Subsurface fluid flow at an active cold seep area in the Qiongdongnan Basin, northern South China Sea

The active Haima cold seep sites were discovered by the remotely operated vehicle on the western part of the northern slope of South China Sea in 2015 and 2016. However, the subsurface structures in the seep area are not well studied, which prevents the further understanding of the evolution of fluid venting system in the active cold seep area. In 2017, a high-resolution 2D seismic line transecting the two main seep sites was acquired and processed. In this study, the subsurface structures were well resolved on the seismic profile. The new observations include the widespread subsurface fluid flow features (i.e., chimney structures and pockmarks) and the pervasively distributed magmatic activities. Seismic indicators for hydrothermal vents were also observed on the seismic section. This new discovery confirms the contribution of magmatic activities to the evolution of subsurface fluid flow in the study area. Minor faults under the recognizable resolution of seismic profile, which can act as conduits for the subsurface fluid flow, were also identified in the fine-grained sediment sequences. Overall, these results provide new insights into the evolution of subsurface fluid flow in the study area.