贵州紫云剖面P/T界面附近碳氧同位素的变化及生物绝灭事件  

THE VARIATION OF ISOTOPES(C,O) AND THE ORGANISM EXTINCTION EVENT ACROSS THE P/T BOUNDARY IN ZIYUN SECTION, GUIZHOU PROVINCE

作　　者：王国庆[1] 夏文臣[1] 

机构地区：[1]中国地质大学地球科学学院,武汉430074

出　　处：《地学前缘》2000年第2期339-344,共6页Earth Science Frontiers

基　　金：国家自然科学基金资助项目!(496 72 12 1)

摘　　要：:贵州南部紫云剖面由上二叠统长兴组的碳酸盐台地边缘沉积体系、下三叠统罗楼组的碳酸盐浅海陆棚沉积体系、以及下三叠统紫云组的半深海深海沉积体系组成。在前两种沉积体系中选取 18块样品进行碳、氧同位素测试。测试的结果表明 :上二叠统长兴组δ13 C平均值为 2 4 8‰ ,保持了较高的正值 ,δ18O平均值为 - 4 19‰ ;在P/T界面附近 ,δ13 C ,δ18O值都有显著的降低 ,δ13 C值由 2 71‰陡降至 - 0 90‰ ,变化幅度达 3 6 1‰ ,δ18O值由 - 5 0 3‰降为- 9 4 6‰ ,变化幅度可达 4 4 3‰ ;下三叠统罗楼组下部 ,δ13 C值为负值及低正值 ,出现明显的δ13 C值低异常 ,而δ18O值则比较稳定 ,介于 - 4 6 6‰和 - 5 6 2‰之间 ,平均值为 - 5 2 8‰。罗楼组上部 ,δ13 C值有回升的趋势。由于生物对轻碳具有重要的分馏作用 ,因此 ,P/T界面附近δ13 C值的显著变化反映了一次生物大量绝灭的过程。由δ18O值的变化反映出的生物绝灭的外因主要有温度和盐度两方面。从δ18O值可计算出在P/T界面处古温度有 4～ 5℃的升降 ,这势必影响到狭温生物的生存 ;从δ18O值计算出的Z值来看 ,古盐度也有小幅度的变化 ,加速了狭盐度生物的绝灭。事实上 ,生物的绝灭可能是海平面变化、火山事件。The Ziyun section, located in the south of Guizhou province, is composed of the carbonate reef depositional system, the carbonate muddy shelf depositional system, and the bathyal depositional system.The above three kinds of depositional systems belong to the Changxing Formation of Upper Permian, the Luolou Formation of Lower Triassic, and the Ziyun Formation of Lower Triassic, respectively. Eighteen samples from the former two systems were selected for carbon and oxygen isotope analysing. The analysing results show that in the Changxing Formation of Upper Permian, the average value of δ 13 C is 2 48‰, and that of δ 18 O is -4 19‰. There are distinct decrease of δ 13 C and δ 18 O crossing the P/T boundary as follows: δ 13 C changes from 2 71‰ in Changxing Formation to -0 90‰ in Ziyun Formation; δ 18 O from -5 03‰ in Changxing Formation to -9 46‰ in Ziyun Formation. In the lower part of Luolou Formation of Lower Triassic, δ 13 C ranges from negative values to small positive values, and δ 18 O from -4 66‰ to -5 62‰. The variation of δ 13 C value reflects a dramatic organism extinction because the organism absorb the carbon 12 firstly. The main factors that resulted in the organism extinction may be the changes of paleotemperature and paleosalinity. The variation of paleotemperature was between 4 and 5 degrees centigrade, which resulted in the extinction of narrow temperature organism. The paleosalinity had a small variation crossing the P/T boundary, which accelerated the extinction process of narrow salinity organism. In general, the integration of the eustasy, the volcanism and the changes of paleotemperature and paleosalinity resulted in the organism extinction during the transition from Permian to Triassic.

关 键 词：P/T界面 碳氧同位素 生物绝灭事件 紫云剖面 

分 类 号：P597[天文地球—地球化学] Q911.5[天文地球—地质学]