The relationship between submarine canyon fill and sea-level change: an example from Middle Miocene offshore Gabon, West Africa

A series of Middle Miocene submarine canyons has been mapped in offshore Gabon, West Africa using a combination of seismic facies analysis and well information. Three distinct seismic facies are recognized in the canyon fill; the evolution of these facies is inferred to be related to sea-level change. During sea-level lowstand, deposition was characterized by lateral accretion on the southern canyon wall whilst progressive erosion occurred on the northern wall. This depositional pattern was controlled by a local coast-parallel current, that flowed northwestwards along West Africa during the Middle Miocene. As relative sea level rose, the erosion on the northern wall ceased and the canyons were filled by sediments showing an aggradational stratal pattern. Finally, during the early part of the transgression, the canyons were filled with horizontal or subhorizontal sedimentary strata. The sedimentary fill is thought to consist of alternating sands and mud within its lower part, but as relative sea level rose, clayey sediments gradually dominated the canyon fill.