The 2D seismic data were used to discuss the migration of the Beikang forebulge in the southern South China Sea and its impact on trap formation.The strata overlying the Early Miocene Unconformity(EMU)

a regional unconformity

could be simply categorized as draping and horizontal layer series in the Nansha sea area.The draping layer series overlie the EMU directly

show parallel seismic reflection characters of continuous thin layers and thicken southeastward

suggesting suspended sediments.While the horizontal layer series were deposited synchronously in structural lows and continuously onlapped and overlay the draping strata formed early.They are mixed thick sedimentary layers of turbidites and suspended sediments featuring discontinuous or weak seismic reflection.Judged by the migration of onlap reflection termination and thickening of the draping strata

the forebulge has migrated southeastward during its uplifting since the Mid-Miocene

indicating a process of intense flexure and equilibrium rebound occurring at the thinned continental crust in the Nansha sea area.The forebulge migration has caused the formation of a host of buried hills

with the draping and horizontal series of strata serving as favorable seals

which in turn will be conducive to the formation of traps.