Strontium Isotope Analysis Research Articles

The provisioning of nineteenth century Zulu capitals, South Africa: Insights from strontium isotope analysis of cattle remains

This study examines animal provisioning at royal capitals in the Zulu Kingdom, the most powerful polity in south-eastern Africa during the nineteenth century (c. 1816–1879). Historical records indicate the royal family and its retainers at the king’s residence (royal amakhanda) were supported by the collection of surpluses from rural chiefdoms and special herds and crops worked by the army, while regiments were largely sustained by the homesteads from which they originated. It is implied that cattle were acquired through a combination of local production, tribute from allied chiefdoms, and plunder from raiding. In this paper, we present the first archaeological evidence for cattle mobility through Sr ratios (87Sr/86Sr) for 46 cattle teeth and one sheep/goat tooth from King Dingane’s capital at uMgungundlovu in the emaKhosini basin (1828–1839). Relative to a local biologically available strontium isotope framework we establish for the basin, the results show that over half the cattle were raised within the basin. Regional isotopic data indicate cattle were transferred from herd land to the west of the capital, by tribute or expropriation in the south of the kingdom, and raiding is suggested by cattle from areas controlled by the Swazi Kingdom to the north.

Ostrich eggshell bead strontium isotopes reveal persistent macroscale social networking across late Quaternary southern Africa

Hunter-gatherer exchange networks dampen subsistence and reproductive risks by building relationships of mutual support outside local groups that are underwritten by symbolic gift exchange. Hxaro, the system of delayed reciprocity between Ju/'hoãn individuals in southern Africa's Kalahari Desert, is the best-known such example and the basis for most analogies and models of hunter-gatherer exchange in prehistory. However, its antiquity, drivers, and development remain unclear, as they do for long-distance exchanges among African foragers more broadly. Here we show through strontium isotope analyses of ostrich eggshell beads from highland Lesotho, and associated strontium isoscape development, that such practices stretch back into the late Middle Stone Age. We argue that these exchange items originated beyond the macroband from groups occupying the more water-stressed subcontinental interior. Tracking the emergence and persistence of macroscale, transbiome social networks helps illuminate the evolution of social strategies needed to thrive in stochastic environments, strategies that in our case study show persistence over more than 33,000 y.

The spatial distribution and geochemical variation of fault and fracture hosted calcite and gypsum cements in the eastern Bristol Channel Basin

Abstract The spatial distribution and geochemical variation of fault- and fracture-hosted cements can be used to reconstruct the evolution and migration of pore fluids in sedimentary basins. Geochemical data, from stable oxygen and carbon isotope and strontium isotope analyses, of calcite and gypsum cements provide valuable insights into the source of pore fluids and their evolution in the eastern Bristol Channel Basin. Overall, at both an outcrop-scale and a basin-scale there were no observable relationships between the dip angle and direction of fractures with the oxygen and carbon isotopic composition of calcite cements, indicating that the movement and distribution of fluids in fractures is not controlled by the orientation of fracture opening. Radiogenic strontium isotopic compositions of calcite and gypsum cements indicate at least two different mineralising fluid compositions that are strongly controlled by the lithologies (fossiliferous limestones and shales, and marls with gypsum nodules, respectively) in which they occur. These fluids originated as connate pore fluids that were altered during the diagenesis of their host lithologies. Mineralising fluids within the Lower Jurassic Lias Group are characterised by enriched oxygen and strontium isotopic compositions and relatively depleted carbon isotopic compositions, associated with the alteration of labile minerals and carbonaceous fossils. Mineralising fluids within the Triassic Mercia Mudstone Group have enriched strontium isotopic compositions as a result of the interaction of fluids with evaporitic intervals. The mineralising fluids were redistributed through migration along faults and their associated damage zones. This study highlights the importance of integrating a range of geochemical analyses when attempting to understand the source of fluids and their evolution through time. The findings from this study can also be applied to nearby petroleum producing basins, e.g. the Wessex Basin, where equivalent rocks are economically significant source rocks and caprocks and have experienced similar structural histories.

