu-res and decorative elements from the capital of Roman Lusitania, Augusta Emerita (Méri-da, Spain). These artefacts found on display at the Spanish National Museum of Roman Art comprise a representative record of ar-chaeological pieces from different decorative programmes dated from the end of the 1st century BC to the end of the 2nd century AD.

A multi-method approach combining polari-zed-light microscopy, cathodoluminescence, X-ray powder diffraction, and stable C and O isotope analysis was applied to identify the marble provenance. The comparison of the results with the available databases confirms the use of different white marble varieties from the Estremoz Anticline (Portugal) as well as some Carrara and well-known marbles from Greece

Key-words:

White marbles, Estremoz Anticline marbles, Almadén de la Plata marbles, Augusta Emerita, archaeometry, provenance.

Introduction

Roman aesthetic taste by choosing marble as a noble material for arts and architecture is well known especially during and after the Augustan period. Various quarries were exploited at diffe-rent times in the past due to great demand in the Graeco-Roman world, the period also referred to as classical antiquity.

Fig.1. Geographical setting of Augusta Emerita (star symbol), the principal white marble quarries in Hispania and some of the classical marbles of the Mediterranean

area. Iberian marbles from the Ossa Morena Zone include the quarries of the Estremoz Anticline district (EA), Almadén de la Plata district (AP), Viana do Alentejo

and Alconera. In the Betic Chain: the quarries of the Málaga district (mainly dolomitic marbles of Mijas-Coín) and the quarries of the Almería district. Abbreviation for

classical marbles cited in the text: Carrara (C), Thasos (T), Pentelikon (Pe), Hymettos (H), Paros (Pa), Naxos (Na), Göktepe (G), Aphrodisias (A), Dokimeion (D)

and Proconnesos (Pr). Location of the archaeological sites named in the text are given. Large or small cubes are a district of quarries or an isolated quarry, respectively.

Studies on marbles used to decorate complex architectural projects are aimed at obtaining detai-led historical and archaeological data of the origin and building history of the monuments. In the case of the white statuary used to embellish public spaces, the identification of the source of mar-ble provides not only valuable information on trading patterns and economic history, but also on the workshops. In recent years, this research has focused more attention on the scientific commu-nity and white marble provenance studies have made great progress (e.g., Maniatis, 2009; Gutié-rrez Garcia-M. et al., 2012). Databases of combined mineralogical as well as chemical and physical parameters aim to help discriminate between ancient quarrying areas.

4PILAR LAPUENTE 1,* TRINIDAD NOGALES-BASARRATE 2 HERNANDO ROYO 1,3 and MAURO BRILLI 4

Cerbuna, 12, 50009 Zaragoza, Spain * Corresponding author, e-mail: [email protected] Museo Nacional de Arte Romano, 06800 Mérida, Spain

3 Institut Català d´Arqueologia Clàssica, Pl. Rovellat, s/n, 43003 Tarragona, Spain4 Istituto di Geologia Ambientale e Geoingegneria, CNR. Area della Ricerca Roma1 - Via Salaria km 29.300, 00015 Monterotondo St, Roma, Italy

PILAR LAPUENTE 1,* TRINIDAD NOGALES-BASARRATE 2 HERNANDO ROYO 1,3 and MAURO BRILLI 4



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The results sometimes fail to match well with the comparative parameters. These discrepancies are due to the lack of certain samples in the databases, either because some ancient quarrying sources still remain undiscovered or because they have become erased after years of intensive qua-rrying activity. Moreover, not all databases include the same samples and the same methods; while some are based on mineralogical-petrographic and C-O stable isotopic data (e.g., Lazzarini et al., 1980; Herz, 1987; Moens et al., 1992; Gorgoni et al., 2002; Capedri et al., 2004), others deal with electron paramagnetic resonance data, stable isotopes and certain petrographic parameters such as the maximum grain size (MGS) (e.g., Attanasio et al., 2000, 2006; Polikreti & Maniatis, 2002). Cathodoluminescence microscopy, combined with stable isotopes, has been used for known classical quarrying areas (e.g., Barbin et al., 1989, 1992; Blanc, 1999), as well as in Central Europe (Jarč & Zupančič, 2009; Št’astná et al., 2009).

A further setback has arisen with the recently reported discovery of ancient quarries in Asia Minor (Attanasio et al., 2009). The high quality of white Göktepe marbles, located close to Aphrodisias, offers a new panorama to consider in the study of marble origin (Fig. 1). Their physical and com-positional similarities to other classical marbles such as Carrara and Dokimeion, makes provenance determination more complex (Lapuente et al., 2012).







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The provenance of Hispanic white marble artefacts is an even more di-fficult task. Not only does it require the application of several techniques, but also the archaeological criteria must not be overlooked since, toge-ther with imported marbles, extensive use was made of high-quality local marbles (Fig. 1).

From among the Iberian marble quarries exploited in Roman times (Àl-varez et al., 2009), two source areas were widely used in the SW part of Hispania. Both are located in the same geological unit, the Ossa Morena Zone of the Iberian Massif, but in a different Roman administrative pro-vince. These are the so-called marbles of the Estremoz Anticline district, located in Lusitania, and those from the Almadén de la Plata district, in the Baetica Roman province (Fig. 1).

This paper reports the archaeometric study of 51 white marble sculptures and decorative archi-tectural elements used in the most emblematic public spaces of Augusta Emerita, the capital of Roman Lusitania. The main objective is to distinguish between imported and local marbles. For economic and administrative reasons, the nearby Estremoz Anticline marbles would surely be the most abundant source employed in the development of Augusta Emerita. But, on the other hand, the selection of pieces studied, mostly finely carved, may well include imported marbles from the Mediterranean area.

