Characteristics and Geological Significance of Seismites of the Yanchang Formation, Upper Triassic, Ordos Basin

Many earthquake-related seismites were discovered in the Chang 6-Chang 8 of the Yanchang Formation, Upper Triassic, southern Ordos Basin. Having surveyed the cores of wells, many typical deformation structures were discovered, such as syn-sedimentary micro fractures, stone veins, vibration liquefaction, deformation structure, earthquake breccia and load-casts and balls-and pillows types, etc. The complete vertical sequence of seismite of Well Ta 17, which include shattered rock bed, ladder-shaped faulted bed, vibration liquefaction deformation structure bed, liquefied sandstone vein bed, rubble bed and homogenized bed. The discovery of seismite can be used to interpret the tectonic evolvement of the basin. In Late Triassic, with the closing of Qinling and the sea slot of Southern Qilian, the south-north thrust band appeared strong activity. It was the direct inducing factors of the seimo-deposition in Yanchang Formation.and provided the evidence for the turbidite of Chang 6-Chang 8 of the Yanchang Formation, southwestern Ordos Basin, and the outsider trigger mechanism of the turbidite is earthquake activity.