Abstract: Study on the Nandong Section of South China reveals that the Devonian Frasnian-Famennian (F-F) bio-event was a stepwise mass-extinction. The devastating diversity loss occurred in the latest linguiformis Zone, which was 0.1 Ma in duration. Across the F-F boundary there are three nickel-iridium moderate anomaly beds, which are also enriched in chalcophile elements, and also accompanied with the carbon isotope negative anomalies and microtektites. The last Ni-Ir anomaly was followed immediately by tsunamis. In fact, the F-F event is an integrative event-biotic, geochemical, sedimentologic. Such integrative events occurred five times in the Middle and Upper Devonian with a frequency of 4.6×10^-6a^-1. This frequency approximates to the frequency of the impact of 1 km sized asteroids on Earth, estimated by Shoemaker(1990). The possible cause of the F-F mass-extinction is herein discussed. Asteroids(probably 1 km sized) struck the Earth with a frequency of 4.6×10^-6a^-1. These impacts intensified the global(or vast regional) hydrothermal activities on fracture zones, with anomalous Ni-Ir and chalcophile deposits ensuing. The main Ni-Ir excess might have a hydrothermal origin. Hydrothermal metal toxicity might be one of the kill mechanisms in mass-extinction. Sea level change and regressive anoxia excursion were ongoing phenomena which might create appropriate stagnant condition for the preservation of element excess, but might not be the main causative factor of mass-extinction.

Key words: Frasnian-Famennian event, chemo-biostratigraphy, Devonian

摘要： 对广西南洞剖面的研究表明，弗拉阶-法门阶(F-F)生物事件(也称为Kellwasser生物事件)是阶梯式灭绝事件，生物种类锐减发生于linguiformis带最晚期，持续时间约为0.1Ma。在F-F界线有3个Ni-Ir异常层, 该异常层同时也富含亲铜元素，并伴有碳同位素负异常以及微玻陨石。紧随着覆盖有海啸岩。F-F事件实际上是生物-地球化学-沉积综合事件。像这样的综合事件,在中、晚泥盆世共发生了5次。发生的频率为4.6×10^-6a^-1。讨论了F-F大灭绝事件的可能原因。

关键词: 弗拉阶-法门阶事件, 化学-生物地层学, 泥盆纪