Baseline bioavailable strontium isotope values for the investigation of residential mobility and resource-acquisition strategies in prehistoric Cambodia

Strontium (Sr) isotope ratios (⁸⁷Sr/⁸⁶Sr) measured in human skeletal material can increase one's understanding of the residential behaviour and resource-acquisition strategies of past populations. The paper maps bioavailable ⁸⁷Sr/⁸⁶Sr variation in 183 plant and soil samples across Cambodia. Bioavailable ⁸⁷Sr/⁸⁶Sr, as measured in plants, differs significantly between four major geological units. The data set will support future investigations of skeletal material from Cambodian archaeological sites. Baseline ⁸⁷Sr/⁸⁶Sr data should be applied judiciously to skeletal populations, and in concert with other lines of evidence, to identify potential geographical outliers rather than to ascribe specific locations from which individuals may have moved.     

Tracing population mobility in the Aegean using isotope geochemistry: a first map of local biologically available Sr/Sr signatures

Strontium isotope ratio (⁸⁷Sr/⁸⁶Sr) analysis of archaeological human skeletal remains is an efficient method of investigating past population movement and residential mobility by determining probable geographical origins for the individuals examined. For this to be achieved, however, a map of biologically available ⁸⁷Sr/⁸⁶Sr signatures across the region investigated is needed. This paper presents a first such map for the Aegean, based on ⁸⁷Sr/⁸⁶Sr values recovered mainly from archaeological animal dental enamel and modern snail shells from sites largely distributed in the southern part of this region. Although not exhaustive, this comprehensive dataset of local biologically available ⁸⁷Sr/⁸⁶Sr signatures shows a marked difference between Mainland sites of the Pindos and Parnassos zones and the islands of south-eastern Aegean crossed by the Sub-Pelagonian zone (0.70808–0.70869), and sites in the central Cyclades and the north-eastern Aegean islands falling into the Attic-Cycladic metamorphic belt and the Vardar zone, respectively (0.70926–0.71187). Biologically available ⁸⁷Sr/⁸⁶Sr values from sites on central Euboea in the Pelagonian zone, south-eastern Attica and the western Cyclades in the Attic-Cycladic metamorphic belt, and on Crete in the Gavrovo zone are also relatively high (0.70853–0.70931), but lower than those recorded for the central Cyclades and the north-eastern Aegean.     

The Movement and Exchange of Dogs in the Prehistoric Caribbean: An Isotopic Investigation

This study explores the feasibility of using strontium isotope (⁸⁷Sr/⁸⁶Sr) analyses of enamel from domestic dogs (Canis familiaris) to investigate networks of exchange in the prehistoric Circum‐Caribbean. Dog teeth were obtained from burial and domestic contexts from two prehistoric sites (Anse à la Gourde and Morel) on Grande‐Terre, Guadeloupe (Lesser Antilles). Strontium isotope results were compared with local biosphere ⁸⁷Sr/⁸⁶Sr data at the scale of the site, island and archipelago. The isotope results indicate both local and nonlocal origins with three dogs (30%) identified as nonlocal (one from Anse à la Gourde and two from Morel). The variance in ⁸⁷Sr/⁸⁶Sr ratios of the nonlocal dog teeth is consistent with diverse multiple origins external to the island of Grande‐Terre but consistent with origins from other islands of the Lesser Antilles. The diverse origins of the nonlocal dog samples indicate that the prehistoric circulation of dogs occurred at multiple scales from regional to long distance. Significantly, the ⁸⁷Sr/⁸⁶Sr ratios of some of the dog teeth are comparable with values of nonlocal humans at Anse à la Gourde determined in previous studies. It is possible that these comparable ⁸⁷Sr/⁸⁶Sr ratios result from similar natal origins, for example if individuals were migrating to Guadeloupe with dogs. The results of this study contribute to an ongoing regional investigation of the economic, social and political roles of animals and animal remains and the multiscalar networks of prehistoric mobility and exchange in the Circum‐Caribbean region. Copyright © 2013 John Wiley & Sons, Ltd.     

