SOFT SEDIMENT DEFORMATION AND GENESIS OF THE EARLY-MIDDLE JURASSIC YANAN FORMATION, ORDOS BASIN

The paleoearthquake-related soft sediment deformation structure plays a role in revealing the tectonic activity of basin and periphery in basin evolution. Based on the core description and field survey of Yanan Formation in Ordos Basin, the soft sediment liquefaction deformation layers are identified in DT3522 well in the southwest of Dingbian and the Yanhe section in Ansai, including the liquefaction-related pillow beds, liquefied sandstone vein, liquefied breccia, mud volcano and 9 deformation structures such as load structure and ball-and-pillow structure. Through study on the correlation between soft sediment deformation layers and deformation characteristics, combined with regional tectonic setting, it is believed that there are 3 stages of paleoseismic activities with the earthquake from weak to intense in the late sedimentary period of Y7 oil layer in Yanan Formation, Ordos Basin.