OSL Ages of the Clovis, Late Paleoindian, and Archaic Components at Area 15 of the Gault Site, Central Texas, U.S.A

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Journal of Archaeological Science: Reports 7 (2016) 94–103

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OSL ages of the Clovis, Late Paleoindian, and Archaic components at Area 15 of the Gault Site, Central Texas, U.S.A.

K. Rodrigues a,⁎, W.J. Rink b,M.B.Collinsc,T.J.Williamsc, A. Keen-Zebert d,G.I.Lόpez e a Department of Geological Sciences and Engineering, University of Nevada, Reno, 1664 N Virginia St, Reno, NV 89557, United States b School of Geography and Earth Sciences, McMaster University, 1280 Main St. W., Hamilton, Ontario L8S 4K1, Canada c Department of Anthropology, Texas State University, 601 University Drive, San Marcos, TX 78666, United States d Division of Earth and Ecosystem Sciences, Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89503, United States e Luminescence Dating Laboratory, CENIEH (Centro Nacional de Investigación sobre la Evolución Humana), Paseo Sierra de Atapuerca 3, Burgos 09002, Spain article info abstract

Article history: The Gault Site, Texas, U.S.A., affords a near-complete regional prehistoric sequence from an ~2 m-thick alluvial Received 31 August 2015 sedimentary interval. Age estimates on Clovis, Late Paleoindian, and Archaic components were obtained using Received in revised form 10 March 2016 optically stimulated luminescence (OSL) dating of silt-sized quartz grains. The luminescence characteristics of Accepted 11 March 2016 the quartz are favorable, showing normal equivalent dose distributions and no evidence of incomplete zeroing. Available online 12 April 2016 The artifacts span Clovis to Archaic forms, and their ages are generally in excellent agreement with independent radiocarbon ages from ﬁve other Texas sites. The mean OSL age of the Clovis deposits of 12,900 ± 700 a agrees Keywords: Quartz with the known Clovis ages from Central Texas and a generalized model that places the Clovis occupation of Cen- Optically stimulated luminescence dating tral Texas between ~13,600 to 13,000 cal BP (Holliday, 2000). This study indicates that accurate age determina- Clovis tions can be made using OSL on silt-sized quartz grains at Gault. Paleoindian © 2016 Elsevier Ltd. All rights reserved. Archaic

1. Introduction the midden are diagnostic of the Early, Middle, and Late Archaic as well as the Late Prehistoric periods in the archaeological chronology of Excavations at the Gault Site (Fig. 1) have yielded a near-complete Central Texas (Collins, 2002), spanning ages from ~9,000 to 500 BP regional prehistoric sequence that includes a major Clovis settlement/ (Collins, 2004). Across most of the site, nearly a century of looting has workshop. The site is located in Central Texas, U.S.A., in southwestern destroyed the integrity of the midden, but the underlying predominant- Bell County, approximately 70 km north of Austin (N Lat 30.892246, ly fluvial strata were left intact (Collins, 2002). These intact fluvial W Lon 97.709739). It is situated on Buttermilk Creek, a first and deposits host a stratified sequence of Paleoindian components. second-order stream valley with small but reliable springs flowing 5.5 Intermittent investigations between 1991 and 2013 include 15 block to 6.0 m below the surrounding surface of the Edwards Plateau, a Creta- excavations containing stratified prehistoric cultural components. The ceous limestone upland. There are abundant high quality chert outcrops Gault project is focused on investigating the early part of the local chro- at and near the site. The area conforms to the Balcones Canyonlands nology (notably Clovis and older-than Clovis intervals). The analytical ecotype as found near the southern and eastern margins of the Edwards efforts of this investigation are continuing, and some of the current ar- Plateau (Diamond et al., 1987), and therefore, was an excellent habitat chaeological interpretations are subject to future refinements. Early for hunting and gathering groups. Every defined interval in the regional Paleoindian lithic components were encountered in 9 of the excavation prehistoric chronology of Central Texas is represented by time- blocks (c.f. Collins, 2007: Fig. 4.2). Two of these blocks, Areas 12 and 15, diagnostic artifacts at the Gault Site, prima facie evidence that the local- have also yielded evidence of cultural components predating Clovis. ity has seldom failed to meet human needs (Collins, 2007). Early components recognized on the basis of time-diagnostic artifacts An extensive and dense Holocene anthropogenic deposit that is re- in Areas 12 and 15 include Clovis, Folsom, and Dalton; these are overlain gionally categorized as a burned rock midden (Collins, 2007; Thoms, by strata containing several early, regionally-defined, diagnostic artifact 2009) characterizes the upper deposits across most of the site area forms. The focus of this paper is on the dating of the Clovis and post- and is up to 2 m thick in places (Collins, 2002). Cultural materials in Clovis cultural components in Area 15. In this work we use various abbreviations for reporting radiocarbon and luminescence ages. For radiocarbon ages, we have followed Stuiver ⁎ Corresponding author. and Reimer (1998) and Anonymous (2005),where‘BP’ means explicitly E-mail addresses: [email protected] (K. Rodrigues), [email protected] “ ” ‘ ’ (W.J. Rink), [email protected] (M.B. Collins), [email protected] (A. Keen-Zebert), conventional radiocarbon years before AD 1950 ,whereas cal BP [email protected] (G.I. Lόpez). means “calibrated radiocarbon years.” For luminescence dating we use

