• Quantifying Background Components of Low-Level Gas Proportional Counters

      Theodórsson, Páll (Department of Geosciences, The University of Arizona, 1992-01-01)
      I discuss background components of low-level gas proportional counters and show how each component can be estimated based on available data. For more reliable background analysis, further studies are suggested. Based on new information, a generation of low-level gas proportional counting systems for radiocarbon dating may emerge with lower and more predictable background.
    • Radiocarbon AMS Dating of Pollen Extracted from Peat Samples

      Brown, T. A.; Farwell, G. W.; Grootes, P. M.; Schmidt, F. H. (Department of Geosciences, The University of Arizona, 1992-01-01)
      We present 14C AMS measurements and discuss the extraction procedure used on pollen extracted from peat samples. Microscopic examination of the extracts shows that the procedure is sufficient to remove most non-pollen materials and results in an extract that is composed predominantly of pollen. The 14C dates that we obtained for pollen extracts from peat samples associated with the Mazama Ash layer are consistent with the range of bulk-sample dates obtained by others in previous studies. The limited measurement time and resulting precision (+/100 yr) of these initial measurements restrict our ability to draw firm conclusions from a comparison of the pollen extract dates with previous bulk-sample dates. We intend to adjust our procedure to improve the rejection of non-pollen materials and to increase the precision of our 14C measurements on pollen extracts from peat samples in future studies.
    • Radiocarbon Announces the Publication of the Following Special Issues:

      Department of Geosciences, The University of Arizona, 1992-01-01
    • Radiocarbon Anomalies Observed for Plants Growing in Icelandic Geothermal Waters

      Andersen, G. J.; Heinemeier, Jan; Nielsen, H. L.; Rud, Niels; Thomsen, M. S.; Johnsen, Sigfús; Sveinbjörnsdóttir, Árný; Hjartarson, Arni (Department of Geosciences, The University of Arizona, 1992-01-01)
      We have studied plant remains in thick beds of lacustrine sediments in the upper part of the Markarfljót drainage area in southern Iceland. We collected small samples of plant species from the same horizon and 14C dated them at the Aarhus AMS Dating Laboratory. Terrestrial plants yielded an age of 9 ka BP, whereas aquatic moss (Fontinalis antipyretica Hedw.) yielded the surprisingly old 14C age of 16 ka BP. We believe the age of the terrestrial plants reflects the true age of the sediment. The anomalously old 14C age of the aquatic moss may be an effect of geothermal water on the moss, as the area is known to be geothermally active today. Modern aquatic moss growing in geothermal water showed a similar 14C anomaly, with measured ages ranging from 6 to 8 ka BP, which may be explained by the equally old ages measured for the corresponding water samples. The 14C content of geothermal springs and neighboring rivers in the area ranges from 9 to 50 pMC, equivalent to an apparent age of 20-5.5 ka BP.
    • Radiocarbon Chronology of Late Neolithic Settlements in the Tisza-Maros Region, Hungary

      Hertelendi, Ede; Horváth, Ferenc (Department of Geosciences, The University of Arizona, 1992-01-01)
      We investigated chronological questions of five Late Neolithic settlements in the Hungarian Tisza-Maros region. Fifty new radiocarbon dates provide an internal chronology for the developmental phases of the tell settlements, and place them into the wider framework of the southeastern European Neolithic. An example is presented of how a unique type of stratigraphic excavation helps the interpretation of radiocarbon data, which are in contradiction with the stratigraphic position of the samples.
    • Radiocarbon Dating of Anodonta in the Mojave River Basin

      Berger, Rainer; Meek, Norman (Department of Geosciences, The University of Arizona, 1992-01-01)
      A 450-year correction is required to make Anodonta 14C dates comparable to 14C dates on other materials in the Mojave River basin. The internal stratigraphic consistency of 34 conventional 14C dates on Anodonta in this drainage basin indicates that such dates are usually reliable. The validity of most conventional 14C dates in the Mojave River basin may be a product of the basin's crystalline bedrock in a region usually typified by thick Paleozoic carbonate sections.
    • Radiocarbon Dating of Bone Osteocalcin: Isolating and Characterizing a Non-Collagen Protein

