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Based on the results of thin section observation, grain size analysis, environmental scanning electron microscopy, whole rock mineral quantitative analysis and fluorescence element analysis, the microscale sedimentary characteristics of sedimentary sand debris flow and turbidity flow were studied in details after a systematic sampling of the seventh member of Yanchang Formation (Chang 7) of Xunyi and Yaoqu areas of Ordos Basin. The results showed that: (1) The clastic particles deposited in the sand debris flow were in a disordered arrangement, while the turbid flow deposition(section A of the Bouma sequence) has a more obvious directional arrangement, indicating the former is characterized by overall rapid transport, while the latter is characterized by traction flow, indicating a low density. Both of them contain pyrites. (2) The probability curve of the sand debris flow sandstones showed a two-stage pattern, reflecting the characteristics of traction and drainage. According to microscopic observation, its source could be shallow water or land river. The probability curve of the turbid flow sandstones shows a single stage pattern, reflecting the characteristics of gravity flow. (3) The paleoenvironment of the Chang 7 sedimentary period of Yaoqu area is dry and cold. The eluviation of sandy debris flow is weaker than that of turbid flow in most periods. (4) For elemental compositions, the Sr/Ba ratios of both sandy debris flow sandstonesand associated mudstones were lower than those of turbidity current, which indicates that it has stronger dilution effect on lake water and faster injection speed. The Sr/Cu ratios of Yaoqu area were lower than those of Xunyi area, and the relative rainfall is more abundant. In addition, the Zr content in sandy debris flow sandstones is higher than that in turbidity flow sandstones, which indicates that it had stronger debris transport capacity. (5) Through the quantitative analysis of the whole rock and clay by X-ray diffraction, there is no obvious difference in clay composition and mixed layer ratio between them, but there were differences in mineral composition of the whole rock. Since the contents of quartz and clay showed great difference, a division template of them has been established, which can quantitatively distinguish sandy debris flow sandstones, turbidity flow sandstones and the transition section.