A B S T R A C TThis study focuses on the analysis of high-resolution seismic profiles, integrated with sedimentological, echosounder, SRTM and satellite image datasets, of the Brazilian continental shelf adjacent to the Rio Grande do Norte State, NE Brazil. Located in the northeast of Brazil, the State of Rio Grande do Norte is bounded by two main coastal and shelf systems: the eastern coastal-shelf, from the Sagi River to the Touros High, and the northern coastal-shelf, extending from Touros High to Tibau. This shelf represents a modern, highly dynamic mixed carbonate-siliciclastic system characterized by reduced width and shallow depths as compared with other parts of the Brazilian shelf. It has an average width of 40 km, the shelf-break lying at a depth of ~ 60 m. This shelf is subject to the full strength of the westerly South Equatorial current combined with high winds and moderate to high tides and waves. A sharply defined stratigraphic boundary, probably between the Pleistocene and Holocene deposits, is clearly to be observed in the seismic record. Incised-valleys extending from the main river mouths (e.g.the Potengi, Açu, and Apodi) to the shelf break dominate the area investigated and may indicate periods of lower sea level. R E S U M OEste estudo está direcionado ao conhecimento da plataforma continental brasileira adjacente ao Estado do Rio Grande do Norte, NE do Brasil, através da analise de perfis sismicos de alta resolução integrados a dados sedimentológicos, batimétricos, SRTM e imagens de satélites. O Estado do Rio Grande do Norte, localizado no nordeste do Brasil, apresenta dois sistemas costeiros-plataformais: Setor Este, do Rio Sagi (divisa PB-RN) ao Alto de Touros e Setor Norte, do Alto de Touros a Tibau (divisa RN-CE). Esta plataforma representa um sistema plataformal moderno misto (carbonático-siliciclástico), altamente dinâmico. É caracterizado por sua reduzida largura e águas rasas, quando comparado com outras partes da plataforma brasileira. A plataforma apresenta largura média de 40 km e a sua quebra encontra-se a profundidades médias de 60 m. A plataforma é sujeita a ação da corrente sul equatorial, combinada a ventos fortes e variação de maré moderada a alta e/ou ondas. Um limite estratigráfico fortemente definido, provavelmente entre os depósitos Pleistocênicos e Holocênicos, pode ser bem observado e vales incisos, estendendo-se a partir dos principais rios (como por ex., Potengi, Açu e Apodi) dominam a área investigada.
A B S T R A C TThis study focuses on the Quaternary sea level changes in the Apodi-Mossoró Estuary and adjacent shelf, Northeastern Brazil, based on the analysis of high-resolution seismic profiles, integrated with echosounder, SRTM and satellite image data. We use these data to develop a relative stratigraphy. An incised-valley extending from the Apodi-Mossoró Estuary onto the shelf dominates the investigated area. In very shallow waters (down to 10 m depth) the channel lies mainly in a NW-SE direction, changing to NE-SW in waters below10 m, in the form of a J-shaped valley. The southern flank of the shallow channel presents an abrupt morphology, probably determined by a residual scarp due to neotectonic reactivation of a pre-existing fault. This incised-valley can be correlated with a former river valley formed during the late Pleistocene fall in sea-level. The base-level change related to this drop in sea level can be regionally expressed on seismic lines as a laterally-continuous stratigraphic surface named Horizon I, interpreted as representing the sub-aerial exposure of the continental shelf. Many incised valleys were excavated on this exposed shelf, including that of the Apodi-Mossoró Estuary and its incised valley system. This incised valley has lain buried since the Holocene transgression. The Holocene sediments present sub-horizontal layers, or they have filled the incised valley with oblique features. R E S U M OEste estudo utiliza a integração de dados sísmicos de alta resolução, batimétricos, SRTM e imagens de satélite para desenvolvimento da estratigrafia relativa visando entender as variações do nível do mar durante o Quaternário no estuário do rio Apodi-Mossoró e plataforma adjacente, nordeste do Brasil. A principal feição identificada foi um canal submerso, na plataforma interna, parcialmente preenchido, provavelmente relacionado com o sistema de vales incisos formado durante o rebaixamento do nível do mar no Pleistoceno. O canal apresenta duas direções principais (NW-SE e NE-SW), em forma da letra J, aparentemente controladas pelas estruturas tectônicas da Bacia Potiguar. A margem oeste do canal é relativamente soerguida em relação à margem leste. Com base nos dados sísmicos foi possível identificar uma descontinuidade presente em toda a área, interpretada como o limite Pleistoceno/Holoceno, bem como sismofácies referentes a padrões de preenchimento e sedimentação do canal submerso e da plataforma durante a subida do nível do mar no Holoceno.
