A análise batimétrica e sísmica de alta resolução realizadas na Plataforma Continental Externa e Talude ao largo da Ilha de São Sebastião permitiu elaborar um modelo morfológico e sedimentar para região. A Plataforma Continental Externa apresenta uma morfologia extremamente irregular, com presenças de montiformas, escarpas e depressões erosivas. Estas feições e os seus sedimentos superficiais são de origem carbonáticas. Na região da quebra da Plataforma e Talude superior ocorre um intenso processo erosivo, causada pela ação da Corrente do Brasil ao longo do tempo, formando canais e escarpas na região. Ao longo do Talude observam-se inúmeras feições que estão distribuídas por faixas de profundidade. Nos setores mais rasos observam-se há presença de ondas de sedimento e pockmarks ativos e inativos. Abaixo dos 1000 metros as feições predominantes são os canais e depósitos contorníticos, como o Canal de Santos, que possui expressão regional, localizado paralelamente ao talude. Esses depósitos e canais contorníticos são formados e retrabalhados pela incidência das Correntes de Contorno Intermediária (CCI) e da Corrente Contorno Profunda, que sofreram variações ao longo do tempo. / The analysis of high-resolution bathymetric and seismic data from the Outer Continental Shelf and Slope in front of São Sebastião\'s Island allowed us to elaborate a morphological and sedimentary model for the region. The Outer Continental Shelf has an extremely irregular morphology, with the presence of montiforms, scarp and erosive depressions. These features and surface sediments are carbonate. In the shelf break and upper slope occurs an intense erosion, caused by the action of the Brazil Current through time, forming channels and scarps in the area. It was observed that the features over the slope are distributed by depth ranges. In shallower sectors was found active and inactive feature such as sediment waves and pockmarks. Below 1000 meters the predominant features are channels and contourite deposits such as Santos\'s Channel, which has a regional expression and is located parallel to the slope. The formation and rework of these features occurs by the incidence of intermediate boundary current (IBC) and deep boundary current (DBC) and their variation through time.

A análise batimétrica e sísmica de alta resolução realizadas na Plataforma Continental Externa e Talude ao largo da Ilha de São Sebastião permitiu elaborar um modelo morfológico e sedimentar para região. A Plataforma Continental Externa apresenta uma morfologia extremamente irregular, com presenças de montiformas, escarpas e depressões erosivas. Estas feições e os seus sedimentos superficiais são de origem carbonáticas. Na região da quebra da Plataforma e Talude superior ocorre um intenso processo erosivo, causada pela ação da Corrente do Brasil ao longo do tempo, formando canais e escarpas na região. Ao longo do Talude observam-se inúmeras feições que estão distribuídas por faixas de profundidade. Nos setores mais rasos observam-se há presença de ondas de sedimento e pockmarks ativos e inativos. Abaixo dos 1000 metros as feições predominantes são os canais e depósitos contorníticos, como o Canal de Santos, que possui expressão regional, localizado paralelamente ao talude. Esses depósitos e canais contorníticos são formados e retrabalhados pela incidência das Correntes de Contorno Intermediária (CCI) e da Corrente Contorno Profunda, que sofreram variações ao longo do tempo. / The analysis of high-resolution bathymetric and seismic data from the Outer Continental Shelf and Slope in front of São Sebastião\'s Island allowed us to elaborate a morphological and sedimentary model for the region. The Outer Continental Shelf has an extremely irregular morphology, with the presence of montiforms, scarp and erosive depressions. These features and surface sediments are carbonate. In the shelf break and upper slope occurs an intense erosion, caused by the action of the Brazil Current through time, forming channels and scarps in the area. It was observed that the features over the slope are distributed by depth ranges. In shallower sectors was found active and inactive feature such as sediment waves and pockmarks. Below 1000 meters the predominant features are channels and contourite deposits such as Santos\'s Channel, which has a regional expression and is located parallel to the slope. The formation and rework of these features occurs by the incidence of intermediate boundary current (IBC) and deep boundary current (DBC) and their variation through time.

