• 14C Laboratories

      Department of Geosciences, The University of Arizona, 1995-01-01
    • 16th International Radiocarbon Conference

      Department of Geosciences, The University of Arizona, 1995-01-01
    • 1996 Price List

      Department of Geosciences, The University of Arizona, 1995-01-01
    • 3rd International Symposium

      Department of Geosciences, The University of Arizona, 1995-01-01
    • A Note on Calibration Curves

      van der Plicht, J.; McCormac, F. G. (Department of Geosciences, The University of Arizona, 1995-01-01)
    • A Radiocarbon Chronology for Prehistoric Agriculture in the Society Islands, French Polynesia

      Lepofsky, Dana (Department of Geosciences, The University of Arizona, 1995-01-01)
      I discuss a suite of 29 radiocarbon age determinations from four valleys on the islands of Mo'orea and Raiatea in the Society Archipelago. These dates provide the first sequence for the development of prehistoric agricultural production and human-induced environmental change in the Society Islands. Indirect evidence of small-scale agriculture, and by association, human occupation, dates to at least the 7th-10th centuries AD. Agricultural sites themselves date from the early 13th century AD until the late prehistoric/early historic period, with most agricultural activity clustering at the end of the temporal sequence. Valleys with the greatest arable potential were cultivated earlier than less preferred sites. Evidence for extensive landscape transformation in the Opunohu Valley, likely associated with clearing for agricultural purposes, begins soon after the earliest evidence for cultivation and continues throughout prehistory. A larger sample of 14C determinations from stratigraphic excavations in both archaeological sites and "off-site" contexts is required to address many as yet unanswered questions about the prehistoric social and economic development of the Society Islands.
    • Associate Editors

      Department of Geosciences, The University of Arizona, 1995-01-01
    • Author Index Volume 37, Nos. 1 and 3, 1995

      Department of Geosciences, The University of Arizona, 1995-01-01
    • Comparing 14C Histograms: An Approach Based on Approximate Randomization Techniques

      Dye, Tom (Department of Geosciences, The University of Arizona, 1995-01-01)
      An approximate randomization technique for comparing 14C histograms is described and illustrated with an example from Hawai'i. The technique determines intervals of significant difference in the histograms, rather than providing a single number summary.
    • Errata

      Department of Geosciences, The University of Arizona, 1995-01-01
    • Extraction of 14C from Pore Water in Unsaturated Rock Using Vacuum Distillation

      Davidson, G. R.; Hardin, E. L.; Bassett, R. L. (Department of Geosciences, The University of Arizona, 1995-01-01)
      We discuss a vacuum-distillation method for obtaining representative 14C samples from dissolved inorganic carbon in rock pore-waters. Distillation offers four advantages over current centrifugation and compression methods for obtaining pore-water carbon: 1) carbon recovery is possible from rocks that will not yield water by centrifugation or compression; 2) the mass required for 14C analysis can typically be obtained in a single extraction, eliminating the need for storing and combining multiple pore-water collections; 3) water and carbon are extracted and isolated simultaneously, reducing the number of required steps and the potential for contamination; and 4) distillation requires less equipment at lower cost than centrifugation or compression. In this study, isotopic fractionation resulting from incomplete recovery of carbon during distillation was too high for stable isotope applications, but was relatively minor for 14C applications. The lighter isotopes were favored in the recovered phase, resulting in samples depleted in 14C by a maximum of 4%. Mass balance calculations indicate that there may be a significant reservoir of carbon absorbed to mineral surfaces that is only partially removed by this method. Incorporation of adsorbed carbon into the recovered sample did not measurably alter the 14C activity.
    • From the Editor

      Long, Austin (Department of Geosciences, The University of Arizona, 1995-01-01)
    • Further Evidence of Changing Stability of the Atmosphere

      Hartwig, Sylvius (Department of Geosciences, The University of Arizona, 1995-01-01)
    • Improved Radiocarbon Age Estimation Using the Bootstrap

      Aczel, Amir D. (Department of Geosciences, The University of Arizona, 1995-01-01)
      This paper proposes the use of the statistical bootstrap technique as an aid in combining radiocarbon date estimates. The rationale for the use of the bootstrap is the theoretical result that, even if individual date estimates are normally distributed, their combination by the usual formula results in a random quantity that is not normal but rather a mixture of distributions. The bootstrap is a non-parametric, computer-intensive technique. This technique can better estimate the actual distribution of the combined age, leading to more precise confidence intervals. While the bootstrap cannot solve the multiple-intercepts problem in calibration, it can nonetheless lead to better estimates. The benefits of using the bootstrap are especially noticeable when sample sizes are small (as is the case in other applications of this technique).
    • Locating Archaeological Horizons with 14C Sediment Dating: The Case of the Lost City of Helike

