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Quaternary geochronology
Elsevier
Quaternary geochronology

Elsevier

1871-1014

Quaternary geochronology/Journal Quaternary geochronologyAHCIISTPSCI
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    Luminescence dating of mass-transport sediment using rock-surface burial methods: a test case from the Baksan valley in the Caucasus Mountains

    Semikolennykh, D.Kurbanov, R.Murray, A. S.Cunningham, A. C....
    13页
    查看更多>>摘要：Mass-transport sediments are generally difficult to date directly by existing methods. Conventional luminescence dating of sand is unsuitable because the short transport distances provide little opportunity for bleaching. However, larger clasts are often exposed to sunlight for prolonged periods before becoming entrained in mass-movements, and these clasts have the potential to be used for rock-surface luminescence dating. Mass-transport is a major component of landscape change in mountain regions; in the Baksan valley, Caucasus Mountains, high uplift rates and high precipitation create a rapidly eroding landscape where preservation of sediments is poor. The area is particularly prone to destructive debris flows, because of the large quantity of detrital material in the catchments. The debris-flow and hillslope sediment the Baksan valley are used here to test the applicability of rock-surface burial dating to mass-transport sediment. We find that colluvial clasts show a high degree of bleaching and give reproducible ages, with a large colluvial deposit dated to the early-mid Holocene. The bleaching of debris flow clasts is more variable - we suppose due to the more complex transport history of the clasts, with opportunities for lengthy storage in moraines or colluvium. Overall, the results are encouraging, and suggest that rock-surface methods can provide a useful approach to mass-transport dating in mountainous regions. However, improved targeting of samples and measurement efficiency is desirable for widespread application.
      原文链接:
    • NSTL
    • Elsevier

    Advances and limitations in establishing a contiguous high-resolution atmospheric radiocarbon record derived from subfossil kauri tree rings for the interval 60-27 cal kyr BP

    Hogg, Alan G.Lorrey, Andrew M.Turney, Chris S. M.Palmer, Jonathan G....
    13页
    查看更多>>摘要：Radiocarbon dating is the most widely applied and reliable dating technique for providing chronological control during Marine Isotope Stage 3 (MIS3; -60-27 cal kyr BP). Past variations in the atmospheric concentration of radiocarbon mean a calibration curve is required. IntCal20 and SHCal20 calibration curves covering MIS3 are presently largely based on non-atmospheric records which, in combination with larger radiocarbon (C-14) dating uncertainties, results in significant smoothing and reduced resolution in calibration curve structure. Floating tree ring radiocarbon chronologies that are wiggle-matched to other palaeo records (particularly to Hulu Cave spe-leothems) have the potential to provide detailed structure to the MIS3 portion of extant calibration curves. New Zealand subfossil kauri (Agathis australis) trees are long-lived and are useful for constructing temporally-floating MIS3 atmospheric radiocarbon datasets. This paper presents extant and emerging data from several important Northland subfossil kauri locations (Omaha, Babylon Coast, Bream Bay, Kai Iwi Lakes, Mangawhai). We show the span of seven floating MIS3 kauri sequences (individual trees and chronologies) from which sequential radio-carbon series covering a total of 7556 years is now in development (representing 23% of the period 60-27 cal kyr BP). We also report radiocarbon dates for an additional 34 ancient kauri from MIS3 that can provide additional coverage. After these floating subfossil wood sequences have been produced, close to 40% of MIS3 (12,420 years) will be covered by contiguous subfossil kauri radiocarbon measurements. Based on our findings, we discuss the prospects and limitations for obtaining a highly resolved and precise atmospheric radiocarbon calibration curve comprehensively covering MIS3 using subfossil kauri.
      原文链接:
    • NSTL
    • Elsevier

    Revised ?R values for the Barents Sea and its archipelagos as a pre-requisite for accurate and robust marine-based C-14 chronologies

    Pienkowski, Anna J.Husum, KatrineFurze, Mark F. A.Missana, Amandine F. J. M....
    17页
    查看更多>>摘要：The calibration of marine C-14 dates requires the incorporation of regionally specific marine reservoir offsets known as delta R, essential for accurate and meaningful inter-archive comparisons. Revised, regional delta R ("AR(R)') values for the Barents Sea are presented for molluscs and cetaceans for the two latest iterations of the marine calibration curve, based on previously published pre-bomb live-collected and radiocarbon-dated samples ("AR(L)'; molluscs: n = 16; cetaceans: n = 18). Molluscan ARR, determined for four broad regional oceanographic settings, are: western Svalbard (including Bj & oslash;rn & oslash;ya), -61 +/- 37 C-14 yrs (Marine20), 94 +/- 38 C-14 yrs (Marine13); Franz Josef Land, -277 +/- 57 C-14 yrs (Marine20), -122 +/- 38( 14)C yrs (Marine13); Novaya Zemlya, -156 +/- 73 C-14 yrs (Marine20), 0 +/- 76 C-14 yrs (Marine13); northern Norway, -86 +/- 39 C-14 yrs (Marine20), 74 +/- 24 C-14 yrs (Marine13). Molluscan ARR values are considered applicable to other marine carbonate materials (e.g., fora-minifera, ostracods). Cetacean ARR are determined for toothed (n = 10) and baleen (n = 8) whales, and a combined toothed-baleen group (n = 18): toothed,-161 +/- 41( 14)C yrs (Marine20), 1 +/- 41( 14)C yrs (Marine13); baleen, -158 +/- 43 C-14 yrs (Marine20), 8 +/- 41 C-14 yrs (Marine13); combined baleen-toothed whales,-160 +/- 41( 14)C yrs (Marine20), 4 +/- 49 C-14 yrs (Marine13). Where identification and separation of baleen and toothed whales is impossible the combined AR(R) term may be used. However, we explicitly discourage the application of existing cetacean AR(R) terms to other marine mammals. Our new ARR values are applicable for as long as those broad oceanographic conditions (circulation and ventilation) have persisted, i.e., through the Holocene. We recom-mend using the latest iteration of the marine calibration curve, Marine20, which seems to better capture the time-variant nature of R compared to Marine13. More delta R-L datapoints for both molluscs and cetaceans would improve the accuracy and precision of delta R-R. In the meantime, our new delta R terms facilitate the calibration of marine( 14)C dates across the region, paving the way for meaningful and accurate late Quaternary histories and inter-regional comparisons.
      原文链接:
    • NSTL
    • Elsevier

