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'''Comment on Higham et al. (2015) re New Chronology for Northeast Thailand'''

Posted by JoyceWhite on 15 Oct 2015 at 22:09 GMT

Comment on Higham et al. (2015) re New Chronology for Northeast Thailand

By Joyce White
Director of the Ban Chiang Project
University of Pennsylvania Museum

“Models are affected by the quality of data included. The neat graphics and mathematical terminology produced by programs such as OxCal can give the illusion of a robust analysis, even where radiocarbon dates are suspected to be systematically incorrect…” (Wood 2015:63)

Declaration of competing interests

PLOS ONE has invited me to comment on Higham et al. (2015). PLOS ONE stipulated that I declare competing interests of which I have several, including that I did not give the Higham team permission to date the Ban Chiang human bone samples. The particular competing interest that PLOS ONE requested that I state is that I (along with Elizabeth Hamilton, White and Hamilton 2009; White 2008) have published results that are disputed in Higham, Douka, and Higham’s (2015) new chronology for northeast Thailand. The commentary below shows why their proposed chronology and the dating for Ban Chiang in particular should not be accepted pro forma or at face value.

Dates for i&i pottery

Higham et al.’s (2015) new chronology relies on Bayesian analyses of predominantly bone and freshwater shell 14C determinations from several sites in northeast Thailand. Based on the discussion below I argue that the bone and shell dates are highly likely to be systematically young probably due to diagenetic alterations not detected in the vetting protocols. That the dates are young can be clearly illustrated with dates from Ban Chiang and Ban Non Wat (BNW) associated with i&i (incised and impressed) pottery that several regional specialists (e.g., Bellwood et al. 2013:160; Higham et al. 2011a; Higham and Rispoli 2014; Rispoli 2007; Rispoli et al. 2013) use as one signal of the “Neolithic” expansion in mainland Southeast Asia.

Recently Bellwood et al. (2013) have presented radiocarbon evidence from charcoal and food residue samples from the site of An Son in southern Vietnam for a basal stratigraphic horizon from which An Son’s i&i pottery was recovered. In their lengthy discussion of the validity of their dates, along with comparisons of congruent dating from sites in central Thailand (especially Nong Nor and Khok Phanom Di) with comparable pottery, they (2013:155) provide a ballpark range of c. 2400-1800 B.C. calibrated for this pottery style. Their thorough discussion does not accept the “old wood” argument for rejecting their numerous charcoal dates. Although they note that in an ideal situation, Bayesian methods might be used to model the calibrated dates, there are sufficient sample and stratigraphic uncertainties that Bellwood et al. state (2013:154), “[u]nder these conditions it is possible that modeling would produce results that are importantly wrong.”

Using this recent Bellwood et al. dating for i&i pottery in southern Vietnam and central Thailand (calibrated 2400-1800 B.C.) as a regional benchmark time range for this regional style, how do the Higham et al. (2015) dates from shell and bone in association with i&i pottery compare? To illustrate this point, I examine shell dates from Ban Non Wat burials and bone dates from Ban Chiang burials associated with this pottery style.

At Ban Non Wat, two shell dates come from burials with i&i pottery, OxA-16700 (3100 ± 28 BP) with Burial 86, and OxA-18133 (3170 ± 27 BP) with Burial 28. (Discussions of vessels from these Ban Non Wat burials as examples of i&i pottery are also found in Rispoli et al. 2013, Figures 6 and 8.) Bone dates from Ban Chiang burials with i&i pottery come from Early Period Phase I and Phase IIc. Ban Chiang BC Burial 44 from Phase I has an i&i vessel (illustrated in White 1986:90) and a bone date OxA-25015 (3242± 26 BP). From Ban Chiang Phase IIc, the double burial Ban Chiang BC Burials 43 and 45 were interred with a large i&i pot, and both burials have bone dates. (See White 2008:96 for an illustration of this EP IIc vessel type; see also White 1986:91.) OxA-25014 (2984± 26 BP) is from Ban Chiang BC Burial 43, and OxA-x-2438-16 (2958 ±29 BP) is from Ban Chiang BC Burial 45. Even at the 95.4% confidence level, not one of the Ban Non Wat shell or Ban Chiang bone dates reported by Higham et al. (2015) even peripherally overlap with Bellwood et al.’s (2013) benchmark span for i&i pottery, as can be seen in Figure 1.

