Tectonic subsidence of the Zhu 1 Sub-basin in the Pearl River Mouth Basin, northern South China Sea

Abstract

The Pearl River Mouth Basin, which is situated on the northern margin of the South China Sea, has attracted great attention not only because of its tectonic setting but also because of its abundant hydrocarbon resources. We have analyzed the Cenozoic tectonic subsidence history of 4 drilled wells and 43 artificial wells from the Zhu 1 Sub-basin of the Pearl River Mouth Basin by back-stripping, using newly interpreted seismic profiles. We also calculated the average tectonic subsidence rates of the four sags in the Zhu 1 Sub-basin. The rifting and post-rifting stages are separated by abrupt changes in the tectonic subsidence curves and average subsidence rates. In the eastern sags of the Zhu 1 Sub-basin, tectonic subsidence started to slow at ca. 30 Ma, compared with ca. 23.8 Ma in the western sags. This probably corresponds to the timing of break-up and suggests that rifting in the Pearl River Mouth Basin ended earlier in the eastern sags than in the western sags. Anomalously accelerated tectonic subsidence occurred at 17.5–16.4 Ma during the post-rifting stage, with average subsidence rates as high as 301.9 m/Myr. This distinguishes the Pearl River Mouth Basin from classical Atlantic passive continental marginal basins, which demonstrate exponentially decaying post-rift tectonic subsidence.