Colapso gravitacional e estruturação da seção marinha da bacia da Foz do Amazonas no contexto de múltiplos níveis de destacamento

• Autor(a) principal: Silva, Rodrigo Jorge Perovano da
• Data de Publicação: 2009
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Federal Fluminense (RIUFF)
• Texto Completo: https://app.uff.br/riuff/handle/1/18464
• topic: Geologia marinha; Geofísica marinha; Arquitetura sedimentar; Estratigrafia sísmica; Margem equatorial; Tectônica gravitacional; CNPQ::CIENCIAS EXATAS E DA TERRA::OCEANOGRAFIA::OCEANOGRAFIA GEOLOGICA::GEOFISICA MARINHA

The Amazon deep-sea fan is part of the Foz do Amazonas Basin. It comprises a thick prograding siliciclastic prism (~ 10 km thick) related to the Amazon River input since Upper Miocene (~10 Ma). Gravity-driven deep-water fold-and-thrust belts stand as the most remarkable structures along the margin, deforming both the deep-sea fan and earlier marine sequences (Lower Cretaceous-Middle Miocene). Thrust structures, imaged by 2D multichannel seismic profiles, were driven by gravity in a linked extensional-contractional system gliding on weak levels, and driven by sedimentary loading and by the bathymetric slope. Extension is characterized by both basinward- and landward-dipping normal faults on the shelf and upper slope. Downdip contraction induced detachment folds and thrust faults leading to the formation of piggy-back basins. Sliding of the sedimentary section took place along distinct detachment surfaces and, apparently, at different stages of the margin s evolution. At least three main stratigraphic levels have acted as detachment surfaces, at either regional or local scale. An ancient fold-and-thrust belt (poorly imaged on seismic profiles) slides on the basal detachment surface in the central area. The most conspicuous fold-and-thrust belts, running all along the Upper Amazon Fan (down to ~2000 m) detach on an intermediate décollement surface of regional extent. The geometry and structural complexity of these gravitational thrust belts vary along strike, owing to lateral changes in the development of depocenters. Depocenters are significantly more complex along the Northwestern Compartment (where the major margins depocenters are located) and exhibiting evidence of long-lasting deformation from multiple partially-overlapping fronts that resulted in further shortening and its impact on the bathymetry (scarps up to 500 m high). To the South, the system is restricted to pairs of active reverse faults causing no major seabottom relief (inactivated belt) on the South-eastern Compartment. Gravity sliding on the uppermost detachment surface occurs locally, giving rise to antithetic normal faults that segment the main depocenters. To the extreme North and South of the basin, where the sedimentary cover is thinner, gravity structures associated with the uppermost detachment surface differ broadly from features previously described, comprising families of proximal normal growth faults with no downdip toe thrusts.