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~(137)Cs和~(210)Pb_(ex)是湖泊沉积物断代常用的两种核素,沉积物中核素的深度分布,不但随核素的大气沉降量变化,也与流域环境变化和沉积后核素的再分布有关。我国环境复杂,人类活动强烈,~(137)Cs和~(21)Pb_(ex)深度分布的非理想曲线常见于我国一些湖泊的沉积物。本文简要介绍了湖泊沉积物~(137)Cs和~(21)Pb_(ex)深度分布理想曲线和断代基本原理,在参阅大量有关中国湖泊沉积物~(137)Cs和~(21)Pb_(ex)断代文献的基础上,讨论了~(137)Cs和~(21)Pb_(ex)非理想深度分布曲线的解译和沉积物断代的几个常见问题。主要观点如下:1)我国湖泊沉积物不存在所谓的1974年和1986年蓄积峰;2)一些湖泊沉积出现的非单峰型~(137)Cs深度分布曲线,可能与人类活动或湖流扰动湖泊底泥、流域侵蚀产沙环境变化和~(137)Cs主要来源于冰川融水补给等因素有关;3)沉积物中的核素垂向运移,不改变剖面中1963年~(137)Cs蓄积峰的位置,不影响其断代标志意义;4)流域环境突发事件引起的沉积剖面中的~(137)Cs和~(21)Pb_(ex)明显异常,是断代的可靠标志等。最后介绍了根据沉积剖面~(137)Cs和~(21)Pb_(ex)总量与本底值对比,求算沉积速率的核素质量平衡法。
~ (137) Cs and ~ (210) Pb_ (ex) are the two kinds of nuclides commonly used in the sediments of lacustrine sediments. The depth distribution of nuclides in sediments not only varies with the amount of atmospheric sedimentation of nuclides but also with environmental changes And the redistribution of nuclides after deposition. China’s environment is complex and human activities are intense. The non-ideal curves of 137 Cs and ~ 21 Pb-ex depth are common in the sediments of some lakes in China. In this paper, the ideal distribution curves of ~ (137) Cs and ~ (21) Pb_ (ex) sediments in lakes and their basic principles of faulting are briefly introduced. ex), several common problems about the interpretation of non-ideal depth profiles of ~ (137) Cs and ~ (21) Pb_ (ex) and the dating of sediments are discussed. The main points are as follows: 1) There is no so-called accumulation peak in 1974 and 1986 in China’s lake sediments; 2) The non-unimodal 137 Cs depth distribution curve in some lake sediments may be related to human activities or lake disturbance The changes of sediment and lake sediment in the lake sediments are mainly related to the supply of glacier melt water; 3) The vertical migration of nuclides in the sediments does not change from 1963 to 137 in the section, The location of Cs accumulation peak does not affect the signification of the origin of the dikes. (4) The 137 Cs and 21 Pb_ (ex) anomalies in the sedimentary profile caused by the environmental emergencies in the basin are obviously reliable indicators of the dikes. Finally, the nuclide mass balance method for calculating the deposition rate is introduced according to the comparison of 137 Cs and ~ 21 Pb ex sediments with the background value.