Dunragit, the Prehistoric Heart of Galloway Appendix 2: Luminescence Dating of Samples from Sand Layers – Site 6A

By A J Cressell, D C W Sanderson and W Bailie

Click back to the Dunragit Monograph Contents 1.0 Summary 1

2.0 Introduction 1

3.0 Methods 1 Sampling and Sample Preparation 1 Water Contents 1 HRGS and TSBS Sample Preparation 1

4.0 Quartz Mineral Preparation 2

5.0 Measurements and Determinations 2 Dose Rate Determinations 2 Quartz SAR Luminescence Measurements 3

6.0 Results 4 Dose Rates 4 Quartz Single Aliquot Equivalent Dose Determinations 4 SAR Quality Parameters 4 Equivalent Dose Determinations and Distributions 5 OSL Ages 5 5 7.0 Figures 7

8.0 Tables 10

Summary Extensive excavations were undertaken prior to the construction of the re-routed A75 to the south of the village of Dunragit, between Stranraer and Glenluce in Dumfries and Galloway. At Myrtle Cottage (Site 6A), initial exploratory investigations identified significant structures of possible Iron Age date set within a former dune system, potentially an earlier foreshore, with accumulation of sand layers among the structures. Samples were collected in November 2012 between the two best-preserved structures, to identify the stratigraphic relationships between these structures. The basal layers consist of a natural deposit consistent with raised beaches from the mid Holocene tidal high stand, with an occupation layer dated to 1540 ± 290 BC below the structures on the site, suggestive of human activity significantly pre-dating the structures. The OSL dates indicate that there was a period of occupation on the site between approximately 400 and 100 BC. The wall for Structure 2 cuts through these occupation layers and the natural, and is dated to AD 350 ± 240 with approximately contemporary layers deposited outside this structure potentially from the material excavated from the wall cut. The wall for Structure 1 is dated to AD 400 ± 190 and cuts through the AD 100-300 material, and thus may slightly postdate the wall cut for Structure 2.

Introductioin Dunragit, situated between Stranraer and Glenluce in Dumfries and Galloway, is the site of a series of Neolithic monuments. Above ground, Droughduil Mound is a prominent feature in the landscape and has been dated using Optically Stimulated Luminescence (OSL) to c. 2500 BC (Sanderson et al. 2003, Thomas et al. 2015). To the north of the mound is an early Neolithic timber cursus monument and late Neolithic palisaded enclosure complex, excavated between 1999 and 2002 (Thomas 2015). The work reported here relates to extensive excavations undertaken along the route of the re- routed A75 to the south of the village of Dunragit. The excavations, summarised in Arabaolaza et al. (2015), uncovered a Neolithic settlement, possibly related to the nearby monuments, two Bronze Age cemeteries and six Iron Age roundhouses. At Myrtle Cottage, initial exploratory investigations identified significant structures of possible Iron Age date. These structures are set within a former dune system, potentially an earlier foreshore, with accumulation of sand layers among the structures. Samples were collected in November 2012 between the two best-preserved structures on Site 6A, to identify the stratigraphic relationships between these structures. These are shown in OSL Figures 1 and 2 (taken from Arabaolaza et al. 2015).

Methods Sampling and Sample Preparation Samples were collected by GUARD Archaeology Ltd. during excavations in November 2012, with 15 cm long, 18 mm internal diameter plastic tubes driven into exposed sections after cleaning back material that had been exposed to daylight. Each sample was given a laboratory (SUTL) reference code upon receipt at SUERC, as summarised in OSL Table 1. OSL Figure 3 shows the locations of the OSL samples in the east and west facing sections of slot 9, with the plan of this section of the excavation in OSL Figure 2.2 (Illustration 2.64).

Water Contents The tube samples were weighed, saturated with water, and re-weighed. Following oven drying at 50°C to constant weight, the actual and saturated water contents were determined as fractions of dry weight. This data was used, together with information on field conditions to determine water contents and an associated water content uncertainty for use in dose rate determination.

HRGS and TSBS Sample Preparation From each of the tube samples, 20 g of the dried material was put into petri dishes, enclosed in black plastic, and counted unsealed for high-resolution gamma spectrometry (HRGS) and thick

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source beta counting (TSBC; Sanderson 1988). Bulk quantities of material from six locations, weighing approximately 200 g, were used for environmental dose rate determinations. These dried materials were transferred to high-density-polyethylene (HDPE) pots and sealed with epoxy resin for HRGS. Each pot was stored for three weeks prior to measurement to allow equilibration of 222Rn daughters.

