Journal of Archaeological Science 38 (2011) 1119e1126
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Microarchaeology of a collective burial: cova des Pas (Minorca) Dan Cabanes a, *, Rosa Maria Albert b a b
GEPEG, Kimmel Center for Archaeological Science, Dept. of Structural Biology, Weizmann Institute of Science, 76100 Rehovot, Israel GEPEG, Dept. of Prehistory, Ancient History and Archaeology, University of Barcelona, c/ Montealegre 6-8, 08001 Barcelona, Spain
a r t i c l e i n f o
a b s t r a c t
Article history: Received 7 October 2010 Received in revised form 16 December 2010 Accepted 16 December 2010
FTIR and phytolith analyses have been used to understand the exceptional preservation of the organic remains at the burial cave of Cova des Pas (Minorca), and to obtain high-resolution data of the plant remains present in the sediments. The presence of sodium nitrate and gypsum suggests a relatively dry environment that has enabled the preservation of the organic material, and contributed to the natural mummification. The dry conditions also favored phytolith preservation. Grass inflorescence phytoliths are abundant all over the site suggesting that phytolith accumulations might have an anthropogenic origin and are related to the burial ritual. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Phytoliths FTIR Burial cave Minorca
1. Introduction Cova des Pas is a small burial cave near the town of Ferreries (Fig. 1). The cave was discovered by speleologists from Minorca during the spring of 2005. The entrance of the cave is located in the wall of a gully, at 15 m above the bottom. Thus the access to the cave during ancient times was only possible with ropes. The excavation took place between September 2005 and February 2006 and uncovered 70 individuals, whose bodies appeared to be tied up with ropes, wrapped in shrouds, and then deposited in the cave (Fullola et al., 2007). This was clearly a funerary site. The first burials were deposited around 1100 BC, at the end of the Bronze Age, although the largest number of inhumations took place between 900 and 800 BC (Van Strydonck et al., 2010), during the first Iron Age, known locally as the Talaiotic culture. Gullies had important cultural significance, due to their strategic geographic location connecting the inland to the coast. They also had ritual connotations, as indicated by the fact that the caves present in these gullies were commonly used for funerary practices (Gili et al., 2006). The uniqueness of Cova des Pas resides in the exceptional preservation of organic materials, which enabled the recovery of human soft tissues such as fragments of brain, lungs, muscle tissues, hairs, scalp and also coprolites and skin fragments from different animals.
* Corresponding author. E-mail addresses:
[email protected] (D. Cabanes),
[email protected] (R.M. Albert). 0305-4403/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jas.2010.12.008
Other uncommon archaeological remains such as wood stretchers, used to transport the bodies, branches and vegetal ropes were also preserved (Fig. 1). This preservation made it possible to conduct multidisciplinary research focusing on three different subjects: i) identification of the populations living in the area from the II to the I millennium BC, their DNA sequences, their age, sex, pathologies, parental relationships, etc.; ii) shed more light on the taphonomical processes that are responsible for this extraordinary preservation and iii) acquire a better understanding of ritual and post-mortem processes used by Mediterranean societies, 3000 years B.P., the treatment of bodies, etc. Another important characteristic of Cova des Pas is the preservation of vegetal remains in the form of small branches located on top of some of the bodies, as well as ropes and wooden stretchers used to transport and deposit the bodies. Two whole stretchers were recovered. This extraordinary preservation strongly suggests that other vegetal remains might also be present in the cave. Thus different botanical studies such as pollen, wood identification and phytoliths were conducted, first to identify the plant remains preserved and secondly to obtain as much information as possible on the presence of plants in the cave. As some of these plants are probably associated with the funerary practices, they may shed more light on the uses, significance and symbolism of plants in funerary contexts. In addition, since phytoliths become part of the sediments, their preservation relates to sedimentary conditions. Thus phytoliths are a useful tool for understanding post-depositional processes. For this purpose it is necessary to study the sediment minerals and the
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Fig. 1. Location of the site, map showing the location of the samples inside the site and detail of one of the bodies with well preserved organic material.