Comparisons of calcium sources between arboreal and ground‐dwelling land snails: implication from strontium isotope analyses

AbstractCalcium (Ca) is an essential element for many animal species, especially for land snails with shell structures. The availability of Ca imposes constraints on their growth and survival as well as their density and distribution. However, little is known about how they obtain Ca in a natural environment. For example, many species of land snails feed on lichens, but lichens have Ca in the form of calcium oxalate, making it difficult for animals to utilize. Therefore, we predicted that lichens or a representative food source of land snails is not necessarily a major source of Ca, and there may be another source for shell development. The strontium isotope ratio (87Sr/86Sr) is a useful index for estimating the source of Ca. With this technique, we estimated Ca sources of an arboreal land snail, Euhadra brandtii sapporo, and tested the hypothesis described above. The data for the 87Sr/86Sr ratio show that E. brandtii sapporo did not obtain Ca from lichens and moss in tree canopies, although the data for the δ15N and δ13C show that the species’ main food source may be lichens and moss. We also conducted the isotope analysis of Ezohelix gainesi as a reference, which inhabits the forest floor. The data of δ15N and δ13C show E. gainesi may feed mainly on litter. The 87Sr/86Sr ratio was markedly different from that of arboreal E. brandtii sapporo, and this ground‐dwelling snail likely obtains Ca from ground litter or soil. Our results indicate that Ca sources are different between arboreal and ground‐dwelling land snails, and the former obtains Ca through something other than its major food sources, perhaps from stemflow and precipitation. Differences in the two species indicate that land snails utilize different Ca sources depending on their habitats.

Analysing Sr isotopes in low‐Sr samples such as single insects with inductively coupled plasma tandem mass spectrometry using N2O as a reaction gas for in‐line Rb separation

RationaleStrontium isotopes are valuable markers of provenance in a range of disciplines. Limited amounts of Sr in low‐mass samples such as insects mean that conventional Sr isotope analysis precludes their use for geographic origins in many ecological studies or in applications such as biosecurity. Here we test the viability of using inductively coupled plasma tandem mass spectrometry (ICP‐MS/MS) with N2O as a reaction gas for accurately determining Sr isotopes in insects with Sr < 100 ng.MethodsStrontium isotopes were determined in solution mode using ICP‐MS/MS with 0.14 L/min N2O as a reaction gas to convert Sr+ into SrO+ for in‐line separation of 87Sr from 87Rb. The Sr isotope reference standards NIST SRM 987, NIST SRM 1570a and NIST SRM 1547 were used to assess accuracy and reproducibility. Ten insect species collected from the wild as a proof‐of‐principle application were analysed for Sr concentration and Sr isotopes.ResultsUsing ICP‐MS/MS we show for the first time that internal mass bias correction of 87Sr16O/86Sr16O based on 88Sr16O/86Sr16O works to give for NIST SRM 987 a 87Sr/86Sr ratio of 0.7101 ± 0.012 (RSD = 0.17%) and for NIST SRM 1570a a 87Sr/86Sr ratio of 0.7100 ± 0.009 (RSD = 0.12%), which are within error of the accepted values. The first 87Sr/86Sr ratio of NIST SRM 1547 is 0.7596 ± 0.0014. Strontium analyses were run on 0.8 mL of 0.25–0.5 ppb Sr, which equates to 2–4 ng of Sr. Strontium isotope analysis with a precision of >99.8% can be achieved with in‐line separation of 87Sr from 87Rb at least up to solutions with 25 ppb Rb.ConclusionsA minimum of 5 mg of insect tissue is required for Sr isotope analysis. This new ICP‐MS/MS method enables Sr isotope analysis in single insects, allowing population‐scale studies to be feasible and making possible applications with time‐critical uses such as biosecurity.

Biological diversity in an Islamic archaeological population: A radiogenic strontium isotope and craniometric analysis of affinity in Ottoman Romania.

Written accounts, as well as a previous craniometric study, indicate that migrations of non-Europeans and conversions of Europeans to Islam define Ottoman communities in Early Modern Europe. What is less clear are the roles of migration and admixture in generating intra-communal variation. This study combines craniometric with strontium isotope data to compare the cranial affinities of locally born and immigrant individuals. We predict that locally born individuals are more likely than non-locals to show evidence of admixture. Radiogenic strontium isotope data for 21 Ottomans were compared against archaeological faunal values. Sixteen individuals with intact crania were also measured and compared against two comparative source populations from Anatolia and Europe. Discriminant function analysis assigned unclassified Ottoans to either comparative group based on typicality probabilities, with potential admixture established via intermediate morphology between the two source populations. Strontium isotope values revealed relatively high proportions of non-locals, consistent with high mobility documented historically. The sexes differed, with more males classifying as "typically Anatolian" than females. Locals and non-locals also had different cranial affinity patterns, with most classifying either as "typically Anatolian" or "typically European." Contrary to expectation, none of the locals were identified as intermediate, suggesting admixture rates were relatively low. Consistent with historical records, the results revealed high levels of extra-regional migration, with most individuals identifiable as either typically Anatolian or European. Moreover, locals and non-locals differed craniometrically, with no signs of admixture between Anatolian migrants and European converts in locals. This suggests intra-communal divisions were maintained.

