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
Saiu agora em novembro o número especial da Geo-Marine Letters, comemorativo dos 50 anos do PGGM (Programa de Geologia e Geofísica Marinha). Este número especial reune 23 trabalhos de pesquisadores brasileiros principalmente na área da geologia e geofísica marinha. Oito destes trabalhos são contribuições dos GTs 1.1 e 2.1 do inctAmbTropic. Os trabalhos e respectivos links encontram-se listados abaixo:
Shallow sedimentation of Natal shelf and coastal erosion implications, NE Brazil
Structural controls on the morphology of an extremely narrow, low-accommodation, passive margin shelf (Eastern Brazil)
Organic matter in the deltaic clinoform of the São Francisco River (Eastern Brazil)
Quantifying the high coastal dynamics of tropical mesotidal barrier island-spit systems: case study in Northeast Brazil
Geodiversity as an indicator to benthic habitat distribution: an integrative approach in a tropical continental shelf
Antecedent topography controls preservation of latest Pleistocene-Holocene transgression record and clinoform development: the case of the São Francisco delta (eastern Brazil)
The Santo Antônio Bank: a high-resolution seismic study of a deflected ebb-tidal delta located at the entrance of a large tropical bay, eastern Brazil
Statistical approach on mixed carbonate-siliciclastic sediments of the NE Brazilian outer shelf
Pesquisadores integrantes do Inct AmbTropic II, do Gupo de Trabalho 1.2 Recifes e ecossistema coralinos, acabam de publicar o artigo "Diversity patterns of reef fish along the Brazilian tropical coast" na revista científica Marine Environmental Research.
Nesse trabalho eles estudaram 100 recifes ao longo de 2.000 km da costa para entender como se distribui a diversidade de peixes nos recifes de coral do Brasil.
"Descobrimos que a maior parte das espécies são raras, geralmente ocorrendo em número reduzido ao longo de toda costa, exceto em determinados tipos de recifes onde foram mais abundantes.
Essa grande proporção de espécies raras revela uma maior vulnerabilidade das comunidades de peixes recifais. Nem compreendemos o potencial danoso de perder estas espécies, pois várias delas são muito pouco estudadas, justamente por serem difíceis de achar. Ao conseguirmos determinar que estes peixes preferem certos recifes, podemos identificar quais locais são prioritários para dedicar esforços e assim garantir sua conservação."
Se você se interessou sobre o trabalho, ele estará disponível em https://authors.elsevier.com/a/1bcDTW5UJDWLr até o dia 10 de outubro, para download livre de cobranças. Após este período, você poderá acessar o artigo em www.doi.org/10.1016/j.marenvres.2020.105038 mas você pode ser cobrado pelo acesso à versão completa do trabalho.
English version
In our work “Diversity patterns of reef fish along the Brazilian tropical coast”, recently published in Marine Environmental Research, we studied a hundred reefs spanning 2.000 km over the tropical Brazilian coastline, aiming to understand how the diversity of Brazilian coral reef fishes is distributed. We found out that most species are rare, occurring in reduced numbers in most sites, but that in some types of reefs they had higher abundances. This greater proportion of rare species reveals a higher vulnerability of reef fish communities. We cannot discern the deleterious implications of losing rare species yet, as they are barely studied because they are hard to find. Nevertheless, as we determine types of reefs they prefer, we can identify priority sites to dedicate measures to assure their conservation.
If you are interested in this work, you can get full access to the article at https://authors.elsevier.com/a/1bcDTW5UJDWLr
This link will be available until October 10th and you are welcome to read or download. No sign up, registration or fees are required. After this period, you can access our paper at www.doi.org/10.1016/j.marenvres.2020.105038 but you can be charged to access the full version of the manuscript.