• 14C Dating of the Upper Paleolithic Site at Krems-Hundssteig in Lower Austria

      Wild, E. M.; Neugebauer-Maresch, C.; Einwögerer, T.; Stadler, P.; Steier, P.; Brock, F. (Department of Geosciences, The University of Arizona, 2008-01-01)
      The open-air archaeological site at Krems-Hundssteig is a well-known Upper Paleolithic site located in Lower Austria. The site was discovered in the late 19th/early 20th centuries when a large number of archaeological remains were collected during the course of loess quarrying. Although no systematic excavation has ever been performed, Krems-Hundssteig has been described since its discovery as typical of the Aurignacian period in this region based on the numerous archaeological finds; accordingly, the culture has been named Kremsien by some authors. Surprisingly, the artifacts found in a recent excavation adjacent to this location showed solely Gravettian features, calling into question the original assignment to the Aurignacian. Although the earlier assignment was supported by a radiocarbon date of ~35 kyr BP (Hahn 1977), new accelerator mass spectrometry (AMS) 14C dates proved that the recently excavated cultural layer originates from the Gravettian period. Older paleosols were also detected by sondage drillings at some depth below it. The new results indicate that a large Aurignacian level and a substantial complex of Gravettian layers are present in this area. Therefore, it must be assumed that more than 1 cultural level was affected and destroyed by the historic loess quarrying, and that the assemblage of Krems-Hundssteig artifacts, traditionally ascribed to the Aurignacian, might be interspersed with Gravettian pieces.
    • Bayesian Refinement of a Stratified Sequence of Radiometric Dates from Punta de Chimino, Guatemala

      Bachand, Bruce R. (Department of Geosciences, The University of Arizona, 2008-01-01)
      Bayesian analysis of 6 radiocarbon and 2 luminescence determinations from Punta de Chiminos acropolis provides subcentury chronometric accuracy for a Protoclassic hiatus and a more decisive, incipient Early Classic abandonment. For the latter event, sensitivity tests and a redundant modal value pattern reduce the period of historical interest from a few centuries to several decades. The findings aid in selecting between 2 historical scenarios and demonstrate that improved chronological accuracy is attainable for sites and contexts lacking calendrical dates.
    • Development of Sample Pretreatment of Silk for Radiocarbon Dating

      Kim, Kyeong Ja; Southon, John; Imamura, Mineo; Sparks, Rodger (Department of Geosciences, The University of Arizona, 2008-01-01)
      We have developed sample pretreatments for silk for radiocarbon dating. Characteristics of silk under different types of pretreatment were investigated, as well as the behavior of dye and possible contaminants. We found that dye could be removed completely, together with all other foreign materials bigger than 1.2 m, using a glass microfiber filter after decomposition with 6N HCl. The decomposed proteins were concentrated using Centriprep ultrafiltration concentrators with 3 different molecular weight cut-offs. By taking a molecular weight fractionwhich selects for secondary structures of silk protein14C dating of silk samples can be made more reliable. This study confirms that uniformly fractured polypeptide chains of silk provide an appropriate fraction for 14C age dating to select silk protein against dye particles and undecomposed foreign contaminants.
    • Estimated Reservoir Ages of the Black Sea since the Last Glacial

      Kwiecien, O.; Arz, H. W.; Lamy, F.; Wulf, S.; Bahr, A.; Röhl, U.; Haug, G. H. (Department of Geosciences, The University of Arizona, 2008-01-01)
      Accelerator mass spectrometry (AMS) radiocarbon dating of ostracod and gastropod shells from the southwestern Black Sea cores combined with tephrochronology provides the basis for studying reservoir age changes in the late-glacial Black Sea. The comparison of our data with records from the northwestern Black Sea shows that an apparent reservoir age of ~1450 14C yr found in the glacial is characteristic of a homogenized water column. This apparent reservoir age is most likely due to the hardwater effect. Though data indicate that a reservoir age of ~1450 14C yr may have persisted until the Blling-Allerd warm period, a comparison with the GISP2 ice-core record suggests a gradual reduction of the reservoir age to ~1000 14C yr, which might have been caused by dilution effects of inflowing meltwater. During the Blling-Allerd warm period, soil development and increased vegetation cover in the catchment area of the Black Sea could have hampered erosion of carbonate bedrock, and hence diminished contamination by old carbon brought to the Black Sea basin by rivers. A further reduction of the reservoir age most probably occurred contemporary to the precipitation of inorganic carbonates triggered by increased phytoplankton activity, and was confined to the upper water column. Intensified deep water formation subsequently enhanced the mixing/convection and renewal of intermediate water. During the Younger Dryas, the age of the upper water column was close to 0 yr, while the intermediate water was ~900 14C yr older. The first inflow of saline Mediterranean water, at ~8300 14C yr BP, shifted the surface water age towards the recent value of ~400 14C yr.
    • Obituary: Grant Kocharov

