Abstract: The superpressure mud seams developed in the mudstone layers of the Xiaoquangou Formation of the U.Triassic and the Jianghe Formation of the L.Jurassic in the Tuositai Area of the west end on the southern margin of the Junggar Basin and those in the Anjihaihe Formation on the south margin.The superpressure mud seams in the first two formations occurred during the late stages under the major tectonic uplifts and the excellent self-closed conditions while those in the Anjihaihe Formation formed under the disequilibrium between the compaction-discharge flows of the mud seams and the hydrocarbon generation.However,the superpressure mud seams could be the cause both for the well-development of extrusion structures and the excellent sliding sheet for the gravity decollement structures.