• Calibrated 14C Ages of Jomon Sites, NE Japan, and Their Significance

      Omoto, K.; Takeishi, K.; Nishida, S.; Fukui, J. (Department of Geosciences, The University of Arizona, 2010-01-01)
      The traditional archaeological chronology in the Japanese Islands during the Jomon period was essentially based on the relative age given to cord-impressed patterns marked on pottery, as well as the shape of the pottery and the thickness of the cultural layers that were excavated. We aimed to correlate the classical archaeological chronology with calibrated radiocarbon dates, to posit a new chronology for the Jomon period in northeastern Japan. We calibrated 80 accelerator mass spectrometry (AMS) 14C dates from NE Japan and reconstructed a chronological timetable for Hokkaido and the Tohoku District. We collected 43 samples from 5 shellmounds and 2 archaeological sites on Hokkaido Island and 4 shellmounds in the Tohoku District in order to determine the calibrated age of their sites. R values used on Hokkaido Island and the Tohoku District were between 282 and -158 yr and between 0 and -40 yr, respectively. The large R value for the eastern part of Hokkaido Island indicates the influence of the Oyashio Current, while an anomalous R value was obtained from northern Hokkaido Island. These figures show larger apparent R values than those from southwest Japan (Nakamura et al. 2007). The calibrated Jomon period in the investigated area was from 2000 to 200 yr younger than the previous chronology. Calibrated 14C ages of the shellmounds investigated ranged between ~6000 and 3000 yr, correlating to the Early Jomon and Final Jomon periods as indicated by the former archaeological chronology of Honshu Island.
    • Chronology of the Obi-Rakhmat Grotto (Uzbekistan): First Results on the Dating and Problems of the Paleolithic Key Site in Central Asia

      Krivoshapkin, A. I.; Kuzmin, Y. V.; Jull, A. J. T. (Department of Geosciences, The University of Arizona, 2010-01-01)
      The Obi-Rakhmat Grotto is one of the key Paleolithic sites in Central Asia. Archaeological excavations have revealed 22 strata containing archaeological materials. Lithic assemblages from all cultural layers display features similar to both late Middle Paleolithic blade industries and early Upper Paleolithic complexes in Southwest Asia and the Siberian Altai Mountains; this suggests a gradual Middle-to-Upper Paleolithic transition occurred in western Central Asia. Hominid remains found at Obi-Rakhmat (layer 16) show a mixture of archaic and modern traits. Different chronometric methods (radiocarbon, optically stimulated luminescence [OSL], U-series, and electron spin resonance [ESR]) were applied to the site's deposits. It appears that 14C dates are more reliable in terms of correspondence to the general framework of the Paleolithic of Central Asia and neighboring regions, and after critical analysis and the deletion of outliers, the upper part of the site's cultural sequence can be dated between 36,000-41,400 BP (layer 7) and ~48,800 BP (layer 14.1). The U-series dating results are less secure due to the high uranium content and the presence of detritus, which contaminates dated sediments (travertine). The OSL dating gave uniform ages for all cultural succession (~8 m of deposits), and confirms a very rapid sedimentation rate. Results of ESR dating depend greatly on the choice of uptake model. Dates calculated for the early uptake to some extent correspond to 14C data. The linear uptake chosen by Skinner et al. (2007) makes sediments very old (about 55,000-90,000 yr ago), which contradicts 14C dates and does not correspond well to the regional archaeological context.
    • Chronostratigraphic Sequence of Santuario della Madonna Cave (Calabria, Southern Italy): AMS Radiocarbon Data from a New Excavation Area

