Sedimentological And Geochemical Responses Of Geological Events At The Ordovician-silurian Boundary

Key geological events occurred at the Ordovician-Silurian boundaries in the world.For example,the global glacier in late ordovician had significantly impacted on the Late Ordovician Hirnantia paleoenvironment,paleoclimate and paleontology.It directly led to the changes of ecosystem in the whole earth.Many geological events happened during this period caused to the effects of the equator and low latitudes was recorded by stratum of the Ordovician-Silurianin south china.The stone lacquer liaowufeng group-Longmaixi section is located in the hinterland of the Yangtze platform,which responds to the geological events at that time from the facies,paleontological combination and paleoenvironment,and this profile is located in Yichang City,Hubei Province,the standard point of the distance is very close,and it has a continuous outcrop,Fossils are rich,Exposed to the Wufeng group and the Longma River group of black shale clip in the multi-layer potassium porphyry,is a good material for studying the geological events of the Upper Ordovician-Lower Silurian line.In this paper,the combination of strata,lithofacies facies and mineral assemblages of Liaowufeng Formation-Longmaxi Formation is studied in detail.In this paper,the formation,lithological facies and mineralogy of the formation,lithological facies and mineral mineralization of the five peaks group of stone column are studied in detail.According to the difference of the rock facies,a detailed field observation description,measurement and sampling was carried out from the top of the linxiang group to the bottom of the dragon marxi group.Stone paint overall thickness of about 12 meters,liao profile from bottom to top of lithofacies LinXiang group respectively nodular limestone,text is black shale interbed and volcanic tuff,bei group containing higher carbonaceous siliceous carbonaceous silty dolomite and creek,the dragon group black shale.Through the analysis of the classification of different rock samples,the black shale,boundary dolomite microscope observation and examination of potassic porphyry rocks off the clay minerals(mainly for the montmorillonite)and other ultrasonic oscillation of heavy mineral separation experiment and scanning electron microscope.The separation of ultrasonic oscillations was carried out twice,separating the heavy minerals from pyrite,barite,solitary stone,quartz and zircon,etc.In the scanning electron microscopy,the crystal and energy spectra were observed.There are two main types of pyrite,a form of strawberry aggregate,aggregate diameter of 10-20 um,another is the single crystal cube form,particle size between 50-100 um,individual single crystal grain size is larger than 100 um.The zircon appears in a short column with a particle size of about20 um.The crystalline form of quartz minerals in quartz clusters appears in the form of a double cone,with a large diameter difference between 10-90 um.The main components of solitary stone are Ce,La,Nd,etc.The five peaks and the longmarxi formation in the liao section are rich in organic carbon.According to the results of previous studies,the content of organic carbon isotopes can be used to determine the climatic conditions of geological history.Therefore,the experiment of organic carbon isotope content of 12 samples was found in the samples of the liao section.But because after the diagenetic,stone lacquer liao's HuaYingShan regional tectonic movement is frequent,make stone paint liao profile of organic carbon test results with others in yichang GSSP standard points to the results measured by sampling is bigger,so the content of organic carbon isotopic experiment results are insufficient to determine the climate conditions during the age of the geological history.Comprehensive text is set in stone lacquer liao profile of field observations,and a series of laboratory study found: five mountains period stone paint liao profile events happened repeatedly volcanic eruption,volcanic eruption event is accompanied by five mountains and graptolite biological explosive reproduction.Stone paint liao profile of the five mountains group formation black shale interbed and volcanic tuff,there are a large number of graptolite black shale(graptolite facies black shale)liao region is one of the pillars of five mountains period paint deep-water reduction environment,volcanic tuff,prove that this text period volcanic eruptions have occurred many times.