Direct Accelerator Mass Spectrometry Research Articles

A direct-AMS assessment of Re-Os in a Cigar Lake uranium ore specimen

The decay constant of 187Re is known to change when its inner shell electrons are ionized; the possibility of a small change occurring in a terrestrial radioactive environment has not been assessed. A recently completed multi-isotope survey of uranium ore concentrates (UOC) has prompted the question. As an extension of that work, using direct accelerator mass spectrometry (direct-AMS), this paper reports a closer investigation of such possibility in an unaltered natural rock specimen of the Cigar Lake uranium ore, containing wt.30–60 % uranium oxide. Stimulated by this research goal, the direct-AMS quantification methods were first investigated, and later tested in connection with the Re-Os assessment. Complete sets of measurement of the anion beams of 185ReOn−, (187Re+187Os)On− and 189OsOn− (n = 0–5) were carried out to find suitable sputter target matrices that would yield self-consistent solutions of (187Os/189Os)Today and (187Re/185Re)Today. These two quantities are best determined by these multi-beam measurements to be 4400 ± 500 (2σ) and 1.635 ± 0.060 (2σ), respectively. The sample is then reasoned to contain [Re/Os]Initial ∼42,000. These results do not show apparent 187Re decay constant changes, but cannot rule out the possibility, either. As a quick follow-up inspection, a simplified approach was used to surveying 187Re/185Re in a series of uranium-concentrated materials, in which this ratio was all measured somewhat smaller than the natural known value. This work was also intended to be a pilot feasibility study of using the direct-AMS method as a form of sensitive secondary ionization mass spectrometry (SIMS) for rapid Re-Os assessment in mg-sized raw minerals and environmental samples.

A late Pleistocene Wood Turtle (<i>Glyptemys insculpta</i>) from Iowa, USA: response of the taxon to glaciation and formation of the current range

The partial shell of a Wood Turtle (Glyptemys insculpta) was collected from the West Branch of the East Nishnabotna River in southwestern Iowa, near Malvern. By direct accelerator mass spectrometry, it radiocarbon dates to the late Pleistocene (10 220 ± 30 years before present [BP], 11 975–11 813 calibrated years [cal] BP). Other subfossil evidence indicates that Wood Turtles moved far south of their current range, into the southeastern United States, in response to late Pleistocene glaciation. The specimen suggests that the species also moved south and west, into a previously undocumented western range, where favourable habitat and, in particular, somewhat cooler summer temperatures prevailed until ~10 200 cal BP. My assessment of the Holocene subfossil record suggests that establishment of the western portion of the current range may have occurred within the past 1000 years. Phylogenetic analysis and direct radiometric dating of subfossil specimens are needed to determine additional details about the late Pleistocene dispersal of Wood Turtle and the postglacial formation of their current range.

Morphological analysis and radiocarbon dating of non-returning boomerangs from Cooper Creek/Kinipapa (Northeast South Australia)

In this article we present the results of a morphological analysis of four mostly complete non-returning boomerangs and one shaped wooden fragment recovered in 2017 and 2018 from Cooper Creek near Innamincka in South Australia’s far northeast. This archaeological collection forms one of only six known/published wooden artefact assemblages in the country. We also detail the results of the direct accelerator mass spectrometry radiocarbon (AMS 14C) measurement of the artefacts which range from circa 275–175 BP (1650–1830 cal AD, median ages reported). Given that the age estimates obtained for the artefacts are from the recent period, we have complemented the morphological analysis by interpreting the assemblage within the context of ethnohistorical records and Traditional Owner knowledge. The assemblage reveals a variety of forms and functions representative of the diverse cultural activities and daily lives of the Aboriginal people who lived near significant waterholes in the Cooper Creek region during this period. The boomerangs also preserve manufacture and use-wear traces, providing insights into the life histories of each implement. In addition to their likely use as projectiles, our results indicate that the boomerangs were probably used for fighting, hunting, digging, fire management and possibly in ceremonies. Predictions for climate change in the region threaten to alter the conditions that allowed the preservation of these artefacts which may negatively affect the potential survival of other wooden objects that remain in the environment.

