Depositional characteristics and coal forming environment of Yacheng Formation, Qiongdongnan basin

The depositional characteristics, coal-accumulation law and coal forming environment of Yacheng Formation in coal-bearing strata are studied based on the analysis of the core, logging, and data of petrology, anthracology and coal property. On the basis of the analysis, the coal accumulation model was came up. Yacheng Formation can be divided into three members, which are memberⅠ, member Ⅱ and member Ⅲ. Yacheng Formation is the later period sedimention of graben basin, which was composed of peddy sandstones, grit, medium-sandstone, mudstone, carbargilite, caustobiolith(coal). Sandstones have some instable constituents, such as feldspar, detritus, mica and so on in which quartzose arkose, lithic arkosic wacke and so on are more common.Mudstone is rich in plant detritus and has higher organic content. Coal accumulation model of fan dalta near the shallow sea and shoreland was found in Qiongdongnan basin. And the coal forming environment is basically similar with the paralic one in Paleogenein period of South China. So many coal seams are of the main characteristics. Marine fossils and glauconite and other marine authigenic minerals can be found. The terrestrial higher plants (pteridophytes) and a few aquatic plants became the main coal forming plants.