Channelised and Open-slope processes of mass sediment transport: their morphological and seismic characterisation from selected Atlantic high productivity regions

The study investigates processes of mass sediment transport in two geologically unique Atlantic margins influenced by high primary productivity, i.e. the Mauritanian and Uruguayan margins. Whereas the Mauritanian margin is dominated by hyper-arid conditions, the Uruguayan margin, on the other hand, is dominated by fluvial sediment inputs. Investigations of the Mauritanian margin are centred on two major features, i.e. the Cap Timiris Canyon and the Mauritania Slide Complex, using combined analyses of hydroacoustic and high resolution multi-channel seismic (MCS) data. An area offshore Uruguay, which is dominated by extensive slope instabilities and mass sediment transport, was also investigated with high resolution MCS data. Results of the study suggest margin physiography have played a key role in pre-determining the style of mass sediment transport which, in both margins, is characterised by a sharp transition from channelised flow processes to large scale mass sediment movements in open slope environments. Entry points of major fluvial systems along the coast were likely to have given rise to canyon processes which were significantly enhanced by the presence of regional structural lineations as in the case of Cap Timiris Canyon. The open slope areas allowed undisturbed rapid sediment build-up leading to extensive slope instabilities. Build-up of excess pore-pressures constitutes the most important trigger mechanism for the large-scale sediment failures in both margins. The mass sediment movements were facilitated by widespread lithological weak layers which were exploited as glide planes. The high marine productivity in the regions significantly elevated organic inputs into both margins and, consequently, enhanced the generation of excess pore pressures as well as the formation of the mud-rich lithologic weak layers. The thesis provides fundamental insights for understanding canyon processes and open slope mass sediment movement along passive continental margins influenced by high productivity.