纹层计年与^(137)Cs、^(210)Pb法对比研究东北二龙湾玛珥湖现代沉积速率

A Comparative Study on Model Sedimentation Rates with Varve Dating,^(137)Cs and ^(210)Pb Dating in Erlongwan Maar Lake,NE China

通过对东北二龙湾玛珥湖顶部无扰动岩心显微研究,证明此岩心发育有良好的年纹层。据精确统计,0~5.5cm间为36个年纹层,纹层计年的误差为4%~7%,年纹层厚度为1.1~2mm不等,平均沉积速率为1.53mm/a,5.5cm处对应于1965年。而二龙湾沉积物(从6.5cm到5.5cm)岩心的137Cs比活度值急剧增加,从(4.67±0.29)dpm/g增加到(12.06±0.47)dpm/g,在5.5cm处有一个较为明显的蓄积峰值,这一峰值被确认对应为1963年全球137Cs散落的高峰期。另外据210Pbex比活度CIC模式,5.5cm处约为1962年,这和137Cs比活度曲线的1963年时标相一致。印证了纹层计年的精确性,完全可以建立高分辨率时间序列。

Detailed investigations were carried out on the upper undisturbed sediments from Erlongwan maar lake, NE China, which are better annually laminated sediments （varve）. Varve couple appears as dark-and light-coloured layers. Based on varve dating of large thin sections under microscope, 36 varve couples, with 4%-7% discrepancy , 1.1-2 mm varve thickness and 1.53 mm/a rate of sedimentation were found in the upper part of the core （0-5.5 cm）, and 5.5 cm correlates to the year of 1965. However, Radiometric dating shows that the highest ^137Cs activity appears at 5.5 cm depth , assumed to correlate to the 1963 maximum of emission due to the nuclear bomb testing. ^137Cs activities increase quickly from 6.5 cm to 5.5 cm （ from 4.67±0.29 dpm/g to 12.06±0.47 dpm/g ）. In addition , By calculating of ^210Pbex（CIC） , 5.5 cm depth corresponds with the 1962. As a result, ^210Pbox（CIC） and ^137 Cs dating show a good agreement with the varve dating. Varve dating is exact and varve sediments can offer an effective means of acquiring high-quality palaeoenvironmental records.