The continental margin in the area west of Shetland was subjected to repeated and extensive ice sheet advances during the Late Pleistocene. Seabed imagery, seismic survey and borehole core data show the Late Devensian ice sheets expanded across the continental shelf three times, two of these advances reaching the shelf edge. On the inner shelf, where present-day water depths are generally less than 100m, only thin sediments from the last retreat phase and exposed rock surfaces remain, all other deposits from earlier phases having been removed by the last advance. On the mid to outer shelf elements of all three phases are preserved, including lodgement and deformation tills, melt-out and water-lain till sheets, in-filled hollows left by stagnant ice decaying in situ and a series of large recessional and terminal moraines. In addition, there is evidence of shallow troughs and overdeepend basins which indicate preferential ice-drainage pathways across the shelf which were formerly occupied by ice streams. At the shelf edge, a thick wedge of glacigenic sediment forms a transition from the till sheets and moraines of the shelf to debris flows composed of glacigenic sediments on the upper slope. Shelf-edge moraines show an architecture indicating floating ice in modern water depths over approximately 180m, suggesting the West Shetland ice sheet was no more than about 250m thick. The upper and middle slope is dominated by glacigenic debris flows which are focused in the slope areas below the proposed ice stream discharges at the shelf edge. The mid-to-lower slope has been subjected to contour current activity which has re-worked much of the glacigenic sediment in this position. The lower slope and floor of the Faroe-Shetland Channel are marked by either large debris flow lobes of glacigenic sediment or thin glacimarine muds deposited from suspension. A conceptual model of the glacigenic development of a passive continental margin based upon the West Shetland example shows the deposited sequence for both advance and retreat phases of a glacial cycle, and the actual preserved sequence which might be expected in the rock record. The model also shows that ice sheet buoyancy, thickness, and to a lesser extent, basin subsidence, are the most important factors in the deposition and preservation of a glacially-influenced marine sequence.

Temperate mixed carbonate-siliciclastic sediments and authigenic minerals are the current surficial deposits at shelf and slope depths (30-1015 m water depth) on the north Kaipara continental margin (NKCM) in northern New Zealand. This is the first detailed study of these NKCM deposits which are described and mapped from the analysis of 54 surficial sediment samples collected along seven shorenormal transects and from three short piston cores. Five surficial sediment facies are defined from the textural and compositional characteristics of this sediment involving relict, modern or mixed relict-modern components. Facies 1 (siliciclastic sand) forms a modern sand prism that extends out to outer shelf depths and contains three subfacies. Subfacies 1a (quartzofeldspathic sand) is an extensive North Island volcanic and basement rock derived sand deposit that occurs at less than 100-200 m water depth across the entire NKCM. Subfacies 1b (heavy mineral sand) occurs at less than 50 m water depth along only two transects and consists of predominantly local basaltic to basaltic andesite derived heavy mineral rich (gt30%) deposits. Subfacies 1c (mica rich sand) occurs at one sample site at 300 m water depth and contains 20-30% mica grains, probably sourced from South Island schists and granites. Facies 2 (glauconitic sand) comprises medium to fine sand with over 30% and up to 95% authigenic glauconite grains occurring in areas of low sedimentation on the outer shelf and upper slope (150-400 m water depth) in central NKCM. Facies 3 (mixed bryozoan-siliciclastic sand) consists of greater than 40% bryozoan skeletal material and occurs only in the northern half of the NKCM. Facies 4 (pelletal mud) occurs on the mid shelf (100-150 m water depth) in northern NKCM and comprises muddy sediment dominated by greater than c. 30% mixed carbonatesiliciclastic pellets. Facies 5 (foraminiferal mud and sand) contains at least 30% foraminifera tests and comprises two subfacies. Subfacies 5a consists of at least 50% mud sized sediment and occurs at gt400 m water depth in southern NKCM while subfacies 5b comprises gt70% sand sized sediment and occurs at mid to outer shelf and slope depths in the northern NKCM. vi A number of environmental controls affect the composition and distribution of NKCM sediments and these include: (1) variable sediment inputs to the NKCM dominated by inshore bedload sources from the south; (2) northerly directed nearshore littoral and combined storm-current sediment transport on the beach and shelf, respectively; (3) offshore suspended sediment bypassing allowing deposition of authigenic minerals and skeletal grains; (4) exchange between the beach and shelf producing similar compositions and grain sizes at less than 150 m water depth; and (5) the episodic rise of sea level since the Last Glaciation maximum approximately 20 000 years ago which has resulted in much sediment being left stranded at greater depths than would otherwise be anticipated. Sedimentation models developed from other wave-dominated shelves generally do not appear to apply to the NKCM sediments due to their overall relative coarseness and their mosaic textural characteristics. In particular, the NKCM sediments do not show the expected fining offshore trends of most wavedominated shelf models. Consequently, sandy sediments (both siliciclastic and authigenic) are most typical with mud becoming a dominant component in southern NKCM sediments only at greater than 400 m water depth, over 350 m deeper than most models suggest, a situation accentuated by the very low mud sediment supply to the NKCM from the bordering Northland landmass.