This study is based on comparisons of mineralogical-petrographic characteristics, ca-thodoluminescence and C-O stable isotope data, using the same methodology on an extensive marble collection, of both Iberian and classical marble sources. The latter include varieties from Carrara, Pentelikon, Hymettos, Paros, Naxos, Thasos, Procon-nesos, Dokimeion and Göktepe (Fig. 1). Additional information from literature has been used to check the possible imported marbles. The Hispanic quarry marbles da-tabase applied is available elsewhere (e.g., Lapuente, 1995; Lapuente & Turi, 1995; Lapuente & Blanc, 2002; Lapuente et al., 2000, 2002; Àlvarez et al., 2009; Origlia et al., 2011). Besides the Estremoz Anticline and Almadén de la Plata marbles, other local sources of white marbles from Ossa Morena Zone, such as those of Alconera, and Viana do Alentejo are also included in the comparative database, since their coloured varieties at least were employed in Roman times (Fig. 1). The study is completed with a revision of the best para-meters that may facilitate the Estremoz Anticline and Almadén de la Plata marble discrimination and an updated isotopic diagram for both white marble sources.

Being originally from the same Ossa Morena Zone, both Estremoz Anticline and Almadén de la Plata marbles exhibit similarities in physical and compositional parameters, which make it more difficult to ascertain the marble origin of Hispanic artefacts. However, their discrimination is es-sential because it helps to improve our knowledge of the trading routes and commerce of the Iberian raw material as well as the cultural connections of both administrative Roman provinces (Nogales & Beltrán, 2008).

Moreover, both marbles which were greatly appreciated by Romans living in Hispania have re-cently been identified in archaeological remains outside Iberia (e.g., Antonelli et al., 2009; Origlia et al., 2011), which opens a new perspective for consideration in the marble provenance analy-ses, as these marbles until now were thought to be destined exclusively for local markets







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Augusta Emerita (Mérida, Spain) was a Ro-man colony founded by Augustus in 25 BC as a settlement for the veteran soldiers dischar-ged from the Legions V (Alaudae) and X (Ge-mina) after the Cantabrian wars (Keay, 1988). Located in the current Badajoz province of the Extremadura region, the town was entirely de-signed as an example of Roman urbanization beside the Guadiana River.

Throughout time, it became an administrati-ve, economic and cultural centre and even the capital of the Lusitanian province, a territory with a well organized hinterland of agricultural estates whose mineral resources favoured its development. Augusta Emerita maintained its prosperous position beyond the time of the fall of the Roman Empire. In 1993, the archaeo-logical ensemble of Mérida was declared a UNESCO World Heritage Site.

The city was located about 300 km inland at a strategic intersection between two main roads Other local routes ensured not only a rapid access of soldiers from one region to another, but also a regular supply of agricultural and mineral goods. Fluvial routes, however, were only partially navigable.

The so called “Pulo do Lobo” waterfall on the Guadiana River impedes the direct fluvial access to the At-lantic Ocean. The inland location of the colony and the occurrence of abundant high-quality local Estremoz Anticline marbles could have lessened the trading of imported marbles, contrary to other Hispanic capitals such as Tarraco.

The regular exploitation of the Estremoz Anticline marbles would have started sometime in the 1st century AD, as no evidence exists of previous use (Nogales et al., 2008). Marble is associated with the Romanization of Lusitania and played an important role as a support for political propaganda, especially through the sta-tuary images (Álvarez & Nogales, 2003; Nogales 2003, 2009, 2011).

Archaeological setting

The whole Roman Lusitanian province was supplied with Estremoz Anticline marbles for statuary, decorative-architectural elements and epigraphy (Nogales et al., 1999, 2008; Lapuente et al., 2000; Mañas & ––Fusco, 2008; Àlvarez et al., 2009; Taelman et al., 2013). Coloured Estremoz Anticline marbles served to pave the orchestra of the Augusta Emerita Theatre and enormous columns of dark grey veined marbles from the Pardais region decorate its frons scaenae (Nogales, 2003). The Lusitanian Estremoz Anticline marble products spread, at least, to points as far up as Gijón in the north of Hispania (Vidal & García-Entero, in press) and down to Volubilis (Morocco) in the Maurita-nia province (Antonelli et al., 2009). These were attested by archaeometric studies in some sites of the Baetica province, such as Regina Turdulorum (Royo et al., 2010). However, as each of these two Roman provinces was under different administrative control (Keay, 1988) and had its own source of raw materials, inter-trading between both provinces would have been minimal.

The quarrying of the Alma-dén de la Plata marbles would have started in the Late Au-gustan period as shown by their use in the pavement with inscription in front of the orchestra of the Theatre of Italica (Santiponce, close to Seville).

They were widely distribu-ted in the Baetica province,

though particularly restricted to its western zone (Rodríguez, 2008; Àlvarez et al., 2009; Rodríguez et al., 2012).

A Roman inscription found in the Almadén de la Plata location mentions the existence of a pagus marmorarius, suggesting that the quarry may have formed part of a special administrative district (Beltrán et al., 2011; Rodríguez et al., 2012

Figure 2. Geological sketch of the Ossa Morena

Zone (OMZ) in the Iberian Massif (modified from Ro-

dríguez-Fernández, 2004). The main marble quarries

are the Estremoz Anticline (EA) and the Almadén

de la Plata (AP) districts. The latter is located right

on the tectonic junction with the South Portuguese

Zone (SPZ). Other marble quarries cited in the text

are Viana do Alentejo (VA) and Alconera (Alc). The

Central Iberian Zone (CIZ) is the northern limit of

the OMZ. The upper right insert of Hispania shows

the setting of Augusta Emerita (star symbol), the

areas of the administrative Roman provinces of Lu-

sitania and Baetica and the location of EA and AP

marble districts in the OMZ (vertical striped area).







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The Almadén de la Plata mar-bles, which reached a massive exploitation during the 1st to the 3rd century AD, have been iden-tified in sites along the navigable course of the Guadalquivir River, as well as at different points along the Atlantic coast of Baetica, al-though not on its Mediterranean coast.

They were jointly used together with marbles from Mijas-Coin (current Málaga province) sharing trade routes with North Africa (Beltrán & Loza, 2008; Beltrán et al., 2011; Origlia et al., 2011).

Geological setting

Augusta Emerita and the local marble sources (Estremoz Anticline and Almadén de la Plata mar-bles) are located in the Ossa Morena Zone, one of the most controversial geological units of the Iberian Massif (Fig. 2).

