四合屯及其周边地区义县组火山活动对生物灾难事件的影响

EFFECTS OF VOLCANIC ACTIVITY ON THE BIOLOGICAL CATASTROPHIC EVENT OF YIXIAN FORMATION IN SIHETUN AND ADJACENT AREA

野外填图证实 ,四合屯及其周边地区热河生物群化石主要产于义县组下部的沉凝灰岩和中部的内陆湖泊相沉积岩之中。综合研究还发现 ,上述化石层之中发育有火山弹、湖泊相枕状熔岩以及数层火山碎屑和火山灰物质 ;在产有珍稀鸟类、爬行类以及早期被子植物化石的岩石中 ,As,Hg ,S的含量明显高于相关的对比层。种种迹象表明 ,四合屯及其周边地区的义县组火山活动所产生的熔岩流和有毒。

Based on the field mapping, we recognized that 'Jehol Biota' fossils occurred mainly in tuffite of the lower part and inner lake sedimentary beds of the middle part of Yixian F. in Sihetun and the adjacent area. Comprehensive study also shows that there are volcanic bomb, pillow lava, tephra and volcanic ash developed in the fossil beds. The rocks of fossil rich sedimentary beds (containing precious birds, reptiles and early angiosperms) abounded with more toxic elements such as As, Hg and S than the other beds. All evidences indicate that the lava flow, tephra, ash and toxic gases of the volcanic activities are the main factors that caused the biological hazard and the fossil preservation of 'Jehol Biota' in Sihetun and the adjacent area.