• 14C Ages and Magnetic Stratigraphy in Three Australian Maars

      Barton, C. E.; Potach, H. A. (American Journal of Science, 1980-01-01)
      Detailed radiocarbon chronologies from three volcanic crater lakes (maars) in southeast Australia are examined in relationship to the magnetic mineral stratigraphies within lakes, and the magnetic secular variation stratigraphy between lakes. Some implications for magnetic dating are considered.
    • 14C in the Southern Indian Ocean

      Geyh, M. A. (American Journal of Science, 1980-01-01)
      14C measurements were carried out on sea water samples collected in 1973, in the Indian ocean. The results obtained for 9 vertical profiles between 27 degrees S and 48 degrees S are presented. In surface water, the bomb 14C content is maximum at middle latitudes. A time lag relative to the north hemisphere bomb 14C delivery is apparent. In the more southern latitudes, 14C content remains very low.
    • Age Structure of Holocene Coastal Sediments: Gulf of Carpentaria, Australia

      Rhodes, E. G.; Polach, H. A.; Thom, B. G.; Wilson, S. R. (American Journal of Science, 1980-01-01)
      Shells in beach-ridge and chenier Holocene deposits from the Gulf of Carpentaria, Queensland, have been dated by radiocarbon. Possible contamination of carbonate by post-depositional diagenetic processes, isotopic fractionation, ocean reservoir environmental effect, and association of biological age of sample material with depositional event have been examined in order to validate dating of samples from this environment. A numerical methodology used for comparing 'groups' of 14C dates strongly supports morphostratigraphic evidence that time discontinuities occur within both chenier and beach-ridge sequences. Four episodes are recognized in each area, all younger than ca 5800 years ago, the time when sea level reached its postglacial maximum in the Gulf of Carpentaria. To some extent, these episodes are out of phase, reflecting different modes of strandline accumulation.
    • Carbon Isotope Measurement as an Index of Soil Development

      Ladyman, S. J.; Harkness, D. D. (American Journal of Science, 1980-01-01)
      14C and 13C enrichment values are reported for a series of surface soil profiles which represent the progressive transition from mor to mull humus induced by birch (Betula pendula) colonization. Variations in Deltaand delta-13C, which range between 85 to 154 ppm modern and -28.1 to -25.3 ppm (PDB), respectively, reflect changes in the rate and mode of organic decomposition. The most marked alterations in soil character occur over the first few decades following the introduction of birch, with clear isotopic evidence for the deeper penetration and accelerated mineralization of organic material.
    • Direct Detection of 14C at the Harwell Tandem

      Shea, J. H.; Conlon, T. W.; Asher, James; Read, P. M. (American Journal of Science, 1980-01-01)
      Direct detection of 14C using the Harwell 6MV Tandem accelerator has been achieved using a gaseous ion source. The implications of our results for the use of such sources in this role and for the machine, in general, are discussed.
    • Climate Periods in Trees and a Sea Sediment Core

      Pandolfi, L. J.; Kalil, E. L.; Doose, Paul Robin; Levine, L. H.; Libby, L. M. (American Journal of Science, 1980-01-01)
      Chemical components in a sea sediment core from the Santa Barbara Basin show the same periodic variations as do stable isotope variations in a Japanese cedar.
    • Workshop on 14C Reporting

      Stuiver, Minze (American Journal of Science, 1980-01-01)
    • W. F. Libby and the Archaeologists, 1946-1948

      Marlowe, Greg (American Journal of Science, 1980-01-01)
      Archaeologists began to participate in cross-disciplinary endeavors in the 1930's, albeit on a very limited basis. The passage of time found members of that discipline unprepared for collaboration with physical scientists when W F Libby announced the development of the radiocarbon dating method. Libby proposed to apply to archeologic and geologic samples techniques based on ideas that were completely foreign to archeology.... The initial reactions of archeologists were sometimes amusing but more often significant, for they led to the foundation and emergence of the radiocarbon chronology that has so profoundly affected our understanding of prehistory (Johnson, 1967, p 165). To date, our historical knowledge about the nature, function, and impact of the early (1946-1948) relations between Libby and American archaeologists has come to us in the form of published anecdotes, many of which contain inaccurate information. The author's access to W F Libby's private 14C correspondence, combined with data obtained from interviews with some of the principal participants throughout this period, offers many new or different insights into the nascent years of radiocarbon dating. When, and under what unexpected cricumstances, did Libby first encounter representatives of the achaeologic community? What strategies were employed to facilitate diffusion of knowledge about 14C dating across disciplinary boundaries? How did archaeologists respond to the introduction or "intrusion" into their field of Libby's radioactive age-measurement tool?
    • 14C Dating of Recent Crustal Movements in the Persian Gulf and the Iranian Makran

