Differential subsidence and gravity collapse of the eastern and western Niger Delta lobes: Evidence from 2-D kinematic structural modelling

Abstract

The Niger Delta prism is well-known and has been described as gravitationally deformed above an overpressured shale décollement, leading to complex geometries. However, it remains unclear whether failures were initiated simultaneously and propagated synchronously over time in the eastern and western parts of the delta. This study investigates this issue using backstripping and kinematic structural restoration of regional 2-D seismic cross-sections from the eastern and western Niger Delta lobes (ENDL and WNDL). Our results suggest that the Niger Delta is controlled by the interplay between gravitational collapse processes and the crustal architecture of a divergent margin. At the delta scale, gravitational extension typically exceeds gravitational contraction, with intervening overpressured shales partially accommodating strain. Gravitational contraction initiated earlier in the offshore ENDL (Early Messinian) compared to the offshore WNDL (Plio-Pleistocene), but the WNDL has been relatively more active and has spread faster than the ENDL. A dip in the ENDL basal décollement facilitated more basinward translation of the lobe, coupled with gravity spreading due to delta lobe progradation in the Late Tortonian. In contrast, the relatively gentle dip of the offshore WNDL's regional décollement, aided by depositional loading, favoured rapid gravity spreading of the lobe in the Plio-Pleistocene. Cross-section restoration suggests that the ENDL localizes subsidence on the modern shelf, while the WNDL shows homogeneous spatial subsidence. The inferred differential spatial subsidence along the ENDL and WNDL cross-sections could be linked to (i) differences in crustal architecture (oceanic versus intermediate) and/or (ii) differences in geodynamic location (strike-slip versus divergent setting).