Clay mineral characteristics and its geological significance in argillaceous rock in eastern margin of Ordos basin

In order to study the paleoclimatic characteristics of the Carboniferous-Permian and its relationship with coal formation in eastern margin of Ordos basin, XRD diffraction analysis and SEM methods are used to study the composition of clay minerals and its geological significance. The results show that the mixed layer of kaolinite, illite and smectite are the major clay minerals in argillaceous rock, followed by illite and chlorite. The vertical distribution of clay minerals in argillaceous rock reflects that kaolinite in Shanxi Formation of Qiaotou section, Palougou section, upper of Chengjiazhuang section has high content. And the bottom of Taiyuan Formation of Qiaotou section, the upper of Taiyuan Formation and the middle of Benxi Formation in Chengjiazhuang section have high content of kaolinite too. Illite has high content in Shanxi Formation of each section. Chlorite has higher content in the middle and the upper of Shanxi Formation and lower content in Taiyuan Formation. Under the SEM, clay minerals are in regular shape and do not have obvious erosion marks. Illite crystallinity is 0.42°△2θ~0.63°△2θ, with an average of 0.47°△2θ, which has good crystallization, I/S interstratified ratio has an average value of 25.1%. According to the characteristics of authigenic clay minerals, the overall paleoclimate was warm and humid, short-term dry-cold climate existed in early Taiyuan Formation and middle-late Shanxi Formation. Paleoclimate and sedimentary environments reflected mutually the change process of coal accumulation, and are the key factors to control coal accumulation in the study area.