Figure 1: Dates associated with i&i burial pottery from Ban Non Wat and Ban Chiang in comparison with Bellwood et al.’s (2013) benchmark dating range for i&i pottery in southern Vietnam and central Thailand.

http://figshare.com/s/018...

In addition, it is also possible to compare shell dates from Ban Non Wat with bone dates from Ban Chiang for their most similar examples of i&i pottery to evaluate if the two sample types cross-date well. The vessel from Ban Non Wat Burial 28 and the vessel with double burial Ban Chiang BC B. 43 and 45 have notable commonalities. They are large globular to ovoid i&i pots with shoulders decorated with a distinctive zone of incising and impressing in complex motifs. The decorated shoulder zones are separated from their lower cordmarked bodies with an applique cord. Individuals were interred inside both vessels, an infant in the Ban Chiang vessel (Pietrusewsky and Douglas 2002:408) and an old adult male in the BNW Burial 28 vessel (Higham and Wiriyaromp 2010:27). Remarkably, the Ban Non Wat shell date again does not even peripherally overlap with the Ban Chiang bone dates at 95.4% confidence levels. The Ban Chiang bone dates in particular fall far younger (on the order of 500 years) than Bellwood et al.’s benchmark span for i&i pottery.

These data strongly indicate that the bone and shell dates are both incompatible with each other when dating comparable cultural phenomena, and are also systematically too young relative to regional dating for the i&i pottery style. Given the internal consistency of the bone and shell dates within individual sites (and Higham et al. 2015 present no sites that have both bone and shell dates), one can argue that the young bias is generalizable overall to the bone and shell dates from Ban Chiang and Ban Non Wat. Therefore, both the bone and shell dates are considered at best termini ante quem, or dates before which the target archaeological event occurred.

Bayesian analysis cannot correct inherently flawed data as the above quotation by Wood (2015) notes. Thus the Bayesian analyses of the bone dates from Ban Chiang and the shell dates from Ban Non Wat have likely produced results that are “importantly wrong” as Bellwood et al. (2013:154) warn can occur when the input data are flawed.

Why might the shell and bone be producing inaccurately young dates?

Shell Dates

It is suitable to begin with the shell dates, as they provide the majority of the dates used in the Bayesian modelled “index” chronology for Ban Non Wat as well as from other sites in the upper Mun River Valley reported by Higham et al. (2015). The presentations of shell dates in Higham et al. (2015) show concern for contamination that may produce dates that are too old--an “old shell” or reservoir effect--with no attention being paid to the possibility of a “young shell effect” from post-depositional chemical changes (diagenesis) such as are noted by Webb et al. (2007). Higham et al.’s focus on a possible reservoir effect in BNW shell dates appears unwarranted, as the lack of limestone in the Ban Non Wat environment would mitigate against any likely incorporation of old 14C into the shell samples.

In their effort to identify recrystallization that can signal contaminated specimens, Higham et al. (2015:4/20) only mention that, “A shell fragment was… tested for recrystallization using the Feigl staining method; when no recrystallization was observed the fragment was crushed and prepared for dating.” The Feigl protocol tests for the presence of secondary calcite on aragonitic carbonates according to Higham (2015). However, this argument completely misses the point raised by Webb et al. (2007) on vetting protocols for freshwater shell for recrystallization. Tests only for calcite will not detect the recrystallization of aragonite that can occur under certain geochemical conditions.

