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通过对中国黄土高原南缘的段家坡黄土—红粘土剖面 Ga/M 边界(2.48MaBP)上下地层中5种微颗粒和土样微量元素的研究,进一步确定了下更新统午城组黄土底部记录着两次撞击事件的信息。较早的一次记录于 L38中,年代为2.53—2.48MaBP,以多种撞击成因或与之有关的微颗粒为标志,且有丰度为58.3×10~(-12)g/g 的 Ir 异常和14.3×10~(-9)g/g 的 Au 异常给与确证。这是一次真正的 N/Q 界面撞击事件,在气候地层上与从上新统红粘土向更新统黄土的过渡相一致,在磁性地层上与从高斯正极性向松山反极性的转变相联系。较晚的一次记录于 S37中,年代为2.43—2.42MaBP,在多种微颗粒标志中,还包括含有 Ir 异常分别为3.89×10~(-6)g/g 的宇宙尘和2.15×10~(-8)g/g 的生物球粒。文中用综合成因模式解释了不同特性的撞击记录共存的现象,并指出中国黄土在天文地质研究方面尚蕴藏着大量信息。
Based on the study of five kinds of microparticles and soil trace elements in the upper and lower strata of the Ga / M boundary (2.48MaBP) section of the loess-red clay section of the southern segment of the Loess Plateau in the southern margin of the Loess Plateau, Record the impact of two events. The earliest was recorded in L38 with an age of 2.53-2.48MaBP and was characterized by a variety of collisional causes or associated microparticles with an Ir anomaly of abundance of 58.3 × 10 ~ (-12) g / g And 14.3 × 10 ~ (-9) g / g of Au anomaly to confirm. This is a true N / Q interfacial impact consistent with the transition from the Paleocene red clay to the Pleistocene loess on the climate stratigraphy and to the magnetic strata linked to the reversal of polarity from the positive Gaussian to the Songshan. A later record was recorded in S37 with an age of 2.43-2.42MaBP, including cosmic dust with Ir anomalies of 3.89 x 10 ~ (-6) g / g and 2.15 x 10 ~ (-8) g / g of biological pellets. In this paper, the phenomenon of coexistence of impact records with different characteristics is explained by means of comprehensive genesis model. It is pointed out that Chinese loess contains a large amount of information in astronomical geology.