Monte Arci Research Articles

Chert exploitation and production in Sardinia during the Neolithic

This research deals with the modes of chert exploitation in Sardinia during the Neolithic, combining information on major chert sources identified across the island with the technological analysis on several stratigraphic reliable series. It focuses on the changes in raw material selection and on the evolution of technological behaviours between the 6th and the 4th millennium BCE. The data collected in this work allowed us either to shed a light on the role this lithic resource played in the production systems of Neolithic communities in Sardinia, and to catch differences in the modes of procurement, depending on the chronology and location of the sites. During the Early Neolithic, lithic raw material circulation in Sardinia did not occur through organized networks, but it seems to have relied on the high mobility of the local groups. It is only at the end of the 5th millennium BCE that well-organized exchange circuits started operating. These involved mainly obsidian and this raw material apparently consolidated in time, due to the role carried out by San Ciriaco and Ozieri Middle to Late Neolithic cultures in the control and development of the Monte Arci obsidian supply. Chert was never involved in these networks and was mainly exploited locally and opportunistically. However, from the end of the Neolithic, some outcrop in the Oligo-Miocene basin of Perfugas was exploited on a supra-local scale and for a relatively short period.

Intra-source provenance study on Monte Arci (Sardinia) obsidian by pXRF: Role of the data acquisition and analysis tools

In this work, a detailed study of Monte Arci obsidian sub-sources using the increasingly accessible technique of pXRF is presented based upon a large dataset of 68 geological samples, for the development of X-ray fluorescence-based analytical standardless procedure. In addition, a non-conventional (for obsidian provenance study) direct application of multivariate analysis on XRF spectra (continuous variables), rather than absolute concentrations or intensity ratios (discrete variables) is proposed.Results from different softwares and data analysis approaches (bi-/trivariate versus multivariate) were compared. In a blind test, the bi-/trivariate approach led to the correct assignment for the main SA, SB, and SC sub-sources, taking into account averaged values of intensity ratios with their standard deviation obtained from three independent measurements. A high intra-source variability for the SB subgroups was detected (almost 13% of error in the assignment, 9 samples out of 68). A non-conventional application of multivariate analysis was carried out directly on the XRF spectra and correct assignments were obtained for SA, SB1, SC groups, while 71% of the SB2 samples were correctly identified. The non-destructive analysis on 14 archaeological samples from Su Carroppu (Carbonia, southwestern Sardinia) rockshelter and from the Middle Neolithic (MN) 422 structure of the open-air dwelling site at Cuccuru is Arrius (Cabras, central-western Sardinia) permitted to test the method and hypothesise their provenance. The comparison with visual characterization or previous analyses by Particle Induced X-Ray Emission (PIXE) permitted to verify the correct provenance assignment of all artifacts for the bi-/trivariate method, and for 12/14 samples in the case of the multivariate one. The standardless analytical approach proposed in this work can represent a more general method exploitable for other obsidian sources, other glassy materials, besides other materials of archaeological interest.

Intra-Source Provenance Study on Monte Arci (Sardinia) Obsidian by pXRF: Role of the Data Acquisition and Analysis Tools

Intra-Source Provenance Study on Monte Arci (Sardinia) Obsidian by pXRF: Role of the Data Acquisition and Analysis Tools

Chlorine as a Discriminant Element to Establish the Provenance of Central Mediterranean Obsidians

Abstract Chlorine is a minor element present in obsidians in quantities greater than in average igneous rocks. The chlorine concentration in obsidians is generally low, of the order of tenths of wt %, but it exhibits an appreciable differentiation among geological sources. Despite these characteristics, chlorine has rarely been taken into consideration as a possible indicator of obsidian provenance and it does not appear in the chemical analytical tables accompanying the geochemical characterisation of obsidian samples. In this work, after an overview of chlorine geochemistry and cycle, we present thirty-one new electron microprobe (EPMA) analyses, including Cl, of geologic obsidians sampled from the four sources of the Central Mediterranean, exploited in prehistoric times (Monte Arci, Palmarola, Lipari and Pantelleria). The results are compared with 175 new EPMA analyses, including Cl, of archaeological obsidians already characterised in previous work and of known provenance. As such it was possible to ascertain that each source has a characteristic chlorine concentration, showing the utility of its use in the studies of obsidian provenance. Furthermore, given that the solubility of chlorine in silicate melts is correlated to its alkali content, in particular sodium, we assessed the efficacy of simple binary graphs Cl vs Na2O to better constrain the provenance of the obsidian samples.