Occurrences of carbonate-cemented nodules and concretions exposed on the seafloor that contain cements with light carbon isotopes, indicating a contribution of methane-derived carbon, are commonly interpreted to be indicators of seafloor fluid venting. Thus, their presence is commonly used as an indicator of the possible occurrence of methane gas hydrate within the near subsurface. While some of these carbonates exhibit facies that require formation on the seafloor, the dominant fine-grained lithology associated with these carbonates indicates they were formed as sedimenthosted nodules within the subsurface and are similar to nodules that are obtained from the subsurface in Deep Sea Drilling Project, Ocean Drilling Project, and Integrated Ocean Drilling Project boreholes. Here we present the hypothesis that the occurrence of these carbonates on the seafloor may instead indicate areas of persistent seafloor erosion.

The continental margin off Nova Scotia (the Scotian margin) forms the northern edge of the North American Basin. The Cenozoic stratigraphy and geological history of the outer margin is not well known. This study examines aspects of the Upper Cretaceous-Cenozoic geological history of the outer Scotian margin addressing the following objectives: 1) determine the geological history of a large deep-water depocenter, 2) investigate processes that led to deep-water unconformity formation in the study area, 3) determine the role of deep-ocean circulation in margin evolution, 4) examine the effects of morphological heritage on subsequent depositional patterns. High quality 2-D and 3-D seismic reflection data along with lithostratigraphic and biostratigraphic data from hydrocarbon exploration wells provide the basis for this investigation. The seismic stratigraphy of a large deep-water depocenter along the western Scotian margin was broadly divided into four units. Unit 1 (Upper Cretaceous-Upper Eocene) is attributed to repeated, widespread erosion events interspersed with periods of hemipelagic and pelagic, carbonate-rich sedimentation. Unit 2 (Lower Oligocene-Middle Miocene) consists of a variety of seismic facies overprinted by dense, small-offset faults. Unit 3 (Middle Miocene-Upper Pliocene) is dominated by sediment drift deposition. Unit 4 (Upper Pliocene-present) is characterized by channel development and gravity flow deposition. The processes that led to regional seismic stratigraphic horizons were complex. Both large mass-wasting events and along-slope bottom currents contributed to the formation of unconformities in the study area. Most of the succession preserved in the depocenter belongs to seismic units 2 and 3. These deposits are mainly confined to the area seaward of the Abenaki carbonate bank and landward of shallow salt structures below the slope. Locally, however, modification of the slope profile through mass-wasting and bottom current processes greatly influenced subsequent depositional patterns. The Cenozoic geological evolution of the study area was strongly affected by northeast-to-southwest flowing bottom currents. The earliest indication of bottom current activity was in the Eocene. Upper Miocene and Pliocene sediment drifts represent >50% of the preserved stratigraphic section in the thickest part of the depocenter. It is clear that along-slope sedimentary processes were far more important in shaping the margin than previously understood.

No description available.

Eventos climáticos ocorridos no planeta deixam registros no ambiente, com os quais é possível realizar reconstruções das condições ambientais. No oceano, o destino de grande parte da matéria orgânica é o sedimento; assim o estudo de colunas sedimentares preservadas, testemunhos, fornece um registro de informações sobre os processos biológicos, geológicos e químicos ocorridos no passado e de como esses processos responderam às mudanças ambientais. No presente trabalho foram analisados sedimentos superficiais marinhos ao longo da margem continental superior do Sudeste do Brasil de forma a validar a utilização de marcadores geoquímicos orgânicos na região e foi analisado um testemunho cuja base aponta para 35.000 anos e que engloba importantes eventos climáticos ocorridos no planeta: eventos Heinrich 3, 2 e 1, o Último Máximo Glacial e o evento Younger Dryas, de forma a realizar uma reconstrução paleoceanográfica desse período. Os resultados dos marcadores orgânicos moleculares nas amostras superficiais, quando comparados com outros trabalhos realizados na região, mostraram que os marcadores respondem corretamente aos processos sedimentares na margem continental do Sudeste do Brasil e que a utilização de alquenonas como indicadores de temperatura superficial marinha na região é válida. A análise do testemunho permitiu correlacionar as variações de temperatura da água superficial do mar e variações do nível do mar com o fluxo de material terrígeno para o meio marinho nos últimos 35.000 anos, além de identificar os eventos climáticos citados e verificar a influência desses eventos para a região da margem continental superior do Sudeste do Brasil. Os resultados mostraram uma variação de temperatura superficial marinha de até 4°C entre o Último Máximo Glacial e o Holoceno e mostraram que, para a região, não ocorreu a anti-fase térmica entre o Atlântico Norte e o Atlântico Sul citada em diversos trabalhos realizados no Atlântico Sul, durante os eventos climáticos citados. / Climatic changes produce environmental signatures with which it is possible to reconstruct past environmental conditions. In the ocean, the fate of most of the organic matter is the marine sediment. Sediment core analyses reveal a unique reservoir of biological, chemical and geological information about past processes and how they responded to the environmental changes. In the present work, marine surface sediments from the Southeastern Brazilian Continental Margin were analyzed to verify the efficiency of organic geochemical markers in this area. Sediment core from the Southeastern Brazilian upper slope were also analyzed to carry out a paleoceanographic reconstruction. The core covers a time period of 35,000 years, where important climatic changes occurred, such as the Heinrich events 3, 2 and 1, the LGM, and the Younger Dryas events. Surface sediment results for geochemical markers were comparable with other works developed in the area, efficiently describing the processes that occur there. The alkenone based SST was also comparable with observations from multinational programs, being valid for this area. The core analyses showed correlations between SST and sea level variations with changes in terrestrial organic matter flow to the ocean over the last 35,000 years, allowed the identification of previously mentioned climatic events and the verification of the influence of these events on the Southeastern Brazilian Continental Shelf. Results showed that the SST varied up to 4.5°C between the LGM and the Holocene indicating that at this region a thermal antiphasing between southern and northern Atlantic Ocean SST during the last 35,000 years did not occur.

