Constraints from the Geomorphological Evolution of Namibia from the Offshore Stratigraphic Record

Joe Cartwright¹ and Roger Swart^2
1Cardiff University, Cardiff, United Kingdom
²Consultant, Windhoek, Namibia

The continental margin of Namibia is an ideal setting for the study of plume/margin interactions and for stratigraphic analysis of continental denudational history. We present a synthesis of observations made from over 20,000km of offshore seismic data. From these we correlate significant stratigraphic events in the offshore with important landscape elements onshore in order (1) to constrain the temporal evolution of the onshore geomorphology and (2) to explain features in the sedimentary transport systems offshore that have their origins in fluvial evolution onshore.

We have defined all the major deltaic depocentres and can relate these to drainage evolution. We conclude that there was a significant phase of uplift of the inner part of the margin during the Late Cretaceous to early Eocene along most of the margin. This is expressed as a major shallow marine planation surface, and truncation indicates over 500m of uplift close to the modern coastline position. This uplift varied along strike, and induced the formation of numerous submarine canyons. Reconstruction of depth sections shows that the Great Escarpment cannot be related to rift margin fault systems except over a strike length of some 200km in the central region of the margin. Elsewhere along its 1500km length, it appears to have developed by retreat from the well-defined hinge zone separating the rotationally subsiding offshore sector from the static or uplifted elements of the continental interior. We see no direct evidence for plume-related uplift prior to the Late Cretaceous i.e. some 50My after the eruption of the Etendeka flood basalts.

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