Direct AMS 14C Analysis of Carbonate

ABSTRACTWe have investigated the possibility of direct accelerator mass spectrometry radiocarbon (AMS 14C) measurement of carbonate samples at ANSTO using the STAR 2 MV tandem accelerator. Each carbonate sample was powdered, mixed with metal powder and pressed into an aluminum cathode for direct carbonate measurement by AMS 14C. Of the three high-purity metal powders (Fe, Nb, and Ag) used in our investigation, Nb was found to be the best metal, which delivered higher carbon beam currents and lower background. Beam currents for targets containing the optimal carbonate mass of 1.5–2.0 mg were ∼8% of those obtained from graphite targets of standard size (>0.5 mg C). Typical measured blank for Carrara marble (IAEA-C1) of ∼40 ka was obtained. Background-corrected 14C values of carbonate targets agreed well with their associated values obtained from high-precision analysis of graphite targets within 2σ uncertainties. Typical precision of this rapid AMS analysis was ∼1% for samples <8 ka. Despite lower precision for carbonate target ages (compared to standard graphite target ages), these ages are useful for palaeobiological applications where a large number of dates are required, such as time-averaging studies.

EARLIEST MICROBOTANICAL EVIDENCE FOR MAIZE IN THE NORTHERN LAKE MICHIGAN BASIN

There is no recorded maize (Zea maysspp.mays) from sites predating circa cal AD 800 in the northern Lake Michigan or Lake Superior basins of the western Great Lakes, despite the presence of maize microbotanicals including phytoliths and starches in Michigan, New York, and Quebec as early as 400 cal BC. To evaluate the potential for an earlier maize presence in the northern Lake Michigan basin, samples of carbonized food residues adhering to 16 ceramic vessels were obtained from the Winter site (20DE17) located on the Garden Peninsula in the northern Lake Michigan basin. Each sample was split and sent to two analysts. Both analysts identified low incidences of maize starch and phytoliths in multiple samples, with overlapping identifications on several. Three direct accelerator mass spectrometry dates on the carbonized residues reveal maize incorporated into the residues as early as the second century cal BC, 800 years before any regional macrobotanical evidence. Although the method of dispersal cannot be determined, these results support the proposition that initial northern dispersal of maize in the region may have been nearly 800 years earlier than macrobotanical evidence would suggest and is consistent with the timing of its introduction to the lower Great Lakes area.

Size Matters: Radiocarbon Dates of <200 µg Ancient Collagen Samples with AixMICADAS and Its Gas Ion Source

AbstractFor many of archaeology’s rarest and most enigmatic bone artifacts (e.g. human remains, bone ornaments, worked bone), the destruction of the 500 mg material necessary for direct accelerator mass spectrometry (AMS) dating on graphite targets would cause irreparable damage; therefore many have not been directly dated. The recently improved gas ion source of the MICADAS (MIni CArbon DAting System) offers a solution to this problem by measuring gaseous samples of 5–100 µg carbon at a level of precision not previously achieved with an AMS gas ion source. We present the results of the first comparison between “routine” graphite dates of ca. 1000 µg C (2–3 mg bone collagen) and dates from aliquots of gaseous samples of <100 µg C (<0.2 mg bone collagen), undertaken with the highest possible precision in mind. The experiment demonstrates the performance of the AixMICADAS in achieving reliable radiocarbon measurements from <0.2 mg collagen samples back to 40,000 14C BP. The technique has great implications for resolving chronological questions for key archaeological artifacts.

The late-Holocene avifaunal assemblage from the island of Palagruža (Croatia): The earliest record of the Northern Gannet in the Adriatic Sea

The late-Holocene bird remains retrieved during archaeological excavations on pelagic island of Palagruža, Croatia, were analysed. The results of the analysis revealed presence of representatives of nine families: Procellariidae, Sulidae, Ardeidae, Accipitridae, Phasianidae, Rallidae, Laridae, Strigidae and Corvidae. Among the bird remains, the most numerous were remains of the Northern Gannet, Morus bassanus, which were widely distributed in the Mediterranean during the late Pleistocene. The finding of the Northern Gannet bones on Palagruža represents the first fossil record of this species in the Adriatic Sea and indicates a possible breeding site on the island. The direct Accelerator Mass Spectrometry (AMS) radiocarbon dating on two gannet bones revealed the age of 2878 ± 34 and 2694 ± 45 yr BP. Gannet bones from Palagruža were some 6000 years younger than other fossil records of that species from the Mediterranean. It is possible that during the gannet’s northward distributional shift, probably caused by centennial climatic variability and human pressure, gannet colony on that remote island in the Adriatic lasted longer than in the rest of the Mediterranean and existed until the late-Holocene. Lower sea-surface temperatures compared with the eastern Mediterranean, higher nutritive productivity and remoteness of Palagruža provided adequate breeding opportunities during that period.

