乌兰泡沼泽的^(210)Pb、^(137)Cs测年与现代沉积速率

^(210)Pb and ^(137)Cs Dating and Modern Sedimentationrate in the Wulanpao Marsh,Inner Mongolia Autonomous Region

通过对乌兰泡沼泽沉积物柱芯样品进行210Pb、137Cs测年分析表明,柱芯剖面上有明显的1963年及1975年137Cs蓄积峰,这些蓄积峰对乌兰泡沼泽的现代沉积有明显的时标意义。根据210PbCRS模式,可以计算出每个样品深度所对应的年代,在该沉积柱芯中与137Cs时标吻合很好。通过质量深度与年代分析,乌兰泡的沉积速率并不稳定,变化比较大,表明乌兰泡近200年来沉积环境不稳定。210Pb、137Cs两种计年方法的结合有助于认识沉积速率变化较大的沼泽的沉积状况,也有助于加深对核素计年方法的理解。

Environmental ^210 pb and ^137 Cs dating techniques were applied to determine recent sedimentation rates. ^210 pb and ^137 Cs were analyzed for the Wulanpao marsh sediment core in Inner Mongolia Autonomous Region. In the core, there were obvious in peaks 1963 and 1975, which were important age characteristics for the Wulanpao marsh sediment. The sedimentation rate of the Wulanpao marsh was about 0.365 g ·cm^-2 · a^-1 by ^137 Cs time marker（1963） and 0.385 g cm^-2 · a^-1 by ^137 Cs time marker（ 1975）. ^210 pb （CRS） dating showed a good agreement with the ^137 Cs dating. The limit depth of ^210 pb was 47 cm, which corresponded to the age of 1819. The average sedimentation rate from 1819 to 2005 was about 0.271 g cm^-2 · a^-1. The abnormal variations of ^210 pb activity could be found in the profile. The relative high value of ^210 pb at the depth of 17cm might be also linked with the maximum value in 1963 due to the nuclear bomb testing producing both ^137 Cs and ^210 pb. The relative low value of ^210 pb at the depth of 5 cm might be due to human activities that induced high sediment input. The sedimentation rate was changeable in the Wulanpao marsh by analyzing the mass depth and ages, which showed that the sedimentation environment was changeable in recent 200 years either. The combination of these radionuclide dating methods was useful to understand the substantial sedimentation process of the wetland where sedimentation rates change rapidly.