COMPLEMENTARY COMPOSITIONAL ANALYSIS OF FORMATIVE PERIOD CERAMICS FROM THE TEOTIHUACAN VALLEY

COMPLEMENTARY COMPOSITIONAL ANALYSIS OFFORMATIVE PERIOD CERAMICS FROM THE

TEOTIHUACAN VALLEY*

B. A. ALEX

Anthropological Archaeology and Human Evolutionary Biology, Peabody Museum, Harvard University, 11 Divinity Avenue,Cambridge, MA 02138, USA

D. L. NICHOLS

Department of Anthropology, Dartmouth College, Hanover, New Hampshire 03755, USA

and M. D. GLASCOCK

Research Reactor Center, University of Missouri,1513 Research Park Drive, Columbia, Missouri 65211, USA

During the Classic Period, Teotihuacan was an economic centre of central Mexico, but littleis known about the development of this system. This paper presents a pilot study in multi-method analysis of Formative Period (1500/1400 BC – AD 150) ceramics from the TeotihuacanValley. Pottery was characterized by instrumental neutron activation analysis, laser ablationinductively coupled plasma mass spectrometry, thermal ionization mass spectrometry andpetrography. It appears that most pottery was made from local raw materials that differ fromlater Postclassic materials. Some inter-village interaction is suggested by stylistic choices,and one settlement had a group of ceramics made from unequivocally distinct raw materials.The study demonstrates how complementary methods can be used to draw greater anthropo-logical meaning from compositional differences.

KEYWORDS: TEOTIHUACAN VALLEY, CERAMICS, INAA, LA–ICP–MS, SR ISOTOPES,PETROGRAPHY

INTRODUCTION

In about 1000 years, the Teotihuacan Valley transformed from a marginal region ofsmall villages to the sociopolitical core of central Mexico. By the end of the Formative Period(1500/1400 bc – ad 150), Teotihuacan was the largest city in the New World, with unprecedentedand unrivalled political dominance (Millon et al. 1973; Sanders et al. 1979; Millon 1981; Charl-ton and Nichols 1997). It is clear that at its peak Teotihuacan was a major economic centre. Whatis unclear is how this system emerged. What was the nature of relations between surrounding andantecedent villages?

This paper presents a pilot study in multi-method analysis of ceramics from Formativesettlements in the Teotihuacan Valley. Considerable debate has occurred over the best methodof pottery characterization (e.g., Stoltman et al. 2005; Neff et al. 2006). The pursuit is prob-lematic because ceramic composition reflects many influences, including provenance, process-ing, use and diagenesis (Blackman 1992; Burton and Simon 1996; Neff et al. 2003). However,

*Received 5 June 2011; accepted 16 October 2011

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Archaeometry 54, 5 (2012) 821–834 doi: 10.1111/j.1475-4754.2011.00652.x

© University of Oxford, 2012

complementary methods can distinguish compositional influences: the best methods of potterycharacterization are multiple methods (Rice 1987, 326; Pollard and Heron 2008, 101; Tite2008).

Pottery was assigned to groups based on bulk elemental composition measured by instrumentalneutron activation analysis (INAA). The meaning behind compositional differences was theninvestigated using laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS)for targeted elemental characterization, thermal ionization mass spectrometry (TIMS) for stron-tium isotope ratios and thin-section petrography for mineralogy. The settlements appear to havebeen primarily making their own pottery from local resources, which may differ from laterPostclassic resources. One group of ceramics was made from unequivocally distinct raw mate-rials. Although only a small number of samples were analysed, the study demonstrates howcomplementary methods can be used to move beyond traditional sourcing questions and drawgreater anthropological meaning from compositional differences.

