Journal of Archaeological Science (1997) 24, 773–778

Oxygen-Isotope Ratios in Quartz as Indicators of theProvenance of Archaeological Ochres

M. A. Smith*

Department of Archaeology & Anthropology, The Australian National University, Canberra, ACT, Australia 0200

S. Pell†

Research School of Earth Sciences, The Australian National University, Canberra, ACT, Australia 0200

(Received 31 January 1995, revised manuscript accepted 20 September 1996)

The oxygen-isotope ratios of fine-grained quartz extracted from ochre samples can provide an indicator of ochreprovenance. A pilot study on a small series of red ochres from central Australia shows that ochres from differentgeological provinces can be distinguished using this technique. Oxygen-isotope ratios of fine-grained quartz could beused in conjunction with other geochemical methods either to verify the regional provenance of an ochre or to screena collection for material of exotic origin. ? 1997 Academic Press Limited

Keywords: OXYGEN-ISOTOPE RATIOS, PROVENANCE, RED OCHRE, CENTRAL AUSTRALIA.

Introduction

H igh-grade red ochre was a much-valuedcommodity in Aboriginal Australia. Themost desirable red ochres were from well-

known quarries such as Wilgie Mia, Bookartoo,Toolumbunner and Karrku (Clarke, 1976; Jones,1984a,b; Peterson & Lampert, 1985; Sagona, 1994)(Figure 1). Historically, ochre from major sources wasmoved by trade or exchange over hundreds of kilo-metres throughout the arid interior of the Australiancontinent (Mulvaney, 1976). Haematite and other redochres are frequently found in the earliest levels ofarchaeological sites across the continent (e.g. Bowler &Thorne, 1976; Smith, 1987; Morse, 1993), includingsites dating to 40–60,000 years ago (Roberts, Jones &Smith, 1990; Roberts et al., 1994). The potential forgaining fresh insights into regional interconnectionsand the movement of goods and people in prehistoryhas been recognized by archaeologists. What isrequired, however, is some means of identifying thesource of ochre found in archaeological sites andespecially some means of distinguishing ochres fromexotic or extra-regional sources as these are usually ofmost interest from the perspective of reconstructinglong-distance exchange networks.There are various methods for determining the geo-

chemical characteristics of ochres (Clarke, 1976;

7730305–4403/97/090773+06 $25.00/0/as960159

Clarke & North, 1991; David, Clayton & Watchman,1993; Sagona, 1994; David et al., 1995). To date noneof these have been entirely satisfactory, but we reporthere a technique which could be used in conjunctionwith other methods either to verify the regionalprovenance of an ochre or to screen a collection formaterial of exotic origin. The technique uses theoxygen-isotope (O-isotope) ratios of fine-grainedquartz extracted from ochre samples as an indicator ofochre provenance.

MethodsBasis of the method

This method is based on the premise that the stableO-isotope ratio (18O/16O) of quartz grains accuratelyrecords that of their parent rock types. This value hasbeen shown in numerous studies to be most resistant toalteration and isotopic exchange in low-temperatureenvironments (Clayton, Jackson & Sridhar, 1978) andcan therefore be used to characterize different rocktypes (see Blatt, 1987).Fine-grained sediments usually contain quartz from

a number of different parent rock types, each of whichhas its own O-isotope ratio. Quartz grains from each ofthese parent rocks are combined together in the sedi-ment, thereby giving it a distinct O-isotope signature.Studies of the O-isotope ratios of quartz separatedfrom glacial, fluvial and aeolian sediments and soilshave utilized this principle to determine the provenanceareas for the quartz grains (e.g. Clayton et al., 1972;

*Present address: National Museum of Australia, GPO Box 1901,Canberra, ACT, Australia 2601.†Present address: Graduate School of Education, University ofQueensland, Brisbane, Qld, Australia 4072.

? 1997 Academic Press Limited

774 M. A. Smith and S. Pell

Jackson et al., 1972; Churchman et al., 1976;Lawrence, 1979; Jackson, 1981; Chartres, Chivas &Walker, 1988; Pell, 1994).Many red ochres are of sedimentary origin, either as

sedimentary infill in joints and fractures in bedrock oras beds of ferruginized sandstone or laterite (e.g.

Sullivan & Opik, 1951; Keeling, 1984; Sagona &Webb, 1994). These ochres often contain an appreci-able proportion of quartz. For example, SEM/EDXAanalysis of the ochres listed in Table 1 showed thattheir SiO2 content ranges from 20–54%. Much of this isin the form of quartz grains of various size grades and

Uluru(Ayers Rock)

WesternAustralia

Wilgie Mia

NorthernTerritory

Queensland

SouthAustraliaBookartoo

Moana

Victoria

NewSouthWales

Toolumbunner

Tasmania

Karrku

Mt Liebig

Putarti

ClelandHills

Puritjarra

Ulpunyali

Lawa

50 km0

George Gill ra.

