中扬子地区震旦──寒武系界线附近事件地层学

Event Stratigraphy near SinianCambrian Boundary in Central Yangzi Area

湘西北杨家坪和鄂西峡东两条剖面的震旦寒武系界线附近均发育一层厚几厘米至几十厘米的白色粘土层，该粘土层之下普遍发育有小壳化石，在粘土层之上则未发现。地球化学分析结果显示，这一粘土层上的碳同位素及Ｉｒ，Ｏｓ，Ａｕ等稀有元素含量有明显变化。认为这是外星撞击事件引起的，它直接造成了小壳化石的绝灭。

There is a white clay layer of several centimeters and tens of centimeters in thick near SinianCambrian boundary both in Yangjiaping district of northwestern Hunan and the east Yangzi Gorge of western Hubei,central Yangzi areaA good lot of smallshell fossils are discovered below the clay layer and few of themabove it The geochemical analysis indicates that carbonisotope and rare elements such as iridium, osmium and gold vary obviously in content in the clay layerIt is believed that this phenomenon is caused by extraterrestrial impacts resulting immediately in extinction of smallshell fossilsThe SinianCambrian boundary is discussed based on the event stratigraphy