Discussions have been focused not only on the geodynamic significance of its boundaries and the exis-tence of two different orogenic cycles, but also on the complex structural-deformation and metamorphic evolution of specific areas. According to the different tectonic events of the Late Proterozoic to the Late Palaeozoic, the Ossa Morena Zone exhibits dense network of wedge-shaped domains with a complex in-ternal structure. The Ossa Morena Zone represents a continental arc accreted to the Iberian Autochthon during the Neoproterozoic-earliest Cambrian Cadomian orogeny (Quesada, 1991; Eguiluz et al., 2000; Simancas et al., 2004; Sánchez-García et al., 2008).

Metamorphism, deformation and igneous activity involved left-lateral displacement of the entire conti-nental lithosphere (Eguiluz et al., 2000). Progressive rifting, during the Late Cambrian to Early Ordovi-cian favoured the emplacement of alkaline magmatism into a marine carbonate platform.







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During the Variscan orogeny, the Ossa Morena Zone underwent a complex structural evolution, governed mainly by transpressional tectonics under sinistral wrench conditions with associated regional metamor-phism (Quesada, 1991; Silva & Pereira, 2004).

On the southern border of the Ossa Morena Zone, along its contact with the South Portuguese Zone, the occurrence of a continuous band of amphibolites (metabasites) has been interpreted as a dis-membered ophiolitic sequence (Fig. 2). Along this contact, a com-plex Variscan syn-metamorphic shear zone sealed the suture be-tween the oceanic and continental crusts (Apalategui et al., 1990). On a regional scale, the intense Variscan deformation obliterated the effects of previous Cadomian events. Variscan regional meta-morphism was generally of low grade (greenschists) but thermal domes (with high temperature at low pressure) developed locally (e.g., Abalos et al., 1991; Eguiluz et al., 2000; Díaz Azpiroz et al., 2004; Simancas et al., 2004; Sánchez-García et al., 2008).

One of the Variscan macrostructures in the Ossa Morena Zone is the Estremoz Anticline, located in the Alto Alentejo province of Portugal, about 110 km west of Augusta Emerita. It is an elongated NW-SE trending anticline, about 40 km long and 5-7 km wide (Fig. 2). The current 400 marble qua-rries are concentrated near the locations of Estremoz, Pardais and Borba. Some evidence of ancient extraction is still visible in this area (Mañas & Fusco, 2008; Nogales et al., 2008).

The Estremoz Anticline marbles of our database (Lapuente & Turi, 1995; Lapuente et al., 2000; Àlvarez et al., 2009) were collected along the Variscan structure, preferentially in its southern half, closer to the location of Augusta Emerita, and include samples from Pardais, the area at the SE ter-mination of the Estremoz Anticline that offers the best-quality white marbles (Carvalho et al., 2008).

Three main Variscan tectonic phases have usually been distin-guished in the Estremoz Anticline. According to Carvalho et al., (2008), the D1 episode (Middle Devonian age) produced the iso-clinal recumbent westward-verging folds with N-S oriented axes. Schistosity with bedding transposition and a low-grade regional metamorphism were also the result of the D1 episode. Prograde thermal metamorphism is associated with magmatic pulses loca-lly affecting the terranes of the Ossa Morena Zone. With a pro-gressive deformation, the D2 episode assigned to the Late Car-boniferous age (Quesada, 1991) developed NW-SE trending fold axes and NW-SE left-lateral shear zones, with discrete occurren-ce, showing deformation stages from ductile to brittle. Finally, du-ring a late Variscan event, the Estremoz Anticline was segmented by a network of NE-SW trending fractures, some associated with dolerite dikes.

The light-coloured varieties, namely the white and cream coloured marbles, are found throughout the entire complex. Greyish to pink-reddish coloured streaks are loca-lly frequent. The pink marbles, currently the most commercial materials, are associated with veined varieties interlayered with green metavolcanic roc-ks. Grey and dark grey marbles occur either as len-ses in the light-coloured unit or in more continuous levels at the top of the carbonate sequence. Brec-

ciated marbles associated to the NW-SE shear zones range from just a few centimetres up to 10 m in thickness (Carvalho et al., 2008).

Similar Early Paleozoic lithostratigraphic sequences are distributed over various areas of the Ossa Morena Zone (Fig. 2). One of these, with certain variations, is the tectono-metamorphic terrane known as “Almadén de la Plata Core” (Abalos et al., 1991), located where the Ossa Morena Zone meets the South Portuguese Zone (Fig. 2).







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Along the Sierra Los Covachos close to the Almadén de la Plata location, several ancient Almadén de la Plata marble quarries were identified (Bel-trán et al., 2011)These Almadén de la Plata marbles show similar colours and varieties to

those from the Estremoz Anticline district. Detailed information on Almadén de la Plata marbles, regarding their petrographic varieties and archaeolo-gical features have recently been reported by Ontiveros et al. (2012) and Rodríguez et al. (2012), respectively.

On a regional scale, the structure and metamorphic evolution of the “Almadén de la Plata Core” is related to the syn-metamorphic shear zone located at the southern border of the Ossa Morena Zone (Abalos et al., 1991). The low-grade regional metamorphism related to the early Variscan crustal thickening involved a prograde history that reached temperatures of crustal anatexis conditions apparently caused by mantle upwelling (Díaz Azpiroz et al., 2004; Eguiluz et al., 2000). By Late Carboniferous, subsequent retrogression was related to thrust movements along ductile shear zones that emplaced amphibolites from the southern border of the Ossa Morena Zone onto the South Por-tuguese Zone. Extensional structures were generated through reactivation and tectonic inversion of major thrusts and shear zones.

The Almadén de la Plata white marbles with metavolcanites form part of the uppermost metamor-phic sequence which towards the bottom is composed of schists, black quartzites, calc-silicate rocks, blastomylonitic gneisses, migmatites and amphibolites (Díaz Azpiroz et al., 2004).

