THE Cananéia graben This paper aims to contribuite for the best understanding of the geological evolution of Cananéia-Iguape coastal plain by using Gravity method. Gravity survey was performed on Cananéia-Iguape region in the southern part of the State of São Paulo, Brazil. The survey was conducted on 280 gravity stations along this area, which has never been surveyed before by using this method. Analysis of achieved data allowed the identification of two significant gravity anomalies: one refers to a prominent gravity high related to the basement rock reached at a deph of 47 meter (well IGG-1) ;the other one, refers to a large gravity low and corresponds to a thick sediment basin located in the central portion of Cananéia Island and southern part of Comprida Island. Two topographic profiles of the basement rock in the surveyed area were achieved by analysing the gravity data along two longitudinal modelled cross-sections of Comprida Island. It shows a thickening of the sedimentary deposit towards the continent in the area of gravity low. The interpretation of gravity data in conjunction with geological and aeromagnetic data shows that the evolution of this coastal plain may be conditioned by a system of normal faults, which may define the graben here named Cananeia Graben.
. Abstract: Cananéia-Iguape coastal system is located in the Southem part ofSão Paulo State. A 72 km long barrier beach named Ilha Comprida separates it from the Atlantic OceanoBased on studies of the evolution of channel margins, bottom sediment distribution and hydrodynamic pattem of the Cananéia-Iguape system, a relationship between the general pattem of water circulation (tidal currents and time variable river discharge) and the spatial distribution of bottom sediments within the system were stablished. Sedimentary structures, like large sand waves (1-2 m heigth and 20 to 30 m length), were identified in the central part ofthe studied area (Ponta do Frade -Mar de Cananéia) as also near the Subauma river (Mar Pequeno). These bottom structures are the result of strong tidal currents acting over sandy sediments, originated from quatemary deposits. The dividing point between the ebb tidal currents of opposite direction were inferred through the asymmetry of sand waves indicating in the middle of Mar Pequeno channel, about 10 km apart from the former inferred point.. Resumo: O sistema Cananéia-Iguape é separado do oceano pela Ilha Comprida, com aproximadamente 70 km de extensão, tendo como limites ao sul e ao norte, respectivamente, as desembocaduras de Cananéia e Icapara. Estudos sobre as modificações na configuração das margens do sistema, no padrão de distribuição sedimentar, bem como sobre o conhecimento do padrão hidrodinâmico evidenciaram a interrelação existente entre os mecanismos de circulação geral, condicionados principalmente pelas correntes geradas pelas marés e a variação temporal de descarga de água doce, e a distribuição espacial dos sedimentos de superficie dos fundos dos canais. Dentre as feições sedimentares identificadas nas superficies de fundo destacam-se as ocorrências de marcas onduladas de grande porte (1 a 2 metros de altura e comprimentos de onda de 20 a 30 metros) concentradas no canal entre a Ponta do Frade (Mar de Cananéia) e a foz do Rio SubaÚ1na(Mar Pequeno). Estas feições de fundo resultam da dinâmica junto aos fundos dos canais, sob forte influência das correntes de maré, sobre sedimentos predominantemente arenosos, cujas fontes atuais são os depósitos quatemários de planície costeira depositados durante os eventos transgressivos/regressivos quatemários. A análise das orientações das correntes de maré, indicadas pelas marcas onduladas assimétricas, permite concluir que o local que representa, no processo hidrodinâmico da área, o ponto de inversão do sentido das marés vazantes, anteriormente atribuído à área da Pedra do "Tombo", apresenta-se, na verdade, deslocado cerca de 10 km no sentido SW.