‘a’ (annum i.e. years ago), which gives the estimated time interval be- sampling intact soil monoliths that preserved samples of this strati- tween deposition and the time of sample measurement. graphic sequence (Supplementary Table 5). Three ages from stratum 5 range from 12,690 ± 700 a to 11,160 ± 640 a (average ~ 11,930 a), an 1.1. Regional archaeology and chronology age that is consistent with the interpretation that Clovis and Folsom artifacts resting on a deflated surface were buried in post-Folsom flood Gault affords an unusually complete record of the local Texas prehis- events (Collins, 2003). Two OSL ages from stratum 7 are 13,800 ± tory, extending from the Late Pleistocene to the time of early contacts 800 a and 12,940 ± 800 a which are consistent with the interpretation between Europeans and Native Americans. A moderately well- that non-diagnostic artifacts in zones 7 and 8 are likely Clovis (Collins, constrained, radiocarbon-based regional cultural chronology extending 2003). A single age of 15,770 ± 890 a for zone 9 may indicate that the from ~9,000 to 500 cal BP is in use at Gault for the Archaic, Late Prehis- very small assemblage of cultural flakes from that stratum predate Clo- toric, and Historic periods (Collins, 2004; Johnson and Goode, 1994; vis (Collins, 2003). Prewitt, 1981; 1985). Time-diagnostic artifact types recovered in our An intensive program of luminescence dating (infrared stimulated excavations provide the basic chronological framework employed in luminescence [IRSL] on fine-grained feldspar) was employed at the this study (Fig. 2). The Gault chronology extends back in time into the Debra L. Friedkin Site (Fig. 1, #4) some 250 m downstream of the pre-Archaic and helps define a series of Paleoindian intervals some of Gault Site by Waters and colleagues during excavations in 2006–2009. which are regional (identified by projectile point types Wilson, St. Results appear in a brief note (Waters et al., 2011a) and are clarified Mary's Hall, Golondrina-Barber, and Texas Angostura, collectively span- by Jennings (2012). Five luminescence ages for the Folsom interval, ning the interval, ~11,200 to 9,400 cal BP) and others of which are re- 2.5 cm thick, and two ages for the Clovis interval, 2.5 cm thick are regional expressions of cultural manifestations of much wider ported (Supplementary Table 4). Ages associated with Folsom range geographic distributions (with diagnostic types Clovis, Folsom, and Dal- from 11,870 ± 760 to 12,925 ± 845 a, (average ~ 12,300 a), and are rea- ton, spanning the interval, ~13,500 to 11,700 cal BP). The chronological sonably close to the generally accepted range of ~12,850 to ~11,900 cal framework employed in this report for the Paleoindian intervals draws BP for this culture (c.f. Meltzer, 2006: 1). Clovis ages, ranging from on the general regional chronology (Collins, 2004), a Paleoindian- 13,090 ± 830 to 13,780 ± 885 a (averaging ca. 13,400 a), indicate an specific synopsis for Texas (Bousman et al., 2004), published dating re- age in agreement with the commonly expected range of ~13,450 to sults from five specific sites, and selected studies from the broader ex- ~12,780 BP (c.f. Meltzer, 2009: 254). panse of North America (Supplementary Tables 2–7). Radiocarbon as Stafford (1998) employed 96 radiocarbon determinations on char- well as luminescence ages are included in this pre-existing framework. coal, charred hyacinth bulbs, bone, shell, sediment, and soil in develop- The overall working chronology in use at Gault excavation Area 15 is de- ing a chronostratigraphy for the Wilson-Leonard Site, located 40 km rived and integrated from these sources for the Clovis component and is south of the Gault Site in a similar, Balcones-Canyonlands setting summarized in Supplementary Tables 2–5. (Collins and Mear, 1998). Cultural materials at Wilson-Leonard reside A generalized Clovis radiocarbon age range on the southern plains in a sequence of fluvial, pond, and colluvial deposits approaching 7 m from ~13,500 to 13,000 cal BP has been derived by vetting numerous ra- in total thickness with an overall time range of N14,000 years ago to diocarbon ages run over the past five decades from sites widely dis- the present. The two earliest cultural components at Wilson-Leonard persed across the United States (Holliday, 2000). Subsequently, were inferred by Collins (1998: 123-159) on the basis of lithic produc- Waters and Stafford (2007: 1123-1124) have proposed a significantly tion technology to be of Clovis and Folsom affinities. Neither of these constrained age range of ~13,100 to 12,900 cal BP (11,050 to constitutes a robust archaeological assemblage because sample sizes 10,800 BP), but this has been criticized as it “lacks solid evidence or are small and no completely unambiguous diagnostic artifacts were empirical support” (Haynes et al., 2007). Previous dating of Clovis found (Collins, 1998: 123-159). Furthermore, the geologic contexts components in Texas provides a further basis for evaluating the age of are relatively complex and include indications of turbation. For these Clovis in Area 15 at the Gault Site. This regional data set (Supplementary reasons, along with the varying results from the array of materials Tables 2-5) includes radiocarbon as well as luminescence ages for Clovis dated, Stafford (1998: 1039-1063) presents an inferred from a total of five sites (Aubrey, Pavo Real, Debra L. Friedkin, and Gault chronostratigraphy for the site based on multiple lines of evidence. He Area 8); there is also relevant geochronological evidence from the Wilson-Leonard Site (see Fig. 1). Ages of 11,590 ± 93 and 11,542 ± 111 BP (Ferring, 2001)onchar- coal from the Clovis component at the Aubrey Site (Fig. 1, #2) in north Central Texas produce a calibrated range of 13,595 to 13,220 (2σ) and 13,576 to 13,143 (2σ) cal BP respectively (IntCal 13, OxCal 4.2, Bronk Ramsey, 2009). Waters and Stafford (2007) do not include this early date or those from Pavo Real (Fig. 1,#3)andWilson- Leonard (Fig. 1, #5) sites in their analysis. The small assemblage of cultural materials from the lowest stratigraphic levels at the Wilson- Leonard Site, 30 km south of the Gault Site, has technological affinities with Clovis. An age estimate of ~ 13,500 cal BP has been extrapolated from overlying radiocarbon dates as the Clovis deposits yielded no dat- able material (Collins, 1998: 140–145; 280–281). This is another regional indication that Clovis may predate ~13,100 cal BP as suggested by Waters and Stafford (2007). At the Pavo Real site (Fig. 1, #3) in south Central Texas, excavations by personnel of the Texas State Department of Highways and Public Transportation in 1979–80 recovered early cultural materials from strata 4 through 9, as follows: stratum 4, mixed Archaic and Paleoindian; stratum 5, mixed Clovis and Folsom; stratum 6, non-diagnostic; stratum 7, probably Clovis; stratum 8, probably Clovis; and stratum 9, unas- signed but possibly pre-Clovis (Collins, 2003). Optically stimulated luminescence (OSL) ages were obtained for strata 5, 7, and 9 by Fig. 1. Location of the Gault Site (1) and the major Clovis sites discussed in the text. 96 K. Rodrigues et al. / Journal of Archaeological Science: Reports 7 (2016) 94–103