Quartz Mineral Preparation Approximately 20 g of material was removed for each tube and processed to obtain sand-sized quartz grains for luminescence measurements. Each sample was wet sieved to obtain the 90-150 and 150-250 μm fractions. The 150-250 µm fractions were treated with 1 M hydrochloric acid (HCl) for 10 minutes, 15% hydrofluoric acid (HF) for 15 minutes, and 1 M HCl for a further 10 minutes. The HF-etched sub-samples were then centrifuged in sodium polytungstate solutions of c. 2.58, 2.62, and 2.74 g cm-3, to obtain concentrates of potassium-rich feldspars (<2.58 g cm-3), sodium feldspars (2.58-2.62 g cm-3) and quartz plus plagioclase (2.62-2.74 g cm-3). The selected quartz fraction was then subjected to further HF and HCl washes (40 % HF for 40 mins, followed by 1M HCl for 10 mins). All materials were dried at 50°C and transferred to Eppendorf tubes. The 40 % HF-etched, 2.62- 2.74 g cm-3 ‘quartz’ 150-250 µm fractions were dispensed to 10 mm stainless steel discs for measurement. 16 aliquots were dispensed for each sample the purity of which was checked using a Hitachi S-3400N scanning electron microscope (SEM), coupled with an Oxfords Instruments INCA EDX system, to determine approximate elemental concentrations for each sample.

Measurements and Determinations Dose Rate Determinations Dose rates were measured in the laboratory using HRGS and TSBC. Full sets of laboratory dose rate determinations were made for all samples. HRGS measurements were performed using a 50% relative efficiency “n” type hyper-pure Ge detector (EG&G Ortec Gamma-X) operated in a low background lead shield with a copper liner. Gamma ray spectra were recorded over the 30 keV to 3 MeV range from each sample, interleaved with background measurements and measurements from SUERC Shap Granite standard in the same geometries. Sample counts were for 80 ks. The spectra were analysed to determine count rates from the major line emissions from 40K (1461 keV), and from selected nuclides in the U decay series (234Th, 226Ra + 235U, 214Pb, 214Bi and 210Pb) and the Th decay series (228Ac, 212Pb, 208Tl) and their statistical counting uncertainties. Net rates and activity concentrations for each of these nuclides were determined relative to Shap Granite by weighted combination of the individual lines for each nuclide. The internal consistency of nuclide specific estimates for U and Th decay series nuclides was assessed relative to measurement precision, and weighted combinations used to estimate mean activity concentrations (Bq kg-1) and elemental concentrations (% K and ppm U, Th) for the parent activity. These data were used to determine infinite matrix dose rates for alpha, beta and gamma radiation. Beta dose rates were also measured directly using the SUERC TSBC system (Sanderson 1988). Count rates were determined with six replicate 600 s counts on each sample, bracketed by background measurements and sensitivity determinations using the Shap Granite secondary reference material. Infinite-matrix dose rates were calculated by scaling the net count rates of samples and reference material to the working beta dose rate of the Shap Granite (6.25 ± 0.03 mGy a-1). The estimated errors combine counting statistics, observed variance and the uncertainty on the reference value. The dose rate measurements were used in combination with the assumed burial water contents, to determine the overall effective dose rates for age estimation. Cosmic dose rates were evaluated by combining latitude and altitude specific dose rates (0.185 ± 0.01 mGy a-1) for the site with corrections for estimated depth of overburden using the method of Prescott and Hutton (1994).

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Quartz SAR Luminescence Measurements All measurements were conducted using a Risø DA-15 automatic reader equipped with a 90Sr/90Y β-source for irradiation, blue LEDs emitting around 470 nm and infrared (laser) diodes emitting around 830 nm for optical stimulation, and a U340 detection filter pack to detect in the region 270-380 nm, while cutting out stimulating light (Bøtter-Jensen et al. 2000). Equivalent dose determinations were made on sets of 16 aliquots per sample, using a single aliquot regeneration (SAR) sequence (cf. Murray and Wintle 2000). Using this procedure, the OSL signal levels from each individual disc were calibrated to provide an absorbed dose estimate (the equivalent dose) using an interpolated dose-response curve, constructed by regenerating OSL signals by beta irradiation in the laboratory. Sensitivity changes which may occur as a result of readout, irradiation, and preheating (to remove unstable radiation-induced signals) were monitored using small test doses after each regenerative dose. Each measurement was standardised to the test dose response determined immediately after its readout, to compensate for changes in sensitivity during the laboratory measurement sequence. The regenerative doses were chosen to encompass the likely value of the equivalent (natural) dose. A repeat dose point was included to check the ability of the SAR procedure to correct for laboratory-induced sensitivity changes (the ‘recycling test’), a zero dose point is included late in the sequence to check for thermally induced charge transfer during the irradiation and preheating cycle (the ‘zero cycle’), and an IR response check included to assess the magnitude of non-quartz signals. Regenerative dose response curves were constructed using doses of 1, 2, 4, 6, and 8 Gy, with test doses of 1.0 Gy. The 16 aliquot sets were sub-divided into four subsets of four aliquots, such that four preheating regimes were explored (220°C, 240°C, 260°C, and 280°C). This procedure is similar to that successfully used for the dating of Droughduil Mound (Sanderson et al. 2003). The data were processed to determine quality parameters for the SAR procedure, with any aliquot which failed these tests rejected from further analysis, as follows. 1. The sensitivity (c Gy-1) was determined from the response to the first test dose 2. The sensitivity change is determined from the difference between the last and first test dose responses divided by the number of measurement cycles, as a percentage of the first test dose. 3. The recycling ratio is the ratio of the normalised OSL measurement for the repeat of the first regenerative dose divided by the normalised OSL measurement for the first regenerative dose. This should be unity. 4. The zero-cycle response is the normalised OSL measurement following the zero dose cycle. This should be zero. 5. The IR response is the ratio of the response to IR stimulation following a 1Gy dose to the response to blue stimulation following a 1Gy dose. This should be zero. 6. The dose recovery test uses the response to the first test dose normalised using the response to the first regenerative dose to confirm that the curve fitting returns the test dose value. This should be 1Gy. For each regenerative dose, the OSL counts normalised using the corresponding test dose are plotted against dose and an exponential rise to maximum curve fitted through the data. These are plotted for the average of each of the four pre-heating groups and for all samples (the plots for all samples are shown in the Appendix A), and any differences between the pre-heating groups noted. Any aliquots showing significantly different dose responses compared to the other aliquots are removed from the analysis. The equivalent dose for each aliquot is determined by interpolation of the normalised natural OSL counts to the fitted curve.

