The Wan’an Basin is a strike-slip and pull-apart basin formed by the tensile stress derived from the dextral strike-slip movement of the Wan’an fault on its east side. Based on the relationship of two-way travel time vs. depth between stacking velocities from the seismic data and drilling data from wells, four megasequence boundaries were identified: MB1, the top of the acoustic Pre-Tertiary basement; MB2, the top of the Oligocene (24 Ma); MB3, the Late Miocene (8 Ma); and MB4, the Early Pliocene(4 Ma).Above each megasequence boundary (MB), there is a megasequence (MS).