Comparison of fluoride and direct AMS radiocarbon dating of black bear bone from Lawson Cave,Missouri

Abstract

After a 20-year hiatus (1955–1975) during which few archaeologists discussed fluoride dating, the method again received attention in the 1980s and 1990s when some argued for its validity. As a dating method, fluoride dating depends on the rate at which fluorine ions replace hydroxyl ions in osseous tissue. The rate of replacement is influenced by the properties of the skeletal part (SP), sediment chemistry (K), and sediment hydrology (H), and the replacement rate influences estimates of time. Calibrated AMS radiocarbon assays of 10 black bear (Ursus americanus) femora from a natural-trap cave in central Missouri are weakly correlated with fluorine concentrations, determined by neutron activation analysis in the 10 femora. Despite minimal variation in SP, K, and H, results indicate fluoride dating can be considered a valid dating method only in cases when the chronological validity of its results are confirmed with independent chronometric data. As similarities in fluorine amounts across specimens increase, provenience information and bone orientation data as well as fine resolution data on K and H become critical to the application of fluoride dating.     

Preliminary U-series and Thermoluminescence dating of excavated deposits in Liang Bua sub-chamber,Flores, Indonesia

We report the results of a test excavation of deposits in a limestone cave sub-chamber located beneath the main chamber of Liang Bua, Flores, Indonesia; the discovery site of the small hominin species, Homo floresiensis. Well-preserved remains of extinct Pleistocene fauna and stone artefacts have previously been identified on the surface of a sediment cone within the sub-chamber. Our excavation of the deposits, at the base of the sediment cone in the sub-chamber (to 130 cm depth) yielded only a few fragmentary bones of extant fauna. Uranium/Thorium (U-series or U/Th) dating of soda straw stalactites excavated from 20 to 130 cm in depth demonstrates that the excavated sediments were deposited during the Holocene. Red Thermoluminescence (TL) dating of the sediments at the base of the excavation (130 cm depth) indicates these sediments were last exposed to sunlight at 84 ± 15 ka (thousand years), similar to red TL ages of cave sediments from the main chamber. Together, these results indicate that the surface faunal remains, which are morphologically analogous to Pleistocene finds from the main chamber excavations, were transported to the sub-chamber relatively recently from the main chamber of Liang Bua and probably originated from conglomerate deposits at the rear of the cave and from deposits around the front entrance. There is no evidence for hominin occupation of the sub-chamber, instead it seems to have acted as a sink for cultural materials and fossil remains transported from the surface via sinkholes. Despite the small number of finds from the test excavation, it is possible that more extensive excavations may yield additional transported cultural and faunal evidence at greater depths.     

Uranium series dating reveals a long sequence of rock art at Altamira Cave (Santillana del Mar,Cantabria)

The rock art in Altamira Cave was the first ensemble of Palaeolithic parietal art to be identified scientifically (Sautuola, 1880). Due to the great thematic, technical and stylistic variety of the art in the cave, which constitutes one of the most complete Palaeolithic art ensembles, Altamira was listed as World Heritage by UNESCO in 1985. Uranium-series dating has recently been applied to figures on the decorated ceiling in the cave. Several motifs are partly covered by thin layers of calcite precipitates, whose formation process is datable by this method. The results provide the date when the calcite formed, which gives a minimum age for the underlying depictions. These results confirm that the parietal art at Altamira was produced during a prolonged period of time, at least 20,000 years (between 35,000 and 15,200 years ago), and that part of the ensemble corresponds to the Aurignacian period.     

A comparison of the treatment of errors in radiocarbon dating calibration methods

The application of radiocarbon dating to archaeological samples generally requires calibration of ¹⁴C dates to calendar ages and interpretation of dating errors. In this paper, four recent methods of age calibration are assessed, particularly with regard to their quality of error treatment. Recent experimental research has suggested that commonly quoted errors on “raw” ¹⁴C dates may require enlargement to more realistic levels, which, when incorporated in the calibration schemes, produce a considerable increase in the size of the typical calibrated interval. A general decrease in the sensitivity of ¹⁴C dating using single, “normal precision” dates is implied. Thus typical calibrated age intervals range from 300 to 1300 years (approximate 95% confidence level), with little improvement resulting if “high precision” calibration systems are used to correct “normal precision” dates. Of the four methods considered here, that proposed by Neftel is found to provide the most objective, flexible, comprehensive and “easy to use” scheme. This method is particularly recommended for its treatment of errors both on the dates to be calibrated and on the calibration curve itself.     

