Earth Science Frontiers ›› 2022, Vol. 29 ›› Issue (4): 55-72.DOI: 10.13745/j.esf.sf.2022.1.2

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Quaternary Qiongdongnan Basin in South China Sea: Shelf-edge trajectory migration and deep-water depositional models

MA Chang1(), GE Jiawang1,2,*(), ZHAO Xiaoming1,2, LIAO Jin3, YAO Zhe3, ZHU Jitian3, FANG Xiaoyu2, XIANG Zhu1   

  1. 1. School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, China
    2. Guangdong Laboratory of Southern Marine Science and Engineering-Zhanjiang, Zhanjiang 524000, China
    3. Research Institute of Haikou Branch, CNOOC, Haikou 570100, China
  • Received:2021-08-10 Revised:2021-09-28 Online:2022-07-25 Published:2022-07-28
  • Contact: GE Jiawang

Abstract:

The shelf-edge trajectory is comprehensively controlled by tectonics, sediment supply, sea level and climate, and its migration and evolution are closely related to the deep-water depositional systems. The shelf-edge clinoform stacking pattern, sediment-budget partition in deep-water areas and reservoir evaluations are current geoscience hot topics. Based on the newly acquired high-precision, high-density 2D seismic data of the Qiongdongnan Basin (QDNB), this paper quantitatively characterized the Quaternary shelf-edge trajectory and identified three trajectory types in QDNB: flat to slightly rising, moderately rising and steeply rising types. Since 2.4 Ma the temporal evolution of the shelf-edge trajectory in QDNB can be divided into three stages with lateral differences: 2.4-1.9 Ma, mainly the slightly rising type; 1.9-0.8 Ma, the slightly rising type in the western part and moderately rising type in the eastern part; 0.8 Ma-present, the moderately rising type in the western part and steeply rising type in the eastern part. The vertical migration of the shelf-edge trajectory is jointly controlled by the rise and fall of sea level caused by climate change and associated with sediment supply. The differences in tectonic activity and provenance supply lead to lateral variations of the shelf-edge trajectory and progradation or aggradation stacking patterns. According to the above studies, when the shelf-edge trajectory angle, α, is between 0° and 4°, the continental slope canyons are small-scaled and shallow mostly, with developments of multistage large-scale submarine fan deposits in the deep-water area but less mass-transport deposits (MTDs). When 4° <α< 35° the continental slope canyons increase in scale, with occurrences of both submarine fan deposits and MTDs. When 35°<α<90° a few but steep continental slope canyons are developed, along with developments of mainly large-scale MTDs in the deep-water plains, almost without submarine fan deposits. Since the Quaternary the temperature in QDNB continues to drop while the East Asian winter monsoon increases significantly, causing the sediment supply to increase; while decreasing sea level results in progradation at the northwestern shelf edge. In comparison, frequent fault activities and relatively low sediment supply at the northeastern shelf edge result in a much shorter slope advance distance and developments of multistage MTDs. Results of this study have theoretical significance for the predictions of continental shelf-edge system and deep-water deposition in QDNB and other basins.

Key words: Qiongdongnan Basin, Quaternary, shelf-edge trajectory, quantitative characterization, deep-water depositional system

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