Abstract This research seeks to test the hypothesis that the rheology of submarine gravity-flows influences the planform geometry of associated fan lobe deposits. If this control exists, seismic geomorphology has the potential to predict the sedimentary characteristics of these deposits by analysing relatively simple seismic outputs such as time structure maps and amplitude maps. This predictive power could potentially aid the identification of prospective reservoirs through automated processes of seismic interpretation. In this work, Upper Cretaceous and Neogene deep-water reservoirs from East and West Africa with porosity in excess of 20% and multi-Darcy permeability were analysed. The overall external geometry of the reservoirs was described by integrating seismic amplitude extractions, structure and isochron maps derived from high-quality 3D seismic data. The maps were generated from detailed interpretation of the top and base reservoir reflections. Core photos of the reservoirs were integrated into the seismic project and their examination allowed the identification of dominant sedimentary facies, enabling a proposal for the classification of these deposits in terms of flow processes. The research indicates that the confinement of flows exerts an obvious control on the shape of the deposits and results in sedimentary bodies with marked elongation at the seismic scale. However, analysis of the reservoirs at the core scale indicated that they are dominated by massive, poorly sorted, medium- to coarse-grained sandstones, commonly with floating oversize clasts, as well as beds with disrupted laminae and sandy conglomerates. These characteristics may indicate ‘depositional freezing’ from high-density flows with yield strength, which may also have contributed to the limited lateral spread of the deposits analysed. The research also highlights the importance of the non-unique relationship between sedimentary processes and external geometries of the resulting deposits at the seismic scale. This means that deposits with similar geometries may have markedly different sedimentary characteristics. This work highlights the increasing importance of integrating detailed seismic geomorphology studies with an accurate examination of core data to validate models of gravity flow processes and test their predictive value.

Abstract 3D seismic data provide new insights on c. 2 km thick Cenozoic post-transform slope sediments and fluid-flow phenomena along the Nigerian Transform Margin. The study documents large-scale mass-transport deposits (MTDs), deep-water channels, sediment waves, and a range of fluid-flow phenomena such as pockmarks, pipes, seabed mound and gas hydrates. They are observed from Pliocene-aged sediments and distributed above structural highs, regional faults, and active and relict deep-water channels in the eastern part of the area, closest to the Niger Delta cone. The fluid-flow features are interpreted to be indicative of an active petroleum system in the deeper subsurface and from fluid migration along planes of deep-seated faults. MTDs are mapped at multiple levels and the volume of failed sediments increased through time within the western part of the study area. The repeated and increased volume of MTDs in the area is attributed to an increased rate of sedimentation through time and slope gradient during the late Cenozoic. The presence of repeated MTDs and fluid-flow phenomena on the Nigerian Transform Margin has implications for installations of offshore facilities as they constitute potential geohazards. The study also documents, for the first time, polygonal fault systems offshore Nigeria.