Fig. 2. Lower part of the Central Texas archaeological chronology, adapted from Collins (2004:Fig. 3.9a). Projectile points shown were recovered from Area 15 and are representative of the types discussed in text; Clovis (1); Folsom (2); Dalton (3); St Mary's Hall (4); Angostura (5); Martindale (6); Hoxie (7); Gower (8); Andice (9); Bell (10). Not to Scale. bounds Folsom (the “Bone Bed Component”) at Wilson-Leonard to be- IRSL ages (Supplementary Table 3) on ﬁne feldspar grains from levels tween ~11,400 and 11,000 BP (~12,900–13,300 cal BP) and places Clovis containing the Clovis assemblage were obtained: 13,220 ± 740 and between an upper boundary of greater than ~11,400 BP (~12,900 cal BP) 12,920 ± 700 a (Waters et al., 2011b). and a lower boundary of greater than ~11,500 BP (13,400 cal BP). In the case of Folsom, this range is greater than the generally expected range 1.3. Gault Site stratigraphy and artifact distribution in Area 15 of ~12,850 to ~11,900 cal BP (Meltzer, 2006:1), whereas for Clovis, the younger end of the range matches that of the generalized range but the Area 15 is the only known place where the midden largely escaped older end of the range is earlier than what is generally accepted (though damage from looting and where the midden is at its thickest (~1.8 m). not out of line with the early age reported for Clovis at the Aubrey Site). The generalized distribution of cultural components with depth is Pre-existing chronometric controls for the age of Dalton are not shown in Fig. 3. All elevations at the site and reported in this paper are robust. Many dated radiocarbon samples of questionable association, based on an arbitrary site datum of 100.00 m. The excavation block mostly run in the 1950s and 1960s, range from ~9,100 to ~11,200 BP was a 56 m2 grid which was gradually stepped down in meter incre- and have large errors of estimate (Goodyear,1982: 385). Four radiocar- ments. Excavation was conducted in this grid in 1 m by 1 m squares in bon ages and one OSL age for Dalton (Supplementary Table 7) range arbitrary levels of 5 cm deep from 93.00 m and below. Archaic and from ~11,500 to 12,310 cal BP, and average close to 12,000 cal BP. In Late Prehistoric diagnostic artifacts generally occur in this midden in their assessment of available evidence, Anderson et al. (1996) consider proper stratigraphic order and intact burned rock features are present, Dalton to be a Late Paleoindian manifestation that falls within a narrow but, there is also considerable mixing of temporal markers presumably range of ~11,900 to 11,700 cal BP. For present purposes, since all of the owing to prehistoric anthropic turbation and introduction of older arti- ages (except for Dust Cave) in Supplementary Table 7 are statistically facts into younger deposits which are characteristic of such middens indistinguishable with the ~11,900 to 11,700 BP time range, we follow and related sites of the region (c.f. Ricklis, 1994: 244). Anderson et al. (1996) and accept their placement in the two or three Two lithological units occur beneath the midden: a ~ 1.2 m-thick centuries following 12,000 BP. silty clay, and a ~ 0.25 m-thick ﬂuvial gravel (Fig. 3). The gravel rests on Cretaceous-age Comanche Peak limestone bedrock. Within the silty 1.2. Previous dating work at Gault clay sediment, a sequence of Late Paleoindian components (~50 cm thick) overlies a Clovis component (~25 cm thick) (see Fig. 3). A time- Excavations in Area 8 of the Gault Site in 2000 by students under the diagnostic Dalton point was recovered in situ at an elevation of direction of Michael Waters and Harry Shafer documented a strati- 93.05 m, overlying a zone of some 40 Clovis diagnostic artifacts (a Clovis graphic sequence with Clovis artifacts in geologic units 3a and 3b. Two point, prismatic blades and fragments, a blade core, bifacial preforms, K. Rodrigues et al. / Journal of Archaeological Science: Reports 7 (2016) 94–103 97

Fig. 3. Stratigraphic proﬁle of Area 15 indicating artifact elevations and associated OSL elevations and ages. All elevations given in meters (m) based on an arbitrary site datum. The Gower range includes Hoxie and Martindale points. St. Mary's Hall points were recovered in good stratigraphic context at 93.10 m and 93.31 m. Elevations and ages correspond to those shown in Table 3. Not to scale because of photographic distortion in lower portion of the frame. 98 K. Rodrigues et al. / Journal of Archaeological Science: Reports 7 (2016) 94–103

Table 1 Gault Area 15: Sediment radioisotope and OSL characteristics. Selected DE's used for ﬁnal ages reported in Table 3 are distinguished with bold font.

238 232 3,4 Sample Burial depth (m) U Th K Measured moisture Aliquot size CAM DE Over-dispersion Number of accepted name (ppm)1 (ppm)1 (%)1 content (%)2 (mm) (%) aliquots/total aliquots measured

09-01 1.24 2.83 ± 0.10 12.52 ± 0.79 1.86 ± 0.050 10 1 17.2 ± 0.6 11.0 ± 4.0 21/24 3 19.6 ± 0.2 6.0 ± 1.0 48/48 09-01b 1.24 2.68 ± 0.10 12.77 ± 0.79 1.78 ± 0.047 12 1 18.0 ± 0.7 12.0 ± 3.0 20/24 3 19.6 ± 0.1 2.2 ± 0.7 48/48 09-02 1.42 2.53 ± 0.10 13.30 ± 0.90 1.70 ± 0.046 11 1 19.9 ± 0.07 0 48/48 3 18.5 ± 0.2 3.2 ± 0.8 24/24 09-03 1.66 2.75 ± 0.10 12.87 ± 0.83 1.62 ± 0.044 15 1 21.8 ± 0.3 1.0 ± 4.0 23/24 3 20.6 ± 0.3 6.8 ± 1.1 47/48 09-04 1.92 2.60 ± 0.10 11.00 ± 0.68 1.18 ± 0.032 10 1 23.3 ± 0.6 11.0 ± 1.9 24/24 3 23.7 ± 0.1 0 47/48 09-05 2.10 2.87 ± 0.10 13.55 ± 0.85 1.32 ± 0.037 10 1 27.5 ± 0.3 0 24/24 3 25.8 ± 0.1 0.7 ± 1.7 48/48 09-06 2.25 3.18 ± 0.10 11.58 ± 0.71 1.24 ± 0.034 9 1 28.0 ± 0.3 0 24/24 3 26.9 ± 0.3 6.1 ± 0.9 48/48 11-01 0.87 2.64 ± 0.10 12.86 ± 0.86 1.79 ± 0.045 7 0.5 18.4 ± 0.2 7.0 ± 0.3 47/48 11-16 1.58 2.57 ± 0.10 11.87 ± 0.81 1.13 ± 0.029 11 0.5 24.8 ± 0.3 7.6 ± 0.3 48/48 11-02 1.76 2.85 ± 0.10 11.80 ± 0.81 1.12 ± 0.028 13 0.5 28.5 ± 0.4 8.5 ± 0.4 48/48 11-08 2.20 3.10 ± 0.10 11.92 ± 0.79 1.23 ± 0.035 7 0.5 28.2 ± 0.2 0 48/48 11-13 2.20 3.52 ± 0.10 13.32 ± 0.88 1.32 ± 0.031 6 0.5 30.4 ± 0.4 8.3 ± 0.4 48/48 11-17 2.26 3.28 ± 0.10 13.17 ± 0.89 1.25 ± 0.031 3 0.5 31.4 ± 0.4 6.0 ± 0.3 48/48 11-09 2.68 2.68 ± 0.10 11.89 ± 0.68 1.060 ± 0.028 9 0.5 34.5 ± 0.2 3.5 ± 0.2 48/48 11-15 2.55 2.88 ± 0.10 12.25 ± 0.84 1.18 ± 0.029 11 0.5 34.5 ± 0.3 3.9 ± 0.2 48/48 11-07 2.60 2.87 ± 0.10 12.09 ± 0.80 1.21 ± 0.035 8 0.5 35.3 ± 0.4 4.5 ± 0.2 48/48 11-03 2.76 2.57 ± 0.10 10.94 ± 0.62 1.034 ± 0.027 15 0.5 27.0 ± 0.3 4.6 ± 0.2 48/48

