3d Seismic Analysis of Cenozoic Slope Deposits and Fluid Flow Phenomena Along the Nigerian Transform Margin

Abstract

High-resolution 3D seismic data covering an area of 2,845 km2 provide new insights on slope deposits and fluid-flow phenomena along the Nigerian Transform Margin, focusing on the ~ 2 km thick Cenozoic post-transform succession. The study documents large-scale mass-transport complexes, deep-water channel complexes, sediment waves, and a wide range of fluid flow phenomena. The focused fluid flow phenomena include pockmarks, vertical pipes, seabed mounds and gas-hydrate related bottom simulating reflections. They are observed from Pliocene-aged sediments and distributed above structural highs, regional faults and active and relic deep-water channels in the eastern part of the study area, closest to the Niger Delta cone. The identified fluid flow features could be indicative of an active petroleum system in the deeper subsurface, and fluids could have migrated along planes of deep-seated, regional faults. The mass- transport deposits are mapped at multiple levels and the volume of failed sediments increased through time such that they constitute very significant portion of the entire stratigraphic succession (up to 25%) within the western part of the study area. The repeated and increased volume of mass transport deposit in the area is attributed to increased rate of sedimentation through time, slope gradient and probably increasing amplitude of sea level change during the late Cenozoic. The presence of repeated mass-transport deposits and fluid flow phenomena on the Nigeria Transform Margin has implications for installations of offshore facilities as they constitute potential geohazards. The study documents, for the first time, polygonal fault systems offshore Nigeria, adding to the global inventory of polygonally-faulted claystones, and suggesting a more oceanic dominated mudstone sedimentation than nearer the Niger Delta.