New insights into turbidity currents and their deposits in channel mouth settings

  • Jonathan Brian Wilkin

Student thesis: Doctoral ThesisDoctor of Philosophy

Abstract

Turbidity currents, are inherently sensitive to changes in topography. This sensitivity means that the hydrodynamic properties of turbidity currents may be rapidly altered either by changes in slope angle or relative changes in confinement. The relative severity of these changes has important implications for the expected hydrodynamic responses of turbidity currents, but also their interactions with the seabed, and their resultant deposits. This thesis investigates the links between hydrodynamics and deposits of high-density turbidity currents (HDTC) within channel-mouth settings, but also how flow deposit interactions drives the formation of submarine lobes. It achieves this by combining multiple complimentary datasets including experimental research of singular and sequential high-density turbidity currents undergoing an abrupt slope break and loss of confinement, sedimentological fieldwork in the Miocene-aged intramontane Tabernas Basin, SE Spain, and a seafloor study focused on two terminating submarine channels located offshore of Senegal.

Experimental results demonstrate that erosional and bypass features within channel-mouth settings need not be formed by hydraulic jumps. Results describe how HDTCs undergo flow relaxation, a process which elevates their shear velocities causing bypass as their structure collapses towards the bed elevating calculated densimetric Froude numbers. Equally, non-dimensional analysis of the autogenic stacking patterns of submarine-lobe elements finds that lobe-element properties are directly influenced by the interactions of HDTCs with antecedent basin-floor topography. Field results from the Tabernas Basin describe how rapidly transitioning turbidity currents produce complex sedimentological facies. These are characterised by supercritical sediment waves, scours, and high-aspect ratio channels interpreted to have formed within the inner-fan region of a sand-rich submarine fan. Results of the seafloor study links high-resolution geophysical data to a series of sediment cores in order to study the sedimentology, distribution, and hydrodynamic processes that produced a series of unconfined supercritical sediment waves (i.e. net-depositional cyclic steps and antidunes) and large seafloor scours (i.e. isolated, amalgamated, and net-erosional cyclic steps).
Date of Award2024
Original languageEnglish
SupervisorAlan Cuthbertson (Supervisor), Sue Dawson (Supervisor), Dorrik Stow (Supervisor) & Uisdean Nicholson (Supervisor)

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