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现代沉积的210Pb计年
引用本文:万国江.现代沉积的210Pb计年[J].第四纪研究,1997,17(3):230-239.
作者姓名:万国江
作者单位:中国科学院地球化学研究所环境地球化学国家重点实验室!贵阳,550002
摘    要:210Pb具有百年时间尺度沉积计年的重要价值。210Pbex计年假设:沉积物是封闭系统;进入水体的210Pb能有效地转移到沉积物中并不发生沉积后迁移;非过剩210Pb与其母体226Ra保持平衡。210Pbex计年可用稳定输入通量-稳定沉积物堆积速率模式、常量初始浓度模式或恒定补给速率模式。沉积物柱芯必须保持原态并以0.5~1cm间隔分截;用相应层节226Ra校正。沉积物表层混合作用及222Rn的丢失可能导致顶部210Pbex异常。季节性缺氧湖泊沉积物顶部可能存在210Pb及210Po的再迁移。210Pb与137Cs两种计年方法原理上具有根本差别。210Pb,137Cs与沉积纹理方法对比是准确计年的重要保证。

关 键 词:210Pb计年  现代沉积
收稿时间:1997-05-17
修稿时间:1997-05-25

210Pb DATING FOR RECENT SEDIMENTATION
Wan Guojiang.210Pb DATING FOR RECENT SEDIMENTATION[J].Quaternary Sciences,1997,17(3):230-239.
Authors:Wan Guojiang
Affiliation:State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry,Chinese Academy of Sciences, Guiyang 550002
Abstract:210Pb, a daughter of Uranium-series, which widely spreads in nature is valuable in dating for sedimentation on 100 year scale. 210Pb dating has the following basic assumptions: (1) constants for sediment source and accumulation rates, and 210Pbex input flux in a closed system; (2) 210Pb in the waters of lakes or estuaries removed by sediment efficiently; (3)210Pb in the sediment without post-depositional transportation,and (4) an equilibrium of supported 210Pb in the sediment with its progenitor, 226Ra.210Pbex dating models are described as follows: (1) Constant Flux-Supply of sediment accumulation rate (CFS) model11]; (2) Constant Initial Concentration (CIC) model12];and (3) Constant Rate of Supply of 210Pb (CRS) model,i. e., Constant Flux (CF) model1,13]. Sediment cores, which must be undisturbed, are cut into 0.5-1cm slices for recent sedimentation reties. 210Pb activity is determined by γ-spectroscopy directly or α-spectroscopy after radio-chemical process. It is appropriate to correct 210Pbex in the sediment core employing 226Ra in the same layers. 210Pbex abnormal distribution in the upper sediment may result from mixing20-22] or 222Rn loss23]. In seasonally anoxic lakes, it is possible for the upper sediment to exist 210Po remobilization. Based on the stable isotope composition of lead (206Pb /204Pb, 207Pb /204Pb,208Pb /204Pb), it can be identified if the lead was removed into soluble-carbonate from non-carbonate and diffused through pore-water26-28], which probably causes post-depositional loss14,15,24,25] and effects the 210Pb dating. The dating principles are substantially different between 210Pb and 137Cs, and partly emphasis on molecule diffusion properties of 137Cs is impractical. In dating application for recent sedimentation, comparison of 210Pb method with 137Cs time-market and varve counting is very important for correcting results. It is key for further approach to systemically investigate geochemical behavior of 210Pb under different conditions systemically.
Keywords:~(210)Pb dating  recent sedimentation
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