Influence of two-phase extension on the fault network and its impact on hydrocarbon migration in the Linnan sag, Bohai Bay Basin, East China

• Published in: Journal of structural geology Vol. 145; p. 104289
• Main Authors: Wang, Di, Wu, Zhiping, Yang, Linlong, Li, Wei, He, Chuan
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.04.2021
• Subjects: Fault evolution; Fault networks; Hydrocarbon migration; Linnan sag; Non-coaxial extension; Linnan sag; Hydrocarbon migration; Fault networks; Fault evolution; Non-coaxial extension
• ISSN: 0191-8141; 1873-1201
• DOI: 10.1016/j.jsg.2021.104289

Multiphase rifts produce fault networks formed by the non-coaxial faults, these networks evolve through the formation of new faults and pre-existing faults. Pre-existing faults have a great influence on the formation of new faults under later regional stress, resulting in a complex fault network. Here, abundant 3D seismic and log data are used to reveal the evolution of fault networks in the Linnan sag in southwestern East China, a complex basin that experienced multiple phases of extension during the Cenozoic and developed NE-SW-, ENE-WSW- and E-W-striking faults. (1) During deposition of the Kongdian formation (65-50 Ma), NE-SW-striking faults formed under regional NW extension. In contrast, the ENE-WSW-striking and E-W-striking faults are younger, as they show no impact on the Ek formation. (2) During deposition of the Shahejie 4 formation (50-42 Ma), faults of all orientations (NE-SW, ENE-WSW and E-W) were active. However, the pre-existing NE-SW-striking faults show dextral strike-slip characteristics. The ENE-WSW-striking faults in the central parts show shear properties. The minor faults controlled by the regional extension and local strike-slip faulting near the pre-existing NE-striking faults strike NE, and the E-W-striking faults are distributed far from the pre-existing fault. These phenomena all indicate that the stress field changed from NW-SE to N-S extension in this stage. (3) During deposition of the Shahejie 3 formation (42-38 Ma), all fault activity was the strongest, and NE-striking faults began to connect and control basin deposition. The ENE-WSW-striking faults became longer. The density of E-W-striking faults increased. (4) During deposition of the Shahejie 2-Dongying formations (38–23.5 Ma), all fault activity weakened, and the Linnan sag received sediment. These observations demonstrate that later extension with a different direction can form local stress near pre-existing faults and that faults with new strikes can enhance the geometric and kinematic complexity in the fault network in the late stage. This study provides a reference for the interpretation of other multiphase rift, where two-phase extension fault networks were controlled by regional and local stresses, the reactivated pre-exist faults and newly-formed faults coexist in non-coaxial extension. Additionally, such fault networks can have important controlling effects on the distribution of hydrocarbon accumulation. •We indicate that the regional stress direction in Linnan area changed from NW-SE (~65-50Ma) to SN (~50-42Ma).•The fault network evolution is often controlled by the regional stress, the local stress and the pre-existing fault.•We discusse the influence of the fault network formed by two-phase extension on the hydrocarbon migration.