      Calcagnile, L.; Tinè, V.; Quarta, G.; D'Elia, M.; Fiorentino, G.; Scarciglia, F.; Robustelli, G.; Abate, M.; La Russa, M. F.; Pezzino, A. (Department of Geosciences, The University of Arizona, 2010-01-01)
      The Santuario della Madonna Cave, located near Praia a Mare (Cosenza), along the northwestern coast of Calabria (southern Italy), has an impressive stratigraphy, with occupation phases spanning from the late Paleolithic to the advanced phases of the Middle Bronze Age. Recently, a new excavation area has been opened in the cave from which short-lived vegetal remains were sampled and submitted for accelerator mass spectrometry (AMS) radiocarbon dating. The aim of this study was to define an accurate chronology of the different cultural aspects and to explore the potentialities resulting from application of advanced statistical tools for 14C data analysis in such a context.
    • Developing Ultra Small-Scale Radiocarbon Sample Measurement at the University of Tokyo

      Yokoyama, Y.; Koizumi, M.; Matsuzaki, H.; Miyairi, Y.; Ohkouchi, N. (Department of Geosciences, The University of Arizona, 2010-01-01)
      We have developed accelerator mass spectrometry (AMS) measurement techniques for ultra small-size samples ranging from 0.01 to 0.10 mg C with a new type of MC-SNICS ion source system. We can generate 4 times higher ion beam current intensity for ultra-small samples by optimization of graphite position in the target holder with the new ionizer geometry. CO2 gas graphitized in the newly developed vacuum line is pressed to a depth of 1.5 mm from the front of the target holder. This is much deeper than the previous position at 0.35 mm depth. We measured 12C4+ beam currents generated by small standards and ion beam currents (15-30 mu-A) from the targets in optimized position, lasting 20 min for 0.01 mg C and 65 min for 0.10 mg C. We observed that the measured 14C/12C ratios are unaffected by the difference of ion beam currents ranging from 5 to 30 mu-A, enabling measurement of ultra-small samples with high precision. Examination of the background samples revealed 1.1 mu-g of modern and 1 mu-g of dead carbon contaminations during target graphite preparation. We make corrections for the contamination from both the modern and background components. Reduction of the contamination is necessary for conducting more accurate measurement.
    • Dietary Habits and Freshwater Reservoir Effects in Bones from a Neolithic NE German Cemetery

      Olsen, J.; Heinemeier, J.; Lübke, H.; Lüth, F.; Terberger, T. (Department of Geosciences, The University of Arizona, 2010-01-01)
      Within a project on Stone Age sites of NE Germany, 26 burials from the Ostorf cemetery and some further Neolithic sites have been analyzed by more than 40 accelerator mass spectrometry (AMS) dates. We here present the results of stable isotope and radiocarbon measurements together with reference 14C dates on grave goods from terrestrial animals such as tooth pendants found in 10 of the graves. Age differences between human individuals and their associated grave goods are used to calculate 14C reservoir effects. The resulting substantial reservoir effects have revealed misleadingly high 14C ages of their remains, which originally indicated a surprisingly early occurrence of graves and long-term use of this Neolithic burial site. We demonstrate that in order to 14C date the human bones from Ostorf cemetery, it is of utmost importance to distinguish between terrestrial- and freshwater-influenced diet. The latter may result in significantly higher than marine reservoir ages with apparent 14C ages up to ~800 yr too old. The carbon and nitrogen isotopic composition may provide a basis for or an indicator of necessary corrections of dates on humans where no datable grave goods of terrestrial origin such as tooth pendants or tusks are available. Based on the associated age control animals, there is no evidence that the dated earliest burials occurred any earlier than 3300 BC, in contrast to the original first impression of the grave site (~3800 BC).
    • Dietary Reconstruction and Reservoir Correction of 14C Dates on Bones from Pagan and Early Christian Graves in Iceland