    Testing less-conventional methods to date a late-pleistocene to Holocene eruption: Radiocarbon dating of paleosols and Cl-36 exposure ages at Pelado volcano, Sierra Chichinautzin, Central Mexico

    Guilbaud, Marie-NoelleAlcala-Reygosa, JesusSchimmelpfennig, IreneLuise Arce, Jose...
    12页
    查看更多>>摘要：Despite their significance for estimating hazards and forecasting future activity, dating young volcanic deposits and landforms (< 50,000 yrs old) remains a challenge due to the limitations inherent to the different isotopic chronometers used. The Trans-Mexican Volcanic Belt is one of the most active and populated continental arcs worldwide, yet its temporal pattern of activity is poorly constrained. Such deficiency is particularly problematic for the Sierra Chichinautzin Volcanic Field (SCVF) that is located at the doorstep of Mexico City and Cuernavaca and is hence a major source of risk for these cities. Existing ages for this area derive mostly from either radio-carbon on charcoal, which is rare and may be contaminated, or Ar-40/Ar-39 on rock matrix, which is poorly precise for this time period and rock type. Here, we focus on the Pelado monogenetic volcano, which is located in the central part of the SCVF and erupted both explosively and effusively, producing a large lava shield and a widespread tephra blanket. This unique eruptive event was previously dated at similar to 12 calibrated (cal) kyrs BP, using radiocarbon dating on charcoal from deposits related to the eruption. To test alternative dating approaches and confirm the age of this significant eruption, we applied two less conventional techniques, radiocarbon dating of bulk paleosol samples collected below the complete tephra sequence at nine sites around the shield, and in-situ Cl-36 exposure dating of two samples of an aphyric lava from the base of the shield. Radiocarbon paleosol ages span a continuous time interval from 13.2 to 20.2 cal kyrs BP (2 sigma), except for one anomalously young sample. This wide age spread, along with the low organic contents of the paleosols, may be due to erosive conditions, related to the sloping topography of the sampling sites and the cool and relatively dry climate of the Younger Dryas (11.7-12.9 ka), during which the Pelado eruption probably occurred. The two Cl-36-dated lava samples have consistent ages at 1 sigma analytical errors of 15.5 +/- 1.4 ka and 13.2 +/- 1.2 ka, respectively, yielding an average age of 14.3 +/- 1.6 ka for this lava flow. The high full uncertainty in Cl-36 ages (24%) is due to high rock Cl content. We conclude that paleosol radiocarbon dating is useful if numerous samples are analyzed and climatic and relief conditions at the time of the eruption and at the sites of tephra deposition are considered. The Cl-36 dating technique is an alternative method to date volcanic eruptions, as it gave consistent results, but in the specific case of Pelado volcano, the high Cl content in the analyzed rocks increases the age uncertainties.
      原文链接:
    • NSTL
    • Elsevier

    Beta dose heterogeneity in sediment samples measured using a Timepix pixelated detector and its implications for optical dating of individual mineral grains

    Fu, XiaoRomanyukha, Anna A.Li, BoJankowski, Nathan R....
    18页
    查看更多>>摘要：Single-grain optical dating has been widely used to estimate depositional ages for Quaternary sediments. An understanding of the sources influencing the dispersion of equivalent dose (D-e) estimates from individual grain measurements is essential for accurate age determination. Beta microdosimetry (i.e., beta dose deposition at the sub-millimetre scale) is a known cause of spread in single-grain D-e values, so the detection and assessment of beta dose rate (D-beta) variation is important to properly interpret these data. Here we demonstrate the application of Timepix, a pixelated detector that directly measures in situ beta emissions based on cluster analysis, to determine the beta microdosimetry of natural sediment samples from a cave deposit in Russia and a sand dune in Australia. We describe a Timepix measurement and data processing procedure for natural sediments, and establish sample specific calibration curves using associated sample radioelement concentrations to convert Timepix count rates into estimates of D-beta. On the basis of the Timepix analysis, a 2D 'heat map' of D-beta at sub-millimetre resolution was obtained for each sample. Our results show that the D(beta )estimates are heterogeneous and their non-uniformity gives rise to 9 & nbsp;+/- 4 to 26 & nbsp;+/- 5%& nbsp; overdispersion in the single-grain D-e distributions for the samples examined here. We discuss the likely sources of D-beta heterogeneity, based on micromorphological investigations of these sediment samples, which include a variety of materials present in natural deposits associated with D-beta 'hot' and 'cold' spots. A comparison of the D-beta dispersion with that of the corresponding single-grain D-e values shows that the scatter among the latter can be fully or partly explained by beta microdosimetry and other known sources of overdispersion.
      原文链接:
    • NSTL
    • Elsevier