白垩-第三纪界线样品异常铱的赋存状态及其地质意义

 通过对地质样品中铱的赋存状态研究及对残渣相中微粒的透射电镜分析,得出:在K-T界线样品中铱主要存在于残渣相中,不利于地球化学过程富集铱;铱在残渣相的富集与有机不溶物的存在没有必然联系;白垩-第三纪的生物绝灭事件中有火山活动参与;K-T界线事件的触发物为地外物质撞击。最后提出了K-T界线样品异常铱来源于地外物质撞击和火山喷发的混合模型。

CHEMICAL SPECIES OF ANOMALOUS IRIDIUM AND IMPLICATION OF INSOLUBLE SPHERULES IN THE CRETACEOUS-TERTIARY BOUNDARY CLAY

The geological samples: Cretaceous-Tertiary (K-T) boundary clay, meteorite, volcanic lava and ultrabasic rock were separated into carbonate, metal, sulfide, oxide, silicate and acid-resistant residue by using a selective chemical dissolution procedure developed in our laboratory. Some conclusions are drawn after analyzing the chemical specialization of anomalous iri-dium in the above samples and especially after studying the characteristics of insoluble spherules in the residue phase. (1) The fact that most of iridium present in residue phase in samples from K-T boundary is probably associated with high-temperature process, disfavours the hypothesis of geochemical enrichment of anomalous iridium; (2) The iridium enrichment did not be necessarily associated with kerogen. The high content of Ir in kerogen probably occurred after deposition as a result of Ir redistribution within the sediments; (3) Some particles discovered in the residue phase of K-T boundary samples are believed associated with volcanic eruption and that implies the participatation of volcanism in the extinction event at the end of Cretaceous; (4) Extraterrestrial impact was the trigger of K-T event. Then, we propose a mixed model by which the extant anomalous Ir in K-T boundary clay is interpreted as a combined effect of extraterrestrial impact, volcano eruption and post- depositional redistribution.