Atualizado: 27 de abr. de 2021
Saiu publicado no periódico Ocean and Costal Management (IF=2.482) um novo trabalho no âmbito do inctAmbTropic Fase II intitulado "Evaluation of decadal shoreline changes along the Parnaíba Delta (NE Brazil) using satellite images and statistical methods" de autoria de Thiago Augusto Bezerra Ferreira , André Giskard Aquino da Silva, Yoe Alain Reyes Perez, Karl Stattegger e Helenice Vital, que investiga o comportamento da linha de costa do delta do Parnaíba no período 1984-2017. O trabalho concluiu que a redução na descarga fluvial do rio Parnaíba entre 1995-1999 e 2009-2012 foi a causa principal do recuo erosivo experimentado pelo delta.
Comportamento da linha de costa do delta do Parnaíba entre 1984-2017. Vermelho: erosão. Verde: progradação.
ABSTRACT
This study investigated changes of the shoreline position in the Parnaíba River Delta (PRD), which is in an underdeveloped and sparsely populated area. The general behavior of the shoreline between 1984 and 2017 was analyzed using 12 Landsat satellite images and the Digital Shoreline Analysis System (DSAS) software. DSAS applied statistical methods, such as Weighted Linear Regression (WLR) and End Point Rate (EPR), to define whether the shoreline was retreating or accreting. Data analysis revealed that, on a decadal time scale (33 years), 52% of the PRD shoreline retreated under erosional conditions, while 48% accreted. Accretion mainly occurred at the vicinities of the river mouth, especially eastward where the highest progradation rate was observed (maximum of 29 m/year). Shoreline retreat, up to 9 m/year, occurred predominantly in the western part of the PRD and away from the river mouth. However, changes of the general behavior of the shoreline (retreat/accretion) were observed at an inter- decadal time scale, which were positively related to variations in river discharge. Variations of river discharge are directly dependent on the rainfall amount along the drainage basin that, in this region, is controlled by climatic conditions such as El Niño and La Niña. Therefore, the reduced river discharge observed between 1995- 1999 and 2009–2012 (El Niño periods), was the major cause the triggered the observed coastal retreat (>6 m/ year) on PRD shoreline during these periods. Consequently, the variability of natural factors, such as river discharge and rainfall, are the main drivers of shoreline changes on PRD, since anthropogenic impacts have hitherto only marginal effects on the delta region and on the drainage basin of the Parnaíba river.
O trabalho completo pode ser acessado em: https://doi.org/10.1016/j.ocecoaman.2020.105513
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
Amanhã, dia 01 de dezembro de 2020, às 14h ocorrerá uma palestra com o professor Dr. José Maria Landim Dominguez, coordenador do GT 1.1 - Deltas e Erosão da Linha de Costa, em transmissão ao vivo para o canal do YouTube da Pós-Graduação de Geologia da Universidade Federal da Bahia. Link
Não perca!
