Radiocarbon最新文献

There are now 101 radiocarbon dates from the long Paleolithic and post-Paleolithic culture-stratigraphic sequence in El Mirón Cave, Cantabrian Spain. Here we report on two dates on bone from two different humans whose remains were found in disturbed surface sediments in the cave vestibule rear and that confirm the existence of burials in addition to previously reported residential occupations in the vestibule front pertaining to the Chalcolithic and early Bronze Age periods (ca. 5500–3500 cal BP). In another attempt to resolve problems of stratigraphic incoherence of dates from the early Magdalenian periods in the vestibule rear, six new assays on faunal remains from Levels 119, 117, 114, 108, and 106 were run at Queen’s University in Belfast. There continue to be date inversions in the Lower Magdalenian range of levels that may be explained by a combination of intensive anthropic and rodent activity, major rock fall, slope wash and gravity-caused object movements, as well as possible problems in following some thin levels during excavations over a large area and across many years of work in the cave vestibule interior, particularly in the absence of any layers that are culturally sterile or even poor. Nonetheless, the coherent age of the Initial Magdalenian is fully confirmed by a new date from Level 21 in the vestibule front at ca. 22,000–20,500 cal BP), as is the general age range of the Lower Magdalenian (ca. 20,500–18,000 cal BP).

Seven accelerator mass spectrometry radiocarbon (AMS 14C) dates (7260±106∼7607±95 BP averaged 7444±103 BP) on a giant oyster shell, collected from an ancient shore of the Taipei Basin, are similar to the LSC (liquid scintillation counting) 14C age (7260±46 BP) of a grass sample inside the shell. The calibrated 14C ages of the C. gigas by Marine20 are 7490±240∼7805±230 cal BP (average 7660±96 cal BP), generally agreed with the calibrated LSC 14C ages of the grass and the oyster shell. Combined with other 14C ages of shoreline samples in the Taipei Basin, it is evident that sea level rose from 8600 to 7600 cal BP and reached a stand higher than modern sea level. During this marine transgression, the sedimentation rate along the shoreline was very high because 14C dating was not able to detect age differences for 4–5 m thick sediment sequences. Sixty-nine analyses of δ18O and δ13C from the oldest part of the shell exhibit clear seasonal cycles, with a 4-year period of growth in the 5.5-cm section. According to the δ18O values, the ancient oyster grew in a warmer-than-present shoreline environment, suggesting that the current absence of the giant oyster in Taiwan is not due to warming conditions.

Marine radiocarbon (14C) ages are an important geochronology tool for the understanding of past earthquakes and tsunamis that have impacted the coastline of New Zealand. To advance this field of research, we need an improved understanding of the radiocarbon marine reservoir correction for coastal waters of New Zealand. Here we report 170 new ΔR20 (1900–1950) measurements from around New Zealand made on pre-1950 marine shells and mollusks killed by the 1931 Napier earthquake. The influence of feeding method, living depth and environmental preference on ΔR is evaluated and we find no influence from these factors except for samples living at or around the high tide mark on rocky open coastlines, which tend to have anomalously low ΔR values. We examine how ΔR varies spatially around the New Zealand coastline and identify continuous stretches of coastline with statistically similar ΔR values. We recommend subdividing the New Zealand coast into four regions with different marine reservoir corrections: A: south and western South Island, ΔR20 –113 ± 33 yr, B: Cook Strait and western North Island, ΔR20 –171 ± 29 yr, C: northeastern North Island, ΔR20 –143 ± 18 yr, D: eastern North Island and eastern South Island, ΔR20 –70 ± 39 yr.

The absolute dating of mortar by accelerator mass spectrometry (AMS) has been the subject of renewed interest for several years. International intercomparison campaigns, called MODIS (MOrtar Dating Intercomparison Study), have been carried out. The first MODIS-1 campaign highlighted limitations in mortar dating, due to the similarity between the primary material to be dated (binder) and the contaminant (exogenous CaCO3). Methods have since emerged to overcome this problem and the need for a good preliminary characterization has been proven. The Laboratoire de Mesure du Carbone 14 (LMC14) took part in the second intercomparison campaign, MODIS2, by applying thermal decomposition increments to distinguish the carbonated binder, the organic matter contaminants (late in formation pyrogenic carbonate, LDH) and limestone. The LMC14 results on MODIS2 are quite conclusive on “pure” re-carbonated lime mortar binders containing little contaminant geological limestone but show their weaknesses for mortars heavily contaminated in Dolomites, which are difficult to discern from the binder. Recommendations for users of radiocarbon (14C) dating on mortar-based materials are made in the conclusion.