      Dergachev, Valentin; Ostrykov, Valery; Gladysheva, Olga; Koudriavtsev, Igor; Ogurtsov, Maxim; Dreschoff, Gisela; Jungner, Högne (Department of Geosciences, The University of Arizona, 2008-01-01)
    • New 14C Ages on Cellulose from Diprotodon Gut Contents: Explorations in Oxidation Chemistry and Combustion

      Gillespie, Richard; Fifield, L. Keith; Levchenko, Vladimir; Wells, Rod (Department of Geosciences, The University of Arizona, 2008-01-01)
      We report radiocarbon ages on cellulose isolated from the gut contents of a Diprotodon found at Lake Callabonna, South Australia. The maximum age obtained corresponds to a minimum age of 53,400 BP for this extinct giant marsupial. This is older than, and hence consistent with, the generally accepted Australian megafauna extinction window. We argue that dichromate and other strong oxidants are less selective than chlorite for lignin destruction in wood, and our results suggest that ages approaching laboratory background can be obtained using a repeated pretreatment sequence of chlorite-alkali-acid and measurement of the sometimes discarded 330 C combustion fraction.
    • Zinc Reduction as an Alternative Method for AMS Radiocarbon Dating: Process Optimization at CIRCE

      Marzaioli, F.; Borriello, G.; Passariello, I.; Lubritto, C.; De Cesare, N.; D'Onofrio, A.; Terrasi, F. (Department of Geosciences, The University of Arizona, 2008-01-01)
      The pretreatment of samples for radiocarbon measurements, transforming a variety of materials into graphite solid targets, represents a critical point in the accelerator mass spectrometry (AMS) procedure. We describe the new, state-of-the-art CIRCE AMS preparation laboratory, particularly the setup and optimization of an alternative method, the zinc reduction method, for graphite target production, compared to the more common hydrogen reduction method. Measured 14C values on standard and blank samples reduced via zinc reaction revealed mean background levels, accuracy, and sensitivity comparable to those obtained by our conventional hydrogen reaction lines. Zinc line reduction at the CIRCE laboratory represents an effective and powerful alternative to the conventional hydrogen reduction, ensuring higher sample throughput with lower costs at a comparable performance level.
    • Methods of Separating Soil Carbon Pools Affect the Chemistry and Turnover Time of Isolated Fractions

      Castanha, Cristina; Trumbore, Susan; Amundson, Ronald (Department of Geosciences, The University of Arizona, 2008-01-01)
      A variety of physical and chemical techniques are used to fractionate soil organic matter, but detailed comparisons of the different approaches and tests of how separation methods influence the properties of isolated organic matter pools are lacking. In this case study based on A horizon samples of 2 California coniferous forests soils, we 1) evaluate the effects of root removal and ultrasonic dispersion on the properties of the 2 g cm3 light fraction and 2) compare the properties of fractions obtained by sequential density separations of ultrasonically treated soil with those obtained by density followed by acid/base hydrolysis (Trumbore et al. 1996). A root-removal effort based on hand-picking visible roots reduced the radiocarbon content and increased the estimated turnover time of the light fraction by roughly 12%. Root-removal protocols that vary between investigators thus can potentially confound variability in carbon cycling for this fraction caused by environmental factors, such as climate. Ultrasonic dispersion did not have a clear effect on the light fraction C and N content or isotopic signature, but led to a decrease in the % C and C/N of the recovered heavy fractions, and losses of 1219% of the total soil C to the sodium metatungstate density solution. Sequentially isolated density fractions clearly differed in mineralogy and organic matter chemistry, but natural-abundance 14C analyses indicated that distinct mineral phases did not correspond to unique C-turnover pools. Density fractions containing kaolinite group minerals alone and in combination with hydroxy-interlayered vermiculite were found to harbor both fast and slow cycling carbon. In contrast, severe chemical treatment isolated a carbon pool with the lowest overall 14C content and longest inferred mean turnover time. Overall, our results show that care must be taken when relying on physical (density) separation to isolate soil fractions with different dynamics, as the details of treatment will influence the results.
    • Radiocarbon Reservoir Ages and Hardwater Effect for the Northeastern Coastal Waters of Argentina

