东太平洋中部始新世/渐新世界线陨石撞击的地球化学证据

Geochemical Features of the Meteorite Impact Around Eocene/ Oligocene Boundary Layer in Central Eastern Pacific Region

对于 ODP提供的深海钻探 5 73B孔始新统顶部 -渐新统底部的地质样品进行了化学分析、等离子体光谱分析、等离子体质谱分析和微玻璃陨石的挑选等 ,结合附近区域的其它地质资料 ,探讨了东太平洋中部始新世末、渐新世初地层的地球化学特征。根据始新世末期东太平洋地区多种海洋微体古生物灭绝、大面积微玻璃陨石 (或微球粒陨石 )分布、地球化学特征异常等 ,说明该时期有明显的突变性地质事件发生 ,很可能是由于陨击作用造成的。

The geochemical features of the strata from the Upper Eocene to Lower Oligocene in the central eastern Pacific are studied by analysing the samples from the Site 573 provided by the ODP and other information in this area. The boundary layer between the Eocene and Oligocene is a layer of metalliferous claystone which is about 3.4m thick. The metalliferous claystone is of special geological and geochemical characteristics and contains abundant Fe and Fe-group elements such as Ni,Co and Ir, which may imply that this layer was formed by an extraterrestrial impact.Microspherules (microtektites or microkrystites) are also found in the layer, especially at the bottom of the layer. These characteristics indicate that the formation of the metalliferous claystone may have some relationship with meteorite impact. According to the characteristics and composition of the strata between the Late Eocene and the Early Oligocene, the extinction of many organisms, and the distribution of microspherules, we suggest that a catastrophic event might have occurred at the end of the Eocene in the central Eastern Pacific. The catastrophic event may have been caused by a meteorite that impacted the Pacific Plate.