Abstract
The relationship among the southern Nigeria’s inland basins is a direct result of formative tectono-sedimentary interaction within and adjacent to the basins. A full understanding of the nature of these interactions, especially how they were controlled by the structural dynamics of the basins, remains a challenge. This work investigates the mechanisms that directly defined the structural events and sedimentary processes, and the hydrocarbon generation and trapping processes in the Anambra Basin. Insight from regional cross-sections was used to highlight a genetic link among the tier-basins from the distal offshore to the onshore, across the Cretaceous – Paleogene (K-Pg) that outcrops in the Enugu Axis. This Axis was defined and illustrated as the geographical region where the axial plane of the Enugu crestal high projects to the surface.
A regional seismic line was interpreted, and the results corroborated with those from well data and
field studies to show a relatively continuous structural trend, from the oceanic to the continental crust
and their overlying formations. This showed that the Enugu Axis of the Anambra Basin is an anchor
point, a projection of the paleo-margin serving as a transition from laterally depth-equivalent but
diachronous deposits, to highs in the Benue Trough. The Cenozoic major synthetic faults, and the
initiation of displaced blocks in the Niger Delta, are deeply rooted and controlled by the Cretaceous
events, including the rifting and magnetic intrusions. These highs and lows affecting the top of the
Cretaceous deposits are the drivers that locate and lead to the activation of blocks that slide above the
base of the Akata Formation, or equivalent base, of the Cenozoic Niger Delta formations. These
magmatic events are relatively near surface and exposed beyond the Anambra Basin, in the Benue
Trough. This understanding provides a premise for study of the Cretaceous basins using information
from the well-known geology of the associated Niger Delta, who’s seismic, well and other subsurface
data abound.
This work used such data and methods to analyze the roles of the basins’ structural activities in defining
the proven petroleum systems and prospects in the area. A similar pattern of deposition in the present-day continental shelf margin explains the clinoform morphology at the subsiding slopes of the late
Cretaceous Anambra Basin delta and the pressure transmission that leads to hydrocarbon leaks, gas
flares and retained petroleum prospects in the Enugu Axis. A new “plane-wing” concept further
explains the anomalies, fold structures and very high dips or upturned units observed in the Benue
Trough.