      Vita-Finzi, Claudio (American Journal of Science, 1980-01-01)
      Radiocarbon dating of mollusks and barnacles from fossil shoreline deposits in the Persian Gulf and on the coast of Iranian Makran is being used to assess the extent and rate of recent crustal deformation in the area. Samples are selected with the help of x-ray diffraction and of light and scanning electron microscopy; whenever possible, two or more ages are determined for each locality on monospecific samples. Age/height values have been used to compute local uplift rates by allowing for sea-level fluctuations, but eustatic controversy can be avoided by limiting the analysis to fault chronology and to relative vertical movements between dated sections. Short counting times on large, carefully pretreated samples would supply the numerous, cheap, low-resolution ages required to follow up the preliminary results obtained by the survey.
    • Ages of Charcoal Samples of Geomorphological Interest in Northeast Hungary

      Csongor, Eva; Borsy, Zoltán; Szabó, Ilona (American Journal of Science, 1980-01-01)
      There are extended wind-blown sand territories in the northeastern part of the Great Hungarian Plain. Wind-blown sand migration periods were distinguished by means of radiocarbon age determination of charcoal samples found in the same type of a thin soil layer of chernozem character in different sand dune exposures. The ages of the samples were determined by proportional counter, and are around 12,000 years BP. This thin fossil soil layer, which is regionally spread in the northeast Hungarian wind-blown sand areas, presents a chronological mark between the blown sand forms evolved in the last glacial period and in the Holocene.
    • 14C Interlaboratory Comparison in the UK: Experiment Design, Preparation, and Preliminary Results

      Otlet, R. L.; Walker, A. J.; Hewson, A. D.; Burleigh, R. (American Journal of Science, 1980-01-01)
      An interlaboratory comparison experiment for 14C measurements has been organized jointly by the Harwell and British Museum laboratories to include the working radiocarbon laboratories of the United Kingdom. The experiment has been run along the lines of that organized by the IAEA for tritium and has explored the problems of sample preparation, verification of equivalent levels, and presentation of results. Samples of benzene representing 5 age equivalent levels between twice modern and 20,000 years old have been prepared and distributed for measurement either by direct counting (liquid scintillation) or full process tests. Preliminary results received show excellent agreement both between laboratories and in comparison with the known relative activities of the prepared solutions. The possibility of extending the experiment to cover different sample types and a wider distribution of testing laboratories is briefly discussed.
    • Unreliability of 14C Dates from Organic Matter of Soils

      Gilet-Blein, Nicole; Marien, Gérard; Evin, Jacques (American Journal of Science, 1980-01-01)
      Contamination by recent carbon and the turnover of organic matter make dating of ancient soils difficult. In order to isolate the oldest organic fraction of sediments, two main extraction methods were previously proposed: 1) alkaline solubilization of humus that separates humins, humic acids, and fulvic acids, and 2) successive hydrolyses that solubilize increasingly resisting products. Both preparation methods were tested on the same actual or fossil soils of different pedologic types from five geologic profiles on which other chronologic data are available. Analytic results show that 14C ages obtained from alkaline extraction products differ according to the duration of treatments and characteristics of soils: while hydrolysis should yield more homogeneous results and isolate oldest fractions. It seems likely that true ages of geologic formations were never obtained from their organic matter and that the oldest organic fraction, contemporaneous with the sediment formation, completely disappears. Thus, most ages from 14C dating of organic matter of soils must be too recent.
    • Soil Dating by Fractional Extraction of Humic Acid