Petrographic and spectroscopic (FT-IR) study of Western Mediterranean obsidians geological sources and of a lithic collection from Ustica Island (Sicily)

I n this study we applied petrochemical methods (SEM-EDS; FT-IR) in order to characterize a group of obsidian flakes collected at Ustica island (Sicily). Despite the absence of obsidian geological outcrops, a lot of obsidian fragments still emerging from the lands of Ustica testify that the island was a major import center of obsidian during the prehistory. On this island, there are some prehistoric settlements, dated from the Neolithic to the Middle Bronze Age (6000- 1200 BC), in which the use of obsidian continued until the beginning of metals age. Our study includes: i) Macroscopic and microscopic optical observations, which allowed selecting 18 obsidian flakes (starting from 50 obsidian flakes) on the base of their morphological characteristics. ii) Density measurements (hydrostatic balance). iii) Scanning electron microscope determination (SEM-EDS) of major elements of the obsidian glasses and minerals. Results of our analyses were compared with 12 geological samples collected in obsidian sources from Monte Arci (Sardinia), Palmarola, Lipari and Pantelleria, i.e. the four most exploited obsidian sources of the ancient world in the Western-Central Mediterranean. This study confirms the presence of the Lipari and Pantelleria sources (Sicily) in our obsidian set. iv) We also determined (by FT-IR) the hydration degree of some obsidian flakes in order to detect a possible hydration gradient between the rim and the core of the flake sample. The width of the hydration rim, if any, can be used for an approximate evaluation of the age of the tool.

Obsidian economy on the Cauria Plateau (South Corsica, Middle Neolithic): New evidence from Renaghju and I Stantari

This paper aims to study and compare the obsidian economies of Renaghju and I Stantari, two neighbouring Neolithic sites located on the Cauria plateau (south-western Corsica). The occupation phase 3 of Renaghju and phase 1 of I Stantari, both attributed to the Middle Neolithic (fifth millennium BC), have provided respectively 112 and 99 obsidian artefacts. With the aim of completing our rather lacunary knowledge of the obsidian consumption behaviours in place in Corsica during this period, the entire assemblages have been geochemically characterised virtually non-destructively using LA-ICP-MS at SOLARIS (Southern Cross University [SCU]). Our analyses revealed that, while the obsidian raw materials were exclusively sourced from the Monte Arci complex in Sardinia (SA, SB2, and SC sub-types only), rather different consumption patterns are observed for the two sites despite their comparable nature (megalithic sites) and geographical proximity (400 m apart). These differences in obsidian consumption on adjacent sites could be explained by their divergent functions (ceremonial site [Renaghju] vs. ceremonial locus and large settlement [I Stantari]), or eventually point towards the need for a readjustment of the chronological attribution of the I Stantari phase 1 occupation level.

Obsidian Studies in the Prehistoric Central Mediterranean: After 50 Years, What Have We Learned and What Still Needs to Be Done?

AbstractObsidian sourcing studies have been conducted in the central Mediterranean for more than 50 years. Detailed studies have been done on the geological sources on four Italian islands, and many analytical methods have been used to successfully distinguish between them. The ability to conduct analyses using those minimally (LA-ICP-MS) or totally (XRF, pXRF) non-destructive to artifacts has led to >10,000 analyses just in the last decade. Along with the ability to assign artifacts to specific geological subsources, and an increased number of studies of techno-typology, this has allowed interpretations to be made about source access and territorial control, craft specialization and the chaîne opératoire, as well as the modes, frequency, and directions of movement and how that varied spacially and temporally. Obsidian especially from Lipari and from Monte Arci in Sardinia traveled hundreds of kilometers on a regular basis starting in the Early Neolithic. By the Late Neolithic, in some areas there was selection of specific obsidian sources and subsources, and differences in production methods and tool typology. Obsidian distribution and usage in the central Mediterranean continued over four-and-one-half millennia, in many areas well into the Bronze Age. There is much more still to do integrating these different studies, especially use-wear studies, along with those of lithic and other materials that also played a role in prehistoric transport and trade systems.