Movement of agricultural products in the Scandinavian Iron Age during the first millennium AD: 87Sr/86Sr values of archaeological crops and animals in southern Sweden

ABSTRACT In this paper, we examine the exchange of crops and livestock through the application of strontium (87Sr/86Sr) isotope analysis on cereal grains and faunal tooth enamel from the regional center of Uppåkra and three nearby settlements in Scania, southern Sweden, dating to the first millennium AD. Around a third of the fauna have non-local 87Sr/86Sr values, indicating the import of livestock from several different regions. After cleaning, almost all of the cereal grains have non-local 87Sr/86Sr values, which is surprising given the nearby abundance of fertile agricultural soils. We therefore suggest considering non-locally grown crops to be those whose 87Sr/86Sr values fall outside the normal distribution; if this approach is used, around 20% of the analyzed crop samples are interpreted as having grown non-locally. This study demonstrates the potential of combining strontium isotopic data of archaeobotanical and zooarchaeological material for gaining insights into the movement of agricultural products in prehistory.

Biological diversity in an Islamic archaeological population: A radiogenic strontium isotope and craniometric analysis of affinity in Ottoman Romania

Biological diversity in an Islamic archaeological population: A radiogenic strontium isotope and craniometric analysis of affinity in Ottoman Romania

A coherent method for combined stable magnesium and radiogenic strontium isotope analyses in carbonates (with application to geological reference materials SARM 40, SARM 43, SRM 88A, SRM 1B)

We undertook 87Sr/86Sr analyses for a range of carbonate bearing geological reference materials, and combined these with δ26Mg for a subset of samples. Following chemical purification in a series of chromatographic extractions, isotope ratios were measured by Multi-Collector-ICP-MS using a Plasma II (Nu instruments, Wrexham, UK). To validate efficient sample digestion procedures of carbonate fractions, total samples were treated with either 3 mol l−1 HNO3 and 0.5 mol l−1 HCl, respectively. Results of both leaching procedures are identical within reproducibility. Reference values for SRM 88A (formerly NBS 88A), SRM 1B (formerly NBS 1B), SARM 40, SARM 43, JDo-1, JLs-1, and San Carlos olivine range from 0.70292 to 0.73724 in 87Sr/86Sr and from -2.80 to -0.41 ‰ for δ26Mg, respectively. This set of geological reference materials can be used for sedimentary rock material with different carbonate mineral and matrix composition as quality control measurements of combined stable Mg and radiogenic Sr isotope analyses.•We present a protocol that facilitates the chemical separation of Mg and Sr in carbonate bearing geological reference materials including 87Sr/86Sr and δ26Mg of certified reference materials.

Laser ablation strontium isotope analysis of human remains from Harlaa and Sofi, eastern Ethiopia, and the implications for Islamisation and mobility

ABSTRACT The ancient city of Harlaa in eastern Ethiopia was occupied between the mid-6th and early 15th centuries AD and played a significant role as a trading centre with links internationally. Besides goods, these trade links also served in spreading cultural and religious ideas between continents, including Islamic traditions which became prevalent in Ethiopia during this time. Here, we present the first strontium isotope analysis of human remains from an Islamic site in Ethiopia. Results show that individuals buried following Islamic traditions include people born and raised both in Harlaa itself and also in rural communities from the surrounding hinterland, revealing a resident local Muslim community and potential co-existence of Muslim and non-Muslim individuals across economic sectors. The repeatability of results produced by laser ablation in human teeth sampled multiple times around the tooth cusp is also confirmed, although small differences between simultaneously-forming molar elements from a single individual were observed.

