A submarine fan generated by the interaction of gravity flow and contour current: a case study from the Baiyun Sag of the northern South China Sea at 13.8 Ma

Although interest in submarine fan has grown with the rapid development of the oil exploration technologies, there is still little research about the Baiyun submarine fan system developed within the lowstand system tract (LST)... [ view full abstract ]

Although interest in submarine fan has grown with the rapid development of the oil exploration technologies, there is still little research about the Baiyun submarine fan system developed within the lowstand system tract (LST) of SQ13.8 in the northern South China Sea margin. Based on 3D seismic volume and well logging data, we will first describe its seismic and lithologic features, and then discuss the controlling factors.
The submarine fan system, which covers an area of approximate 360 km2, is generally dome-shaped. The thickest part is 150 m high and thins gradually all around. Through the interpretation of well longing data, we found that although the fan bears relative high GR value, it decreases quickly in the top of LST. Also, the seismic profiles showed that the seismic events are high amplitude, medium frequency and moderate to low continuity. These two characteristics indicate that the silts together with fine-grained sand are dominated. However, we surprisingly notice that there are not any canyons or other obvious transport paths directly connected to this submarine fan. Further study showed that approximately 40 km northwest of the fan in falling-stage system tract (FSST), a well-developed canyon can serve as the sediment transport path and in its downstream direction there are only a few sediments.
Since SB13.8 corresponded to a dramatic falling of third-order sea level in the middle Miocene, the discrepancy between new slope equilibrium profile and former slope topography increased, which directly led to rapid progradation together with intense erosion in the upper continental slope and shelf to keep its balance. Simultaneously, the southwestward migration of the four shelf-margin delta lobes in the period of FSST to LST indicates the source from paleo Pearl River had continual shifted from right above the submarine fan to its northwest. Interaction of the two factors above triggered the seaward transportation of sediments to slope toe by gravity flow. Meanwhile, the contour current soon took its place to dominate the northeastward sediments distribution. Ultimately, the interaction of gravity flow and contour current reshaped the distribution pattern of them.