We have analyzed two recently acquired multichannel seismic profiles across the Reed Bank area, South China Sea. A detailed seismic interpretation coupled with drilling data has proved the occurrence of a wide carbonate platform, developed between the Late Oligocene and the Early Miocene (32-20 Ma). The top of these carbonates is an important regional unconformity, corresponding to a strong and continuous seismic reflector. An age of about 20 Ma is inferred for this reflector, acting as a regional unconformity marking the cessation of seafloor spreading with an erosional/non-depositional hiatus, spanning 3 or 4 m.y. The time interval during which the carbonate platforms formed is concurrent with the opening of the South China Sea. The reconstruction of the tectonic subsidence in this area has shown a decrease in rate of subsidence during the drifting stage (32-17 Ma), indicating that the whole Reed Bank area was in a tectonically stable and shallow water environment for more than 10 m.y., favoring the development of shallow water carbonates. With a sharply increased subsidence rate after the end of spreading (17 Ma) and a continuously increased sea level, the carbonate platforms were drowned and died, except some structural highs with reef buildups, where the carbonate sedimentation continued to Middle Miocene. We suggest that delayed tectonic subsidence in Reed Bank area might have been related to a secondary mantle convection under the rift lasting more than about 10 m.y.

We identify the seismic characteristics about the carbonate platform and other types of reefs in the Reed Bank area, South China Sea, based on a more than 220 km long multi-channel seismic reflection profile. From the Late Oligocene to Early Miocene, carbonate platforms were well developed featured with highamplitude continuous reflections at the top and low-amplitude parallel reflections within. Reefal carbonate build-ups continued in structural highs almost up to the Middle Miocene, and even to present in the Reed Bank. The development of carbonate platforms and reefs were controlled by the tectonics and sea level changes in the study area synthetically. During the drifting stage of SCS the Reed Bank area was in a relatively stable condition. An everlasting shallow marine environment and low sediments input favored the formation of carbonate platforms. A sudden thermal subsidence after the cessation of SCS's opening in the Early Miocene and the continue rising of sea level made the carbonate platform drown and die. Reed Bank basin is a very promising area for further exploration work.