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Inora Newsletter #46
Discoveries

FIRST RADIOCARBON DATING OF OXALATE CRUSTS
OVER SPANISH PREHISTORIC ROCK ART


Open-air rock paintings were discovered in the eastern Iberian Peninsula at the beginning of the 20th century. By the start of the 21st century, more than 800 such sites were included in the UNESCO World Heritage List (Rock art of the Mediterranean Basin in the Iberian Peninsula). Three main different styles have been described up to now. Levantine, Macroschematic and Schematic arts were identified as different expressions of hunter-gatherers and first farmer and herder groups, and so, as an important aspect of an evolutionary cultural change from the last predatory groups to productive economies. The chronology of these styles was derived from the images themselves, or from stylistic parallels with well dated artefacts, such as decorated ceramics.

Historiography

Nowadays, clear parallels have been established for Macroschematic and Schematic arts, but serious doubts remain about the Levantine art itself. Levantine art is mainly painted in red and is characterized by naturalistic animal and human figures depicted in complex scenes such as hunting. After its discovery in 1903, it was considered as the Mediterranean counterpart of Cantabrian cave art, and so of Palaeolithic age. Soon after that, discoveries occurred in all the regions near Mediterranean Spain. The Palaeolithic theory was held up to the 1950’s. Then, a Palaeolithic age assignment was challenged because no glacial fauna was depicted, because the art was always found in open rock shelters instead of deep caves, and because painting techniques were different, as only plain colours and silhouettes without volume depiction were used in Levantine art. The frequent superimpositions of Levantine figures over schematic ones was taken to be the evidence of differences in their chronology. Thus, Levantine art was supposed to begin in the Mesolithic and develop up to the beginning of the Bronze Age. This position is still held by some researchers.

Fig. 1. Location map.
Fig. 2. Cueva del Tío Modesto rock shelter.

In the 1980’s a new style was discovered in the Alicante province by Mauro Hernández who called it Macroschematic. Some years before, Levantine art had several times been found painted over long linear and zigzag motifs, as was also the case at some sites with Macroschematic art.


Fig. 3. Cueva del Tío Modesto main panel.
We may observe the frequent superimposition of styles at this site. Sample positions have been indicated, as well as motif 123 from the 3rd stage.

In the 1980’s a new style was discovered in the Alicante province by Mauro Hernández who called it Macroschematic. Some years before, Levantine art had several times been found painted over long linear and zigzag motifs, as was also the case at some sites with Macroschematic art. So it became obvious that Levantine art was not the oldest of the open-air rock art traditions in Mediterranean Spain. Researchers soon proposed stylistic parallels for the big humans with raised arms known in Macroschematic art with Neolithic Cardial ceramics. They considered that impressed motifs on ancient Neolithic Cardial ware depicted the same kind of “orants” painted in shelters, so they were considered to be of the same age as the impressed wares (5460-5230 cal BC) based on the Cova de l’Or (Alicante) archaeological sequence. Furthermore, abstract motifs of Schematic art also have parallels in the Cardial ware, so the Neolithic appears to be the departure point for those three styles.

However, many researchers do not agree with the hypothesis. All these chronological proposals are based on idealistic considerations of style, in a linear evolutionary fashion, that consider Levantine style as time-bound in a short or in a long sequence. But up to this current study, no absolute dating directly related to the paintings had been obtained. Three main obstacles to getting dates are: first, the general paucity of organic material in paintings; second, the absence of charcoal – even in black paintings; finally, the small size of the majority of these figures make it difficult to find good places to sample for AMS 14C dating. Nevertheless, it is evident that we need to look for an accurate base to firmly establish the archaeological chronology of the paintings.

Cueva del Tío Modesto

In the last few years we have been carrying out a multidisciplinary research project in Sierra de las Cuerdas (Cuenca). One of its main objectives has been to get a first answer to those chronological problems. We chose Cueva del Tío Modesto (Fig. 1-3) initially because of several reasons: the complex series of superimpositions on the main panel, the superb preservation of Levantine figures, and the presence of a thick greyish patina that covered the whole of the panel. This Triassic red sandstone painted shelter was discovered in 1998 and was quickly placed behind an iron fence, so no recent anthropic damage has occurred, except that caused by the installation of the fence itself.

