The high resolution sedimentary filling in Qiongdongnan Basin, Northern South China Sea

Abstract

Abstract The high density (2 km × 6 km), high resolution (19 sequence boundaries) seismic reflection profiles and 42 industrial wells (including VSP data, gamma ray, sonic and density logs) are now available in Qiongdongnan Basin to the northwest of South China Sea. Then we explored the time–depth relationships of strata, obtained the compaction curves of shale and sand, and recovered the original sediment thickness. Furthermore, we calculated the sediment budget and analyzed the deepwater sedimentation processes. The thickest sediment of Qiongdongnan Basin is more than 16 km. The temporal–spatial distribution of sedimentation is characterized by three stages i.e. syn-rift stage (45–21 Ma), early post-rift stage (21–10.5 Ma) and late post-rift stage (10.5–0 Ma). The distribution of sedimentation in deepwater is mainly controlled by the sediment source and transportation routes. The NE trended, S-shaped central canyon is ~ 430 km in length and inferred to firstly develop at 10.5 Ma in the east of Qiongdongnan Basin, then evolve westwards and form at ~ 5.5 Ma in the west. The canyon was significantly filled by sediment in 5.5–4.2 Ma and 4.2–3.8 Ma, during which the sediment can be transported from west to the Baodao and Changchang Sags in the east. Four stages of sedimentary accumulation in Qiongdongnan Basin were identified. They are 86 m/myr in 45–36 Ma, 200–300 m/myr in 36–15.5 Ma, 90–130 m/myr in 15.5–5.5 Ma and 150–630 m/myr since 5.5 Ma. It is markedly different from that of Yinggehai–Song Hong basin in some periods, i.e. the early Oligocene (36–30 Ma) and the early to middle Miocene (21–10.5 Ma), which suggest the Qiongdongnan Basin may have other provenances besides the Red River, such as Hainan Island and Indochina.