1 U, Th, and K values determined by NAA at the Nuclear Reactor facility of McMaster University. 2 Water content as a fraction of dry weight determined from laboratory measurements. 3 All 0.5 mm CAM DE calculations made using σb = 0.045 which was determined based on results of dose recovery experiments. No σb value was used for measurements on either 1 mm or 3 mm aliquots. 4 An instrumental uncertainty of 1.5% was incorporated into all analyses.

Table 2 Gault Area 15: Environmental radiation dose rates and OSL ages. Final ages reported in Table 3 are distinguished with bold font.

Sample name Burial depth External alpha External beta External gamma Cosmic dose rate Total dose Aliquot size CAM burial age (m) dose rate dose rate dose rate (μGy/a)1 rate (mm) (a)3,4 (μGy/a) (μGy/a) (in situ)(μGy/a) (μGy/a)2

09-01 1.24 170 ± 14 1923 ± 50 1052 ± 0 194 ± 19 3345 ± 43 1 5,100 ± 300 3 5,900 ± 300 09-01b 1.24 168 ± 14 1854 ± 39 1052 ± 0 194 ± 19 3275 ± 42 1 5,500 ± 300 3 5,900 ± 300 09-02 1.42 169 ± 15 1792 ± 40 1117 ± 0 191 ± 19 3269 ± 42 1 6,100 ± 300 3 5,600 ± 300 09-03 1.66 171 ± 14 1753 ± 38 1140 ± 0 188 ± 19 3258 ± 41 1 6,600 ± 300 3 6,200 ± 300 09-04 1.92 152 ± 12 1386 ± 30 959 ± 0 186 ± 19 2689 ± 32 1 8,700 ± 400 3 8,800 ± 400 09-05 2.10 179 ± 15 1573 ± 34 1024 ± 0 182 ± 18 2965 ± 37 1 9,300 ± 400 3 8,700 ± 400 09-06 2.25 171 ± 14 1511 ± 31 1027 ± 0 180 ± 18 2895 ± 34 1 9,700 ± 400 3 9,300 ± 400 11-01 0.87 171 ± 13 1829 ± 38 1017 ± 0 204 ± 20 3227 ± 41 0.5 5,700 ± 300 11-16 1.58 152 ± 12 1350 ± 29 1015 ± 0 188 ± 19 2711 ± 32 0.5 9,100 ± 400 11-02 1.76 167 ± 12 1373 ± 29 1077 ± 0 186 ± 19 2809 ± 32 0.5 10,100 ± 400 11-08 2.20 174 ± 16 1479 ±32 1023 ± 0 180 ± 18 2862 ± 35 0.5 9,900 ± 400 11-13 2.20 196 ± 17 1626 ± 31 984 ± 0 180 ± 18 2993 ± 35 0.5 10,200 ± 500 11-17 2.26 170 ± 13 1406 ± 31 944 ± 0 180 ± 18 2706 ± 31 0.5 11,600 ± 500 11-09 2.68 135 ± 11 1311 ± 27 964 ± 0 175 ± 18 2591 ± 30 0.5 13,200 ± 600 11-15 2.55 114 ± 9 1273 ± 30 936 ± 0 176 ± 17 2506 ± 33 0.5 13,600 ± 600 11-07 2.60 170 ± 14 1446 ± 32 948 ± 0 176 ± 18 2747 ± 35 0.5 12,900 ± 600 11-03 2.76 153 ± 11 1262 ± 26 897 ± 0 174 ± 17 2492 ± 29 0.5 11,900 ± 800

1 Cosmic dose rate value calculated using an overburden density of 2 g/cm3, accounting for depth of sample. All cosmic dose rates were calculated assuming linear sediment accu- mulation rates. 2 Total dose rates include internal alpha dose rates of 5.6 ± 1 μGy/a and internal beta dose rates of 0.8 ± 0.2 μGy/a, which were calculated based on assumed internal U and Th concentrations in the quartz of 0.0665 ± 0.0214 ppm and 0.1135 ± 0.0424 ppm respectively (Rink and Odom, 1991). 3 All burial doses were modeled from the population of individual aliquot DE's using the CAM (Galbraith et al., 1999). All CAM DE calculations for 0.5 mm aliquots were made using σb =

