Provenance analysis of Roman stone artefacts from sedimentary rocks from the archaeological site near Mošnje , NW Slovenia

This study deals with the macroscopic and microfacies characterisation of Roman stone artefacts excavated in 2006 from a Roman villa rustica near Mošnje (NW Slovenia) with the aim of defining their provenance. A total of 28 representative finds (querns, mortars, whetstones, tooled and rounded stones, a fragment of stone slab, mosaic tesserae and two architectural elements one with a relief) made of clastic and carbonate sedimentary rocks were examined. Comparison was made with rock samples taken from quarries and gravel bars close to the archaeological site, as well as from larger distance to the site. The majority of artefact sampled is composed of Upper Palaeozoic quartz sandstones, which are found as pebbles in gravel bars close to the archaeological site; while 2 samples were from Quaternary coarse grained clastic rocks which can be found in local glacio-fluvial sediments. Other finds were made of four different Mesozoic shallow-water limestones which outcrop in different areas of Central and SW Slovenia. The nearest Lower Jurassic biopelmicritic limestones are found at the western periphery of Ljubljana in Podutik. Cretaceous miliolid limestones and biocalcarenitic limestones with rudists are common in the successions of the Dinaric Carbonate Platform in SW Slovenia (for example, on the Trieste-Komen Plateau), NE Italy and SW Croatia. This indicates that the limestones for architectural elements, stone mortars and tesserae were brought to Mošnje from distant locations. Smaller stone tools are likely to have been made at the location of the archaeological site from material gathered locally, mostly pebbles from clastic rocks, which were accessible and suitable for tooling.


Introduction
During construction of a section of motorway (Vrba-Peračica) in the Gorenjska region NW Slovenia near the village of Mošnje, a Roman villa rustica was discovered (Fig. 1). The villa was built in the first half, respectively no later than the middle of the 1 st century A.D., and had been used until the end of the 2 nd century (lux & saGaDin, 2012). The villa rustica consisted of five masonry buildings built on the support wall. The largest and best preserved was the easternmost building that contained a residential area with baths. More than six thousand individual artefacts were collected, consisting of tools, jewellery, coins, pottery and other finds; most dating from the period between the 1 st and the 4 th centuries A.D. (lux, 2008). Among numerous stone finds are the querns, whetstones, mortars, two architectural elementsone with a relief and one similar to altar, black and white mosaic and other functional and decorative objects.Despite various archaeological finds of Roman stone artefacts within Slovenia there has been only a small number of publications regarding the provenance of the archaeological stone materials. KraMar (2009) published a short review of the stone material from this archaeological site, Košir (2011) analysed pyroclastic rocks finds from the Mošnje site, while similar analysis from other parts of Slovenia include stone material from Emona (Brecelj et al., 1989;raMovš, 1990;šašel Kos, 1990;raMovš, 2002;rižnar, 2010), studies of querns from Central and Coastal Slovenia (horvat & žuPančič, 1987) and NE Slovenia (Djurič et al., 2005;Djurič & Müller, 2009;KraMar & Dolenec, 2013).
The aims of the present study were: • to define and describe the sedimentary rocks used for various artefacts and stone articles found at the villa rustica near Mošnje, • to compare the stone materials with the samples from quarries and gravel bars close to and further away from the archaeological site in order to determine their provenance.

Geological setting
The archaeological site near Mošnje is located in an intramontane basin known as the Gorenjska Basin (vraBec & FoDor, 2006). Tectonically the basin is located in the northeastern corner of the Adria-Europe convergent margin, situated at the contact between Southern Alps (northern margin) and External Dinarids (southern margin). The geological basement of the basin and its margins is quite complex; composed of mainly clastic Carboniferous-Permian strata, Mesozoic carbonate rocks and Oligocene to Miocene clastic and volcanoclastic rocks (GraD & Ferjančič 1974;GraD & Ferjančič, 1976;Buser & cajhen 1978;Buser, 1980). The basin itself is filled with Quaternary alluvial and fluvial deposits from the Sava River and its tributaries. Pebbles found in these deposits are mainly composed of Permian Val Gardena sandstones, Lower Triassic conglomerates, Middle Triassic limestones with cherts and sandstones, Upper Triassic Dachstein limestones and Upper Cretaceous reddish marls (jurKovšeK, 1986;Buser, 2004;žuPanec & herlec, 2004).