      Sveinbjörnsdóttir, Á. E.; Heinemeier, J.; Arneborg, J.; Lynnerup, N.; Ólafsson, G.; Zoëga, G. (Department of Geosciences, The University of Arizona, 2010-01-01)
      In this study, delta-13C and delta-15N of bone samples from 83 skeletons (79 humans, 2 horses, and 2 dogs) excavated from pagan and early Christian graves from 21 localities in Iceland are used to reconstruct diet of the early settlers in Iceland and possible differences in diet depending on the distance between the excavation site and the seashore. We have radiocarbon dated 47 of these skeletons and used the carbon isotopic composition (delta-13C) to estimate and correct for the marine reservoir effect (the 14C difference between terrestrial and mixed marine organisms). The reservoir-corrected ages lie in the range of AD 780-1270 (68.2% probability). Reservoir age corrections were checked by comparing 14C dates of a horse (terrestrial diet), a dog (highly marine diet), and a human (mixed diet) from the same burial. The range in measured marine protein percentage in individual diet is from about 10% up to 55%, mostly depending on the geographical position (distance from the sea) of the excavation site. We had access to the skeleton (AAR-5908) of the Skálholt bishop Páll Jónsson whose remains are enshrined at the Episcopal residence in Skálholt, southern Iceland. According to written sources, the bishop died in AD 1211. Using our dietary reconstruction, his bones were about 17% marine, which is within the range of human skeletons from the same area, and the reservoir-corrected calibrated 14C age of the skeleton is in accord with the historical date.
    • Dietary Reconstruction of the Okhotsk Culture of Hokkaido, Japan, Based on Nitrogen Composition of Amino Acids: Implications for Correction of 14C Marine Reservoir Effects on Human Bones

      Naito, Y. I.; Chikaraishi, Y.; Ohkouchi, N.; Mukai, H.; Shibata, Y.; Honch, N. V.; Dodo, Y.; Ishida, H.; Amano, T.; Ono, H.; et al. (Department of Geosciences, The University of Arizona, 2010-01-01)
      The relative contribution of marine-derived carbon in the ancient diet is essential for correcting the marine reservoir effect on the radiocarbon age of archaeological human remains. In this study, we evaluated the marine protein consumption of 3 human populations from the Okhotsk culture (about AD 550-1200) in Hokkaido, Japan, based on stable carbon and nitrogen isotopic compositions in bulk bone collagen as well as the nitrogen isotopic composition of glutamic acid and phenylalanine. Despite the similarity of carbon and nitrogen isotopic composition of bulk collagens, nitrogen isotopic composition of their constituent amino acids suggests differences in fur seal contributions among northern Hokkaido (0-24% for Kafukai 1, 0-10% for Hamanaka 2) and eastern Hokkaido (78-80% for Moyoro) populations. It suggests that nitrogen composition of glutamic acid and phenylalanine could provide a detailed picture of ancient human subsistence.
    • Direct Absorption Method and Liquid Scintillation Counting for Radiocarbon Measurements in Organic Carbon from Sediments

      Faurescu, I.; Varlam, C.; Stefanescu, I.; Cuna, S.; Vagner, I.; Faurescu, D.; Bogdan, D. (Department of Geosciences, The University of Arizona, 2010-01-01)
      In this paper, we investigate a procedure for radiocarbon determination in forest soil and slurry from lake sediments. The total carbon in these samples can be both inorganic and organic. Inorganic carbon can be analyzed in a straightforward manner using the direct absorption method by sample acidification and CO2 capture. For organic carbon, we investigate a hybrid method using the wet-oxidation of organic carbon followed by direct absorption. To evaluate the wet-oxidation processes with potassium dichromate (K2Cr2O7) and potassium permanganate (KMnO4), we performed several experiments using different quantities of soil and sediments in order to establish the quantity of CO2 for each type of sample. The 2 methods offer comparable results for 14C-specific activity (about 0.234 0.024 Bq/g C), values that are expected for these kinds of samples. We also investigated the possibility of isotopic fractionation occurring during CO2 production from raw material by measuring 13C levels from samples and obtained CO2.
    • Early Bronze Age Strata at Tell Ghanem al-Ali along the Middle Euphrates in Syria: A Preliminary Report of 14C Dating Results

