Comprehensive Study On Coal Bearing Strata Of Taiyuan Formation In Shanxi Block And Boundary Division Of Carboniferous-permian

Since 1870s,the coal bearing rocks study in the Shanxi province has been getting deeper and deeper.There are at least 10 different approaches to the boundary of the Shanxi province,and no universal consensus has been obtained so far.As standard layer in North China,it is necessary to clarify and determine the boundary of the Xishan section in the Taiyuan district.In the late Paleozoic,the North China is in a unified of epicontinental sea environment.The difference in direction and time of seawater intrusion,made the sedimentary-tectonic environment in Shanxi province is more complicated than that of other areas,which make the comparison of coal seams in the province difficult.The later reconstruction will also bring confusion to the formation regularly and causes of the coal-bearing rocks in Shanxi province.The northern part of the North China plate was sutured with the Siberian plate in the Permian period,and the southern margin and the Yangtze Plate were sutured in the Triassic period.In the Shanxi block,the time difference of south and north of North China plate collations with neighboring plate,the topography in Late Paleozoic coal-bearing rock changed from low in the north to low in the south,the thickness of the limestones and the number of layers,the correlation between the thickness of the coal bed and the number of layers,did the above factors were relevant?Should transgressive surface in the late Paleozoic to transform from north to south be a good sign of stratigraphic?coal?comparison and stratigraphic division?Based on the stratigraphic paleontology,coal petrology,coal geochemistry,structural geology,mathematical statistics,and other theories and techniques,this paper conducts an analysis and research on the Late Paleozoic coal bearing series in Shanxi block.For research on the control and influence of coal metamorphism,tectonic environment,the paleomagnetic polarity conversion,the geochemical analysis of coal samples,and the relationship with the sedimentary environment of the main coal seam in the Taiyuan formation.On the basis of this,the author tries to determine the boundary between the Carboniferous and Permian strata by comparing the main coal seams formed in the same?or similar?period in the lower part of Taiyuan formation.Through the discussion of the influence and control relationship of the tectonic activity on the marine transgression-regression,puts forward the unique role and feasibility of constructing geological methods for stratigraphic boundary demarcation.In addition to determining the boundary of Carboniferous and Permian,it also attempts to discuss the zoning characteristics of coal-bearing rocks in the late Paleozoic in Shanxi Province,so as to provide basic information for the exploration of gas and coal-bed methane in the study of geological structure and energy and mineral resources in Shanxi block.The main conclusions are indicated as follows:1.Through the study of late Paleozoic coal-bearing rock series in Shanxi block,established the main coal seam of the lower part of Taiyuan formation which can be compared in the entire province scope.The distribution and occurrence of limestone and coal seams in Taiyuan formation in late Paleozoic have obvious regularity.In the south of Datong-Pingshuo coalfield,the coal seam and limestone in Taiyuan formation have a great symbiotic relationship,as the interlayer of coal and limestone.While in Datong coalfield,the limestone almost absent.In addition,there are well relative in seawater intrusion and the development of coal seam and limestone.In the direction of the seawater intrusion,the number of layers and the thickness of the limestone are gradually decreased and even disappeared.Based on this regular,combined with the analysis and study of previous data,the coal seam can be considered at the same level.The main coal seams that can be mined in the lower part of Taiyuan formation in Datong and its north are 5#coal seam;in Ningwu and Baode is 9#coal seam;in Xishan of Taiyuan is 8#coal seam;and in Dongshan of Taiyuan and Qainshui basin is 15#coal seam.The determination of this comparable seam horizon serves as a basis for the study of the Carboniferous-Permian boundary.This study proposed that the layers of the Carboniferous-Permian boundary in different regions are different.The main bases are as follows.According to the occurrence condition of paleontology,the boundary should be set at the bottom of 8#coal seam.However,due to the lack of comparative paleontological basis for the stratum under 8#coal seam,it is difficult to draw a definite boundary layer.The microscopic observation