phytolith contexts. Understanding the preservation state of the phytoliths is also important for obtaining high-resolution data regarding the ancient landscape and the exploitation and use of vegetal resources, in this case for burial purposes. With the exception of cases such as Cova desMorts (Bergadà and de Nicolás, 2005), Cova des Càrritx and Cova des Mussol (Lull et al., 1999), Torre d’enGalmès (Pérez-Juez et al., 2007), or Biniparratx the use of microarchaeological techniques to study archaeological sediments is still uncommon in Minorcan archaeology. This paper intends to shed more light on this subject, but also aims to demonstrate the possibilities of using FTIR and phytoliths analyses to interpret past mortuary practices beyond the visible record. 2. Materials and methods For phytolith analyses a total of 21 samples were collected from Cova des Pas. Table 1 shows the list of the samples analyzed together with their provenance in the cave and their association with the human remains. Fig. 1 shows the locations of the samples and Table 2 provides a description for the stratigraphic units identified during the excavation. The extraordinary preservation of the vegetal material, allowed us to analyze 6 of the exceptionally well preserved remains such as ropes, wood stretcher and branches, and compare their phytoliths assemblages to those in the sediments. Of these 6 samples, 4 are from processed vegetal material such as ropes and wood from the wood stretchers, and two are from non-processed vegetal remains from the dicotyledonous branches that were directly associated with some of the individuals. The analysis of the wood remains has the advantage of providing us with direct information on phytolith production in plants growing in the area during the Talaiotic period. Furthermore, the study of the preserved wood fragments enables us to identify phytoliths from decaying wood that has not survived through time and therefore has become part of the sediments. The 14 remaining samples are sediments from different areas of the cave; 9 of them directly related to the human bodies, one was collected from an area apparently not related to the burial at the back of the cave, and the remaining 4 from a section close to one of the walls. In addition, phytoliths from ancient bird guano pellets in the cave were sampled.
Phytolith extraction took place at the laboratory of the Department of Prehistory, Ancient History and Archaeology of the University of Barcelona, and was made following the method of Albert et al. (1999). The phytolith number calculation was based on the Acid Insoluble Fraction (AIF), which is the fraction of the sample that remains after the acid treatment, and where phytoliths are present. The use of phytolith number per gram of AIF allowed the comparison between samples irrespectively of the diagenesis suffered by the sediment (Albert et al., 1999, 2000, 2003; Cabanes et al., 2009, 2010; Karkanas et al., 2002). Slides were prepared using Entellan New (Merck) and analyzed under the petrographic microscope (Olympus BX41) at 400; digital images were taken with a digital camera Olympus Camedia C-5060 and stored with Olympus DP Soft 5.0 software. Previous results (Albert and Weiner, 2001) indicate that the counting of only 50 phytoliths with diagnostic morphologies gives an error in the interpretation of 40%, whereas the counting of 200 diagnostic phytoliths gives an error of around 20%. We have analyzed samples usually with many more diagnostic phytoliths, but some samples had only 50 phytoliths identified. We take into account the high error margin in their interpretation (40%; Albert and Weiner, 2001). Morphological identification of phytoliths was based on standard literature (Twiss et al., 1969; Piperno, 1988, 2006; Mulholland and Rapp, 1992), as well as on the modern plant reference collection from the Mediterranean area (Albert and Weiner, 2001; Albert et al., 2000; Tsartsidou et al., 2007). When possible, the terms describing phytolith morphologies follow anatomical terminology, and otherwise they describe the geometrical characteristics of the phytoliths (Table 3). The International Code for Phytolith Nomenclature was also