A PRELIMINARY STUDY ON SEDIMENTARY ENVIRONMENTSAND LOW OF COAL CONCENTRATION OF CARBO-PERMIANCOAL-BEARING SEQUENCES IN REGION OF COUNTY HUO,HUOXI COAL BASIN,PROVINCE SHANXI

Huoxi coal basin is one of the six large coal basins in Province Shanxi. The study on sedimentary environments was carried out by complex methods including 55 isopach maps of main coal seams and sand bodies, a lot of trace elements analysis, X-ray diffraction analysis and DTA of clay minerals, rock identification under microscope, etc. The composition of coal-bearing sequencse, rock structur e probability cumulative curves of sandstone grain-size, electric log, analysis data of trace elements and the shape of coal seams and sand bodies are illustrated in detail. On basis of all these environmental criteria the coal-bearing formation was devided into six cycles and each environment was analysed. The middle Carboniferous Benxi Group is mainly lagoon-tidal flat deposits. The Upper Carboniferous Taiyuan Group is mainly lower delta-plain deposits. The lower Permian Shanxi Group is mainly upper delta-plain deposits. The thickness and distribution of coal seams are appe-arently controled by depositional environments. In this area,besides the good coal forming condition in environments of transition zone, as revealed by J.C. Home et al (1978), good coal forming condition exist in the environments of upper delta-plain and lago-ontidal flat too. There are two kinds of space relationship between the thicker belts of coal seam and the underlying sand body. First kind is superimposed position. Second kind is staggered position. First kind includes two varieties. One is coal seam formed on basis of tidal beach-barrier, the other is coal seam formed in environments of distributary mouth bar and distributary channel on lower parts of lower deltaplain. Second kind is coal seam formed in environments of distributary channel in transition zone and upper deltaplain. The thicker belts of coal seam and underlying sand body are in staggered position. The space relation-ship of thicker belts of coal seam and underlying sand body not only can play positive rolefor coal searching and exploration, and slso can serve as a new useful criterion for environmental analysis.