BACKGROUND

The Teotihuacan Valley encompasses approximately 600 km2, in the north-east Basin of Mexico(BOM) (Sanders et al. 1979, 74) (Fig. 1). During the Formative Period, the Teotihuacan Valleytransformed from a low-density scatter of roughly equivalent villages to a state-level society withone extremely nucleated and populated centre of Teotihuacan (Millon et al. 1973; Millon 1976,1981; Sanders et al. 1979; Sanders 1981; Parsons 1989). Craft specialization was diverse inproducts and scale (Millon et al. 1973; Spence 1984; Solís 2009). Obsidian and ceramics wereproduced in complex systems of complementary workshops. Over 200 ceramics workshopsexisted within Teotihuacan throughout its occupation and goods were traded across Mesoamerica(Krotser and Rattray 1980; Spence 1981; Santley 1984; Krotser 1987; Sheehy 1992; Hopkins1995; Cowgill 1997; Sullivan 2006; López Pérez 2009; Pastrana 2009). However, little isknown about ceramic production or craft specialization in the Teotihuacan Valley before ClassicTeotihuacan.

Pottery was collected and classified during the Teotihuacan Valley Survey, part of the BOMSurvey that ran from 1960 to 1975 under William T. Sanders (Sanders et al. 1975; Sanders et al.1979, 435–49). The sample (n = 105) is from four Middle to Late Formative sites: Altica, CerroXiquillo, Venta de Carpio and Cuanalan (Fig. 1). The small (~4 ha) Middle Formative settlementof Altica lies less than 10 km from the Otumba obsidian source and may have been used as apreform production site (Sanders et al. 1975; Tolstoy et al. 1977). Also in the mountains, CerroXiquillo was established in the Middle Formative. By the Late Formative, it seems to have growninto a community of settlements that cultivated land around Altica, as the settlement declined(Sanders et al. 1975, 144). The lakeshore site of Venta de Carpio experienced significant occu-pation in the Middle Formative, Early Classic and Late Postclassic periods. The site’s lowpopulation densities, low-prestige ceramic assemblage and location on agriculturally unproduc-tive, saline soil suggest that Venta de Carpio was a specialized salt-production centre (Tolstoy andGuénette 1965; Sanders et al. 1975; Sanders et al. 1979). Salt production at Venta de Carpioand obsidian reduction at Altica may indicate some degree of economic integration. Lastly, thelakeshore site of Cuanalan has a Late Formative assemblage reflecting the full range of domesticactivity for an agricultural village (Sanders et al. 1975).

The Teotihuacan Valley belongs to the Mexican Volcanic Belt (Mooser et al. 1974). Most claysare andesitic, but rhyolitic, dacitic and basaltic–andesitic clays also occur (de Terra et al. 1948;Slayton 1985; Garraty 2006, 106). Gamio (1979) found several contemporary clay sources in the

822 B. A. Alex, D. L. Nichols and M. Glascock

© University of Oxford, 2012, Archaeometry 54, 5 (2012) 821–834

Figu

re1

Site

sw

ithi

nth

eTe

otih

uaca

nVa

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,in

the

nort

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icsa

mpl

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from

Mid

dle

For

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uill

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Lat

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orm

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tion

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ough

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For

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5).

Formative Period ceramics from the Teotihuacan Valley 823


Teotihuacan Valley, including one between the sites in this study. Chemical sourcing within theBOM is challenging because clays have formed from widespread, overlapping ash falls (Slayton1985; Hopkins 1995, 281). Eastern highland sources can be distinguished by a north–southincrease in Cr and Fe relative to Al (Minc 1994, 2009; Neff and Glascock 1998, 2000; Neff et al.2000). Lacustrine sources differ by a compositional gradient, rather than as patch sources ofdistinctive geochemistry. North–south trends in geochemistry can distinguish geographical sub-divisions, but the boundaries between these subdivisions are arbitrary (Nichols et al. 2002;Garraty 2006). The Teotihuacan Valley is one such subdivision.

METHODS

Bulk elemental concentrations were measured by INAA according to ceramic procedures atthe University of Missouri Research Reactor (MURR) (Glascock 1992; Neff 2000). Elementalconcentrations for 33 elements were tabulated in ppm and converted to logarithms for statisticalmanipulation in the program GAUSS. Principal components analysis (PCA) and Mahalanobisdistances were used to create groups of similar composition (Bieber et al. 1976; Glascock 1992).

