3D seismic geomorphology of submarine channel-levee systems in salt-related slope setting: a case study from the western deepwater Egypt

Abstract

High resolution 3D seismic dataset has been used to examine gravity-driven deposits from the Plesitocene to present-day in the structurally complex area of the western Nile deepwater. The underlying Messinian salt and its associated faults and the existence of fluid-migrated features generated local seabed topography that affected sedimentation and seismic facies distribution. Seismic interpretation combined with planform analysis of attribute maps were utilized to define five seismic facies which are distinguished by amplitude strength, reflections, and geometry. The observation of the temporal and spatial relationship of five seismic units using isochron map analysis offers an insight into seismic stratigraphy development which can be described in three main phases. The first phase is characterized by the deposition of two main mass transport deposits (seismic unit 1 and 2). The second phase is defined by the development of channelized-fan deposit (seismic unit 3). The final phase is characterized by the deposition of near-seabed MTD and present-day channel-levee system (seismic unit 4) and the development of major mud diapirs (seismic unit 5). Spectrally decomposed and colour-blended seismic volume analysis combined with seismic facies interpretation in seismic cross-section have been useful to morphologically investigate and quantify three submarine channels and their associated elements (e.g. thalweg and erosional depth longitudinal profile, levee width and thickness). The results revealed an architectural element variation and the channel pathways with respect to local seabed topography. Increases in sinuosity are related to decreases in channel axis gradient and followed by evidence of channel aggradation Levee thickness development shows an overall decrease in thickness and width downslope with local variations due to structural bathymetry changes (e.g thickness increase towards the hanging wall of the main fault). Overall a change downslope from degradational to aggradational following equilibrium profile is observed. This is evidenced by a deeply incised channel erosional depth in the upperslope and increasing in sinuosity in the lower slope. Sinuous form is observed when the channel experiences a shallow gradient and availability of accommodation space followed by the development of lateral accretion packages (LAPs). Local structural growth (e.g. minibasin and anticline) has a big influence on the channel path geometry. Submarine channel deposit is often a prominent reservoir target in many deepwater explorations around the world. A near-seafloor study with a higher seismic resolution may give an analogue to image turbiditic reservoir architecture. Therefore, this study improves the understanding in the interaction of sedimentation and structural variations which can be applied to hydrocarbon exploration to predict control and distribution of deepwater turbiditic reservoirs.