followed where possible (Madella et al., 2005). FTIR analyses were conducted on samples from the line of squares 8 and L (n ¼ 19), in addition to the same 14 sediment samples analyzed for phytoliths. Also samples from modern and fossil guano, wood and ropes found in the cave, as well as the bedrock, were analyzed through the FTIR to clarify the origin of the minerals in the sediments. The study took place at the Laboratory of the Servei de Recursos Científics i Tècnics (SRCiT) of the Universitat Rovira i Virgili at Tarragona using a Jasco 680 plus spectrometer, and at the Kimmel Center for Archaeological Research at the Weizmann Institute of Science in
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Table 1 Description of the samples, location in the site, mineralogical composition according to the FTIR results, percentage of Acid Insoluble Fraction (AIF), percentage of organic material, calculation of number of phytoliths in 1 g of AIF, number or phytoliths morphologically identified, and the percentage of weathered morphotypes. Description Samples used for phytolith analysis Ropes Ropes Branches on top of shroud individual 33 Branches individual 33 Wood stretcher Wood stretcher Samples used for phytolith and FTIR analyses Ancient guano pellet Sediment below skin and ropes Sediment below rope Sediment next to branches 7964 Sediment below and between branches ind. 33 with remains of shroud and microfauna Sediment below individual 33, in-between branches Sediment below wood stretcher individual 37 sub adult Sediment below individual 47 adult Sediment light brown close to wall next to individual Sediment dark brown in front of face individual 6 (with part of brain) Sediment reddish in contact with bedrock at the back of the cave. Section close to the cave-wall superficial level, contact with guano Section close to the cave-wall sediment in contact with UE2 and bones Section close to the cave-wall sediment between bones UE2 Section close to the cave-wall sediment below bones in contact with bedrock Samples used for FTIR analysis Modern guano pellet Sediment sample Sediment sample Sediment sample Sediment sample Sediment sample Sediment sample Sediment sample Sediment sample Sediment sample Sediment sample Sediment sample Sediment sample Sediment sample Sediment sample Sediment sample Sediment sample Sediment sample Sediment sample Sediment sample
Field number
Provenance
FTIR
% AIF
5088 e 8367 7964 7642 6448
UE2 UE2 UE2 UE2 UE2 UE2
7J 9I 6K 6L
e e e e e e
4.9 4.3 1.4 0.6 3.3 10
N. Phytoliths in 1 g of sediment
N. phytoliths identified
% weathered
0 4.3 2.3 1.7 0.1 0.2
5000 2000 19,000 100 10,000 100,000
13 1 158 2 31 122
e e 7 e e 7.4
e 5560 5659 7638 8368
UE2 UE2 UE2 UE2 UE2
8L 9I-10I
42.4 17.8 24.8 49.7 27.3
26.3 6.3 11.1 7.8 20.3
2000 9000 50,000 70,000 27,000
22 23 84 253 41
9 e 16.7 9.9 22.6
8369
UE2 6K
Gyp, Sn, Cl, Qz
37.1
12.2
74,000
93
15.1
10,351
UE2 8J
Sn, Gyp, Cl, Qz
24.7
15.5
22,000
39
e
10,352 8372
UE2 10K UE2
Cl, Gyp, Sn, Dah, Qz Cl, Sn, Gyp, Ca, Qz
49.1 52.3
3.5 3.3
560,000 52,000
992 145
6 12.4
8373
UE2 5K
Sn, Gyp, Cl, Dah, Qz
38.6
9.3
73,000
271
11.4
8374
8N
Cl, Dah, Ca, Sn, Qz
56.9
1.6
195,000
625
10.7
8375
UE1 11L
Sn, Ca, Cl, Gyp, Qz
30.3
6.8
121,000
310
6.1
8376
UE1 11L
Sn, Gyp, Cl, Dah, Ca, Qz
34
3
143,000
427
9.4
8377
UE2 11L
Cl, Gyp, Sn, Qz, Ca
46.5
3.4
195,000
469
11.9
8378
UE2 11L
Cl, Gyp, Sn, Qz, Ca
52.8
3
475,000
530
6
e 3L 4L 5L 6L 7L 8L 9L 10L 11L 8E 8F 8G 8H 8I 8J 8K 8M 8N 8O
Org. mat., Sn, Ph, Ca, Qz, Cl Cl, Sn, Ca, Gyp Sn, Ca, Qz Sn, Cl, Gyp, Qz, Ca Sn, Qz, Gyp, Ca Sn, Cl, Gyp, Qz, Ca Sn, Gyp, Cl, Ca, Qz Sn, Gyp, Ca, Qz Cl, Sn, Gyp, Ca, Qz Sn, Gyp, Cl, Ca, Qz Ca, Sn, Gyp, Qz Sn, Ca, Cl, Gyp, Qz Sn, Gyp, Cl, Ca Sn, Gyp Cl, Ca, Qz Sn, Cl, Qz, Gyp Sn, Gyp, Cl, Ca, Qz Sn, Gyp, Cl, Qz Sn, Cl, Qz, Gyp, Ca Gyp, Cl, Sn, Qz, Ca Cl, Ca, Qz, Sn
e e e e e e e e e e e e e e e e e e e
9L
6L 6K
Sn, Sn, Sn, Sn, Sn,
Cl, Org mat., Ph, Ca Ca, Cl, Gyp Gyp, Cl, Ca Gyp, Cl, Ca, Dah Gyp, Cl
% Organic
e e e e e e e e e e e e e e e e e e e
e e e e e e e e e e e e e e e e e e e
e e e e e e e e e e e e e e e e e e e
Ca, Calcite; Cl, clay; Dh, Dahllite; Gyp, Gypsum; Ph, Phosphate; Qz, Quartz; Org. mat., Organic material; Sn, Sodium nitrate.