Lake Amadeus

Petermann ra.

Ehrenberg ra.

Gardiner ra.

Figure 1. The location of Puritjarra rock shelter in relation to ochre sources mentioned in the text.

Table 1. Oxygen-isotope ratios and quartz percentages for ochre samples. All samples are raw ochre. N5/24-6 is ochreexcavated from Puritjarra rock shelter. Paterson X was collected from Aboriginal people at Uluru (Ayers Rock). Theother specimens are from various ochre quarries

Sample SiO2 (%)Number ofanalyses

Mean ä18O‰(SMOW)

Range ä18O‰(SMOW)

N5/24-6 54 3 11·8&0·20 11·7&12·1Ulpunyali 43 3 11·7&0·21 11·6&12·0Karrku 30 2 11·8&0·22 11·7&12·0Paterson X 34 3 12·3&0·15 12·1&12·4Bookartoo 20 2 13·8&0·50 13·5&14·2

Oxygen-Isotope Ratios in Quartz 775

is clearly visible in polished sections using back-scatterscanning electron microscopy (SEM) methods to ex-amine the fabric and petrology of the ochres. Analysisof the O-isotope ratios of these quartz inclusionstherefore offers a means of tracing the provenance ofochre found in archaeological sites. However, becausesediments within each geological province have similarO-isotope ratios, the principal value of this techniqueis in rapidly screening the ochres recovered from anarchaeological site to identify materials derived fromsources in other geological provinces, or which havebeen transported significant distances. These are pre-cisely the specimens that are of most archaeologicalinterest from the point of view of long-distanceexchange.In the case of ochre deposits of hydrothermal origin

(as in vein haematites), or sedimentary ochres devel-oped directly adjacent to quartz veins, the quartz willshare the O-isotope (ä18O) signature of nearby veins,rather than represent an average of the rocks contrib-uting to sediments in a particular basin. As the outcroparea of vein quartz in Australia is small compared toother rock types (e.g. granite, sandstone) it is unlikelythat this will be a major problem in interpretingO-isotope values for quartz from sedimentary ochres.However, ä18O values alone will not be sufficient toidentify exotic ochres securely in an archaeologicalassemblage. We suggest the method be used to screenan assemblage to identify ochres warranting furtheranalysis of mineralogy and trace-element composition.For vein haematite the ä18O values will identifymaterial from different vein systems.

Separation of quartz from ochresQuartz separates for O-isotope analysis were preparedby the following methods adapted from Syers et al.(1968), Sridhar, Jackson & Clayton (1975) andJackson, Savin & Clayton (1976).Starting initially with 5–10 g of dry bulk ochre

sample:

(1) remove heavy accessory minerals using tetra-bromoethane (C2H2Br4) (density 2·70 g/cm

3);(2) remove iron-oxide (haematite) coatings using hot

(100)C) 3 M HCl (1 h). This step was repeated untilthe red coloration was removed from the sample;

(3) remove remaining accessory minerals (e.g. feldsparand clays) using 6 M H2SiF6 (6 h);

(4) wash twice in demineralized water under gentleultrasonic agitation.

The effectiveness of the procedure outlined abovewas assessed by means of a quantitative analysis ofaluminium (Al) (using an Inductively Coupled ArgonPlasma Spectrometer (ICP)), and the method wasshown to reduce the quantities of feldspars, clays andother accessory minerals present in quartz separates tothe level where they have a negligible influence on theä18O value of quartz.

Determination of oxygen-isotope ratioThe stable O-isotope ratio of quartz is generally givenusing the ä18O nomenclature as defined below and isquoted relative to the international standard V-SMOW(Vienna-Standard Mean Ocean Water).Oxygen for isotopic analysis was released quantita-

tively from dried and out-gassed 10–15 mg quartzsamples by reaction with bromine pentafluoride at550)C (Clayton & Mayeda, 1963). Oxygen liberated bythis technique was quantitatively converted to CO2by platinum-catalysed reaction with an incandescentgraphite rod and the ä18O ratio of the resultant gasmeasured using a Finnigan MAT-251 mass spec-trometer. Oxygen-isotope ratios (ä18O) are reported inper mil (parts per thousand, ‰) relative to the standardV-SMOW, defined as having a ä18O value of 0·0‰.On this scale, a value of &9·64‰ is accepted for theAfrican Glass Standard NBS-28. The mass spec-trometer working gas used in this study was the ANUsilica glass standard, ANU-Si (13·25‰). Followinganalysis, a raw ä18O value was calculated relative to theworking standard. The expression used for calculatingä18O is:

d18OV-SMOWSample (‰) =

5(18O/16OSample)"(18O/16OStandard)6#1000(1)

18O/16OStandard

This value was then fitted to a regression line calcu-lated using the two calibrating standards to obtain a

776 M. A. Smith and S. Pell

final value relative to V-SMOW. Precision of theanalytical technique for replicate analysis of theANU-Si standard is better than &0·2‰.

