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Direct radiocarbon dating of prehistoric cave paintings by accelerator mass spectrometry This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2003 Meas. Sci. Technol. 14 1487 (http://iopscience.iop.org/0957-0233/14/9/301) Download details: IP Address: 137.99.26.43 The article was downloaded on 24/08/2013 at 09:04 Please note that terms and conditions apply. View the table of contents for this issue, or go to the journal homepage for more Home Search Collections Journals About Contact us My IOPscience

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Page 1: Direct radiocarbon dating of prehistoric cave paintings by accelerator mass spectrometry

Direct radiocarbon dating of prehistoric cave paintings by accelerator mass spectrometry

This article has been downloaded from IOPscience. Please scroll down to see the full text article.

2003 Meas. Sci. Technol. 14 1487

(http://iopscience.iop.org/0957-0233/14/9/301)

Download details:

IP Address: 137.99.26.43

The article was downloaded on 24/08/2013 at 09:04

Please note that terms and conditions apply.

View the table of contents for this issue, or go to the journal homepage for more

Home Search Collections Journals About Contact us My IOPscience

Page 2: Direct radiocarbon dating of prehistoric cave paintings by accelerator mass spectrometry

INSTITUTE OF PHYSICS PUBLISHING MEASUREMENT SCIENCE AND TECHNOLOGY

Meas. Sci. Technol. 14 (2003) 1487–1492 PII: S0957-0233(03)57428-8

Direct radiocarbon dating of prehistoriccave paintings by accelerator massspectrometryHelene Valladas

Laboratoire des Sciences du Climat et de l’Environnement, Unite mixte CEA-CNRS,Batiment 12, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France

Received 13 December 2002, accepted for publication 26 February 2003Published 29 July 2003Online at stacks.iop.org/MST/14/1487

AbstractAdvances in radiocarbon dating by accelerator mass spectrometry now makeit possible to date prehistoric cave paintings by sampling the pigment itselfinstead of relying on dates derived from miscellaneous prehistoric remainsrecovered in the vicinity of the paintings. Presented below are someradiocarbon dates obtained at the ‘Laboratoire des Sciences du Climat et del’Environnement’ for charcoal used in the execution of prehistoric paintingsdecorating two French caves: Cosquer and Chauvet. The presentation of thedates will be preceded by a short discussion of the experimental procedureused in our laboratory (pigment sampling, chemical treatment, etc). Theages obtained so far have shown that the art of cave painting appeared earlyin the Upper Palaeolithic period, much earlier than previously believed. Thehigh artistic quality of the earliest paintings underlines the importance ofabsolute chronology in any attempt to study the evolution of prehistoric art.

Keywords: AMS carbon-14 dating, prehistoric cave paintings, charcoal,Upper Palaeolithic, Cosquer cave, Chauvet cave

1. Introduction

Until quite recently cave paintings were dated according tostylistic criteria loosely associated with dates obtained forarchaeological remains found in the vicinity of decoratedsurfaces. About two decades ago radiocarbon dating wasrevolutionized when accelerator mass spectrometric (AMS)techniques allowed for the dating of organic samples weighingas little as 1 mg. Paintings done in charcoal could now besampled without visibly damaging the paintings. In additionto wood charcoal, which has received the most attention (Rowe2001, Valladas et al 1992, Igler et al 1994), beeswax (Nelsonet al 1995) and plant residues (Watchman and Cole 1993,Hedges et al 1998) used in the paintings have also been dated.Below we present the approach used at the Laboratoire desSciences du Climat et de l’Environnement (LSCE) to datePalaeolithic charcoal drawings and paintings and discuss theresults obtained in two French caves.

2. Problems peculiar to the dating of prehistoricpigmentsThe first problem, to which there is no simple scientific answer,has to do with the question of the age of the charcoal at the

time of execution of the painting. Did the artists use freshlymade charcoal, leftover material from prior cave occupation(Bednarik 1994) or a mixture of charcoals of several origins?The possibility that fossil charcoal could have been usedcannot be excluded either (Bednarik 1994). To compoundthe problems there is also the possibility that some paintingswere retouched by a later generation of artists. Some ofthese questions can be answered by examining the natureand composition of the pigment under a scanning electronmicroscope, others require meticulous in situ examination ofthe pigment layer with a good magnifying glass.

The sampling, the first step of the dating process, is doneafter preliminary analysis has revealed that the black pigmentcontains charcoal. In some instances the wood could beidentified as belonging to the species Pinus.