Migration in the Nile Valley during the New Kingdom period: a preliminary strontium isotope study

The value of strontium isotope analysis in identifying immigrants at numerous archaeological sites and regional areas has been demonstrated by several researchers, usually by comparing ⁸⁷Sr/⁸⁶Sr values of human tooth enamel and/or bone with the local strontium isotope signature determined by faunal and environmental samples. This paper examines the feasibility of using ⁸⁷Sr/⁸⁶Sr ratios to investigate residential mobility in the Nile Valley region, specifically at the New Kingdom period (∼1050–1400 BC) archaeological site of Tombos (ancient Nubia). Archaeological and textual information regarding this period indicates that immigrant Egyptians and local native Nubians were likely interacting at this site during a period of Egyptian colonial occupation. The results of this study suggest that non-local individuals may be distinguished from locals using ⁸⁷Sr/⁸⁶Sr values and that colonial agents in the Tombos population were probably both local native Nubians and immigrants.     

Oxygen and strontium isotopes as provenance indicators of fish at archaeological sites: the case study of Sagalassos,SW Turkey

In this paper, we investigate the potential use of oxygen and strontium isotope ratios (δ¹⁸O_p and ⁸⁷Sr/⁸⁶Sr) measured in archaeological fish enamel as provenance indicators. δ¹⁸O_p and ⁸⁷Sr/⁸⁶Sr were measured in a suite of archaeological carp remains recovered from the Anatolian townsite of Sagalassos dated to the Early Byzantine period (AD 450–650) and compared to that of modern fish, river and lake waters from the Anatolian region. We used sequential leaches in weak acetic acid to remove diagenetic Sr from fossil tooth enamel, monitoring the effectiveness of this approach by measuring the Sr/Ca ratios of the leachates via an isotope dilution thermal ionization mass spectrometry method (ID-TIMS). δ¹⁸O_p values mostly excluded a riverine origin. ⁸⁷Sr/⁸⁶Sr ratios of one fish overlapped with the ⁸⁷Sr/⁸⁶Sr signatures of two lakes in the Anatolian region, and at least one lake (Gölcük) could be removed as a candidate owing to a very distinctive ⁸⁷Sr/⁸⁶Sr signature not found in any of the fish remains. Most of the tooth samples analyzed could not be assigned a precise geographical origin since the ⁸⁷Sr/⁸⁶Sr ratios measured in enamel did not match that of any of the local lakes selected as potential origin. This result suggests that carp may have originated from lakes that have not yet been sampled, although this conclusion is not supported by other archaeological evidence. Alternatively, the lack of correspondence between lakes and fish Sr isotope ratios highlights several possible sources of uncertainties including spatial heterogeneity in ⁸⁷Sr/⁸⁶Sr ratio within a lake, the contribution of dietary strontium to the ⁸⁷Sr/⁸⁶Sr ratio of fish tooth enamel, and post-mortem alteration of the tooth Sr isotope signal during fossilization. In spite of the high precision of the strontium isotope analyses and the wide range of variation in the surface waters of the Anatolian lakes and rivers, this method may remain limited to distinguishing between lakes situated in regions of bedrock of very distinct age and geology until these sources of uncertainty are more fully investigated.     

From the Piedmont to the Coast: LA-ICP-MS 87Sr/86Sr evidence for short-term,long-distance mobility in the American Southeast

Mounting evidence suggests that the Archaic Southeast shell mound builders had large-scale trade networks and engaged in social aggregations. Here, incremental ⁸⁷Sr/⁸⁶Sr values were measured by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) in third molar enamel samples of 11 individuals interred in the Middle Archaic Harris Creek shell burial mound in St. John's River Valley (SJRV), Florida. Results reveal that SJRV residents engaged in short-term, long-distance mobility up to the Piedmont margin and excursions into coastal areas, consistent with direct trading and social gatherings. Two individuals are interpreted as migrants from central Tennessee, suggesting a link to the Ohio River Valley shell mound builders.     

