Acoustic and biological characteristics of seafloor depressions in the North Yellow Sea Basin of China: Active fluid seepage in shallow water seafloor

• Published in: Marine geology Vol. 414; pp. 34 - 46
• Main Authors: Liu, Xiaoyu, Feng, Xiuli, Sun, Yongfu, Chen, Yilan, Tang, Qiuhua, Zhou, Xinghua, Dong, Lifeng, Fan, Shiliang, Jiao, Pengfei, Wang, Kemeng, Wen, Wu, Lu, Bo
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.08.2019
• Subjects: Acoustic characteristics; Backscatter intensity; Northern Yellow Sea Basin; Paleo-channels; Pockmark; Seafloor seepage; Seafloor seepage; Northern Yellow Sea Basin; Pockmark; Paleo-channels; Backscatter intensity; Acoustic characteristics
• ISSN: 0025-3227; 1872-6151
• DOI: 10.1016/j.margeo.2019.05.002

High resolution multibeam bathymetry revealed the occurrence of numerous craterlike depressions, so-called pockmarks, in the sea floor of the North Yellow Sea Basin (NYSB). To investigate whether these pockmarks are related to any type of fluid flow or gas seepage from subsurface stratum, acoustic survey and box samplings were conducted in a selected area containing several typical pockmarks. This allowed for an integrated analysis of the morphology, distribution, and subsurface strata as well as a direct comparison of seafloor characteristics among different areas inside and outside of a pockmark. Additionally, surface sediments were analyzed for particle structure and grain size. Based on the combination of multibeam bathymetry and backscatter intensity data, 282 seafloor depressions were accurately identified. Moreover, the formation of pockmark can be attributed to existence of gas chimneys and other shallow gases revealed by shallow seismic profile records in the subsurface strata. Sediments inside and outside the pockmark showed remarkable discrepancies in terms of grain size, and benthic fauna. Additionally, strong internal reflection area was observed inside the depressions where benthic habitats are abundant and sediments contain strawberry pyrite and carbonate cementation. Side scan sonar also recorded sediment plumes in the water column, which indicates that the pockmarks are still active. Several “pearl-string-like” accumulations of pockmark were found in the study area, which well agree with the distribution of buried channels and lakes. These results thus provide new insights in interpreting shallow water fluid seepage, with implications for our current knowledge of overall sedimentation process in offshore continental shelves. •Active fluid seepage in shallow water continental shelf environment•Shallow-gas related acoustic features recorded on sub-bottom acoustic data•Benthic fauna anomalies, and strawberry pyrite associated with seafloor seeps•The large but shallow pockmarks can be ascribed to low fluid pressure.•String like distribution of pockmarks controlled by subsurface buried channels.