• Ice-Core Dating of the Pleistocene/Holocene Boundary Applied to a Calibration of the 14C Time Scale

      Hammer, Claus U.; Clausen, Henrik B.; Tauber, Henrik (American Journal of Science, 1986-01-01)
      Seasonal variations in 18O content, in acidity, and in dust content have been used to count annual layers in the Dye 3 deep ice core back to the Late Glacial. In this way the Pleistocene/Holocene boundary has been absolutely dated to 8770 BC with an estimated error limit of +/- 150 years. If compared to the conventional 14C age of the same boundary a value of Delta-14C = 53 +/- 13 per mil is obtained. This Delta-14C value suggests that 14C levels during the Late Glacial were not substantially higher than during the Postglacial.
    • Identification, Extraction, and Preparation of Reliable Lime Samples for 14C Dating of Plasters and Mortars with the “Pure Lime Lumps” Technique

      Pesce, Giovanni L. A.; Ball, Richard J.; Quarta, Gianluca; Calcagnile, Lucio (Department of Geosciences, The University of Arizona, 2012-10-15)
      Radiocarbon dating was first applied to historic lime mortars during the 1960s. However, despite the relative simplicity of the technique in principle, a number of subsequent studies have highlighted important aspects that should be considered. One of the most significant of these challenges arises from sample contamination by carbonaceous substances such as incompletely burnt limestone and aggregates of fossil origin containing “dead” 14C. More recent studies have shown that in the majority of old lime-based mixtures the contamination problem can be avoided through selection of pure lime lumps. These particular types of lumps are believed to originate from areas where the lime is incompletely mixed with the aggregate. It has been demonstrated that even a single lime lump can provide sufficient material for a 14C date of the mortar from which the lump was taken (Pesce et al. 2009). This paper describes the practical challenges associated with location, extraction, and preparation of 4 lime lumps extracted from 2 new sites for 14C dating. These include distinguishing the lime lumps from other lumps present in the matrix and the removal of material surrounding the lime lump. The coherence of 14C dating with other archaeological information on the chronology of historic sites is highlighted through case studies.
    • IFAN Radiocarbon Laboratory Measurements I

      Ndeye, Maurice; Sene, Matar; Diallo, Alpha Oumar (Department of Geosciences, The University of Arizona, 2011-01-01)
      Results obtained from a liquid scintillation counter using BGO (Bi4Ge3012) tubes have produced more precise radiocarbon dates in our laboratory. Duplicate analyses confirm the electronic stability of the counter with a background of 0.1 cpm. Our 14C dates agree well with those from another laboratory (Paris 6-LOCEAN). Most of the 14C dates in this study were obtained on samples taken from different archaeological sites. Calibration of the various dates with the appropriate software (CALIB 5.0 in our case) allows better interpretation of the results and their importance in this understudied region. In this paper, we investigate the performance of the counter by analyzing samples from archaeological and marine sites in Senegal and Mauritania, and report the results in our first laboratory date list.
    • Illinois State Geological Survey Radiocarbon Dates I

      Kim, Stephen M.; Ruch, R. R. (American Journal of Science, 1969-01-01)
    • Illinois State Geological Survey Radiocarbon Dates II

      Kim, Stephen M. (American Journal of Science, 1969-12-31)
    • Illinois State Geological Survey Radiocarbon Dates III

      Coleman, Dennis D. (American Journal of Science, 1972-01-01)
    • Illinois State Geological Survey Radiocarbon Dates IV

      Coleman, Dennis D. (American Journal of Science, 1973-01-01)
    • Illinois State Geological Survey Radiocarbon Dates IX

      Liu, Chao-Li; Riley, Kerry M.; Coleman, Dennis D. (American Journal of Science, 1986-01-01)
    • Illinois State Geological Survey Radiocarbon Dates V

      Coleman, Dennis D. (American Journal of Science, 1974-01-01)
    • Illinois State Geological Survey Radiocarbon Dates VI

      Coleman, Dennis D.; Liu, Chao Li (American Journal of Science, 1975-01-01)
    • Illinois State Geological Survey Radiocarbon Dates VII

      Liu, Chao Li; Coleman, Dennis D. (American Journal of Science, 1981-01-01)
    • Illinois State Geological Survey Radiocarbon Dates VIII

      Liu, Chao-Li; Riley, Kerry M.; Coleman, Dennis D. (American Journal of Science, 1986-01-01)
    • Illinois State Geological Survey Radiocarbon Dates X

