• Late Pleistocene-Recent Atmospheric delta-13C Record in C4 Grasses

      Toolin, Laurence J.; Eastoe, Christopher J. (Department of Geosciences, The University of Arizona, 1993-01-01)
      Samples of Setaria species from packrat middens, herbarium specimens and modern plants preserve a record of delta-13C of atmospheric CO2 from 12,600 BP to the present. No secular trend is detected between 12,600 and 1800 BP, when the mean value of delta-13C during that period was -6.5 +/- 0.1 per mil (the error is the standard deviation of the mean). Our value agrees with delta-13C averages of pre-industrial CO2 from polar ice cores, and differs significantly from modern regional (-8.2 +/- 0.1 per mil) and global (-7.7 per mil) values, which are higher because of fossil fuel burning.
    • Letters to the Editor

      Caldararo, Niccolo (Department of Geosciences, The University of Arizona, 1993-01-01)
    • Radiocarbon Ages of Lacustrine Deposits in Volcanic Sequences of the Lomas Coloradas Area, Socorro Island, Mexico

      Farmer, Jack D.; Farmer, Maria C.; Berger, Rainer (Department of Geosciences, The University of Arizona, 1993-01-01)
      Extensive eruptions of alkalic basalt from low-elevation fissures and vents on the southern flank of the dormant volcano, Cerro Evermann, accompanied the most recent phase of volcanic activity on Socorro Island, and created the Lomas Coloradas, a broad, gently sloping terrain comprising the southern part of the island. We obtained 14C ages of 4690 +/- 270 BP (5000-5700 cal BP) and 5040 +/- 460 BP (5300-6300 cal BP) from lacustrine deposits that occur within volcanic sequences of the lower Lomas Coloradas. Apparently, the sediments accumulated within a topographic depression between two scoria cones shortly after they formed. The lacustrine environment was destroyed when the cones were breached by headward erosion of adjacent stream drainages. This was followed by the eruption of a thin basaltic flow from fissures near the base of the northernmost cone. The flow moved downslope for a short distance and into the drainages that presently bound the study area on the east and west. The flow postdates development of the present drainage system and may be very recent. Our 14C data, along with historical accounts of volcanic activity over the last century, including submarine eruptions that occurred a few km west of Socorro in early 1993, underscore the high risk for explosive volcanism in this region and the need for a detailed volcanic hazards plan and seismic monitoring.
    • A Simplified Approach to Calibrating 14C Dates

      Talma, A. S.; Vogel, J. C. (Department of Geosciences, The University of Arizona, 1993-01-01)
      We propose a simplified approach to the calibration of radiocarbon dates. We use splines through the tree-ring data as calibration curves, thereby eliminating a large part of the statistical scatter of the actual data points. To express the age range, we transform the +/- 1 sigma and +/- 2 sigma values of the BP age to calendar dates and interpret them as the 68% and 95% confidence intervals. This approach bypasses the conceptual problems of the transfer of individual probability values from the radiocarbon to the calendar age. We have adapted software to make this calibration possible.
    • Radiocarbon Dating of Paleoseismicity Along an Earthquake Fault in Southern Italy

      Calderoni, Gilberto; Petrone, Vincenzo (Department of Geosciences, The University of Arizona, 1993-01-01)
      On 23 November 1980, a major earthquake (M3 = 6.9) struck a large area of the southern Apennines (Campania and Lucania regions, southern Italy). This seismic event, the largest in Italy over the last 80 years, almost completely destroyed 15 villages and caused extensive damage to other towns, including Naples. The quake produced the first well-documented example in Italy of surface dislocation, represented by a fault scarp 38 km long. We undertook a study that included 14C dating of organic materials from layers displaced by paleoseismic events to assess the seismologic hazard for the area. We collected peat and charred wood samples from the walls of two trenches excavated across the 1980 fault at Piano di Pecore di Colliano, Salerno, where the sedimentary suite is faulted and warped by five quakes (including that of 1980). This produced comparable vertical throw and deformation patterns. Chronological data for pre-1980 events, coupled with detailed stratigraphic analysis, yielded a dip-slip rate and a recurrence interval of 0.4 mm/yr and 1700 yr, respectively.
    • 15th International Radiocarbon Conference