Israel, using a Nicolet 380-FTIR. In both cases approximately 1 mg of each sample was grounded and mixed with 80 mg of KBr in an agate mill. The resulting mix was compressed to form a pellet that was inserted in the sample holder of the spectrometer. Each sample was scanned 32 times at a range of 4000e400 cm1, with a resolution of 4 cm1. The results were compared to standard reference collections from the Kimmel Center for Archaeological Research. 3. Results The mineralogical study shows roughly a similar composition for all the samples (Table 1). The presence of clay, calcite or quartz
in different amounts is common in these cave sediments. Nevertheless, together with these minerals, other minerals have been identified such as gypsum, sodium nitrate as an important presence of organic material. Some of the samples include dahllite, but the origin of this mineral in Cova des Pas is more related to the presence of microfaunal bones in the sample rather than to diagenetic processes (Karkanas, 2010). Gypsum and sodium nitrate can be considered as authigenic minerals and are present in large amounts in most of the samples analyzed. When looking at the spatial distribution, there is a major presence of calcium carbonate near the entrance of the cave and a lower presence of sodium nitrate at the back of the cave. Interestingly, the samples from the preserved
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Table 2 Field description of the stratigraphic units at Cova des Pas. Modified from Sintes et al. (2006). Stratigraphic Description unit SU-1
SU-2
SU-3
Brown loose sediment spread over the surface of the cave. Around 3 cm thick, composed of disaggregated cave-wall fragments, bird guano, and bird pellets related with microfaunal remains. No archaeological remains were found in this unit except for some wood fragments and few human bones with no anatomical connection. Dark brown sediment, around 40 cm thick. Composition similar to SU-1 but with lower amounts of bird guano and microfaunal remains. This unit contains several human remains in anatomical connection. In the central area of the cave the sediment is slightly darker. In some locations higher concentrations of microfaunal remains have been detected during the excavation. Near the cave wall the color of the sediment is lighter and clays are more abundant. Along with human remains, the list of objects recovered includes small tin rings, bracelets, a spear point, a bronze needle, leather containers with wood and bone stoppers, and several wood stretchers. Reddish sediment below SU-2, 20 cm thick. Immediately above the bedrock possibly formed by natural processes and does not have any evidence of human activity. No archaeological remains have been found except for few microfaunal bones, and intrusion of human teeth and phalanges from the unit above.
SU-4 Sandstone bedrock, irregular, easily disaggregated.
wood stretcher and the ropes (fibers) show a high presence of sodium nitrate. Fossil and modern guano from the cave have slight differences, however both infrared spectra show clay, abundant sodium nitrate, high amounts of undefined organic material, calcite and residual gypsum.
Diagnostic phytoliths were identified in most of the samples in sufficient numbers to conduct reliable morphological interpretation. The only three samples in which less than 50 phytoliths were identified have not been included in the phytolith morphological analyses, since the error margin is then close to 50%. Table 1 shows, together with the locations and descriptions of the samples, the main results obtained from the study, namely percentage of AIF, estimated numbers of phytoliths per gram of sediment, number of phytoliths morphologically identified and the percentage of weathered phytoliths. The reference samples analyzed (wood stretcher, ropes, branches), showed a low amount of phytoliths, and only two samples, one corresponding to branches, and a second one from one of the wood stretchers, contained a minimum amount of phytoliths necessary to perform a reliable phytolith morphological interpretation. The weathered phytoliths percentage is low in all the samples, indicating that siliceous minerals have not been severely affected by specific mineralogical conditions. As expected, Table 1 shows that the reference samples (branches, wood stretchers and ropes) present an AIF % notably lower in respect to the sediment samples. Interestingly the two wooden stretchers show different results in terms of percentage of AIF and amount of phytoliths per gram sediment. One possible explanation for this difference is that they correspond to two different types of trees. Phytoliths have a high variability production in dicotyledonous trees, whereas in some species they are scarce or hardly present (Tsartsidou et al., 2007), in other species they can be common, although never in high number (Albert and Weiner, 2001). The identification of the wood used to construct the stretchers showed that different woods were used to produce them, all of them corresponding to local species such as Rhamnusalaternus/Phillyrea and Pinus sp. (Sole et al., in preparation). The ancient bird guano sample yielded a high percentage of organic material, but a low number of phytoliths that cannot be morphologically interpreted.
