The Sedimentary Cycles Characteristics And Coal-accumulating Environment Of Upper And Lower Shihezi Formations (P_2-3), Western Henan

Based on the work done by our predecessors, and relying on the materal of the outcrops, well logging, cores, etc., selecting two outcrops, which are Dafengkou inYuzhou and xiaye in Jiyuan, as the measured profile, collecting data of drilling 12-20 in Pingdingshan, as well as other monographs,references, combining the information of outcrops, drillings and testing analysis, this paper has a comprehensive study on the characteristics of the sedimentary system, deposit types, sedimentary facies, sedimentary subfacies and microfacies, and divides the base-level cyclic sequences in the Upper and Lower Shihezi Formations, infers the lifting rules of base-level, review the cycle characteristics, draws out stratigraphic isopach map and sand-mud ratio contour map of the strata and the lithofacies palaeogeography maps, on this basis the coal-accumulating environment of the upper and lower Shihezi Formations in west Henan has been discussed.With the theory of modern sedimentation, this paper has a detailed analysis on features of sedimentary facies, sedimentary subfacies and microfacies in west Henan, divides the sediment types based on the sedimentary subfacies, including eight types of the upper delta plain, seven kinds of the lower delta plain, three kinds of the delta front. Then the stratigraphic column and formation phase histogram of the Upper and Lower Shihezi Formations in Dafengkou of Yuzhou city, drilling 12-20 of Pingdingshan city, xiaye area of Jiyuan city were drawed respectively.Applied the base-level cycles to the division of sequence stratigraphy of the Upper and Lower Shihezi Formations in western Henan, the medium-term, short-term base-level sequence formation are divided respectively in drilling 12-20 of Pingdingshan, Dafengkou of Yuzhou and xiaye of Jiyuan. 8 medium-term base-level cycles are identified in Pingdingshan 12-20, all symmetrical cycle; 41 short-term cycles, in which 20 symmetrical and 21 asymmetrical, non-symmetrical short-term cycles were mainly retrogradation in order to darken up, any shallowing-upward aggradational cycle was not development; 7 mid-cycles are identified in profile of Dafengkou, in which 6 symmetrical cycles, 1 asymmetric cycle, the half-cycles of upward shallowing, short-term cycles of 23 Among them, 10 symmetrical cycles and 13 non-symmetric cycles, there are two kinds of non-symmetric cycles which includes upward shallowing ones and upward darker ones; 4 medium-term cycles are identified in Xiaye area, in which 3 symmetrical cycles, 1 asymmetric cycle, the half-cycles of upward shallowing, 14 short-term cycles, including seven symmetrical short-term cycles, 7 non-symmetrical short-term cycles.The changement and Superimposition of structural type of the short-term base-level cycles in the process of medium-term base-level in various regions respectivelyhave been Explored.The stratigraphic isopach map, Sand-mud ratio contour map on Upper and Lower Shihezi Formations in Henan Province have been drawn, and lithofacies palaeogeography maps on the strata with facies-comparation method. It was a lower delta plain in the central region of west Henan, due to an increased bifurcation of distributary channel and the development of interdistributary, only some unstable thin coal seams which only can be taken up partially were formed. In the south of this area, the interdistributary became broader, formed larger stream swamp after filling with silt level. Locally abandoned delta body, as well as the edge of the vast bay environment, is also conducive to the extensive development of coal accumulation, the multi-layered coal seams formed are thick, and more stable. It tells that the coal-accumulating environment of the study area should primarily be deltic interdistributary peat bog, peat flat is not developed, with the delta continue to move forward, the scope of coal accumulation is even greater.