We present new evidence for the existence of a large pockmark field on the continental slope of the Santos Basin, offshore southeast Brazil. A recent high-resolution multibeam bathymetric survey revealed 984 pockmarks across a smooth seabed at water depths of 300–700 m. Four patterns of pockmark arrays were identified in the data: linear, network, concentric, and radial. Interpretation of Two-dimensional multi-channel seismic reflection profiles that crosscut the surveyed area shows numerous salt diapirs in various stages of development (e.g. salt domes, walls, and anticlines). Some diapirs were exposed on the seafloor, whereas the tops of others (diapir heads) were situated several hundreds of meters below the surface. Extensional faults typically cap these diapirs and reach shallow depths beneath the seafloor. Our analysis suggests that these pockmark patterns are linked to stages in the development of underlying diapirs and their related faults. The latter may extend above salt walls, take the form of polygonal extensional faults along higher-level salt anticlines, or concentric faults above diapir heads that reach close to the seafloor. Seismic data also revealed buried pockmark fields that had repeatedly developed since the Middle Miocene. The close spatio-temporal connection between pockmark and diapir distribution identified here suggests that the pockmark field extends further across the Campos and Espírito Santo Basins, offshore Brazil. Spatial overlap between the pockmark field topping a large diapir field and a proliferous hydrocarbon basin is believed to have facilitated the escape of fluid/gas from the subsurface to the water column, which was enhanced by halokinesis. This provides a possible control on fossil gas contribution to the marine system over geological time.
A estratigrafia rasa da Ilha Comprida, localizada no litoral sul do Estado de São Paulo, foi analisada em detalhe através de perfis de radar solo penetrante (GPR), executados ao longo da estrada que corta transversalmente a ilha em sua porção extremo sudeste. O GPR constitui-se num método geofísico de alta resolução, com vasta aplicação em estudos de áreas costeiras. Registros de excelente qualidade obtidos neste estudo possibilitaram a visualização de características da estratigrafia rasa da Ilha Comprida, que foram correlacionadas ao modelo evolutivo descrito para a área. A interpretação dos dados revelou a ocorrência de três unidades estratigráficas, separadas por contatos bastante conspícuos identificados nos registros. As duas unidades superiores corresponderiam a depósitos holocênicos, formados em eventos transgressivo e regressivo, sendo este último responsável pela formação de cordões arenosos claramente identificados nos registros.
An experimental investigation has been carried out using GPR -Ground Penetrating Radar method in Taquari River, located in Pantanal Matogrossense BasinBrazil, in order to understand the silting process on the river bottom and also to map the channels along the river, that is essential to local navigation. Many GPR profiles have been carried out in Lower Taquari river, near Santa Maria and Porto Santa Luzia farms. Preliminary interpretations were encouraging, allowing to located the channels of the river and the occurrence of very big sand deposits, showing the viability of GPR application to Taquari river sedimentation process studies. All data collected are now been analysed in order to understand the local dynamic sedimentation process, as part of a MSc. Dissertation in progress by an IAG-USP student. Results from these geophysical investigations are going to serve as guidance to multidisciplinary studies of Pantanal Program, by government of Mato Grosso do Sul State.Keywords: GPR-Ground Penetrating Radar, Taquari River, Pantanal Wetland, silting up, River Channel. RESUMOUm levantamento experimental GPR (Ground Penetrating Radar) foi realizado no Rio Taquari, na Bacia do Pantanal Matrogrossense, Brasil, visando entender os processos de assoreamento na base do Rio e mapear os canais ao longo do Rio, que são essenciais para a navegação local. Muitos perfis GPR foram realizados no baixo Taquari, próximos à Fazenda Santa Maria e à Fazenda Porto Santa Luzia. Interpretações preliminares foram interessantes, permitindo localizar os canais do Rio e a ocorrência de grandes depósitos de areia, mostrando a viabilidade das aplicações do GPR em estudos de processos de sedimentação no Rio Taquari. Todos os dados adquiridos estão sendo analisados visando entender a dinâmica local nos processos de sedimentação, como parte de uma dissertação de mestrado em andamento por um estudante no IAG-USP. Os resultados deste levantamento geofísico servem com um guia para os estudos multidisciplinares do Programa Pantanal do governo do Estado do Mato Grosso do Sul.Palavras-chave: GPR-Ground Penetrating Radar, Rio Taquari, Pantanal Matogrossense, assoreamento, canais do rio.
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