Estimation of Real-World Turbidity Current Durations from the Modelling of Levee Paleocurrent Evolution
Abstract
Seafloor channels are the main conduits through which turbidity currents transport sediment to the deep ocean. These channels are commonly self-confined by levees that can stretch laterally for distances orders of magnitude larger than the channel widths. As well as being potentially important hydrocarbon reservoirs, levees arguably represent the best record of flow history due to lower erosion rates than intrachannel locations. It is common for currents to exhibit a large degree of superelevation and overspill, resulting in significant overbank flow across the levee system. Extensive vertical and lateral accretion of the levees suggests large amounts of sediment are being transported in this flow. Here we integrate field, laboratory and numerical simulation data to allow the identification of key flow processes that characterise this overbank flow, at previously unseen levels of both temporal and spatial resolution. These processes include the rotation of the flow towards the current direction in the channel throughout the duration of individual currents, with a greater degree of rotation seen in levee-proximal vs. levee-distal settings. This phenomena is shown, for the first time, to occur in both laboratory scale flows and numerical simulations. Field evidence of this process has also been previously inferred from vertical variations in measured paleocurrent directions within individual ancient sandy levee deposits measured in a range of locations across the levee and was the basis for a conceptual process-based model. Parameterisation of this rotation enables a new approach to estimating real-world flow durations, based upon the magnitude of the current and the degree of observed flow rotation. Accurate modelling of overbank flow also provides us with a key tool in analysing levee aggradation and, subsequently, the coupling of internal and external channel development.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMEP42A..06K
- Keywords:
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- 1825 Geomorphology: fluvial;
- HYDROLOGYDE: 1847 Modeling;
- HYDROLOGYDE: 1862 Sediment transport;
- HYDROLOGY