      Maniatis, Yannis; Facorellis, Yorgos; Soter, Steven; Katsonopoulou, Dora; Kromer, Bernd (Department of Geosciences, The University of Arizona, 1995-01-01)
      In 373 BC a catastrophic earthquake and seismic sea wave destroyed Helike, a Greek city near Aigion on the southern shore of the Gulf of Corinth. The ruins were buried by sediments of unknown depth, leaving no trace of the city. We here discuss the radiocarbon dating of organic sediment samples recovered from seven boreholes drilled on the coastal plain in the area where ancient sources located Helike. Most of the samples apparently acquired a substantial addition of older carbon from natural sources, and hence their apparent ages are older than the true ages of sedimentation. However, if we assume that the addition is systematic, we can use the apparent ages to show that the sedimentation rate was initially rapid (about 1 cm yr-1) for the strata between 40 and 10 m below the surface, and then decreased by an order of magnitude about 6500 yr ago. A related change in the sediment deposition at about the same time has been found in many other marine deltas throughout the world, probably due to the deceleration of the global sea-level rise. We conclude that in the boreholes sampled by the present data, the horizon corresponding to ancient Helike is less than 8 m deep.
    • On Cosmic-Ray Exposure Ages of Terrestrial Rocks: A Suggestion

      Lal, Devendra (Department of Geosciences, The University of Arizona, 1995-01-01)
      An important recent development in the field of geomorphology has been the application of in-situ cosmic-ray-produced nuclides to obtain model erosion rates and surface exposure ages. These concepts emerged some four decades ago in studies of cosmogenic nuclides in meteorites, but cannot generally be used analogously for terrestrial rocks. The differences in the two cases are outlined. For the case of steady-state erosional histories, the terrestrial surface exposure ages depend on the half-life of the radionuclide studied. A suggestion is made for presenting the surface exposure ages, which allows a clear definition of the meaning of the estimated exposure ages. In the case of a discrete exposure history, the meaning of "exposure age"—which should more appropriately be called "event age"—is however quite unambiguous.
    • Organizing Committee & International Committee

      Department of Geosciences, The University of Arizona, 1995-01-01
    • Palynological and Sedimentological Evidence for a Radiocarbon Chronology of Environmental Change and Polynesian Deforestation from Lake Taumatawhana, Northland, New Zealand.

      Elliot, M. B.; Striewski, B.; Flenley, J. R.; Sutton, D. G. (Department of Geosciences, The University of Arizona, 1995-01-01)
      We present pollen diagrams and sedimentological analyses from a lake site within an extensive dune system on the Aupouri Peninsula, Northland. Five thousand years ago, a regional Agathis australis — podocarp-broadleaf forest dominated the vegetation, which manifested an increasing preponderance of conifer species. Climate was cooler and drier than at present. From ca. 3400 BP, warmth-loving species such as A. Australis and drought-intolerant species, Dacrydium cupressinum and Ascarina lucida, became common, implying a warm and moist climate. The pollen record also suggests a windier climate. The most significant event in the record, however, occurred after ca. 900 BP (800 cal BP) when anthropogenic deforestation commenced. A dramatic decline in forest taxa followed, accompanied by the establishment of a Pteridium-esculentum-dominated community. Fire almost certainly caused this, evidenced by a dramatic increase of charcoal. Sedimentological evidence for this site indicates a relatively stable environment before humans arrived and an increasingly unstable environment with frequent erosional events after human contact.
    • Radiocarbon in Tropospheric CO2 and Organic Materials from Selected Northern Hemisphere Sites

      Druffel, Ellen R. M.; Griffin, Sheila (Department of Geosciences, The University of Arizona, 1995-01-01)
      Radiocarbon was measured in atmospheric CO2 from La Jolla, California and in living organic materials from six sites in the northern hemisphere. Atmospheric CO2 Delta-14C values from La Jolla agreed with those previously published records from China Lake, California (Berger et al.1987) and Vermunt, Austria (Levin et al.1985). Delta-14C values of fruit and grain samples that grew during 1980 agreed with the atmospheric CO2 Delta-14Cmeasurements. Most of the Delta-14C results of fruit and corn samples stored since the 1940s agreed with tree-ring Delta-14C values for the same time period. In general, agreement was found between the atmospheric CO2 or tree-ring Delta-14C records available for the Northern Hemisphere and the Delta-14C signatures of rapidly exchanging organic matter pools examined in this study. Exceptions were the Delta-14C values of carbonate from egg shells and that of organic carbon from egg insides, which demonstrate that bicarbonate and organic carbon within the egg follow different biochemical pathways.