Padrão morfológico e sonográfico da plataforma continental interna adjacente ao setor Leste da Ilha de Santa Catarina

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Filosofia e Ciências Humanas, Programa de Pós-Graduação em Geografia, Florianópolis, 2015Este trabalho apresenta resultados sobre o padrão morfológico e sonográfico da antepraia e plataforma continental interna, adjacente ao setor leste da Ilha de Florianópolis, entre o complexo praial Barra da Lagoa - Moçambique e a Ponta dos Ingleses. Uma área total de 18 Km² foi sondada, entre 3 e 25 m de profundidade, com 100% de sobreposição. Os dados foram aquisitados com um interferômetro EdgeTech 4600, 540 kHz, o qual forneceu imagens de sonar de varredura lateral, batimetria de varredura, bem como retroespalhamento. Através das imagens de sonar de varredura lateral (SVL) foi possível identificar a presença de diferentes tipos de refletores (sedimento) e suas feições associadas, bem como medir o comprimento das formas de leito e feições. Os resultados, sobre a composição do leito, foram validados utilizando os dados de retroespalhamento, bem como as classificações supervisionada e não supervisionada, além de amostras de sedimento obtidas in situ. A batimetria de varredura proporcionou informações sobre a morfologia e declividade da plataforma continental interna, além da altura e perfil das formas de leito e feições. No complexo praial Barra da Lagoa - Moçambique foi identificado feições denominadas sorted bedforms, que são depressões formadas por areia grossa e mal selecionada com a presença de marcas onduladas, adjacente a uma areia fina e bem selecionada. Estas depressões variaram entre 0,5 e 1 metro em relação ao leito e apresentaram largura entre 5 e 450 m, e comprimento entre 10 e 900 m, perpendiculares a linha de costa, caracterizando uma plataforma continental interna heterogênea, composta por areia grossa (1 mm) e areia fina (0.2 mm). Através das imagens de SVL e da batimetria de detalhe em frente a Ponta das Aranhas, identificou-se a presença de megaondulações, classificadas como assimétricas, catenárias com comprimento de onda entre 6 e 15 m e altura entre 0,5 e 1,2 m. Visto que a forma destas apresentou uma assimetria para norte, assim indicando um transporte de sedimento neste mesmo sentido, caracterizando uma transposição sedimentar (sediment bypassing) ao longo do promontório. Devido a este transporte para norte, foi observado um acumulo de sedimento na parte central do promontório, sendo esta feição classificada como shelf sand body (SSB).Na plataforma continental interna e antepraia do Santinho foi identificada uma sequencia de formas de leito, que evoluiu de marcas onduladas simétricas, para assimétricas, sinuosas, então lunares e leito plano. As feições simétricas apresentaram comprimento de onda de 1 m, enquanto que as simétricas sinuosas, entre 1 e 1,5 m e as lunares, 2 e 5 m. Com a batimetria de varredura, foi possível observar que esta sequência teve seu inicio em 12 m de profundidade, indicando a provável profundidade de fechamento. A altura das marcas onduladas simétricas variou entre 0,05 e 0,15 m, das assimétricas sinuosas, 0,15 e 0,30 m e das lunares 0,25 e 0,50 m. O perfil das formas assimétricas apresentaram a maior inclinação em direção à costa, indicando a direção de migração destas feições. Esta sequência de formas de leito foi formada pela interação da assimetria do movimento orbital da onda com o leito, a qual aumenta à medida que a profundidade diminui. Em frente a Ponta dos Ingleses, através das imagens de SVL foi observada a presença de megaondulações tanto na parte central quanto norte. Estas apresentaram comprimento entre 5 e 12 m, altura variando entre 0,5 e 1 m e foram classificadas como assimétricas, catenárias. O perfil destas megaondulações indicam que estas migram em sentidos opostos, ou seja, as feições presentes na parte central do promontório, apresentaram a face com maior inclinação para norte, enquanto que as feições no norte do promontório, apresentaram a maior inclinação para oeste/sudoeste. Assim, através do perfil das megaondulações, foi possível notar a presença de correntes em sentidos opostos, as quais acabaram por gerar estas feições. Também foi observado que entre estas feições ocorre um acumulo de sedimento, sendo a feição resultante deste acumulo classificada como SSB.Abstract : This study investigates the shoreface and inner continental shelf morphology and seafloor geoacustics pattern adjacent to the eastern sector of Florianópolis Island, between Barra da Lagoa - Moçambique beaches and Ingleses headland. An 18 km² area was surveyed, between 3 to 25 m depth with 100% of coverage. The data was acquired with an interferometer EdgeTech 4600, 540 kHz, which provided side scan sonar images, swath bathymetry and backscatter. Through side scan images it was possible to identify different sediment types and associated features, as well to compute the length of those bedforms and features. The seafloor patterns were validated with backscatter data, as well with supervised and unsupervised classification and sediment samples. Swath bathymetry provided information about morphology and inner continental shelf slope, together with bedforms shape and elevation. At Barra da Lagoa - Moçambique beach, sorted bedforms were identified, which consist of depressions containing rippled coarse sand surrounded by well sorted fine sand. These features varies from 0,5 to 1,0 m in relief, 5 to 450 m wide and 10 to 900 m long, and are shoreline perpendicular, characterizing an heterogeneous inner continental shelf, composed by coarse sand (1 mm) and fine sand (0,2 mm). Side scan images and swath bathymetry was used to identify megaripples in front of Aranhas headland, classified as asymmetrical, catenary with wavelength in the order of 6 to 15 m and height between 0.5 to 1.2 m. Its profile presented a steeper lee angle, which reflects a northward bedload transport, an indicative of northerly headland sand bypassing. This northward sand transport has resulted in sediment accumulation along the central section of the promontory, and was classified as shelf sand body (SSB). The Santinho inner continental shelf and shoreface contained a shoreward bedform sequence that evolved from symmetrical ripples, to asymmetrical, long crested than to lunate ripples and finally to a flat bed near the breaker zone. The symmetrical ripples presented wavelength in the order of 1 m, while the long crested between 1 to 1.5 m and the lunate, 2 to 5 m. Swath bathymetry revealed that this sequence started around 12 m depth, indicating the possible closure depth. The height of the symmetrical ripples varied between0.05 to 0.15 m, while the asymmetrical long crested, 0.15 to 0.30 m and the lunate ones, 0.25 to 0.50 m. The asymmetrical bedforms has a steeper angle shoreward, indicating the direction of migration. This bedform sequence is a result of the interaction of the wave orbital asymmetry with the seafloor, which increases as depth decreases. In front of Ingleses headland, side scan images showed megaripples in the central and southern section, with wavelength between 5 to 12 m and height in the order of 0.5 to 1 m, being classified as asymmetrical, catenary. The profile of the megaripples indicates that they migrate in opposite direction, it means, the bedforms in the central section presented a steeper angle northward, while the features in the northern section presented the steeper angle southward. Based on the profile of the megaripples, it was possible to notice the presence of currents in opposite directions, which may have generated those megaripples. Also, it was observed that between those opposing megaripples field a sediment accumulation is occurring, and also was classified as shelf sand body (SSB)