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Results Dose Rates HRGS results are shown in OSL Table 2, both as activity concentrations (i.e. disintegrations per second per kilogram) and as equivalent parent element concentrations (in % and ppm), based in the case of U and Th on combining nuclide specific data assuming decay series equilibrium. Infinite matrix alpha, beta and gamma dose rates from HRGS are listed for all samples in OSL Table 3, together with infinite matrix beta dose rates from TSBC. Beta dose rates from HRGS are in generally good agreement with those determined from TSBC. For the bulk samples, the gamma dose rates for the samples from the Structure 3 furnace (SUTL3019 and 3020) are significantly higher than those from the other samples, reflecting higher activity concentrations (OSL Table 2) often associated with heated materials, and are not considered representative of the gamma dose rate from the general environment. The mean and standard error for the remaining four bulk samples are used to estimate an environmental gamma dose rate. The water content measurements are given in OSL Table 4, together with the assumed values for the average water content during burial. The field water contents are very low (<3 % of dry weight) suggesting a very well drained site, consistent with the sandy nature of the material. The previous measurements of sand from the nearby Droughduil Mound also showed similar field and saturated water contents (Sanderson et al. 2003). Working values of water content of 5 ± 5 %, biased towards the lower (field) values since it is thus expected that these sediments drain rapidly, this working value for water content was also applied to the Droughduil Mound samples. Effective beta dose rates to the HF-etched 150-250 μm quartz grains are given in OSL Table 4 (the mean of the TSBC and HRGS data, accounting for water content and grain size), together with the estimate of the gamma dose rate (average of HRGS data, accounting for water content, and environmental dose rate from bulk samples). The total effective dose rate is the sum of these plus a cosmic contribution. These dose rates are also similar to the Droughduil Mound samples.

Quartz Single Aliquot Equivalent Dose Determinations For equivalent dose determination, data from single aliquot regenerative dose measurements were analysed using the Risø TL/ OSL Viewer programme to export integrated summary files that were analysed in MS Excel and SigmaPlot. Composite dose response curves were constructed from selected discs and when possible, for each of the preheating groups from each sample, and used to estimate equivalent dose values for each individual disc and their combined sets. Dose response curves (shown in Appendix 2) for each of the preheating temperature groups and the combined data were determined using a fit to a saturating exponential function. Probability density functions (PDFs) and Abanico plots were generated to describe the dose distributions, and are shown in Appendix A.

SAR Quality Parameters SAR quality parameters are given in OSL Table 5. These consist of the number of aliquots which passed the quality criteria with the number of aliquots dispensed. For the aliquots which pass the quality criteria the mean sensitivity determined from the initial test dose response and the change per cycle, the mean recycling ratio, mean zero cycle response, mean IR response and the mean recovered dose signal are also tabulated. The materials all give sensitivities in the range 650-3500 c Gy-1, though for SUTL3015 the initial measurements included a large number of aliquots with very low sensitivities and a second set of 16 aliquots carrying larger quantities of quartz were dispensed to produce a sufficient number of aliquots carrying quantifiable signals. Additional sets of 16 aliquots were also dispensed for SUTL3017 and 3018 to improve the definition of the dose distributions for these samples, see next section below. In most cases the sensitivity increases moderately (approximately 5-10% per cycle) during the run, with the exception of SUTL3015 where the sensitivity decreases. Recycling ratios are consistent with unity, with the exception of SUTL3015 the zero-cycle signals are very small, and for all samples the IR signals are small and dose recovery consistent with unity.

