Genetic Stratigraphy Analysis of the Coal Measure and Genesis of the Main Coal Seam in Huating Coal-producing Area

Directed by the theory of the genetic stratigraphic analysis and basin analysis, simultaneously referring to the idea of seismic stratigraphy, the authors have reconstructed the stratigraphic sequence and its correlation, and further subdivided the coal measure(including Fuxian and Yan'an Formation) into five sedimentary episode, i. e.,Episode I (equivalent to Fuxian Formation) is composed of braided river deposits with provenance supply from west to east, and it is merely distributed in stripped shape in the middle part of the Huating area;Episode Ⅱ consists of pluvial and alluvial deposits with a provenance supply from south to north, and it is widely distributed in the Huating area. The main coal seam is found in the upper part of plurial alluvial deposits. Episode Ⅲ is a combination of distributary lacustrine delta deposits and shore to shallow lake deposits. Direction of provenance supply is from north to south;Episode Ⅳ is made up of lacustrine and swamp deposits;Episode Ⅴ is partly eroded,the direction of provenance supply of Episode Ⅳ and Ⅴ is not clear. The coal measure of the Huating coal-producing area underwent on evolutionary history i. e. first rifting and then depressing, in which Episode Ⅰ,Ⅱ and Ⅳ stand for a development period of rift basin, and Episode Ⅳ and Ⅴ indicate the stablely depressing period.Although there are more than ten coal seams in the Huating area, the workable seam is only No. 8 bed. Based on the research data of synsedimentary structure activity, anthraeology,depositional environment and coal-forming botany, the authors point out that the formation of coal seam with great thickness has a close relation to the special coal-forming conditions, and above all, the most favorable climate, together with synsedimentary structure activity, keeps a dynamic equilibrium between the accumumlation rate of a vast swamp and the swamp weather table in a long period.In addition, this paper has also discussed the problem of coal classification from the viewpoint of sedimentology, indicating that coal seams with great thickness in Huating area can be divided into two types; one is "aggradation type" coal that has a stable V/I ratio,implying the stability of water table during peat accumulation; and the other is "progradation type" coal that has an increasing V/I ratio, implying that the gradual rising of paleo-water table has changed peat accumulation.