Discovery of pockmarks in the Zengmu Basin, southern South China Sea and the implication -- Journal of Oceanology and Limnology,2023,41(2):757-768

	Cite this paper:
	Yanlin Wang, Guanghong Tu, Junhui Yu, Pin Yan, Yongbin Jin, Changliang Chen, Jie Liu. Discovery of pockmarks in the Zengmu Basin, southern South China Sea and the implication[J]. Journal of Oceanology and Limnology, 2023, 41(2): 757-768

Discovery of pockmarks in the Zengmu Basin, southern South China Sea and the implication

Yanlin Wang^1,2, Guanghong Tu³, Junhui Yu^1,2, Pin Yan^1,2, Yongbin Jin^1,2, Changliang Chen^1,4, Jie Liu^1,2

1. Key Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Innovation Academy of South China Sea Ecology and Environmental Engineering, Chinese Academy of Sciences, Guangzhou, 510301, China;
2. Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou), Guangzhou, 511458, China;
3. Guangzhou Marine Geological Survey, Ministry of Natural Resources, Guangzhou, 510075, China;
4. University of Chinese Academy of Sciences, Beijing, 100049, China

Abstract:

The Zengmu Basin located in the shallow water area of the southern South China Sea, is rich in oil and gas resources, within which faults and mud-diapir are developed, but it is unknown whether oil and gas migrate to the seafloor surface. The newly collected multibeam data across the Zengmu Basin reveal a large number of depressions, with depths of 2-4 m, widths of several tens of meters, large distribution range of 1.8-8 km along survey line, up to ~50 km, and their backscatter intensity (-26 dB) is much greater than that of the surrounding area (-38 dB). Combined with the developed mud-diapir and fracture structures, and abundant oil and gas resources within this basin, these depressions are presumed to be pockmarks. Furthermore, more than 110 mono-sized small circular pockmarks, with a depth of less than 1 m and a width of 5 m, are observed in an area of less than 0.03 km², which are not obliterated by sediment infilling with high sedimentation rate, implying an existence of unit-pockmarks that are or recently were active. In addition, seismic profiles across the Zengmu Basin show characterization of upward migration of hydrocarbons, expressed as mud-diapir structures, bright spots in the shallow formation with characteristics of “low frequency increase and high frequency attenuation”. The sub-bottom profiles show the mud-diapir structures, as well as the gas-bearing blank zones beneath the seafloor. These features suggest large gas leaking and occurrence of large amounts of carbonate nodules on the seafloor. This indicates the complex and variable substrate type in the Zengmu Basin, while the area was once thought to be mainly silty sand and find sand. This is the first report on the discovery of pockmarks in the Zengmu Basin; it will provide basic information for submarine stability and marine engineering in China’s maritime boundaries.

Key words: South China Sea|Zengmu Basin|dense pockmarks|gas leaking|substrate type

Received: 2022-03-01 Revised:

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