Sr isotope ratios (87Sr/86Sr) have been widely used for sourcing geological, biological andarchaeological materials (e.g., Dash 1969; Ericson 1985; English et al. 2001), but rarely mea-sured in ceramics (but see Li et al. 2005, 2008). We measured the Sr isotope ratios of eightceramics and three clays (two raw, one fired) by TIMS. Samples were dissolved in the high-temperature/pressure Picotrace digestion system according to the system manual’s procedure forsilicates. About 100 mg of each sample was dissolved in a 2:3:3 cocktail of HNO3, HF and HClO4.After evaporation, dried samples were redissolved in HNO3 (1.4 ml), tartaric acid (1.25 ml) andH2O (7 ml), and heated to 100°C for 1 h. Sr (~1000 ng) was separated by two-phase columnchromatography and samples were loaded on to high-purity W filaments with a Ta2O5 slurry(Birck 1986; Sharma et al. 2007). TIMS was conducted on the Dartmouth Triton instrument instatic mode. Samples were heated to ~5 V and emission was recorded for 200 detections. Theaverage of fractionation corrected values were taken as the isotopic ratios. The average sampleerror was 1 0.000007 (2s). NIST 987 Sr standards had a precision of 1 0.000014.

A subset of ceramics (n = 31) was prepared as petrographic thin sections by Arizona QualityThin sections. Petrographic analysis was cursory, intended to identify differences in inclusionsize, shape and kind. More thorough analysis, including petrography of raw materials, couldresolve emergent questions of this study.

Four ceramics were characterized by LA–ICP–MS to investigate elemental differences in theclay matrix. Analysis was performed in the Dartmouth College Trace Elements Analysis Core onthe Thermo Element 2 ICP–MS with laser attachment. Petrographic thin sections were subjectedto three ablation lines that targeted the clay and avoided mineral inclusions. The instrument wasset to detector frequency 10 Hz, laser size 100 mm, power 0.55, fluence 10 J cm-3 and gasflow rate 0.830 l min-1. Each run consisted of 60 s of background collection and 100 s ofdata collection. Before and after each ceramic, NIST glass standard SRM-610 was measured.Elements with high eigenvectors in PC1 (Na, Mg, Si, Ca, Mn, Rb, Sr, Sb, Cs, Ba and U) werequantified (Gratuze et al. 2001; Speakman and Neff 2005). The average background was sub-tracted from each measurement of signal counts per second (cps). Each signal measurement wasdivided by Si cps at that time, to yield ratios of X/Si, which were averaged for the run. The signalintensities X/Si (cps) were divided by the actual concentrations X/Si (ppm) in the standard tocalculate sensitivity. X/Si (cps) ratios were divided by sensitivities to correct for instrumentalmass bias.



RESULTS

INAA and PCA revealed three composition groups, Groups 1, 2 and 3 (G1, G2 and G3) (Fig. 2).Mean elemental compositions of each group are listed in Table 1 and full elemental compositionsand sample information are available upon request. Sixteen ceramics were unassigned and fourwere assigned to Group 1b (G1b) because they fell below 90% probability of group membership.On nearly all elemental and primary principal components axes, G1 is a tight, isolated cluster. G2and G3, however, almost exclusively segregate by Ba concentration or principal component 2(PC2). Eigenvectors, which quantify the contribution of each element to principal components,show that PC2 is primarily defined by Ba concentration. G1 samples are enriched in U, Sb,Cs and Rb, and depleted in Sr, Ca, Na and Mn, relative to G2 and G3 samples.

Ceramic compositions were compared to the compositions of BOM clays (n = 165) previouslyanalysed at MURR (Neff and Glascock 1998; Nichols et al. 2002). BOM clays are most similarto G3 ceramics (Fig. 2). Of Teotihuacan Valley (TV) clays, 22/30 overlap with G3, eight appearto belong to G2, and no clays fell into the compositional space of G1. When ceramics wereprojected on to clays, nearly all G3 ceramics fell into TV clay compositional space, althoughwidespread BOM clays share this region.