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Equivalent Dose Determinations and Distributions For each sample, the mean, weighted mean, and a robust mean were calculated, as given in OSL Table 6. For SUTL3015, the majority of aliquots carry natural signals in excess of the saturation value for the fitted exponential rise to maximum dose response curves which for these samples where the dose responses were measured for doses up to 8 Gy, therefore additional regenerative doses from 8 to 32 Gy were added to allow quantification of the equivalent dose for this sample. This, along with the different luminescence behaviour inferred from the quality parameters (OSL Table 5) is consistent with the field observations that this sample is from natural deposits below the archaeological layers. The dose distributions for the other samples (see Appendix B) show single peaks, in some cases quite broad as a result of uncertainties in the equivalent doses of individual aliquots, suggesting that these materials do represent events where the quartz entered the deposits with little residual luminescence signal. There are some examples where one or two aliquots carry a much larger signal that would be associated with small quantities of material carrying a residual signal. The maximum values of the probability density functions and kernel density estimates correspond closely to the weighted means, and thus this has been used.

OSL Ages The calculated ages for these samples are given in OSL Table 7, combining the preferred stored dose estimate (OSL Table 8) with the total dose rate (OSL Table 4).

Discussion and Conclusions OSL Table 8 and OSL Figure 5 summarise the samples and the dates determined by OSL measurements. The basal layer (SUTL 3015, context 143) was identified in the field as a natural deposit. The OSL age is consistent with the mid Holocene tidal high stand, which along the Solway resulted in sea levels up to 4 m OD between 5.0 and 7.5 ka BP producing raised beaches, mud flats and saltmarsh features in the landscape subsequently lifted to c. 10 m OD by ongoing isostatic rebound. This natural deposit is overlain by an occupation layer (SUTL3009, context 147) observed below the structures on the site, with foundation cuts through it, which has an OSL date of 1540 ± 290 BC. This suggests human activity on the site significantly before the building of the structures excavated. The occupation layers inside Structure 2 are dated to 350 ± 200 BC for the primary occupation layer (mean of SUTL3008 and 3011, context 115) and 200 ± 170 BC for the layer above this (SUTL3006, context 138). Outside Structure 2, there are two older samples in the lower layer at 210 ± 200 BC (mean of SUTL3013 and 3016, context 136) and significantly younger samples in the upper layer at AD 220 ± 140 (mean of SUTL3012 and 3017, context 135). There is considerable consistency in the dates for lower layers both inside and outside the structure, with a younger layer present outside the structure. The two samples above the earliest occupation layer inside Structure 1 give OSL dates that are consistent within uncertainty, with a mean date of AD 200 ± 150 (SUTL3007 context 135 and SUTL3010 context 136). This is also consistent with the two samples from context 135 outside Structure 2, though significantly younger than the OSL date for the samples from context 136 outside Structure 2 suggesting that within Structure 1 this context has been disturbed introducing younger material associated with the Structure 1 wall cut. The youngest samples analysed are from the fills of the wall cuts for Structure 2 (SUTL3014 context 131) at AD 350 ± 240 and Structure 1 (SUTL3018, context 077) at AD 400 ± 190. These samples are contemporary with each other within uncertainties, and may be contemporary or slightly post-dating the occupation layers inside Structure 1 and the upper layer between structures 1 and 2. If these dates are associated with the construction of these structures then the wall for Structure 2 has cut through the earlier 400-100 BC occupation layers, producing a layer of similar age to the wall cut outside the structure, and the wall cut for Structure 1 possibly slightly

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post-dates this as it also cuts into AD 100-300 materials approximately contemporary with the Structure 2 wall cut.

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Figures

OSL Figure 1: Overall plan of site 6A, from Arabaolaza et.al. (2015) (see Illus 264).

OSL Figure 2: Structures 1 (right centre), 2 (top right) and 5 (top left), from Arabaolaza et.al. (2015).

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OSL Figure 3: Section drawings of slot 9 showing the OSL sample locations

OSL Figure 4: Plan of the part of the excavation including structures 1, 2 and 3 (same as OSL Figure 1.2).

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OSL Figure 5: Section drawings of slot 9 with OSL dates.