0.045 which was determined based on results of dose recovery experiments. No σb value was used for measurements on either 1 mm or 3 mm aliquots. 4 All CAM burial ages were calculated using a moisture content of 10% reflecting the average of all measured samples with the exception of sample 11-03 where an age was calculated using a 20% moisture content. See Section 2.4 in the text for details. K. Rodrigues et al. / Journal of Archaeological Science: Reports 7 (2016) 94–103 99 and characteristic debitage), found between elevations ~92.80 m and Table 3 ~92.55m. Gault Area 15: OSL ages and cultural stratigraphy. Component Diagnostics Elevation Age Sample 1 1.4. Setting for optical luminescence dating at the Gault Site (m) (a) name Archaic 94.38 5,700 ± 300 11-01 Andice/Bell/Calf Creek Archaic 94.06 5,900 ± 300 09-01 The alluvial setting of the excavations around the Gault Site, and the (94.00–94.90 m) fluvial nature of most of the deposits creates a poor environment for the Archaic 94.06 5,900 ± 300 09-01b Archaic Gower, Hoxie, Martindale 93.88 6,100 ± 300 09-02 preservation of organic remains. This severely limits the usefulness of Archaic(93.72–94.07 m) 93.64 6,600 ± 300 09-03 radiocarbon dating techniques, a common problem in the region (c.f. Paleoindian Angostura 93.54 9,100 ± 400 11-16 Collins, 2004: 109; Stafford, 1998: 1039, 1063-1066). Luminescence Paleoindian(93.07–93.53 m) 93.38 8,800 ± 400 09-04 dating offers the best available dating method. This technique reveals PaleoindianSt. Mary's Hall 93.36 10,100 ± 400 11-02 Paleoindian(93.10–93.31 m) 93.20 9,300 ± 400 09-05 the amount of time that has elapsed since crystalline materials were Paleoindian 93.05 9,700 ± 400 09-06 last exposed to sunlight. Details about the physical basis of this tech- PaleoindianDalton 93.03 9,900 ± 400 11-08 nique and its application are outlined in Rhodes (2011) and Duller Paleoindian(93.00–93.20 m) 93.02 10,200 ± 500 11-13 (2008). Paleoindian 92.97 11,600 ± 500 11-17 Clovis In spite of the predominantly clay-rich fluvial deposits hosting the Clovis 92.72 13,200 ± 600 11-09 (92.55–92.80 m) early archaeological components, OSL dating is useful owing to the Clovis 92.68 13,600 ± 600 11-15 long-term aeolian transportation of quartz and feldspar grains onto Clovis 92.60 12,900 ± 600 11-07 the site area (Luchsinger, 2002); these grains evidently derive from Clovis 92.57 11,900 ± 800 11-03 extensive exposures of Precambrian granites and related igneous and Mean Clovis Age = 12,900 ± 700 metamorphic rocks in the Central Mineral Region centered some 140 km west-southwest of the Gault Site (Barnes, 1981). Note that elevations and ages correspond to Fig. 3. 1 All elevations are based on an arbitrary site datum of 100.00 m.

2. Methods between 32 and 63 μm were mounted with silicon spray on aluminum discs using one of three mask sizes: 3 mm, 1 mm and 0.5 mm. 2.1. Sample locations An initial equivalent dose (DE) was estimated by comparing the natural OSL signal (preheat temperature = 200 °C) of three aliquots to the In this paper, we report ages for seventeen samples collected from regenerated OSL given by a single dose for each sample. A second iden- Area 15 of the Gault Site. Of these, four samples (11-03, 11-07, 11-09, tical regeneration dose was applied to the same three aliquots and the and 11-15) were taken from the Clovis deposits (between ~92.80 and IRSL signal was measured as a check for feldspar contamination. If no ~92.55 m depths), eight samples (09-04, 09-05, 09-06, 11-02, 11-08, IR signal decay was observed, and the ratio of IRSL to regenerated OSL 11-13, 11-16, and 11-17) were extracted from the Paleoindian deposits signal was b1% for all aliquots, it was assumed there was no significant (between ~93.55 and ~92.90 m depths), and five samples (09-01, 09- feldspar contamination (Lόpez and Rink, 2008). In our tests, IR signal 01b, 09-02, 09-03, and 11-01) were extracted from the Archaic levels decays were not present, and all samples had IRSL/OSL ratios which within the midden deposits (between ~94.38 and ~93.60 m depths). were significantly b1%. Of the seventeen samples discussed in this paper, seven were Thermal transfer and dose recovery tests were performed to deter- collected in 2009 (those with the prefix “09”) while the remaining 10 mine the final D preheat temperature (Murray and Wintle, 2000, were collected during 2011 (those with the prefix “11”). The primary E 2003). For both tests, twelve aliquots from each sample were optically focus area for sampling the Paleoindian and Clovis deposits was bleached by blue light illumination for 40 s, followed by a 10,000 s the eastern half of Area 15 (6 m2) within the deepest 12 squares pause and another 40 s illumination. For the dose recovery test, the ali- (3 m × 4 m). Ages from the Archaic levels were extracted from those quots were given a known dose. Both tests continued with the standard areas without disturbance by features or previous looting pits. The loca- single aliquot regeneration (SAR) protocol (Murray and Wintle, 2000), tions of these samples are listed in Supplementary Table 1. except the preheat temperatures varied (160, 200, 240, 280 °C), with 3 aliquots from each sample receiving a different preheat temperature. 2.2. Sample collection and preparation For each sample, the dose recovery test was used to determine which

preheat temperature produced a DE closest to the given dose. Once Samples were collected by hammering 4.5 cm diameter steel tubes the preheat temperature was determined, the thermal transfer test into vertical, clean open sections. The 2009 samples were prepared at was analyzed to ensure that no charge transfer was induced at the the School of Geography and Earth Sciences at McMaster University in given temperature. UV-filtered, subdued orange lighting. The 2011 samples were prepared The SAR protocol was conducted on 24 or 48 aliquots to determine a at the Department of Geosciences at Murray State University, Murray, final DE. These were illuminated for 100 s at 125 °C. The background KY in subdued red fluorescent lighting fitted with Lee 106 filters. All (the last 4 s) of the OSL decay curve was subtracted from the “fast” com- OSL samples were analyzed at McMaster University. Pure quartz grains ponent (first 0.4 s) to determine the samples' luminescence signal. Ex- were obtained using chemical preparation methods outlined in Aitken ponential fits were made to the dose response data to determine (1998), including HCl and H O digestions to remove carbonates and or- 2 2 individual DE values. Aliquots were required to pass the following ganics, wet sieving to obtain desired grain size fraction (32–63 μm), and criteria for further analysis: b10% test dose error, b10% recycling ratio heavy liquid separation using lithium polytungstate (LST) to remove error, b10% paleodose error and a TN signal greater than 3σ above heavy minerals and feldspars. No HF etching was employed. background.