Much More Than a Glass: The Complex Magnetic and Microstructural Properties of Obsidian

Obsidian is a natural volcanic glass in which nanocrystalline and microcrystalline phases can coexist with the glassy one. In this paper, magnetic properties of Monte Arci obsidians are investigated by an experimental approach commonly applied to synthetic nanostructured materials and rarely to natural ones, and correlated with the mineralogical composition and microstructure. Among the different crystalline phases, the iron-containing components are found to be responsible for a great variety of magnetic behaviors, including paramagnetism, antiferromagnetism, ferromagnetism, and superparamagnetism. The combined use of powder X-ray diffraction (PXRD), 57Fe Mossbauer spectroscopy, DC magnetometry, and transmission electron microscopy (TEM/HRTEM) provides new insights in the Monte Arci obsidian: (i) the presence of magnetite nanoparticles spread into the glassy matrix; (ii) the presence of an antiferromagnetic phase responsible for a discontinuity at about 45 K; (iii) exchange bias phenomena, for the first ...

Obsidians artefacts from Renaghju (Corsica Island) and the Early Neolithic circulation of obsidian in the Western Mediterranean

The site of Renaghju has the largest excavated area of any Neolithic site on the island of Corsica (Western Mediterranean). Its lowest layer, exposed over a few hundred meters square contained a rich Early Neolithic Cardial ceramic and lithic industry dated by 14C to the second half of the 6th millennium BC. Obsidian, a raw material exogenous to the island, comprises ca. 15 % of the chipped stone industry. The provenance of 622 obsidian artefacts (84 % of the total assemblage) was determined through a combination of visual characterization, together with noninvasive particle-induced X-ray emission spectroscopy (PIXE) and energy dispersion spectrometer of a scanning electron microscope (SEM-EDS) on millimeter-sized polished fragments. This is, by far, the largest sample of obsidian artefacts analyzed from a Corsican Neolithic site. All but one of the artefacts was found to be made of obsidian from sources associated with the volcanic complex of Monte Arci on the nearby island of Sardinia. Obsidian from each of the three major Monte Arci sources exploited during the Neolithic were identified, with a predominance of obsidians of the SA and SB2 types over the SC type. Only one artefact was shown to be made of obsidian from another source, namely, that on the island of Palmarola, in the Pontine Archipelago. The Monte Arci obsidian were procured in the form of small nodules that were then reduced on site, the knappers primarily producing flakes using an expedient and intensive technology. This tradition involved the production of very few types of formal implements, including geometrics and carving/boring tools, forms that are typical of the Tyrrhenian Cardial Early Neolithic. This is the earliest Neolithic culture on Corsica, whose appearance coincides with a major colonization of both Corsica and Sardinia. The significant presence of Sardinian obsidians in the southwestern Corsican site of Renaghju attests to early contacts between groups inhabiting these islands from the 6th millennium BC, while the Palmarola obsidian indicates occasional contacts with groups living on the Italian Peninsula. Alternatively, this “exotic” raw material’s presence at Renaghju might be viewed as the result of frequent and intensive movements of the first colonists in the Tyrrhenian area.

New data and provenance of obsidian blocks from Middle Neolithic contexts on Corsica (western Mediterranean)

The provenance of twelve un-worked blocks and one part-knapped block recovered from the surface of five Middle Neolithic sites in the vicinity of Porto Vecchio, southeastern Corsica (western Mediterranean), was determined by ion beam analysis (PIXE). This is the first such discovery on Corsica of actual raw blocks of this exotic material. Twelve of these samples come from sources associated with the Monte Arci volcanic complex of Central-West Sardinia, with six each of the SA and SC chemical types. The only possible origin for the remaining block is Lipari, a raw material previously only attested by three artifacts from a Neolithic site of NW Corsica. This piece is aberrant for its unusual facies and its poor quality, making it quite unsuitable for knapping, and by extent distinct from the high quality glassy obsidian from Lipari that was used regularly by Neolithic peoples. This raises the question of the archaeological significance of this surface find.

