广东省南雄盆地白垩系—第三系交界恐龙绝灭问题

广东省南雄盆地中的红层可划分为三个群五个组,大致代表了晚白垩世—始新世的沉积.根据绝对年龄、古地磁测定结果和脊椎动物化石组合性质的综合分析,位于地磁极性带 29R 上部的坪岭组和上湖组之间的分界线被确定为 K/T 界线.对晚白垩世恐龙蛋的研究表明,不同"种"的恐龙蛋是在地磁极性带 29R 的中、下部,也就是说在白垩系—第三系交界之前20～30万年期间绝迹的.而且在这一时期内,所有已发现的蛋壳中,绝大多数蛋壳的厚度和显微结构都显示出明显的病理特征,例如根据随机取样统计,Macroolithus yaotunensis 蛋壳异常结构的出现率,最高可达75%.产生病态恐龙蛋壳的生理机制可以根据发生在现生鸟类的相同病理特征来解释.进一步分析恐龙蛋壳的微量元素和稳定同位素组成,结果显示, Pb, Cu, Mn 等9种元素丰度变化在这一时期达到最大峰值, δ~(18)O 也出现正异常.在这一基础上提出,微量元素的污染和气候突然的变化妨碍了正常蛋壳结构的形成,导致了恐龙的绝灭.这一绝灭过程大约经历了20～30万年.

EXTINCTION OF THE DINOSAURS ACROSS THE CRETACEOUS-TERTIARY BOUNDARY IN NANXIONG BASIN, GUANGDONG PROVINCE

Dinosaurs were giant reptiles on land during the Mesozoic era, but they all vanished from the earth in the global events of terminal Cretaceous turnover. This is a significant and perplexed question in the history of vertebrate evolution. During the past ten years the impact theory proposed by Alvarez and others (1980) and by Hs (1980) has drawn considerably scientific and public interest, thus evoked a heated dispute. The extinction of the dinosaurs appears to be a global phenomenon. However, the best record so far we can use to discuss this issue comes from the West Interior of North America (Archibald, 1982, 1987; Archibald et al., 1982; Russell, 1982; Sloan et al., 1986; Smit et al., 1987; van Valen et al., 1977), and the available information from other regions such as European Mediterranean (Erben et al., 1979; Erben, 1983), Peru (Marshall et al., 1983) or China (Zhao, 1978) are very little or incomplete. Interdisciplinary investigations on the redbed facies of Late Cretaceous to Early Tertiary passage beds in Nanxiong Basin, Guangdong Province have been continued by a Sino-German team (members mentioned in the acknowledgements) since 1983. Important results have been made on the general geology, magnetostratigraphy, isotopes, trace elements and microstructure of dinosaur eggshells. These will provide new evidence for defining the Cretaceous-Tertiary boundary at Nanxiong Basin and for exploring the global events occurring at that time, especially the dinosaur extinction problem that is currently being debated. As the final publication of the systematic study by both the Chinese and German authors may probably be delayed for some time, a brief report on the work by the present authors is given here.