• Age Discrepancies with the Radiocarbon Dating of Sagebrush (Artemisia Tridentata Nutt.)

      Geib, Phil R. (Department of Geosciences, The University of Arizona, 2008-01-01)
      When ancient hearths at open archaeological sites do not yield carbonized annual plant remains or other high-quality samples, wood charcoal is commonly used for radiocarbon dating. Sagebrush (Artemisia tridentata Nutt.), a shrub frequently used for fuel across much of the western United States, seems a potentially better candidate for 14C dating than tree wood since the possibility for significant age discrepancy might be less. A comparison of multiple assays from single features reveals that sagebrush can overestimate age more than even tree wood charcoal. A plausible cause of this appears to be persistence of the shrub on the ground surface for an extended interval after death, such that use as fuel almost invariably occurs hundreds of years after fixation of carbon. The potential for age discrepancy may decrease as population density increases because the demand for fuel wood would have resulted in a more rapid turnover of the fuel biomass. This is not true for Archaic period foragers of western North America when population levels were likely quite low and residential mobility quite high.
    • AMS Radiocarbon Dating of Wood Samples from the Angkor Monuments, Cambodia

      Uchida, E.; Cunin, O.; Shimoda, I.; Takubo, Y.; Nakagawa, T. (Department of Geosciences, The University of Arizona, 2008-01-01)
      In the Angkor monuments of Cambodia, pieces of wood remain (as head frames of doorways, crossbeams, ceiling boards, etc.) in the following 8 monuments: Bakong, Lolei, Baksei Chamkrong, North Khleang, Angkor Wat, Banteay Kdei, Bayon, and Gates of Angkor Thom. Accelerator mass spectrometry (AMS) radiocarbon dating carried out on 15 wood samples collected from the above 8 monuments revealed that most of the wood samples are original, except for the head frame of a doorway in Baksei Chamkrong, the ceiling boards in the northwest tower, and a crossbeam with pivot hole in the southwest tower of the Inner Gallery of Angkor Wat. The 14C age for the head frame of a doorway in the inner wall under the central tower of North Khleang supports the hypothesis that the inner walls are additions from a later period.
    • Atmospheric 14C Variability Recorded in Tree Rings from Peninsular India: Implications for Fossil Fuel CO2 Emission and Atmospheric Transport

      Chakraborty, Supriyo; Dutta, Koushik; Bhattacharyya, Amalava; Nigam, Mohit; Schuur, Edward AG; Shah, Santosh K. (Department of Geosciences, The University of Arizona, 2008-01-01)
      Radiocarbon analysis in annual rings of a teak tree (Tectona grandis) is reported in comparison with previously published results. Samples (disks) were collected from Hoshangabad (22 degrees 30'N, 78 degrees E), Madhya Pradesh, in central India. The previously published sample was collected from Thane (19 degrees 12'N, 73 degrees E), Maharashtra, near the west coast of India (Chakraborty et al. 1994). Two short 14C time series were reconstructed with these tree samples to capture the bomb peak of atmospheric 14C and the spatial variability in this record. These time series represent the periods 1954-1977 and 1959-1980 for Hoshangabad and Thane, respectively. The 14C peaks in these places appear around 1964-1965. The Hoshangabad tree records a peak delta-14C value of 708 +/- 8‰, which conforms to the peak value of Northern Hemisphere Zone 3 as described in Hua and Barbetti (2004). But the peak 14C at Thane is somewhat less (630 +/- 8‰) probably due to the dilution by fossil fuel CO2 free of 14C emanating from the neighboring industrial areas. This depletion of peak values has been used to estimate the local emission of fossil fuel CO2, which is approximately 2.3% of the background atmospheric CO2 concentration.
    • Calendar Age of Lisakovsky Timbers Attributed to Andronovo Community of Bronze Age in Eurasia