SEM-EDS characterization of western Mediterranean obsidians and the Neolithic site of A Fuata (Corsica)

During the Neolithic, obsidians of the Monte Arci (Sardinia) volcanic complex were by far more used in the northern Tyrrhenian area than those of the three other source-islands (Lipari, Palmarola, Pantelleria) in the western Mediterranean. It is shown that merely determinations of content for six major elements with a scanning electron microscope by energy dispersion spectrometry (SEM-EDS) are sufficient to distinguish the four types of Monte Arci obsidians. Because of the compositional similarities between these obsidian types, a multivariate analysis is recommended in provenance studies. Although SEM-EDS, electron microprobe-wavelength dispersion spectrometry (EMP-WDS) and particle induced X-ray emission (PIXE) give essentially concordant results in the determination of these six element contents, subtle technique-related biases prevent the combination of SEM-EDS, EMP-WDS and PIXE data on source samples for provenance purposes. An SEM-EDS test-study reveals the first occurrence of obsidians of Lipari for the A Fuata Middle to Late Neolithic site of NW Corsica (north of Sardinia), in addition to the usual Monte Arci obsidians. Similar to EMP-WDS, the SEM-EDS technique requires only millimeter-sized fragments.

Chert and obsidian procurement of three Corsican sites during the 6th and 5th millenniums BC

Provenance studies of Corsican siliceous raw materials used during, the Neolithic focused mainly on obsidian. They showed an almost systematic use of Monte Arci sources (Sardinia). Chert studies have long been dodged, whereas the multiplicity of potential origins, in Sardinia and in continental areas, may provide complementary spatial information about diffusion patterns and interaction phenomenon in the Middle Tyrrhenian during the Neolithic. We studied obsidian and chert industries of three Corsican sites: Renaghju (Early Neolithic), Monte Revincu and Vasculacciu (both Middle Neolithic). In order to assign a provenance, 2241 chert archaeological samples were characterized by petrographic approaches and 100 obsidian artefacts were submitted to geochemical analyses. Each site provides a specific trend regarding relative abundances of raw materials, provenance and consumption patterns. Considered in the wider perspective of the Neolithic Corsican context, results reveal procurement variations from a chronological as well as a geographical point of view. Those variations may echo economic and social evolutions undergone in Neolithic societies of the Tyrrhenian area.

Obsidians in the Rio Saboccu (Sardinia, Italy) campsite: Provenance, reduction and relations with the wider Early Neolithic Tyrrhenian area

Technologic analyses of Neolithic obsidian assemblages are quite rare in Sardinia, like in the wider Western Mediterranean. Such an approach is presented here in conjunction with a visual/instrumental provenance study for the Rio Saboccu Early Neolithic (EN) site, which yielded more than 1000 obsidian artefacts. It is shown that this mostly expedient industry was realized from a non-opportunistic exploitation of the four obsidian types of the nearby Monte Arci (Sardinia) volcanic massif. The choice of the raw materials was chiefly guided by their intrinsic knapping qualities and in function of the maximum size of the expected final products; hence some selection in the (primary and/or secondary) sources exploited. The obsidian industries of EN sites from the northern Tyrrhenian area present clearly some affinities with that of Rio Saboccu and of other EN Sardinian sites, mainly those located in its vicinity. This suggests a regional influence of the EN communities settled in the proximity of the Monte Arci.

Obsidian from Pulo di Molfetta (Bari, Southern Italy): provenance from Lipari and first recognition of a Neolithic sample from Monte Arci (Sardinia)

Twenty-four obsidian artefacts of the Neolithic Age were found at the large karstic doline of Molfetta (near Bari) along the Southern Italian Adriatic coast. Non-destructive chemical analyses of the glass, by SEM-EDS, allowed their source rock regions to be determined. Twenty-three of the studied artefacts had been traded from the island of Lipari. Only one sample had a glass composition and microphenocrysts (biotite, pyroxene and feldspar) that indicate provenance from the Monte Arci area of Sardinia, in particular from the Perdas Urias (SC) outcrops. The attribution of this artefact to Sardinia enlarges the geographical pattern of Monte Arci obsidian exploitation and distribution from island to Southern Italy during the Middle to Late Neolithic.