Two striking patterns emerged when composition groups were compared to sites. First, all G1and G1b ceramics (12/12) were found at Altica, along with some G2 ceramics (11/19). Second,nearly all high-Ba G2 samples (18/19) were from the piedmont sites of Altica and Cerro Xiquillo,while most low-Ba G3 samples (56/58) were from the lakeshore sites of Venta de Carpio andCuanalan. Numerous studies have observed high-Ba ceramics from highlands and low-Ba ceram-ics from coastal or lacustrine zones, and attributed this pattern to diagenesis in differing burialenvironments (Neff et al. 1988, 1990, 2003; Sheehy 1992). This hypothesis was tested withfurther statistics. When Ba is removed from PCA, G2 and G3 overlap on all principal componentaxes. Next, a Welch’s t-test was performed to compare the mean concentrations of each elementbetween G2 and G3. Using a Bonferonni corrected a-level, no significant differences werefound for 25/33 elements. The difference in Ba concentration was significant (p = 9 ¥ 10-10). K,

Figure 2 INAA revealed three ceramic composition groups. Ellipses represent 90% confidence of group membership,while points represent Basin of Mexico clays (Neff and Glascock 1998; Nichols et al. 2002).



Tabl

e1

Mea

nsan

dst

anda

rdde

viat

ions

ofIN

AA

elem

enta

lco

ncen

trat

ions

for

each

cera

mic

grou

p

G1

G1b

G2

G3

All

Mea

n(p

pm)

sM

ean

(ppm

)s

Mea

n(p

pm)

sM

ean

(ppm

)s

Mea

n(p

pm)

s

As

3.25

0.76

8.92

6.86

2.42

0.54

2.80

0.95

3.06

2.03

La

34.9

03.

0034

.18

8.71

20.9

52.

9220

.57

3.17

22.2

45.

76L

u0.

460.

030.

440.

150.

280.

040.

250.

040.

280.

08N

d30

.60

3.47

29.2

98.

0821

.69

3.42

21.5

13.

6522

.34

4.76

Sm6.

170.

766.

152.

355.

000.

544.

780.

724.

940.

90U

2.86

0.37

4.83

3.18

1.34

0.27

1.38

0.39

1.63

1.03

Yb

3.08

0.25

3.10

1.08

2.04

0.21

1.83

0.34

2.01

0.54

Ce

71.1

25.

8463

.72

15.4

845

.11

5.79

44.8

25.

5447

.54

10.0

4C

o12

.52

1.78

10.8

53.

4615

.07

3.22

17.8

93.

3916

.69

4.03

Cr

146.

075.

2397

.28

24.6

712

2.63

28.5

212

1.61

26.7

512

4.15

37.1

4C

s9.

720.

366.

731.

612.

570.

292.

780.

553.

492.

08E

u1.

260.

161.

080.

381.

330.

161.

370.

151.

330.

19Fe

4090

0.11

353

0.08

4275

5.63

165

7.88

4040

5.12

423

3.59

4378

2.26

435

9.50

4281

3.08

500

6.44

Hf

6.20

0.44

6.28

0.85

5.54

0.47

5.74

0.51

5.75

0.58

Ni

39.1

327

.26

44.3

449

.32

52.2

314

.22

43.7

920

.61

43.6

324

.42

Rb

147.

776.

7610

9.04

28.5

246

.47

4.53

51.2

75.

8160

.09

29.0

2Sb

0.76

0.09

1.41

1.00

0.30

0.06

0.28

0.07

0.39

0.35

Sc19

.57

1.00

15.6

90.

7813

.73

1.43

14.0

11.

1214

.49

2.04

Sr12

4.28

21.8

595

.75

45.1

555

1.06

61.9

553

6.71

145.

3149

6.08

198.

81Ta

1.12

0.04

1.11

0.23

0.74

0.10

0.75

0.08

0.78

0.17

Tb

0.78

0.10

0.84

0.46

0.70

0.10

0.63

0.12

0.66

0.15

Th

11.4

70.

