Morphology and architecture of the present canyon and channel system of the Zaire deep-sea fan

Abstract

The Zaire deep-sea fan is one of the largest fans in the world still affected by turbidite sedimentation along a unique active meandering turbidite channel. This active channel is fed by turbidity currents, which are generated at the Zaire River mouth, and flow via a deeply entrenched canyon across the shelf and the continental slope. Based on a detailed study of the morphology and architecture of the present Zaire Canyon/Channel, several main zones can be defined (the canyon, the upper-fan valley, the upper and the lower channel-levee system leading into distal lobes). They are characterised by different behaviours in terms of erosion, transport and sedimentation within the canyon/channel. An important characteristic of the Zaire Canyon/Channel is the deep incision of the thalweg, well below the regional sea floor along its whole path. The origin of this entrenchment may be linked to the incision of the Zaire Canyon back across the shelf during the last sea-level rise. This incision of the canyon has allowed the continuity of turbidite activity during the Holocene, in maintaining the connection between the canyon head and the river mouth (in contrast to most of other large deep-sea fans, which are generally inactive during highstands). The entrenchment of the Zaire Canyon/Channel limits the overflow of turbidity currents and the turbidite sedimentation over levees, and prevents avulsion along the upper part of the Zaire Channel. Most of the sediment transported in turbidity currents are probably led down to the lower channel-levee system and the distal lobes.