Table 3 List of phytolith morphotypes identified, morphotype attribution to the type of plant and plant part in which phytolith was formed, presence of each morphotype, and equivalence to the International Code for Phytolith Nomenclature (Madella et al., 2005). Presence: 1, 0e5%; 2, 5e20%; 3, 20e50%; 4, >50%. Phytolith morphotype
Attribution
Presence
Equivalents (Madella et al., 2005)
Bulliform (fan and pillow shape)
Grass leaves
1
Cylindroid smooth/rugose Ellipsoid echinate Ellipsoid smooth/rugose surface Hair Hair awn Hat shape Indet Irregular echinate/verrucate Irregular rugose Long cell dendritic/echinate/verrucate Long cell polylobate Long cell wavy Papillae Parallelepiped blocky Parallelepiped elongate smooth/scabrate Parallelepiped thin rugose Parallelepiped thin smooth Platelet Short cell bilobate Short cell rondel Short cell saddle Silica skeleton long cells echinate Silica skeleton long cells smooth/rugose Silica skeleton long cells wavy Silica skeleton polyhedral/spheroid/jigsaw Spheroid echinate Spheroid smooth/rugose Stomata cells tracheary Trichome/prickle
Monocots Sedges Wood/bark dicots Dicot leaves Grass inflorescence Sedges Indet Fruit seeds dicots Wood/bark dicots Grass inflorescences Grass leaves Grass leaves Grass inflorescences Wood/bark dicots Monocots Wood/bark dicots Grass leaves Dicot leaves Grasses C4 Grasses C3 Grasses C4 Grass inflorescence Monocots leaves/stems Grass leaves Dicot leaves Palms Wood/bark dicots Dicot leaves Dicot leaves Grass leaves
2 1 1 1 1 1 1 1 1 4 1 1 1 1 1 1 1 1 1 2 1 1 1 1 1 1 1 1 1 1
Parallelepipedal and cuneiform bulliform cell Elongate, cylindric
Acicular/hair cell
Elongate echinate/dendritic long cell Cylindrical polylobate Epidermal long cell crenate Papillae Parallelepipedal Elongate Tabular/trapeziform Tabular/trapeziform Bilobate short cell Rondel short cell/trapeziform short cell Saddle short cell Silica skeleton Silica skeleton Silica skeleton long cell crenate Silica skeleton (honeycombed) Globular echinate Globular granulate/globular smooth Stomata Tracheid Acicular hair cell/prickle
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The sediment samples show a relatively low AIF percentage, with an average of 38%, which indicates that the sediments are mostly dominated by non-siliceous material. Based on the FTIR analyses, the soluble minerals are mainly sodium nitrate, gypsum and calcite. Similar AIF percentages have been observed in the sample from the back of the cave. Samples with higher amounts of clay and quartz are located, in general, far from the burials in areas with less anthropogenic activity, suggesting that this might be the natural mineralogical composition of the cave sediments. The number of phytoliths per gram of sediment varies notably among samples (Table 1). It is worth noting the sample below the adult individual 47 (sample field number 10,352), which had phytolith concentration significantly higher than other samples in corresponding contexts, as well to the burials. In the samples from the section near the wall, the numbers of phytoliths increase downward, and the lowermost sample contains twice as many phytoliths per gram as the others. On the other hand there are not significant morphological differences between phytoliths. Two possible reasons may explain this; one is that there was an accumulation of plant remains at the bottom of the cave, and the second is that the phytoliths may somehow have been transported downwards. Recent experiments show that vertical movement of phytoliths in soils is highly dependent on their size. If this was the case at Cova des Pas we should expect differences in the phytoliths assemblages depending on the sample depth in the profile (Fishkis et al., 2010). Regarding the preservation of phytoliths, there seems to be a higher dissolution in individuals 33 and 37. This is consistent with the presence of calcite in higher amounts at the entrance of the cave. Calcite can buffer the pH to around 8.2 (Shahack-Gross et al., 2004), and the presence of water may contribute to the phytolith dissolution, which is higher in alkaline environments (Fraysse et al., 2009; Piperno, 2006 and references therein). Hence, in the case of Cova des Pas, in the area near the entrance of the cave, there might have been some water movement that dissolved some of the phytoliths. This dissolution does not seem to be significantly high. The phytolith morphological composition showed a dominance of grass phytoliths in most of the samples, as well as other monocotyledonous plants such as sedges. Other groups corresponding to dicotyledonous plants from the leaves and branches were also identified (Fig. 2).