7111

.70

2.34

5.99

0.52

5.51

0.70

6.26

2.09

Zn

161.

139.

5712

1.59

27.3

260

.17

7.93

67.4

26.

6077

.81

36.5

5Z

r16

9.16

11.3

317

2.37

33.6

913

3.41

28.0

814

1.99

20.5

714

4.43

24.9

5A

l11

310

3.81

283

4.67

9500

0.04

930

3.45

103

359.

256

810.

8110

352

6.09

563

9.48

103

685.

807

732.

83B

a84

5.41

124.

2587

1.55

420.

491

723.

3047

7.63

476.

6010

8.91

778.

4852

6.26

Ca

670

0.81

124

2.22

815

5.12

328

6.38

2627

1.15

272

3.40

2738

9.84

806

7.66

2600

7.28

1424

5.30

Dy

4.70

0.51

5.02

2.14

3.76

0.50

3.38

0.69

3.60

0.86

K22

327.

1890

4.88

1768

7.10

538

6.94

1035

9.19

236

7.60

1390

1.80

280

6.61

1383

9.78

401

0.10

Mn

341.

2512

6.06

332.

7019

1.04

657.

9412

3.54

797.

7216

2.77

713.

4021

5.63

Na

592

9.99

639.

675

464.

7646

8.69

1622

6.47

157

2.89

1781

5.41

142

2.61

1582

2.61

435

1.19

Ti

554

1.15

252.

474

850.

4239

0.93

503

9.19

549.

335

761.

3897

8.54

557

7.03

959.

61V

188.

6515

.82

203.

4899

.10

93.4

314

.03

109.

5820

.90

117.

1938

.60



Rb, Na, V, Mn, Zn and Ti also showed significant differences. Based on these patterns, G2 andG3 will be combined under the working hypothesis that compositional differences are due to postdepositional alterations.

The Sr isotope ratios of eight ceramics and three clays were measured by TIMS (Table 2).Figure 3 shows 87Sr/86Sr (TIMS value) plotted against the inverse Sr concentration (INAA value)of ceramics and clays, compared to previously measured geological materials from Mexico. Withthe exception of the G1 ceramic, the materials had Sr isotope ratios within the known range ofMexican Volcanic Belt geology (Torres-Alvarado et al. 2000). The G1 ceramic exhibits lower Srconcentration (107 ppm) and a higher isotope ratio (0.713633 1 7), which is well above theMexican Volcanic Belt range and similar to the values for dacite–rhyolite from the Sierra MadreOccidental and Precambrian basement rock from Oaxaca (Ruiz et al. 1988a,b; Torres-Alvaradoet al. 2000). The G1b ceramic is intermediate between the G1 ceramic and the others. Thevariation in Sr isotope ratios of G2/3 ceramics, unassigned ceramics and clays exceeds theanalytical uncertainty; these materials have different Sr isotope ratios.

LA–ICP–MS measured the elemental make-up of clay matrices of four ceramics from Altica—two from G1 and two from G2. Bivariate plots of elements with high PC1 eigenvectors show thatthe clay of G1 ceramics is distinct from that of G2 ceramics (Fig. 3).

Petrography revealed differences between G1/1b and other ceramics (Fig. 4). G1/G1b ceram-ics have mid-size (~0.5 mm diameter), subrounded volcanic clasts. Elongate pores often containmid-large (0.5–1.0 mm) inclusions that appear black under plain polarized light and betweencrossed polars, but with golden ribbons in reflected light. These optical properties occur whenorganic material is subjected to high temperatures and pressures, such as in coal (Taylor et al.1998). The black inclusions may be the remains of fired plant temper—a hypothesis supportedby contemporary and historical Mesoamerican potters’ frequent use of cattail fluff as temper

Table 2 Strontium isotope ratios measured by TIMS and Sr concentrations measured by INAA of eight ceramics andthree clays. Oaxaca basement values from Ruiz et al. (1988)

MURR ID Group and origin Srconcentration

(ppm)