To protect the visual integrity of the drawings, pigmentis scraped from rock cracks or from the thickest layers.If the charcoal is well preserved and thick enough, it is bestto collect the sample from a limited area of a figure. Whenpossible, two or more samples from different portions of apainting should be taken in order to get several dates and checkthe age spread. Otherwise, if the pigment layer is too thin and

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SAMPLE PREPARATION

Acid (HCl, 0.5M)High - purity H2O

Deposition on pre-cleaned quartz filter

Basic treatmentNa4P2O7 , NH3 (aq), NaOH

Charcoal Humic fractionAcid (HCl, 1M) Precipitation andH2O collection on a

quartz filter

Drying Drying

Heating, 1hr at 300 - 320°C Heating, 1hr at 280°Cin a stream of oxygen in a stream of oxygen

Oxidation at 850°C for 7 hours

Purification and determination of CO2 pressure

Catalytic reduction to graphite

Compression to a pellet used as target

AMS measurement

Sample transferred to a combustion tube containing CuO and Ag wire and sealed under vacuum

Figure 1. A diagram illustrating the experimental procedure.

has to be scraped from several points, sometimes far apart, onegets an average date. The collected samples, usually weighingfrom 10 to 100 mg, often contain calcite grains or clay fromthe rock face, in addition to wood charcoal. To-date, calciumoxalate, which can be an important contaminant (Watchman1990, Russ et al 1996, Hedges et al 1998) of outdoor parietalart in semi-arid regions (particularly in the vicinity of cacti,lichens, for example), has not been detected in paintings insideWest European caves.

A major problem, inherent in all methods of radiocarbondating, is the possible presence of extraneous carbon (Hedgeset al 1989). Exposure of a paintings renders a cave painting’spigment particularly vulnerable to contamination. The degreeof contamination depends on when and how the caves werediscovered. For obvious reasons, caves sealed until recentlyand not open to the public should give the most reliable dates.

In caves frequently visited in the past the most commonorganic contaminants come from contact with visitors’ hands,cloth fibres, acetylene lamp soot, etc. Moreover, allcaves harbour a variety of microorganisms whose growth isstimulated by emanations from the human body (Laiz et al1999). One must also consider contamination by carbonic,humic or fulvic acids transported by underground waters.

The great majority of contaminants introduce carbon youngerthan the pigment charcoal and if not eliminated by a propertreatment will produce a date more recent than the true one.

3. Sample treatment

The sample pre-processing used to date the Palaeolithiccharcoal drawings and paintings has been described in recentpublications (Valladas et al 1999, 2001a). The treatment ofcharcoal varies in intensity according to the sample size. Itinvolves a succession of ‘acid–base–acid’ treatments whichfirst dissolve the carbonates that may have come from thelimestone wall or ground water, then humic acids arising fromthe transformation of organic matter, and bacteria or otherliving microorganisms. A schematic representation of thetreatment steps is shown in figure 1.

The residue from the initial acid bath is retained on apre-cleaned quartz-frit filter and subjected to the subsequentbasic treatment. This treatment, gentle at first, is increasedin intensity according to the fragility of the sample. Onebegins with a dilute solution of sodium pyrophosphate whoseconcentration is increased progressively. Aqueous ammoniaof gradually increased concentration is used next, followedby sodium hydroxide treatment in cases of alkali-resistantpigments. As a rule, the treatment stops when the filtratebecomes highly coloured. The coloration suggests that notonly have the outer grain layers been stripped, but that a goodfraction of the original charcoal has passed into solution. If thetreatment is not interrupted in time, no charcoal might be leftfor dating. The remaining charcoal grains are washed againwith aqueous HCl. After the chemical treatment, the purifiedcharcoal or humic acids collected on another quartz filter areheated in a stream of oxygen for about an hour between 280and 320 ◦C to remove some additional organic contaminants.

Whatever remains is oxidized to carbon dioxide, thenreduced to graphite and compressed into pellets for theaccelerator (Arnold et al 1987). The purification processeliminates more than 90% of the original mass leaving us withpellets usually containing from 0.5 to 1 mg of carbon (tables 1and 2, column 3).

This procedure has been tested on a piece of charcoalfrom an Upper Palaeolithic layer (Solutrean). The piece wasbroken into several subsamples, of which some were subjectedto very strong chemical treatment, others treated in the sameway as the pigment samples and still others subjected tochemical but not thermal treatment. We found that a strongchemical treatment did not give significantly different resultsfrom the weaker treatment usually reserved for the paintings,and that the thermal treatment did eliminate some additionalcontamination by more recent carbon, since the samples thustreated gave slightly older ages. The results also confirmed thegood reproducibility of our protocol (Valladas et al 2001a).