The DE distributions were plotted using two graphical methods: fre- 2.3. Details of OSL measurements and analysis of OSL data quency histograms and radial plots (Galbraith, 1990). Final DE values used for age calculation were determined using the central age model

Luminescence measurements at McMaster were conducted on a (CAM; Galbraith et al., 1999). A σb value, determined based on results RISØ OSL/TL-DA-15 reader using blue light LED stimulation (470 nm) of dose recovery experiments, was added in quadrature to all DE esti- and a 7 mm-thick Hoya U-340 ﬁlter (270–400 nm). A calibrated 90Sr mates made on 0.5 mm aliquots to account for variability caused by in- beta source was used to perform laboratory irradiations. Quartz grains, strumental error and intrinsic luminescent properties (see Table 1 100 K. Rodrigues et al. / Journal of Archaeological Science: Reports 7 (2016) 94–103 footnotes). Additional details of the sample measurements and in situ font. All CAM ages are reported in Table 2 and our ﬁnal age determina- dosimetry are provided in footnotes of Tables 1 and 2. tions summarized in Table 3.

Examples of the narrow spread in DE values are shown for two sam- 2.4. Radiation dosimetry ples in Fig. 4, using both a histogram and a radial plot. All aliquots show relative errors of b5%, while those in the lower panel (sample with zero Beta and alpha dose rates were based on neutron activation analysis over-dispersion) are all less than about 3%. Data from the two samples (NAA) of 232Th and 40K and delayed neutron counting (DNC) analysis of shown in Fig. 4 have the highest and lowest over-dispersion in the sam- 238U (conducted at the McMaster University Nuclear Reactor). Conver- ple set reported herein, and show no evidence of incomplete bleaching sion of radioisotope concentrations to dose rates was done using the or other forms of disturbance. data of Guérin et al. (1998) with the addition of 235U dose rates based The dose rates were derived from four different types of radiation on its expected natural abundance in relation to 238U (1 part 235Uto exposure (alpha, beta, gamma and cosmic; Table 2). The external beta 137 parts 238U). Untreated subsamples of the original samples were dose rate dominates the total dose rate, with the gamma dose rate mak- used to determine the elemental concentrations of radioactive 238U, ing up the bulk of the remainder. The external alpha dose rate and the 232Th, and 40K(Table 1). NAA/DNC-based dose rates were calculated cosmic dose rates are minor contributions of b5% each. Since the cosmic assuming radioactive equilibrium in the 238U and 232Th decay chains. dose rate is determined by long-term burial depth, the rate of accumu- Beta absorbed fractions were taken from Guérin et al. (2012). Details lation of sediment above a given sample is not an important factor in the associated with dose rate calculations are given in the footnotes of age determination. Importantly, the alpha dose rate for our samples at Table 2. External gamma dose rates were obtained in situ at all sample Gault, which is the one most sensitive to variations in long-term mois- locations during both 2009 and 2011 collection expeditions using a ture content, does not play a significant role here, thus reducing the Harwell 4 channel gamma spectrometer, set up as a scintillometer overall sensitivity of age estimate to moisture relative to other studies using triple point calibration conducted at the University of Oxford by where the external alpha dose rate is more significant (see discussion Steven Stokes. For age calculation, we assume secular equilibrium in section). the U-series decay chain. Table 3 and Fig. 3 present our OSL ages in relation to the cultural After the end portions exposed to light in the field were removed components in the unit from which each sample was taken. Clovis from the sample tubes, the moisture content for each sample was mea- ages range from 10,800 ± 500 to 13,600 ± 600 a, with a mean and stan- sured in the laboratory using either these end portions or a large portion dard deviation (1σ) of the four Clovis OSL ages being 12,900 ± 700 a. of the remainder of recovered sediment (Table 1). For age calculation, Ages from the Paleoindian deposits above Clovis show some variation we use an average of the laboratory measured moisture contents that with elevation and range from 8,800 ± 400 to 11,600 ± 500 a were found throughout the profile (10%) for all samples excluding the (Table 3). Ages from the Archaic deposits show good stratigraphic lowermost sample in the section (sample 11-03) for which we report agreement, although some mixing has occurred in these deposits 20% moisture age results. This is because of eyewitness observations owing to a number of cut-and-fill hearths excavated into the midden. that the lower portions of the site, typically below about 92.60 m, during Ages range from 5,700 ± 300 to 6,600 ± 300 a (Table 3). the years of excavation are often much wetter than the overlying portions. Currently, it is necessary to run pumps continuously in the exca- 4. Discussion vation area below 92.60 m elevation even in the season of deciduous vegetation transpiration; ground water is higher in the winter. Clovis ages from Area 15 of the Gault Site were found to be in good agreement with the existing archaeological and geochronological data 3. Results from Central Texas, U.S.A. (Supplementary Tables 2–5). As discussed above, the Archaic and Late Prehistoric diagnostic artifacts in this mid- The 238U concentrations in the sediment were found to increase den generally occur in proper stratigraphic order but there is also slightly with depth in the site, ranging from about 2.5 to 3.5 ppm some mixing of temporal markers owing to prehistoric anthropic (Table 1). The 232Th concentrations were variable over the same depth turbation (Fig. 3). Cut and fill structures near a given sample can cause interval, but ranged from about 11 to 13.5 ppm, thus the ratio of Th/U changes in the dose rate during burial and therefore OSL ages based is about 4. This is expected from these samples dominated by terrigenous on proximal sediment may not be valid owing to changes during burial. clays because such clays normally exhibit the 4:1 ratio close to average These cut-and-fill features were avoided during sample extraction and crustal values. The K concentration was found to decrease with depth, the ages from the Archaic levels confirm that very little mixing of sedi- ranging from 1.85 down to about 1.1 ppm. Laboratory-measured mois- ments within the Archaic midden deposits occurred. The three youngest ture content ranged from 3 to 15% with an average of 10%. Archaic OSL ages of 5,700 ± 300 a (at 94.38 m of elevation), 5,900 ± The samples displayed favorable luminescence characteristics 300 a (at 94.06 m), and 5,900 ± 300 a (at 94.06 m) (Fig. 3, Table 3), (Table 1), apparently owing to the long-distance aeolian transport are associated with a significant Andice/Bell assemblage (Calf Creek Ho- from a granitic terrain into the quartz-poor, carbonate-dominated rizon), identified on the basis of the points as well as the distinctive di- Edwards Plateau. The samples exhibited large proportions of aliquots agnostic notching flakes (Garrett and Ayala, 2014; Ayala, 2014). These that passed all the acceptance criteria (in most cases 100% of those test- ages agree well with the published ages of 5,955–5,815 cal BP for the ed, e.g. 24/24 or 48/48; see Table 1). Over-dispersion (a statistical mea- Calf Creek Horizon in Central Texas reported by Lohse et al. (2014),pro- sure of the spread of doses among the individual aliquots) of the viding independent evidence that OSL at Gault renders accurate age es- individual aliquot DE values was very small, ranging from 0 to 12%, timates. Below this, along with Early Archaic projectile points (including and therefore the CAM was used to compute the overall DE value used Gower, Hoxie, and Martindale), sequentially older OSL ages were found, in age determinations. No clear trend in over-dispersion values with al- reaching a maximum value of 6,600 ± 300 a at an elevation of 93.64 m. iquot diameter was found. There also appears to be no systematic rela- Beneath the Archaic components of the midden, the Late tionship between aliquot size and CAM DE for the samples that we Paleoindian deposits were found in the upper ~0.65 m of the silty clay measured. For cases where two different aliquot diameters were stud- deposit (Fig. 3). Prehistoric anthropic turbation has impacted the strat- ied, our final age determinations for that sample were based on a choice igraphic order of the temporal markers in the upper zone of the Late of the CAM DE from the aliquot size that showed the lowest over- Paleoindian deposits, but there is good agreement between those dispersion of the two studied. In the case of 5 of 7 samples, this also time-diagnostic artifacts considered to be in primary context and their meant selecting datasets with a significantly larger number of data associated OSL ages in three cases (see Table 3). In the first case, points. In Tables 1 and 2 these choices are distinguished with bold Angostura points associated with OSL ages in the range of 10,100 ± K. Rodrigues et al. / Journal of Archaeological Science: Reports 7 (2016) 94–103 101