A strontium isotope analysis on the relationship between ritual tooth ablation and migration among the Jomon people in Japan

Distinct patterns can be discerned in the extensive ritual tooth ablation found among the human skeletal remains of the Late–Final Jomon period (ca. 3200–2800 cal BP) in Japan. Based on comparative observations of sex and grave patterns in the skeletal remains, two major patterns in ritual tooth ablation, termed type 4I and type 2C, have been assigned to locals and immigrants, respectively. In order to test this hypothesis, strontium (Sr) isotope (⁸⁷Sr/⁸⁶Sr) analyses were performed on human skeletal remains from the Yoshigo shell mound in Aichi Prefecture, central Japan. Plants in the surrounding area were also examined to illustrate the geographic ⁸⁷Sr/⁸⁶Sr distribution. The Sr isotopic variation in human tooth enamel (⁸⁷Sr/⁸⁶Sr = 0.70868–0.71028) was greater than that in human bones (⁸⁷Sr/⁸⁶Sr = 0.70871–0.70943). Individuals with higher Sr isotope ratios in their tooth enamel than seawater Sr values of 0.7092 can be identified as immigrants (36% of population). The presence of these isotopically identified immigrants between both type 2C and type 4I individuals does not support the previous hypothesis. The intra-population ⁸⁷Sr/⁸⁶Sr distribution of tooth enamel of type 2C individuals showed a significantly higher mean ratio than that of type 4I individuals, suggesting a higher proportion of immigrants among the former.     

The consequences of Wari contact in the Nasca region during the Middle Horizon: archaeological,skeletal, and isotopic evidence

During the Middle Horizon (AD 650–1000), the Wari polity expanded its sphere of control in various regions of the Andes, including Nasca on the south coast of Peru. The nature of the interaction between Wari and local communities varied. This study explores the consequences of Wari contact in the Nasca region at the site of La Tiza, which includes individuals dated to the Early Intermediate, Middle Horizon, and Late Intermediate periods. Using evidence for burial ritual along with demographic, paleopathological and isotopic data, population composition, mobility, diet, and health are investigated. δ¹³C data indicate a relatively stable diet through time at La Tiza with evidence for continued maize consumption, and paleopathological results indicate health problems associated with this type of diet. δ¹⁸O and ⁸⁷Sr/⁸⁶Sr data suggest that most of the individuals buried at La Tiza were local to the area. However, two female adults from the Middle Horizon burials are characterized as nonlocal based on δ¹⁸O and ⁸⁷Sr/⁸⁶Sr values and several individuals overlap with the ⁸⁷Sr/⁸⁶Sr local range for the Wari heartland. In conjunction with the use of new tomb types during this period these results highlight the ideological and populational changes occurring with Wari contact at La Tiza.     

BRONZE AGE CHILDHOOD MIGRATION OF INDIVIDUALS NEAR STONEHENGE,REVEALED BY STRONTIUM AND OXYGEN ISOTOPE TOOTH ENAMEL ANALYSIS*