Broadening the Scope of Bone Anvils: Direct AMS14C Dating from the Island of Menorca (Western Mediterranean)

AbstractThis article presents the results of direct accelerator mass spectrometry (AMS) radiocarbon dating of a new bone anvil retrieved in the Iron Age–Roman site of Montefí (Ciutadella), in the southwest of the island of Menorca (western Mediterranean). The radiometric date confirms the chronology obtained through the stratigraphy and typological analysis of ceramics (1st–3rd century AD), and indicates that this bone-made tool not only represents the first archaeological anvil from the island but also constitutes the earliest evidence in the western Mediterranean. This ancient date is more consistent with the known eastern regional chronology and reinforces the importance of obtaining direct AMS14C dates to refine artifact chronologies.

A renewed archaeological and archaeobotanical assessment of house sites at Kuk Swamp in the highlands of Papua New Guinea

ABSTRACTHouse sites located on the wetland margin at Kuk Swamp in the Upper Wahgi Valley of Papua New Guinea were excavated in 1972 and 1973. Macrobotanical remains collected during excavation of domestic contexts were collected and subject to preliminary identification. Renewed macrobotanical analysis of these remains provides a more reliable foundation for their taxonomic identification to species or genus level. Plant remains include sugar cane (Saccharum officinarum) and probable sweet potato (Ipomoea batatas). Direct accelerator mass spectrometry (AMS) dating of macrobotanical remains provides a reliable basis for determining the antiquity of the house sites and differentiates at least two periods of settlement.

Early Evidence for Domestic Chickens (Gallus gallus domesticus) in the Horn of Africa

AbstractDomestic chickens (Gallus gallus domesticus L. 1758) are one of the most valued farm animals in the world today. Chickens are widespread and economically and socially significant in Africa. Despite their importance, little is known about the nature of their introduction and subsequent integration into African economies. One reason for this is the morphological similarity of domestic chickens to wild galliform birds in Africa such as guineafowl and francolin. Here, we present direct dates and morphological evidence for domestic chickens recovered from Mezber, a pre‐Aksumite (>800–450 BCE) rural farming settlement in northern Ethiopia. Key morphological markers differentiated these domestic chickens from francolins. The Mezber direct chicken element accelerator mass spectrometry (AMS) dates of cal 820–595 BCE and indirect/charcoal AMS dates of cal 921–801 BCE constitute the earliest osteological evidence for chickens in Africa. Chicken bones in the domestic food waste of an early rural settlement at Mezber and their presence in later Aksumite urban contexts show that chickens were integrated into diverse Ethiopian highland settings. The Mezber specimens predate the earliest known Egyptian chickens by at least 550 years and draw attention to early exotic faunal exchanges in the Horn of Africa during the early first millennium BCE. These findings support previous archaeological, genetics and linguistic data that suggest maritime exchange networks with South Arabia through ports along the African Red Sea coast constitute one possible early route of introduction of chickens to Africa. Copyright © 2016 John Wiley & Sons, Ltd.

Middle Holocene Taphonomy and Paleozoology at the Prairie-Forest Border, the Itasca Bison Site, MN

The Itasca Bison site near the prairie-forest border in central Minnesota is important to understanding the cultural and ecological role of bison in the upper Midwest during the middle Holocene. Recent reanalyses of this assemblage support the original interpretation of a taphonomically complex, fluvially modified site. Despite this taphonmic complexity, the role of humans in the butchering and possible accumulation of some of the bison fauna is also supported, although not as the only mechanism of accumulation. The bison assemblage is slightly biased toward males, and seasonality estimates are spread throughout the year. New direct accelerator mass spectrometry dates indicate a minimum of two highly mixed depositional events: one at 7970–7790 cal B.P. and an earlier event between 8520 and 8180 cal B.P.

Questioning Postclassic Continuity at Baking Pot, Belize, Using Direct AMS14C Dating of Human Burials

Archaeologists working in the Belize Valley have argued for the persistence of Maya populations from the Classic (AD 300–900) through Postclassic (AD 900–1500) periods since Gordon Willey's groundbreaking settlement survey and excavation work in the 1950s. This is contrary to the trajectory recorded in some parts of the Maya region where there is clear evidence for political disruption and population decline at the end of the Classic period. The argument for continuous Classic to Postclassic occupation in the Belize Valley remains ambiguous due to researchers' reliance on relative ceramic chronologies. This article reports the results of direct accelerator mass spectrometry (AMS) radiocarbon dating of human skeletons (n= 12) from the important center of Baking Pot, Belize, which is thought to provide some of the best ceramic evidence for continuity in the valley. The AMS dates show a long span of mortuary activity between the Middle Preclassic and Late Classic periods (405 cal BC to cal AD 770), with a hiatus in activity during the Early Postclassic (cal AD 900–1200) and subsequent activity in the Late Postclassic (cal AD 1280–1420). These results are not consistent with the idea that Baking Pot was occupied continuously from the Classic through Postclassic periods. This work highlights the need for additional AMS14C work at Baking Pot and elsewhere to establish absolute chronologies for evaluating the political and demographic collapse of Classic Maya regional centers.

