Filling history and post-breakup acceleration of sedimentation in Baiyun Sag, deepwater northern South China Sea

Abstract

The Baiyun (白云) sag in the southern Pearl River Mouth basin is the largest and deepest sag in deepwater northern South China Sea. Researches and exploration in this sag have revealed many distinct features of the sag. This article reports its filling history through backstripping of depth data of interpreted sequence boundaries. Maps of sediment rates of 10 sequences from 49 Ma to the present were constructed, showing the spatio-temporal variation of the sediment rate. Three stages of sediment infilling, 49–17.5 Ma, 17.5–10.5 Ma, and 10.5–0 Ma, were divided by abrupt changes of sedimentary patterns. If the breakup of the South China Sea took place at ∼30 Ma, significant post-breakup acceleration of sedimentation was observed at 17.5–15.5 Ma and 13.8–12.5 Ma, indicating acceleration of subsidence at these times. We propose that the onset of strong post-breakup subsidence at ∼17.5 Ma was an important tectonic event that changed the pattern of sedimentation from discrete and medium-rate deposition centers in both main and south subsags to restricted but high-rate deposition in the main subsag. The cause and implications of this newly recognized event need to be investigated.

Keywords

filling history / post-breakup acceleration of sedimentation / Baiyun sag / deepwater basin / South China Sea

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