Sample preparation for accelerator-based radiocarbon dating

Although several efficient sample preparation methods have been devised for conventional radiocarbon dating, the advent of the accelerator mass spectrometer (AMS) dating technique with its much smaller sample requirement and different counting method has meant that new preparation routes have had to be developed. Techniques used for the Oxford AMS system are described in this paper.     

江西仙人洞遗址两万年前陶器的年代研究

陶器的出现使得人类生存和社会行为发生了重要转变。我们对江西万年仙人洞遗址出土陶器进行了年代研究、对陶片和碳十四测年样品层位关系开展地层显微结构分析,结果显示遗址出土最早的陶片年代为距今19,000～20,000年,比东亚和其他地区的陶器早了2000～3000年。洞穴内遗存证明这些陶器是在末次冰盛期由采集狩猎者所制造,可能被用做炊煮器。说明陶器在农业出现以前一万年甚至更早就被制造和使用了。     

The archaeology of radiocarbon accelerator dating

Accelerator mass spectrometry (AMS) allows radiocarbon dating to be carried out by direct counting of¹⁴C atoms, rather than the conventional counting of radioactive disintegrations. The result is that samples up to 1000 times smaller can be handled. The approach was tested in principle by 1977 and for archaeological operation by 1983. More than 2000 samples per year are now being dated worldwide. The machines can now operate to about ± 80 years or better. Dates older than 40,000 years have not yet been achieved, but the ability to use small samples has already had considerable impact on dating the period 10,000–30,000 years ago. Bone is an ideal material for the new technique, since amino acids can normally be isolated and purified from gram-size samples. Studies of the origins of domestication are aided by the dating of individual grains and seeds. Because small samples can be mobile in the soil, careful sample selection strategies and procedures are required. The full impact of the technique can be assessed only through the rapid and comprehensive publication of archaeological results.     

The application of luminescence dating in American archaeology

Luminescence dating is underutilized in American archaeology given the theoretical advantages of direct dating that it confers. Recent advances in understanding the physical processes underlying the method have also made it more reliable as a dating tool. This research as well as potential applications is reviewed.     

U-series dating of soda straw stalactites from excavated deposits: method development and application to Blanche Cave, Naracoorte, South Australia

This study aimed to further test the method, reported by St Pierre et al. (2009), to develop robust chronologies of deposits in limestone caves through U/Th (Uranium/Thorium or U-Series) dating of soda straw stalactites. The chronology of fossil bearing deposits at Blanche Cave was further constrained with thermal ionisation mass spectrometry (TIMS) U/Th dating of 17 additional soda straw stalactite samples, and results were compared to recalibrated ¹⁴C ages of charcoal. The results support the assertion that soda straw stalactites can provide ages close to the time of sediment deposition and may be used as reliable chronological markers, particularly for periods reaching or beyond the radiocarbon dating limit. The application of an enhanced cleaning technique facilitated the reduction of detrital Th in samples, significantly increasing age accuracy and precision. Additionally U/Th age accuracy and precision was increased through the application of site-specific measured U/Th ratios to correct for the detrital ²³⁰Th component in samples.     

Pre-screening techniques for identification of samples suitable for radiocarbon dating of poorly preserved bones

Under certain environmental conditions, post-depositional diagenetic loss of bone collagen can severely reduce the number of bones from a particular archaeological site that are suitable for stable isotopic analysis or radiocarbon dating. This study examined nearly 300 bones from 12 archaeological sites across southern England known to yield poor or variable preservation to try to identify one, or more, pre-screening technique(s) that would indicate suitable collagen preservation for radiocarbon dating. The most reliable method was shown to be the percent nitrogen (%N) of whole bone powder, which has an 84% chance of successfully predicting whether or not a bone will yield sufficient (i.e. >1% weight) collagen for dating.     

Hayonim Cave: a TL-based chronology for this Levantine Mousterian sequence

The thermoluminescence dating method was applied to 77 heated flints from the Mousterian layers of Hayonim Cave in order to provide a precise TL-based chronology for this important Levantine sequence. A detailed dosimetric study was performed by using 76 dosimeter capsules and revealed strong spatial dose-rate variations. In parallel, Fourier transform infrared spectrometry enabled the identification of various mineral assemblages in the sediments of the cave and to localize the boundaries of these assemblages. By comparing these two data sets, it is shown that low dose-rate values (∼500 μGy/a) are systematically recorded in areas where the calcite-dahllite (CD) assemblage is preserved, whereas higher values (up to 1300 μGy/a) are associated with the leucophosphite, montgomeryite, variscite and siliceous aggregates (LMVS) assemblage. The dosimetric and mineralogical information was combined in order to assess, where possible, the dose-rate experienced by each flint during its burial. Some of the flint samples analyzed were too close to mineral assemblage boundaries and were therefore discarded. This rigorous selection led to TL ages ranging from 230 to 140 ka for the lower part of the Mousterian sequence (layers F and Lower E), which contains lithic industries characterized by blade production using the laminar method.     

