【摘要】 本文记述了用放射化学和仪器中子活化分析,测定了广西黄茆泥盆系—石炭系剖面,包括铱在内的近40种元素丰度的结果。发现泥盆系—石炭系界线层存在铱的异常。其峰值为156ppt,相对于下伏地层的富集因子为12。与铱同步富集的还有金、镍、钴、砷、锑等亲铁和亲硫元素。讨论了造成铱等元素丰度异常的原因。无论是地外成因,还是火山成因都无法完满解释。真正的异常机制还有待深入研究。更多还原

【Abstract】 Elemental abundance variations across a Devonian/Carboniferous (D/C) boundary section located at Huangmao, Guangxi Zhuang Autonomous Region, China, have been investigated by INAA and RNAA. Abundances of Ir, Au, Ni, Co, Cr, As, Sb, Se, U and V in the D/C boundary shale (14 cm thick) are 156 ppt, 14.5 ppb, 494 ppm, 51.4 ppm, 113 ppm, 109 ppm, 16.4 ppm, 16.8 ppm, 55.3 ppm and 709 ppm, higher than the background values of the underlying and overlying stratigraphic samples by a factor of 20—100.The geochemical anomaly at the D/C boundary is correlated with the mass extinction, e.g. of Palmatolepic graidis expansa, Pseudopolygnathus trigonicus and other conodont species, especially of the Clymenides. It implies that an event occurred at the end of the Devonian. But neither volcanic eruption nor extraterrestrial impact can explain the geochemical anomaly.更多还原