Abstract
Abstract Tectonically controlled topography influences deep-water sedimentary systems. Using 3-D seismic reflection data from the Levant Basin, eastern Mediterranean Sea, we investigate the spatial and temporal evolution of bedforms on a deep-water fan cut by an active normal fault. In the footwall, the fan comprises cyclic steps and antidunes along its axial and external portions, respectively, which we interpret to result from the spatial variation in flow velocity due to the loss of confinement at the canyon mouth. Conversely, in the hanging wall, the seafloor is nearly featureless at seismic scale. Numerical modeling of turbidity currents shows that the fault triggers a hydraulic jump that suppresses the flow velocity downstream, which thus explains the lack of visible bedforms basinward. This study shows that the topography generated by active normal faulting controls the downslope evolution of turbidity currents and the associated bedforms and that seafloor geomorphology can be used to evince syn-tectonic deposition.
Highlights
Deep-water fans form the largest sediment accumulations on Earth (Menard, 1955; Jobe et al, 2018) and are archives of past tectonic and climatic events (Blum et al, 2018)
While antidunes are formed by supercritical turbidity currents (Fr > 1), cyclic steps are related to transcritical flows, as each step is bounded at its upstream and downstream end by a hydraulic jump, which is a short zone over which the flow experiences a rapid transition from shallow and supercritical (Fr > 1) to thick and subcritical (Fr < 1) (Parker and Izumi, 2000; Fildani et al, 2006; Cartigny et al, 2011; Kostic, 2011)
Name the Bedform Bounding fault (BBf), generates a 35-km-long and up to 18-m-high fault escarpment at the seafloor, which dips at 35° seaward (Figs. 1 and 2)
Summary
Deep-water fans form the largest sediment accumulations on Earth (Menard, 1955; Jobe et al, 2018) and are archives of past tectonic and climatic events (Blum et al, 2018). Turbidity currents reaching a supercritical status (i.e., densimetric Froude number [Fr] > 1) form bedforms that are considered to be building blocks of deep-water depositional systems (Covault et al, 2017). These bedforms are thought to be responsible for the inception of new slope channels and canyons (Fildani et al, 2013); they shape channel-lobe transition zones and fans (Postma et al, 2016) and focus the accumulation of plastic litter at the seafloor (Zhong and Peng, 2021). It has been proposed that seafloor rugosity, either generated internally (Guiastrennec-Faugas et al, 2020; Heijnen et al, 2020) or caused by external factors (Ercilla et al, 2002; Covault et al, 2014; Maier et al, 2017), controls the velocity of (near)
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