      Panyushkina, Irina P.; Mills, Barbara J.; Usmanova, Emma R.; Cheng, Li (Department of Geosciences, The University of Arizona, 2008-01-01)
      We measured radiocarbon ages of 22 decadal replications and 1 bulk group from 5 tree-ring specimens using acid-base-acid pretreatment and accelerator mass spectrometry (AMS). The study has the goal of refining the precision and resolution of a segment of the conventional Bronze Age chronology in the Eurasian steppe attributed to the multicultural community known as Andronovo. The archaeological timbers were gathered from 3 cemeteries at the Lisakovsky cluster of sites in Kazakhstan, where there is a prominent Andronovo occurrence that appears to show evidence of overlapping Alakul and Fedorovo cultures in the southern margin of the Eurasian steppe. The new set of Andronovo calendar dates derived from 14C wiggles and a composite floating tree-ring chronology places the cultural overlap from 1780 to 1660 cal BC. Results indicate older ages of artifacts from the Lisakovsky site than were previously determined by the typological chronology, shifting them from the Late Bronze Age to also include the transition between the Middle and Late Bronze Age. The chronological order of the Lisakovsky cemeteries provides strong evidence of contemporaneity of the Alakul and Fedorovo cultures in the Tobol River Valley for a portion of the 120-yr period of occupation. We discuss an application of the dated Alakul-Fedorovo overlap to the relationship and origin of different groups of the Andronovo community in the Ural region. Our results demonstrate the substantial power that tree rings from Bronze Age timbers provide for developing a precise and highly resolved calendar chronology of prehistoric human occupation in the Eurasian steppe during the 2nd millennium BC.
    • Comparison of Radiocarbon Ages from Different Organic Fractions in Tropical Peat Cores: Insights from Kalimantan, Indonesia

      Wüst, Raphael A. J.; Jacobsen, Geraldine E.; van der Gaast, Haitse; Smith, Andrew M. (Department of Geosciences, The University of Arizona, 2008-01-01)
      Various organic fractions of an Indonesian tropical peat deposit were dated using radiocarbon accelerator mass spectrometry (AMS). Four different depth layers, deposited during the last 28,000 14C yr, were analyzed and the data compared to bulk sample analyses. The pollen extracts consistently produced the oldest dates. The bulk samples (<250 mu-m and <100 mu-m) often yielded the youngest dates. The age difference between the individual fractions depended on the layer depth and hence the true age of the sampled peats. The age discrepancy was highest (~16,000 14C yr) in the oldest peat material. We interpret this to be a consequence of the input of organic matter over a long period of time, with peat oxidation and/or no peat accumulation during the last glacial maximum (LGM). The age discrepancies were smaller (between 10 and 900 14C yr) for the Holocene peat samples. It was concluded that the pollen extract fraction might be the most reliable fraction for dating tropical peat deposits that are covered by deeply rooting vegetation.
    • Comparisons and Interpretations of Charcoal and Organic Matter Radiocarbon Ages from Buried Soils in North-Central Colorado, USA

      Mayer, James H.; Burr, George S.; Holliday, Vance T. (Department of Geosciences, The University of Arizona, 2008-01-01)
      The reliability of radiocarbon ages based on soil organic matter (SOM) from Holocene buried soils in Middle Park, Colorado, is assessed by comparison with ages of charcoal. On average, 14C ages of SOM from buried surface horizons are 880 +/- 230 14C yr younger than charcoal ages from the same horizon. Humic acid (HA) and low-temperature (400 degrees C) combustion residue (LT) fractions are 390 +/- 230 and 1290 +/- 230 14C yr younger than charcoal ages, respectively, and HA ages are on average 860 +/- 140 14C yr older than LT fractions. We interpret the offsets between 14C ages of charcoal and SOM fractions and the consistent offsets between the HA and LT fractions to reflect the duration of pedogenesis and different residence times of the SOM fractions examined here. The stratigraphic coherence of charcoal 14C ages suggests short residence time on the landscape, with little subsequent reworking. 14C ages of HA and LT fractions are complimentary to charcoal, and HA ages are interpreted to represent minimum ages for the onset of pedogenesis and LT ages are considered maximum ages for burial. The 14C chronology from buried soils indicates an episode of hillslope erosion in Middle Park during the early Holocene, followed by a long period of land surface stability and soil formation between 9000-4500 BP. Two episodes of late Holocene hillslope erosion between 3500-2500 and 1000-500 BP correspond with warming recognized in the Colorado Front Range, while surface stability and soil formation between 2500-1000 BP is contemporaneous with evidence for cooling at higher elevations.
    • Contents

      Department of Geosciences, The University of Arizona, 2008-01-01
    • Editorial Board

      Department of Geosciences, The University of Arizona, 2008-01-01
    • Erratum: Marine Reservoir Corrections: St. Helena, South Atlantic Ocean

      Lewis, Colin A.; Reimer, Paula J.; Reimer, Ron W.; Bruce, Ian (Department of Geosciences, The University of Arizona, 2008-01-01)
    • New Marine ΔR Values for the South Pacific Subtropical Gyre Region

