云南省泸沽湖、洱海现代沉积物中^(210)Pb,^(137)Cs的垂直分布及其计年

Vertical Distribution of ~ (210)Pb and ~ (137)Cs and Their Dating in Recent Sediments of Lugu Lake and Erhai Lake, Yunnan Province

云南省沪沽湖、洱海^（２１０）Ｐｂ_（ｅｘ）的垂直分布受 Ｆｅ、Ｍｎ循环下^（２１０）Ｐｏ和^（２１０）Ｐｂ沉积后再迁移的影响，分别表现为三种不同的剖面分布特征．^（２１０）Ｐｂ_（ｅｘ）计年的沉积物堆积速率分别为０．０５０－０．０５１ｇ·ｃｍ^（－２）ａ^（－１）和０．０４４－０．０４５ｇ·ｃｍ^（－２）ａ^（－１），反映百年时间尺度上的堆积结果．沪沽湖、洱海^（１３７）_（Ｃｓ）的垂直剖面分布虽然受分子扩散作用的影响，但并没有改变其峰值位置．沪沽湖深水湖区^（１３７）Ｃｓ计年的沉积物堆积速率为０．０４５ ± ０ ００４ｇ·ｃｍ^（－２）ａ^（－１）（１９６４年时标）．按不同时标，洱海^（１３７）_（Ｃｓ）计年的沉积物堆积速率为对．０４８±０．００３９·ｃｍ^（－２）ａ^（－１）（１９６４年时标），０．０４７ ± ０．００２９·ｃｍ^（－２）ａ^（－１）（１９７５年时标），０．０４６±０ ００５ｇ·ｃｍ^（－２）ａ^（－１）（１９８６年时标）．三种时标给出的沉积物堆积速率一致，其平均值为０．０４７±０．００２９·ｃｍ^（－２）ａ^（－１），与^（２１０）Ｐｂ_（ｅｘ）计年方法获得的数值吻合．

Two plateau lakes (Lugu Lake and Erhai Lake) with different conditions are selected to show ^(210)Pb geochemical behavior.^(210) Pb and ^(137),_ (Cs) vertical profiles in sediments are measured by the Multichannel Analysis System (Caberra 100) in order to attain creditable sediment accumulation rates. By the Fe-Mn circulation, ^(210)pb_(ex) vertical distribution in the sediments of Lugu Lake and Erhai Lake shows three types of distribution characteristics. But this has no influence on the ^(210)Ph_(ex) dating result. Sediment accumulation rates of Lugu Lake and Erhai Lake are 0. 050- 0. 051 g cm^(-2) a^(- 1) and 0. 044 - 0. 045 g' cm^(-2) a^(- 1) respectively by ^(210) pb_(ex). method which repsents the average sediment accumulation result on 100-year scale. The discrepancy between the ^(137) _(Cs) vertical distribution characteristics and the depositional fluxes is probably caused by the Cs diffusion in early-diagenesis process. However, the Cs diffusion does not change the location of Cs peaks. Sediment accumulation rate of Lugu Lake is 0. 045 ± 0. 0049' cm^(-2) a^(-1) by~ (137)_ (Cs) time marker (1964), and that of Erhai Lake is 0. 048 ± 0. 0039' cm^(-2)a^(-1) (1964), 0. 047 ± 0. 0029. cm^(-2)a^(-1) (1975 ), and 0. 046 ± 0. 0059' cm^(-2) a^(-1) (1986 ) respectively which reflects the average sediment accumulation result.