O presente trabalho tem como enfoque o estudo de foraminíferos planctônicos, na margem continental Sudeste Brasileira, entre São Sebastião, SP e Cabo de São Tomé, RJ através do levantamento das espécies existentes no plâncton. Buscou conhecer a distribuição sazonal e vertical na coluna d?água (0 a 100 m de profundidade) das espécies de foraminíferos planctônicos, correlacionar a presença desses organismos a fatores abióticos e bióticos no meio ambiente. Comparar a composição da biocenose e da tanatocenose assim como, realizar análise tafonômica das carapaças depositadas no fundo oceânico, a fim de avaliar o registro sedimentar desses organismos e considerar a utilização de assinaturas tafonômicas em carapaças de foraminíferos planctônicos na compreensão dos processos hidrodinâmicos na área de estudo. Para isso, foram analisadas amostras de plâncton, coletadas no verão/2002 e inverno/2002, e amostras de sedimento. Foram aplicadas metodologias usuais em análises de foraminíferos planctônicos. Foi possível reconhecer que há grande diferença sazonal na abundância e no tamanho de foraminíferos planctônicos na margem continental Sudeste Brasileira. A distribuição vertical desses organismos no verão parece estar relacionada à profundidade da camada de mistura, variação da temperatura na água, e à cadeia alimentar. No intervalo de profundidade entre 0 m e 40 m, predominam Globigerinoides ruber (pink) e Globigerinoides ruber (white). As espécies Globigerina bulloides, Neogloboquadrina dutertrei e Globigerinella siphonifera predominam entre 40 m e 60 m de profundidade, ao passo que entre 60 m e 80 m de profundidade ocorrem Globorotalia menardii, Orbulina universa e Globigerina falconenis. O registro sedimentar das espécies de foraminíferos planctônicos encontrado na área de estudo reflete a biocenose, podendo assim ser utilizado em análises ambientais e paleoceanográficas. As assinaturas tafonômicas observadas refletem as condições hidrodinâmicas locais. / The present work focuses on the study of planktonic foraminifera on the southeast Brazilian continental margin between São Sebastião, SP and São Tomé, RJ. This was done by means of a survey of the existing species in the plankton. The seasonal and vertical distribution in the water column (0-100 m depth) of the planktonic foraminifera species was also determined. In addition, a comparison of the biocenose and of the tatocenose was carried out as well as a tafonomic analysis of the tests deposited in the bottom. This was done in order to evaluate the sedimentary record of these organisms and consider the possibility of using tafonomic signatures in planktonic foraminifera tests in order to better understand the hydrodynamic processes in the study area. For this, plankton samples collected in the summer and winter of 2002, as well as sediment samples, were analyzed. Methodologies common to planktonic foraminfera analysis were applied. The results show that there is a great seasonal difference in abundance and size of the planktonic foraminifera on the southeast Brazilian continental margin. The vertical distribution of these animals in the summer seems to be related to the depth of the mixture layer, variations in water temperature, and to the food chain. In the depth interval between 0 m and 40 m, there was a predominance of Globigerinoides ruber (pink) and Globigerinoides ruber (white). The species Globigerina bulloides, Neogloboquadrina dutertrei and Globigerinella siphonifera are predominate between 40 and 60 m. On the other hand, between 60 and 80 m Globorotalia menardii, Orbulina universa and Globigerina falconenis occur in greater quantities. The sedimentary record of the species of planktonic foraminifera found in the study area reflect the biocenose, being therefore appropriate for the usage in environmental and paleoceanographic analyses. The tafonomic signatures observed reflect the local hydrodynamic conditions.

