Résumé
The growth of the Amazon fan has been accompanied by recurrent fan-wide megaslides,and by gravitational collapse on shale detachments to form extensional and compressionalbelts across the shelf and upper slope, respectively. Seismic datasets show the compressionalbelt (500-2250 m water depth) to contain a gas hydrate system characterised by bottomsimulatingreflection (BSR) patches aligned with thrust-folds, in places rising towards ventlikeseafloor morphologies. Multibeam data acquired in 2016 across part of the belt revealeddozens of gas flares rising from seafloor mounds. The wider extent of degassing is unknowndue to a lack of acoustic imagery, notably below the compressional front. Here we examinefluid expulsion from the Amazon fan using acoustic data acquired in water depths of 100-4100 m during the 2023 AMARYLLIS-AMAGAS I campaign, and 3D seismic data availableacross parts of the upper slope (ANP Brazil). Over 400 gas flares are identified in depths of100-1900 m, with peak abundance near the upper limit of the methane hydrate stability zone(MHSZ) in depths of 570±40 m. About half of flares rise from mounds and/or depressions,half from areas of smooth or faulted seafloor. A semi-automated training approach was usedto capture sub-circular morphologies from bathymetric data (4-50 m grids) for morphometricanalysis. Over 500 features are identified in depths of 275-2265 m, comprising mounds (59%),complex forms (28%) and depressions (13%); the majority (> 96%) are . Our results indicatewidespread fluid expulsion from the Amazon fan within the extensional and compressionalbelts, versus a lack of evidence for venting in greater water depths. The primary controlon degassing of the fan appears to be gravity-driven tectonism, which provides pathways forfluid escape within and above the MHSZ. This is a contribution to studies of gas hydratedynamics and slope stability in the context of the MEGA project (ANR-22-CE01-0031).