Materials and methods
A total of 28 stone finds were sampled for petrographic analysis (Table 1). Eighteen of these samples were also microscopically examined (Tables 2, 3). Among sampled finds were querns, whetstones, tooled and rounded stones, stone mortars, a fragment of stone slab, two architectural elements -one with relief, the other similar to altar and black and white mosaic tesserae. In addition, 21 comparative samples, taken from identified potential source areas in vicinity and more distant localities to Mošnje (Tables 4, 5), were used for comparison (Table 6). These potential source areas were determined on the basis of the rock type and the characteristics of the stone artefacts, a detailed review of existing literature on provenance of the Roman stone materials and a review of the geology of the research area (jurKovšeK, 1986;Brecelj et al., 1989;raMovš, 1990;raMovš, 2002;Buser, 2004;žuPanec & herlec, 2004;Bavec, 2008;jurKovšeK, 2010;rižnar, 2010).
Potential provenance areas included following localities (Fig. 2,Tables 4,5): • in vicinity to the archaeological site pebbles of clastic rocks were taken from the gravel bars of the Sava River near Lancovo ( Fig. 2

Archaeological samples
The results of analyses of samples indicate the use of a diverse variety of rock material. Two major groups were identified: smaller tools, such are querns and whetstones, mostly made of various medium to coarse-grained quartz sandstones, and mosaic tesserae and larger items, such as architectural elements, made of different limestones (Plate 1, figs. 1-8; Plate 2, figs. 9-16; Plate 3, figs. 17-18). Macroscopic description-common characteristics: Rock samples are grey to yellowish brown, medium to coarse grained, in places laminated quartz sandstones. Some also contain larger (1-5 mm) grains. Usually these rocks are strongly weathered exhibiting grey-greenish weathered surfaces.

Microscopic description:
The rocks structure is mostly heterogeneous, usually composed of 80 % grains and 20 % of matrix. Some are laminated (ANM 159, ANM 161, ANM 167). Grain sizes range from 0.05 to 0.8 mm, only rarely larger grains (2.5-25 mm) are present (ANM 163, ANM 164, ANM 165, ANM 167, ANM 187). They are poorly sorted, sub-angular to angular and elongated to isometric, and show no visible orientation. Often are coated with red haematite. Contacts between the grains are long and concavo-convex. Grains are represented mainly by mono and polycrystalline quartz grains (45-60 % of all), with irregular edges and undulose extinction. Others are lithic grains (25-45 % of all) mostly of igneous rocks, but also grains of slates, siltstones, limestones, sandstones, and cherts are present. These are rare and present only in some samples: micas ( Grey medium grained quartz-calcareous conglomerate, probably of Quaternary age (Plate 2, fig. 11).
Facies 1.C. Dark grey fine grained mica-quartz breccia (ANM 186 (quern)) Macroscopic description: Fine-grained dark grey matrix-supported breccia with up to 5 mm large quartz clasts, embedded in the dark matrix with mica flakes.
Microscopic description: Breccia is homogeneous, consisting of 85 % matrix and 15 % of grains. The grains range in size from 0.12 to 0.80 mm, are very well sorted, angular to sub-angular and of different shapes. Quartz grains dominate (60 %), while muscovite and weathered feldspars are subordinate. Matrix is of sericite (75 %) and finegrained quartz (25 %).