Eguiluz et al., 2000). By Late Carboniferous, subsequent retrogression was related to thrust movements along ductile shear zones that emplaced amphibolites from the southern border of the Ossa Morena Zone onto the South Portuguese Zone. Extensional structures were generated through reactivation and tectonic inversion of major thrusts and shear zones. The Almadén de la Plata white marbles with metavolcanites form part of the uppermost metamorphic sequence which towards the bottom is composed of schists, black quartzites, calc-silicate rocks, blastomylonitic gneisses, migmatites and amphibolites (Díaz Azpiroz et al., 2004). These marbles might be correlated to Cambrian carbonate material elsewhere in the Ossa Morena Zone (Crespo-Blanc, 1992).

The Estremoz Anti-cline and Almadén de la Plata marbles are similar-looking meta-morphic rocks deri-ved from comparable Cambrian-Ordovician carbonate sequen-ces with intercalated volcanic rocks. Both carbonate sequences within a broadly re-gional metamorphic belt were subject to a complex structural tectono-metamorphic evolution with pro-gressive and conti-nuous deformation as-sociated to shear zo-nes. As a consequence of the specific location on the tectonic sou-thern boundary of the Ossa Morena Zone, the Almadén de la Pla-ta marbles underwent locally intensive duc-tile deformation with syntectonic recrystalli-zation, while in the Es-tremoz Anticline mar-bles the shear zones occur discretely.







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Studied samples

The Spanish National Museum of Roman Art of Mérida is both a cultural and research institution created to explain the process of the Romanization of Hispania through its outstanding collections of Roman artefacts found in numerous excavations made in Augusta Emerita throughout the last two centuries.

They were chosen as representatives of the most emblematic statuary and decorative programmes of the major public buildings of Augusta Emerita: 13 samples are from the Theatre; 4 from the Tem-ple of Diana; 7 from the Provincial Forum, from which 4 were re-used in the monument of Santa Eu-lalia martyr, built in the 4th century AD; 17 pieces coming from the Coloniae Forum; a further piece is a fragmented statue which could be part of a commemorative monument of the triumph against barbarian tribes; 8 pieces are from the Mithraeum House and the final sample was originally from the Mars Temple. Archaeological details are available elsewhere (Álvarez & Nogales 2003; Nogales, 2007, 2011) and a selection of the studied pieces is shown in Fig. 3.

Fifty-one archaeological marble pieces dating from the Augustan period till the end of the 2nd cen-tury AD were selected for sampling (Table 1).

After visual inspection, a sample chip was discretely chiselled off. To avoid defacing the piece, samples could not always be taken from the most representative area to identify the marble source. They are all white marbles, some with light cream tones and/or pinkish patches besides pink streaks; others have either millimetric grey veins or folded streaks in grey or in pinkish-red-dish colours. Images of the coloured details of the white marble objects are displayed in Fig. 4. Evidence of superficial decay can be seen in some but in general most exhibit an exceptional state of conservation. The studied pieces, their possible chronology and the superficial description of the archaeological marble pie-ces are reported in Table 1.







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Methodology

Several analytical techniques were applied to characterize the 51 marble artefacts. Thin sections were made from 49 samples and the weathered surfaces were previously abraded to avoid possible contamination, before their powdering. X-ray powder di-ffraction (XRPD) was carried out on 50 sam-ples using an automatic Philips PW 1130/00 diffractometer (CuKα radiation at 40 kV, 20 mA; data recorded in the 3o -70o 2 ran-ge, 1o/min, 2s/step). Polarized-light opti-cal microscopy and cathodoluminescence microscopy were used on 49 samples and stable C and O isotopes were determined in 50 of them.

Optical microscopy was used to examine the mineralogy, fabric, texture, grain boundary sha-pe and to determine the MGS. These parameters have a particular diagnostic significance for dis-criminating the provenance of many ancient mar-bles, combined with other analytical results (e.g., Lazzarini et al., 1980; Moens et al., 1992; Lapuen-te et al., 2000; Gorgoni et al., 2002, Capedri et al., 2004; Attanasio et al., 2006). The presence of do-lomite was checked by XRPD and under cathodo-luminescence microscopy. The latter was carried out with CL8200 Mk5-1 cold equipment coupled to a NIKON Eclipse 50iPOL OM. The electron energy was 15-20 kV and the beam current was opera-ted at 250-300 A. The observed luminescent co-lours, their intensity and distribution in each sam-ple were recorded with an automatic digital NIKON COOLPIX5400 camera.

The cathodoluminescence images taken were automatically controlled (29 mm focal length, f/4.6 aperture, 1 s exposure, ISO-200) to obtain comparative images of the cathodoluminescence inten-sity (brightness). It is well known that the cathodoluminescence characteristics of carbonates are related to their chemical impurities. The colour of calcite and dolomite under Cathodoluminescence microscopy can be described by the combination of yellow, orange and red. Dolomite usually exhibits a red luminescence while calcite is typically yellow-orange but occasionally shows a dull blue lumi-nescence (Boggs & Krinsley, 2006).

The optical cathodoluminescence images were checked with those available from several classical quarrying areas (Barbin et al., 1989, 1992; Lapuente et al., 2012) and from ancient Iberian qua-rries (e.g., Lapuente et al., 2000; Lapuente & Blanc, 2002; Àlvarez et al., 2009). To better unders-tand the comparison, cathodoluminescence images from the Iberian marble database and some classical marbles will be shown

Oxygen and carbon isotopes were determined by isotope ratio mass spectrometry with Finnigan MAT 252 equipment. A Finnigan MAT Kiel II automatic preparation device was previously used (15 mg) for phosphoric acid digestion at 72 ºC and CO2 purification. The results were expressed in terms of usual delta notation (13C and 18O) in ‰ relative to the international reference standard PDB (McCrea, 1950). Analytical precision was better than 0.1 ‰ for both isotopic determinations. In calculating the 18O values, the phosphoric acid fractionation factor of 1.01025 for calcite was used (Sharma & Clayton, 1965). The isotopic signatures of the archaeological pieces were compared with those of the main classical marbles reported elsewhere (e.g., Moens et al., 1992; Gorgoni et al., 2002; Attanasio et al., 2006, 2009). Iberian isotope databases were also used (e.g., Lapuente & Turi, 1995; Lapuente et al., 2000; Alvarez et al., 2009; Origlia et al., 2011).