      Ajie, H. O.; Kaplan, I. R.; Hauschka, P. V.; Kirner, Donna; Slota, P. J. (Department of Geosciences, The University of Arizona, 1992-01-01)
      Osteocalcin, a non-collagen bone-matrix protein, has been examined as a possible source of autochthonous 14C data in fossil bones where collagen has been seriously degraded. Extraction procedures for osteocalcin yield a wellcharacterized product that can be clearly distinguished from collagen. The Gla content indicates that osteocalcin is present in the fossil bones at levels similar to the range present in modern bone. However, it appears to be extracted primarily as proteolytic polypeptide fragments rather than as an intact protein. Concordant 14C determinations are obtained on osteocalcin and gelatin extracts from the same bone when the collagen is relatively well preserved. However, increasing discordances in the 14C values of the osteocalcin and gelatin fractions are associated with reduced concentrations of the gelatin extract in the bone.
    • Radiocarbon Dating of Copper-Preserved Organics

      Beukens, R. P.; Pavlish, L. A.; Hancock, R. V.; Farquhar, R. M.; Wilson, G. C. (Department of Geosciences, The University of Arizona, 1992-01-01)
      The small but vital role of 14C dating in archaeometric research is clearly shown in the copper project reported herein. The 14C ages place a time perspective on the "Old Copper Culture Complex," substantiating early Libby dates that had been questioned. The respective roles of INAA, PGE and Pb isotope work are briefly summarized. A long tradition of heat treatment from Paleoindian stone to Archaic copper is suggested.
    • Radiocarbon Dating of Fourteen Dead Sea Scrolls

      Bonani, Georges; Ivy, Susan; Wölfli, Willy; Broshi, Magen; Carmi, Israel; Strugnell, John (Department of Geosciences, The University of Arizona, 1992-01-01)
      The name Dead Sea Scrolls refers to some 1200 manuscripts found in caves in the hills on the western shore of the Dead Sea during the last 45 years. They range in size from small fragments to complete books from the holy scriptures (the Old Testament). The manuscripts also include uncanonized sectarian books, letters and commercial documents, written on papyrus and parchment. In only a few cases, direct information on the date of writing was found in the scrolls. In all other cases, the dating is based on indirect archaeological and paleographical evidence. To check this evidence, radiocarbon ages of 14 selected scrolls were determined using accelerator mass spectrometry. The calibrated radiocarbon ages agree well, except in one case, with the paleographic estimates or the specific dates noted on the scrolls.
    • Radiocarbon Dating of Groundwater in a Confined Aquifer in Southeast Arizona

      Robertson, Frederick N. (Department of Geosciences, The University of Arizona, 1992-01-01)
      Radiocarbon, delta-13C and major-element data were used to construct a geochemical framework for interpretation of the hydrological flow system in the lower San Pedro basin, southeastern Arizona, USA. The 14C and major-element data show a regional confined aquifer that extends throughout most of the basin. Groundwater ages, after correcting for chemistry, are greater than 10 ka BP. The groundwater ages do not increase in a downvalley direction, the assumed direction of groundwater movement in most intermontane basins in the region, but along general flow paths normal to the mountains toward the center of the basin. Recharge to the confined aquifer originates from infiltration of precipitation and runoff near the alluvium-mountain contact along the Galiuro Mountains and is discharged by evapotranspiration along the center of the basin. The hydrogeological concept of the 14C model is supported by the water chemistry and by the mass transfer defined by the chemical model. Weathering of primary silicate minerals in the confined aquifer does not occur downvalley, but only along the direction of flow. Hydraulic conductivities calculated for the aquifer from 14C velocities are about an order of magnitude slower than those determined through hydrological methods. The lower hydraulic-conductivity values are attributed to a thick confining layer overlying the discharge area along the San Pedro River.
    • Radiocarbon Dating of Iron Artifacts

