Pottery from the Underworld. A petrological analysis of a selected group of Neolithic - Middle Bronze Age ceramics from the caves of Central Sardinia

Size: px

Start display at page:

Download "Pottery from the Underworld. A petrological analysis of a selected group of Neolithic - Middle Bronze Age ceramics from the caves of Central Sardinia"

Garry Joseph
5 years ago
Views:

1 Proceedings of the 39 th International Symposium for Archaeometry, Leuven (2012) Pottery from the Underworld. A petrological analysis of a selected group of Neolithic - Middle Bronze Age ceramics from the caves of Central Sardinia M.G. Gradoli 1 1. Geologist, MA in Archaeology, PhD researcher in Archaeology (Ceramics Technology), University of Leicester (UK) ggradoli@yahoo.it ABSTRACT Fifty prehistoric pottery sherds, ranging from the Late Neolithic to the Middle Bronze Age, from three different types of excavated caves were studied using a petrographic microscope. This was in order to investigate how raw materials were selected and mixed by ancient potters and whether a local cultural and technological style could be determined. Five different fabric groups and classes were identified, taking into account the prevalent geological nature of the aplastic inclusions. They are: metamorphic (with grog), volcanic, felsic (quartz in a red matrix), felsic (with biotite) and calcareous sand. A peculiar technological style in use among potters in the area was identified: the tempering of new Bronze Age pottery with the Final Neolithic burnt grog from Is Janas Cave. KEYWORDS Archaeology, Operational Sequence, Pottery Petrology, Provenance Analysis, Technological Style. Introduction Nine ritual caves were recognised by the author between 2005 and 2007 in the Barbagia di Seulo area in central Sardinia. Following their presentation by Gradoli and Meaden at the 2008 EAA Meeting, an International Project was started in 2009, in which the author has participated, including cave excavations. The present work is based on my MA dissertation on Pottery Petrology at the University of Leicester (UK). It is included as a specialist study in the research project Journeys to the Underworld: Ritual Transformations of Persons, Objects, and Caves in Prehistoric Central Sardinia, directed by Dr Robin Skeates, Department of Archaeology of the University of Durham (UK), and funded by the British Academy, the Prehistoric Society and the Fondazione Banco di Sardegna. Fifty samples were carefully selected from ceramics recovered during the 2009 and 2010 archaeological excavations in three different types of ritual caves (a large complex cave system, a small chamber burial and a spacious rock shelter) in a mountainous region in Central Sardinia, near the village of Seulo (Fig. 1). The area had never been studied from an archaeological viewpoint and proved to be very rewarding, as each cave contained rich prehistoric ritual deposits that could be dated from the Middle-Late Neolithic ( Cal BC Cal BC) to the Bronze Age ( Cal BC). Aim of the study and research queries The main aim of the study was to apply, for the first time in Sardinia, the principles of Ceramic Petrology to the Middle- Neolithic and Early Bronze Age pottery set excavated in the ritual caves of Seulo and to start compiling a Prehistoric Pottery Data Bank for Central Sardinia. Research queries were directed towards investigating: 1) how raw materials were selected and mixed by ancient potters and whether a typical local tradition, reflecting their social, cultural and natural environment, could be determined; 2) how direct examination of rocks and sediments in the area, together with my expertise as a professional geologist, could be used in a provenance study to assert the extremely close similarities between the pottery fabrics studied under the polarising microscope and potential raw material sources in the area; 3) whether the people who inhabited the area and performed rituals inside those caves had manufactured this pottery specifically for the ritual occasion, using special decoration patterns, shapes and fabrics and how this could shed light on the type of visual environment they may have perceived and experienced during the rites. Petrographic analysis of the pottery The petrographic analysis of the 50 pottery sherds selected was carried out on prepared 0.03mm-thick thin sections taken from the sherds in their original state, using an Axioskop 40 Zeiss polarising microscope equipped with an Axiocam MRc 5 camera. The method and terminology applied were those proposed by Whitbread (1989 and 1995). A descriptive vocabulary was used to better maintain objectivity during data recording and separate interpretation from description. Five different groups of fabrics were identified (Table 1): METAMORPHIC (with grog) Number of samples: 31(Table 1 and Figure 2) 215

