CHANGING TREND AND INFLUENTIAL FACTORS OF COAL BEDS NOS .16-20 IN DONGRONG AND DONGHUI EXPLORED AREAS.JIXIAN COALFIELD

Jixian coal field is 8-10 km wide from east to west and 50 km long from south to north, with an area of 500 km².The coal field is an asymmetrical syncline slan-ting to ward the north, with a gentle east limb and a teep west limb. The major object explored is C hengzihe group, including tens of coal beds.In exploration，it has been found that there are a large number of exploitable coal beds with great thickness in the southern part, but local parts of the sa me coal bed become thin. or branch and pinch towards the north.In this paper the author pick up sections Nos.16-20 of the coal beds for analysis .Judging from the Changing trends of the isolines of the thickness of the coal beds and the strata, the thickness of the coal bed changes obviously with that of the stratigraphic thickness.By using mathematical statistics method of regression anaiysis, it can be seen that primary influential factors for contemporaneous variation are subsidence range and sedimentary environment.Thus,some simple numerical concepts of this section can be expressed follows:(1)As the stratigraphic thickness is 80-110m and the sand-conglomerate thickness is 50-80m. this belongs to the relative stable region, and coal-bearing is in good condition.(2)As the stratigraphic thickness is less than 80m and the sand-conglomerate thickness is less than 50m, this belongs to the relative upwarped region,and coal-bearing is in bad condition.(3)As the stratigraphic thickness is more than 110m and the sand-conglome-rate thickness is more than 80m, this belongs to the relative subsidence region and coal-bearing is in bad condition.Thus, it can be seen that coal一forming conditions given above are controlled by stratigraphic thickness(subsidence range)and relative stability of sedimentation.The main factor of coal formation is the assemblage relation of various environments in which rock association is taken as a representation、whereas organism is substantial condition of coal formation.