Contrasting lifestyles are recorded by the isotope composition of Bronze Age Beaker people (c. 2500–2000 bc ) from three burial sites (Boscombe Down, Normanton Down and the ditch around Stonehenge) at or near to the Stonehenge monument in Wiltshire, southern England. Seven individuals (three adults, a sub‐adult, two juveniles and an infant) were recovered from a single grave at Boscombe Down. Strontium and oxygen isotope analysis of tooth enamel from two teeth (a premolar and third molar) from each of three of the adults in this grave (referred to as Boscombe Bowmen) show that they had all shared a pattern of mobility and migration during their lives. The three adult males spent their early childhood (as represented by data from the premolar teeth) in an area with a radiogenic ⁸⁷Sr/⁸⁶Sr isotope signature of around 0.7135. They each then moved, during early adolescence (as represented by the third molar results), to a less radiogenic area, where they acquired an ⁸⁷Sr/⁸⁶Sr signature of around 0.7112. This implies that they must then have travelled to the Stonehenge area of Wiltshire at a later time in their lives. Wales provides the closest area with rocks that supply suitable ⁸⁷Sr/⁸⁶Sr ratios and δ¹⁸O isotope compositions for these individuals, although other areas of Palaeozoic rock, such as Scotland and parts of Europe, cannot be ruled out. Enamel from the two juveniles from the Boscombe Down burial yields ⁸⁷Sr/⁸⁶Sr ratios of 0.7098 and 0.7099, and strontium concentrations for both of 55 ppm. The very close match of the data for the two juveniles supports the possibility that they were raised in the same environment. The difference in strontium isotope data between the juveniles and three adult males described above shows that the children did not come from the same homeland as the adults with whom they share a grave. The two adult males from the single burials at Normanton Down, and from Stonehenge itself, had static lifestyles and show no evidence of migration, in contrast to the Boscombe Bowmen. Their oxygen and strontium data are consistent with a childhood in the Stonehenge area.     

Monks on the move? An assessment of mobility at the medieval Nubian monastery of Ghazali,Sudan (ca. 680–1,275 CE)

The location of Ghazali monastery away from the Nile valley within the relatively isolated environs of the Bayuda desert presents a landscape suggestive of mobility toward the monastery by those who chose to reside there as monks. To assess this potentiality, a sample of 37 individuals from the monastic cemetery (Cemetery 2) were analysed for ⁸⁷Sr/⁸⁶Sr and δ¹⁸O to assess residency during dental enamel formation. The data generated bring into question the nature of mobility to Ghazali monastery, particularly in regard to the potential movement of people from the Nile valley, adjacent desertic landscapes, and further afield.     

Variation in strontium isotope ratios of archaeological fauna in the Midwestern United States: a preliminary study

Strontium isotope values (⁸⁷Sr/⁸⁶Sr) in bone and tooth enamel have been used increasingly to identify non-local individuals within prehistoric human populations worldwide. Archaeological research in the Midwestern United States has increasingly highlighted the role of population movement in affecting interregional cultural change. However, the comparatively low level of geologic variation in the Midwestern United States might suggest a corresponding low level of strontium variation, and calls into question the sensitivity of strontium isotopes to identify non-local individuals in this region. Using strontium isotopes of archaeological fauna, we explore the degree of variability in strontium ratios across this region. Our results demonstrate measurable variation in strontium ratios and indicate the potential of strontium analysis for addressing questions of origin and population movement in the Midwestern United States.     

Strontium Isotopes in the Investigation of Early Glass Production: Byzantine and Early Islamic Glass from the Near East*

⁸⁷Sr/⁸⁶Sr ratios have been determined for glasses from four production sites, dated to between the sixth and the 11th centuries, in the Eastern Mediterranean region. On the basis of elemental analyses, the glasses at each location are believed to have been melted from different raw materials. Two glass groups, from Bet Eli‘ezer and Bet She‘an, in Israel, are believed to have been based upon mixtures of Levantine coastal sands and natron, and have ⁸⁷Sr/⁸⁶Sr ratios close to 0.7090, plus high elemental strontium, confirming a high concentration of modern marine shell (⁸⁷Sr/⁸⁶Sr ~ 0.7092) in the raw materials. The isotopic compositions of these two groups of glasses differ slightly, however, probably reflecting a varying ratio of limestone to shell because the sands that were utilized were from different coastal locations. Natron‐based glasses from a workshop at Tel el Ashmunein, Middle Egypt, have ⁸⁷Sr/⁸⁶Sr values of 0.70794–0.70798, and low elemental strontium, consistent with the use of limestone or limestone‐rich sand in the batch. High‐magnesia glasses based on plant ash, from Banias, Israel, have ⁸⁷Sr/⁸⁶Sr values of 0.70772–0.70780, probably reflecting the isotopic composition of the soils that were parental to the plants that were ashed to make the glass. Strontium and its isotopes offer an approach to identifying both the raw materials and the origins of ancient glasses, and are a potentially powerful tool in their interpretation.     