and fluorescence spectrum analysis of geochemical elements were carried out in this research.Combined the obtained data and previous research results,it can be found that,deposition environments during peat stage of the main coal seams in different coal basins are different.Taking Pingshuo coalfield as an example,during the peat swamp stage,11#coal seam has already gone through the seawater retreat.The conversion of seawater advancing and retreating from north to south and from south to north should occur between the Wujiayu limestone and the Miaogou Limestone,that is,within the Jinci sandstone.2.In the late carboniferous-early Permian,the seawater was invaded from the western margin of Ordos,Benxi and Huainan to the north,northwest and west,which led to the two transgressive waves from the north to the south and then from the south to the north in the east of Lvliang mountain,and at least one time in the west of Lvliang mountain.The transgressive surface can be referred to index surface in large regional comparison and prediction the distribution of limestone and coal seams,also provided evidence for the correlation between structure and seawater transgressive,the control of tectonic activity and the thickness and layers of the coal seam and limestone.In the sedimentary of Benxi formation,the seawater intrusion from north to south,sedimentary 20m thickness limestone in Datong area,while only two layers of limestone with little thickness,even absent in the middle and south of Shanxi province.In Taiyuan formation,the seawater intrusion from southeast to north,development six layers limestone in Jinchegn area,while 1² layers mudstone in the Pingshuo-Datong coalfield.The thickness of coal seam also experienced the same trend.The thickness of the coal seam in Benxi formation was thick in the north and thinner in the south,on the contrary in Taiyaun formation.This provides a good basis for predicting the distribution of the coal seam and limestone.3.Tectonic movement of the plate control and influence the course and direction of seawater transgressive and regressive,and also control and influence the distribution regularity of limestone and coal seam.Before the Yangtze plate,Siberian plate was a collision and spited with North China plate.In the south and north of Shanxi block,the direction change of seawater intrusion is similar to that of plate collision time and its spatial distribution.The transgressive surface can be used as the boundary line in the upper Carboniferous?Benxi formation?and the lower Permian?the upper strata in Taiyuan formation?.In addition,it also can be used to predict the thickness and its distribution of limestone and coal seam.The difference of coal quality and metamorphism degree of coal seam in Shanxi province can distinguish it into two parts.With the Lvlaing mountain as the boundary,its west is the Baode-Liulin district,which belongs to the eastern margin of the Ordos basin,and its east is Datong-Qinshui district.The metamorphic strip of the coal in the Baode-Liulin district is in NNW direction,and the metamorphic strip of the coal in the Datong-Qinshui district is in NNE direction.Metamorphism degree of coal is characterized by low in north and high in south,the maximum metamorphic coal is located in the middle-south part of Qinshui basin.Based on the test data and collected information to analysis the sample in Sanggan river of the northern and the central area of Fenhe river,found that the buried depth and vitrinite reflectance?Ro,max?has a good correlation,besides the part of Shuozhou-Jingle area.However,the Baode-Xiangning area in the west of Lvliang mountain,which belongs to the eastern margin of the Ordos basin,the buried depth and vitrinite reflectance?Ro,max?in some locations in a negatively correlated.By the flat and vertical distribution of the coal ash,the coal ash in Taiyuan formation is characterized by the low in west and south but high in east and north,and its belt distribute obviously from the north to the south,such as the rich belt in the north,the medium belt in the middle and the low belt in the south east.It was found that is a variation of a different horizon in the same coal seam was not regularity,and the top and bottom of the layer and the ash variation in the seam were varied.4.According to the geochemical study of coal,combining the results of sequence stratigraphy and coal chemistry,it is concluded that the 11#coal seam of the Carboniferous-Permian in Shanxi province was in transgression environment,so the boundary of the Carboniferous-Permian should be at the bottom of the 8#,9#,15#coal seam,or lines in the upper of Jinci sandstone to the 11#coal seam.The content variation of components in coal seam reflects the