2 Fig. 1. The area under study. Green dots indicate the caves, red dots the surface sites surveyed. Elaboration: Robin Skeates. Period: samples n. 1, 5, 6, 7, 8, 9, 10, 11 and 12 are Middle Bronze Age Bonannaro B phase, while all others are Late Neolithic Ozieri Culture. Fabric class characteristics: this is a rather heterogeneous fabric class with considerable variation in the quantity of grog and its composition. Other minor variations are linked to the quantity of mono and polycrystalline quartz and shale fragments and to the degree of coarseness of the inclusions. The micromass is generally optically inactive, but 9 Middle Bronze Age samples present optical activity. The latter characteristic indicates possible firing at a relatively low temperature, permitting the clay to retain part of its original crystalline structure. Discussion: Samples showing optical activity are all from the Middle Bronze Age and were found at Is Bittuleris Cave (n. 1, 5, 6) and at Su Cannisoni rock shelter (n. 7, 8, 9, 10, 11, 12). All other samples show optical inactivity and were found at Is Janas Cave (Late Neolithic). Here, the majority of pottery sherds show macroscopic signs of having been burnt, with either hard carbonized concretions or highly decomposed surfaces and edges. Thus indicating that they were fragmented before and during their burning, rather than subsequently during the performance of rites. This feature is also visible on a microscopic scale, as most of the grog used to temper the pottery is burnt or contains, in its groundmass, other small burnt inclusions. The original pottery used to temper them can be identified from their composition, matching the main fabric groups found in the caves studied. The Middle Bronze Age sherds are not macroscopically burnt but are tempered with burnt grog as well. The archaeological context suggests a possible cooking function for those from Is Janas Cave, often found in association with animal bones. The group of 7 sherds from Is Bittuleris Cave was associated with successive primary burials. At Su Cannisoni rock shelter, ceramics were deposited as part of an open-space rite in which only selected body parts, especially human skulls and long bones, were taken from upper Is Bittuleris Cave to be deposited in the rock shelter as part of secondary burial practices (Skeates 2010). They were later affected by severe weathering, due to the exposed position of the rock shelter, as shown under the polarizing microscope by re-deposition of secondary calcite, which filled channels and vughs in the macromass. The mineralogical nature of the most abundant inclusions is consistent with a source deriving from the Paleozoic metamorphic basement outcropping (see geological map in Figure 6) on the slopes of the Ingurtipani and Maragosu stream valleys or directly from river 216