Diet and mobility in Middle Archaic Florida: stable isotopic and faunal evidence from the Harris Creek archaeological site (8Vo24), Tick Island

We explore diet and mobility in Middle Archaic Florida using human burials and faunal remains from the Harris Creek archaeological site (8Vo24) on Tick Island. We conducted stable carbon and oxygen isotopic (δ¹³C, δ¹⁸O) analyses of 50 human enamel samples and strontium isotopic (⁸⁷Sr/⁸⁶Sr) analysis of a subset of 10. Most individuals (46/50) subsisted on local freshwater and terrestrial resources, with relatively depleted δ¹³C values (C₃) and δ¹⁸O values matching those of central and north Florida water resources within the St. Johns River valley. Eight of 10 burials have local, within valley ⁸⁷Sr/⁸⁶Sr values. Two human burials yield marine δ¹³C and ⁸⁷Sr/⁸⁶Sr values, which we interpret as evidence for across valley movement from the coast. Another two individuals show depleted δ¹⁸O values, likely obtained from northern rivers. We also identified potential food resources and non-local foods from the Harris Creek faunal assemblage. We found six species with estuarine and marine habitat preferences; two of which, whelk and quahog, indicate that people of Harris Creek traveled to or traded with coastal areas.     

Baseline data for Andean paleomobility research: a radiogenic strontium isotope study of modern Peruvian agricultural soils

While the use of radiogenic strontium isotope values to examine paleomobility is increasingly common in the Andes, and beyond, many questions about baseline variability remain. To better understand baseline radiogenic strontium isotope compositions in the Andes, we present new ⁸⁷Sr/⁸⁶Sr values from Peruvian soil samples. Modern soil samples were collected from agricultural fields from the following areas in central and southern Peru: Arequipa, Atico, Camaná, Chala, Cusco, Ica, Ilo, Lima, Mejía, Moquegua, Nazca, Ocoña, Palpa, Pisco, Puno, Tacna, and Yauca. Samples were partially dissolved to better approximate the bioavailable strontium. Radiogenic strontium isotope values from the partially dissolved soil samples range from ⁸⁷Sr/⁸⁶Sr?=?0.70202 to 0.71894 and, for all soil samples, have a mean of ⁸⁷Sr/⁸⁶Sr?=?0.70773?±?0.00166 (1σ, n?=?114). In general, the ⁸⁷Sr/⁸⁶Sr values measured for soil samples collected from modern agricultural fields reflect the expected ⁸⁷Sr/⁸⁶Sr values based on bedrock geology. Comparing our new soil data with published radiogenic strontium isotope data for bedrock, soil, water, and faunal samples provides constraints on the regions in the Andes that can, and cannot, be distinguished through radiogenic strontium isotope analysis.     

Spatial variation of biologically available strontium isotopes (Sr/Sr) in an archipelagic setting: a case study from the Caribbean