Raman microscopy on tiny samples of pigments (≈ 1 mm2) from selected pictographs indicates that their main component is hematite, a-Fe2O3 (Fig. 4). No organic binders were found by Raman analysis. Therefore, it is questionable that paintings could be used for direct AMS 14C dating. Nevertheless, the Raman spectra of samples of the greyish crust show bands of calcium oxalate monohydrate, whewellite (Fig. 4). Oxalate accretions on rock surfaces are usually attributed to the metabolic activity of fungi and lichens that live or have lived on the surfaces. Thus, AMS 14C dating of oxalates may be used to establish maximum ages for pictographs painted on top of those accretions or minimum ages for paintings that are covered with oxalate.

Previously, four pictorial phases had been proposed for this shelter. After examining superimpositions in situ with a stereoscopic microscope, we noted a different stratigraphy, with six painting episodes of various styles

Fig. 4. Raman spectrum of the pigment sample 16-16.09700.001:129. Peak wavenumbers and assignment are indicated:
w. whewellite; h. hematite.

Fig. 5. Calibration curve of TMD2 sample.

Click diagrams for enlargements.

(Fig. 3). The earliest painting episode consists of a series of 33 vertical zigzag lines. All other phases are superimposed over them. Painted over zigzags lines, the image that follows is that of a Levantine wild-goat hunting scene. The third phase, another Levantine hunting scene, is superimposed over the former. Both hunting scenes have parallels in the mid-Levantine sequence at other places, according to chronostylistic approaches. The 4th phase is on the left side of the panel, where three linear human figures cover zigzags and a Levantine archer from the 2nd or 3rd Levantine phase. The 5th phase is formed by several dotted lines and an anthropomorphic figure covering the 3rd phase on the right of the panel. The 6th and most recent episode is a group of orange vertical lines covering the 3rd and 5th painting episodes.

We have also examined the taphonomic processes at work in this shelter. The main panel is suffering flaking from its bottom towards the top. We have identified at least three levels in the present morphology of the panel. Most of the figures were painted on the primary level, which is fully covered with an oxalate crust, so that most paintings appear to be covered by this older accretion. Some flakes have broken from the bottom of the panel as in motif 123 (Fig. 3), and the newly exposed surfaces were then covered by a more recent deposit of oxalate. Finally, additional flakes are apparent in both levels, but oxalate has not yet formed on the surfaces left exposed by the more recent spalling.

To get chronological information, we sampled oxalate at three points, taking into consideration flaking and superimposition. TMD1 sample is related to the 2nd level of the panel and to the loss of motif 123. TMD2 sample is from the upper right of level 1; TMD3 from the upper left of level 1. The dates are: TMD2 6180 ± 35 BP (2 sigma: 5230-5010 cal BC) (Fig. 5); TMD3 5855 ± 35 BP (2 sigma: 4800-4610 cal BC); TMD1 2800 ± 35 BP (2 sigma: 1050-840 cal BC). They are roughly coherent, because the last two samples have a similar date, and the younger age for TMD1 represents the later flaking moment of level 1. That coherence from the two widely separated parts of the panel suggests an approximately uniform deposition when averaged over a few millennia.

Radiocarbon dating of these samples was accomplished by applying the technique of selective oxidation of organic carbon to remove any contaminant organic matter before sending the samples to the Center for Accelerator Mass Spectrometry of the Lawrence Livermore National Laboratory for radiocarbon analyses. Carbonate minerals have not been detected. TMD2 and TMD3 samples are clearly related to the oxalate layer that is covering the 1st-3rd pictorial phases, and probably also the 4th and 5th. We have observed in a thin layer section that paintings from the 1st and 3rd phases are embedded within the oxalate crust. Now, we are trying to get a deeper knowledge of the oxalate deposition process, so we can develop a more meaningful archaeological valuation of these dates. In this respect, it must be remembered that the older dates we obtained are not necessarily the absolute chronological limit of this panel. Rather, it is the dating of the weighted average of the oxalate crust accumulated along time in these two places.

Acknowledgements

This work was financed by the Consejería de Cultura de la Junta de Comunidades de Castilla La Mancha, Universidad de Castilla La Mancha (UCLM), European Regional Development Fund (ERDF) and the Universidad Nacional de Educación a Distancia (UNED).

Juan Francisco RUIZ, – jfruiz@jfrl.jazztel.es
Martí MAS, – mmas@geo.uned.es
Antonio HERNANZ, – ahernanz@ccia.uned.es
José María GAVIRA – jm.gavira@ccia.uned.es
1-2 Departamento de Prehistoria y Arqueología and Departamento de Ciencias y Técnicas Fisicoquímicas (UNED, Madrid).


Marvin W. ROWE, – marvin.rowe@qatar.tamu.edu
Department of Chemistry (Texas A&M University)


Karen L. STEELMAN – ksteel@uca.edu
Department of Chemistry (Central Arkansas University)


Bibliographie

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