Application of Laser Ablation ICP-MS for characterization of obsidian fragments from peri-Tyrrhenian area

Abstract This paper presents the results of a geochemical study on obsidian fragments by Inductively Coupled Plasma Mass Spectrometry associated with Laser Ablation (LA-ICP-MS). This analytical method, almost non-destructive, has proven to be a powerful tool for “in situ” determination of trace elements, and is very useful in characterizing and determining the provenance of obsidian fragments of archeological interest. Its major advantage is that 29 trace and rare earth elements can be analysed in a very short time, without any sample manipulation. Analyses were carried out on 27 representative obsidian samples, collected from the main geological outcrops of Sardinia and the minor islands of Lipari, Pantelleria and Palmarola, in the peri-Tyrrhenian area, and on eight obsidian fragments recovered from three different Italian archeological sites of Neolithic age. The geological samples show variable trace element and REE compositions, and differences in Cs, Y, Zr, Nb, Ba, La, Nd, Ho, Er and Yb were great enough to allow the various source areas to be distinguished. The fragments fall into seven compositional groups. Three, which are homogeneous but clearly distinct from each another, include the Lipari, Palmarola and Pantelleria samples. The other four groups refer to the obsidian of Monte Arci in Sardinia, already known in the literature as SA, SB1, SB2 and SC. LA-ICP-MS established the definite origin and source areas of the artefacts. Analytical results indicate that, for obsidian samples from the peri-Tyrrhenian area, significant geochemical differences exist in their trace and REE compositions, which identify their source areas and establish their provenance for archeometric purposes.

Diffusion of obsidian in the Mediterranean basin in the neolithic period: A trace element characterization of obsidian from Sardinia by instrumental neutron activation analysis

Obsidian samples from Monte Arci in Sardinia (Italy) have been characterized by their minor and trace element concentration in order to find discriminating parameters useful to provenance the prime matter of obsidian artifacts. Obsidian samples were collected both at the SA, SB and SC outcrops and far away from them. All samples were submitted to INAA. The trace element concentration appears to be very useful to discriminate the three flows. Multivariate statistical analysis confirms the satisfactory distinction between the three sources. The assignment of the samples collected far away from outcrops to a specific flow (SC) validates the hypothesis that obsidian blocks might have been washed out by alluvial events.

SEM–EDS analysis of western Mediterranean obsidians: a new tool for Neolithic provenance studies

The contents of Na, Al, Si, K, Ca and Fe of 99 obsidians from the western Mediterranean islands of Lipari, Palmarola, Pantelleria and Sardinia were determined with the energy-dispersive spectrometer of a scanning electron microscope (SEM–EDS). The Na and in a lesser way other elements contents characterize any obsidian source-island. In Sardinia (80 samples), the four Monte Arci obsidian geochemical types can be discriminated from binary diagrams of element contents or by a discriminant analysis based on the six elements measured. It is concluded that SEM–EDS offers a new option for Neolithic obsidian provenance studies in this region. To cite this article: F.-X. Le Bourdonnec et al., C. R. Geoscience 338 (2006).

A map of the Monte Arci (Sardinia Island, Western Mediterranean) obsidian primary to secondary sources. Implications for Neolithic provenance studies

Four types of obsidians from the Monte Arci volcanic complex (Sardinia) were used by Neolithic men in the North Tyrrhenian area of the western Mediterranean. A map of their occurrences from primary sources (mother rocks) to distant secondary deposits in the surrounding plains is presented. Some 1457 specimens were macroscopically characterized and in addition ~15% of them fingerprinted from their elemental compositions as determined by electron microprobe, neutron activation analysis or ion beam analysis. The results show that secondary sources, up to now largely neglected in provenance studies of ‘archaeological’ obsidians will have from now to be taken into account. To cite this article: C. Lugliè et al., C. R. Palevol 5 (2006) .

