Geomorphology and sedimentary features in the Central Portuguese submarine canyons, western Iberian margin

摘要: Abstract The Central Portuguese submarine canyons (Nazare, Cascais and Setubal–Lisbon canyons) dissect the Western Iberian margin in an east–west direction from continental shelf, at water depths shallower than 50 m, down to Tagus abyssal plains, exceeding 5000 m. We present analysis of geomorphology sedimentary processes that can be inferred observed morphology three canyons, based on a compilation swath bathymetry data TOBI deep-towed side-scan sonar imagery. This first complete detailed mapping reveals substantial differences their morphologies downslope evolution. are divided into sections: 1) canyon head upper reach, 2) middle canyon, 3) mouth distal part. heads reaches severely indented they characterised, Nazare by sinuous V-shaped valleys entrenched within high walls occupied rock outcrops dissected gullies. is complex, with multiple branches axial gradients signs mass wasting. Middle sections, slope, display incisions perched, stacked terraces, affected debris avalanches originating walls. At base show many characteristics channel-lobe transition zones: erosional features such as isolated amalgamated chevron scours, depositional bedforms mud gravel waves. Pervasive scouring occurs up 95 km beyond mouths. By contrast, opens 27 km wide 94 km long channel, whose flat-bottomed thalweg sediment waves, irregular, comet-shaped crescentic second-order channel. Transverse, kilometre-scale waves occupy overbank area southern channel margin. result erosive processes, subsequent transport deposition, instability, whereas inherited tectonic fabric controls location. Morphological between explained main mechanisms driving activity. Overall, these morphological suggest have acted efficient conduit deep basin, transporting large quantities material sea during high-energy events.