Resumo Diversos estudos de superfície e subsuperfície têm sido realizados sobre a Plataforma Continental Norte do Rio Grande do Norte com o objetivo de se obter sua caracterização física dos sedimentos do intervalo cronoestratigráfico do Cenozóico. O presente estudo sintetiza os resultados obtidos no âmbito geológico e geomorfológico desses trabalhos, complementando-os com novos dados de batimetria e sensoriamento remoto. Esses dados associados aos dados preexistentes de sedimentologia permitiram a delimitação de três ambientes distintos sobre a plataforma e a caracterização das principais feições desses ambientes. O primeiro ambiente foi caracterizado como plataforma interna, a qual apresenta predominância de sedimentos siliciclásticos envolvendo extensos campos de dunas longitudinais sendo limitada pela isóbata de 15 m. O segundo ambiente é a plataforma média a qual caracteriza-se pela ocorrência mista de sedimentos siliciclás-ticos e bioclásticos e dunas transversais entre as isóbatas de 15 e 25m. O terceiro ambiente é a plataforma externa, com sedimentos bioclásticos e proeminentes desníveis batimétricos, sendo mais estreita e com declividade superior a da plataforma média. Essa porção, de plataforma externa, limita-se com a plataforma média por uma extensa linha de antigas rochas praiais na isóbata de 25 m e com o talude continental na isó-bata de 40 m. O talude e o sopé continental apresentam um grande desnível até a planície abissal a cerca de 2000 m. Algumas feições como vales incisos e corpos arenosos isolados interceptam esses três ambientes e geralmente estão associados a controles estruturais provavelmente neotectônicos. Palavras-chave:Plataforma continental, geomorfologia, batimetria e sensoriamento remoto. Abstract Partitioning geomorphology review of the North Continental Shelf of Rio Grande do Norte, Brazil. Different works deal with surface and subsurface geomorphology on Modern ContinentalShelf of Rio Grande do Norte state. Their objectives were the physical characterization of Cenozoic deposits. This paper resumes the obtained results in those previous geomorphology works and inserts new bathymetric and remote sensing data. These data associated with sedimentological data allow a better delimitation of this continental shelf into three different environments: One environment is the inner shelf. In this place there are siliciclastics sediments and large longitudinal dunes under bathymetric depth of 15 meters. The other environment is the mid shelf. This region has a mix of siliciclastic and carbonate sediments, and transversal dunes between 15 and 25 meters deep. The last environment is the outer shelf. Carbonates sediments are dominants in this area. This part of the shelf is narrow between 25 and 40 meters depth. An old beachrock chain at the 25 m isobath marks the limit between mid-and outer shelf. The shelf passes seawards into a steep slope; it extend until the basin plain, about 2000 meters. Others bedforms area also present on this shelf, such as shelf canyons, reefs, isolated shallow-ma...
We examined the abundances of two species of benthic foraminifera that host algal endosymbionts (SBF) in two sedimentary reefal areas (Pirangi and Maracajaú) of Rio Grande do Norte (RN, Brazil). The original dataset is based on 95 samples collected in winter in 2013 and 2014 by divers or grab samplers, and is compared to other known Brazilian reefs. The tests of Amphistegina gibbosa were conspicuous in sediments associated with coral and coral-rubble substrata, whereas tests of Amphisorus hemprichii were best represented in sediments associated with seagrass. Our studies also have revealed that populations of these species are depauperate near tourism sites in Pirangi, as the area is affected by trampling from tourist activities. In the Maracajaú area, these populations are healthier, except at sites severely affected by tourism. Differences in microhabitats of the two taxa are likely to be associated with the degree of anthropogenic influence on the inner shelf at Pirangi compared to the offshore Maracajaú area.
The agglutinated foraminifera Trochammina hadai Uchio (1962), a dominant species in Japan, first appeared as an invasive species in San Francisco Bay, US, in 1983. Trochammina hadai's first appearance in the Brazilian coastal waters of Flamengo Inlet, Ubatuba, Sao Paulo State, is recorded nearly three decades later, in two of thirty-four sediment samples collected in the western portion known as "Saco do Ribeira" in 2010. By 2014 and 2015, the species was found alive in 78% of the samples with relative abundance reaching 18%. We suggest this recent colonization was most likely the result of an introduction by anchor mud on commercial fishing boats and recreational vessels or from fishing bait, and the species' proliferation due to its suitability to live in anthropogenically-induced stressed environmental conditions of the inlet that has affected the ecological dominance of this benthic community.
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