Regional variations in oxygen-isotope data acrossAustraliaTo date, only a small number of studies havebeen carried out examining the O-isotope ratios ofrocks and sediments from Australia. Wilson (1981)examined whole-rock samples from the granite/greenstone terrane of the Yilgarn Block (WesternAustralia) and reported ä18O (whole-rock values) ofapproximately 7·9&0·8‰. Correcting for the 1–2‰difference between quartz separated from granites andgranodiorites and their whole-rock signatures (Taylor& Epstein, 1962), the ä18O values reported by Wilson(1981) have corrected values for quartz of approxi-mately 9·4‰. Similarly, in studies of granites fromthe Berridale Batholith and New England Fold Beltof eastern Australia, O’Neil & Chappell (1977) andO’Neil, Shaw & Flood (1977) recorded whole-rockä18O values which after correction, give ä18O valuesof quartz for I- and S-type granites of approxi-mately 9·9–11·4‰ and 11·4–14·0‰, respectively. TheO-isotope values of quartz separated from granulitesand related intrusive rocks from the Musgrave Block(central Australia) have ä18O values of between 7·6 and9·3‰ (Wilson, Green & Davidson, 1970).Cartwright, Power & McLatchie (1994) obtained

O-isotope values from vein quartz samples taken fromcentral Australia of between 14 and 17‰. Similarstudies on vein quartz by Golding & Wilson (1987) andGray, Gregory & Durney (1991) have reported ä18Ovalues of 10–13‰ from the Yilgarn Block and 16–19‰from Ordovician sediments in Victoria, respectively. Itis considered, however, that the amounts of vein quartzcontributing to the overall sedimentary system inAustralia will be far outweighed by the contributionsfrom other rock types. In most cases, therefore, veinquartz will have only a minimal effect on the overallä18O signature of quartz sediments.The O-isotope ratios of quartz taken from sedimen-

tary deposits (mainly dune sands overlying sedimen-tary basins) are characteristically higher than thosefrom the basement rocks discussed earlier. Thisincrease is believed to be due to the presence ofsecondary low temperature (high ä18O) quartz over-growths formed on the surface of the original quartzgrains after deposition within a sedimentary basin(Pell, 1994). These overgrowths, along with the mixingof quartz grains from different basement rocks, givematerial from each sedimentary basin a characteristicO-isotope value. Sand samples taken from dunes over-lying the western Officer Basin or Great VictoriaDesert give a mean ä18O value of 9·5‰, while those inthe centre and east of the basin have a mean value of11·0‰. In both the Simpson and Strzelecki Deserts(overlying the Eromanga Basin) and in the Great

Sandy Desert (Canning Basin) quartz samples have amean ä18O value of approximately 11·3‰, while thosefrom the Mallee Dunefield (Murray Basin) in south-eastern Australia have a mean value of 12·2‰ (Pell,1994).

MaterialsTo test the archaeological utility of the method wecarried out a pilot study on a small series of red ochresfrom central Australia (Table 1). The samples includeochre from two ethnographical ochre mines in centralAustralia (Karrku and Ulpunyali) in rock formationsof different geological age; an archaeological specimen(N5/24-6) from Puritjarra rock shelter; and two ochres(Paterson X and Bookartoo) from different geologicalprovinces, included here as inter-regional comparisons.Figure 1 shows the locations of ochre sources men-tioned in the text. All of the samples discussed beloware of raw ochre rather than prepared pigment.

Puritjarra rock shelter (N5/24-6)N5/24-6 is an archaeological specimen of ochre exca-vated from stratigraphical contexts dating to 13,000 at Puritjarra rock shelter (Smith, 1987, 1988, 1989).With respect to petrology and chemistry, N5/24-6 isrepresentative of the red ochre found in late Pleistocenelevels at this site. Like most of the archaeologicalspecimens, N5/24-6 appears to be a piece of rawunaltered ochre rather than processed pigment orpaint. It is a soft fine-grained red ochre with mica, andclear subrounded quartz inclusions from 100–200 ìm,set in a fine-grained haematite cement.Comparison of the archaeological ochres with

samples from known quarries in central Australia,using XRD, quantitative SEM/EDXA data on majorand minor oxides, ICP/MS analysis of trace elementcomposition, and back-scatter SEM examination offabric and petrology, suggests that Karrku is the likelysource of the red ochre in late Pleistocene contexts atPuritjarra, including N5/42-6.

