Radiocarbon最新文献

Northern Arizona University, Flagstaff, Arizona, USA, recently installed a MIni CArbon DAting System (MICADAS) with a gas interface system (GIS) for determining the 14C content of CO2 gas released by the acid dissolution of biogenic carbonates. We compare 48 paired graphite, GIS, and direct carbonate 14C determinations of individual mollusk shells and echinoid tests. GIS sample sizes ranged between 0.5 and 1.5 mg and span 0.1 to 45.1 ka BP (n = 42). A reduced major axis regression shows a strong relationship between GIS and graphite percent Modern Carbon (pMC) values (m = 1.011; 95% CI [0.997–1.023], R2 = 0.999) that is superior to the relationship between the direct carbonate and graphite values (m = 0.978; 95% CI [0.959-0.999], R2 = 0.997). Sixty percent of GIS pMC values are within ±0.5 pMC of their graphite counterparts, compared to 26% of direct carbonate pMC values. The precision of GIS analyses is approximately ±70 14C yrs to 6.5 ka BP and decreases to approximately ±130 14C yrs at 12.5 ka BP. This precision is on par with direct carbonate and is approximately five times larger than for graphite. Six Plio-Pleistocene mollusk and echinoid samples yield finite ages when analyzed as direct carbonate but yield non-finite ages when analyzed as graphite or as GIS. Our results show that GIS 14C dating of biogenic carbonates is preferable to direct carbonate 14C dating and is an efficient alternative to standard graphite 14C dating when the precision of graphite 14C dating is not required.

This article discusses the absolute chronology of burials from the 3rd and 2nd millennia BC discovered under the mounds of three barrows in the Kordyshiv cemetery in western Ukraine. Its aim is to create a chronological model of the burials by modeling 27 AMS 14C dates obtained from 21 individuals buried in single and collective graves. Dietary analysis of stable carbon (δ13C) and nitrogen (δ15N) isotope values are presented. The Bayesian modeling of the 14C dates from the three Kordyshiv barrows revealed the extremely important role of these monuments as long-term objects used for ritual purposes. At the end of the 3rd millennium BC, the epi-Corded Ware Culture (epi-CWC) community erected a mound over the central burial in Barrow 2, then interred the graves of three additional deceased. After several hundred years Barrow 2 was reused by Komarów Culture (KC) communities from the Middle Bronze Age (MBA) who interred their deceased in the existing mound. The oldest monument with MBA burials was Barrow 3, in which the dead were buried in a two-stage sequence before and after the mid-2nd millennium BC. The youngest dated grave was Burial 1 in Barrow 1, comprising a collective burial that was interred between 1400 and 1200 BC. The additional analyses of carbon and nitrogen isotopes show significant differences in the diet of epi-CWC individuals buried in Barrow 2 from the individuals representing the KC.

Estimation of residence time of groundwater, particularly in regions with inadequate surface waters are very important for formulating sustainable groundwater management policies. We developed a technique for extracting dissolved inorganic carbon (DIC) quantitatively from water for measuring its 14C contents and presented the analytical details here. We also measured stable carbon isotope ratio (δ13C) in soil CO2 and groundwater DIC to correct the groundwater 14C ages. In addition, 14C in soil CO2 were measured for making necessary correction in the initial activity of the recharging water. The corrected 14C contents in the groundwater samples were used to estimate their residence times employing Lumped Parameter Models (LPM), a set of mathematical models to account for the processes that take place during transport from the recharge to the sampling spots. We present a case study focused on the calculation of radiocarbon ages and residence times for a groundwater sample collected from the campus of Physical Research Laboratory in Ahmedabad, Gujarat, India. The study also includes estimations of groundwater residence times using previously measured 14C ages of groundwater samples from Gujarat, India. Various factors controlling the groundwater ages in the LPM and their applicability are discussed.

A low-cost and computer-controlled graphitization system connected to an elemental analyzer (EA) has been designed and built at the NTUAMS Lab. This semiautomatic system equips 6-unit reactors for the graphitization of CO2 with H2 on the iron catalyst. The entire procedure takes about 7 hours for iron conditioning, sample combustion and loading, and graphitization. The system can produce good-quality graphite for samples containing 0.5–1.6 mg carbon mass, with the pressure yield of graphitization ranging from 57.7% to 87.1%. The average values of OXI and OXII agree well with the consensus value, but the result of ANU sucrose was observed to be slightly higher than the reported one. The background samples of anthracite over ten months yielded an average of 0.38±0.10 pMC (n=21) corresponding to a 14C age of 45 kyr BP. Intercomparison samples L and M of FIRI exhibit that the measured 14C ages are almost identical to the consensus values and have a small spread in these values. The system has been carrying out graphitization for total organic carbon (TOC) of peat samples, and providing a more efficient and convenient way for AMS 14C dating.

Dates from recently excavated Gangetic site of Sakas in Bihar, India, place it at ca.1800–1100 BC. The ceramic and lithic chronologies have been interpreted as Early Farming, Transitional and Chalcolithic/Developed Farming in date. However, depending on where in the Ganges Plains is studied, the time frame of Early, Developed and Advanced Farming periods varies widely, from 7th millennium to 2nd millennium BC and beyond, making the chronological framing of absolute dates within a regional scheme highly complex. In this paper we report the new radiocarbon results from Sakas and note how while these are critical for cementing the absolute dating of the site, until such time as a more stable periodization linked not only to relative and absolute dates but also human lifeways within the different zones of the Ganges plains is created, there remains difficulties in understanding how Sakas and other sites of similar date fit into the changing social, cultural and economic systems in this region.

Based on the study of the primary documentation related to the excavations carried out by Eurico Miller in the 1970s at Abrigo do Sol, Mato Grosso (Brazil), we propose a new reading of the stratigraphic and chronological information obtained from this rock shelter. Despite the apparent incongruity in the chrono-stratigraphic distribution of published dates, a detailed examination of the stratigraphy and field notes allowed us to identify a chronometric sequence with regular distribution between the Middle Holocene and the Late Pleistocene periods for the Abrigo do Sol site. We present here the original documents related to radiocarbon dating and their analysis. We finally show the implications of this study for understanding this site and the discussions related to the ancient settlements of the Amazon forest.