| The studied area is located in an open-pit coal mine on the northeastern margin of the Qinshui Basin,and the coal bearing strata in the Taiyuan-Shanxi formation are well exposed,which is very suitable for the sedimentology study of the Taiyuan-Shanxi formation.On the basis of the outcrop observation and microscopic analysis of the Laowuling field,the petrological characteristics of the Taiyuan-Shanxi formation in the Laowuling section are analyzed,and the types of the sedimentary facies are divided and analyzed.Combined with the existing geological background data and drilling data in the Qinshui Basin and its adjacent areas,the well section maps are drawn and the coal seam coal accumulation characteristics as well as coal accumulation control factors of the Taiyuan-Shanxi formation in the Laowuling and adjacent areas are analyzed.The main results obtained are as follows:1.The Taiyuan formation in the old Wuling section is generally a marine and terrestrial transitional sedimentary environment.The lower member of the Taiyuan formation is formed in the distributary channel-distributary Bay-peat swamp-swamp facies.The main sedimentary environment in the middle part of the Taiyuan formation is carbonate platform and lagoon.The main sedimentary environments of the upper member of the Taiyuan formation are distributary channel-distributary Bay-peat swamp-swamp facies.The Shanxi formation is a positive sequence of three sections of the delta plain facies,and the specific sedimentary facies are distributary channel-distributary Bay swamp facies.2.In the middle part of the Taiyuan formation,there is a dark mud shale and thick coal seam with peat bogs and swamps.The total thickness is more than 10 meters,and the coal seam thickness is about 6 meters.The coal seam develops in the middle and top of Shanxi formation.There are three layers of coal seam in the middle part,with a total thickness of 8 meters.4 layers of coal seam develops at the top,the total thickness of which is about 7 meters.3.Under the observation of polarizing microscope,the outcrop sandstone thin sections of the Taiyuan Shanxi formation in several blocks were analyzed and the sandstone was classified and named.It is found that the outcrop sandstone types of the Taiyuan Shanxi formation in the old Wuling are all lithic sandstone,and the cuttings content is between 30-45%.Most of the fractures in the rock are filled with carbonate.4.In North China,the regional thick coal seam is deposited in the middle part of the Taiyuan formation,which is widely and continuously distributed.During the period of the Shanxi formation,the studied area was mainly the sedimentary environment of the delta plain.Because of the inhomogeneity of the continental coal formation,most of the coal seams were distributed along the channel,generally located in the Bay,the coal seams were bifurcated,the thickness was small,while the stability was poor.It is presumed that the southern region of Lu'an may be a relatively uplifting area in the period of Taiyuan formation,and the thick coal seam deposits in the Taiyuan formation are formed from low to high and from north to south.5.According to the phenomena reflected by the profile of the wells,it is concluded that the main factors for the control of coal accumulation in the Laowuling and adjacent areas include the depth of water,the topography,the accumulation of organic matter and the sedimentary environment.Based on the study of the lithology,sedimentary facies and coal accumulation rules of the Lao Wuling section in the northeastern Qinshui Basin,this paper analyzes the main controlling factors of coal accumulation in the study area,and provides Basic research materials for the exploration of coal bed gas. |
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