Shallow gas seismic structures: forms and distribution on Santa Catarina Island, Southern Brazil

Este artigo apresenta a distribuição espacial das estruturas de gás raso e as classifica com base em dois conjuntos de dados de registros sísmicos diferentes com o CHIRP, um na Lagoa da Conceição (CL) e o outro na Baía Norte (NB), ambos na Ilha de Santa Catarina, sul do Brasil. Os dados de sonar de varredura lateral da CL foram usados para facilitar a interpretação. Os dados sísmicos de subsuperfície (SB) foram processados e interpretados por meio do software SeisPrho e os dados obtidos com o sonar de varredura lateral (SSS), pelo software SonarWiz5. A medida espacial foi realizada por intermédio de GIS. As estruturas de gás raso foram definidas de acordo com as formas apresentadas nos registros sísmicos (eco-caráter). Na CL, as acumulações rasas de gás foram encontradas sob a forma de escapes nas exsudações e feições apresentando estruturas de gás superficial, entre a superfície e 8,20 ms (cerca de 12,3 m). Estas acumulações de gás foram encontradas na forma de Cobertura Acústica com Plumas Acústicas associadas, além de Sombra Negra. As pockmarks foram observadas no fundo da lagoa, ligadas aos escapes de gás (diâmetro médio de 0,97 ± 0,19 m e densidade de 54 a 242 unidades por 50 m2). Na NB observou-se três tipos de estruturas de gás raso no perfil sísmico, ou seja, de Cobertura Acústica, Pináculos de Turbidez e Plumas Intrssedimentares. A profundidade variou da superfície até 12,10 ms (cerca de 18,15 m). Em ambos os ambientes, o gás é expelido a partir do sedimento para a coluna de água. As pockmarks na CL e na NB, as feições de pluma acústica e os sedimentos ricos em enxofre total validam essa evidência.This paper presents the spatial distribution of shallow gas structures and classifies them on the basis of two different data sets of CHIRP seismic records, one from the Conceição Lagoon (CL) and the other from North Bay (NB), both on Santa Catarina Island, Southern Brazil. Side scan sonar data from the CL were used to facilitate the understanding. The sub bottom (SB) seismic data were processed and interpreted by means of the SeisPrho software, the side scan sonar (SSS) data by SonarWiz5 software and the spatial extension being measured with the help of GIS. The shallow gas structures were defined in accordance with their shapes in the seismic recordings (echo-character). At the CL, shallow gas accumulations were found in the form of seepages and features presenting shallow gas structures between the surface and 8.20 ms (around 12.3 m). Accumulations of gas were found in the form of Acoustic Blanking with Acoustic Plume, and also Black Shadows. Pockmarks were found on the lagoon floor and associated with gas seepages (average size diameter 0.97 ± 0.19 m and density from 54 to 242 units per 50 m2). In the NB three types of shallow gas features were found in the seismic profile, namely Acoustic Blanking, Turbidity Pinnacles and Intra-sedimentary plumes. The depth varied from the surface to 12.10 ms (around 18.15 m). In both environments, the gas is escaping from the sediment into the water column. The Pockmarks in the CL and the Acoustic Plume features and sediment rich in total sulfur in the NB validate these findings