Fig. 4. Examples of multi-grain DE distributions obtained for two samples with the highest and lowest over-dispersion values. Results are presented as both histograms and radial plots. The upper panel shows results from sample 11-02 with an over-dispersion of 8.5%. The lower panel shows results from sample 11-08 with an over-dispersion of 0%. The central value, denoted as a dashed line on the radial plot, represents the weighted mean of the DE's in each sample respectively.

400 to 8,800 ± 400 a are in good agreement with a range of ~9,000 to changed over the course of sediment burial at the Gault Site. Some 8,000 a suggested by Dial et al. (1998) at Wilson-Leonard and with a have suggested that wetter environmental conditions may have possi- range of ~10,000 to 9,000 a suggested by Thoms and Mandel (2007) bly existed in the area during the middle Holocene (eg. Winkler, (see Fig. 3, Table 3). In the second case, St. Mary's Hall points are closely 1990). However, by increasing the moisture content to 20% in these associated with an OSL age of 9,300 ± 400 a, well in agreement with a levels to increase the ages, then it could be expected that the lower range of ~10,200 to ~8,700 a suggested by “Late Plainview” at Horace units containing Clovis would also have experienced such higher mois- River Site (Bousman, Baker & Kerr, 2004) which are actually St. Mary's ture content, resulting in an age overestimate. If unattributed elevated Hall points (Bousman pers. Comms. 2016) (See also Bousman and moisture content is involved in the age underestimation of any samples Oksanen, 2012). In the final case, the Dalton component is associated in the Late Paleoindian levels, it seems it would have to be localized with OSL ages in the range of 9,700 ± 400 to 11,600 ± 500 a. The latter within those levels. This could be true if the Clovis levels did contain a of these two agrees with the existing age estimates for Dalton of 11,900 much larger proportion of rocks which did not absorb as much moisture to 11,700 cal BP (Anderson et al., 1996), but the other age is significantly relative to the total pore space containing moisture in the higher Late younger for reasons that are unclear. The same is true for the other age Paleoindian levels. Excavations and profiles show an increase in calcium of 9,900 ± 400 a which is also associated with Dalton elements. This carbonate development at the Clovis level which may contribute to may be the result of upward artifact displacement, bio-turbation, or higher moisture above. This should be addressed by future research. geo-turbation. Bio-turbation has been known to potentially introduce The mean age of the Clovis deposits (Table 3) is 12,900 ± 700 a younger grains into a deposit, making its OSL age too young in some (±1σ), which yields a range of ~13,600 to 12,200 a. This is in agreement cases (eg. Bateman et al., 2003, 2007; Rink et al., 2013). with the known Clovis ages from Central Texas, and a generalized model For the Folsom component, the OSL ages are also too young, but a that places the Clovis occupation of Central Texas between ~13,500 to reason for this is more evident. The only diagnostic Folsom material 13,000 cal BP (Holliday, 2000). The Gault OSL ages overlap the Clovis was recovered from a large cut-and-fill anthropic feature making tem- ages from stratum 7 at Pavo Real, which range from 13,800 ± 800 cal poral assignation difficult. The feature, identified as a complex series BP to 12,940 ± 800 cal BP (Collins, 2003) and with the Wilson- of burnt rock ovens overlying each other, starts at approximately Leonard Site which has an age of ~13,500 cal BP (c.f. Collins, 1998: 93.00 m, close to two OSL ages of 10,200 ± 500 and 11,600 ± 500 a. 140-145; 280-281) for the Clovis artifacts. Our ages are also in agree- These ages are about 1,000 to 2,000 years younger than the expected ment with two Clovis ages from the nearby Debra L. Friedkin Site of time range for Folsom of about 12,850 to 11,900 a (c.f. Meltzer, 2006: 13,090 ± 830 a and 13,780 ± 885 a. 1). Their younger age is what would be expected if they were Inter-comparison within Gault itself shows that each of the feldspar transported as older elements into the cut and fill feature composed of IRSL ages on fine-grained feldspar of 13,220 ± 740 a and 12,920 ± 700 a younger sediments. It is highly likely that these Folsom artifacts were from Gault excavation area 8 (Waters et al., 2011b; and Supplementary uncovered during the first phases of the pit feature construction and Table 3 in this study) are statistically indistinguishable from the may, in fact be associated with the older 11,600 ± 500 a sample. 12,900 ± 700 a mean age for OSL ages on silt-size quartz grains from There is also a possibility that some of the age underestimations that Area 15 (see Table 3), demonstrating a degree of consistency among we observed in the Folsom and Dalton components may be the result of the two luminescence dating techniques used at Gault. Research at the unattributed elevated moisture content. There is some uncertainty Gault Site is on-going to confirm this initial dating sequence and the about the long-term levels of moisture content and how they have lithostratigraphy across the valley floor. 102 K. Rodrigues et al. / Journal of Archaeological Science: Reports 7 (2016) 94–103