Webb et al. (2007:805) note that up until recently “…vetting techniques for freshwater shells have been based on the assumption that diagenetic alteration would yield calcite.” By using Raman spectroscopy they found calcite-free diagenetic alteration, whereby aragonite precipitated instead of the more common calcite under certain geochemical conditions, specifically high magnesium: calcium ratios and salinity. They state:

“The reliability of bivalve shells for dating rests partly on the ease with which subsequent diagenetic alteration can be recognized; typically, wherein original shell aragonite is replaced by calcite in meteoric environments. Here we document… freshwater bivalve shells wherein meteoric diagenesis involved syntaxial overgrowth of aragonite cement on original aragonite shell biocrystals. Aragonite cement was identified in situ using Raman microspectroscopy and formed rather than calcite as a result of unusually high Mg:Ca ratios in local groundwaters. Thus, altered shells contain diagenetic 14C, rendering their dates unreliable, but they may slip past common vetting techniques because (1) epitaxial cements are not readily apparent petrographically because they are in optical continuity with adjacent biocrystals; (2) X-ray diffraction indicates that no calcite is present; (3) alteration is not apparent in cathodoluminescence studies; and (4) stable isotopes of C and O are difficult to interpret in shells that originate in terrestrial meteoric environments. Hence… groundwater chemistry should be considered before accepting bivalve-based radiocarbon dates uncritically.” (Webb et al. 2007:803)

Routine vetting techniques such as those used at Oxford and other labs employing XRD are likely to miss the precipitated aragonite (Busschers et al. 2014), but Raman spectroscopy is sensitive to spectra not detected with XRD and can identify the precipitated aragonite (Webb et al. 2007).

The potential for precipitated aragonite introducing exogenous young carbon is likely high given the soil chemistry of Ban Non Wat, and in fact northeast Thailand generally. The high magnesium:calcium ratios and salinity that are related to aragonite recrystallization are associated with sediments from old sea beds. Much of northeast Thailand overlies old sea beds of such richness that salt extraction is an important industry region-wide. As such, it seems highly likely that shell from sites in northeast Thailand would have diagenetic changes that would introduce young carbon and contraindicate their reliability for 14C dating. Higham et al. (2015) do not mention incorporating these soil chemistry issues as part of their assessments. Yet King et al. (2011) report on soil chemistry studies at Ban Non Wat that found high soil concentrations of magnesium and sodium, specifically the elements that can signal likely diagenetic contamination of shell by young carbon (Webb et al. 2007).

The protocols described by Higham et al. (2015) for evaluating their shell dates did not rule out diagenetic contamination by young carbon. Taylor and Bar-Yosef (2014: 74) conclude that the “use of non-marine shells for dating should probably be restricted to situations where… detailed studies of the geochemistry of the freshwater environment have been done.” Given that the problematic groundwater chemistry at BNW was apparently not taken into consideration in the vetting and interpretation of the Ban Non Wat and other Upper Mun River Valley shell dates, and that the shell was not assessed with techniques such as Raman spectroscopy that can detect the problematic aragonite recrystallization, the shell dates in Higham et al. (2015) are suitably considered termini ante quem, following the examples of Busschers et al. (2014), Lai et al. (2014), and Webb et al. (2007).

Bone Dates

The dates for Ban Chiang used by Higham et al. (2015) rest on what they term bone “collagen.” Evidence is presented above that Ban Chiang bone dates are younger than shell dates from Ban Non Wat for comparable cultural deposits, and far younger than the dating for the comparable i&i ceramic horizon in southern Vietnam and central Thailand (cf. Bellwood et al. 2013). Why might the bone dates be so young?

