The Coupling Relationship Between Volcanic Activities And Biological Catastrophic Events Of Yixian Formation In Sihetun Area, Western Liaoning, China

Sihetun is a typical area reprsenting the coupling relationship between volcanic activity and biological catastrophic events. Based on the strata classification and the characteristic study of volcanic activities, the fossils of Jehol Biota, the fossil beds of Yixian Formation and the related volcanic rocks are well studied in this paper with theoretic support of volcanology, geochemistry, petrology and palaeontology. The main object is to investigate the coupling relationship between volcanic activity and biological catastrophic events, including its occurring time, place and material characters. For the first time, the spot of volcanic material source of fossil-bearing beds is defined in this paper. On the basis of previous researches,the author put forward a new academic viewpoint of making good use of the character of biological catastrophic events, the geochemistry data of fossils and fossil-bearing beds to realize the mutation of paleo-environment.. The study will be helpful for the resolution of important problems about Jehol Biota, such as the geological background of the source, migration and disaster event. And what's more, this paper may be a contribution to recognize the environmental effects of volcanic activities, the main inner planet events. The study in this paper covers five aspects. 1. Based on the stratum comparison and characteristic study, the Yixain Formation can be classified into three members that were formed by volcanic activities of three periods respectively. 2. The fossils of Jehol Biota occurred in tuffite or sedimentary beds of the first and second member of Yixian formation. The fossil buried phase of Jeho Biota can be divided into three types, that is, coarse fragment phase, middle fragment phase and fine fragment phase. And there are three types of important biological catastrophic events respectively, that is, psittacosaurus disaster event, the aquatic animal (e.g. bivalves) disaster event and vertebrate (bird and reptile etc.) disaster event. 3. According to the analysis of volcanic record in fossil beds and the isotopic data, the paper makes a systemic comparison between the fossil beds and the related volcanic rocks. The coupling relationship between volcanic activity and biological catastrophic events, including its occurring time, place and material characters, are well investigated. And for the first time, the spot of volcanic material source of fossil-bearing beds is defined: Houyanzigou edifice and Libalanggou edifice is the volcanic material source of the psittacosaurus beds of the first member and lake-phase fossil beds of the second member of Yixian Formation respectively. 4. The analysis of geo-chemical abnormal indicates that there were mutations of paleo-environment at the aspect of oxidation-reduction system, as well as the saltness and water level of the paleo-lake. A comprehensive research confirms that the volcanic activity resulted in the high level of toxic element abnormal, such as As, Hg and S. The disaster beds of Jehol Biota correspond to the beds with paleo-environmental mutation. 5. The special element comparison of biochemical abnormal indicates that the fossils of Yixian Formation couple with its fossil-bearing beds at the respect of the high level toxic element abnormal. On the other hand, the average content of Ba, Sr and ΣREE in fossils are higher than that in the fossil-bearing beds. The types and the range of volcanic hazard that resulted in the biological catastrophic event are discussed at the end of this paper. As another discussion, the author sets up a sketch model of the evolution of volcanic activity and biological event. The full text is about 120 thousand words.