14C terrestrial ages of nine Antarctic meteorites using CO and CO2 temperature extractions

As a continuation of the work reported in R. P. BEUKENS et al. (Proc. NIPR Symp. Antarct. Meteorites, 1,224,1988), a suite of Yamato and Trans-Antarctic Mountains meteorites have been analyzed for their ^C content, to give an estimate of their terrestrial age. Further information on the samples\u27 terrestrial history may be obtained from analysis of separate carbon species evolved at different temperatures. We report on data obtained from CO and CO_2 separations from a low temperature (500℃ to 900℃) and high temperature (≈1600℃) fraction from each sample. Three Allan Hills meteorites, ALH-77232 (H4), ALH-78112 (L6) and ALH-78130 (L6), give terrestrial ages >29000 years, and probably represent limit ages due to in situ production. Three other Trans-Antarctic meteorites, BTN-78002 (L6), MET-78028 (L6) and RKP-78002 (H4), give finite ^C ages between 15000 and 27000 years. Three Yamato meteorites, Y-8011 (L6), Y-81132 (H5) and Y-82095 (L3), give ages between 16000 and 22000 years. The low temperature components indicate that recent weathering and atmospheric exchange has taken place for at least four (and possibly six) of the meteorites; ALH-78112,ALH-78130 and Y-81132 have low temperature activities that suggest an earlier exposure and weathering

High-Precision Intercomparison at IsoTrace

From the International Workshop on Intercomparison of Radiocarbon Laboratories.I conducted a high-precision comparison at the 0.2% to 0.3% level with samples supplied by the radiocarbon laboratory of the Quaternary Research Center at the University of Washington (QRC). Four samples with ages ranging from modern to > 50,000 BP were dated in a blind test. The absence of cosmic-radiation background in AMS dating is a major advantage for dating samples > 35,000 BP. The reliability of AMS dates > 35,000 BP depends entirely on understanding the contamination processes. By comparing results with laboratories capable of sample enrichment, such as QRC, it is possible to identify and estimate the intrinsic 14C in the background samples as well as the contamination introduced by sample preparation.This material was digitized as part of a cooperative project between Radiocarbon and the University of Arizona Libraries.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Progress at the IsoTrace Radiocarbon Facility

From the 12th International Radiocarbon Conference held in Trondheim, June 24-28, 1985.Since August 1984 over 100 samples have been analyzed. 12C, 13C, and 14C isotopes were measured after acceleration and all dates were corrected for natural and preparation-induced fractionation. A precision of better than 1.0% was obtained for samples 10,000 yr BP or less and these results were shown to be reproducible at precision levels as low as 0.3%. An accuracy of better than 1.0% was demonstrated for the same age range by analyzing samples which were previously dated with the conventional technique. The machine background, measured on blank sample holders in a clean ion source, yielded a count rate equivalent of 0.015 +/- 0.007% modern.This material was digitized as part of a cooperative project between Radiocarbon and the University of Arizona Libraries.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Radiocarbon Dates from Neolithic and Bronze Age Hunter-Gatherer Cemeteries in the Cis-Baikal Region of Siberia

Extensive radiocarbon dating of human remains from Neolithic and Bronze Age hunter-gatherer cemeteries in the Cis-Baikal region of Siberia has been undertaken as a part of the multidisciplinary examination of this material conducted by the Baikal Archaeology Project (BAP; http:// baikal.arts.ualberta.ca). Due to the large number of analyzed samples, this paper reports the 14C results only in the context of the basic archaeological information about each of the cemeteries. Comprehensive evaluation, analysis, and interpretation of this entire data set will be undertaken in separate publications. In fact, the dates for one such cemetery have already been examined on 2 recent occasions (Weber et al. 2004, 2005).The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Fired glaciofluvial sediment in the northwestern Andes: Biotic aspects of the Black Mat

International audienceFired glaciofluvial beds in outwash considered to date from the onset of the Younger Dryas Event (~ 12.9 ka) in the northwestern Venezuelan Andes are considered equivalent to the Black Mat deposits described in other areas of North and South America and Europe. It may be equivalent to sediment recovered from other sites containing beds with spikes of cosmic nuclides and charcoal indicating the presence of widespread fire, one of the signatures of the Black Mat conflagration that followed the proposed breakup of Comet Encke or an unknown asteroid over the Laurentide Icesheet at 12.9 ka. In the northern Andes at Site MUM7B, sediment considered coeval with the Black Mat contains glassy carbon spherules, tri-coatings of C welded onto quartz and feldspar covered with Fe and Mn. Monazite with excessive concentrations of REEs, platinum metals including Ru and Rh, possible pdf's, and disrupted/brecciated and microfractured quartz and feldspar from impacting ejecta and excessive heating summarize the data obtained so far. The purpose of this paper is to document the physical character, mineralogy and biotic composition of the Black Mat