5. Conclusion Bronk Ramsey, C., 2009. Bayesian analysis of radiocarbon dates. Radiocarbon 51 (1), 337–360. Collins, M.B., 1998. Early Paleoindian Components. In: Collins, M.B. (Ed.), Wilson-Leonard, The OSL chronology established in this paper for the Gault Site indi- An 11,000-year Archeological Record of Hunter-Gatherers in Central Texas. Studies in cates some excellent stratigraphic agreement between the ages and the Archeology 31, Texas Archeological Research Laboratory, The University of Texas and Archeology Studies Program, Report 10, Texas Department of Transportation, Envi- temporal-diagnostic artifacts recovered during excavation, while dis- ronmental Affairs Division, Austin, pp. 123–159. agreement with expected ages from other sites was also found. The Collins, M.B., 2002. The Gault Site, Texas, and Clovis Research. Athena Rev. 3 (2), 31–41 best results were found in the Archaic and Clovis levels. The Clovis age (2002 100-101). range is not incompatible with either Holliday (2000), Waters and Collins, M.B., 2003. Paleoindian Pavo Real. In: Collins, M.B., Hudler, D.B., Black, S.L. (Eds.), Pavo Real (41BX52): A Paleoindian and Archaic Camp and Workshop on the Balcones Stafford (2007),orMeltzer (2009), and therefore contributes strength Escarpment, South-Central Texas. Studies in Archaeology 41, Texas Archeological to existing ideas about the Clovis age range. Research Laboratory, The University of Texas at Austin, Archeological Studies Pro- In the Late Paleoindian levels, we found some agreement with ex- gram, Report 50, Environmental Affairs Division, Texas Department of Transporta- tion, Austin, pp. 83–190. pectations but age underestimation in others. It is possible that our Collins, M.B., 2004. Archeology in Central Texas. In: Perttula, T.K. (Ed.), The Prehistory of choices in moisture content values led to some of the age underesti- Texas. Texas A&M University Press, College Station, pp. 101–126. mates we observed. Other sources of the few OSL age mismatches Collins, M.B., 2007. Discerning Clovis Subsistence from Stone Artifacts and Site Distributions on the Southern Plains Periphery. In: Walker, R.B., Driskell, B.N. (Eds.), could be related to site formation processes or post-burial processes. Al- Foragers of the Terminal Pleistocene in North America. University of Nebraska though anthropic turbation has caused a number of artifacts to move Press, Lincoln and London, pp. 59–87. upwards through the deposits, there is little evidence of the downward Collins, M.B., Mear, C.E., 1998. The Site and Its Setting. In: Collins, M.B. (Ed.), Wilson- Leonard, An 11,000-year Archeological Record of Hunter-Gatherers in Central movement of artifacts. Where artifacts have been recovered from eleva- Texas. Studies in Archeology 31, Texas Archeological Research Laboratory, The Uni- tions lower than expected, they have been found within the cut-and-fill versity of Texas and Archeology Studies Program, Report 10, Texas Department of features that are intrusive into the Late Paleoindian deposits from the Transportation, Environmental Affairs Division, Austin, pp. 5–32. fi Dial, S.W., Kerr, A.C., Collins, M.B., 1998. Projectile Points. In: Collins, M.B. (Ed.), Wilson- Archaic midden deposits. Signi cantly, the Clovis deposits remain un- Leonard, An 11,000-year Archeological Record of Hunter-Gatherers in Central disturbed in this stratigraphic sequence. Texas. Studies in Archeology 31, Texas Archeological Research Laboratory, The Uni- The dating sequence from Gault conforms to the independently- versity of Texas and Archeology Studies Program, Report 10, Texas Department of – dated chronological periods established for Central Texas, including Transportation, Environmental Affairs Division, Austin, pp. 313 446. Diamond, D.D., Riskind, D.H., Orzell, S.L., 1987. A framework for plant community classi- those ages from the Andice/Calf Creek deposits, Angostura, St. Mary's fication and conservation in Texas. Tex. J. Sci. 39, 202–221. Hall, Clovis, and to some extent, Dalton. With most of the ages in correct Duller, G.A.T., 2008. Luminescence Dating: Guidelines in Using Luminescence Dating in stratigraphic order, considerable confidence can be placed in the OSL Archaeology. English Heritage, Swindon. Ferring, R., 2001. The Archaeology and Paleoecology of the Aubrey Clovis Site (41DN479), dating results presented herein. Denton County. Department of Geography, University of North Texas, Denton, Texas. Supplementary data to this article can be found online at http://dx. Center for Environmental Archaeology. doi.org/10.1016/j.jasrep.2016.03.014. Galbraith, R.F., 1990. The radial plot: graphical assessment of spread in ages. Nucl. Tracks Radiat. Meas. 17, 207–214. Galbraith, R.F., Roberts, R.G., Laslett, G.M., Yosida, H., Olley, J.M., 1999. Optical dating of Acknowledgments single and multiple grains of quartz from Jinmium rock shelter, northern Australia: Part 1 Experimental design and statistical models. Archaeometry 41, 339–364. Garret, S., Ayala, S., 2014. Depositional Integrity of Area 15 at the Gault Site – Utility of This research was funded in part by NSF Grant 0920549 to Texas Geomagnetic Analysis and Diagnostic Notching Flakes. Poster presented at the 79th State University, San Marcos, by The Gault School of Archaeological Re- Annual Meeting of the Society for American Archaeology. Texas, Austin. search, and by private donors. TJW and MBC also wish to acknowledge Goodyear, A.C., 1982. The chronological position of the Dalton Horizon in the Southeast- ern United States. Am. Antiq. 47 (2), 382–395. The Summerlee Foundation. Illustrations used in Figs. 1, 2, and 3 are Guérin, G., Mercier, N., Adamiec, G., 1998. Dose-rate conversion factors: update. Ancient courtesy of the Gault School of Archaeological Research, produced by TL 29 (1), 5–8. TJW and Sergio Ayala. WJR acknowledges funding from the Natural Sci- Guérin, G., Mercier, N., Nathan, R., Adamiec, G., Lefrais, Y., 2012. On the use of the infinite matrix assumption and associated concepts: a critical review. Radiat. Meas. 47, ences and Engineering Research Council of Canada. WJR and AKZ also 778–785. thank Nancy V. Williams and Steve Howard for help with sample acqui- Haynes, G., Anderson, D.G., Ferring, C.R., Fiedel, S.J., Grayson, D.K., Haynes, C.V., Holliday, sition. 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