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Results

The results of the mineralogical-petrographic examination, the main cathodoluminescence charac-teristics and the 18O and 13C (PDB) values are displayed in Table 2. All pieces are calcitic mar-bles and five main groups of samples (A, B, C, D and E) were separated based on the MGS. They range from very fine (Group A) to coarse grained (Group E) marbles. Their mineralogical-petro-graphic and cathodoluminescence characteristics together with their isotopic signatures facilitate differentiation thereby mostly confirming the established groups.

6.1. Very fine grained marbles (Group A)

Five samples (nos. 1, 2, 17, 25 and 49) consist of very fine grained marbles with a MGS < 0.6-0.7 mm in length. Their texture is a typical isotropic fabric, mostly homeoblastic and granoblastic polygonal. Samples 25 and 49 show a slightly anisotropic fabric, in places with a preferred crysta-llographic orientation. The grain shapes have mainly straight to slightly curved boundaries. Their cathodoluminescence characteristics are variable and range from homogeneous brown to hetero-geneous dark orange with a patchy distribution of the intensity (Fig. S1, freely available online as Supplementary Material linked to this article on the GSW website of the journal, http://eurjmin.geoscienceworld.org/). Dolomite, quartz, iron ore and plagioclase are rare accessory minerals, in accordance with the pure white colour. Their isotopic values, with 18O (PDB) between -1.41 and -2.32 and 13C from 1.93 to 2.14, are distinctive from the rest of the samples (Table 2).

6.2. Fine grained marbles (Group B)

Samples nos. 3, 6, 15, 22, 26, 27, 29, 40, 41, 44, 46 and 48 are fine grained calcitic marbles, with MGS < 1.1 or 1.2 mm long, with the exception of sample 29 which is slightly finer (MGS < 0.9 mm). Macroscopically, the analysed samples are mainly pure white or whitish in light cream tint, but sample no. 6 is white with pinkish patches (Table 1, Fig. 4l).

Their anisotropic fabric shows different foliation microstructures such as elongated shape grains of calcite, crystallographic preferred orientation and grain size variations in irregular bands. (Fig. 5a, b, S2). Dolomite is sporadic but in samples 6, 41 and 48 constitutes lenticular aggregates of microcrystals. Evidence of dynamic recrystallization is also shown, such as polysynthetic twinning, undulatory extinction and small intracrystalline subgrains

The crystal boundaries, mainly sutured from indented to embayed, less frequently curved and rarely straight, are also a typical response of syntectonic recrystallization (Blenkinsop, 2000). Accessory granular quartz is always present, either associated to the finest-grained calcite bands, or dispersed between the coarser grains, and/or occasionally as tiny particles (< 25 m). Sam-ples nos. 15, 27 and 29 show amoeboid poikilitic quartz which ranges between 0.15 to 0.75 mm in diameter. Other accessory minerals are K-feldspar (sample no. 3), very scarce iron minerals (sam-ples nos.15, 22, 40, 41 and 44) and flakes of muscovite and phlogopite associated to the preferred orientated lenticular aggregates of microdolomite with iron oxides (sample no. 6). Phyllosilicates in veins (muscovite and/or chlorite) were visually observed in artefacts nos.15 and 29 (Fig. 4b, c).

Their cathodoluminescence distribution (Figs. 5a, b, S2) is heterogeneous in dark orange with faint to medium intensities (nos. 3, 26, 27, 44 and 46), or medium to moderately strong inten-sities associated either to yellow luminescent intergranular (nos. 22, 40), or to red luminescent microdolomites aggregates (nos. 6, 41, 48). In particular, sample 6 shows non luminescent pat-ches where iron ores are concentrated. Samples nos. 15 and 29 show a heterogeneous strong to faint patchy cathodoluminescence intensity distribution (Fig. S1). Despite the variability in the cathodoluminescence patterns, a common feature in all these fine grained marbles is the presence of calcite with intracrystalline cathodoluminescence zoning, either with concentric or sector zoning appearance (Reeder, 1991).

Their isotopic 18O values range from -4.68 to -6.15 ‰, and 13C from 1.03 to 2.65 ‰. Ne-vertheless, most of the samples in Group B exhibit rather uniform isotopic compositions (Table 2), especially for 18O values.







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6.3. Medium grained marbles (Group C)

Marbles of group C (Table 2), with MGS between 1.4 mm and 1.9 mm in length, comprise 20 samples (nos. 4, 5, 7, 11, 12, 13, 14, 19, 20, 21, 23, 28, 30, 32, 33, 35, 36, 39, 45 and 50). All samples of this group are pure white or white with light coloured tint (Table 1, Fig. 4). Some ex-hibit creamy to greyish patches (nos. 14, 19, 20, 23, 28 and 39) and also a pink streak (no. 19). Their anisotropic fabric generally shows the same deformation microstructures as those exhibited by the fine grained marbles (Group B). However, samples nos. 30, 32, 36 and 45 have a slightly homeoblastic texture with scarce signs of intracrystalline deformation and faint to medium catho-doluminescence intensities. On the contrary, samples 4, 5, 7, 12, 21, 28 and 35 are characterized by their heteroblastic mortar texture with a heterogeneous cathodoluminescence distribution. The dark cathodoluminescence, shown by many porphyroclasts or relics, stands out against the ma-trix (small grains around them) which exhibits a brighter medium intensity (Figs. 5c, S2). Sample no. 33 shows abundant signs of intracrystalline deformation but its cathodoluminescence-pattern differs in the moderately strong cathodoluminescence intensity (Figs. 5d, S2). In samples nos. 11, 14, 19, 20, 23, 28, 39 and 50, different microstructures are exhibited in a millimetric scale, combining zones with a relatively homeoblastic and granoblastic polygonal texture, with others in which calcite shows evidence of ductile deformation. A common cathodoluminescence feature is the presence of intracrystalline zoned cathodoluminescence calcite with faint-medium-strong in-tensity distribution from the core to the boundaries. Grain boundary shape exhibits mainly inden-ted boundaries, embayed or deeply sutured. Quartz is always present in small rounded grains or in tiny disperse particles and occasionally in amoeboid poikilitic grains (samples nos.14 and 19). Other accessories occur in the whitish varieties with light coloured patches. They are clustered as microgranular aggregates of dolomite containing scarce micas (muscovite and/or phlogopite) and iron oxide impurities which are concentrated in millimetric bands or in irregular veins, non lumi-nescent under cathodoluminescence (Figs. 5e, S3).