sedimentary environment of the coal seam in the peat stage.Sample data of main coal seam in Taiyuan formation showed that the content sum of vitrinite and inertinite was greater than 90%,and the mineral content of coal was between 7%and 13%,with an average of about 11%.From the relative changes of content,the accumulation of peat swamp environment in Datong,Ningwu,Hedong,Qinshui,and Xishan coalfield was transformed from relative humidity to relatively arid.The combination and ratio of coal oxidation,such as CaO/Fe₂O₃,CaO/MgO,Ca/?Ca+Fe?,SiO₂+Al₂O₃,Fe₂O₃+CaO+MgO and Fe₂O₃+CaO+MgO/SiO₂+Al₂O₃,can reflect the type and concentration of fresh-salt in the formation of peat bogs.The SiO₂/Al₂O₃,CaO/?Fe+CaO?and CaO/MgO in coal ash can refer to the amount of land source material and the type of peat accumulation.Combined with the feature of paleontology,can reflect its different sedimentary environment in 11#coal seam of Ningw-Pingshuo area,in 8-9#coal seam of Xishan district,in 15#coal seam in Lingchuan area of Qinshui basin.8-9#coal seam sedimentary in continental environment of peat bogs,while 11#coal seam and 15#coal seam sedimentary in fluctuating transgression environment of peat bogs.On the one hand,it reflects the difference of the sedimentary environment in different regions,and on the other hand,it also shows that when the Taiyuan formation deposited,the initial sea transgression should be under the 11#coal seam.5.Based on the distribution characteristics of paleontology,the lithology and seawater intrusion direction,the boundary division of Carboniferous and Permian lines in the under of 8#,9#,15#,or its lower layer,as a boundary surface in times of different areas.Abundance and differentiation degree of fauna from south to north,from bottom to top is in increasing tendency,shows the number and thickness of coal seam increase from bottom to top in sequence,also verified variation in seawater intrusion range.Limited by the difference in the sedimentary environment of sea water,the abundance of conodont is large in the early and height stage of transgression while reduced in regressive,large in the middle-lower limestone of Taiyuan formation while reduced in upper limestone.According to the changes of lithology in the sedimentary sequence of Taiyuan formation,the lithology of the upper part is gradually thinner from north to south,and in the deposit environment of sandy conglomerate-coal seam and sandy mudstone interlayer-limestone-coarse sandstone,the thinnest of coal seam is in Qinshui area,the increases to the north.In the lower part of Taiyuan formation,the types of lithology,thickness and layers of limestone is gradually increased from north to south,with the coarse sandstone tended to be less,worse in coal-bearing property.The thick coal seam was development in Datong-Ningwu area,and thinner to the south.In view of that above,it is possible to place the boundary division of the Carboniferous-Permian into the bottom or the following level of the thick coal seam.According to relative sea level change and transgressive coal formation,the change on the thickness and layers of coal seam and limestone,known that the horizon with coal deposits gradually increased with the gradual withdrawal of sea water out of the research area,and the correlation between the marine layer and coal horizon was positively correlated.The abundant coal belt and coalescence center along the coastline move to southward.Based on this,sea conversion interface in Taiyuan formation,from north to south,from south to north,under 8#coal seam of Xishan section in Taiyuan area,the under 15#coal seam in Qinshui basin,the under 9#coal seam in the north of Ningwu area,is place from the bottom of 11#coal seam to the upper layer of Jinci sandstone.Therefore,in Shanxi province,the boundary between Upper Carboniferous and Lower Permian in the northern part of Xishan coalfield,such as Ningwu,Pingshuo,Baode,et al.is 9#coal seam;in Xishan of Taiyuan is 8#coal seam and in Dongshan of Taiyuan or Qinshui basin is 15#coal seam.This means that the boundaries of Carboniferous-Permian are respectively at the bottom of the 8#,9#and 15#coal or the lower layer.The boundaries determination of the Carboniferous-Permian,the synchronicity of the coal seam thickness and limestones layers,the decrease or the disappearance of the coal seam thickness and its number of limestone layers to the direction of the seawater intrusion direction reduction,the regional features of the lvliang mountain revealed in the coal bearing series of Shanxi block,which important on theory and practical significance for the in-depth study of the distribution law and the cause of coal,gas and oil distribution and the exploration of energy resources in Shanxi province.