      Nakamura, T.; Hoshino, M.; Tanaka, T.; Yoshida, H.; Saito, T.; Tsukada, K.; Katsurada, Y.; Aoki, Y.; Ohta, T.; Hasegawa, A.; et al. (Department of Geosciences, The University of Arizona, 2010-01-01)
      We collected charcoal fragments during an archaeological excavation at the Tell Ghanem al-Ali site, located on the lowest terrace of the middle Euphrates River, and measured their radiocarbon ages with accelerator mass spectrometry (AMS). Two trenches, Square-1 and Square-2, were dug on the slope of the tell; 8 building levels were detected in the Square-2 trench. In total, 31 charcoal samples were collected from the 2 trenches, and their calibrated ages ranged from 3100-2900 cal BC at the lowest building level to 2400-2050 cal BC at the uppermost layers of the mound, and concentrated in the period 2650-2450 cal BC. The pottery fragments collected on the surface of the mound before the excavation survey was started, as well as those collected from the sediment layers during the excavation, were assigned on the basis of typological sequences to the Early Bronze Age (EB)-III and EB-IV periods. Thus, the concentrated dates (2650-2450 cal BC) obtained by 14C dating are consistent with the age estimated by archaeological contexts. However, the oldest dates of the lowest level (level-7) go back to 3100-2900 cal BC, and these dates may suggest the existence of the human residence prior to the EB period at the site, and may therefore lead to a revision of the oldest age limit of the EB period currently accepted in the region.
    • Editorial Board

      Department of Geosciences, The University of Arizona, 2010-01-01
    • Environmental Changes of the Aral Sea (Central Asia) in the Holocene: Major Trends

      Krivonogov, S. K.; Kuzmin, Y. V.; Burr, G. S.; Gusskov, S. A.; Khazin, L. B.; Zhakov, E. Y.; Nurgizarinov, A. N.; Kurmanbaev, R. K.; Kenshinbay, T. I. (Department of Geosciences, The University of Arizona, 2010-01-01)
      Changes of the Aral Sea level have been observed in 3 sediment boreholes, 2 outcrops, and associated archaeological sites. The obtained results are supported by 25 radiocarbon dates. Major trends of lake-level changes have been reconstructed in some detail for the last 2000 yr, and additional data provide an outline of fluctuations throughout the Holocene. Several distinct changes are shown to precede the modern, human-induced regression of the Aral Sea. These include: 1) the latest maximum in the 16th-20th centuries AD (53 m asl); 2) a Medieval "Kerderi" minimum of the 12th-15th centuries AD (29 m asl); 3) the early Medieval maximum of the 4th-11th centuries AD (52 m asl); and 4) a near BC/AD lowstand, whose level is not well established. Since then, events are only inferred from sparse data. The studied cores contain several sandy layers representing the lowering of the lake level within the Holocene, including the buried shore-bar of ~4500 cal BP (38 m asl), and shallow-water sediments of ~5600 cal BP (44 m asl), 7200 cal BP (28 m asl), and 8000 cal BP (26.5 m asl).
    • Establishing a Firm Chronological Framework for Neolithic and Early Dynastic Archaeology in the Shangluo Area, Central China

      Zhu, Y.; Cheng, P.; Yu, S-Y.; Yu, H.; Kang, Z.; Yang, Y.; Jull, A. J. T.; Lange, T.; Zhou, W. (Department of Geosciences, The University of Arizona, 2010-01-01)
      Technological and theoretical advancements in modern radiocarbon chronology make the precise dating of archaeological and geological events possible. Here, we show examples of how these state-of-the-art methods can be used to establish and refine the archaeological cultural chronology for the Shangluo area in the Qinling Mountains of central China. In this study, the Donglongshan and Zijing sites were dated using the high-precision accelerator mass spectrometry (AMS) 14C method. Also, detailed magnetic-susceptibility measurements were conducted at both sites to gain preliminary information about past climate changes. The 14C dates, after being treated with Bayesian statistics, provide a firm constraint on the archaeological chronological framework for this area. Within this framework, the Malan loess-Holocene soil transition can be placed at 10,400-10,090 BC, while the duration of the Yangshao and Longshan cultures was dated to ~4200-2900 and ~2900-2100 BC, respectively, revealing an undisrupted history of human occupation in this area until the early dynastic period. Magnetic susceptibility values began to increase in the early Holocene, indicating a progressive amelioration of regional climate. The widespread development of paleosol during the middle Holocene indicates that warm and wet climate conditions prevailed, providing a favorable environmental context within which the Yangshao culture thrived. Magnetic susceptibility values then decreased from ~2100 BC when the Xia Dynasty started, and loess accumulated again, pointing to cooling and drying climate conditions that may have led to a cultural transition from the Neolithic to the dynastic civilization.
    • Estimation of Long-Term Trends in the Tropospheric 14CO2 Activity Concentration