Isotopic signatures are quite uniform, ranging from -4.89 to -5.74‰ (18O) and from 1.12 to 2.21 ‰ (13C) values, except sample no. 33 with -5.97 ‰ (18O) and 2.93 ‰ (13C).

6.4. Medium to coarse grained marbles (Group D)

Group D consists of samples 8, 9, 10 and 51. Their MGS, ranging from 1.8 and 2.1 mm in length, is at the limit between medium to coarse grained marbles. They are white calcitic marbles with isotropic fabric and heterogranoblastic texture and no evidence of strain. Grain boundary shapes are mainly curved to straight. Under cold equipment, optical cathodoluminescence exhibits a uni-form non-luminescent pattern (Fig. S1). No accessories were detected. Their isotopic signature, with 18O values from -2.85 to -2.92 ‰, is distinctive due the highly positive 13C values ran-ging from 5.06 to 5.26 ‰ which are the highest among all the analyzed samples.

6.5. Coarse grained marbles (Group E)

Nine samples (nos. 18, 24, 31, 34, 37, 38, 42, 43 and 47) are white or whitish coarse grained marbles with the MGS ≥ 2mm in length, most of them range between 2 and 2.5 mm, but sample no. 43 reaches up to 3.2 mm in diameter. The latter sample is the only marble in this group E, which has an isotropic fabric and heterogranoblastic texture with scarce signs of intracrystalline deformation. Its grain boundary shape is mostly embayed, but also curved and slightly indented. Moreover, the absence of quartz and dolomite as accessories is significant. A heterogeneous, very faint to medium patched luminescent with relics is shown by cathodoluminescence (Fig. S1).

On the contrary, the other samples of this Group exhibit anisotropic fabric with microstructures associated to dynamic recrystallization, especially samples nos. 18, 31 and 47 which have a mor-tar texture, with faint to medium cathodoluminescence intensity and distinctive zoned calcite with dark cores or relics (Figs. 5f, S3). Samples 24 and 42 exhibit a peculiar cathodoluminescence-pa-ttern with concentric oscillatory bright/faint luminescence (Figs. 5g, S3). Additionally, samples nos. 34, 37 and 38 show mainly homeoblastic texture, gently layered with deformed shape grains (nos. 37 and 38), with straight, slightly curved and occasionally indented grain boundary shape. Their medium to faint cathodoluminescence intensity shows a brighter yellow to orange lumines-cence especially concentrated between the grain boundaries (Figs. 5h, S3).







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Updated characterization of the Estremoz An-ticline vs. Almadén de la Plata marbles

In order to identify the most suitable parameters to be applied for discriminating the Estremoz Anticline and Almadén de la Plata marbles, an updated characterization is provided here, taking into account our own published and unpublished data and other data in literature. Our marble collection from the Estremoz Anticline district consists of over one hundred samples collected from six quarries, preferentially in the southern half of the anticline (see Geological setting).

However, the differences in physical and/or compositional features of marbles collected at each quarry of this district are minimal and depend greatly on the specific collection of samples taken. Moreover, the petrographic and cathodoluminescence variability found in samples from each qua-rry makes it difficult to highlight the marble fingerprints of each quarry. Consequently, instead of specifying characteristics of a single quarry, it is more reasonable to consider all the quarries of the Estremoz Anticline district as one unique reference group. With respect to the Almadén de la Plata marble district, our database comprises samples collected in the area of Sierra Los Covachos but other recently discovered ancient quarries in this district are under study.

Visually, light coloured marble varieties, from pure white to whitish with cream, pink to greyi-sh tint are commonly found in both the Estremoz Anticline and Almadén de la Plata marble dis-tricts. Their whitish marbles often contain greyish to pink-reddish coloured streaks.

Light grey marbles are discontinuously inter-calated with whitish ones. Dark grey veined and pink varieties, some of the latter alternating with green bands, are much more frequent in the Es-tremoz Anticline district, but not exclusive, since they also occur in other Ossa Morena Zone dis-tricts, as in the Viana do Alentejo marbles.







27

Obviously, the differences in colour are related with compositional variations but as it is clear that Roman workshops selected the pure white and whitish varieties for statuary, the quarry marble characterization must be concentrated on the light coloured varieties when the database is applied to the provenance of statuary white marbles.

Regarding petrography, in both Iberian districts, white marble ran-ges from fine to coarse grain size, with MGS from just below 1mm up to 3.8 mm long (in Almadén de la Plata marbles), and quite occasionally up to 4 mm (in Estremoz Anticline marbles). However, most of the Estremoz Anticline quarry marbles reach up to 2.5 mm in diameter while on the contrary, Almadén de la Plata quarry mar-bles display a wider range of grain sizes, with samples over 2.5 mm in length not being so uncommon.

Fig. 5. Selection of photomicrographs in crossed polarized light and cathodolumines-

cence images. (Scale bar is 1mm). Archaeological samples in the left-hand row. Quarry

samples in the right-hand row. All the images are available online as Supplementary Figs.