      Gómez, Eduardo A.; Borel, C. Marcela; Aguirre, Marina L.; Martínez, Daniel E. (Department of Geosciences, The University of Arizona, 2008-01-01)
      Accelerator mass spectrometry (AMS) radiocarbon dates were obtained for 18 mollusk shells collected alive along the Buenos Aires province coast, Argentina, over the period AD 1914-1935. Reservoir ages were estimated for all samples on the basis of the tree-ring calibration curve for the Southern Hemisphere (SHCal04, McCormac et al. 2004) and the marine ΔR values calculated as the difference between the conventional 14C age and the age deduced from the marine, mixed-layer model calculation (Marine04, Hughen et al. 2004). For most coastal locations, a great ΔR scatter was observed, ranging from 191 to 2482 yr, which is explained by the input of varying content of dissolved carbonate by rivers and groundwater (hardwater effect) and indicates a serious limitation for shell-based 14C chronologies. Within the interior of Baha Blanca estuary, ΔR values ranged from 40 to 50 +/- 46 as a consequence of the local geological particularities of the environment. This suggests that, with some restrictions, the marine calibration curve with standard parameters (ΔR = 0) could be used at this location.
    • Contents

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

      Department of Geosciences, The University of Arizona, 2008-01-01
    • Extended Radiocarbon Calibration in the Anglo-Saxon Period, AD 395-485 and AD 735-805

      McCormac, F. G.; Bayliss, A.; Brown, D. M.; Reimer, P. J.; Thompson, M. M. (Department of Geosciences, The University of Arizona, 2008-01-01)
      Radiocarbon dating has been used infrequently as a chronological tool for research in Anglo-Saxon archaeology. Primarily, this is because the uncertainty of calibrated dates provides little advantage over traditional archaeological dating in this period. Recent advances in Bayesian methodology in conjunction with high-precision 14C dating have, however, created the possibility of both testing and refining the established Anglo-Saxon chronologies based on typology of artifacts. The calibration process within such a confined age range, however, relies heavily on the structural accuracy of the calibration curve. We have previously reported decadal measurements on a section of the Irish oak chronology for the period AD 495-725 (McCormac et al. 2004). In this paper, we present decadal measurements for the periods AD 395-485 and AD 735-805, which extends the original calibration set.
    • First Reported Samples from the Radiocarbon Laboratory of the University of Tennessee Center for Archaeometry and Geochronology: Dates from the McCrosky Island Archaeological Site (40SV43), Sevier County, Tennessee, USA

      Weinand, Daniel C.; Polhemus, Richard R.; Blankenship, Sarah A.; Simek, Jan F. (Department of Geosciences, The University of Arizona, 2008-01-01)
      This study presents the results of archaeological samples submitted for dating at the recently constructed University of Tennessee Center for Archaeometry and Geochronology (UTCAG) radiocarbon dating laboratory (Knoxville, Tennessee, USA). The samples selected for this initial study were obtained from excavations at the McCrosky Island site (40SV43) in Sevier County, Tennessee, USA. Three of the samples dated were split between the UTCAG laboratory and another laboratory to assess the UTCAG laboratory protocols. In an effort to further validate the laboratory methods employed, several other samples were submitted without prior knowledge of contextual data. The dates obtained for these samples were then compared to their association with recovered artifacts and/or archaeological context.
    • A New Method for Analyzing 14C of Methane in Ancient Air Extracted from Glacial Ice

      Petrenko, Vasilii V.; Smith, Andrew M.; Brailsford, Gordon; Riedel, Katja; Hua, Quan; Lowe, Dave; Severinghaus, Jeffrey P.; Levchenko, Vladimir; Bromley, Tony; Moss, Rowena; et al. (Department of Geosciences, The University of Arizona, 2008-01-01)
      We present a new method developed for measuring radiocarbon of methane (14CH4) in ancient air samples extracted from glacial ice and dating 11,000-15,000 calendar years before present. The small size (~20 g CH4 carbon), low CH4 concentrations ([CH4], 400-800 parts per billion [ppb]), high carbon monoxide concentrations ([CO]), and low 14C activity of the samples created unusually high risks of contamination by extraneous carbon. Up to 2500 ppb CO in the air samples was quantitatively removed using the Sofnocat reagent. 14C procedural blanks were greatly reduced through the construction of a new CH4 conversion line utilizing platinized quartz wool for CH4 combustion and the use of an ultra-high-purity iron catalyst for graphitization. The amount and 14C activity of extraneous carbon added in the new CH4 conversion line were determined to be 0.23-0.16 g and 23.57-16.22 pMC, respectively. The amount of modern (100 pMC) carbon added during the graphitization step has been reduced to 0.03 g. The overall procedural blank for all stages of sample handling was 0.75-0.38 pMC for ~20-g, 14C-free air samples with [CH4] of 500 ppb. Duration of the graphitization reactions for small (25 g C) samples was greatly reduced and reaction yields improved through more efficient water vapor trapping and the use of a new iron catalyst with higher surface area. 14C corrections for each step of sample handling have been determined. The resulting overall 14CH4 uncertainties for the ancient air samples are ~1.0 pMC.