This paper presents the results of strontium (Sr) isotope analysis of modern and archaeological animal remains and modern plant samples from the Caribbean region. The goal is to assess if patterns of human mobility can be determined from the archaeological record in an archipelagic setting. The range of variability and spatial distribution of biologically available strontium isotope signatures is reported and data evaluated to determine if sufficient heterogeneity exists to permit the identification of mobility despite the presence of potentially large contributions of marine strontium in island and coastal ecosystems. The (is)landscape is divided into several sub-regions based on the age and lithology of underlying geology and the variability of ⁸⁷Sr/⁸⁶Sr ratios is reported as; mean ⁸⁷Sr/⁸⁶Sr ± 2 standard deviations, number of samples: 1) Volcanic and Intrusive rocks (0.7077 ± 0.0019; n = 162); 2) Cretaceous–Miocene Limestone (0.7085 ± 0.0009; n = 50); 3) Pliocene–Quaternary Limestone (0.7091 ± 0.0004; n = 54); 4) Sedimentary Deposits (0.7094 ± 0.0015; n = 16); 5) Metamorphic Deposits (0.7104 ± 0.0014; n = 6). There are substantial differences between expected ⁸⁷Sr/⁸⁶Sr values based on associated geology and measured ⁸⁷Sr/⁸⁶Sr in flora and fauna samples. These differences emphasize the importance of focusing on bioavailable strontium, as opposed to geological proxies, for estimations of Sr isotope ranges, especially in archipelagic environments. While some overlap exists between the ⁸⁷Sr/⁸⁶Sr ranges of certain sub-regions, other sub-regions possessed limited variation and could be distinguished based on strontium isotope data. This spatial patterning of biologically available strontium indicates that strontium isotope analyses can be successfully applied to the archaeological study of human mobility within the Caribbean region.     

Migration and mobility at the Late Lapita site of Reber–Rakival (SAC), Watom Island using isotope and trace element analysis: a new insight into Lapita interaction in the Bismarck Archipelago

This paper uses strontium isotope (⁸⁷Sr/⁸⁶Sr), oxygen isotope (δ¹⁸O) and Ba/Sr trace element data in archaeological tooth enamel samples to investigate migration and mobility at the Late Lapita site of SAC, Watom Island in the Bismarck Archipelago. Previous archaeological models have identified Lapita mobility at a community level using obsidian distribution patterns and changes in ceramic design, whereas isotope and trace element data can potentially reconstruct prehistoric mobility on an individual level. Human and pig teeth were sampled from SAC and a selection of human teeth were included from the Late–Post Lapita site of Lifafaesing, Tanga Islands as a geographic/geological comparison.The results indicate that there is a large amount of isotopic variation in the Bismarck Archipelago which is useful for identifying non-local individuals and possibly determining their origins. One human individual and several pigs were suggested as coming from elsewhere in the region. Three potentially separate locations were identified for the non-local pigs. It is argued, using the data from SAC, that Late Lapita communities in the Bismarck Archipelago were more mobile than previously assumed. The potential for identifying individual migrants in a Lapita context are discussed in terms of assessing the more subtle aspects of Lapita society in the Southwest Pacific Islands.     

Reconstructing Middle Horizon mobility patterns on the coast of Peru through strontium isotope analysis

The pre-Columbian coastal site of Ancón, Peru frequently has been interpreted as an important outpost of the highland Wari Empire, inhabited by individuals from the sierra and the coast. In order to test this hypothesis, bone–tooth pairs from 35 Middle Horizon (550 AD–1000 AD) Ancón skeletons were analyzed for strontium isotopes, which vary by geologic provenance. Results indicate that 34 of the 35 individuals have ⁸⁷Sr/⁸⁶Sr enamel and bone values higher than Ancón's biologically available strontium isotope range. Nitrogen and carbon isotope data from a subset of the Ancón skeletons suggest that the higher than expected ⁸⁷Sr/⁸⁶Sr values among the Ancón sample likely reflects a diet rich in marine resources rather than migratory activity, and highlight the need to use multiple lines of evidence to track residence change at sites where individuals relied on resources other than locally grown terrestrial foods. The one remaining individual, a young female of elite status, has an enamel strontium isotope signature much lower than the available data for local fauna and soil indicating that she was not raised locally. Her enamel ⁸⁷Sr/⁸⁶Sr ratio fits well within the range of strontium isotope values established for the inland Wari site of Conchopata [Tung, T.A., Knudson, K.J. Social identities and geographical origins of Wari trophy heads from Conchopata, Peru. Current Anthropology, in press.], and suggests that highland, Wari immigrants may have been present at Ancón during the Middle Horizon.     