Os métodos potenciais são conhecidos como uma ferramenta útil para estudos regionais. Na Ibéria Ocidental, a gravimetria e a magnetometria podem ser utilizadas para auxiliar no entendimento de algumas questões sobre a estruturação tectônica offshore. Nesta região, tanto as estruturas geradas pela quebra continental, quanto às herdadas do embasamento variscano, tem uma importante contribuição para a resposta geofísica regional observada com estes métodos. Este trabalho tem como objetivo correlacionar as feições geofísicas observadas com alguns modelos geológicos do arcabouço tectônico da Ibéria Ocidental já publicados na literatura. Mapas filtrados foram usados para auxiliar no reconhecimento de diferentes assinaturas geofísicas, os quais foram calculados a partir dos mapas de gravidade Bouguer e do campo magnético total tais como o gradiente horizontal total, derivada tilt, derivada vertical, e integral vertical. O domínio crustal continental foi definido a partir da interpretação dos dados gravimétricos, utilizando gradiente de gravidade horizontal total da Anomalia Bouguer. Os dados magnéticos, originais e filtrados, foram utilizados para identificar mais três domínios regionais offshore, que sugerem a existência de três tipos de crosta não-siálica. Dois deles são propostos como domínios de transição. A região da crosta de transição mais próxima do continente tem uma fraca resposta regional magnética, e a porção mais distal é um domínio de anomalia de alta amplitude, semelhante à resposta magnética oceânica. O limite crustal oceânico não pôde ser confirmado, mas um terceiro domínio offshore, a oeste da isócrona C34, poderia ser considerado como crosta oceânica, devido ao padrão magnético que apresenta. Alguns lineamentos do embasamento foram indicados na crosta continental offshore. As feições gravimétricas e magnéticas interpretadas coincidem, em termos de direção e posição, com zonas de sutura variscanas, mapeados em terra. Assim, esses contatos podem corresponder à continuação offshore destas feições paleozoicas, como o contato entre as zonas de Ossa Morena-Zona Centro-Ibérica. Nesta interpretação, sugere-se que a crosta continental offshore pode ser composta por unidades do Sudoeste da Península Ibérica. Isto permite considerar que a Falha de Porto-Tomar pertence a uma faixa de deformação strike-slip, onde parte das bacias mesozoicas da margem continental está localizada. / Potential field methods are known as a very useful tool to regional studies. On Western Iberia, gravimetric and magnetometric data could be helpful to understand some questions about the offshore tectonic framework. In this area, both continental break-up features and inherited continental basement structures have a strong contribution to compose the regional geophysical response on gravimetric and magnetometric maps. This work aims to correlate observed geophysical features of the Iberian margin with some geological models about the tectonic framework of Western Iberia, already published on literature. Filtered maps were used to recognize different geophysical signatures, which were computed from both calculated Bouguer gravity and total magnetic field, such as total horizontal gradient, tilt derivative, vertical derivative, and vertical integration. The continental crustal domain was defined from gravity data interpretation using an enhanced total horizontal gradient of Bouguer Anomaly maps. Magnetic data was used to identify three more regional offshore domains that could indicate three types of non-sialic crust. Two of them are proposed as transitional domains. The landward transitional crust has a very weak regional magnetic response, and the seaward one is a high amplitude anomaly domain, similar to oceanic magnetic response. The oceanic crustal boundary was not confirmed, but a third offshore domain, seaward from C34 isochron, could be considered as oceanic crust by its magnetic pattern. Some basement lineaments were indicated in the offshore continental crust. Gravimetric and magnetic features coincide in terms of their direction and position with Variscan suture zones mapped onshore. Therefore these contacts could correspond the offshore continuation of these Paleozoic features, such as the Ossa-Morena Zone and Centro-Ibérica Zone suture zone. In this interpretation, offshore continental crust could be formed by units from Southwest Iberia. It allows considering the Porto-Tomar fault as a part of a swath of strike-slip deformation, where mesozoic basins are located.