3 alluvium, which shows rounded-edged shale fragments and which might have been easily obtained by potters. VOLCANIC Number of samples: 8 (Table 1 and Figure 3) Period: samples n. 3 and 4 are from Is Bittuleris Cave, Bronze Age; samples n. 16, 29, 35, 37 and 48 come from Is Janas Cave, except sample n. 50, found at Is Janas Caveinner room, which is Early Bronze Age, Bonannaro A phase. Fabric class characteristics: The fabric is homogeneous in character and is composed of a fine matrix with inclusions of coarse weathered volcanic rock fragments containing quartz and plagioclases or well-formed phenocrysts of multiple-twinned plagioclases. The groundmass is moderate to poorly sorted. The micromass is optically inactive. Discussion: Samples n. 27, 35, 37 and 48 appear intentionally and extensively burnt, while samples 16 and 29 are moderately burnt. They are all from Is Janas Cave. The mineralogical composition of the inclusions reflects the volcanic nature of local geology, in the part of the Ingurtipani and Maragosu stream valleys where the Riu Sa Luda Formation of the Early Permian Age outcrops: it is made up of coarse to medium-fine sediments with important volcanic components and tuff layers. FELSIC (in a fine red matrix) Number of samples: 4 (Table 1 and Figure 4) Period: samples n. 25, 34, 38 and 46 come from Is Janas Cave, Late Neolithic Age. Fabric class characteristics: The fabric is homogeneous and characterized by packed grains of mono and polycrystalline quartz in a fine red matrix. Optical state: inactive. Discussion: This is a distinctive fabric containing predominantly coarse, sand-size inclusions composed of mono and polycrystalline quartz with rare shale and volcanic fragments. Its composition is consistent with a source deriving from the local Early Permian Riu Sa Luda formation, in which quartz macro and micro conglomerates are found in a reddish sandstone matrix. The fabrics show a high concentration of coarse and medium-coarse inclusions, perhaps for the purpose of withstanding thermal shock during the preparation of meals during rites. FELSIC (with biotite) Number of samples: 4 (Table 1 and Figure 5) Period: sample n. 2 is from Is Bittuleris Cave, dated Middle Bronze Age Bonannaro B phase, while samples 27, 24 and 30 are from Is Janas Cave, Later Neolithic Age. Fabric class characteristics: The fabric is homogeneous. Optical state: inactive. This is a distinctive fabric characterized by packed grains of mono crystalline quartz, with a few volcanic, meta-sandstone fragments and biotitic phenocrysts, the latter often bent and practically oriented in the direction in which the clay paste has been shaped. It could be considered very similar in composition to the Felsic (in a fine red matrix) one, except for the presence of preferentially-oriented biotitic laths and a lesser quantity of polycrystalline quartz. For this reason, the samples were assigned to this group. Discussion: The fabrics have a high concentration of coarse and medium-coarse inclusions, whose purpose might be to withstand thermal shock. The presence of coarse quartz is consistent with a source deriving from nearby valleys in which the Genna Selole formation contains mature, often loose, quartz sandstones. Sample n. 27 shows equal quantities of quartz meta-sandstones and volcanic rock fragments and was inserted in this group due to its similar fabric. CALCAREOUS SAND Number of samples: 3 (Table 1 and Figure 6) Period: all samples are from Is Janas Cave and are Late Neolithic. Fabric class characteristics: The fabric is homogeneous in nature. Optical state: inactive. This fabric is a distinctive one, characterized by common to frequent calcite crystals distributed homogeneously in the groundmass. Discussion: It is a distinctive type of fabric in which calcite crystals are found in a groundmass composed of small quantities of grains of a different nature: quartz metasandstones, shale, plagioclases and grog. The grog pieces are tempered with other burnt grog containing calcite or polycrystalline quartz and phyllites. The calcareous sand fraction might derive from the dolomitic conglomerates in the basal part of the Genna Selole Formation. Provenance study of raw materials Provenance determinations refer to the possible localization of sources for the raw materials used by ancient potters, with the aid of archaeological evidence and knowledge of local geology (Figure 7). The latter was of fundamental importance in the provenance study: the area around the caves was surface-surveyed with the aim of collecting samples from all rocks and river alluvium. Thin sections were then prepared and analysed under the petrographic microscope to identify any possible similarities with the inclusions found inside the prehistoric pottery sherds: indeed, their composition reflected the geological nature of the Permian basin indicated as P on the geological map in Fig. 7. Two dry valleys are present within this basin, and in the past, their waters must have drained the geological formations in the area, from the Paleozoic shale to the Genna Selole Formation, including the quartz conglomerates at the base of the limestone plateaux. This basin was the only place (extremely close to the caves) where the different terms of the geological series could be easily collected and classified by potters. The grog found so abundantly in the sherds from Is Bittuleris Cave and Su Cannisoni rock shelter, often intentionally burnt, could have been re-used as an ethnographic element linking the past to their present time, as an expression of the potters social and cultural identity and as a specific technological style. As an example, Barley 1994, cited by Tite et al. 2001: 317 reports that in a number of ethnographic contexts, old pottery is intentionally reused in making new objects as an act of 217

rebirth, thus reversing the process of time.

and the life cycle (Whitbread 1989: 455). Fig. 2. Sample N. 1, Is Bittuleris Cave, Metamorphic Group.

Gradoli. Fig. 3. Sample N. 4, Is Bittuleris Cave, Volcanic Group.

4 rebirth, thus reversing the process of time. In Ghana too, Gurensi women tempered their pottery with grog as a physical act to represent renewal and the life cycle (Whitbread 1989: 455). Fig. 2. Sample N. 1, Is Bittuleris Cave, Metamorphic Group. Several pieces of burnt grog can be seen. Crossed polars, 2.5x, field of view width 2.4mm. Photo M. G. Gradoli. Fig. 3. Sample N. 4, Is Bittuleris Cave, Volcanic Group. Crossed polars, 5x, field of view width 2.4 mm. Photo M. G. Gradoli. Fig. 4. Sample N. 34, Is Janas Cave, Felsic (in red matrix). Crossed polars, 5x, field of view width 2.8 mm. Photo M. G. Gradoli. 218

Fig. 5. Sample N. 2, Is Bittuleris Cave. Felsic (with biotite). PP, 5x, field of view width 2.4 mm. Photo M. G. Gradoli. Fig. 6. Sample N. 47, Is Janas Cave. Calcareous Sand. Crossed polars, 2.