The extent of contamination by modern carbon duringsample preparation was determined by subjecting severalcharcoals over 100 000 years old (‘blank’ sample without 14C)to the same treatment as our pigment samples. This yieldedbackground contamination that was used to make a suitablecorrection to the calculated pigment ages.

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Direct radiocarbon dating of prehistoric cave paintings by accelerator mass spectrometry

Table 1. Radiocarbon dates for prehistoric paintings at the Cosquer cave. Humic acid dates are written in italics. For pictures of the datedpaintings see Clottes and Courtin (1994). Ly = Lyon, France; GifA = Gif-sur-Yvette, France.

Dateable Date Error (year)Reference carbon (mg) year (BP) 1 sigma

Horse 1 GifA 92416 1.56 18 840 250GifA 92417 0.94 18 820 310GifA 92422 1.23 18 760 220

Feline GifA 92418 1.52 19 200 240

Bison 1 GifA 92419 0.64 18 010 200GifA 92492 1.22 18 530 190GifA 92423 0.26 16 390 260

Megaloceros 1 GifA 95135 1.25 19 340 200GifA 95365 0.12 13 460 330

Horse 7 GifA 98186 0.84 19 720 210GifA 98196 0.29 19 740 340

Deer GifA 98188 0.25 19 290 340

Star mark GifA 96075 0.87 17 800 160

Horse 5 GifA 96072 0.84 24 730 300

Hand 12 GifA 95358 0.63 24 840 340GifA 95372 0.26 23 150 620

Bison 2 GifA 96069 1.79 26 250 350GifA 95195 2.04 27 350 430GifA 95308 0.23 23 080 640

Hand 1 GifA 92409 0.86 27 110 430GifA 92491 1.59 27 110 400GifA 92424 0.44 26 180 370

Hand 19 GifA 96073 1.3 27 740 410

Oval mark GifA 96074 2.12 28 370 440

Soil charcoal Ly-5558 18 440 440Soil charcoal GifA 92348 2.39 20 370 260Soil charcoal GifA 92349 2.17 26 360 440Soil charcoal GifA 92350 2.06 27 870 470

Table 2. Radiocarbon dates for prehistoric paintings at the Chauvet cave (Clottes et al 1995). Humic acid dates are written in italics.(∗Thirteen other dates have been obtained by the LSCE on charcoal samples collected on the ground of the Megaceros Gallery; 11 of themrange between 29 700 and 32 900 and the two other between 25 400 and 26 600 years BP.)

Dateable Date Error (year)Reference carbon (mg) year (BP) 1 sigma

Hillaire ChamberRight rhinoceros GifA 95132 1.4 32 410 720

GifA 95133 1.22 30 790 600

Left rhinoceros GifA 95126 0.8 30 940 610

Running cow GifA 96065 0.69 30 230 530

Horse GifA 98157 20 790 340GifA 98160 0.27 29 670 950

Torch scraping 1 GifA 95129 2.3 26 980 410GifA 95130 1.76 26 980 420GifA 95158 0.308 25 700 850

Megaceros Gallery*Megaloceros GifA 96063 0.85 31 350 620

Soil charcoal Ly-6878 5.000 29 000 400

Salle du FondBison GifA 95128 0.83 30 340 570

GifA 95155 0.42 30 800 1.500

Cierge ChamberTorch scraping 2 GifA 95127 1.22 26 120 400Hearth GifA 99081 1.73 26 230 280

Crane ChamberUnder bear skull GifA 99809 2.27 32 360 490

GifA 99810 1.12 31 390 420GifA 99811 2.21 32 600 490

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Figure 2. Schematic layout of the Gif-sur-Yvette AMS apparatus—‘Tandetron’ (Duplessy and Arnold 1985).

4. Description of tandem mass accelerator

Figure 2 shows a schematic diagram of the Gif-sur-Yvettetandem accelerator (UMS 2004, CNRS-CEA) which is usedto measure 14C/12C and 13C/12C isotopic ratios (for a detaileddescription see Duplessy and Arnold (1985) and Arnoldet al (1987, 1989)).

The apparatus has three major components:

(a) Low-energy ion source: positive caesium ions that arefocused on the carbon sample. The caesium ion beambombards the sample and produces both molecular andatomic negative ions. This step is followed by a firstmass separation so that ion beams of mass 12, 13 and 14are well separated. As a result, the mass 12 consists ofonly the ions 12C−, but the mass-13 beam comprises both13C− and 12CH− and the mass-14 beam comprises 14C−together with unwanted molecules such as 13CH−, 12CH−

2 ,which are roughly 109–1011 times more abundant than the14C− ions to be measured.

