Structural evolution of thrust-related folds and associated fault systems in the eastern portion of the deep-water Niger Delta

The geometry and kinematic evolution of a gravity-driven system consisting of thrust-related folds and associated fault systems located in the detachment fold province of the eastern portion of the deep-water Niger Delta were analyzed using a high-resolution 3D seismic dataset. This paper suggests that the structural evolution of delta progradational units can be divided into six episodes, which together represent a typical evolutionary cycle under gravity-driven processes that have resulted in the formation of distinct thrust-related folds and associated fault systems. An oblique anticline (Anticline E) trending NE-SW is subparallel to the regional transport direction (NNE-SSW) of the delta progradational units and sub-perpendicular to the main trend of the main structures (WNW-ESE). Before the shortening of the H4-H6 period, the region of this anticline was a half-graben associated with a normal fault (F0). Subsequently, during the shortening of the H2-H4 period, this normal fault acted as an oblique lateral ramp along which the half-graben sediments were shortened, forming an oblique anticline. Ultimately, growth of this anticline ceased during the H0-H1 period. The majority of faults associated with Anticline E can be divided into two types. (1) One type includes the domino normal faults generated during the H1-H4 period, these faults located in the west limb, were primarily caused by a secondary gravity-driven mechanism related to the dip of the anticline limb and gradually migrated as the crest or hinge line moved westward in subsequent intervals. The fault spacing and density are negatively and positively correlated, respectively, to the dip of the anticline limb. (2) The other fault type includes the conjugate normal faults generated during the H0-H1 period. These faults are located in the east limb and are related to the reactivated fault F0. These conjugate faults were primarily caused by a combination of local gravitational collapse resulting from the withdrawal of a mobile delta unit and the regional maximum horizontal stress caused by oblique sliding along the trend of F0. The reactivation of F0 was kinematically coupled with Anticline E and the conjugate normal faults through the delta units, and was a key factor in the origin of the anticline and faults.