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Tables Table 1: Summary of Samples and SUERC Laboratory Reference Codes. Samples SUTL3006 3018 are Tube Samples for OSL Dating and Samples 3019-3024 are Bulk Samples for Gamma Spectrometry SUERC Code Site Code Description SUTL3006 Sample 034 Slot 9. context 138. Occupation layer within (130) Structure 2. Slot 9 East interior of (003). context 135.Upper layer of sand formed on the SUTL3007 Sample 035 outside of Structure 2 (130). Similar level to the abandonment/ final use of the structure. Slot 9 West. context 115. Primary occupation layer within foundation cut (130) SUTL3008 Sample 036 of Structure 2. Slot 9. context 147. Occupation layer, underlies layer (136), encountered below SUTL3009 Sample 037 structures 1, 2 and 3. Slot 9 East interior of (077). context 136. Extent 0.3 m thick. Underlies (135) and SUTL3010 Sample 038 similar to (115). Slot 9 East. context 115. Primary occupation layer within foundation cut (130) of SUTL3011 Sample 039 Structure 2. Slot 9 East exterior of (077). context 135. Upper layer of sand formed on the SUTL3012 Sample 040 outside of Structure 2 (130). Similar level to the abandonment/ final use of the structure. SUTL3013 Sample 041 Slot 9 West. context 136. Extent 0.3 m thick. Underlies (135) and similar to (115). SUTL3014 Sample 042 Slot 9 West. context 131. Fill of foundation wall cut (130), Structure 2. Slot 9 West. Context 143. Natural deposit/layer. Truncated by Structure 2's wall- SUTL3015 Sample 043 slot (130). Underlies (115) and (136). Slot 9 East exterior of (077). Context 136. Extent 0.3 m thick. Underlies (135) and SUTL3016 Sample 044 similar to (115). Slot 9 West. Context 135. Upper layer of sand formed on the outside of Structure SUTL3017 Sample 045 2 (130). Similar level to the abandonment/ final use of the structure. Slot 9 East. Context 077. Lower fill of outer foundation trench (074) (Structure 1). SUTL3018 Sample 046 Depth 0.23-0.27 m. SUTL3019 Sample 152 Structure 3. Lowest layer within furnace. Context 461. SUTL3020 Sample 153 Structure 3. Charcoal-rich layer within centre of furnace. Context 434. Structure 3. Spread of dark grey-black silty sand to the south of the furnace. SUTL3021 Sample 164 Context 367. SUTL3022 Sample 394 Structure 3. Fill of wall socket. Context 679. SUTL3023 Sample 403 Overlies natural layer with iron panning (context 195). Context 654. SUTL3024 Sample 426 Fill of posthole set into wall-slot of Structure 2 (130). Context 726.

Table 2: Activity and Equivalent Concentrations of K, U and Th Determined by HRGS SUTL Activity Concentrationa/Bq kg-1 Equivalent Concentrationb No K U Th K/% U/ppm Th/ppm 3006 246 ± 26 14.3 ± 2.9 8.2 ± 2.4 0.8 ± 0.1 1.2 ± 0.2 2.0 ± 0.6 3007 267 ± 42 14.8 ± 2.9 15.6 ± 2.7 0.9 ± 0.1 1.2 ± 0.2 3.8 ± 0.7 3008 296 ± 27 10.8 ± 3.0 18.3 ± 2.2 1.0 ± 0.1 0.9 ± 0.2 4.5 ± 0.5 3009 309 ± 38 14.9 ± 3.1 10.9 ± 3.0 1.0 ± 0.1 1.2 ± 0.3 2.7 ± 0.7 3010 321 ± 36 15.1 ± 3.0 15.7 ± 2.8 1.0 ± 0.1 1.2 ± 0.2 3.9 ± 0.7 3011 307 ± 26 13.0 ± 2.3 10.0 ± 2.3 1.0 ± 0.1 1.1 ± 0.2 2.5 ± 0.6 3012 299 ± 39 20.4 ± 3.5 17.8 ± 2.9 1.0 ± 0.1 1.6 ± 0.3 4.4 ± 0.7 3013 262 ± 28 14.6 ± 2.8 8.9 ± 2.4 0.8 ± 0.1 1.2 ± 0.2 2.2 ± 0.6 3014 295 ± 34 17.0 ± 3.7 16.7 ± 3.1 1.0 ± 0.1 1.4 ± 0.3 4.1 ± 0.8

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Table 2: Activity and Equivalent Concentrations of K, U and Th Determined by HRGS (cont) SUTL Activity Concentrationa/Bq kg-1 Equivalent Concentrationb No K U Th K/% U/ppm Th/ppm 3015 340 ± 27 16.5 ± 2.6 13.2 ± 2.3 1.1 ± 0.1 1.3 ± 0.2 3.3 ± 0.6 3016 351 ± 27 16.0 ± 2.8 14.4 ± 2.3 1.1 ± 0.1 1.3 ± 0.2 3.5 ± 0.6 3017 285 ± 41 17.0 ± 3.2 14.0 ± 2.9 0.9 ± 0.1 1.4 ± 0.3 3.5 ± 0.7 3018 342 ± 28 17.8 ± 2.6 12.9 ± 2.5 1.1 ± 0.1 1.4 ± 0.2 3.2 ± 0.6 3019 383 ± 12 20.3 ± 1.1 19.8 ± 0.8 1.2 ± 0.1 1.6 ± 0.1 4.9 ± 0.2 3020 436 ± 9 25.5 ± 0.9 23.3 ± 0.6 1.4 ± 0.1 2.1 ± 0.1 5.7 ± 0.1 3021 269 ± 10 10.5 ± 1.0 11.5 ± 0.8 0.9 ± 0.1 0.9 ± 0.1 2.8 ± 0.2 3022 402 ± 7 12.2 ± 0.7 14.7 ± 0.5 1.3 ± 0.1 1.0 ± 0.1 3.6 ± 0.1 3023 227 ± 10 10.3 ± 0.9 11.6 ± 0.8 0.7 ± 0.1 0.8 ± 0.1 2.9 ± 0.2 3024 301 ± 7 9.4 ± 0.7 11.7 ± 0.6 1.0 ± 0.1 0.8 ± 0.1 2.9 ± 0.1 a Shap granite reference, working values determined by David Sanderson in 1986, based on HRGS relative to CANMET and NBL standards. b Activity and equivalent concentrations for U, Th and K determined by HRGS (Conversion factors based on NEA (2000) decay constants): 40K: 309.3 Bq kg-1 %K-1, 238U: 12.35 Bq kg-1 ppmU-1, 232Th: 4.057 Bq kg-1 ppm Th-1