      Cresswell, R. G. (Department of Geosciences, The University of Arizona, 1992-01-01)
      During the late 1960s, N. J. van der Merwe (1969) obtained 14C measurements on 11 iron pieces, ranging in carbon content from medium carbon (0.22%) wrought iron (1.2 kg used) to high carbon (3.2%) cast iron (30 g), thereby demonstrating the feasibility of the technique for 14C dating iron. In the early 1980s, Sayre et al. (1982) repeated two of van der Merwe's measurements, and carried out two analyses on a recently rediscovered Elizabethan(?) iron bloom. Thirty grams were required of this medium carbon wrought iron to obtain an age using small proportional counters. A number of iron artifacts have recently been analyzed by accelerator mass spectrometry (AMS) at IsoTrace. Samples ranged in size from 3.4 g of a medium carbon (approximately equal to 0.4%) wrought iron bloom to 274 mg for a high carbon (1.79%) wootz steel fragment. AMS now permits analysis of samples that previously were too small or too valuable to be analyzed. For larger samples, multiple analyses can reveal variations that may aid the evaluation of sample history.
    • Radiocarbon Dating of Lime Fractions and Organic Material from Buildings

      Van Strydonck, Mark J. Y.; van der Borg, Klaas; De Jong, Arie F. M.; Keppens, Eduard (Department of Geosciences, The University of Arizona, 1992-01-01)
      We have dated carbonate fractions and organic material from different types of mortar from two sites in Belgium. We demonstrate the difficulties in obtaining good dates from carbonate samples. We also discuss the need for new types of dating material when the mortar comes from contaminated and disturbed sites, where even charcoal can yield aberrant results.
    • Radiocarbon Dating of Travertines Precipitated from Freshwater

      Mas-Pla, Joseph; Trilla, Josep; Valls, M. L. (Department of Geosciences, The University of Arizona, 1992-01-01)
      We have studied the isotopic composition of recently precipitated travertines to determine the initial 14C activity of ancient travertine deposits. We found that the 14C activity of recent travertines of northeastern Spain was a function of the distance from the spring, resulting in variations in the initial 14C activity of the ancient travertine formations. We calculated the ancient travertine radiocarbon ages by using the ratio between the 14C activity of recent travertines and that of present atmospheric CO2 as the initial 14C activity.
    • Radiocarbon Dating: A Didactic Videotape

      Rauret, Gemma; Mestres, J. S.; García, J. F. (Department of Geosciences, The University of Arizona, 1992-01-01)
    • Radiocarbon Measurements in South Pacific Ocean Waters in the Vicinity of the Subtropical Convergence Zone

      Sparks, R. J.; Drummond, G. W.; Brailsford, G. W.; Lowe, D. C.; Lassey, K. R.; Manning, M. R.; Taylor, C. B.; Wallace, Gavin (Department of Geosciences, The University of Arizona, 1992-01-01)
      Distribution profiles of radiocarbon in dissolved inorganic carbonate have been measured along two transects in the southern Pacific, east of New Zealand. Use of accelerator mass spectrometry, with its small-sample-size capability, made it possible to sample near-surface waters with a depth resolution of a few tens of meters. Sampling of deeper water was guided by salinity and temperature data transmitted by a conductivity-temperature-depth probe. The measurements, taken over the Chatham Rise, show highly structured profiles that can be correlated with known circulation patterns in this region.
    • Radiocarbon Results for the British Beakers

