The Sequence Stratigraphic Framework And Tectonic-controlling Of Coal Occurrence Of Shitouhezi Formation In Hegang Mining Area, Heilongjiang Province

The growth and development of Hegang Basin have experienced 5 phases of rift epoch in the early Early Cretaceous age, depression period in late Early Cretaceous age, chasmic stage in the Late Cretaceous-Paleogene age, fault depression period in Paleogene and rising stage in Neogene and Quaternery. The distribution status, geological structure and other features of coal in Hegang Mine Area are mainly controlled by tectonism in Middle Yanshanian-Middle Himalayan Epoch. The formation of Hegang Basin has gone through such an process: first the transition from pull-apart to shear type, and then the tansformation from left-lateral tensile shear into right-lateral compressive shear type when the late tectonic stress field was changed. As a result, the west wing of the basin was uplifted and then damaged by erosion, while the left wing of the basin subsided and was plunged to be buried.According to the statistical analysis to the structural elements, some rules about the tectonic development in the mine area can be concluded, including the orientation, tapability and equidistance, etc. Mathematical Statistics methods, such as regression analysis and so on, are used to make an statistical analysis on tectonic elements of minor faults and minor folds. The trend surface analysis suggets that the 5 times of trend surface of favourable thickness of No.30 coal seam in the southern area of the mine show the thinning trend from west to east and from north to south.Influenced by multistage tectonic movements, the distribution of the fault structures in Hegang Mine on the plane is characterized by division of the north and the south, and the difference between the west and the east——compared to the southern area, fracture density is greater and structures are more complex in the northern area; at the same time, larger inclined normal faults were developed in the eastern area, with larger displacement, which caused that the strata in the mine area were greatly destroyed. The structure of the mine is mainly composed of faults, partially along with gently folds, also accompanied by multistage volcanic spurting. In the east and the north of this basin, intermediate acidity igneous rock was intensively activated along the faults. The coal controlling structures can be divided into 5 styles, namely anti-oblique fault-block style, conclinal fault-block style, oblique fault-block style, trenched style and obduction style.Based on the high resolution Sequence stratigraphy analysis of Shitouhezi Fm in Hegang Basin, we can divided it into one long-term base cycle, which also can be divided into 5 medium-term base cycles, made up of some short-term base cycles. Besides, short-term base cycles can be classified into 3 styles——asymmetrical cycle with rised base level, asymmetrical cycle with declined base level and symmetrical base cycle.Considered the medium-term base half cycle as the basic element, the research is focused on the lithofacies paleogeographic characters and their evolution laws so as to reveal the controlling roles of lithofacies paleogeography of sequence on the coal accumulation. It is discovered by the research that the long-term base cycle played an important role on controlling the coal accumulation. During the rising process of long-term base level, coal accumulation was getting better, while the intensity of coal accumulation was getting stronger, with the steability of coal bed developing better from worse. Conversely, during the descending process of the long-term based level, they worked on the contrary way.