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利用高灵敏度放射化学中子活化分析方法,对我国陕西段家坡黄土剖面早-中更新统(约0.73 Ma)沉积界线附近铱和其它元素的丰度进行了测定。结果表明,在布容/松山(B/M)古地磁界线附近铱的含量明显增大,最大值为的46.3 pg/g。相对于整个剖面的平均背景值(约15pg/g)大约富集了3倍。用地壳元素钪进行标准化之后,铱异常十分明显,而其它元素在界线附近则没有变化。黄土剖面上铱异常的赋存层位与西南太平洋钻孔(ODP 769A)和东印度洋深海钻孔(ODP 758B)铱异常的赋存层位一致,形成年龄在0.73～0.76Ma左右,并且都与微玻璃陨石层伴生。因此,认为该黄土剖面B/M界线的铱异常的形成与澳-亚微玻璃陨石事件有关。根据黄土剖面B/M界线铱的剩余通量估计撞击体的质量大约为1.3×10~(16)g,相当于直径为951m的球体。
The abundances of iridium and other elements near the sedimentary boundary of the Early-Middle Pleistocene (about 0.73 Ma) in the Loess Section of Duanjiapo in Shaanxi Province, China, were determined by high-sensitivity radiochemical neutron activation analysis. The results show that the content of iridium in the vicinity of B / M paleomagnetic boundary obviously increases, with a maximum value of 46.3 pg / g. The average background (about 15 pg / g) relative to the entire profile is roughly three times enriched. After normalization with the scandium crust element, the anomalies of iridium were very clear, while the other elements did not change near the boundary. The occurrence of anomalous layers of iridium in the loess section is consistent with the occurrence of the iridium anomalies in the Southwest Pacific boreholes (ODP 769A) and the deep-sea boreholes in the East Indian Ocean (ODP 758B), forming an age of about 0.73 to 0.76Ma, Micro-glass meteorite associated. Therefore, it is considered that the formation of the Iridium anomaly on the B / M boundary of the loess section is related to the O-submicrome glass meteorite event. According to the residual flux of iridium in the B / M boundary of loess section, the mass of the impact body is estimated to be about 1.3 × 10 ~ (16) g, corresponding to a sphere with a diameter of 951m.