      Department of Geosciences, The University of Arizona, 1993-01-01
    • AMS-Graphite Target Production Methods at the Woods Hole Oceanographic Institution During 1986-1991

      Gagnon, Alan R.; Jones, Glenn A. (Department of Geosciences, The University of Arizona, 1993-01-01)
      In July 1986, an AMS radiocarbon target preparation laboratory was established at the Woods Hole Oceanographic Institution to produce graphite to be analyzed at the NSF-Accelerator Facility for Radioisotope Analysis at the University of Arizona (Tucson). By June 1991, 923 graphite targets had been prepared and 847 analyzed. Our lab procedures during this time included the careful documentation of weights of all starting samples, catalysts and final graphite yields, as well as the volume of CO2 gas evolved during CaCO3 hydrolysis or closed-tube organic carbon combustions. From these data, we evaluate the methods used in general and in our lab.
    • An Assessment of the Radiocarbon Dating of the Dead Sea Scrolls

      Rodley, G. A. (Department of Geosciences, The University of Arizona, 1993-01-01)
      I suggest, on the basis of a statistical analysis, that recently determined 14Conventional radiocarbon ages" of Dead Sea Scroll documents are offset systematically by about +40 yr, leading to a similar overestimate of the ages of these documents. Much closer agreement with paleographic and specific dates is obtained when a correction of this magnitude is made to the 14Conventional 14C" values. This indicates that 14C dates may convey more precise information about the ages of these documents than initially recognized.
    • Radiocarbon to Calendar Date Conversion: Calendrical Bandwidths as a Function of Radiocarbon Precision

      McCormac, F. G.; Baillie, M. G. L. (Department of Geosciences, The University of Arizona, 1993-01-01)
      Accurate high-precision 14C dating (i.e., +/- 20 yr precision or less on the 14C date) provides the narrowest calendrical band width and, hence, the best age range determination possible. However, because of the structure in the 14C calibration curve, the calendar age range for a given 14C precision is not constant throughout the calibration range. In this study, we quantify the calendar band widths for a range of 14C previsions throughout the calibration range. We show that an estimate of the likely calendar band width in years can be obtained from the expression: Band width (yr) = 2.12 x 14C precision (1 sigma) + 54.6. We also show that calendar band widths are widest around 4000 BP at the start of the Bronze Age, and become narrow through the later Bronze Age and Iron Age and back into the Neolithic.
    • Associate Editors

      Department of Geosciences, The University of Arizona, 1993-01-01
    • Carbon Isotopic Composition of Deep Carbon Gases in an Ombrogenous Peatland, Northwestern Ontario, Canada

      Aravena, Ramon; Warner, B. G.; Charman, D. J.; Belyea, L. R.; Mathur, S. P.; Dinel, Henri (Department of Geosciences, The University of Arizona, 1993-01-01)
      Radiocarbon dating and carbon isotope analyses of deep peat and gases in a small ombrogenous peatland in northwestern Ontario reveals the presence of old gases at depth that are 1000-2000 yr younger than the enclosing peat. We suggest that the most likely explanation to account for this age discrepancy is the downward movement by advection of younger dissolved organic carbon for use by fermentation and methanogens bacteria. This study identifies a potentially large supply of old carbon gases in peatlands that should be considered in global carbon models of the terrestrial biosphere.
    • Intra-Annual Variability of the Radiocarbon Content of Corals from the Galapagos Islands

