Danielle Howlett, Robert Leslie Gawthorpe, Zhiyuan Ge, Atle Rotevatn, Christopher Aiden-Lee Jackson 

Understanding the evolution of submarine channel-lobe systems on salt-influenced slopes is challenging as systems react to seemingly subtle changes in sea-floor topography. The impact of large blocking structures on individual deep-water systems is well documented, but understanding of the spatio-temporal evolution of regionally extensive channel-lobe systems in areas containing modest salt movement is relatively poor. We use 3-D seismic reflection data to map Late Miocene deep-water systems offshore Angola within a c. 450 ms TWTT thick interval. Advanced seismic attribute mapping tied to standard seismic stratigraphic, seismic facies analysis and time-thickness variations, reveals a wide variety and scale of alterations to sediment routing and geomorphology. Five seismic units (SU1-SU5) record a striking change in sediment pathways and structural relief within eight evolving minibasins. Observations within these units include gradual channel diversion through lateral migration during times of relatively high structural growth, opposed to abrupt channel movement via avulsion nodes during times of relatively high sediment accumulation. The results of the study led to the development of conceptual models for influences on deep-water systems during characteristic structural development in the contractional salt domain, these stages being initiation, maturity, and decay. The initiation stage contains small-segmented folds with mostly system bypass, while the maturity stage contains linked high-relief structures and prominent minibasins leading to ponding, large-scale diversion and localized slump deposits derived from nearby highs (SU1-SU3). The less studied final stage of topographic decay contains decreased length and relief of structures leading to a more complicated array of channel-lobe bypass, diversion, ponding and subtle control on avulsion nodes (SU4-SU5). These observations contribute to the understanding of channel-lobe stacking, routing and control over transition zones in tectonically active areas, ultimately improving our general understanding of the effects of significant through to subtle sea-floor topography, and can be a guide in other salt-influenced basins.