A buried submarine canyon in the northwest South China Sea: architecture, development processes and implications for hydrocarbon exploration
Abstract: High-resolution multichannel seismic data enables the discovery of a previous, undocumented submarine canyon (Huaguang Canyon) in the Qiongdongnan basin, northwest South China Sea. The Huaguang Canyon with a NW orientation is 140 km in length, and 2.5 km to 5 km in width in its upper reach and 4.6 km to 9.5 km in width in its lower reach. The head of the Huaguang Canyon is close to the Xisha carbonate platform and its tail is adjacent to the central canyon. This buried submarine canyon is formed by gravity flows from the Xisha carbonate platform when the sea level dropped in the early stage of the Late Miocene (~10.5 Ma). The internal architecture of the Huaguang Canyon is mainly characterized by high amplitude reflections, indicating that this ancient submarine canyon was filled with coarse-grained sediments. The sediment was principally scourced from the Xisha carbonate platform. In contrast to other buried large-scale submarine canyons (central canyon and Zhongjian Canyon) in the Qiongdongnan basin, the Huaguang Canyon displays later formation time, smaller width and length, and single sediment supply. The coarse-grained deposits within Huaguang Canyon provide a good environment for reserving oil and gas, and the muddy fillings in Huaguang Canyon have been identified as regional caps. Therefore, Huaguang Canyon is potential area for future hydrocarbon exploration in the northwest South China Sea. Our results may contribute to a better understanding of the evolution of submarine canyons formed in carbonate environment.
Figure 1. Location map of the study area in the Qiongdongnan Basin on the northwestern South China Sea margin. The black dotted lines present the boundaries of the Pearl River Mouth Basin, the Qiongdongnan Basin and the Yinggehai Basin. The red box indicates the location of Fig. 2. Major topographical features, including Hainan Island, Xisha Islands and Zhongsha Islands are marked.
Figure 3. The Chronostratigraphy profile of the Qiongdongnan Basin from Neogene to Quaternary. The sea level change of Qiongdongnan Basin (QDNB) and global eustatic were adopted from Haq et al. (1987).
Figure 4. The paleogeomorphic map of study area in later Miocene with overlying sediment filling thickness ranging from –4 500 m to –500 m. The red lines indicate the seismic profiles in Figs 5, 6, 7, 8 and 9. The orange area in the northwestern of the map denotes the Huaguang Canyon (HGC), and the orange regions in the southeastern of the map indicate the Zhongjian Canyon (ZJC). HGD: Huaguang depression. XSU: Xisha uplift. ZJD: Zhongjian depression. GLU: Guangle uplift. LDD: Ledong depression. ZC: Zhongjian Canyon.
Figure 5. Cross-sectional seismic profiles across the lower reach of Huaguang Channel (a), the buried channels lies in the middle area of the seismic profile (b), and the sketch profile shows deposits buried in the Huaguang Channel (c). Locations of seismic profiles are shown in Fig. 2. The Huaguang Channel is 9.5 km in width and 90 m in depth. The black box in a indicates the buried channels in b, the orange line in b indicates the basement of Huaguang Channel, the yellow section in c indicates the clastic fillings and grey indicates the muddy fillings.
Figure 7. Cross-sectional seismic profiles across the upper reach of HuaGuang Channel (a), the seismic profile shows that the buried channels are distributed near the upper reach (b), and the sketch profile show deposits buried in the Huaguang Channel (c). Locations of seismic profiles are shown in Fig. 2. The Huaguang Channel is 5 km in width and 135 m in depth. The black box in a indicates the buried channels in Fig. 7b, the orange line in b indicates the basement of Huaguang Channel, the yellow section in c indicates the clastic fillings and grey indicates the muddy fillings.
Figure 8. Cross-sectional seismic profiles across the upper reach of HuaGuang Channel (a), the buried channels are closed to the southwestern area of the seismic profile (b), and the sketch profile show deposits buried in the Huaguang Channel (c). Locations of seismic profiles are shown in Fig. 2. The Huaguang Channel is 2.5 km in width and 375 m in depth. The black box in a indicates the buried channels in Fig. 8b, the orange line in b indicates the basement of Huaguang Channel, the yellow section in c indicates the clastic fillings and grey indicates the muddy fillings.
Figure 6. Cross-sectional seismic profiles across the middle reach of HuaGuang Channel (a), the buried channels are located in the upper region of the seismic profile (b), and the sketch profile shows deposits buried in the HGC (c). Locations of seismic profiles are shown in Fig. 2. The Huaguang Channel is 4.6 km in width and 225 m in depth. The black box in a indicates the buried channels in Fig. 6b, the orange line in b indicates the basement of Huaguang Channel, the yellow section in c indicates the clastic fillings and grey indicates the muddy fillings.
Figure 9. The seismic profile is shown in the Figs 2 and 4. The Xisha carbonate platform and the Huaguang Channel are shown in the cross-sectional seismic profile. The orange line indicates the basement of the Huaguang Channel. The green lines represent the progradation reflection. The high-amplitude reflection indicates the clastic fillings and the strong and high reflections indicate the muddy fillings.
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