(b) Molecular elimination with the tandem accelerator: themass-14 ion beam is then injected in the tube of the tandemaccelerator where the negative ions are first accelerated.A small stream of argon is injected in the centralsection of the instrument so that polyatomic moleculesare dissociated by gas collisions and transformed into amixture of positive ions H, 12C, 13C and 14C ions (mostprobable charge: +3) which are accelerated in the finalsection of the tandem. Their energy is a function of bothmass and charge so that each particle has a unique energysignature.

(c) The final separation, detection and counting of 14C ionsin the high-energy section: the ion beam which leavesthe tandem accelerator is then re-focused and enters anelectrostatic deflector then another magnetic spectrometerwhich allows the ions to be separated according to theirenergy, their mass and their charge. Finally the beamwhich is mainly made of 14C ions with a small fractionof 13C and 12C ions enters a gas-filled (argon–methane)ion chamber, where carbon ions lose their energy by gascollision; the 14C ions are easily detected and separatedfrom the unwanted particles.

To get the sample age, as in the case of conventionalradiation-counter radiocarbon dating, one compares thecalculated 14C/12C and 13C/12C isotope ratios with thoseobtained for reference standards of known age.

Two types of operation are needed to determine the carbonisotopic composition of an unknown sample:

(i) measurement of the number of 14C ions;(ii) successive introduction of mass 12 and 13 beams into the

accelerator without changing its tuning and measurementsof the 12C3+ and 13C3+ beams collected by Faraday cups.

The two sets of measurements are repeated until sufficientcounts have been obtained for the required statistics and theapparent 14C/12C and 13C/12C isotopic ratios to be determined.Without changing the accelerator tuning, the apparent isotopicratios are measured for the reference sample and also for theblank.

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5. Discussion

Whenever enough material is available, multiple datings aredone on the same drawing to test the reproducibility andcoherence of the results, and on the humic acid fractionobtained during the basic treatment to see how much the initialpigment sample might have been contaminated (Batten et al1986). In real life situations one encounters three types ofcases, illustrated by the dates obtained for the Cosquer andChauvet cave drawings listed in tables 1 and 2 (the agesobtained with the humic acid fractions are given in italics).

In case 1 the purified charcoal and the humic acid fractionyield similar results (horse 1, hand R7 in the Cosquer cave,bison and torch scraping 1 in the Chauvet cave). While goodagreement between the two sets of dates generally increasesone’s confidence in the reliability of the dates, one can neverexclude a remote possibility that both fractions may havesomehow been similarly contaminated.

When the two fractions yield different dates the humicacid fraction, which one expects to contain more contaminants,tends to give a lower figure—case 2 (see bisons 1 and 2,Megaloceros 1 at Cosquer cave). In such cases the age of thepurified charcoal is more trustworthy. The less common case 3refers to examples where the humic acid fraction yields an agegreater than the purified charcoal (see the horse in the Chauvetcave and some Altamira bisons (Valladas et al 2001a)). Ingeneral, we have found older dates for a given sample tobe more reliable after noting how much more frequent wascontamination by recent carbon and consequent age-reduction.Exposed pigments can be polluted by organic materials, someof which can resist the chemical treatment meant to eliminatethem. Some samples are so small and fragile that if the solidcomponent is not to dissolve completely the purification has tobe less rigorous. In such cases the humic acid fraction, whichconsists of parts of original charcoal that were dissolved inan alkaline environment and re-precipitated, will give a morecorrect greater age.

6. Results

The tabulated ages obtained for drawings in the Cosquerand Chauvet caves show what type of important informationcan nowadays be obtained by the use of AMS radiocarbondating. These caves, which are currently being studiedby multidisciplinary teams, provided optimum samplingconditions, so that more than one sample of certain figurescould be dated. It was also possible to compare the ages ofdifferent fractions of a given scraping to see if the dates arecoherent. Moreover, by dating some of the abundant charcoalfragments found on the ground near the drawings we wereable to determine the periods of human presence in the cave,a presence that may have been related to artistic activities.