The comparisons among 126 14C dates of Carex samples including separated leaf and root parts with acid (A)-treatment and acid-base-acid (ABA)-treatment, and 48 published 14C dates of bulk peat plants on a 92-cm core from Jinchuan Mire in NE China, indicate old carbon influence (OCI) on the 14C dates. The OCI varies with plant species, pretreatment and peat depth. In vascular peat plants such as Carex, humin fractions (remains after ABA treatment) and humic acids are representative of the original plant precursor, while fulvic acids are regarded as the secondary mobile product which should be removed for 14C dating. ABA- treatment removes both fulvic acids and humic acids, whereas A-treatment gets rid of only fulvic acids. Carex roots uptake more dissolved CO2 in peat water. Carex leaves may use more CO2 (involving degassing CO2) above the peat surface. By removing humic acids throughout ABA treatment, the OCI may vary differently over depth (time). ABA treatment cannot eliminate the fixed OCI in humin fractions of vascular peat plants, instead, this treatment may enhance OCI by removing humic acid which may represent the true age of the plants. In addition, Bacon model results on this core could not show rapid changes in accumulation rate.

The Lagoa Salgada is located in the Paraíba do Sul river delta plain on the coast of Rio de Janeiro state, Brazil, and is one of the few lagoons in the world that have well-developed recent stromatolites. Lagoa Salgada is a hypersaline lagoon formed in a very complex environmental system subjected to terrestrial and oceanic influences under different sea level regimes and climate variations. In addition, sediment and stromatolites are characterized by unusually positive inorganic δ13C VPDB values. For this reason, it has been the target of several geological and paleoenvironmental studies, which, in their great majority, require a geochronological technique in order to determine the changes in the environment over time. When radiocarbon (14C) dating is used, it is necessary to consider some details as the source of 14C in the environment and perform 14C ages calibration accordingly. In the present paper, a bibliographic survey was carried out in order to review the data treatment and improve the environmental evolution discussion based on accurate calibration. Using the Marine20 curve and an undetermined ΔR, we generated growth and depositional models to establish an overview of the formation of this lagoon.

This paper uses a “dates as data” approach to understand how grave good use and cemetery space changed across the early medieval period in England. A series of composite kernel density estimations were created, based on a dataset of nearly 1100 graves with associated radiocarbon dates, from between the fourth and ninth centuries AD. This modeling revealed a previously unrecognized peak in grave furnishing around 600 AD, which coincides with a peak in isolated burials, and a low point for unfurnished graves and for small cemeteries. It argues that this peak is unrecognized as previous models of chronological change have focused only on graves containing chronologically distinctive artifacts and highlights the importance of radiocarbon dating as a way of avoiding this limitation.

Eight atmospheric carbon dioxide samples (as calcium carbonate—CaCO3—precipitates) from Lindesnes site (58ºN, 7ºE), belonging to 1963 and 1980 (four samples from each year) and stored at the National Laboratory for Age Determination (NTNU), have been reevaluated through radiocarbon (14C) analysis. Previous 14C results indicated the presence of a contaminant, which was not removed through different chemical cleansing procedures (e.g., hydrochloric acid—HCl and/or hydrogen peroxide—H2O2). Here, we present a follow up investigation using 14C step-combustion and Fourier-transform infrared spectroscopy (FTIR) analysis. Results from 14C data indicate unsuccessful removal of the contaminant, while further FTIR analysis displayed the presence of moisture. This finding alludes to the possibility that the contaminant is of ambient air-CO2 deeply embedded in CaCO3 powders (within clogged CaCO3 pores and/or bonded to the lattice). Samples were found exposed to air-CO2 and humidity. These conditions may have lasted for years, possibly even decades, leading to the 14C offsets detected here.