Sedimentary response to tectonism in the Campanian–Maastrichtian succession, Anambra Basin, Southeastern Nigeria

Abstract

The study of facies stacking patterns and sedimentary deformation structures in the Enugu–Okigwe area of the Anambra Basin provides understanding of the nature and role of tectonics in the Campanian–Maastrichtian sedimentation. The Anambra Basin-fill contains four third-order sedimentary cycles that document pulses of basin subsidence. Each cycle contains the well-defined three-part vertical succession of facies that typifies incised valley fills. Superimposition of the incised valleys and the proximal fluviatile–distal marine character of depositional systems within each valley sequence, suggest that the Anambra Basin subsided asymmetrically at least three times during the Campanian–Maastrichtian period. Further evidence for the episodic subsidence is the occurrence of seismically-induced soft-sediment deformation structures including soft-sediment folding and faulting, overturned cross-bedding and load structures, at three stratigraphic levels near and below the sequence boundaries. The appearance of the soft-sediment deformation structures is closely timed with the early phase of each episode of tectonic uplift of the Abakaliki region to the east of the Anambra Basin.