      Petchey, Fiona; Anderson, Atholl; Zondervan, Albert; Ulm, Sean; Hogg, Alan (Department of Geosciences, The University of Arizona, 2008-01-01)
      This paper presents 31 new R results of known-age, pre-AD 1950 shells from the South Pacific subtropical gyre region, spanning from the Tuamotu Archipelago in the east to New Caledonia in the west. This doubles the number of available R values for the Oceania region. These values indicate that the regional offset (R) from the modeled radiocarbon marine age has remained relatively constant over the last 100 yr prior to 1950. Variation from the norm can be attributed to various influences including localized upwelling around islands, the presence of a hardwater effect, direct ingestion of old carbon by the live shellfish, or enhanced exchange with atmospheric CO2 as a consequence of photosynthetic activity or increased aeration.
    • New Radiocarbon Dates for the Baden Culture

      Horvath, Tunde; Svingor, S. Éva; Molnár, Mihaly (Department of Geosciences, The University of Arizona, 2008-01-01)
      In 2001-2002, a settlement of the Baden culture was excavated in the vicinity of Balatonőszd. During the rescue excavation along the M7 highway, in an area of 100,000 m2, 2800 pits dug into the subsoil, 320 hearths, and cultural layers rich in material were discovered. The material of the Baden culture represents phases IB-IC (Boleraz), IIA (Transitional), IIB-III (Early Classical) according to Němejcov-Pavkov's (1981, 1998) typological system. We took 20 samples from the large number of human and animal skeletons for radiocarbon dating, of which 16 measurements were successful. These results provide absolute dates for a Baden culture settlement with the longest occupation and the largest excavated surface in Hungary. This provides an opportunity to review the chronological position of the Baden culture, with special emphasis on its beginning and end.
    • Radiocarbon Laboratories

      Department of Geosciences, The University of Arizona, 2008-01-01
    • Sample Dilution for AMS 14C Analysis of Small Samples (30-150 μg C)

      de Rooij, M.; van der Plicht, J.; Meijer, H. J. (Department of Geosciences, The University of Arizona, 2008-01-01)
      We investigated sample dilution as a technique for accelerator mass spectrometry (AMS) radiocarbon analysis of very small samples (down to 30 mu-g). By diluting such samples up to a total weight of 200 mu-g, we can still perform reliable AMS measurements and improve the success rate significantly for targets that are difficult to measure. A disadvantage of this dilution technique is a loss of measurement precision. In addition, calculations of the 14C/12C isotope ratios and the uncertainties therein are not straightforward because of peculiarities in isotope fractionation processes in the AMS system. Therefore, to make sample dilution a routine method in our laboratory, we did extensive theoretical and experimental research to find the optimum conditions for all relevant parameters. Here, we report on the first detailed study dealing with all aspects of sample dilution. Our results can be applied in general. As an illustrative test case, we analyze 14C data for CO2 extracted from an ice core, from which samples of 35 mu-g C or less are available.
    • Very Long-Lived Mollusks Confirm 17th Century AD Tephra-Based Radiocarbon Reservoir Ages for North Icelandic Shelf Waters

      Wanamaker, Alan D., Jr.; Heinemeier, Jan; Scourse, James D.; Richardson, Christopher A.; Butler, Paul G.; Eiríksson, Jon; Knudsen, Karen Luise (Department of Geosciences, The University of Arizona, 2008-01-01)
      Marine sediment records from the north Icelandic shelf, which rely on tephrochronological age models, reveal an average Delta-R (regional deviation from the modeled global surface ocean reservoir age) of approximately 150 yr for the last millennium. These tephra-based age models have not hitherto been independently verified. Here, we provide data that corroborate Delta-R values derived from these sediment archives. We sampled the youngest portion (ontogenetic age) of a bivalve shell, Arctica islandica (L.), for radiocarbon analysis, which was collected alive in 2006 from the north Icelandic shelf in ~80 m water depth. Annual band counting from the sectioned shell revealed that this clam lived for more than 405 yr, making it the longest-lived mollusk and possibly the oldest non-colonial animal yet documented. The 14C age derived from the umbo region of the shell is 951 +/- 27 yr BP. Assuming that the bivalve settled onto the seabed at AD 1600, the corresponding local value of Delta-R is found to be 237 +/- 35 yr by comparison of the 14C age with the Marine04 calibration curve (Hughen et al. 2004) at this time. Furthermore, we cross-matched a 287-yr-old, dead-collected, A. islandica shell from AD 1601 to 1656 from the same site with the live-caught individual. 14C analysis from the ventral margin of this shell revealed a Delta-R of 186 +/- 50 yr at AD 1650. These values compare favorably with each other and with the tephra-based Delta-R values during this period, illustrating that 14C from A. islandica can effectively record 14C reservoir changes in the shelf seas.