$Jurassic Age. The clay samples underwent qualitative X-ray diffraction analysis, which showed the presence of quartz, muscovite and kaolinite - montmorillonite clays.$

5 Fig. 5. Sample N. 2, Is Bittuleris Cave. Felsic (with biotite). PP, 5x, field of view width 2.4 mm. Photo M. G. Gradoli. Fig. 6. Sample N. 47, Is Janas Cave. Calcareous Sand. Crossed polars, 2.5x, field of view width 2.9 mm. Photo M. G. Gradoli. Only one type of residual grey clay was found in the area, always in a peculiar stratigraphic position, at the base of the quartz conglomerate and sandstones of the Genna Selole Formation from the Jurassic Age. The clay samples underwent qualitative X-ray diffraction analysis, which showed the presence of quartz, muscovite and kaolinite - montmorillonite clays. Re-firing tests confirmed that only one type of clay was used in pottery manufacture, perhaps with the addition of iron oxides responsible for the red colour of the fired pottery. Experimental tests Knowing the qualitative composition of the clay sampled (its linear shrinkage, weight loss, and plasticity), clay workability was tested. The clay powder was mixed with some of the rock fragments sampled from the Permian basin using quartz sands, some shale and a piece of burnt Neolithic pottery from Is Janas Cave. They were mixed in the proportions found under the microscope and then fired in an electric kiln in an oxidizing atmosphere (Figures 8 and 9). They were subsequently thin-sectioned and studied under the microscope (Fig. 10). From Table 1, it can be seen that all samples coming from Is Bittuleris Cave and Su Cannisoni rock shelter (Middle Bronze Age) were generally fired under oxidising conditions, even though this is in part masked by a secondary calcite coating due to circulating water. At Is Janas Cave, several sherds still show their original redbrown colours due to the oxidising firing conditions, mixed with the black patina produced by ritual fires lit intentionally. Final discussion The petrological study of local ceramics permitted us to investigate in detail, temporally and spatially, the nature of the ritual and burial contexts of the four caves excavated thus far. During the Middle Neolihtic, Su Longu Fresu I Cave was used for the performance of small-scale rituals involving the primary and secondary burial of human remains, the production of wall paintings, the delineation of space and the offerings of a green stone axe and some obsidian arrowheads. Here, no pottery was found (Skeates, 2010; Gradoli and Meaden 2011 and 2012 a, b, c, d). 219

Fig. 7. Geological map of the region. Red dots indicate the position of the caves studied. From Gradoli 2011.

selected body parts, especially skulls and long bones, were used, quite probably obtained from nearby Is Bittuleris Cave (Skeates 2011; Gradoli and Skeates 2012; Skeates, Gradoli and Beckett, 2013).

6 Fig. 7. Geological map of the region. Red dots indicate the position of the caves studied. From Gradoli During the Bronze Age, the ritual use of Is Janas Cave changed, both as compared to its use in the Neolithic and compared to other Bronze Age caves in the Seulo area, all of which were used as burial places. Is Bittuleris Cave, associated with successive primary burials and grave goods, represents a primary burial site, while Su Cannisoni rock shelter served as a more open ritual space, where only selected body parts, especially skulls and long bones, were used, quite probably obtained from nearby Is Bittuleris Cave (Skeates 2011; Gradoli and Skeates 2012; Skeates, Gradoli and Beckett, 2013). Here, pottery was not burnt intentionally. Fig. 8. The raw materials used for the experimental test. Photo M. G. Gradoli. In the Final Neolithic, Is Janas Cave was used repeatedly for ritual performances involving the consumption of food (implying several people), with the intentional destruction of pottery during the rites. This pottery was composed of coarse and medium ware fabrics intended to withstand thermal shock during cooking. In the Early Bronze Age, only the small inner room of Is Janas Cave was, sporadically, in use, as indicated by the archaeological evidence. Fig. 9. The sherd-like piece after firing. Photo M. G. Gradoli. It might be argued that this peculiar technological style used by the prehistoric potters of Seulo acted as a kind of signature expressing their deep cultural concern. In the Neolithic, the vessels used for rites and ceremonial feasts inside Is Janas Cave were perhaps tempered with grog coming from previous ritual events and deposits, unknown to date. Then, during the Bronze Age, when the nature of the rites performed in Is Janas Cave changed and when new mortuary rites were performed in other caves, an element of 220

the past into their own time (Gradoli, 2011).