87Sr/86Sr

FTV046 1,mountain 114.24 0.713633 1 7FTV033 1b, mountain 162.46 0.706748 1 8FTV052 2, mountain 528.17 0.704486 1 7FTV062 2, mountain 658.21 0.704538 1 10FTV013 3, lake 612.86 0.704453 1 5FTV075 3, lake 390.00 0.704552 1 10AZP633f 3, fired clay 392.45 0.704463 1 8AZP633r 3, raw clay 392.45 0.704489 1 13AZP649r 3, raw clay 347.69 0.704460 1 7FTV105 unassigned, lake 462.97 0.704553 1 8FTV011 unassigned, lake 592.23 0.704436 1 8OAX-3-85 Oaxaca rock 394.20 0.716624 1 7OAX-3(2)-85 Oaxaca rock 393.80 0.716813 1 9OAX-3(3)-85 Oaxaca rock 436.10 0.716797 1 10OAX-4-85 Oaxaca rock 386.90 0.711617 1 10OAX-7-85 Oaxaca rock 578.30 0.703855 1 8OAX-10-85 Oaxaca rock 1227.10 0.704036 1 8



G1

G1

G1b

(a)

(b)

ceramics clays Oaxaca basement

0.00

0

0.704000

0.702000

0.706000

0.708000

0.710000

0.712000

0.714000

0.716000

0.718000

0.001

87S

r/86

Sr

0.002 0.003 0.004 0.005

1/[Sr] (ppm-1)

0.006 0.007 0.008 0.009 0.01

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

G2

Rb/Si x 1000

Sr/

Si x

10

00

Figure 3 (a) Sr isotope ratios measured by TIMS and Sr concentrations measured by INAA. The shaded region from0.703003 to 0.70841 represents the range of measured Mexican Volcanic Belt geology, and the line at 0.71387 representsSierra Madre Occidental dacite–rhyolite (values from Torres-Alvarado et al. 2000; Ruiz et al. 1988). (b) LA–ICP–MS ofclays of two ceramics from G1 and two ceramics from G2. Error bars show the range of averages of three ablation linesrun on each sample. Sr and Rb are shown because of their high eigenvectors in PC1. The pattern of separation isconsistent for elements with high eigenvectors.



(Hopkins 1995, 338). G2/3 ceramics are characterized by small-to-large (>0.3–1.0 mm diameter)clasts of monomineralic quartz and plagioclase. This mineralogy is consistent with the elementalcomposition: G2/3 ceramics have relatively high Ca, Na and Sr, elements present in plagioclaseminerals. G2/3 also contains lower-frequency inclusions of hornblende, mica, olivine and vol-canics. Most clasts were angular, with low sphericity. The possible organic inclusions and porespaces frequent in G1/1b were absent. Hemispherical bowls from Cerro Xiquillo exhibit uniformsize, density and type of mineral inclusions—homogeneity not observed in hemispherical bowlsfrom other sites.

DISCUSSION

Bulk elemental characterization by INAA suggested three composition groups for Middle to LateFormative ceramics from the Teotihuacan Valley (Fig. 2). Two groups differed primarily by Baconcentration and were consolidated into one group (G2/3), following studies that have attributedthis pattern to diagenesis. If this hypothesis is correct, what is the mechanism of alteration? Naand Ba concentrations appear to be negatively correlated in samples from the highlands. Regres-sion of Na on Ba in R software produced coefficients of -0.251 (p = 0.0001) for G2 samples fromthe highlands, -0.211 (p = 0.0737) for G1/1b samples from the highlands, and 0.016 (p = 0.124)for G3 samples from the lakeshore. There is a significant negative correlation for G2 and nosignificant correlation for G3. This pattern suggests Ba enrichment by replacement of Na in thehighlands. The correlation may be weaker in G1/1b ceramics from the highlands because this

(a)

(b)

Figure 4 (a) G1/1b ceramic from Altica in plain polarized (left) and reflected (right) light. The red arrows point toelongate pores with possible fired organic material and gold ribbons in reflected light. The blue arrow points to a volcanicinclusion. (b) G2/3 ceramic from Altica under plain polarized light (left), crossed polars (centre) and reflected light. (Seeonline for a colour version of this figure.)



group is overall compositionally distinct with lower Na concentration, so alterations probablyexperienced different rates and stabilities. The weaker correlation may also be due to the smallsample size of G1/1b. The possibility and mechanism of Ba enrichment could be further inves-tigated with LA–ICP–MS. Ba enrichment may be occurring within specific mineral inclusions orthe general matrix. The latter would be supported by a concentration gradient of Ba decreasingsurface to interior (Picon 1987).

