GENETIC ANALYSIS AND COAL ACCUMULATING FEATURES IN COAL-BEARING STRATA OF CARBONIFEROUS-PERMIN,YONGCHENG COALFIELD

According to the methods of genetic stratigraphy and depositional environments analysis,three kinds of depositional systems and eleven genetic sequences have been recognized in the coal-bearing strata of Yongcheng Coalfield.The paper mainly discusses the depositional characteristics of subtidal carbonate of epicontinental sea and clastic flat.The microcharacteristics and microfacies of carbonate regularly change upward.This is the results of sediments filling to the basin and it conforms to the depositional models of shallowing-upward carbonate-sillisiclastic sequences of epicontinental sea.Tidal channels in the tital flat are dominated and sandmud mixed tidal flat marks are obvious.The most economic coal beds were formed from the swamp types which developed on the abandoned clastic tidal flat and lower delta plain.The major reasons for low ash and sulfur in coal beds are that saline water and active clastic systems were nearly no influence upon the swamps when peats were accumulated.