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The grass family was dominated mostly by phytoliths formed in the inflorescence (Figs. 3aed and 4). This predominance of grass inflorescences points to the fact that these plants were collected outside and brought inside the cave during the flowering season. In relation to the spatial distribution there does not seem to be a preferential location for the deposition of these plants, as they are present in all areas of the cave, including those far away from the burials. The morphological characteristics of the grass short cells indicate that most of the grasses correspond to the festucoid C3 subfamily which is most common in the Mediterranean area and is indicative of a temperate climate (Fig. 3e). Short cells saddle from Chloridoid C4 subfamily, as well as short cells bilobate from Panicoid C4 grasses, have been also identified but in much lower amounts. Panicoid grasses are not common in the region, and bilobate short cells can be also produced by reeds such as Arundo donax, which are abundant in the area. Phytoliths from the reed Phragmines were not identified in any of the samples. In any case the low numbers of Panicoid and Chloridoid short cells indicate that these plants were not common during the formation of the site, or at least were not introduced into the cave. Few phytoliths from palms were also noted at locations away from the burials and in the section. Palms produce many phytoliths and are well preserved in soils (Albert et al., 2009; Bamford et al., 2006; Delhon and Orilac, 2004). Their low number recovered might be attributed to some type of contamination. Sedges have been identified as well although in lower number than the grasses. Phytoliths are abundantly produced in sedges, however these phytoliths, with the exception of the ones produced in the achenes, do not preserve well in soils and are rarely identified in soils and sediment samples (Piperno, 1989; Albert et al., 2006; Bamford et al., 2006). Thus, their identification here implies a good preservation of phytoliths in the cave and, in terms of plant identification to the fact that these water plants were also brought into the cave. Phytoliths from dicotyledonous plants are not abundant and therefore it is not possible to conduct a more detailed taxonomic identification. Phytoliths from wood/bark dominate the dicotyledonous groups and they are probably derived from the branches identified in several of the burials (Figs. 2 and 3f).
Fig. 2. Histogram showing the percentage distribution of the different assemblages in which phytoliths were grouped, according to their taxonomical origin.
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Fig. 3. Microphotographs of phytoliths from Cova des Pas (Menorca). Pictures taken at 400. a) and b) long cell echinate from grass inflorescence; c) papillae cell from grass inflorescence; d) hair phytolith probably from grass awn; d0 ) hair from the awn of Hordeumspontaneum (wild barley); e) short cell from the C3 Festucoid subfamily; f) parallelepiped blocky from dicotyledonous plants, probably bark.
Very few phytoliths were identified in anatomical connection (the so-called multicellular structures, silica skeletons or interconnected cells). Multicellular structures from grasses, when present, are usually related to cultivation processes (Rosen and Weiner, 1994). The higher availability of water produces a higher uptake of monosilicic acid by the plants, and therefore a higher silicification of their cells. Furthermore, a higher silicification tends to keep the phytolith in anatomical connection, as well as to increase the phytolith production and variability. This in turn permits a better identification of the plant in which these phytoliths were formed (Rosen and Weiner, 1994). Nevertheless, multicellular structures are susceptible to breaking by several mechanical processes that may include grinding or trampling (Jenkins, 2009). In Cova des Pas thus, the absence of muticellular structures might be due to the fact that the grasses corresponded to local non-cultivated plants since trampling was not observed in the sediments (M. Bergadà, personal communication). The morphological characteristics of the long cell echinates as well as the papillae cells do not point either to the presence of cultivated plants.