Radiocarbon dating of bone by accelerator mass spectrometry

A companion article describes the sample preparation method used in the production of graphite targets for the Oxford accelerator mass spectrometer (AMS) system. The chemical pretreatment developed for the dating of bone, ivory and tooth samples is described in this paper.     

Optically stimulated luminescence dating of Southern High Plains archaeological sites

The Southern High Plains of North America is rich in archaeological sites, but many are not well constrained chronologically, owing to a lack of material for radiocarbon dating. A program of optically stimulated luminescence (OSL) dating, applying mainly single-grain analyses, was therefore initiated. Many samples have independent age estimates from radiocarbon to check the OSL results, but OSL age estimates are also provided for those sites that otherwise lack secure chronological control. Sediment samples for OSL were obtained primarily from Paleoindian and Archaic localities, though include deposits of more recent age. Through the analysis of single grains, equivalent dose—the numerator of the age equation—is evaluated independently on numerous grains. The distribution of these values is relatively broad for some samples, and this is attributed to post-depositional mixing. Mixing is also evident in some samples with more narrow distributions. Selecting portions of the mixed distributions for age determination allows more accurate dating for some samples, but the nature of the distributions limits the resolution on others, conclusions that cannot be as easily drawn from multi-grain analysis. Where independent age control is available, most OSL results broadly conform; however, some samples show discrepancies that are not readily explained, but may relate to association or dose rate problems. This underscores the desirability of obtaining where possible suites of chronological evidence.     

Characterisation and blind testing of radiocarbon dating of cremated bone

The success of radiocarbon dating of burned or cremated bones depends on the exposed temperature during burning and the degree of re-crystallisation of the inorganic bone matrix. We present a method for characterisation of likely cremated bones by employing visual inspection, infrared spectrometry and carbon stable isotope analysis on the bio-apatite fraction. The method of radiocarbon dating of cremated bones was tested by dating paired samples of bone and associated context materials such as pitch, charcoal and a dendrochronologically dated oak coffin. The dating of these paired test samples were largely performed as blind tests and showed excellent agreement between pitch and bone. The weighted mean age difference of all test samples is observed to −9 ± 60 ¹⁴C yr. To test the indicators and the effects of the degree of burning, a Late-Neolithic human individual has been studied, as this individual exhibits the full spectrum from low temperature burning (charred) to high temperature (“cremated”) from one end of a single bone to the other. This is reflected as a marked step in numerous parameters as well as in a significant difference in ¹⁴C age between the charred and the cremated bone samples.     

Obsidian hydration dating: accuracy and resolution limitations imposed by intrinsic water variability

Obsidian hydration dating typically yields a range of ages for a single chronometric measurement, even after controlling for source chemistry and effective hydration temperature. Previously published data suggest that this range is due to hydration rate variations caused by variability in the concentration of intrinsic water, and specifically hydroxyl ions, in the obsidian. Such variability exists within any given obsidian source, and even within any particular specimen. This paper analyzes the effect on age estimates of intrinsic water variability and concludes that if a controlled sample of obsidian yields a range of ages, there is no way to tell whether the range is due to long site use or to variations in hydroxyl concentration. At present there is no robust and cost-effective protocol for measuring hydroxyl concentration. Suggested guidelines for obsidian hydration dating are developed using a case study. These findings do not invalidate obsidian hydration as a chronometric technique, but they do suggest limits to the temporal resolution achievable.     

Uranium-series dating rock art in East Timor

At many sites throughout the world rock art paintings have been covered by naturally deposited calcite laminations, which we demonstrate can be individually dated by recently improved uranium-series methods. Here we report the application of multi-collector inductively coupled plasma mass spectrometry to measure the ages for carbonate coatings that bracket red pigment at Lene Hara cave, East Timor, which could be evidence of human painting. These analyses establish the feasibility of dating milligram samples of finely layered calcite deposits associated with archaeological evidence of human occupation. In addition to confirming an age of less then 6300 years for the visible red paintings on the carbonate surface we also report a substantially older age of 24,000 to 29,300 years for a similar, older red pigment lamination providing possible evidence for an earlier painting episode.     