      Kigoshi, Kunihiko; Suzuki, Nobuko; Shiraki, Mari (American Journal of Science, 1980-01-01)
      The addition of organic materials derived from the upper soil layer yields, for samples at greater depth, younger 14C dates than the date of deposition. To find a criterion for the contamination with younger carbon in a soil sample, we examined the radiocarbon concentrations in two humic acid fractions and humin taken from the same sample. The humic acid extracted from a soil sample was divided into two fractions HA1 and HA2. HA1 is the first fraction extracted by 30 minutes' heating with 2 percent NaOH solution, and HA2 is the second fraction extracted by 2 hours' heating with 2 percent NaOH solution after the extraction of HA1. The residue was assumed as the humin (HM). Many of the peat or soil samples taken from the layer just above the nonpermeable layer contain appreciable amounts of organic materials transported from the upper layer after the sedimentation of the deposits. For the limited number of cases tested here, there is a trend in which the contaminants are selectively extracted by HAl or HA2. When the soil samples are contaminated the ages of the HA1 and HA2 fractions appeared to differ widely in most cases. Agreement between the HA1, HA2, and HM ages may be used as a criterion for the reliability of the soil dating.
    • Radiocarbon Concentration in the Atmosphere: 8000-Year Record of Variations in Tree Rings: First Results of a USA Workshop

      Klein, Jeffrey; Lerman, Juan Carlos; Damon, Paul E.; Linick, Timothy (American Journal of Science, 1980-01-01)
    • Radiocarbon Activity Measurements of Oolitic Sediments from the Persian Gulf

      Šilar, Jan (American Journal of Science, 1980-01-01)
      Radiocarbon activity of successive parts of Pleistocene and Holocene ooids and mollusk shells from the Persian Gulf, Kuwait, was measured. The inner part of the ooids showed the lowest activity and the cement between grains the highest. Radiocarbon activities correspond to the general stratigraphy and to the position of the sediments. Radiocarbon ages of Pleistocene sediments seem to be very low due to recrystallization of aragonite. Higher radiocarbon activity of cement indicates that atmospheric carbon dioxide was involved in the subaerial diagenetic process. The radiocarbon age of well-preserved mollusk shells seems to be lower than their allegedly Pleistocene geologic age.
    • Progress in Radiocarbon Dating with the Chalk River MP Tandem Accelerator

      Andrews, H. R.; Ball, G. C.; Brown, R. M.; Davies, W. G.; Imahori, Yoshio; Milton, J. D. (American Journal of Science, 1980-01-01)
      The evolution of a tandem accelerator 14C dating system at Chalk River is recounted. Background problems and sources of instability are discussed and solutions are described. Details of sample chemistry and source preparation are presented.
    • Radiocarbon Dating of Pleistocene Bone: Toward Criteria for the Selection of Samples

      Taylor, R. E. (American Journal of Science, 1980-01-01)
      Amino acid composition data and stable isotope ratios (14N, D, and 13C) are being evaluated as sources of information to indicate the presence of non-indigenous organics in bone samples intended for 14C analyses. The study is being conducted in the context of the planned measurement of Pleistocene bone samples by a high energy mass spectrometric 14C detection system.
    • Radiometric Dating with University of Washington Tandem Van de Graaff Accelerator

      Farwell, G. W.; Schaad, T. P.; Schmidt, F. H.; Tsang, M.-Y. B.; Grootes, P. M.; Stuiver, Minze (American Journal of Science, 1980-01-01)
      The University of Washington Model FN tandem Van de Graaff accelerator is being used for the measurement of extremely small isotopic ratios, notably 14C/12C and 10Be/9Be, in a joint project of the Nuclear Physics Laboratory (NPL) and the Quaternary Isotope Laboratory (QL). The experimental arrangements and technical developments are described, and some preliminary results on isotopic ratios in carbon and beryllium are presented.
    • Bomb-Produced Carbon-14 in the Surface Water of the Pacific Ocean

      Linick, T. W. (American Journal of Science, 1980-01-01)
      The distribution of 14C concentrations in the dissolved inorganic carbon in the surface waters of the Pacific Ocean is shown to have a primarily latitudinal pattern with Delta-14C maxima at mid-latitudes in both hemispheres and a minimum at the equator. Oceanographic causes of this phenomenon are discussed.