4. Discussion Few questions arise from the study of Cova des Pas; what is the reason for the extraordinary preservation of some of the organic remains and what is the interpretation of the plant presence in the cave and its relation to burial practices, which is related to the landscape, vegetation and climate? In relation to the first question, the presence of sodium nitrate and gypsum is, with no doubt related to the preservation of the organic matter. These minerals are common in areas with high evapotranspiration and are directly related to a high degree of aridity or a low degree of humidity. In addition, sodium nitrate has been used often as a preservative for food (Binker and Kolari, 1975). The origin of the sodium nitrate may be due to evaporation of ground water on the sediment surface. This may also induce gypsum to form, provided of course the ground water is rich in nitrate and sulphate. This may be related to the decomposition of organic material, including bird guano. FTIR showed that bird guano in the area, independent of its origin (modern or fossil) contains sodium
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Fig. 4. Histogram showing the percentage distribution of grass phytoliths according to their anatomical origin.
nitrate. In addition previous work has detected nitrate in modern pigeon droppings from Hayonim and Kebara caves (Shahack-Gross et al., 2004). Both minerals, gypsum and sodium nitrate, are relatively soluble and are not expected to be preserved in sediments under certain humidity conditions (Shahack-Gross et al., 2004). Hence the microenvironment must have been relatively dry during the last 3000 years, allowing the partial preservation of the organic remains. Besides it could be hypothesized that these minerals, especially sodium nitrate, once formed would help in the preservation and mummification of the recovered remains through the regulation of the humidity and preventing bacterial activity (Bailey et al., 2002). Phytoliths are very well preserved in most of the samples. This might be due to the high aridity of the cave. The presence of calcite indicates that the pH of the sediments can reach 8.2 (Shahack-Gross et al., 2004). In this case, if the cave would have been subjected to a higher humidity it could have caused higher dissolution of phytoliths due to the interaction of water with the calcite. The mineralogical data together with the abundance, excellent conservation and morphological characteristics of phytoliths enabled a detailed study of the vegetal material in the cave. Three possible reasons may explain the high concentration of grasses in the cave: i) grasses were brought into the cave as part of the burial procedures. This may have included other plants based on the palynological studies (S. Riera, personal communication), such as the branches, which might have been part of bouquets; ii) the presence of grasses is the result of contamination by windblown material; iii) the presence of grasses is the result of contamination brought in the cave by post biological activity. The morphological results indicate that the phytoliths are mostly from the inflorescence of grasses; most probably wild grasses. There is a random distribution of phytoliths with no special concentration or selection for different areas. The only difference noted is that in those areas, where the samples were collected below the skins of the burials, the number of phytoliths seem to be lower, indicating that these grasses were deposited either during the burial or later, with no possible determination of how much later. The fact that inflorescence dominated the phytolith record suggests that these plants were brought into the cave during the flowering season, which in the area occurs from April to September. Moreover, the high silicification
observed, points to a later period of the season when phytoliths are well developed, maybe from late spring to autumn. The second possibility which points to the presence of grasses as a result of contamination by wind-blown particles should be ruled out for several different reasons. The first one relates to the good preservation of phytoliths with no signs of pitting on their surface as would be expected in wind-blown particles (Krinsley and Doornkamp, 1973). Moreover, if the phytoliths accumulated as a consequence of wind transportation we might expect preferential areas of deposition, or wind traps. This is not the situation at Cova des Pas since phytoliths appear to be randomly distributed all over the cave which is unlikely according to the configuration of the cave (Fig. 1). Also, the location of the cave in a closed gully at about 15 m above the valley floor, does not favor the deposition of wind-blown phytoliths in such abundance (Wallis, 2001). Furthermore, the elevate presence of phytoliths in the cave cannot be justified by the existence of a wind-blown phytolith deposition in the cave. At least some of the plants were introduced into the cave by humans, such as branches that were probably part of bouquets, and the associated flowers. Palynological studies indicate the abundant presence of Brassicaceae plants (S. Riera personal communication). Thus, it is conceivable that some of the plants from the grass family