Expanding the utility of Uranium-series dating of speleothems for archaeological and palaeontological applications

Uranium-series (U-series) dating of speleothems is frequently used for palaeoclimate studies but its archaeological and palaeontological applications are limited to stratigraphically significant speleothem formations, such as flowstones, to provide maximum and minimum temporal points. This study targeted soda straw stalactites for U-series dating. In contrast to other speleothem formations, soda straw stalactites are fragile, have typically short life spans (usually only years but rarely up to a few hundred years) and are frequently incorporated into cave deposits. Results of thermal ionisation mass spectrometry (TIMS) U-series dating of soda straw stalactites from palaeontological excavations at Blanche Cave, South Australia, show that small, dense, clean straws tend to yield ages closest to the time of stratigraphic deposition. A correlation between soda straw U-series ages and radiocarbon ages of charcoal from the site is shown. Multiple soda straw age determinations for a single stratigraphic unit are required in order to verify age concordance. In conjunction with other dating methods, U-series dating of soda straw stalactites may help to significantly constrain the age of stratigraphic units and associated archaeological and palaeontological deposits in order to provide more robust chronologies. Here we advocate the collection of soda straw stalactites at future excavations of limestone cave sites.     

Lichenometric dating and the nature of the excavation of the Huashan Grottoes,East China

The present study aims to identify the timing of the Huashan Grottoes' excavations using the lichenometric dating method. A total of 96 maximum inscribed circle diameters of Rhizocarpon geographicum growing on the ancient architectures and the walls of entrances are measured in the Huashan Grottoes area of southern Anhui, East China. The results show that the period of the grottoes' excavation is estimated to be 450–335 yr BP, or the middle and late Ming Dynasty (1552–1667 AD). The lichenometric dating results are also validated by a lithologic comparison of the grottoes and the surrounding ancient architectures, as well as by the studies on the historical documents and the fragments of ancient porcelain in the grottoes. Furthermore, we infer that the excavation of the inner grottoes might have lasted till the Qing Dynasty (1636–1912 AD), because the lichens chosen for dating are mainly at the grottoes' entrances. The wider significance of this work is that it demonstrates, for the first time, lichenometric dating can be applied in the historical studies on the ancient architectures in East China with a relatively warm and humid climate.     

Palaeomagnetic dating of fluid-flow events in dolomitized rocks along the Highland Boundary Fault, central Scotland

Palaeomagnetic and geochemical studies of Cambrian–Ordovician serpentinite in the Highland Border Complex (HBC), a tectonic terrane along the Highland Boundary Fault (HBF) in Scotland, indicate that the HBF was a conduit for fluids in the Carboniferous–Permian. The fluids caused dolomitization, silicification, and haematite authigenesis. Both red dolomitized serpentinite and relatively unaltered serpentinite were sampled at multiple localities. The unaltered serpentinite contains a poorly defined magnetization with westerly declinations that resides in magnetite and has a pole which plots well off the apparent polar wander path. Most specimens of the red dolomitized serpentinite contain a magnetization with southerly declinations and negative inclinations that resides in haematite. A regional fold test suggests that this magnetization post‐dates tilting and the pole positions for the different locations fall on the Carboniferous to Permian part of the apparent polar wander path. In some specimens of red dolomitized serpentinite, alternating field (AF) demagnetization prior to thermal treatment removes a component with a similar direction. Dolomitized basement rocks along the fault contain a similar although apparently slightly older magnetization. Fluid inclusion and geochemical studies indicate that the fluids were hydrothermal in origin (110–240°C) and had a range of sources. The Carboniferous–Permian magnetization in haematite is interpreted as a chemical remanent magnetization that formed when warm fluids moved along the fault zone and caused haematite authigenesis. The component removed by AF treatment is interpreted as a thermal resetting of primary magnetite by the fluids. The variability of the palaeomagnetic, fluid inclusion, and stable isotope results suggests that there were probably multiple flow events that caused the alteration. The origin of the fluids could be related to the intrusion of late Carboniferous dikes in central Scotland and/or to reactivation of the HBF in the Carboniferous–Permian.     

A review of rock art dating in the Kimberley, Western Australia

This paper critically reviews the various approaches used to estimate the age of the rock art in the Kimberley region of Western Australia. They include: (i) the relative superimposition of styles; (ii) the use of diagnostic subject matter (depictions of extinct animals, stone tool technology, introduced European and Asian objects and animals); (iii) the recovery of a ‘painted’ slab from a dated archaeological unit; (iv) radiocarbon dating of beeswax figures, charcoal pigments, organic matter in overlying mineral deposits and ‘accreted paint layers’ (oxalate rich crusts and amorphous silica skin), pollen grains from an overlaying mud-wasp nest; and (v) optically stimulated luminescence (OSL) dating of quartz grains from overlying mud-wasp nests. Future directions for rock art dating in the Kimberley include uranium-series dating of overlying and underlying mineral deposits.