      Ambers, Janet; Bowman, Sheridan; Gibson, Alex; Kinnes, Ian (Department of Geosciences, The University of Arizona, 1992-01-01)
      The beginning of the Bronze Age in the British Isles has traditionally been marked by the appearance, in the archaeological record, of Beaker assemblages, mainly characterized by the Beaker pottery form itself. Ceramic typologies based on this style, which is undoubtedly continental in origin, have been used both for relative dating and as evidence of the social and economic developments of the period. Systematic radiocarbon dating has been attempted for the continental European Beaker material (Lanting, Mook & van der Waals 1973), but no such program has been carried out on British material. An examination of the existing radiocarbon results for the British Beakers showed many to be flawed in some way, particularly in the use of materials, such as mature wood, where there is no a priori reason for assuming a direct relationship between sample death and context. An attempt has been made at the British Museum to test the validity of archaeologically derived chronologies for the Beaker pottery of the British Isles. This involved analysis of a group of carefully selected human bone samples from Beaker burials, where there is a known direct association between ceramic usage and the cessation of carbon exchange. Twenty such samples have been identified and measured. The results presented here, combined with other previously produced determinations, show no obvious relationship between pottery style and calendar date of deposition.
    • Radiocarbon Variations from Tasmanian Conifers: First Results from Late Pleistocene and Holocene Logs

      Barbetti, Mike; Bird, Trevor; Dolezal, George; Taylor, Gillian; Francey, Roger; Cook, Edward; Patterson, Mike (Department of Geosciences, The University of Arizona, 1992-01-01)
      Dendrochronological studies have begun on two conifer species in the Stanley River area of western Tasmania. The chronology extends to 273 BC for Huon pine (Lagarostrobos franklinii) and to AD 1450 for celery-top pine (Phyllocladus aspleniifolius). Apart from living or recently felled trees, sections have been taken from 58 logs preserved in floodplain sediments. Two of these logs have late Pleistocene ages, centered around 13.0 and 12.7 k 14C yr BP. Four logs are between 8 and 9 ka BP, and one is centered at 7.3 ka BP. The remaining logs have various ages between 6.2 ka BP and the present. 14C measurements have been performed on decadal samples from the two late Pleistocene logs, providing short (260-yr) records of atmospheric 14C variations when plotted against individual ring numbers. Decadal measurements on the 7300-yr-old log have been wiggle-matched with 14C calibration curves from German oak and bristlecone pine. Measurements for the period, AD 1600-1800, show good agreement with northern hemisphere results, and a nearly zero offset between the hemispheres
    • Rapid Production of Graphite Without Contamination for Biomedical AMS

      Vogel, John S. (Department of Geosciences, The University of Arizona, 1992-01-01)
      The application of AMS to the detection of 14C makes possible a new class of sensitive experiments in molecular biology. Such experiments inherently produce large numbers of samples for the determination of biological variability in molecular interactions. The samples vary in 14C concentration over many orders of magnitude. We added TiH2 to aid the reduction of CO2 by zinc in a sealed tube to reproducibly make graphite without sample cross-contamination. The CO2 is transferred from a combustion tube to the reaction tube through a disposable plastic manifold. The sealed tubes are heated to a single-reaction temperature in a muffle furnace. The process is complete within 5 h. Bulk isotopic fractionation in the finished graphite is less than 0.5%.
    • Reaction-Path Formulation of a Simple Dissolution Model for Radiocarbon Dating Groundwater

      Cheng, Songlin (Department of Geosciences, The University of Arizona, 1992-01-01)
      Since the pioneer publication of K. O. Münnich (1957),14C systematics have been used in many hydrogeological studies. Because of the complexity of carbon geochemistry, numerous models have been proposed to correct the dilution effect of "dead" carbon in groundwater. All the 14C correction models for dating groundwater are based on either openor closed-system conditions. I present here a simple model that accounts for the effects of both openand closed-system dissolution of carbonate and aluminosilicate minerals. For systems involving precipitation of carbonate minerals and redox reactions of organic matter, reaction-path simulations are essential for reliable 14C dating of groundwater.