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Semi-automated bathymetric spectral decomposition delineates the impact of mass wasting on the morphological evolution of the continental slope, offshore Israel

October 30, 2019

Understanding continental slope morphological evolution is essential for predicting depositional systems and reservoirs in the adjacent basin. However, present-day slope seafloor-morphology is complicated by shaping processes, which are not readily separable through pure bathymetric analysis. This study aims to explore the utility of bathymetric spectral decomposition in order to separate and characterize interleaved seafloor imprints of mass wasting, and for clarifying their role in the morphological evolution of the slope of the southeastern Mediterranean Sea passive continental margin. Controlled by margin-parallel transport of Nilotic sediments from the south, this margin exhibits an intertwined variety of mass transport features. Our spectral decomposition of digital bathymetry, integrated with interpretation of seismic reflection data, highlights the long-term shape of the slope and separates the observed mass transport elements into several genetic groups: 1) a series of ~25 km wide, now buried slide scars and lobes; 2) slope-parallel bathymetric scarps representing shallow faults; 3) slope-perpendicular, open slope slide scars; .4) bathymetric roughness representing open slope debris lobes; 5) slope confined gullies. Our results provide a multi-scale view of the interplay between sliding and erosive flows, and shallow faulting accommodating internal deformation and salt retreat, in the evolution of continental slope morphology. The base of the slope and focused disturbances are controlled by relatively deep-seated (~1 km) salt retreat, and therefore mimic the Messinian base of slope. The top of the open slope is delimited by faults, accommodating internal collapse of the margin. The now-buried slide scars appear to have been cohesive and slope-confined and have mostly nucleated along the upper slope faults. The collapse of sediments infilling accommodation spaces created by these buried slides nucleated the more recent open slope slides. The open slope slides transported ~10 km3 of sediments, depositing on the lower slope and basin edge an average sediments thickness of ~3 m. Such a thickness is a significant fraction of the sediments accumulated along the base of the studied continental slope within the last <50 ka. South to north changes in population and size distribution of the open-slope slide scars highlight their role in counterbalancing the northwards diminishing sediment supply and helping to maintain a long-term steady-state bathymetric profile. The latest phase slope-confined gullies were presumably created by channeling of bottom currents into recent slide-scar depressions, possibly establishing incipient canyon headword erosion.