GROUP 2. Carbonate sedimentary rocks
Microscopic description: Sample ANM 160 is heterogeneous wackestone to packstone. Grain to matrix ratio is very variable, but on average 65/35. Grains are up to 0.6 mm in size and composed mainly of peloids (around 60 %) and bioclasts (35 %) with some pyrite crystals while intraclasts occur rarely. Bioclasts are of biserial foraminifera and other small foraminifera (Glomospira?), algae (Thaumathoporella?), mollusc shells and ostracoda. Some are unidentifiable. Also, small rounded sparitic grains are present; some of these are probably ooids. Sample ANM 170 shows similar composition, with average grain to matrix ratio 30/70, however here ostracods (50 %) dominate over other bioclasts, small peloidal grains and micritic intraclasts. The matrix in ANM 170 is micrite, while in ANM 160 micrite and microsparite, in places sparry calcite cement is present.
The observed characteristics indicate shallowwater depositional environment. Absence of age-diagnostic fossils prevents stratigraphic determination of this facies, however, based solely on the microfacies characteristic (cf. oGorelec, 2011) the rock is tentatively attributed to the Lower Jurassic.

Microscopic description:
Limestone is homogeneous packstone to grainstone. Grains are bioclasts of small spherical and biserial foraminifera, sparite-filled rudist shell fragments and echinoderms fragments. They are bounded by micrite to microsparite and in places also by sparite.
Based on the presence of the rudist shells we assigned this limestone to a shallow-water environment of Upper Cretaceous age (Plate 2, figs. 15 & 16).

Microscopic description:
Limestone is heterogeneous wackestone, composed of 70 % matrix and of 30 % grains. Grains are randomly distributed, without preferred orientation and up to 0.9 mm in size. The majority of grains are miliolid and other foraminifera. Shells, algae fragments and peloids occur rarely. Matrix is micritic and rarely microsparitic. Sparitic infilling of foraminifera moulds is present.
Based on the abundance of miliolids and other shallow-water grains we believe that the limestone was deposited in a shallow water environment and is probably Cretaceous in age (Plate 3, fig. 18).
Facies 2.D. Laminated dark grey to black bituminous limestone: 1 sample (ANM 133 (black tessera)) Macroscopic description: Laminated black to dark grey micritic limestone with transition to homogeneous dark brown micritic limestone. The rock is intersected by 1 mm thick white calcite veins.

Microscopic description:
The limestone is homogeneous bioturbated and laminated mudstone. The proportion of matrix approaches 90 %. Lamination is expressed as alternating bands of 3 mm thick laminae of clear microsparite with 5 mm thick laminae with higher content of organic matter. In some places we noted traces of bioturbation, oriented perpendicular to lamination. Grains are represented by ostracod fragments and rare particles of amorphous organic matter. Small particles of autogenous pyrite are also present. Amorphous organic matter is common and forms streaks and seams roughly parallel to the lamination.
Abundant presence of fine-grained matrix, lamination and high content of preserved organic matter points to the sedimentation in a hydrodynamically quiet anoxic environment. These conditions are typical for sedimentation in restricted lagoonal or deeper-water environments (Plate 3, fig. 17).

Comparative samples
A total of 21 samples with macroscopic petrographic characteristics potentially comparable with artefacts were taken for further examination. Petrographic analyses have shown that 12 of the comparative samples (Plate 3, figs. 19-24, Plate 4, figs. 25-30) from 6 locations ( Fig.  2) have certain similarities with the investigated archaeological materials. The results of microscopic analysis of these samples are shown in Table 4 and  Table 5, while their significant characteristics are given within the results of comparative analysis in the next subchapter. (Table 4) Samples of local provenance: Pebbles of quartz sandstone (3 selected samples from the Sava River gravel bars in Lancovo: P-1, P-2, P-3) (Plate 3, figs. 19-21): P-1 is a laminated dark grey to dark reddish brown medium grained sandstone. P-2 is reddish brown homogeneous fine grained sandstone. P-3 is a homogeneous grey to dark greenish grey medium grained sandstone with light grains of quartz, feldspars and micas. The rocks are of Upper Palaeozoic age.  fig. 26) is recrystallised and fractured, with anhedral crystals, cut by thin white veins, with a gradual transition to dolomitic limestone of Triassic age.

