Sedimentary influence on the deformation of deep water deposits offshore Nigeria
A volume of 3D seismic data has been used to study the interplay of Cenozoic structural deformation and its relationship to sediment deposition offshore South-West Nigeria. The 3D survey encompasses an area that includes sediments derived from both the Niger Delta in the east and the Benin Embayment to the north. Sediments derived from the Niger Delta are comprised of deep water sands and shales deposited in channel levee turbidites and hemipelagic sheets, whilst those from the Benin Embayment are primarily fine grained and encompass large scale levees.\ud The study area can be divided into two vertically separated tectonic domains, which are divided by a detachment interval. The vertical separation occurs at a level which is coincident with an apron of mass transport deposits which extends beyond the limits of the data, this complex is interpreted to have been deposited at the end of the Cretaceous.\ud The Cenozoic interval has been modified by gravity driven tectonic activity which has resulted in two structurally dissimilar regions, which are separated by a strike slip fault zone. To the west of this strike slip fault zone is a region of primarily compressional deformation, to the east the majority of the deformation is extensional. The structural styles recognised, extension, compression and strike slip motion have been analysed to establish the timing and the causes of the deformation.\ud The influence of the sediment dispersal upon the location and timing of the tectonic deformation has been inferred indicating that structural deformation in this region pre dates the onset of deposition from the Niger Delta. The deformation which occurred prior to the Niger Delta outbuilding was controlled by the sediment dispersal from the Benin Embayment and this earlier, sediment controlled deformation, has subsequently played a role in the modified gravity tectonics which has been observed.
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