Late Oligocene to earliest Miocene deposition at ODP Site 1148 in the northern South China Sea is characterized by slumps and long sedimentation breaks. Tectonic-driven hiatuses occurred from the mid Oligocene (28 Ma) to the early Miocene (23 Ma), with the main hiatus falling at 25 Ma, marked by the base of the slump. The four hiatuses recognized together erased at least 3 Ma of the late Oligocene sedimentary record. A synthesis of lithological, biostratigraphic and geochemical results indicates a stepwise seafloor spreading mode for the late Oligocene South China Sea, climaxing at the "25 Ma transitional event". This series of tectonic events must have resulted from interactions between the Eurasian, Australian and Philippine-Pacific Plates, subsequently leading to a change in seafloor spreading toward the south, where rifting had been more prominent and extension was stronger, probably as a direct response to sinistral strike-slip and extension of the Red River fault. The slumped deposits at Site 1148 provide direct evidence of this spreading transition in the late Oligocene South China Sea.