Samples of distant provenance:
Grey micritic limestones (3 selected samples from an abandoned quarry in Podutik: P-19, P-26 and P-28) (Plate 4, figs. 27 -29) of varying lighter and darker shades with thin calcitic veins, showing individual fossils, with an average size of 3 mm. The rocks are biopelmicrites i.e. grainstones of Lower Jurassic age.
Light grey biocalcarenitic limestone (1 selected sample from the Roman quarry Cava Romana in Aurisina/Nabrežina: Cr-1) (Plate 4, fig. 30) homogeneous in nature with darker fragmented fossils varying from 1 to 3 mm in size in a lighter coarse grained recrystallised carbonate matrix. The rock is a biointrasparite to biointramicrite i.e. packstone to grainstone of Upper Cretaceous age.

6
ANM 167: laminated, light grey, pebbly, medium grained lithic-quartz sandstone with transition to medium grained quartz conglomerate: quartz and lithic grains with fine grained sericite quartz matrix between them (+A).

PLATE 1
Comparison of archaeological and comparative samples GROUP  (Pleničar et al., 2009), while the Val Gardena formation includes red and grey sandstones, shale and conglomerates (sKaBerne, 1995;Buser, 2009). These rocks are found at several locations in NW Slovenia in the Gorenjska region, especially in the South Karavanke and at the hills around Škofja Loka (GraD & Ferjančič, 1976;Buser, 1980). Comparison of the archaeological samples with pebbles collected from gravel bars showed relative similarity in macroscopic characteristics and mineral composition, but they differ in the amount of feldspars (P-2, P-3) and lithic grains. However, due to the rounded shape of some artefacts (Fig. 3) and the presence of even large boulders (of several decimetres in size) of similar sandstones in the surrounding Quaternary fluvial and glacial deposits, we assume that the material for their production was brought from these deposits, located in the close vicinity of the archaeological site. The differences in the composition of the sandstones used to produce the artefacts are considerable and exceed the lateral and vertical facies variations expected in any one quarry, we presume that the material was obtained as pebbles from the gravel bars. Fine grained mica-quartz breccia, from which one quern is made (ANM 186), is presumably of Carboniferous age and such cobbles and boulders can be found in the Quaternary fluvial deposits in the vicinity of the archaeological site as well.

GROUP 2. Carbonate sedimentary rocks
Facies 2. A. Grey pelbiomicritic limestones The samples of darker grey stone mortar (ANM 160) and architectural element, similar to altar (ANM 170) (Fig. 4), are made of pelbiomicritic limestones. Microscopic analysis showed that these microfacies belong to the subtidal shallow-water environment located on a carbonate platform. ANM 187: grey, pebbly, coarse grained quartz sandstone to medium grained conglomerate: irregular contacts between quartz grains (+A).

PLATE 2
According to the geological map of Kranj (GraD & Ferjančič, 1976), shallow-water Upper Triassic and Lower Jurassic limestones exist on the Jelovica Plateau (in the vicinity of the sampling sites of the comparison samples from Kodrasti vrh (KV-1) and Stara Hleva (SH-1)). However they lack any similarity with the investigated artefacts. Furthermore, macroscopic and microscopic characteristics of samples ANM 160 and ANM 170 are in conformance with the samples P-19, P-26 and P-28. The latter were sampled in the vicinity of Podutik near Ljubljana from different Lower Jurassic rock beds, for which such sedimentary depositional environment is proven (novaK, 2003). In addition, Müllner (1879) and after him raMovš (1990) were supposing the existence of ancient quarries and stone masonry workshops at this location.
Facies 2.B. White to light grey biocalcarenitic limestones The material of the lighter grey stone mortar (ANM 185) and architectural element with relief (PN 6178) is biocalcarenitic limestone containing recrystallised small foraminifera, fragments of rudist shells and echinoderms. The presence of the rudist shells indicates an Upper Cretaceous shallow-water environment of the Dinaric Carbonate Platform. These limestones outcrop in SW Slovenia, NE Italy and SE Croatia. In Aurisina/ Nabrežina, near Trieste in Italy, four types of Upper Cretaceous shallow-water limestone from the Dinaric Carbonate Platform are quarried, just as they were in Roman times (Brecelj et al., 1989;cucchi & GerDol, 1986). The most similar to the Mošnje samples is a variety called fiorito, which is also found in the Cava Romana quarry. Similar horizons are found in Slovenia as well, in the Lipica formation (jurKovšeK et al., 1996;raMovš, 2002 The black mosaic tessera (ANM 133) is of laminated dark grey to black bituminous micritic limestone. Such limestone usually formed in an anoxic-deep or shallow water environment. In the immediate vicinity of the archaeological site we did not find any such rocks. Larger quantities suitable for extraction can be found in the Kras region where shallow-water carbonates containing beds of laminated bituminous limestones with cherts are present within the various Cretaceous formations of Cenomanian-Campanian age (jurKovšeK, 2010). šriBar (1995) has shown that the sedimentary environment for the formation of bituminous limestones in Southwestern Slovenia could also exist in areas of «upwelling» and intertidal coastal areas. However, it must be emphasized that similar sedimentation conditions, optimal for development of the laminated bituminous limestones, existed elsewhere at differing times during the Mesozoic. This wide potential area could be reduced in further research by combining geological with archaeological aspects which assume arrival of a mosaist to Mošnje from the area of today's Italy bringing tesserae with himself.

