Tectonic Events Indicated by Late Oligocene Slumped Deposits from the South China Sea

The late Oligocene to earliest Miocene deposition at ODP Site 1148 from the northern South China Sea is characterized by slumps and long sedimentation breaks. Tectonic-driven hiatuses occurred from the mid-Oligocene 28 Ma to 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 sediment record.A synthesis of lithological, biostratigraphic and geochemical resultsindicates 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 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 force was stronger, propably as a direct response to the sinistral strike-slip and extension by the Red River fault. The slumped deposits from Site 1148 provide the direct evidence of this spreading transition in the late Oligocene South China Sea.