KarrkuThe Karrku sample is from the ochre seam at animportant ethnographical ochre mine located approxi-mately 150 km north-west of Puritjarra (Peterson &Lampert, 1985), formed in joints in PrecambrianVaughan Springs quartzite. Karrku ochre is a softearthy specular haematite with sub-rounded quartzgrains up to 400 ìm in a fine haematite cement. Mus-covite (or possibly sericite) forms platey aggregates upto 100 ìm. The presence of quartz clasts indicates theochre deposit is sedimentary infill in joints in the localquartzite rather than vein haematite.

UlpunyaliUlpunyali is an important regional ochre quarry,approximately 65 km south of Puritjarra shelter

Oxygen-Isotope Ratios in Quartz 777

(Hamilton & Vachon, 1985: 43–46). The ochre depositis a friable, moderately well-sorted, coarse-grainedferruginized sandstone formed at the contact ofOrdovician Horn Valley siltstone and Pacoota sand-stone (Bagas, 1988). Ulpunyali ochre is a dark-red orpurple ochre with a very greasy appearance. The ochreis coarse-grained with large sub-rounded quartz grainsof approximately 300–400 ìm set in a ferruginouscement. Fine botryoidal banding and concentric con-cretions around quartz grains indicate that the cementrepresents cavity fillings.In terms of chemistry and petrology, Ulpunyali can

be ruled out as the source of ochres such as N5/24-6but is included here to test whether O-isotope ratiosdistinguish between Karrku and Ulpunyali. The twoquarries are approximately 200 km apart, but lie inrock formations of different geological age.

Paterson XPaterson X is ochre acquired from Aboriginal peopleat Uluru and is believed to come from a source in thePetermann Ranges approximately 200 km south ofPuritjarra. It is an homogenous and extremely fine-grained red ochre with an Al-Si-K-Fe rich groundmass,with minor Mg and Cl. Within this, there are occa-sional angular clasts of the same material up to 40 ìm,consistent with it being a siltstone.

BookartooBookartoo is a well-known ochre mine in the northernFlinder Ranges approximately 1100 km south-east ofPuritjarra. A recent appraisal of the Bookartoo depositshows that the ochre deposit is an earthy haematite,infilling joints and fractures in Cambrian Wilkawillinadolomite directly below the contact with a layer of siltylimestone (Keeling, 1984). Keeling suggests that dia-genesis of this deposit began with initial deposition ofiron sulphides (pyrite) in karst cavities in the dolomite.Prolonged oxidation and arid weathering of this sur-face led to formation and redistribution of haematite injoints and fracture above the water table. Bookartooochre is a distinctive soft friable purple or dark-pinkochre, often with a greasy appearance. Haematite ispresent in the form of large flakes (to 1 mm) and assmaller grains and clots. SiO2 is present as roundedquartz grains, ranging in size from 10 to 100 ìm.Calcite, dolomite and silicates make up a fine groundmass.

Results and DiscussionTable 1 gives the oxygen-isotope ratios for the variousochres.Quartz separated from the Karrku and Ulpunyali

ochre samples gave very similar O-isotope ratios whichranged from 11·7 to 12·0‰ and from 11·6 to 12·0‰,respectively. The similarity between these values

supports the view that O-isotope ratios are unlikely todiscriminate between ochre samples taken from thesame region. The O-isotope data from the archae-ological specimen N5/24-6 are consistent with itbeing derived from the same region as Karrku andUlpunyali, although isotope ratios alone will clearlynot allow us to identify a specific provenance forsedimentary ochres. The most significant results ob-tained in this study were from the Paterson X andBookartoo ochre samples. Quartz separates from thesesamples have O-isotope ratios of 12·3‰ and 13·8‰,respectively, which are significantly different from eachother and, more importantly, are different from thoseobtained from the Karrku and Ulpunyali samples. Onthe basis of these results sample N5/24-6 is unlikely tohave come from Bookartoo, or from the same sourceas Patterson X.These results suggest that O-isotope data could

usefully be applied to archaeological assemblages toscreen collections for ochres derived from sourcesoutside a particular sedimentary basin or which havebeen transported significant distances. In the case ofvein haematite, or ochres formed in metamorphicrocks such as ferruginized quartz mica schists (e.g.David et al., 1995), the technique has the potential toidentify specific sources or to indicate which ochresderive from the same source, even if specific regionalsources are not known. However, the usefulness of thetechnique will be limited by the availability and reso-lution of O-isotope data from potential quartz sourceareas.

AcknowledgementsThis work was carried out while MAS held a ResearchFellowship in the then Department of Prehistory,Research School of Pacific and Asian Studies, ANU.SDP was supported by an ANU Ph.D. Scholarship atthe Research School of Earth Sciences, ANU. Thanksare also due to Mr Joe Cali for his technical assistancein the construction of the oxygen-isotope line,Win Mumford for producing Figure 1, Wal Ambrosefor comments on this paper and also to Ms JoanCowley and Marcela Vitouchova for their help withthe experimental analysis.

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