Maintaining the hypothesis that G2 and G3 represent a single group left two remainingcomposition groups—G1 and G2/3—but it was unclear whether compositional differences aredue to provenance, processing, use or diagenesis. These non-exclusive hypotheses were evaluatedthrough consideration of site, typology and complementary analytical techniques. Diagenesis isan unlikely explanation due to the collection sites of ceramics. All G1 samples (8/8) were foundat Altica, along with G2 samples (11/19). If G1 and G2 ceramics were made from the same rawmaterials and exposed to the same depositional environment, we would expect post-alterationcompositions to be similar. On the contrary, the groups have very distinct elemental concentra-tions, which may show similar trends, such as the possible Ba replacement of Na mentionedabove. It seems more likely that the ceramic groups had initially distinct compositions, subjectedto the same burial environment. Consideration of typology weakens the use hypothesis. Most G1and G2 samples from Altica were visually indistinguishable, with white-slipped or white-slippedincised surface decoration that appears to fit the Early Middle Formative type Zacatenco White(Tolstoy et al. 1977; Whalen and Parsons 1982). Thus, it is unlikely that G1 and G2 ceramicswere used for different purposes.

Additional patterns emerged when the frequencies of decorative techniques were comparedby site. The piedmont sites of Altica and Cerro Xiquillo had a high proportion of white-slip,incised vessels. Contemporaneous Venta de Carpio exhibited a wider variety of surface deco-ration techniques, but no white-slip, incised ceramics. This pattern is consistent with thelarger collection (Sanders et al. 1975). It appears that residents of Altica and Cerro Xiquilloshared a preference for this style, which did not extend to the more distant lakeshore site ofVenta de Carpio. Petrography showed that hemispherical bowls from Cerro Xiquillo exhibiteduniform mineralogy, not observed in this vessel type at other sites. Potters from Cerro Xiquillomay have followed a community-based recipe for these vessels. This possibility, pairedwith site-specific frequencies in decorative techniques, suggests that settlements at this periodproduced their own pottery. However, these patterns may be an artefact of the small samplesize.

Sr isotope ratios corroborated elemental composition groups: G2/3 samples cluster with localclays, the G1 sample appears distinct and the G1b sample has an intermediate value (Table 2 andFig. 3). However, Sr isotopes provided additional information. First, the Sr isotope ratio of the G1sample (0.713633 1 7) was high for a region characterized by recent volcanic activity, and wellabove the range of sampled geological material from the Mexican Volcanic Belt. The G1 ratio ismost similar to geological values from Sierra Madre Occidental dacite–rhyolite and OaxacaPrecambrian basement rock. This similarity does not ‘source’ G1 ceramics or raw materials tothese regions, but provides a pursuable hypothesis. Targeted Sr isotope measurement coulddetermine whether the high ratio is due to clay, inclusions or both, and may provide ratios thatmatch materials to specific geological outcrops. Next, the G1b sample had a Sr isotope ratiobetween the values for the G1 sample and all others. Perhaps G1b samples represent a mixing ofexotic G1 raw materials with common Teotihuacan Valley materials. Lastly, it is noteworthy thatthe non-G1 samples have differing Sr isotope ratios. The ceramics contain greater Sr concentra-tions and more variable isotope ratios than clays. This is the pattern that one would expect if



different Sr-rich tempers were added to the same clay: bulk Sr concentrations would increase andisotope ratios would shift towards those of tempers.