7 historical continuity and sacred potency might have been added to the pottery by using grog from the Neolithic deposits in Is Janas Cave. This implies that Bronze Age potters must have periodically re-entered their ancestors ritual sites to collect burnt pottery sherds to be used in new vessels, incorporating the potency of the past into their own time (Gradoli, 2011). This hypothesis seems to be confirmed by the mineralogical composition of the grog temper, which on the whole, reflects one of the five different fabric groups thus far studied in the area. Fig. 10. Thin-section of sample in Fig. 9. A piece of burnt grog is clearly visible. Photo M. G. Gradoli. Table 1. General characteristics of the fifty pottery samples studied. From Gradoli,

8 Acknowledgements The author would like to thank the Department of Mechanics, Chemistry and Materials of the University of Cagliari for the use of their polarising microscope and X-ray analyses of the clays. References Barley, N Smashing pots: feats of clay from Africa. British Museum Press, London. Gradoli, M. G Pottery from the underworld: a petrological analysis from a selected group of Neolithic- Middle Bronze Age ceramics from the Seulo caves (Central Sardinia, Italy). Unpublished Masters Dissertation. School of Archaeology and Ancient History, University of Leicester (UK). Gradoli, M.G. and Meaden, G.T Underworld and neolithic rituality: the rock art of the Su Longu Fresu Cave, Central Sardinia, Proceedings of the XXIV Valcamonica Symposium - Art and Communication in Pre-Literate Societies, Capo di Ponte, July Gradoli, M.G. and Meaden, G.T a. Discovery of prehistoric sites and rock shelters in the Barbagia di Seulo, South Central Sardinia. In Bergsvik, K-A and Skeates, R (eds), Caves in Context: The Cultural Significance of Caves and Rock shelters in Europe. [Oxford: Oxbow]. Gradoli, M.G. and Meaden, G.T b. Sacred Sites and Sym-bolism in the Neolithic Landscape of Barbagia di Seulo, Central Sardinia. In T. Meaden (Ed.), Archaeology of Mother Earth Sites and Sanctuaries through the Ages, Rethinking symbols and images, art and artefacts from history and prehistory, BAR International Series Gradoli, M.G. and Meaden, G.T c. Neolithic Art and Artefacts in Caves near Seulo in Central Sardinia: Grutta I de Su Longu Fresu. In T. Meaden (Ed.), Archaeology of Mother Earth Sites and Sanctuaries through the Ages, Rethinking symbols and images, art and artefacts from history and prehistory, BAR International Series Gradoli, M.G. and Meaden, G.T d. Prehistoric Occupation and Use of a Cave near Seulo in central Sardinia: The Oval Room at Is Janas Cave. In T. Meaden (Ed.), Archaeology of Mother Earth Sites and Sanctuaries through the Ages, Rethinking symbols and images, art and artefacts from history and prehistory, BAR International Series Gradoli, M.G. and Skeates, R Intellectual and spiritual expression in Central Sardinia during the Neolithic and Bronze Age: the Seulo Cave Project. In The Intellectual and Spiritual Expressions of non-literate People, UISPP CISNEP Conference, Capo di Ponte, Valcamonica, June 2012, ATELIER Editor. Skeates, R Unpublished interim report of the project Journeys to the underworld: ritual transformations of persons, objects, and caves in Neolithic-Bronze Age Central Sardinia. Department of Archaeology, University of Durham. Skeates, R The Seulo Caves Project, Sardinia: a report on archaeological work undertaken in 2009 and Cave and Karst Science, Vol. 38, N. 3, Transactions of the British Cave Research Association. Skeates, R., Gradoli M. G. and Beckett, J The cultural life of caves in central Sardinia: landscape, ritual and memory, Journal of Mediterranean Archaeology, 26.1, pp Tite, M. S., Kilikoglou, V., and Vekinis, G Strength, Toughness and Thermal Shock Resistance of Ancient Ceramics and their influence on Technological Choice. Archaeometry, 43, 3. Whitbread, I.K A Proposal for the Systematic Description of Thin Section towards the Study of Ancient Ceramic Technology. In Maniatis, Y. (ed) Archaeometry: Proceedings of the 25th International Symposium. Elsevier, Amsterdam. Whitbread, I.K Greek Transport Amphorae. A Petrological and Archaeological Study. The British School of Athens, Fitch Laboratory Occasional Paper

Mineralogical and technological investigation of pottery and raw materials for ceramic production. Tel el Farcha, Nile Delta. Egypt.

Maciej Pawlikowski* Mineralogical and technological investigation of pottery and raw materials for ceramic production. Tel el Farcha, Nile Delta. Egypt. */Cath. Mineralogy, Petrography and Geochemistry