Table 3: Infinite Matrix Dose Rates Determined by HRGS and TSBC SUTL HRGS, Drya/mGy a-1 TSBC Dry No Alpha Beta Gamma /mGy a-1 3006 4.72 ± 0.79 0.90 ± 0.08 0.43 ± 0.04 0.96 ± 0.06 3007 6.18 ± 0.81 1.01 ± 0.12 0.54 ± 0.05 1.02 ± 0.13 3008 5.77 ± 0.79 1.07 ± 0.08 0.56 ± 0.04 0.90 ± 0.10 3009 5.35 ± 0.89 1.10 ± 0.11 0.51 ± 0.05 0.90 ± 0.12 3010 6.27 ± 0.86 1.17 ± 0.11 0.58 ± 0.05 1.04 ± 0.15 3011 4.75 ± 0.66 1.05 ± 0.08 0.49 ± 0.04 1.00 ± 0.08 3012 7.82 ± 0.96 1.17 ± 0.12 0.65 ± 0.06 1.16 ± 0.13 3013 4.90 ± 0.77 0.94 ± 0.08 0.45 ± 0.05 0.94 ± 0.12 3014 6.87 ± 1.00 1.11 ± 0.10 0.60 ± 0.06 1.18 ± 0.05 3015 6.13 ± 0.73 1.22 ± 0.08 0.58 ± 0.04 1.06 ± 0.05 3016 6.24 ± 0.76 1.25 ± 0.08 0.60 ± 0.04 1.01 ± 0.04 3017 6.39 ± 0.90 1.08 ± 0.12 0.55 ± 0.06 1.03 ± 0.04 3018 6.37 ± 0.74 1.24 ± 0.08 0.59 ± 0.04 1.16 ± 0.05 3019 8.17 ± 0.28 1.41 ± 0.03 0.74 ± 0.02 - 3020 10.01 ± 0.24 1.66 ± 0.03 0.86 ± 0.01 - 3021 4.47 ± 0.26 0.94 ± 0.03 0.45 ± 0.02 - 3022 5.43 ± 0.19 1.35 ± 0.02 0.61 ± 0.01 - 3023 4.44 ± 0.25 0.82 ± 0.03 0.41 ± 0.01 - 3024 4.24 ± 0.19 1.02 ± 0.02 0.47 ± 0.01 - a based on dose rate conversion factors in Aikten (1983), Sanderson (1987) and Cresswell et al. (2018)

Table 4: Effective Beta and Gamma Dose Rates Following Water Correction

SULT Water Contents/% Effective Dose Rate/mGy a-1 No Field Sat Betaa Gamma Totalb Assumed 3006 0.9 33.9 5 ± 5 0.80 ± 0.06 0.43 ± 0.03 1.41 ± 0.07 3007 0.3 30.1 5 ± 5 0.87 ± 0.09 0.48 ± 0.04 1.53 ± 0.10

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Table 4: Effective Beta and Gamma Dose Rates Following Water Correction (cont)