A reassessment of the presumed Neandertal remains from San Bernardino Cave, Italy

In 1986–1987, three human remains were unearthed from macro-unit II of San Bernardino Cave (Berici Hills, Veneto, Italy), a deposit containing a late Mousterian lithic assemblage. The human remains (a distal phalanx, a lower right third molar and a lower right second deciduous incisor) do not show diagnostic morphological features that could be used to determine whether they were from Homo neanderthalensis or Homo sapiens. Despite being of small size, and thus more similar to recent H. sapiens, the specimens were attributed to Neandertals, primarily because they were found in Mousterian layers. We carried out a taxonomic reassessment of the lower right third molar (LRM3; San Bernardino 4) using digital morphometric analysis of the root, ancient DNA analysis, carbon and nitrogen isotope analyses, and direct accelerator mass spectrometry (AMS) radiocarbon dating of dentine collagen. Mitochondrial DNA analysis and root morphology show that the molar belongs to a modern human and not to a Neandertal. Carbon 14 (14C) dating of the molar attributes it to the end of the Middle Ages (1420–1480 cal AD, 2 sigma). Carbon and nitrogen isotope analyses suggest that the individual in question had a diet similar to that of Medieval Italians. These results show that the molar, as well as the other two human remains, belong to recent H. sapiens and were introduced in the Mousterian levels post-depositionally.

Accelerator Mass Spectrometry14C Dating and the Antiquity of Shell-Tempered Ceramics from the Chesapeake Bay and Middle Atlantic

AbstractCeramics typologies have long been used to build artifact, site, and regional chronologies. Direct accelerator mass spectrometry (AMS)14C dating of shell-tempered ceramics offers a promising tool for updating and improving these chronologies. Few studies have14C dated shell fragments from shell-tempered pottery, however, and questions remain about potential biases from “old shell,” the reservoir effect, and other variables. Forty-five direct AMS14C assays on shell-tempered pottery and associated shell, charcoal, and bone from nine archaeological sites in Virginia and Maryland provide a framework to test this method. AMS14C assays from one site may have problems with old shell, but most of the calibrated direct and associated age estimates overlap. One of our samples is the oldest securely dated shell-tempered pottery in North America at ~1000 cal B.C. Our study demonstrates the promise of AMS14C dating shell-tempered pottery for refining ceramic and regional chronologies in coastal and other areas around the world.

Simple, Rapid, and Cost Effective: A Screening Method for 14C Analysis of Small Carbonate Samples

We have developed a simple, rapid method to screen carbonates for survey applications, which provides radiocarbon dates with decreased precision at lower cost. The method is based on previous work by Longworth et al. (2011) and involves mixing pulverized CaCO3 with Fe powder, followed by pressing into aluminum target holders for direct 14C accelerator mass spectrometry (AMS) measurements. An optimum beam current averaging ∼10% of those produced by >0.7 mg C graphite targets was obtained for carbonate samples of 0.3–0.5 mg (0.04–0.06 mg C). The precision of the method was evaluated by measuring triplicates of 14C reference materials, as well as by comparing results from this rapid method with results from high-precision AMS measurements on graphite (typically 0.2–0.3%). Measurement reproducibility was ∼1.8% (1σ) for samples <10 ka BP, and it increased drastically for older samples. However, t tests on paired samples resulted in p values greater than 0.05, indicating a good correlation between this survey method and the conventional one. An average blank (calcite) of 0.0075 Fm (∼39 ka BP) was achieved. The simplicity of the technique allowed us to process and measure 72 deep-sea coral samples in less than 25 hr.