The Cosquer cave, whose entrance is now 40 m belowsea level, is richly decorated in rock paintings and carvings(Clottes et al 1992, 1997). About 24 dates (table 1) wereobtained for 13 charcoal drawings including animal figures,negative hands and geometric signs. Some pigment samplesscraped from several points of a figure were divided in twoand the two halves were treated and dated separately (horse 1,bisons 1 and 2); they yielded compatible ages, suggesting thatthese paintings were done within a relatively short time period

with charcoal coming from the same tree (or contemporaneoustrees). The paintings can be grouped into two time periodsabout 10 000 years apart (table 1). This fact is in agreementwith the conclusions based on the observation of the decoratedwall (Clottes and Courtin 1994). The first group consistingof negative hands, a bison and an oval sign were dated tobetween 28 000 and 27 000 years ago, during the Gravettianperiod. Except for one horse, the other animals and the star-like sign were dated to between 19 700 and 18 500 years BP,during the Solutrean period. Taking into account the amplitudeof the errors, it is not possible to conclude if each of the twopainting phases lasted a brief period of time or stretched overcenturies. On the other hand, until more drawings are sampledwe cannot tell if a horse and one stencilled hand, which seemto date to about 25 000 BP represent an intermediate period ofdecoration or are the result of more extensive contamination.The time span that separates the two bison (1 and 2) whichare similar and depicted on the same wall is rather surprising.This fact can be interpreted in at least two ways: either thestylistic conventions were maintained over extremely long timeperiods, or the older one was not done with fresh charcoal(Clottes et al 1997). To help us choose between thesealternatives additional dates will be needed. It is noteworthythat charcoal fragments collected on the ground nearby also fallwithin two distinct time intervals: 18 000–20 000 and 26 000–28 000 years, respectively.

Chauvet cave was discovered in Ardeche in December,1994 (Clottes 2001). So far about 40 dates have been obtained(Clottes et al 1995, Valladas et al 2001b): twelve on pigmentsfrom six drawings from different sections of the cave, twofor charcoal scrapings left by visitors who rubbed their torchesagainst the wall and the rest for the charcoal found in abundanceon the ground (table 2). The great majority of dates canbe grouped into two tight clusters representing two time-periods thousands of years apart (29 000–32 500 and 26 000and 27 000 years BP respectively). The animal representationswere dated to between about 32 000 and 30 500 years BP,within the Aurignacian period. The torch scrapings were about27 000 years old, a date not surprising if one notes that in onecase the torch was scraped against a layer of calcite depositedon top of a drawing! So far, there is no drawing dated tothis second period of human occupation. Most of the agesobtained for charcoal collected on the ground surface rangedfrom 26 000 to 32 000 years BP, suggesting the existence of atleast two major episodes of human intrusion before the cavewas sealed off by a rock-fall. The coherence of the datesobtained for the drawings of the Cosquer and Chauvet cavessuggests that the samples were not seriously contaminated.Such satisfactory results can be attributed to the great numberof samples available for dating and to the fact that the cave wassealed by a natural phenomenon during the Pleistocene period.

7. Conclusion

Even though the direct dating of cave paintings is still inits infancy, the few dates reported so far have convinced arthistorians of the need to revise prior ideas on the evolution ofprehistoric art. The Chauvet cave, in particular, indicates thattheories assuming a linear progression from simple to morecomplex composition have to be discarded and that, as early

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as the Aurignacian period, some artists had mastered designand composition (Clottes et al 1995). The AMS radiocarbondating also makes it possible to establish distinct periods ofartistic activity within any one cave.

At the present time the AMS technique does not allow forreliable dating of Palaeolithic drawings done in media otherthan charcoal. Unfortunately, the media most commonly usedin the execution of prehistoric paintings are iron oxide andmanganese oxide (Menu 2000). There is hope that some ofthese may be dateable in the future, since chemical analyseshave revealed that organic binders of plant or animal originwere occasionally used with mineral pigments (Pepe et al1991). The quantities are usually tiny, but improved chemicaltechniques will undoubtedly allow us one day to separate,purify and date such binders.