S2 to S5. Fine grained marbles (Group B) in (a) no. 27 and (b) no. 41; Medium grained marbles (Group C) in (c) no. 28, (d) no. 33 and

(e) no. 20; Coarse grained samples (Group E) in (f) no. 18, (g) no. 24 and (h) no. 37. Quarry samples from the Estremoz Anticline

district are: Fine grained marbles from Pardais in (i) PR-12; Fine-medium grained marbles from Pardais in (j) PR-4 and (k) PR-14;

Medium grained marble from Estremoz in (m) ET-5; and Coarse grained marble from Estremoz in (n) ET-21. All the Estremoz Anti-

cline quarry marbles exhibit heterogeneous faint to moderately strong cathodoluminescence. Quarry samples from the Almadén de

la Plata district are: Fine grained marble in (l) ALM-10309; Fine to coarse grained marble in (o) AP-D2; and Coarse grained marble

with scarce quartz in (p) AP-A3. All the AP marbles display homogeneous moderately strong to very strong cathodoluminescen-

ce patterns and varying amounts of granular quartz related to the creamy and pinkish patches. Note the diversity of maximum

grain size (MGS) and textures in both artefacts and quarry marbles. The combination of petrographic and cathodoluminescence

features help to discriminate Almadén de la Plata and Estremoz Anticline marble sources. After discussion artefact samples (a)

(b) (c) (f) (g) (h) were assigned to the Estremoz Anticline marble district. However sample no. 33 in (d) displays homogeneous ca-

thodoluminescence with moderately strong intensity, compatible with both Estremoz Anticline and Almadén de la Plata marbles.

The right-hand row of Fig. 5 illustrates photomicrographs, in cross-polarized light, of different white quarry marbles from Estremoz Anticline (Pardais and Estremoz) and Almadén de la Plata marbles. For Estremoz Anticline marbles, see e.g. fine grained varieties in Fig. 5i to 5k, and me-dium to coarse grained ones in Fig. 5m and 5n. For Almadén de la Plata marbles,

In both Estremoz Anticline and Almadén de la Plata marbles, the microstructure is extremely va-riable and signs of intracrystalline deformation are very common. Mortar texture is not exclusive to the Almadén de la Plata district, since in all the quarries of the Estremoz Anticline district, even in the Estremoz quarries, the marbles associated to shear zones show inhomogeneous deformation stages from ductile to fragile. In both marble districts, the intra-quarry variation of features affects from macro to microscale and it is not unusual to find different microstructures in one single mar-ble block.

This heterogeneity also concerns the marble identification based on accessory minerals which is very limited in the whitish statuary marbles. As the accessories are concentrated on the coloured pat-ches and veins, the chips collected from the archaeological objects are not always the most representative sample to be compared with the quarry marble. Nevertheless some indications might be useful. Quartz is ubiquitous in all varieties of both districts, whe-ther rounded grains, tiny particles, or amoeboid polikilitic crystals. Occasionally, the rounded partially reabsorbed quartz exhibits a si-milar grain size to that of calcite. They are scattered or grouped in bands, even in polycrystalline aggregates in layers and lenses. In whitish marbles, quartz is concentrated in the pinkish or creamy patches, ranging generally from 1-3 % in volume in Estremoz Anticline marbles, but the content in Almadén de la Plata marbles can be larger (1-5 % volume), mostly concentrated in layers of finer grained calcite.

Comparing petrographic and cathodoluminescence image of Fig. 5 (Figs. S4, S5), it is clear that some Almadén de la Plata marbles contain more quartz than those shown in the Estremoz Anticline mar-bles. In another Ossa More-na Zone marble source, like Viana do Alentejo (Fig. 2), quartz is even more signifi-cantly abundant (Fig. S6).

In both Estremoz Anticline and Almadén de la Plata mar-bles, microdolomite aggregates are associated to the pin-kish or greyish patches together with Fe-bearing opaque minerals and scarce flakes of muscovite and /or phlogopite. Tremolite, restricted to the greyish and greenish varieties, is common in Almadén de la Plata marbles, but not exclu-sive to this district. Disperse cloudy dolomite crystals, with the same size of calcite, have been recognized in pinkish quarry marbles of both districts.







29

Applying optical cathodoluminescence images to the marble provenance, different patterns can be observed which help to discriminate marble quarry areas. The presence of cathodoluminescence zoned calcite that appears to be a single uniform crystal under polarized light, and / or dark cores with clear overgrowths helps to discriminate the Estremoz Anticline marble sources from the Alma-dén de la Plata marbles, compare for instance a coarse grained marble from the Estremoz Anticline (Fig. 5n) and one from the Almadén de la Plata district (Fig. 5p). Regarding cathodoluminescence intensity, the Estremoz Anticline marbles show faint, medium or moderately strong luminescence, while the Almadén de la Plata marbles and also other quarry marbles of the Ossa Morena Zone like Viana do Alentejo, manifest a strong to very strong orange intensity under optical cathodolumines-cence microscopy, as can be observed in the same Fig. 5 (Figs. S4, S5) or in Fig. S6 which includes a Viana do Alentejo marble.

The differences on cathodoluminescence intensity agree with their cathodoluminescence emission registered at the 620-650 nm peak measured by a combination of cathodoluminescence and SEM equipment (Lapuente et al., 2000). While the average va-lue measured in Almadén de la Plata marbles is 110.2, in the Viana do Alentejo marbles it reaches 449.3 and 1131.5, each one measured in two different varieties. On the con-trary, in the Estremoz Anticline marbles the average value

As mentioned, when the marble database is applied to the provenance of statuary white marbles, the comparison must be made with features and parameters measured in white or whitish quarry marbles. This is especially important for the isotopic signature shown in 13C vs. 18O diagrams, as using all the coloured varieties to define theThe isotopic signature of marbles in Group E is quite homogeneous, with values ranging from isotopic field of a single quarry enlarges the geochemical clusters unnecessarily, making their imple-mentation impracticable for marble provenance. In Fig. 6a an updated isotopic diagram is proposed for the Ossa Mo-rena Zone marbles based on the available databases including the isotopic values from the white and whitish Iberian marbles recently reported by Origlia et al. (2011) in a study applied to the provenance of marble artefacts from Thamusida (Morocco).

Discussion

Table 3 summarizes the possible marble sources inferred by the analytical results compared with the available databases.