LA–ICP–MS that avoided mineral inclusions showed that the clays of G1 and G2 samplesfrom Altica differ in elemental make-up (Fig. 3). Petrography revealed mineralogical differencesbetween macroscopically indistinguishable G1 and G2 samples (Fig. 4). Thus, G1 ceramics weremade from entirely different raw materials—clay and inclusions—than G2 ceramics also fromAltica. As Altica is the oldest and easternmost site in this study, perhaps Altica potters had accessto raw materials unavailable to the other settlements. Alternatively, G1 ceramics may be importedware that was copied by local potters in the making of G2 ceramics.

To test these hypotheses, samples were compared to those in the MURR database, an archiveof over 90 000 geological and archaeological materials. The database has been used to defineBOM reference groups associated with Chalco, Texcoco, Tenochtitlan, Tultitlan and Otumba/Teotihuacan Valley (Neff and Glascock 2001; Garraty 2006; Crider 2011). The likelihood thatceramics in this study belong to BOM reference groups was calculated using canonical discrimi-nant analysis. G1/1b ceramics had 0% likelihood for all BOM reference groups. Most G2/3ceramics (37/77) had the highest probability of belonging to the Chalco group. Only nine G2/3ceramics appeared to belong to the Otumba/Teotihuacan Valley group, which encompasses thegeographical region of the sites. Overall, it is difficult to assign Formative ceramics from thisstudy to BOM reference groups, which may be due to the fact that the reference groups are basedon mostly Postclassic ceramics. These differences may reflect temporal shifts in raw materialchoices.

Tolstoy sampled nearly 540 ceramics and figurines from Early and Middle Formative sites inTexcoco regions of the BOM. Neff’s (2009) analysis of the INAA results found two maincomposition groups: a low-Cr group from Chalco, Texcoco and Ixtapalapa–Azcaptozalco and ahigh-Cr group from a production centre in the very southern Basin, probably at Coapexco(Tolstoy 1989; Neff et al. 2000; Neff and Glascock 2000). Six potsherds seem to have comefrom the San Lorenzo region of the Gulf Coast (Blomster et al. 2005). Neff also defined severalsmaller groups, including ZW-1 and ZW-2, with mainly Middle Formative Zacatenco Whiteware (Tolstoy et al. 1977; Whalen and Parsons 1982). Although G1 is compositionally distinctfrom the Tolstoy/Neff Formative groups, it is statistically most similar to ZW-1 and appearsto fit the type Zacatenco White. The ZW-1 group consists of seven samples from six sitesacross the BOM. The sample is small, but it is compelling that vessels of similar type andcomposition—distinct from most BOM ceramics—appear widely distributed in the BOMduring the Middle Formative.

CONCLUSION

Ceramic production and distribution appears to have been mainly village-based in the Middle toLate Formative Teotihuacan Valley. The composition of sampled Formative ceramics differs fromthat of later, mostly Postclassic, ceramics used to define BOM reference groups. Altica had a setof pottery made from distinct clay and inclusions, which shows compositional and typologicalaffinities with a small number of Formative vessels found across the BOM. These results shouldbe investigated by analysis and integration of more Formative vessels into the BOM database.Conclusions are based on bulk compositional and stylistic analysis of 105 ceramics, combinedwith a pilot study of complementary methods on a small subset of vessels. The complementarymethods raised new questions and directions for research, and should be applied to a largersample.



ACKNOWLEDGEMENTS

This work was supported by the Claire Garber Goodman Fund from the Dartmouth CollegeDepartment of Anthropology and the MURR Undergraduate Research Scholarship from the USDOE Innovations in Nuclear Infrastructure and Education. The analytical work at DartmouthCollege was overseen by Brian Jackson in the Earth Sciences ICP–MS laboratory, Mukul Sharmain the TIMS laboratory and Gary Johnson in the petrography laboratory. Hector Neff assisted indata analysis.

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COMPLEMENTARY COMPOSITIONAL ANALYSIS OF FORMATIVE PERIOD CERAMICS FROM THE TEOTIHUACAN VALLEY

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