Submarine Mass Wasting in Carbonate Environment - Preconditions, Triggers, and Consequences

of a dissertation at the University of Miami. Dissertation supervised by Professor Gregor P. Eberli. No. of pages in text. (166) Submarine mass wasting events have been the focus of numerous studies all over the world to derive common preconditions and triggering mechanisms leading to the failure of sometimes substantial amounts of sediment along submarine slopes. The consequences of such failures have implications on the sedimentary architecture of submarine slopes, they constitute an integral part of the depositional system, and can pose geohazards like causing large tsunami waves, or destroying seafloor infrastructure. Especially in areas close to densely populated coastal communities, such geohazards pose a substantial threat. Identifying preconditions and triggers leading to such failures is challenging, as direct observations are limited, and in situ monitoring extremely expensive. This study presents the results of an integrated approach investigating submarine mass movements in the carbonate environment along western Great Bahama Bank using multibeam bathymetric, seismic, geotechnical, and sedimentological data in conjunction with numerical models. Numerical models of past events, documented in high-resolution bathymetric data, show that submarine landslides and large margin collapses along western great Bahama Bank had and have the potential to create devastating tsunami waves leaving the coastal communities of Florida and northern Cuba vulnerable. Rapid propagation through the Straits of Florida makes early warning and mitigation of such events challenging. The history of mass wasting events is documented in the sedimentary record along the slopes between western Great Bahama Bank and the eastern Cay Sal Bank and within the Santaren Channel, with numerous mass wasting events since the Middle Miocene. Whereas the slopes along western Great Bahama Bank are influenced by regularly recurring smaller-scale events, eastern Cay Sal Bank exhibits mass transport deposits at a larger scale, associated with a deep-rooted fault system which relates to Cay Sal’s involvement in the tectonic framework and northward extension of the Cuban fold-andthrust belt. The systematic assessment of bedforms along western Great Bahama Bank yields insight into the processes responsible for sediment deposition and redistribution along the slope. The leeward slopes are influenced by eustatic sea level change, a system of cascading density currents and platform parallel contour currents that lead to the deposition of a Holocene sediment wedge, onlapping onto the steep escarpment, plunge pools at the base of the escarpment, and extensive sediment wave fields along the entire slope. The combination of rapid sediment export during sea level highstands and slow to non-deposition during sea level lowstands, characteristic for carbonate slopes, results in an alternation of fine grained highstand deposits with lithified lowstand layers, containing coarser grained sediment. Undrained shear strength profiles from carbonate slopes all over the world reflect this stratigraphic framework and confirm that the zones of minimal shear strength align with changes in depositional environment and therefore relate to sea level change and sequence boundaries.