Initial assessment of bioavailable strontium at Oldupai Gorge, Tanzania: Potential for early mobility studies

Strontium isotope analysis is a useful tool for tracing mobility and migration in past populations. For it to be employed, the 87Sr/86Sr values of the landscape must be well-understood. Bioavailable strontium is a combination of geological and atmospheric strontium available for use by plants and animals. In this study we begin mapping bioavailable strontium values around the Oldupai Gorge region so that this method may be utilized on archaeological hominins and animals in the future. We analyzed three plants from 33 localities across volcanic and metamorphic bedrock, including the regional drainage sump, Olbalbal. We found that bioavailable strontium in the region is homogeneous overall, with trends towards increasing values to the north and northeast and in Olbalbal. There was no difference between 87Sr/86Sr values of metamorphic and volcanic areas. Migrants from outside the study area with different isotopic values will be easily identifiable from the local residents.As a proof of concept, we analyzed 7 animal teeth (hippopotamus, crocodile, and equid) from Engaji Nanyori, a Bed III and IV site at Oldupai Gorge. We found that enamel and dentine which had been acetic acid treated to remove diagenetic strontium were significantly different from one another. All animals had higher 87Sr/86Sr values than the plant values, suggesting that modern and ancient bioavailable strontium values may have been different, likely due to environmental differences.

Interactions between earliest Linearbandkeramik farmers and central European hunter gatherers at the dawn of European Neolithization

Archaeogenetic research over the last decade has demonstrated that European Neolithic farmers (ENFs) were descended primarily from Anatolian Neolithic farmers (ANFs). ENFs, including early Neolithic central European Linearbandkeramik (LBK) farming communities, also harbored ancestry from European Mesolithic hunter gatherers (WHGs) to varying extents, reflecting admixture between ENFs and WHGs. However, the timing and other details of this process are still imperfectly understood. In this report, we provide a bioarchaeological analysis of three individuals interred at the Brunn 2 site of the Brunn am Gebirge-Wolfholz archeological complex, one of the oldest LBK sites in central Europe. Two of the individuals had a mixture of WHG-related and ANF-related ancestry, one of them with approximately 50% of each, while the third individual had approximately all ANF-related ancestry. Stable carbon and nitrogen isotope ratios for all three individuals were within the range of variation reflecting diets of other Neolithic agrarian populations. Strontium isotope analysis revealed that the ~50% WHG-ANF individual was non-local to the Brunn 2 area. Overall, our data indicate interbreeding between incoming farmers, whose ancestors ultimately came from western Anatolia, and local HGs, starting within the first few generations of the arrival of the former in central Europe, as well as highlighting the integrative nature and composition of the early LBK communities.

Ølby Woman:

The Early Nordic Bronze Age oak coffin burials include some of Europe’s best preserved human remains. Although traditional typological examinations thereof have not always found clear foreign references, recent provenance investigations from Egtved and Skrydstrup suggest that the two women were of non-local provenance. In order to investigate potential mobility patterns and how these might or might not be related to the archaeological evidence, we conducted comprehensive multi-analytical investigations on the Ølby Woman, another key female oak coffin burial. Her grave included large metal items, the remains of a corded skirt and a glass bead recently identified as of Egyptian origin. Strontium isotope analyses of the dental enamel of Ølby’s first, second and third molars investigate her provenance and potential mobility through childhood. Furthermore, we conducted lead isotope analyses and craft technical analyses of her belt plate and sword/dagger. Our results reveal that the Ølby female’s strontium isotope signatures fall within the local baseline, suggesting that she was of local origin. The metal provenance studies and craft technical studies of the belt plate and sword suggest that the objects were manufactured in Scandinavia, while the raw materials for each item were imported from different places in Europe.&#x0D;

Pastoralism and Emergent Complex Settlement in the Middle Bronze Age, Azerbaijan: isotopic analyses of mobility strategies in transformation.

This article explores the scale and seasonal patterns of mobility at the complex settlement site of Qızqala during the Middle Bronze Age (2400-1,500 BCE). By integrating human bone, teeth, and environmental samples this research tests the hypothesis of the persistent importance of community-wide seasonal pastoral transhumance during the early formation of complex settlement systems of the South Caucasus. This research applies stable oxygen and radiogenic strontium isotope analyses on incremental samples of human tooth enamel, bulk tooth enamel, and bone to resolve mobility patterns. Sequential and bulk sampling techniques elucidate seasonal and residential mobility behaviors. Extensive environmental isotope samples of plant and water were collected through regional survey and establish local and regional isotopic baselines, which are compared to human isotope analysis results. Qızqala individuals exhibit low isotopic variability compared to regional contemporaries. 87 Sr/86 Sr ratios from human remains indicate seasonal and residential isotopic variability within the baseline ranges of local landscapes. δ18 O values display erratic patterns, but correspond to seasonal variability with fluctuations between highland and lowland altitudinal zone baseline values. Results suggest that isotopic analysis of multiple elements and sequential enamel samples offers finer resolution on the complexities of human mobility strategies and elucidate the daily lives of often overlooked mobile populations. Higher resolution of individual mobility reveals shared routine behaviors that underscore the importance of diverse social collaborations in forming complex polities in the South Caucasus.

