The Volcanic Event Study In Permian-Triassic Boundary Of Longmen Mountain

There have been five major mass extinctions on earth since Phanerozoic including the biological mass extinction event in Permian-Triassic boundary which is one of the biggest since Phanerozoic geological history.In recent decades,the event is a hot topic of research at home and abroad.Although geologists carried out a detailed and in-depth study of global Permian-Triassic strata from different angles and direction,and put forward a series of hypotheses about the incident,but the reliability for these hypotheses still exists huge controversy.In recent years,with the deepening of research,a lot of evidence of large-scale,high frequency of volcanic events is closely connected with the biological mass extinction event.In this paper,the Paleozoic-Mesozoic boundary strata in the northern section of the Longmen mountains are chosen as the research object,volcanic events in boundary strata are chosen as the theme and the research of volcanic events is carried out.Based on the research about the material composition,genetic significance and element geochemical characteristics of the sedimentary tuff which developed in PTB strata,the intensity and frequency of the volcanic eruptions in Permian-Triassic and its relationship with biological mass extinction event is restored.This paper provide reliable basis for enriching the research contents of the mass extinction caused by the abrupt change of the ancient ecological environment at the turn of the Paleozoic and the Mesozoic and helps to deepen the scientific understanding of the event.The main conclusions are as follows:1.The strata of Permian-Triassic in the northern Longmen mountain is developed in the lower slope and basin facies of the front of carbonate platform under a deep water.It is a continuous slow regression process from Wuajiping formation to Dalong formation and turns to a continuous process of large-scale regional transgression in Feixianguan formation.2.The PTB in Yangjiayan profile is calibrated from petrology and paleontology.According to the traditional stratigraphic division scheme,the PTB is determined at the bottom of the 62 layer(PTB(R));According to the biostratigraphic subdivision scheme,the PTB is determined at the bottom of the 53 layer(PTB(B)).3.Geochemical characteristics of the elements of the tuff indicates: The geochemical anomalies of trace elements are common in the Permian-Triassic strata in the northern segment of Longmen mountain and it shows the combination characteristics of trace elements in magmatic rocks as medium-basic on the whole.4.The study of detrital material composition of the tuff indicates: The greater the zircon abundance in the tuff layer,the larger the detrital grains,and the lower the fragmentation degree of the crystals.5.The volcanic activity is very frequent in the northern segment of Longmen mountain at the Permian-Triassic which has a close relationship between the biological extinction events.The extinction event is a result of the interaction of high intensity and high frequency volcanic eruption cycles...