Shallow gas seismic structures: forms and distribution on Santa Catarina Island, Southern Brazil

Abstract This paper presents the spatial distribution of shallow gas structures and classifies them on the basis of two different data sets of CHIRP seismic records, one from the Conceição Lagoon (CL) and the other from North Bay (NB), both on Santa Catarina Island, Southern Brazil. Side scan sonar data from the CL were used to facilitate the understanding. The sub bottom (SB) seismic data were processed and interpreted by means of the SeisPrho software, the side scan sonar (SSS) data by SonarWiz5 software and the spatial extension being measured with the help of GIS. The shallow gas structures were defined in accordance with their shapes in the seismic recordings (echo-character). At the CL, shallow gas accumulations were found in the form of seepages and features presenting shallow gas structures between the surface and 8.20 ms (around 12.3 m). Accumulations of gas were found in the form of Acoustic Blanking with Acoustic Plume, and also Black Shadows. Pockmarks were found on the lagoon floor and associated with gas seepages (average size diameter 0.97 ± 0.19 m and density from 54 to 242 units per 50 m2). In the NB three types of shallow gas features were found in the seismic profile, namely Acoustic Blanking, Turbidity Pinnacles and Intra-sedimentary plumes. The depth varied from the surface to 12.10 ms (around 18.15 m). In both environments, the gas is escaping from the sediment into the water column. The Pockmarks in the CL and the Acoustic Plume features and sediment rich in total sulfur in the NB validate these findings

Shallow gas seismic structures: forms and distribution on Santa Catarina Island, Southern Brazil

Abstract This paper presents the spatial distribution of shallow gas structures and classifies them on the basis of two different data sets of CHIRP seismic records, one from the Conceição Lagoon (CL) and the other from North Bay (NB), both on Santa Catarina Island, Southern Brazil. Side scan sonar data from the CL were used to facilitate the understanding. The sub bottom (SB) seismic data were processed and interpreted by means of the SeisPrho software, the side scan sonar (SSS) data by SonarWiz5 software and the spatial extension being measured with the help of GIS. The shallow gas structures were defined in accordance with their shapes in the seismic recordings (echo-character). At the CL, shallow gas accumulations were found in the form of seepages and features presenting shallow gas structures between the surface and 8.20 ms (around 12.3 m). Accumulations of gas were found in the form of Acoustic Blanking with Acoustic Plume, and also Black Shadows. Pockmarks were found on the lagoon floor and associated with gas seepages (average size diameter 0.97 ± 0.19 m and density from 54 to 242 units per 50 m2). In the NB three types of shallow gas features were found in the seismic profile, namely Acoustic Blanking, Turbidity Pinnacles and Intra-sedimentary plumes. The depth varied from the surface to 12.10 ms (around 18.15 m). In both environments, the gas is escaping from the sediment into the water column. The Pockmarks in the CL and the Acoustic Plume features and sediment rich in total sulfur in the NB validate these findings