Abstract:

Soft sedimentary structures(SSDs)distribute widely in South Ordos Basin. The main types of SSDs are fault-graded faults structure, liquefied sandstone vein structure, pillow structure, ball and pillow structure, vibrational liquefaction curled deformation structure, torn mudstone fragments, which we can observe in outcrops and wells of Yanchang Formation in South Ordos Basin. SSDs distribute from Chang 9 to Chang 1 vertically, and Chang 7 is the most favourable layer of SSDs in Yanchang Formation，which coincides with the strength change of tectonic activity. SSDs can be observed in the whole south of basin, but southwest contributes more. By comparison, seismic is the main trigger of these SSDs, and part of them is built up by mass flow caused by seismic and volcanic eruption.