Pastoralist strategies and human mobility: oxygen (δ18Op) and strontium (87Sr/86Sr) isotopic analysis of early human remains from Egiin Gol and Baga Gazaryn Chuluu, Mongolia

The steppes of Central Asia have long been inhabited by communities practicing various forms of mobile pastoralism as their primary means of subsistence. This study explores the relationship between human mobility and organizational strategies at two distinct micro-regions situated within the modern-day borders of Mongolia. Our investigation was based on an analysis of oxygen (δ18Op) and strontium (87Sr/86Sr) isotopes in archeological human skeletal remains (n = 30) from Baga Gazaryn Chuluu, situated within the middle Gobi Desert and the Egiin Gol Valley in north-central Mongolia. The results indicate a marked degree of separation in local baseline values between the two regions, and corresponding variation was observed in the human skeletal samples. Intra-regional comparisons found that most individuals appear to have spent their childhood years within a “local” range for each particular region, with several notable exceptions that likely indicate a greater degree of lifetime mobility for certain individuals. Overall, the results support the probability that mobility patterns in the past were related to subsistence strategies developed within the discrete environmental zones that characterize the central regions of Mongolia.

The zooarchaeology and isotopic ecology of the Bahamian hutia (Geocapromys ingrahami): Evidence for pre-Columbian anthropogenic management.

Bahamian hutias (Geocapromys ingrahami) are the only endemic terrestrial mammal in The Bahamas and are currently classified as a vulnerable species. Drawing on zooarchaeological and new geochemical datasets, this study investigates human management of Bahamian hutias as cultural practice at indigenous Lucayan settlements in The Bahamas and the Turks & Caicos Islands. In order to determine how hutia diet and distribution together were influenced by Lucayan groups we conducted isotopic analysis on native hutia bone and tooth enamel recovered at the Major’s Landing site on Crooked Island in The Bahamas and introduced hutias from the Palmetto Junction site on Providenciales in the Turks & Caicos Islands. Results indicate that some hutias consumed 13C-enriched foods that were either provisioned or available for opportunistic consumption. Strontium isotope ratios for hutia tooth enamel show a narrow range consistent with local origin for all of the archaeological specimens. In contrast, analysis of strontium isotopes in modern Bahamian hutia teeth from animals relocated to Florida from The Bahamas demonstrates that these animals rapidly lost their Bahamian signature and adopted a Florida signature. Therefore, strontium should be used cautiously for determining hutia provenance, particularly for individuals that were translocated between islands. Overall, our findings suggest that ancient human presence did not always result in hutia vulnerability and that the impact to hutia populations was variable across pre-Columbian indigenous settlements.

A simple two-stage column chromatographic separation scheme for strontium, lead, neodymium and hafnium isotope analyses in geological samples by thermal ionization mass spectrometry or multi-collector inductively coupled plasma mass spectrometry.

Here, a two-stage column separation scheme is developed for the concomitant isolation of Sr, Pb, Nd, and Hf from geological samples. The first column, which consists of three resin layers (AG50W-X8 ion exchange resin + Ln specific resin + Sr specific resin), separates the high field strength element + rare earth element, Sr and Pb from the matrices. Subsequently, Nd and Hf are further separated from the high field strength element + rare earth element fraction on the second column using 1mL of Ln specific resin. The two-stage column process can be completed within about seven and a half hours for a batch of samples (20-30). The separated Sr fraction was ready for isotope ratio measurements by thermal ionization mass spectrometry. The Pb, Nd, and Hf fractions were converted to nitrate prior to isotopic analyses by multi-collector inductively coupled plasma mass spectrometry. The feasibility of this new procedure is confirmed by the analyses of four international rock standards (BCR-2, AGV-2, BHVO-2, and JB-3), which yielded isotope ratios that were in good agreement with other published data.

Bioarchaeology of Bronze and Iron Age skeletal finds from a microregion in Central Mongolia.