Early Neolithic obsidians in Sardinia (Western Mediterranean): the Su Carroppu case

All the obsidians from the undisturbed Early Neolithic (Cardial ware phase I) layer of the Su Carroppu rock-shelter (Sardinia island) were studied. Their elemental composition and that of obsidians from the Monte Arci (Sardinia) volcanic complex was determined by ion beam analysis (PIXE). A comparison between the composition of Su Carroppu artefacts, analysed non-destructively, and that of Western Mediterranean analysed in the same conditions shows that the archaeological material belongs to the SA, SB2 and SC Monte Arci-types, to the exclusion of the SB1 type. The typological/technological study of this industry allowed us to reconstruct two chaînes opératoires, for the production of blades (using predominantly SC obsidians) and of flakes (based exclusively on SA and SB2 obsidians), respectively, but on the whole, assemblage blade/bladelet production was performed somewhat preferably with SA and SB2 types. Thus, in the earliest EN culture known on the island, ancient man had, for the making of its obsidian toolkit, a highly adaptive behaviour applied to the reduction of different useful obsidian sources.

Industrial mineral occurrences associated with Cenozoic volcanic rocks of Sardinia (Italy): Geological, mineralogical, geochemical features and genetic implications

The most important Industrial Mineral (IM) deposits associated with the Cenozoic volcanics of Sardinia include kaolin, bentonite, and zeolites. Though of less significance, perlite and potassium feldspar, are also important in local and national markets. Bentonite, and to a lesser extent kaolin and perlite, form economically viable deposits and zeolites appear as very important industrial mineral commodities for future economic development. The market situation for potassium feldspar is still under evaluation for use in ceramics. All these deposit types occur as alteration products of Cenozoic volcanic rocks, which were emplaced during three main volcanic cycles: in the Eocene (EC, 55 to 51 Ma), Oligocene–Miocene (OMC, 32 to 13 Ma), and Pliocene–Pleistocene (PPC, 5 to 0.1 Ma). Kaolin, bentonite, zeolites, and potassium feldspar occur as alteration products of the OMC volcanites; perlite occurs as an alteration product of the PPC volcanites. All deposits have generally derived from the alteration of the most acidic members of the Cenozoic volcanic rocks (rhyolites to rhyodacites), but differences among the associated ore-forming phenomena are recognized. Hydrothermal sensu stricto, deuteric alteration and weathering are the most important processes involved in ore formation. Weathering, although of minor importance, can also contribute to enhance the alteration of the deposits formed by hydrothermal and deuteric processes. The extent and type of occurrences are mainly controlled by the local geological and structural features, and the environmental geochemical conditions. Kaolin occurs in three main districts: at Romana and Tresnuraghes it is hosted within ignimbritic sequences, while at Serrenti– Furtei it is found in pyroclastic flows and ash-flow tuffs. Kaolin formed by hydrothermal processes occurs in high-sulfidation ( Romana and Serrenti– Furtei) and low-sulfidation ( Tresnuraghes) type epithermal systems. The alteration is proximal to the feeder conduits and structural setting controls kaolin formation. Bentonite is widespread throughout Sardinia. Deposits occur as stratiform mineral bodies (in situ-altered) within poor welded pumice-rich and ash-rich layers and also as distal fall-out deposits, as lenticular bodies interlayered within the Miocene sedimentary sequences. The former originated by deuteric alteration and formation is mainly controlled by lithology, whereas the second type originated by weathering, which altered the volcanic ash-lenses deposited in lacustrine and/or fluvial–deltaic environments. Zeolites, mainly clinoptilolite and mordenite, are widespread in northern and central Sardinia, and deposits are distal from the vents. Zeolites form in situ-altered and epiclastic mineralization. The former shows higher zeolite contents than the latter, and zeolitization phenomena pervasively affect the ash-rich and pumice-rich layers. Principally deuteric processes gave rise to phreato-magmatic deposit-types and deposits formed in open hydrologic systems. Epiclastic mineralization originated from weathering of the volcanic ash-products. The perlite of Monte Arci (central-southern Sardinia) is associated with the PPC, which consists of a subalkaline sequence (from subalkaline basalts to rhyolitic lavas). Obsidian rhyolitic lavas, affected by weathering, host the mineralization. The weathering process involves complex interactions between non-hydrated volcanic glasses (obsidian) and meteoric water, which was heated circulating below the paleo-surface and formed hydrated glasses (perlite). Potassium feldspar mineralization is associated with low-sulfidation type epithermal systems, and was originated by hydrothermal phenomena sensu stricto. The K-feldspar-rich bodies occur preferentially within the most acidic members (rhyolitic–rhyodacitic pyroclastites) of the volcanic sequence.