References

Arnold A, Bard E, Maurice P, Valladas H and Duplessy J C 198914C dating with the Gif-sur-Yvette Tandetron accelerator:status report and study of isotopic fractionations in the sputterion source Radiocarbon 31 284–9

Arnold M, Bard E, Maurice P and Duplessy J C 1987 14C datingwith the Gif-sur-Yvette Tandetron accelerator: status reportNucl. Instrum. Methods B 29 120–3

Batten R J, Gillespie R, Gowlett J A J and Hedges R E M 1986 TheAMS dating of separate fractions in archaeology Radiocarbon28 698–701

Bednarik R 1994 About rock art dating Int. Newsletter Rock Art 716–18

Clottes J (ed) 2001 La Grotte Chauvet. L’art des Origines (Paris:Seuil)

Clottes J, Chauvet J M, Brunel-Deschamps E, Hillaire C,Daugas J P, Arnold M, Cachier H, Evin J, Fortin P,Oberlin C, Tisnerat N and Valladas H 1995 Les peinturespaleolithiques de la grotte Chauvet-Pont d’Arc, aVallon-Pont-d’Arc (Ardeche, France): datations directes etindirectes par la methode du radiocarbone C. R. Acad. Sci.,Paris II 320 1133–40

Clottes J and Courtin J 1994 La Grotte Cosquer (Paris: Seuil)Clottes J, Courtin J, Collina-Girard J, Arnold M and

Valladas H 1997 News from Cosquer cave; climatic studies,recording, sampling, dates Antiquity 71 321–6

Clottes J, Courtin J, Valladas H, Cachier H, Mercier N andArnold M 1992 La grotte Cosquer datee Bull. Soc. Prehist.Francaise 89 230–4

Duplessy J C and Arnold M 1985 Radiocarbon dating by acceleratormass spectrometry Nuclear Methods of Dating ed E Roth andB Poty (Dordrecht: Kluwer) pp 437–53

Hedges R E M, Bronk C R, Van Klinken G J, Pettitt P B,Nielsen-Marsh C, Etchegoyen A, Fernandez Niello J O,Boschin M T and Llamazares A M 1998 Methodologicalissues in the radiocarbon dating of rock paintings Radiocarbon40 35–44

Hedges R E M, Law I A, Bronk C R and Housley R A 1989The Oxford accelerator mass spectrometry facility:technical developments in routine dating Archaeometry 3199–113

Igler W, Dauvois M, Hyman M, Menu M, Rowe M, Vezian J andWalter P 1994 Datation radiocarbone de deux figures parietalesde la grotte du Portel (Commune de Loubens, Ariege) Bull.Soc. Prehist. Ariege-Pyrenees XLIX 231–6

Laiz L, Groth I, Gonzales I and Saiz-Jimenez C 1999Microbiological study of the dripping waters in Altamiracave (Santillana del Mar, Spain) J. Microbiol. Methods 36129–38

Menu M 2000 Le savoir faire des premiers peintres La Recherche,Hors-Serie 4 56–8

Nelson D E, Chaloupka G, Chippindale C, Alderson M S andSouthon J R 1995 Radiocarbon dates for beeswax figures in theprehistoric rock art of Northern Australia Archaeometry 37151–6

Pepe C, Clottes J, Menu M and Walter P 1991 Le liant des peinturesprehistoriques ariegeoises C. R. Acad. Sci. Paris II 312 929–34

Rowe M W 2001 Dating by AMS analysis Handbook of Rock ArtResearch ed D S Whitley (Walnut Creek, CA: AltaMira) pp139–66

Russ J, Palma R L, Loyd D H, Boutton T W and Coy M A 1996Origin of the whewellite-rich rock crust in the lower Pecosregion of Southwest Texas and its significance to paleoclimatereconstructions Quat. Res. 46 27–36

Valladas H, Cachier H, Maurice P, Bernaldo De Quiros F, Clottes J,Cabrera-Valdes V, Uzquiano P and Arnold M 1992 Directradiocarbon dates for prehistoric paintings at the Altamira, ElCastillo and Niaux caves Nature 357 68–70

Valladas H, Tisnerat N, Cachier H and Arnold M 1999 Datationdirecte des peintures prehistoriques par la methode du carbone14 en spectrometrie de masse par accelerateur Rev.Archeometrie Suppl. 1999 39–44

Valladas H, Tisnerat-Laborde N, Cachier H, Arnold M,Bernaldo De Quiros F, Cabrera-Valdes V, Clottes J, Courtin J,Fortea-Perez J, Gonzales-Sainz C and Moure-Romanillo A2001a Radiocarbon AMS dates for Paleolithic cave paintingsRadiocarbon 43 977–86

Valladas H, Clottes J, Geneste J M, Garcia M, Arnold M,Cachier H and Tisnerat-Laborde N 2001b Evolution ofprehistoric cave art Nature 413 479

Watchman A 1990 A summary of occurrences of oxalates-richcrusts in Australia Rock Art Res. 7 44–50

Watchman A and Cole N 1993 Accelerator radiocarbon dating ofplant-fibre binders in rock paintings from northeasternAustralia Antiquity 67 355–8

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