This paper gives a state of the art report of an ongoing interdisciplinary project on bioarchaeological research on cemeteries in the Upper Orkhon valley, Central Mongolia, in particular at the Maikhan Tolgoi site. The archaeological focus is on the investigation of the development, use and transformation of a ritual landscape in the course of the Bronze and Iron Age. The contribution of physical anthropology is an osteological and archaeometric analysis of the human inhumations with regard to life-style and subsistence economy. A specific topic relates to the emergence of the first mounted nomads in the region. Macro- and microscopical inspection of the skeletons excavated to date reveal that males, females and children had been buried at this exceptional cemetery, and that many of the adults died at a conspicuously advanced age. Palaeodiet was reconstructed by stable carbon and nitrogen isotopes in bone collagen, followed by an isotopic sourcing. We show that freshwater fish was consumed on a regular basis, and that the demands of protein and carbohydrate were largely covered by secondary animal products. First analysis of stable strontium and oxygen isotopes in bone apatite suggests a considerable catchment area of the burial site.

Mapping human mobility during the third and second millennia BC in present-day Denmark.

We present results of the largest multidisciplinary human mobility investigation to date of skeletal remains from present-day Denmark encompassing the 3rd and 2nd millennia BC. Through a multi-analytical approach based on 88 individuals from 37 different archaeological localities in which we combine strontium isotope and radiocarbon analyses together with anthropological investigations, we explore whether there are significant changes in human mobility patterns during this period. Overall, our data suggest that mobility of people seems to have been continuous throughout the 3rd and 2nd millennia BC. However, our data also indicate a clear shift in mobility patterns from around 1600 BC onwards, with a larger variation in the geographical origin of the migrants, and potentially including more distant regions. This shift occurred during a transition period at the beginning of the Nordic Bronze Age at a time when society flourished, expanded and experienced an unprecedented economic growth, suggesting that these aspects were closely related.

Strontium isotope stratigraphy and paleomagnetic age constraints on the evolution history of coral reef islands, northern South China Sea

Abstract Understanding the history of the response of coral reefs to past climate changes can provide valuable information for predicting the future response of modern reefs. However, dating such ancient biotic carbonate is still challenging because of its sensitivity to diagenetic alteration processes, scarcity of well-preserved fossils, and low magnetic mineral content. There have been a long debates about the origin and evolutionary history of coral reefs in the northern South China Sea, mainly due to the lack of direct and reliable age constraints. This provides us with a good opportunity to verify the practicability of different dating approaches, especially the strontium (Sr) isotope analysis of bulk carbonate. Here, we retrieved a 972.55-m-long core from the Xisha Islands to provide a credible chronologic constraint on the carbonate platform evolution. The lithostratigraphy, strontium isotope stratigraphy, and magnetostratigraphy were analyzed throughout the whole reef sequence. The lithostratigraphic results show that the 873.55 m reef sequence developed on an ancient volcaniclastic basement and experienced multiple evolutionary phases. The 87Sr/86Sr results of all 100 bulk carbonate samples vary from 0.708506 to 0.709168 and show a monotonic increase with decreasing depth, except for a few outliers. Trace-element criteria and stable isotope (δ18O and δ13C) methods were applied to these bulk carbonate samples, and results imply that the primary or near-primary seawater 87Sr/86Sr values were likely preserved, although different degrees of diagenetic alteration occurred. In addition, the paleomagnetic results indicate 10 normal polarity and eight reversed polarity magnetozones. Based on the 87Sr/86Sr ratios of the selected 58 samples and paleomagnetic reconstruction of polarity reversals, the bottom of the reef sequence is dated to 19.6 Ma, and the observed polarity chronozones extend from chron C6 (19.722–18.748 Ma) at 866.60 m to present at the top. Based on the new data, we propose a new chronologic framework for the evolutionary history of the reef islands, where: (1) the reefs initiated in the early Miocene (19.6 Ma) and were drowned until 16.26 Ma; (2) during 16.26–10.66 Ma, lagoon to lagoon slope environments prevailed; (3) the lagoon environment progressively transformed into a reef crest environment from 10.66 to 4.36 Ma and 4.36 to 1.59 Ma; and (4) the reef started to be drowned again during 1.59–0 Ma. Our study provides a new and reliable chronologic constraint on the general evolutionary history of the reef islands in the northern South China Sea. Furthermore, the 87Sr/86Sr results from bulk carbonate indicate that strontium isotope stratigraphy is a powerful dating tool only when rigid sample selection, sequential leaching procedures, and strict trace-element and isotopic criteria are applied.