Simple, Rapid, and Cost Effective: A Screening Method for 14C Analysis of Small Carbonate Samples

We have developed a simple, rapid method to screen carbonates for survey applications, which provides radiocarbon dates with decreased precision at lower cost. The method is based on previous work by Longworth et al. (2011) and involves mixing pulverized CaCO3 with Fe powder, followed by pressing into aluminum target holders for direct 14C accelerator mass spectrometry (AMS) measurements. An optimum beam current averaging ∼10% of those produced by >0.7 mg C graphite targets was obtained for carbonate samples of 0.3–0.5 mg (0.04–0.06 mg C). The precision of the method was evaluated by measuring triplicates of 14C reference materials, as well as by comparing results from this rapid method with results from high-precision AMS measurements on graphite (typically 0.2–0.3%). Measurement reproducibility was ∼1.8% (1σ) for samples <10 ka BP, and it increased drastically for older samples. However, t tests on paired samples resulted in p values greater than 0.05, indicating a good correlation between this survey method and the conventional one. An average blank (calcite) of 0.0075 Fm (∼39 ka BP) was achieved. The simplicity of the technique allowed us to process and measure 72 deep-sea coral samples in less than 25 hr.

Radiocarbon Dating the Human Occupation at Sandia Cave, New Mexico

AbstractSandia Cave generated much interest when in the 1940s extinct Pleistocene megafauna were reported in association with what appeared to be a pre-Folsom Paleoindian component. By the 1950s a series of controversies regarding the stratigraphy and dating began to push the site into obscurity. The human occupation at the site has never been directly dated beyond 2250 ± 50 BP, and nonartifactual associated bone will not provide reliable age estimates because of extensive bioturbation, poor provenience, and the fact that the majority of fossils were accumulated by carnivores and rodents, rather than humans. However, a small number of mineralized fragments display human modification, suggesting occasional human activity of some antiquity at the site. One bone tool, one burned bone, and four bones bearing butchery marks were subjected to direct Accelerator Mass Spectrometry (AMS) 14C dating. Unfortunately, mineralized bones did not preserve sufficient collagen to be dated. Two unmineralized specimens (the burned bone and the bone tool) push the direct Chronometric ages for the human occupation at Sandia Cave back to 3447 ± 96 BP. An older Folsom occupation is suggested by associated dates on breccia, but all lines of evidence taken together provide no support for a pre-Folsom human occupation.

Symbolic Use of Terrestrial Gastropod Opercula during the Middle Stone Age at Porc‐Epic Cave, Ethiopia

The Middle Stone Age site of Porc‐Epic in southeastern Ethiopia has produced hundreds of opercula of the terrestrial gastropod Revoilia guillainopsis. Each of these opercula has a central perforation, and the unbroken specimens resemble disc beads. Microscopic examination could not unequivocally confirm their manufacture or use as beads. Their archaeological context indicates that their presence at the site was not the result of natural processes. Direct accelerator mass spectrometry dating of three opercula from different stratigraphic levels has produced ages ranging from about 33,000 to more than 43,000 years old. The opercula do not represent human food refuse but appear to have been collected by the Middle Stone Age occupants of the site for symbolic reasons.

AMS Radiocarbon Dating of Giant Rock Scallop (Hinnites Multirugosus) Artifacts from San Miguel Island, California, USA

For at least 100,000 yr, marine shell beads have been important ornamental and symbolic artifacts intimately associated with the behavior of anatomically modern humans. In California, giant rock scallop (Hinnites multirugosus) beads were once thought to have been used only for the last 1000 yr, where they were considered to be markers of high social status among the Chumash Indians of the Santa Barbara Channel region. Direct accelerator mass spectrometry (AMS) radiocarbon dating of 1 giant rock scallop ornament and 2 beads from San Miguel Island extends the use of this shell for personal adornment to at least 8000 cal BP. Our study emphasizes the importance of direct AMS14C dating of artifacts to enhance cultural chronologies and clarify the antiquity of various technologies and associated behaviors. Our results also caution archaeologists when equating artifact rarity with sociopolitical complexity.

Symbolic Use of Terrestrial Gastropod Opercula during the Middle Stone Age at Porc-Epic Cave, Ethiopia

The Middle Stone Age site of Porc‐Epic in southeastern Ethiopia has produced hundreds of opercula of the terrestrial gastropod Revoilia guillainopsis. Each of these opercula has a central perforation, and the unbroken specimens resemble disc beads. Microscopic examination could not unequivocally confirm their manufacture or use as beads. Their archaeological context indicates that their presence at the site was not the result of natural processes. Direct accelerator mass spectrometry dating of three opercula from different stratigraphic levels has produced ages ranging from about 33,000 to more than 43,000 years old. The opercula do not represent human food refuse but appear to have been collected by the Middle Stone Age occupants of the site for symbolic reasons.