Conclusions
The Roman villa near Mošnje in NW Slovenia was discovered during the construction of a section of motorway (Vrba-Peračica). The numerous stone finds from this archaeological site are comprised of differing stone materials. By microfacies analysis of selected samples, we determined the rock type and attempted to establish the provenance of these materials.
The studied stone artefacts can be divided in to two groups dependent on sedimentary rock type: clastic or carbonate.
Small stone artefacts, such as querns, whetstones and tooled stones, including pebbles with tool marks, are made of clastic sedimentary rocks (Facies 1.A to 1.C). The rocks are mainly quartz sandstones, most likely of Upper Palaeozoic age, although there are also coarse grained materials like conglomerates and breccias from local Quaternary deposits of the Sava River. Fieldwork and data from the Basic Geological Map (GraD & Ferjančič, 1976), clearly shows that similar rocks are present in the Sava gravel bars and terraces, located in immediate vicinity of the archaeological site. Therefore we propose that these small artefacts were most probably produced locally.
Artefacts made of carbonate rocks tell us a different story. Microscopic analysis and comparison with the carbonate samples, taken local to the archaeological site, and with samples from further afield, indicate that the investigated limestone Roman artefacts were not produced locally. The architectural element and grey stone mortar are made of dark grey pelbiomicritic limestone (Facies 2.A), which is tentatively correlated with Lower Jurassic limestones from the vicinity of Podutik near Ljubljana.
The light grey stone mortar and the architectural element with relief are made of white to light grey Upper Cretaceous biocalcarenitic limestone with rudist shells (Facies 2.B). Similar limestones are characteristic for the Upper Cretaceous successions of the Dinaric Carbonate Platform outcropping in the SW Slovenia, NE Italy and SE Croatia. These limestones were quarried in Roman times near Aurisina/Nabrežina in Italy, and are still quarried today. Similar limestones are also typical for the Lipica formation on the Karst in Slovenia. We presume that the two architectural elements were imported to Mošnje from one of these areas, even though an archaeological aspect based on current knowledge favours the Italian extraction site.
The white and black mosaic tesserae composed of Cretaceous miliolid limestone (Facies 2.C) and dark organic-rich laminated limestone (Facies 2.D), respectively might originate from different horizons of the Cretaceous succession typical for the Dinaric Carbonate Platform. These rocks outcrop on the Trieste-Komen Plateau, but also in some other areas in Slovenia, therefore we cannot unequivocally determine their provenance.
The presented study indicates that in the Roman archaeological site near Mošnje smaller and useful consumable items, such as querns and whetstones, were made from locally sourced materials, easily picked from the ground. Conversely, larger items such as stone mortars, and more prestigious such as architectural elements and tesserae, were obtained by quarrying and imported.