Characterisation and gradient constraint of mixed debris flow/braided river dominated fans by analysis of Skeleton Coast fan systems in NW Namibia

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There is a controversy concerning the classification of subaerial fans and their distinction from rivers. On one hand the view of a spectrum of subaerial fans comprising (A) debris flow, (B) braided river and (C) and low sinuosity/meandering river dominated end members has gained considerable acceptance in the scientific community. On the other hand it has been proposed that this spectrum is only incompletely developed and that an obvious natural gap in hydraulic character and depositional slope is existing between large low gradient river floodplains and small high gradient alluvial fans. The latter classification would restrict alluvial fans to debris flow dominated types and exclude fans dominated by rivers.Alluvial fan systems, the Sout, Salt, Messum and Horingbaai Fans, of the Skeleton Coast, northwestern Namibia, potentially bridge a gap between braided river dominated and debris flow dominated fan systems. These fans will be analysed in view of their geometries, drainage networks and controls of channel confinement by means of integrating terrain mapping, laser surveying, satellite and aerial photo imagery as well as SRTM data to develop 3D digital models of the fan surfaces. Logging and dating of lithofacies assemblages in modern and ancient fan successions, directional measurements of palaepurrent indicators and analysis of textural and compositional properties of sediments aim to understand nature and causes of depositional processes, age and duration of activity, recent process history and ancient facies sequences. The project will thus considerable support the understanding of controls on depositional processes associated with fan systems and contribute to an integrated classification. Furthermore, the fans need to be compared with ancient equivalents in order to establish their importance in the rock record. This point of view will contribute to the re-evaluation of fan facies in hydrocarbon exploration, specifically with respect to target generation.