Recently there is greater appreciation in the radiocarbon literature that the ultrafiltered “collagen” product is actually heterogeneous and has other constituents which can produce unreliable radiocarbon dates, depending on soil chemistry, pretreatment protocols, and other factors. A recent inter-laboratory assessment of bone dating compared protocols and results from four radiocarbon labs—Oxford, Groningen, Kiel, and the University of California, Irvine—for a bone sample of well-established age c. 13000 cal. BP (Fiedel et al. 2013). The study found that ”collagen” samples, including some that underwent ultrafiltration at Oxford, were significantly younger than expected for a sample dated in the four different laboratories. Gillespie et al. (2015) also report erroneously young ages from the application of Oxford’s ultrafiltration method. Although some problematic “collagen” dates are noted for Pleistocene contexts with obvious high humic contamination, problematic dates are also found in Holocene contexts. Bones with less than 1% “collagen” yield often have seriously anomalous dates and, though less common, “bones with collagen yields between 1% and 5% have yielded problematic 14C ages, typically at the level of a few hundred years” (Taylor and Bar-Yosef 2014:82).

A probable reason for young “collagen” dates is that contaminants remain in the ultrafiltered samples. Boudin et al. (2013: 2039) recently note, “[u]ltrafiltration of bone collagen… is an effective method for the removal of low molecular weight contaminants from bone collagen but it does not remove high molecular weight contaminants, such as cross-linked humic-collagen complexes [emphasis added].” Furthermore, regarding collagen dating, Marom et al. (2012: 6878) state: “[T]he extracted bulk gelatin can be heterogeneous and include, or be cross-linked to, potential contaminants from the depositional environment, such as humic and fulvic acids, rootlets, cellulose, sediments, and other plant and animal remains including amino acids from bacteria and micro-organisms.”

In “Supporting information,” Higham et al. (2015) note that the bone samples they dated met criteria for suitability for dating, stating that the C:N ratios in bone samples, the routine way ultrafiltration samples are vetted, “were well within acceptable ranges.” However, Marom et al. (2013:705) comment that merely determining that the C:N ratio falls between 2.9-3.6, a routine approach for identifying contamination, is not precise enough to rule out contamination.
The Oxford University Accelerator Unit (ORAU) has recently undertaken analyses of “collagen” extracts from their ultrafiltration protocol in order to investigate the heterogeneity of the product. The study notes that (Brock et al. 2013:445) “…the final product of “collagen” extraction at ORAU appears to be an aggregate consisting of a range of proteins of different molecular weights, including collagen, as well as some other organic matter and inorganic species. Ultrafiltration is removing some, but not all, of the <30kDa fraction from the samples.” They go on to state (Brock et al. 2013:461): “Reaching definitive conclusions regarding what ultrafilters remove from bone “collagen” is rendered more challenging because of the wide spectrum of diagenetic processes and contamination influences on archaeological bone.”

Taylor and Bar-Yosef (2014:77) note that the term “collagen” is being inaccurately used in many publications presenting bone dates. They state that collagen “should be used only when there is some independent data presented that the fraction contains only or primarily the protein collagen. One standard method to demonstrate this analytically is to obtain a profile of the amino acid components of such a fraction… In the absence of this or other appropriate data, the term “total acid insoluble” can be used to correctly characterize this fraction” (Taylor and Bar-Yosef 2014: 77). No amino acid profile has been presented by Higham et al. (2015) to support their claim that only collagen was being dated from Ban Chiang bone or the bone from other sites.

In summary, there is a growing appreciation that the phrase “collagen date” is a misnomer implying a false precision to the ultrafiltered product. Dating publications are beginning to put “collagen” in quotations (e.g., Brock et al. 2013), or use other phrases such as “high-molecular weight” (HMW) fraction (Minami et al. 2013). Taylor and Bar-Yosef (2014:81) also suggest “ultrafiltered gelatin,” or “base-insoluble” fraction, among others in order to more accurately label the dated material.

In light of this review of recent literature discussing the heterogeneity of ultrafiltered product, and the evidence that the Ban Chiang bone dates are significantly young in comparison with other regional evidence for comparable material, the Higham et al. (2015) terminology in calling their bone dates “collagen” likely misrepresents the material actually dated in their bone samples and the accuracy of their results. These problems further support consideration of the Oxford bone dates for Ban Chiang as at best termini ante quem.

