Effects of a regional décollement level for gravity tectonics on late Neogene to recent large-scale slope instabilities in the Foz do Amazonas Basin, Brazil

Geomorphometric Seabed Classification and Potential Megahabitat Distribution in the Amazon Continental Margin

“…Gravity tectonics was the main driver responsible for shaping the erosive and non-erosive continental slope over the time (Reis et al, 2016). The great amount of sediments that reached the shelfslope transition through the geological time generates mass movements that lead to steep scarps and mega slides Reis et al, 2016). Sediment input is related to the heterogeneous continental slope morphometry among sectors.…”

“…Akin to the continental shelf, which presents a great diversity of facies (Dutra, 2018), the Continental Slope Megahabitat could also be further classified in mesohabitats and macrohabitats if other investigation scales are considered. Considering the important role played by the gravitational tectonics in shaping the seafloor, seafloor higher-resolution data have shown that gravitational collapse is expressed at seabed as ridges formed by paired extensional-compressional belts and thrust faults (Reis et al, 2016;Ketzer et al, 2018). In some areas of the upper slope, gas seeps are observed in association with these faults, which could be another important driver for supporting specific deep-sea habitats.…”

“…Figure 4 depicts a few Steeper Slope Classes in a more distal part of the Amazon Fan. It is possible that changes in slope angle, creating a rough topography, are related to seabed deformation due to the mega mass transport deposits (Reis et al, 2016).…”

“…Later on, from Mid-Pleistocene to Holocene, progradation produced a steeper slope prone to failure. Gravitational tectonics was responsible for mass wasting events, forming large megaslides, or mass-transport complexes that mobilized kilometer-thick deposits, extending for thousands of kilometers in the Amazon Fan (Reis et al, 2016).…”

Gas Seeps at the Edge of the Gas Hydrate Stability Zone on Brazil’s Continental Margin

“…Sediment loading in the Rio Grande Cone and in the Amazon deep-sea fan resulted in largescale gravitational collapse, expressed as paired belts of extensional and compressional structures rooted on deep detachment surfaces. In contrast to the mainly stratified internal character of the Rio Grande cone, the Amazon fan is characterised by giant mass transport deposits recording sediment failure from the upper slope [35,44]. High rates of sedimentation (including of organic matter), particularly in the upper Amazon fan, contribute to low geothermal gradients (15-19 °C /km, based on BSR depth and bottom-hole temperatures; [45]), which together with low bottom water temperatures, result in a potential thick gas hydrate stability zone.…”