      Liu, Chao-Li; Asch, D. L.; Fisher, B. W.; Coleman, D. D. (Department of Geosciences, The University of Arizona, 1992-01-01)
      The following is a partial list of samples of archaeological interest processed between February 1981 and October 1985 at the Illinois State Geological Survey (ISGS) Radiocarbon Dating Laboratory. The list contains samples from west-central Illinois that were related to projects conducted by current or former researchers at the Center for American Archeology (CAA) (formerly Foundation for Illinois Archaeology) and Northwestern University, Department of Anthropology, or, as noted, by colleagues from other institutions. Although some of the samples reported here came from non-cultural contexts and are primarily of geological significance, all were from or related to archaeological investigations.
    • Illumination of a Black Box: Analysis of Gas Composition During Graphite Target Preparation

      McNichol, A. P.; Gagnon, A. R.; Jones, G. A.; Osborne, E. A. (Department of Geosciences, The University of Arizona, 1992-01-01)
      We conducted a study of relative gas composition changes of CO2, CO and CH4 during the formation of graphite targets using different temperatures, catalysts and methods. Reduction with H2 increases the reaction rate without compromising the quality of the AMS target produced. Methane is produced at virtually any temperature, and the amount produced is greater at very low temperatures. The reduction of CO to graphite is very slow when H2 is not included in the reaction.
    • Implication of Radiocarbon Dates from Sohr Damb/Nal, Balochistan

      Görsdorf, Jochen; Franke-Vogt, Ute (Department of Geosciences, The University of Arizona, 2007-01-01)
      Sohr Damb/Nal, the type site of the Nal complex, is located in Balochistan, Pakistan. After 1 season of excavation by H Hargreaves in 1924, which made the polychrome Nal pottery widely known, no further work took place until the Joint German-Pakistani Archaeological Mission to Kalat resumed excavations in 2001. So far, 4 seasons of excavations have been undertaken, which have revealed 4 periods of occupation, dated from about 3800 to 2000 BC. The well-stratified assemblages provide new insights into cultural processes and developments, and enhance the comparative frameworks through typological series and a comprehensive set of radiocarbon dates. This information is essential for assessing cross-cultural relations and the date of urbanization. In this paper, the 14C dates from Sohr Damb/Nal are presented and their cultural context is discussed. Period III has several links to sites in Pakistan, Afghanistan, and Iran, such as Miri Qalat IIIbc, Mehrgarh VIVII/ Nausharo I, Quetta III, Mundigak IV, and Shahr-e Sokhta IIIII. Period IV represents a Kulli-Harappan occupation, which is dated to the second half of the 3rd millennium BC.
    • Implications of Dipole Movement Secular Variation from 50,000-10,000 Years for the Radiocarbon Record

      Sternberg, R. S.; Damon, Paul E. (Department of Geosciences, The University of Arizona, 1992-01-01)
      Sparse paleointensity data from 10–50 ka suggest that the average dipole moment (DM) was 50–75% of the average of 8.67 X 1022 A m2 for the past 5 Ma, and 8.75 X 1022 for the past 12 ka. A linear ramp function, increasing the DM from 4 to 8.75 X 1022 A m2 between 50–10 ka BP, generates a total 14C inventory of 126 dpm/cme^2, agreeing very well with an inventory assay of 128 dpm/cme^2, which includes 14C in sediments. With the Lingenfelter and Ramaty (1970) production function and a model DC gain of about 100, this DM function would give a Delta-14C of 500 per mil at 20 ka BP, consistent with the Barbados coral record, and also gives a good match to the Holocene record. A Laschamp geomagnetic event at about 45 ka BP, with a DM of 25% of its average value and lasting 5 ka, would only increase the present inventory by 0.3–1.2 dpm/cme 2, and would probably have only a small effect on Delta-14C at 20 ka BP, but could produce a short-lived 14C spike of over 500 per mil.
    • Implications of Radiocarbon Dates from Potter Creek Cave, Shasta County, California, USA

      Feranec, Robert S. (Department of Geosciences, The University of Arizona, 2009-01-01)
      New dates obtained from the bone collagen of mammals from the deposits in Potter Creek Cave, Shasta County, California, USA, show that these fossils were emplaced over the last 30,000 yr. The dates support the assignment of the fauna in the cave to the late Pleistocene and are contemporaneous to the dates obtained from the fauna of Samwel Cave located 5 km to the north. These new dates do not support previous radiocarbon dates suggesting a Holocene extinction of the extinct bovid Euceratherium collinum, and demonstrate that this and other megafauna were not present in the vicinity after the terminal Pleistocene.
    • Importance of Biospheric CO2 in a Subcanopy Atmosphere Deduced from 14C AMS Measurements