SULT Water Contents/% Effective Dose Rate/mGy a-1 No Field Sat Betaa Gamma Totalb Assumed 3008 0.6 27.8 5 ± 5 0.84 ± 0.07 0.49 ± 0.03 1.52 ± 0.08 3009 0.5 25.1 5 ± 5 0.86 ± 0.09 0.47 ± 0.04 1.52 ± 0.10 3010 0.9 27.9 5 ± 5 0.94 ± 0.10 0.51 ± 0.04 1.63 ± 0.10 3011 0.9 28.9 5 ± 5 0.88 ± 0.07 0.46 ± 0.03 1.52 ± 0.08 3012 2.2 32.6 5 ± 5 0.99 ± 0.09 0.54 ± 0.04 1.71 ± 0.10 3013 0.6 27.5 5 ± 5 0.80 ± 0.08 0.44 ± 0.03 1.43 ± 0.08 3014 1.7 39.3 5 ± 5 0.97 ± 0.07 0.51 ± 0.04 1.67 ± 0.08 3015 1.2 26.7 5 ± 5 0.98 ± 0.07 0.51 ± 0.03 1.67 ± 0.08 3016 1 30.4 5 ± 5 0.97 ± 0.07 0.51 ± 0.03 1.67 ± 0.08 3017 0.5 28.5 5 ± 5 0.90 ± 0.08 0.49 ± 0.04 1.57 ± 0.09 3018 1.3 37.3 5 ± 5 1.03 ± 0.07 0.51 ± 0.03 1.72 ± 0.08 a Effective beta dose rate combining water content corrections with inverse grain size attenuation factors obtained by weighting the 150-250 μm attenuation factors of Mejdahl (1979) for K, U, and th by the relative beta dose contributions for each source determined by Gamma Spectrometry; b includes a cosmic dose contribution

Table 5: SAR Quality Parameters Mean Sensitivity Recycling Recovered SUTL No Aliquots Sensitivity c Change/Cycle Zero Cycle IRSL (%) Ratio Dose Gy-1 (%) 3006 16/16 2100 ± 220 8.0 ± 3.9 1.07 ± 0.07 0.08 ± 0.02 6.1 ± 0.7 1.15 ± 0.06 3007 16/16 1480 ± 350 4.9 ± 7.9 1.02 ± 0.07 0.19 ± 0.06 1.6 ± 1.1 1.08 ± 0.09 3008 16/16 1690 ± 170 6.9 ± 3.8 1.12 ± 0.08 0.07 ± 0.02 1.7 ± 0.6 1.16 ± 0.11 3009 16/16 3530 ± 320 6.1 ± 3.2 0.97 ± 0.03 0.03 ± 0.01 -1.1 ± 0.4 1.04 ± 0.05 3010 16/16 1880 ± 220 11.4 ± 4.8 1.04 ± 0.08 0.01 ± 0.03 2.5 ± 0.6 1.06 ± 0.14 3011 16/16 1920 ± 280 10.6 ± 6.3 1.01 ± 0.06 -0.02 ± 0.03 0.4 ± 0.8 0.99 ± 0.07 3012 15/16 1560 ± 320 11.0 ± 8.6 1.12 ± 0.10 0.19 ± 0.07 -1.8 ± 1.9 1.20 ± 0.21 3013 15/16 2720 ± 150 9.5 ± 2.2 1.01 ± 0.03 0.03 ± 0.01 1.4 ± 0.3 1.05 ± 0.04 3014 16/16 1250 ± 200 6.5 ± 5.8 1.06 ± 0.09 0.00 ± 0.05 13.8 ± 1.5 1.08 ± 0.14 3015 13/32 1260 ± 320 -3.9 ± 6.3 1.05 ± 0.11 0.43 ± 0.08 11.2 ± 3.2 1.36 ± 0.24 3016 11/16 1055 ± 130 9.6 ± 5.0 1.18 ± 0.09 0.04 ± 0.03 4.5 ± 1.5 1.13 ± 0.11 3017 26/32 1090 ± 130 8.5 ± 4.6 1.04 ± 0.06 0.11 ± 0.04 1.5 ± 2.0 1.10 ± 0.09 3018 25/32 1070 ± 120 4.7 ± 3.8 1.00 ± 0.07 -0.01 ± 0.06 3.1 ± 1.4 1.22 ± 0.16

Table 6: Comments on Equivalent Dose Distributions; Preferred Estimates in Bold Comments on Stored Dose Distribution/Individual Weighted Robust SUTL No Mean Samples Mean Mean Distribution peak 1-5Gy, tail to 8Gy. Single low precision 3006 4.3 ± 0.8 3.1 ± 0.2 3.6 ± 0.1 high dose aliquot (16 ± 5Gy) 3007 Distribution peak 1-5Gy, tail to 8Gy. Peak centre at c. 3Gy. 3.0 ± 0.2 2.4 ± 0.2 2.9 ± 0.2 3008 Distribution peak 1-7Gy. Peak centre at c. 3.5Gy. 3.9 ± 0.2 3.6 ± 0.3 3.8 ± 0.1 Distribution peak 3-8Gy. Peak centre at c. 5.5Gy. One 3009 5.9 ± 0.4 5.4 ± 0.2 5.7 ± 0.2 saturated aliquot (>20Gy)