      Svetlik, I.; Povinec, P. P.; Molnár, M.; Meinhardt, F.; Michálek, V.; Simon, J.; Svingor, É. (Department of Geosciences, The University of Arizona, 2010-01-01)
      Fossil CO2 emissions have been diluting the global 14C/C ratio of atmospheric CO2 (Suess effect). We estimated the 14CO2 amount in the atmosphere (and its trend) utilizing the calculated 14CO2 activity concentration in the atmosphere (aacn, reported in mBq m^(-3)). This parameter, calculated from ∆14CO2 and the CO2 mixing ratio (reported in micromoles of CO2 per mole of air), is connected with the 14CO2 quantity in the volume or mass unit of air, which is not influenced by the Suess effect. This parameter can only be influenced by processes linked to 14CO2 emissions/uptake, e.g. associated with atmosphere-biosphere or atmosphere-ocean CO2 exchange as well as by anthropogenic emissions of 14CO2. Results obtained from measurements at Schauinsland station, Germany, indicate a stable amount of 14CO2 in the atmosphere since the early 1990s.
    • Experimental Study on the Origin of Cremated Bone Apatite Carbon

      Hüls, C. M.; Erlenkeuser, H.; Nadeau, M.-J.; Grootes, P. M.; Andersen, N. (Department of Geosciences, The University of Arizona, 2010-01-01)
      Changes of the Aral Sea level have been observed in 3 sediment boreholes, 2 outcrops, and associated archaeological sites. The obtained results are supported by 25 radiocarbon dates. Major trends of lake-level changes have been reconstructed in some detail for the last 2000 yr, and additional data provide an outline of fluctuations throughout the Holocene. Several distinct changes are shown to precede the modern, human-induced regression of the Aral Sea. These include: 1) the latest maximum in the 16th-20th centuries AD (53 m asl); 2) a Medieval "Kerderi" minimum of the 12th-15th centuries AD (29 m asl); 3) the early Medieval maximum of the 4th-11th centuries AD (52 m asl); and 4) a near BC/AD lowstand, whose level is not well established. Since then, events are only inferred from sparse data. The studied cores contain several sandy layers representing the lowering of the lake level within the Holocene, including the buried shore-bar of ~4500 cal BP (38 m asl), and shallow-water sediments of ~5600 cal BP (44 m asl), 7200 cal BP (28 m asl), and 8000 cal BP (26.5 m asl).
    • Fire History of a Giant African Baobab Evinced by Radiocarbon Dating

      Patrut, A.; Mayne, D. H.; Von Reden, Karl F.; Lowy, Daniel A.; van Pelt, Robert; McNichol, Ann P.; Roberts, Mark L.; Margineanu, D. (Department of Geosciences, The University of Arizona, 2010-01-01)
      The article reports the first radiocarbon dating of a live African baobab (Adansonia digitata L.), by investigating wood samples collected from 2 inner cavities of the very large 2-stemmed Platland tree of South Africa. Some 16 segments extracted from determined positions of the samples, which correspond to a depth of up to 15-20 cm in the wood, were processed and analyzed by accelerator mass spectrometry (AMS). Calibrated ages of segments are not correlated with their positions in the stems of the tree. Dating results indicate that the segments originate from new growth layers, with a thickness of several centimeters, which cover the original old wood. Four new growth layers were dated before the reference year AD 1950 and 2 layers were dated post-AD 1950, in the post-bomb period. Formation of these layers was triggered by major damage inside the cavities. Fire episodes are the only possible explanation for such successive major wounds over large areas or over the entire area of the inner cavities of the Platland tree, able to trigger regrowth.
    • Fish Reservoir Effect on Charred Food Residue 14C Dates: Are Stable Isotope Analyses the Solution?

