Shale 3D Flow and Interaction With Basement Faults in the Niger Delta Deep-Water Fold and Thrust Belt

Abstract

Based on a large 3D seismic data set in the deep-water domain of the Niger Delta, this study challenges previous interpretations involving the occurrence of multiple detachments and extensive thrust flats, illustrating timing and mode of shales flow at the toe of the gravity system. Five units of syn-kinematic sediments, reaching a maximum thickness of ∼800 m, accumulated in the tectonically subsiding synclines during fold amplification between ∼9.5 and ∼1.4 Ma. The volumes of syn-kinematic units roughly balance those of the shales accumulated in the thickened cores of WNW trending anticlines. This feature is consistent with folding resulting from buckling controlled by the competence contrast between isopach Cenozoic units and underlying overpressured shales of the Akata Formation. A dense network of NE-SW striking oblique extensional faults offsets a prominent anticline characterized by a NE-SW trend (which is almost perpendicular to the regional fold trend). These faults form a narrow, continuous deformation zone extending for tens of kilometers along and beyond the length of the anticline. The faults, rooting within the shales of the Akata Formation, formed since ∼5 Ma and deform the seabed. Displacement distribution suggests mechanical interaction between isolated fault segments within the deformation zone. The latter is interpreted as the shallow expression of a deep-seated fault zone inherited from the segmented passive margin and marked by gravity and magnetic data. Our results, providing a comprehensive picture of active deformation features and their relationships with deep-seated faults, shed new light into the modes of interaction between gravity systems and underlying basement structures.