<p>The Wushi sag is located in the central part of the Beibuwan Basin, northern South China Sea. Above the thick oily shale unit in the Wushi East subsag, a suite of terrace-like extensional décollement fault systems exists, which, in conjunction with the No. 7 boundary fault, control a complex fault system. This study integrates the high-resolution 3D seismic data and quantitative analysis of fault displacement to analyze the growth history of the complex fault system and to establish a model of fault system evolution in the Wushi East subsag. The findings reveal two phases of fault growth northward migration during the rifting process. The first phase occurred between the rift I phase and the décollement I phase, witnessing fault activity migrating northward from the No. 7 boundary fault to the décollement faults (Fd and Fe) in the hangingwall. The second phase occurred between the décollement I phase and the décollement II phase, with fault activity migrating further northward from Fd and Fe to Fa, Fb and Fd. By the end of the Oligocene, basin inversion controlled the syn- to post-rift transition of the Wushi East subsag. This study bears significant implications for hydrocarbon exploration and for understanding the mechanism underlying the syn- to post-rift process in the north continental marginal basins of the South China Sea.</p>

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Growth History of Complex Fault System and Syn- to Post-Rift Transition in the Wushi East Subsag, Beibuwan Basin

  • Zheng Wang,
  • Ke Xu,
  • Dianjun Tong,
  • Yong Tang,
  • Chen Hu,
  • Jianye Ren

摘要

The Wushi sag is located in the central part of the Beibuwan Basin, northern South China Sea. Above the thick oily shale unit in the Wushi East subsag, a suite of terrace-like extensional décollement fault systems exists, which, in conjunction with the No. 7 boundary fault, control a complex fault system. This study integrates the high-resolution 3D seismic data and quantitative analysis of fault displacement to analyze the growth history of the complex fault system and to establish a model of fault system evolution in the Wushi East subsag. The findings reveal two phases of fault growth northward migration during the rifting process. The first phase occurred between the rift I phase and the décollement I phase, witnessing fault activity migrating northward from the No. 7 boundary fault to the décollement faults (Fd and Fe) in the hangingwall. The second phase occurred between the décollement I phase and the décollement II phase, with fault activity migrating further northward from Fd and Fe to Fa, Fb and Fd. By the end of the Oligocene, basin inversion controlled the syn- to post-rift transition of the Wushi East subsag. This study bears significant implications for hydrocarbon exploration and for understanding the mechanism underlying the syn- to post-rift process in the north continental marginal basins of the South China Sea.