3010 Distribution peak 1-5Gy. Peak centre at c. 3Gy. 3.7 ± 0.6 2.8 ± 0.2 3.2 ± 0.2

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Table 6: Comments on Equivalent Dose Distributions; Preferred Estimates in Bold (cont) Comments on Stored Dose Distribution/Individual Weighted Robust SUTL No Mean Samples Mean Mean Distribution peak 2-7Gy, tail to 10Gy. Peak centre at c. 3011 4.2 ± 0.3 3.7 ± 0.2 4.0 ± 0.1 3.5Gy. Distribution peak 1-6Gy, tail to higher dose driven by 3012 single low precision aliquot (21 ± 61Gy). Peak centre at c. 4.9 ± 1.2 2.9 ± 0.3 3.9 ± 0.4 3Gy. 3013 Distribution peak 1-5Gy, centre at c. 3.5Gy 3.7 ± 0.2 3.30 ± 0.13 3.65 ± 0.05 3014 Broad distribution from 0-8Gy 4.6 ± 0.7 2.8 ± 0.4 4.1 ± 0.1 Regenerative dose range extended to 30Gy due to large 3015 11.1 ± 1.0 8.5 ± 1.0 10.8 ± 0.9 number of saturating aliquots. Very broad distribution. 3016 Broad peak 1-7Gy, skewed to higher dose 4.3 ± 0.5 3.6 ± 0.4 4.1 ± 0.2 3017 Broad distribution 1-6Gy, tailing to >15Gy 3.7 ± 0.3 3.0 ± 0.2 3.5 ± 0.5 3018 Broad distribution 1-7Gy, tailing to >15Gy 3.7 ± 0.4 2.8 ± 0.3 3.5 ± 0.3 errors stated: ± weighted standard deviation (weighted error)

Table 7: Quartz OSL Ages

SUTL No. Dose (Gy) (mGy a-1) Dose Rate Years/ka Calendar Years 3006 3.1 ± 0.2 1.41 ± 0.07 2.22 ± 0.17 200 ± 170 BC 3007 2.4 ± 0.2 1.53 ± 0.10 1.92 ± 0.20 AD 100 ± 200 3008 3.6 ± 0.3 1.52 ± 0.08 2.35 ± 0.23 330 ± 230 BC 3009 5.4 ± 0.2 1.52 ± 0.10 3.56 ± 0.29 1540 ± 290 BC 3010 2.8 ± 0.2 1.63 ± 0.10 1.71 ± 0.17 AD 310 ± 170 3011 3.7 ± 0.2 1.52 ± 0.08 2.40 ± 0.20 380 ± 200 BC 3012 2.9 ± 0.3 1.71 ± 0.10 1.71 ± 0.20 AD 310 ± 200 3013 3.30 ± 0.13 1.43 ± 0.08 2.31 ± 0.18 290 ± 180 BC 3014 2.8 ± 0.4 1.67 ± 0.08 1.66 ± 0.24 AD 350 ± 240 3015 8.5 ± 1.0 1.71 ± 0.11 5.10 ± 0.64 3100 ± 650 BC 3016 3.6 ± 0.4 1.72 ± 0.11 2.16 ± 0.24 140 ± 240 BC 3017 3.0 ± 0.2 1.60 ± 0.14 1.89 ± 0.18 AD 130 ± 180 3018 2.8 ± 0.3 1.77 ± 0.11 1.62 ± 0.19 AD 400 ± 190

Table 8: Summary of OSL Samples and Dates Determined SUERC Site Code Description Age (ka) Date Code Sample 042, SUTL3014 Fill of foundation wall cut, Structure 2. 1.66 ± 0.24 AD 350 ± 240 context 131 Sample 046, SUTL3018 Lower fill of outer foundation trench, Structure 1 1.62 ± 0.19 AD 400 ± 190 context 077 Sample 034, SUTL3006 Occupation layer within Structure 2. 2.22 ± 0.17 200 ± 170 BC context 138

Sample 035, Upper layer of sand outside of Structure 2. SUTL3007 1.92 ± 0.20 AD 100 ± 200 context 135 Abandonment/final use of the structure?

Sample 040, SUTL3012 - 1.71 ± 0.20 AD 310 ± 200 context 135

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Table 8: Summary of OSL Samples and Dates Determined (cont)

SUERC Site Code Description Age (ka) Date Code Sample 045, SUTL3017 - 1.89 ± 0.18 AD 130 ± 180 context 135 Sample 036, SUTL3008 Primary occupation layer within Structure 2. 2.35 ± 0.23 330 ± 230 BC context 115 Sample 039, SUTL3011 - 2.40 ± 0.20 380 ± 200 BC context 115 Sample 038, SUTL3010 Lower layer of sand outside of Structure 2. 1.71 ± 0.17 AD 310 ± 170 context 136 Sample 041, SUTL3013 - 2.31 ± 0.18 290 ± 180 BC context 136 Sample 044, SUTL3016 - 2.16 ± 0.24 140 ± 240 BC context 136

Sample 037, Occupation layer, underlies layer 136. Encountered SUTL3009 3.56 ± 0.29 1540 ± 290 BC context 147 below structures 1, 2 and 3.

Sample 043, SUTL3015 Natural deposit/layer. Underlies 115 and 136. 5.10 ± 0.64 3100 ± 650 BC context 143

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