      Boudin, M.; Van Strydonck, M.; Crombé, P.; De Clercq, W.; van Dierendonck, R. M.; Jongepier, H.; Ervynck, A.; Lentacker, A. (Department of Geosciences, The University of Arizona, 2010-01-01)
      In order to verify the relative dating based on pot type morphology and decoration of the Swifterbant pottery collected at the Final Mesolithic site of Doel "Deurganckdok" (Belgium) and of the Late Iron Age pottery excavated at Grijpskerke (the Netherlands), direct radiocarbon dates were obtained on charred food residue preserved on the inner surface of numerous potsherds. In addition, a number of indirect 14C dates were obtained from samples of organic material. In the case of Doel, the results indicate an important incompatibility between the charred food residue dates and the other dates, the former being systematically older. This difference may be explained by a reservoir effect of the charred food residue, caused by the processing of (freshwater) fish. The 14C dates for the rijpskerke site are in agreement between the charred food residue and the organic material. The stable isotopes of the charred food residue were analyzed to demonstrate fish processing in the pottery, but the results were inconclusive.
    • High-Precision Radiocarbon Dating of the Construction Phase of Oakbank Crannog, Loch Tay, Perthshire

      Cook, G. T.; Dixon, T. N.; Russell, N.; Naysmith, P.; Xu, S.; Andrian, B. (Department of Geosciences, The University of Arizona, 2010-01-01)
      Many of the Loch Tay crannogs were built in the Early Iron Age and so calibration of the radiocarbon ages produces very broad calendar age ranges due to the well-documented Hallstatt plateau in the calibration curve. However, the large oak timbers that were used in the construction of some of the crannogs potentially provide a means of improving the precision of the dating through subdividing them into decadal or subdecadal increments, dating them to high precision and wiggle-matching the resulting data to the master 14C calibration curve. We obtained a sample from 1 oak timber from Oakbank Crannog comprising 70 rings (Sample OB06 WMS 1, T103) including sapwood that was complete to the bark edge. The timber is situated on the northeast edge of the main living area of the crannog and as a large and strong oak pile would have been a useful support in more than 1 phase of occupation and may be related to the earliest construction phase of the site. This was sectioned into 5-yr increments and dated to a precision of approximately 8-16 14C yr (1 ). The wiggle-match predicts that the last ring dated was formed around 500 BC (maximum range of 520-465 BC) and should be taken as indicative of the likely time of construction of Oakbank Crannog. This is a considerable improvement on the estimates based on single 14C ages made on oak samples, which typically encompassed the period from around 800-400 BC.
    • Improved AMS 14C Dating of Shell Carbonates Using High-Precision X-Ray Diffraction and a Novel Density Separation Protocol (CarDS)

      Douka, K.; Hedges, R. E. M.; Higham, T. F. G. (Department of Geosciences, The University of Arizona, 2010-01-01)
      One critical variable in the successful application of radiocarbon dating is the effective removal of carbonaceous contaminants. In the case of marine carbonates, contamination appears usually in the form of secondary low-magnesium calcite, the stable polymorph of calcium carbonate and byproduct of the post-mortem recrystallization or replacement of the autochthonous phase, originally in the form of high-magnesium calcite or aragonite. Depending on the nature of the depositional environment, the secondary phase may be contemporary in age with the original shell carbonate and may have even been derived from it by dissolution-recrystallization processes, or can be an exogenous contaminant of younger or older age. The limited ability of current pretreatment protocols to detect and remove the secondary mineralogical phases prior to dating carbonates has been one of the reasons marine shell and coral 14C determinations are often difficult to validate in terms of their reliability. We have developed a new pretreatment protocol designed to achieve greater reliability and accuracy in the dating of this material. The method entails 2 steps. The first one involves the improved detection and quantification of secondary calcite in aragonite using X-ray diffraction, at a precision of ~0.1% and ~0.8%, respectively. Next, where this is required, a novel density separation step using non-toxic heavy liquids (CarDS) is applied to the diagenetic sample. This enables the clear separation of calcite and aragonite, with only the latter kept for dating. We have applied the new steps, screening and separation, on standard and archaeological examples and our initial results suggest that it is successful and reproducible. In this paper, we describe the method and initial results.
    • Improved Application of Bomb Carbon in Teeth for Forensic Investigation