Group Piece Mine-petrography Cathodoluminescence- Compatible isotopic fields PROVENANCE No. Iberian quarries (OMZ) Classical quarries Fig. 6b Figs. 7a, 7b A 1 Carrara Carrara -- Carrara CarraraA 2 Carrara Carrara -- Carrara CarraraA 17 Carrara Carrara -- Carrara CarraraA 25 Carrara / Göktepe Carrara / Göktepe -- Carrara CarraraA 49 Carrara / Göktepe / EA Carrara -- Carrara CarraraB 3 EA / AP EA EA Pentelikon / Dokimeion EAB 26 EA / AP / Dokimeion EA EA Pentelikon / Dokimeion EAB 27 EA / AP EA EA Pentelikon / Dokimeion EAB 44 EA / AP EA EA Pentelikon / Dokimeion EAB 46 EA / AP / Dokimeion EA EA Pentelikon / Dokimeion EAB 6 EA / AP EA EA Pentelikon / Dokimeion EAB 41 EA / AP EA EA Dokimeion EAB 48 EA / AP EA EA Dokimeion EAB 22 EA / AP EA EA Pentelikon / Dokimeion EAB 40 EA / AP / Dokimeion EA / AP EA Pentelikon EAB 29 EA / AP / Pentelikon EA / Pentelikon EA Pentelikon / Dokimeion EA or Pentelikon?B 15 EA / AP / Pentelikon EA / Pentelikon EA Pentelikon EA or Pentelikon?C 30 EA / AP EA EA Pentelikon / Dokimeion EAC 32 EA / AP EA EA Pentelikon / Dokimeion EAC 36 EA / AP EA EA Dokimeion EAC 45 EA / AP EA EA Dokimeion EAC 7 EA / AP / Dokimeion EA EA Pentelikon / Dokimeion EAC 5 EA / AP / Dokimeion EA EA Pentelikon / Dokimeion EAC 12 EA / AP / Dokimeion EA EA Pentelikon / Dokimeion EAC 35 EA / AP / Dokimeion EA EA Pentelikon / Dokimeion EAC 4 EA / AP / Dokimeion EA -- -- EAC 21 EA / AP / Dokimeion EA EA Pentelikon / Dokimeion EAC 14 EA / AP EA EA Pentelikon / Dokimeion EAC 19 EA / AP EA EA Dokimeion EAC 20 EA / AP EA EA Dokimeion EAC 28 EA / AP / Dokimeion EA EA Pentelikon / Dokimeion EAC 13 EA / AP EA EA Pentelikon / Dokimeion EAC 11 EA / AP EA EA Pentelikon / Dokimeion EAC 23 EA / AP EA EA Pentelikon / Dokimeion EAC 39 EA / AP EA EA EA







31

Conclusions

A multi-method approach to determine unambiguously the provenance of white marbles used in archaeological pieces is always essential, but for the case of discriminating white and whitish mar-bles originally from the Ossa Morena Zone, the combination of mineralogical-petrographic features with C and O isotopes requires, in many cases, the complementary use of an additional technique. Optical cathodoluminescence images applied to this proposal were very useful for the provenance determination of Roman statuary marbles from Augusta Emerita.

Comparing the physical and compositional parameters of the archaeological samples with the avai-lable database, they match well with specific marbles collected in quarries of the southern part of the Estremoz Anticline structure. However, the intra-quarry variability attested through these pa-rameters and the minimal differences found in marbles from different Estremoz Anticline quarries, makes it more reasonable to consider them all together as just one unique reference group. They share mineralogical-petrographic characteristics with the Almadén de la Plata marbles. Neverthe-less, the combination of different techniques facilitates their identification.

A wide range of MGS were measured on the marbles assigned to the Estremoz Anticline district, ranging from 1.1 to 2.5 mm in length. A finer grained sample (MGS < 0.9 mm) was an uncer-tain Estremoz Anticline marble. Since they are white or almost pure white marbles, the number of accessories greatly limits their use in provenance determination. The presence of scarce flakes of phlogopite associated to pinkish patches simplifies their discrimination from other fine grained marbles like Pentelikon, but muscovite and dolomite are common in this classical and both Iberian marbles.

An updated isotopic diagram for the Estremoz Anticline and Almadén de la Plata marbles is propo-sed combining the available databases which facilitates the comparative study of both Iberian mar-ble sources (Fig. 6b).

The coarse grained marbles of the archaeological pieces (MGS > 2mm) assigned to the Estre-moz Anticline marbles have an isotopic signature with 13C values below 1.5‰ (PDB) (Table 2) which clearly fall outside the Almadén de la Plata isotopic field. This parameter might be additiona-lly applied to discriminate coarse grained Estremoz Anticline marbles in other provenance studies concerning Hispanic artefacts. Cathodoluminescence patterns contribute to better identification in cases of isotopic overlapping, like those of Viana do Alentejo or from other coarse grained classical marbles (Fig. 7b). Conversely, though the updated isotopic diagram applied to the provenance of fine and medium grained marbles assists the discrimination between Almadén de la Plata and Es-tremoz Anticline marbles, and additional technique is also required because their isotopic signatu-res partially overlap. Furthermore, even with the additional combination of the cathodoluminescen-ce patterns, certain marbles show common features to both Estremoz Anticline and Almadén de la Plata marbles, making their marble source uncertain.

Regarding the discrimination from the classical marbles, in the isotopic diagram for fine-medium grained white marbles (MGS < 2mm) the updated Almadén de la Plata isotopic field overlaps Pen-telikon and many Estremoz Anticline isotope values of quarry marbles coincide with the Penteli-kon and/or Dokimeion data (Fig. 7a). The use of additional optical cathodoluminescence features facilitates their identification, however even with the assistance of cathodoluminescence, in two samples it was not viable to ascertain between an Estremoz Anticline marble and a Pentelic marble source.

The archaeometric results corroborate the massive use of local marbles from the near Estremoz Anticline marble district located in the same Lusitanian administrative province. But on the other hand, the identification of a moderate number of imported classical marbles also raises new pers-pectives on their particular significance in the decorative programmes to embellish Augusta Emeri-ta, developed during its first centuries. This contribution may well stimulate further archaeological research to better understand the selection and use of local and imported marbles in the SW of Hispania.

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