      Brown, T. A.; Farwell, G. W.; Grootes, P. M.; Schmidt, F. H.; Stuiver, Minze (Department of Geosciences, The University of Arizona, 1993-01-01)
      We report AMS 14C measurements on subannual samples of coral from the Galapagos Islands that span the period, 1970-1973. Both the major 1972 El Niño/Southern Oscillation event and intra-annual changes in regional upwelling of 14C-depleted waters associated with alternation of surface-ocean current patterns are evident in the record. Our data show that the corals preserve a detailed record of past intra-annual variations of the 14C content of surface ocean water.
    • Isotopic Analysis of Groundwater and Carbonate System in the Surdulica Geothermal Aquifer

      Hadžišehović, Munevera; Miljević, Nada; Šipka, Vojislava; Golobočanin, Dušan; Popović, Radule (Department of Geosciences, The University of Arizona, 1993-01-01)
      We present here results of our investigation of the isotopic chemical composition of groundwater and carbonates in the Surdulica geothermal aquifer, Serbia. We considered the effects of carbonate dissolution and measured 13C, 14C, D, 18O, 3H, field pH, temperature, Na+, Ca2+, Mg2+, HCO-3 and other aqueous species from 30 springs and boreholes. Geothermal waters are supersaturated with calcite. Carbon isotope compositions vary with carbonate mineral dissolution. The delta-D and delta-18O of groundwater samples fit the meteoric water line, and indicate that groundwater is recharged mainly from higher altitudes and the cold season. Different groundwater residence times point out two mechanisms for their formation; fissure flow for young waters and standard diffusion processes for old ones.
    • From the Editor

      Long, Austin (Department of Geosciences, The University of Arizona, 1993-01-01)
    • 14C Dating of Laser-Oxidized Organics

      Watchman, A. L.; Lessard, R. A.; Jull, A. J. T.; Toolin, L. J.; Blake, Weston (Department of Geosciences, The University of Arizona, 1993-01-01)
      We used a continuous krypton ion laser to rapidly oxidize milligram-sized fragments of coniferous driftwood of known ages, and dated the resulting carbon dioxide by accelerator mass spectrometry (AMS). AMS 14C ages of non-pretreated young wood from different parts of two logs were within 10% of the ages of conventionally determined alkaline insoluble fractions. The age of the oldest whole wood measured after laser oxidation was within the error ranges of conventional values.
    • Radiocarbon Dates from American Samoa

      Clark, Jeffrey T. (Department of Geosciences, The University of Arizona, 1993-01-01)
      Between 1988 and 1991, I directed five archaeological research projects in American Samoa. The goal of that research was to reveal changes in the prehistoric settlement system of Samoa, from initial colonization of the archipelago to the time of significant European contact. The chronological placement of key sites was an essential facet of the research. A secondary goal was to locate sites with ceramic components, particularly sites with Lapita ceramics, and relate the ceramic assemblages typologically and chronologically to those known for Western Samoa. These investigations generated 16 14C dates from archaeological contexts. I present here the previously unpublished 14C data from those samples, and briefly summarize their importance for understanding Samoan prehistory.
    • A Batch Preparation Method for Graphite Targets with Low Background for AMS 14C Measurements

      Kitagawa, Hiroyuki; Masazawa, Toshiyuki; Nakamura, Toshio; Matsumoto, Eiji (Department of Geosciences, The University of Arizona, 1993-01-01)
      We have developed a method of graphitization from CO2 samples for accurate 14C measurements by accelerator mass spectrometry. Our batch method, using a sealed Vycor tube, reduces the risk of contamination during graphitization and makes it possible to prepare many samples in a short time (typically 20 samples per day).
    • Radiocarbon Updates

      Department of Geosciences, The University of Arizona, 1993-01-01
    • Book Review: The Last Deglaciation: Absolute and Radiocarbon Chronologies, Edouard Bard, Wallace S. Broecker (Eds.)

      Jacobson, G. (Department of Geosciences, The University of Arizona, 1993-01-01)
    • Book Review: The Quaternary of China, Zhang Zonghu, Shao Shixiong, Tong Ghobang, Cao Jiadong (Eds.)

      Davis, Owen K. (Department of Geosciences, The University of Arizona, 1993-01-01)