Understanding the influence of passive continental margin geometry on shallow and deep hydrodynamic and sedimentary processes

• Main Author: Thran, Amanda Chayce
• Format: Thesis
• Language: English
• Published: University of Sydney 2020
• Subjects: numerical modelling; sedimentology; coastal; contourite; tsunami; surface processes; Sea ice
• Online Access: https://hdl.handle.net/2123/22836

The hydrodynamic and sedimentary processes that operate on submerged passive continental margins are often difficult to study due to their remoteness and the sparse data coverage associated with these regions. Numerical simulations provide a powerful experimental framework to investigate such physical processes. In this thesis, a variety of numerical models are used to provide process-based insights into the regional-scale hydrodynamic and sedimentary consequences of margin flows. Margin geometry plays a critical role in preconditioning and modifying three types of flows: along-slope flows, down-shelf and down-slope flows, and cross-shelf flows. In a study of along-slope flows, ocean sea-ice model results indicate that contourite drifts, which are anomalously high accumulations of deep-sea sediments, form in areas that exhibit vigorous bottom current activity. Simulations show that bottom current speeds fluctuate more over contourites, suggesting that contourite formation can be attributed to repeated acute, high-energy bottom current events rather than continuous accumulation under ambient background flow. In a study of down-shelf and down-slope flows, surface and marine process-based simulations indicate that carbonate platforms play a fundamental role in the regional geomorphological development of the mixed carbonate-siliciclastic Great Barrier Reef margin. Finally, in a study of cross-shelf flows, tsunami propagation simulations show that coral reef ecosystems offer varying degrees of protection to the coastline. Various factors related to bathymetry dictate the degree of wave energy attenuation by coral cover. These findings highlight the importance of site-specific seafloor geometry in modulating hydrodynamic and sedimentary processes in margin settings. Additionally, they also provide new mechanistic insights into the hydrodynamic and sedimentary consequences of topographically-mediated margin flows.