might also have been introduced in the cave as a result of funerary practices together with the bouquets and other plant remains. Moreover, some of the branches identified corresponded to the monocotyledonous family (S. Riera personal communication). The faunal studies indicated an abundant presence of micromammals not related to anthropogenic input. Nocturnal birds of prey used the cave as a shelter, judging from the discarded remains of mice and coleopterans (J. Nadal personal communication). According to this, part of the plant presence might be related to this biological activity, and some of these animals may be responsible for bringing grass into the cave. Phytolith analysis of fossil guano does not indicate that bird guano is a major source of phytoliths. The scarcity of dicotyledonous phytoliths may be explained by the differential preservation of the organic material and the differential production of phytoliths in plants. Wood and bark of dicotyledonous plants produce in general small amounts of phytoliths (Albert and Weiner, 2001; Piperno, 1988, 2006; Tsartsidou et al.,
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2007). Therefore their presence is usually under represented in the archaeological record. 5. Conclusions The presence of highly soluble minerals, such as sodium nitrate and gypsum in the sediments of Cova des Pas suggests stable dry conditions inside the cave, which enabled the preservation of the organic remains. These minerals helped to absorb the little humidity present in the sediments and facilitated the natural mummification of the corpses and conservation of vegetal remains by partially inhibiting bacterial activity. The origin of these minerals is related to the decomposition of the organic material, and probably to the guano accumulation, combined with high evaporation rates. The phytolith presence, mostly represented by the inflorescence of grasses, may be mostly related to anthropogenic causes, related to burial practices, together with the wood stretchers, the ropes and the branches (as a bouquet). However, natural phytolith accumulations produced by post-burial biological activity cannot be completely disregarded, even though the study of guano did not support this hypothesis. The dry conditions in the cave enabled the preservation of some of the organic remains, and are responsible for the good phytolith preservation. This is supported by the presence of grass inflorescences all over the cave. The identification of C3 grasses with a small component of C4 grasses attests to a temperate-dry climate. The abundance of grass inflorescence phytoliths suggests that these plants were brought into the cave during the springesummer season. Acknowledgements The research project at Cova des Pas has been financed by Consell Insular de Menorca, Obra Social Caixa Catalunya, and EXCAVA program (Generalitat de Catalunya). D. Cabanes investigation has been supported by a predoctoral grant from the Fundación Atapuerca, and by postdoctoral fellows from ERC project RAIELSP and Beatriu de Pinós program (Departament d’Universitats, Recerca i Societat de la Informació de la Generalitat de Catalunya). We would like to thank Xavier Esteve for his extraordinary help during the paper preparation, and also to Arlene Rosen, Francesco Berna and, specially, Stephen Weiner for their helpful comments. References Albert, R.M., Lavi, O., Estroff, L., Weiner, S., Tsatskin, A., Ronen, A., Lev-Yadun, S., 1999. Mode of occupation of Tabun Cave, Mt Carmel, Israel during the Mousterian Period: a study of the sediments and phytoliths. J. Archaeol. Sci. 26, 1249e1260. Albert, R.M., Bar-Yosef, O., Meignen, L., Weiner, S., 2000. Phytoliths in the Middle Paleolithic deposits of Kebara cave, Mt. Carmel, Israel: study of the plant materials used for fuel and other purposes. J. Archaeol. Sci. 27 (10), 931e947. Albert, R.M., Weiner, S., 2001. Study of phytoliths in prehistoric ash layers using a quantitative approach. In: Meunier, J.D., Coline, F. (Eds.), Phytoliths: Applications in Earth Sciences and Human History. A.A. Balkema Publishers, Lisse, pp. 251e266. Albert, R.M., Bar-Yosef, O., Meignen, L., Weiner, S., 2003. Quantitative phytolith study of hearths from the Natufian and middle palaeolithic levels of Hayonim Cave (Galilee, Israel). J. Archaeol. Sci. 30, 461e480. Albert, R.M., Bamford, M.K., Cabanes, D., 2006. Taphonomy of phytoliths and macroplants in different soils from Olduvai Gorge (Tanzania) and the application to Plio-Pleistocene palaeoanthropological samples. Quatern. Int. 148, 78e94. Albert, R.M., Bamford, M.K., Cabanes, D., 2009. Palaeoecological significance of palms at Olduvai Gorge, Tanzania, based on phytolith remains. Quatern. Int. 193, 41e48. Bailey, R.A., Clark, H.M., Ferris, J.P., Krause, S., Strong, R.L., 2002. The Environmental Chemistry of Some Important Elements, Chemistry of the Environment, second ed. Academic Press, San Diego, pp. 347e414. Bamford, M.K., Albert, R.M., Cabanes, D., 2006. Assessment of the Lowermost Bed II Plio-Pleistocene vegetation in the eastern palaeolake margin of Olduvai Gorge (Tanzania) and preliminary results from macroplant fossil remains and phytoliths. Quatern. Int. 148, 95e112.
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