How do Ban Chiang “rice temper” and “rice phytolith” dates compare to Bellwood et al.’s i&i benchmark dating?

The Higham team has provided extended discussions on potential problems with “rice temper” and “rice phytolith” dates (using quotes to acknowledge a similar problem to “collagen” for issues of sample purity) from Ban Chiang (e.g., Higham et al. 2011b; Higham and Higham 2012; Higham et al. 2015). Some of these dates are one consideration in White and Hamilton’s (2009) model for bronze transmission to Thailand that Higham et al. (2015) challenge. Although no extended discussion is offered here on the many technical issues for “rice temper” and “rice phytolith” dates, one of the technical issues recently has been clarified.

The “rice temper” and phytolith dates used by White and Hamilton in their (2009) argument were published in White (1997) and White (2008). Of “rice temper” dates, only those run at the Arizona Accelerator Mass Spectrometry (AMS) Laboratory were used in White’s chronology. The Ban Chiang “rice temper” dates run at Oxford and published by Hedges et al. (1997) were not included for several reasons, one of which was that the Oxford dates were internally highly inconsistent. The Glusker/White experiments in pretreatment protocols revealed a variety of issues particularly in the sequence of acid and base washes among samples run at Oxford.

However, one issue not apparent at the time of pretreatment protocol experimentation was the different temperatures at which individual radiocarbon labs combusted the pretreated samples. A likely reason for the differences between the Arizona and Oxford sets of Ban Chiang dates is differences between the labs in their 1990s combustion protocols.

Referring to the set of determinations run at Oxford (Hedges et al. 1997), Higham et al. (2011b:588) state that “The Oxford Ban Chiang [rice temper] samples were all combusted at 900° C.” This temperature is thought to release geological carbon from the clay, hence often producing too old dates. However the “rice temper” dates from Ban Chiang published by White (1997, 2008) run at the Arizona AMS Facility were combusted at 400°C in accordance with Arizona’s protocol (correspondence on file in Ban Chiang office). The rationale for the lower temperature is now seen as that “temper-derived carbon tends to be preferentially removed with a lower temperature combustion than the carbon bonded within the clay fraction” (Higham et al. 2011b:588). Currently, direct dating of organic-tempered ceramics using the low temperature combustion protocol is being successfully undertaken in other areas (e.g., Messili et al. 2013). Therefore although “rice temper” samples may not be ideal candidates for radiocarbon dating, unlike the Oxford Ban Chiang “rice temper” dates, the Arizona Ban Chiang “rice temper” dates cannot be arbitrarily dismissed on the basis of combustion temperature because it was in line with combustion protocols in place today.

So how do the Arizona Ban Chiang “rice temper” and “rice phytolith” dates pertinent to i&i pottery compare with Bellwood et al.’s benchmark range for i&i pottery? In Figure 1 are included the two directly relevant dates, the “rice phytolith” date from Early Period Phase I Ban Chiang BC Burial 44, and the “rice temper” date with Early Period Phase IIc Ban Chiang BC Burial 46, another infant burial jar comparable to the BC Burial 43’s vessel discussed above. Note that their 95.4% calibrated ranges are comfortably compatible with the Bellwood et al. (2013) benchmark range for i&i pottery.

Finally one additional Ban Non Wat date is included in Figure 1, the date (OxA-11722, 3680±45 BP) from charcoal recovered from inside Burial 28’s i&i vessel. Because it was so much older than the favored shell date from the same grave (OxA-18133), it was dismissed as having an old wood effect (Higham et al. 2011a:247). Yet the charcoal date is the one that is consistent with Bellwood et al.’s (2013) benchmark range for i&i pottery.