Pastoralist Mobility in Bronze Age Landscapes of Northern Kazakhstan: 87Sr/86Sr and δ18O Analyses of Human Dentition from Bestamak and Lisakovsk

ABSTRACT

The role of migration and mobility of people across the steppe has often been cited as key to Bronze Age developments across Eurasia, including the emergence of complex societies in the steppe and the spread of material culture. The central Eurasian steppe (CES) is a focal point for the investigation of the shifting nature of pastoral societies because of the clear transition in archaeological patterning that occurred from the Middle (MBA) to Late Bronze Age (LBA). The spread of LBA (1700–1400?cal BC) Andronovo cultural materials found across wide swaths of the steppe provide indirect evidence for broad scale interactions, but the degree to which people moved across the landscape remains poorly understood. This study takes a first step into documenting human movement during these critical periods through strontium (⁸⁷Sr/⁸⁶Sr) and oxygen (δ¹⁸O) isotopic analyses of tooth enamel recovered from human individuals buried in the cemeteries of Bestamak (MBA) and Lisakovsk (LBA) in northern Kazakhstan. Strontium isotope results, referenced against the distribution of contemporary bioavailable strontium in the vicinity of both sites, suggest local communities engaged in small-scale mobility with limited ranges. Reduced strontium and oxygen isotopic variation visible in humans from Lisakovsk suggests mobility decreased from the Middle to Late Bronze Age likely indicative of a shift in resource and landscape use over time.     

PATTERNS OF IRON AGE HORSE SUPPLY: AN ANALYSIS OF STRONTIUM ISOTOPE RATIOS IN TEETH*

This paper presents a pilot study of strontium (Sr) isotope ratios from Iron Age horse tooth enamel samples. It compares ⁸⁷Sr/⁸⁶Sr ratios from horse teeth to estimates for local ranges of biologically available strontium, to investigate whether horses were being bred at the sites where their remains were discovered. A horse from Middle Iron Age Rooksdown, Hampshire, was not bred at the site but, rather, came from as far away as Wales, Scotland or continental Europe. Horse teeth from Middle Iron Age Bury Hill, Hampshire, returned ⁸⁷Sr/⁸⁶Sr values typical of local chalkland.     

Strontium isotope ratios in fossil teeth from South Africa: assessing laser ablation MC-ICP-MS analysis and the extent of diagenesis

This study tests the precision and accuracy of laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) for measuring strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) in fossil teeth from Swartkrans and Sterkfontein in South Africa, and explores the extent of diagenesis in these specimens. Compared to solution MC-ICP-MS or thermal ionization mass spectrometry (TIMS) methods, LA-MC-ICP-MS can be faster and less expensive, but has lower precision and accuracy. We found that ⁸⁷Sr/⁸⁶Sr ratios in fossil rodent teeth measured by LA-MC-ICP-MS were offset from solution values by a mean of 0.0005 ± 0.0010 (2σ). Because of the very wide spread of biologically available ⁸⁷Sr/⁸⁶Sr ratios (∼0.710 to ∼0.790) in the region, LA-MC-ICP-MS is more than sufficient for assessing the geographic origins of the fossil rodents. The concentration of strontium in modern and fossil enamel from the area is statistically indistinguishable, as is the range of ⁸⁷Sr/⁸⁶Sr ratios in modern rodents and fossil rodents from Swartkrans. Thus, there is little evidence of diagenetic Sr in the fossil enamel. In contrast, the fossil dentine may contain up to ∼50% diagenetic strontium, although many dentine ⁸⁷Sr/⁸⁶Sr ratios are still far removed from the background cave value of 0.729. We propose that LA-MC-ICP-MS will also be of use for investigating the geographic origins of other, non-rodent fossil teeth from the Sterkfontein and Swartkrans collections, and may prove of similar utility at other suitable sites.