Bottom current influence on deep-marine sedimentary systems

  • Arne Fuhrmann

Student thesis: Phd


Sediment gravity flows transfer vast amounts of sediment, anthropogenic pollutants and organic carbon into the deep-marine realm where they form some of the biggest sedimentary systems in the world. Here, they may interact with margin parallel bottom currents that affect the flows and their deposits. The degree of interaction is governed by the frequency and strength of both along- and down-slope processes which are ultimately controlled by large scale, external forcing such as climate, tectonics and sea-level, as well as local controls. The aim of this thesis is threefold: i) Understand the influence of bottom currents on deep-marine sediment gravity flow systems; ii) Describe the external and internal mechanisms that control the stratigraphic evolution of these sedimentary systems across different scales; iii) Develop generic sedimentological models that help understand and predict these systems globally. These aims are achieved by combining high resolution sea-floor data and near bed bottom current measurements from offshore Mozambique with extensive, high resolution 3D seismic reflection and a total of 1.5 km of core data from ancient sedimentary systems offshore Tanzania. Modern bottom current velocities, orientation and sea-floor morphologies are used to infer the palaeo-current circulation and the evolution of deep-marine sedimentary systems along the East African Margin. The key findings of this research are: 1) the presence of a northwards flowing intermediate near- bed bottom current along the Tanzanian Margin; 2) asymmetrical levee-drift deposits evolve along the down current side of deep-marine channel complexes (in respect to the bottom current). Their facies stacking pattern depends on the frequency of highly energetic, sediment laden turbidity currents that are superimposed on quasi-steady bottom currents; 3) long term stratigraphic stacking patterns are controlled by large scale forcing mechanisms such as climate, tectonics and sea-level as these ultimately control the temporal interaction of turbidity- and bottom currents; 4) individual channel complexes show along system variations in facies stacking patterns and asymmetry that is controlled by topography (drift or tectonic), gravitational asymmetrical overspilling along channel bends and slope parallel/oblique channels, as well as local increases of bottom current strength; 5) terminal lobe complexes along bottom current influenced margins are mainly influenced by bottom current related relief. Sedimentary signals of bottom current influence observed in core are limited to lobe off-axis and fringe deposits where turbidity currents wane and are subject to modification by bottom currents. The results of this study emphasize the importance of bottom currents in controlling the morphology and facies variability of deep-marine sedimentary systems.
Date of Award31 Dec 2020
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorMads Huuse (Supervisor)


  • Channel
  • Lobe
  • Ocean currents
  • Contourite
  • Turbidite
  • Mixed-turbidite-contourite system
  • Deep-water systems

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