Cânion do São Francisco: nova publicação do inctAmbTropicII

Saiu publicado na revista Geomorphology (IF = 3.819) um novo trabalho no âmbito do inctAmbTropic Fase II intitulado “Continuous canyon-river connection on a passive margin: The case of São Francisco Canyon (eastern Brazil)” de autoria de Rafael Fonseca Ribeiro, José Maria Landim Dominguez, Alana Aderne Santos, e Adriane Gonçalves de Araújo Nunes Rangel. Este trabalho investiga a origem do cânion do São Francisco à partir da integração de levantamentos com batimetria multifeixe, sísmica 3D e trabalhos anteriores publicados por pesquisadores do inctAmbtropic, além de aprofundar o conhecimento sobre a região do delta do São Francisco. Também apresenta pela primeira vez um mapeamento detalhado do talude superior na região.

Localização do cânion do São Francisco e sua relação com o delta homônimo.

Principais feições mapeadas no cânion do São Francisco e regiões vizinhas do talude superior.

ABSTRACT

Submarine canyons play a major role in sediment transfer to the deep sea. When connected with fluvial systems, they can produce large submarine fans, whose sandy bodies have a high potential as petroleum reservoirs. Although canyon-river connections are common on passive margins during lowstands, they are rare during highstands. So far, the only canyon in the Western South Atlantic to have exhibited continuous river connection throughout the Quaternary, regardless of sea level position, is the São Francisco Canyon (SFC) in eastern Brazil. In this study, we used multibeam and 3D seismic records integrated with previously published data to investigate the reasons for the continuous canyon-river connection in the area of the São Francisco River. The SFC comprises two compartments: The Upper and the Mid Canyon. The Upper Canyon indents 15 km of the shelf and acts as an erosive feeder trunk to the São Francisco Submarine Fan. When it emerges on the continental slope (Mid Can- yon), depositional processes dominate; the canyon now begins to meander and the thalweg is bordered by nu- merous terraces and levees. Five stratigraphic units have accumulated in the region of the canyon head since the beginning of the Oligocene. Initially, sedimentation had a uniform aggradational character (Unit 1), which later became more discontinuous in association with the development of reef build-ups (Unit 2) and of a low-lying area around the canyon head. This depression was partially infilled by siliciclastics (Unit 3) and later incised by a precursor of the SFC (Unit 4). The depression still has a morphological expression in the shelf nowadays as a bathymetric low (BL), within which the São Francisco River has built its delta (Unit 5). We hypothesize that the origin and evolution of the SFC is associated with three main factors: (i) breaching by the canyon head of thick carbonates rimming the shelf break; (ii) development of the shelf depression referred above; and (iii) major continental drainage reorganization. Continuous canyon-river connection was ensured by this shelf de- pression, which helped funnel siliciclastic sediments to the canyon and precluded lateral changes to the lower river trunk. Morphological features, such as axial incision of mass movement deposits is suggestive of some, although very limited, modern canyon activity. This case study contributes to a better understanding of river- basin sediment pathways, particularly on passive margins, which are of great importance for the successful ex- ploration of submarine fan systems.

O trabalho completo pode ser acessado em: https://doi.org/10.1016/j.geomorph.2020.107549