      Wang, N.; Shen, C. D.; Ding, P.; Yi, W. X.; Sun, W. D.; Liu, K. X.; Ding, X. F.; Fu, D. P.; Yuan, J.; Yang, X. Y.; et al. (Department of Geosciences, The University of Arizona, 2010-01-01)
      While radiocarbon is widely applied in dating ancient samples, recent studies reveal that 14C concentrations in modern samples can also yield precise ages due to the atmospheric testing of thermonuclear devices between 1950 and 1963. 14C concentrations in both enamel and organic matter of 13 teeth from 2 areas in China were examined to evaluate and improve this method of forensic investigation. Choosing enamel near the cervix of the tooth can reduce the error caused by the difference between the sample formation time and whole enamel formation time because tooth enamel formations take a long time to complete. A proper regional data set will be helpful to get an accurate result when calculating the age of the sample (T1) by the CALIBomb program. By subtracting the enamel formation time (t), the birth date of an individual (T2) can be confirmed by enamel F14C from 2 teeth formed at different ages. Calculated enamel formation dates by 14C concentration are basically consistent with corresponding actual values, with a mean error of 1.9 yr for all results and 0.2 yr for the samples formed after AD 1960. This method is more effective for dating samples completed after AD 1960. We also found that 14C concentrations in organic matter of tooth roots are much lower than atmospheric concentrations in root formation years, suggesting that the organic material keeps turning over even after tooth formation is complete. This might be a potential tool for identification of death age to extract a proper component for 14C dating. We also observed that delta-13C values between hydroxyapatite and organic matter indicate that isotopic fractionation during the biomineralization is 8-9‰ more positive in mineral fractions than in organic matter.
    • Is More Precise Dating of Paleoindian Expansion Feasible?

      Fiedel, S. J.; Kuzmin, Y. V. (Department of Geosciences, The University of Arizona, 2010-01-01)
      Recent efforts to precisely date the florescence of the Clovis culture in North America have been hampered by both practical and theoretical problems: 1) The era of Clovis expansion (about 11,200-10,700 BP or 13,200-12,700 cal BP) coincides with the gap between the anchored central European tree-ring sequence (back to 12,400 cal BP) and the floating Bolling-Allerod sequence; 2) Clovis seems to immediately precede the onset of the Younger Dryas (YD) stadial. The "black mats" of the US Southwest appear to mark the regional occurrence of this climatic downturn. However, the timing and means of long-distance propagation of this climatic event are not yet well understood. Greenland ice cores (GISP2, GRIP, and NGRIP) remain poorly synchronized, with a discrepancy of 100 to 250 yr for the date of onset (as late as 12,700 cal BP, or as early as 12,950 cal BP); 3) The YD onset was accompanied by a rapid drop of radiocarbon ages from 11,000 to 10,600 BP in less than a century. The mechanism causing this was probably a change in overturning circulation in the North Atlantic. Do variable Clovis ages, often from what appear to be single-occupation contexts, reflect this "cliff" effect, slightly earlier minor reversals during the late Allerd, or simply the practical limitations of precision of the 14C method? 4) Dates for Fishtail or Fell I sites (with fluted, stemmed points) in southern South America are statistically indistinguishable from Clovis dates in North America. Does this imply very rapid population expansion, diffusion of tool-making techniques through long-established local populations (as argued by Waters and Stafford 2007), or abnormally large interhemispheric 14C offsets? 5) Are recent ostensibly high-precision collagen-derived dates for Paleoindian-associated fauna (e.g. horse and mammoth) reliable? Are interlaboratory blind tests of the new filtration processes necessary?