Conclusions

The shell and bone dates presented in Higham et al. (2015) are highly likely to be systematically young, and their Bayesian modelling has produced a profoundly flawed chronology for northeast Thailand, not the “master key” or meaningful “anchor” upon which to interpret the appearance of metallurgy and its possible impact on prehistoric societies. The bone and shell dates do not overlap with each other for closely comparable cultural phenomena, and they are far younger than the dated evidence for comparable phenomena in other parts of Southeast Asia, such as at An Son (Bellwood et al. 2013).

Unless An Son’s basal horizon’s current dating is rejected by Bellwood et al. and they revise their dating of that horizon to c. 1500 B.C. on the basis of different dating, I see no reason to arbitrarily disregard the phytolith date from Ban Chiang BC B.44 on the basis that it “might” be flawed. Instead I observe that it, and the “rice temper” date from EP IIc, are consistent with the larger regional picture advocated by several other regional specialists for dating i&i pottery and for, “a ‘Greater Mekong’ cultural network dating from about 2500 B.C. onward” (Bellwood et al. 2013:160). Therefore, the beginning of the Ban Chiang cultural tradition and Early Period Phase I is considered to date from the late 3rd millennium B.C. regardless of the bone dates presented by Higham et al. (2015).

The clear example of inaccurately young dating for i&i pottery by bone and shell from Ban Chiang and Ban Non Wat provides grounds to suspend acceptance of shell and bone dates for the prehistoric chronology of Thailand until the technical issues are resolved and regionally consistent site sequences emerge.

Only a brief additional comment is offered on one of the larger premises of the Higham et al. (2015:15/20) article, that their new chronology helps to demonstrate a relationship between the appearance of bronze in northeast Thailand and “a rapid rise of a hereditary elite.” There are methodological grounds regarding stratigraphy and taphonomy for questioning the supposed relationship that I will not address here. Nevertheless, supposing it was the case that the appearance of metal had a rapid impact in encouraging hereditary social hierarchy at the site of Ban Non Wat, it would be a highly anomalous occurrence in the prehistory of early metallurgy. With the research undertaken in recent decades on early metallurgical societies, including those using bronze, (e.g., see contributions in Roberts and Thornton 2014), archaeometallurgists now recognize that metal technology usually appears initially in a region in small quantities and insignificant roles (Thornton and Roberts 2014). Only after considerable periods of time, such as centuries after its first appearance, might metal become prominent in archaeological assemblages. Finally, metal, including bronze, rather rarely became a prestige good that was exclusively controlled or consumed by elite (Thornton and Roberts 2014:2).

Rather than a “star burst” metaphor for typical early metal technology adoption, a more apt metaphor for the typical course of metal technology transmission and adoption could be something like “metal technology comes in on little cat feet.” Even if it turns out that the first adoption of copper-base metallurgy at Ban Non Wat did, at that particular site, correlate with the development of marked status differentials (different taphonomic interpretations make this a debatable point, however), this highly atypical occurrence would need much more thorough theoretical explanation than Higham et al. have provided. The occurrence of metal grave goods in ordinary graves in contemporaneous sites like Ban Chiang, Ban Na Di, and Non Nok Tha (called “poor” by Higham [2015] despite one Non Nok Tha bronze age burial having 16 bronze bangles) argues for a value system localized to Ban Non Wat or perhaps the upper Mun River Valley, not generalizable to Thailand or Southeast Asia as a whole.

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Competing interests declared: PLOS ONE has invited me to comment on Higham et al. (2015). PLOS ONE stipulated that I declare competing interests of which I have several, including that I did not give the Higham team permission to date the Ban Chiang human bone samples. The particular competing interest that PLOS ONE requested that I state is that I (along with Elizabeth Hamilton, White and Hamilton 2009; White 2008) have published results that are disputed in Higham, Douka, and Higham’s (2015) new chronology for northeast Thailand. The commentary below shows why their proposed chronology and the dating for Ban Chiang in particular should not be accepted pro forma or at face value.