      Grootes, P. M.; Farwell, G. W.; Schmidt, F. H.; Leach, D. D.; Stuiver, Minze (Department of Geosciences, The University of Arizona, 1989-01-01)
      14C concentrations in the stem cellulose of a Sitka spruce from the Pacific coast of Washington respond to changes in atmospheric 14CO2 concentration within 5-6 weeks. Delta-14C values for cellulose were consistently lower than those of the corresponding clean troposphere during rapid increase in atmospheric 14C caused by nuclear weapons tests (1962-64). Possible reasons for this include: 1) a delay of days or weeks in incorporation of recent photosynthate, 2) the use of stored photosynthate, and 3) photo-assimilation of biospheric decay CO2. We estimate that the influence of process 1 is small or negligible. The respective contributions to the total carbon deposited as radial stem growth in our Sitka spruce then are 2) <15% (possibly 0), and 3) 10-23% (13%-28% if the possible effect of root respiration is included in the biosphere d:cay component). We plan to test this concept by looking for a vertical 14C gradient in the 1963 growth ring of a tree located in a dense forest canopy; we do not expect to find such a gradient in a similar tree from a strongly wind-washed location.
    • Improved AMS 14C Dating of Shell Carbonates Using High-Precision X-Ray Diffraction and a Novel Density Separation Protocol (CarDS)

      Douka, K.; Hedges, R. E. M.; Higham, T. F. G. (Department of Geosciences, The University of Arizona, 2010-01-01)
      One critical variable in the successful application of radiocarbon dating is the effective removal of carbonaceous contaminants. In the case of marine carbonates, contamination appears usually in the form of secondary low-magnesium calcite, the stable polymorph of calcium carbonate and byproduct of the post-mortem recrystallization or replacement of the autochthonous phase, originally in the form of high-magnesium calcite or aragonite. Depending on the nature of the depositional environment, the secondary phase may be contemporary in age with the original shell carbonate and may have even been derived from it by dissolution-recrystallization processes, or can be an exogenous contaminant of younger or older age. The limited ability of current pretreatment protocols to detect and remove the secondary mineralogical phases prior to dating carbonates has been one of the reasons marine shell and coral 14C determinations are often difficult to validate in terms of their reliability. We have developed a new pretreatment protocol designed to achieve greater reliability and accuracy in the dating of this material. The method entails 2 steps. The first one involves the improved detection and quantification of secondary calcite in aragonite using X-ray diffraction, at a precision of ~0.1% and ~0.8%, respectively. Next, where this is required, a novel density separation step using non-toxic heavy liquids (CarDS) is applied to the diagenetic sample. This enables the clear separation of calcite and aragonite, with only the latter kept for dating. We have applied the new steps, screening and separation, on standard and archaeological examples and our initial results suggest that it is successful and reproducible. In this paper, we describe the method and initial results.
    • Improved Application of Bomb Carbon in Teeth for Forensic Investigation

      Wang, N.; Shen, C. D.; Ding, P.; Yi, W. X.; Sun, W. D.; Liu, K. X.; Ding, X. F.; Fu, D. P.; Yuan, J.; Yang, X. Y.; et al. (Department of Geosciences, The University of Arizona, 2010-01-01)
      While radiocarbon is widely applied in dating ancient samples, recent studies reveal that 14C concentrations in modern samples can also yield precise ages due to the atmospheric testing of thermonuclear devices between 1950 and 1963. 14C concentrations in both enamel and organic matter of 13 teeth from 2 areas in China were examined to evaluate and improve this method of forensic investigation. Choosing enamel near the cervix of the tooth can reduce the error caused by the difference between the sample formation time and whole enamel formation time because tooth enamel formations take a long time to complete. A proper regional data set will be helpful to get an accurate result when calculating the age of the sample (T1) by the CALIBomb program. By subtracting the enamel formation time (t), the birth date of an individual (T2) can be confirmed by enamel F14C from 2 teeth formed at different ages. Calculated enamel formation dates by 14C concentration are basically consistent with corresponding actual values, with a mean error of 1.9 yr for all results and 0.2 yr for the samples formed after AD 1960. This method is more effective for dating samples completed after AD 1960. We also found that 14C concentrations in organic matter of tooth roots are much lower than atmospheric concentrations in root formation years, suggesting that the organic material keeps turning over even after tooth formation is complete. This might be a potential tool for identification of death age to extract a proper component for 14C dating. We also observed that delta-13C values between hydroxyapatite and organic matter indicate that isotopic fractionation during the biomineralization is 8-9‰ more positive in mineral fractions than in organic matter.