No description available.

Sedimentary organic matter contains many compounds that have no obvious biogenic precursors, so their formation and occurrence are of geochemical interest. The first part of this thesis (chapters 2-5) discusses the results obtained from studying hydrocarbon racemates. Some of the compounds identified are also suggested as intermediates in the formation of alkylnaphthalenes identified in chapters 6-7. The second part of this thesis (chapters 6-11) covers the identification of a range of alkylnaphthalenes and alkylphenanthrenes in sedimentary organic matter. Possible pathways for the formation of these hydrocarbons are outlined and their application as probes into the processes of petroleum formation are described.In chapter 2 the use of permethylated cyclodextrin capillary gas chromatography columns to separate hydrocarbon racemates are reported. Chapter 3 reports the synthesis of 1,2,2,5-tetramethyltetralin and 1,2,2,5,6-pentamethyltetralin and identifies them as racemates in crude oil. They are proposed as intermediates in the formation of sedimentary alkylnaphthalenes (identified in chapters 6 and 7).The identification of isodihydro-ar-curcumene in sedimentary organic matter is described in chapters 4 and 5. It co-occurs in crude oil with dihydro-ar-curcumene and is suggested to originate from this compound via a sedimentary rearrangement process. Chiral GC-MS techniques have been used to show the presence of both enantiomers of these compounds in crude oils. The elution order of the enantiomers has been established using reference compounds of known configuration. The effects of maturity and biodegradation on dihydro-ar-curcumene and isodihydro-ar-curcumene enantiomers is reported. Optically pure dihydro-ar-curcumene from natural products undergoes rapid racemisation in the subsurface, yielding a racemic mixture before the onset of significant oil formation. ++ / 1,2-Alkyl shifts on the aromatic ring also begin at an early stage to yield isodihydro-ar-curcumene and these processes continue with increasing maturity. Laboratory experiments using proton and clay catalysts (Lewis acid catalyst) show that the alkyl shift reaction is catalysed by both proton and Lewis acids, and racemisation is only catalysed by Lewis acids. A moderately biodegraded crude oil has been shown to be depleted in the R enantiomer of dihydro-ar-curcumene and an extensively degraded oil has dihydro-ar-curcumene depleted relative to isodihydro-ar-curcumene.The identification of a number alkylnaphthalenes and their possible origins in sedimentary organic matter is described in chapters 6 and 7. In chapter 6 a previously unreported tetramethylnaphthalene (TeMN) was identified in petroleum. This compound is structurally similar to bicyclic compounds of microbial origin and these are suggested as a likely source, via a tetralin intermediate identified in chapter 3. In chapter 7 isomeric pentamethylnaphthalenes previously unreported in sedimentary organic matter are reported. These isomeric pentamethylnaphthalenes (PMNs) were identified in a number of crude oils and sediments, ranging in age from Proterozoic to Tertiary. 1,2,3,5,6-PMN is suggested to form predominantly from the aromatisation of drimanoid precursors via 1,2,2,5,6-pentamethyltetralin identified in chapter 3. In laboratory experiments, the other pentamethylnaphthalenes were generated from 1,2,3,5,6-PMN in proportions that reflect the relative stability of the isomers. By analogy, the other PMNs in sediments are suggested to arise via acid catalysed isomerisation or transalkylation processes. A maturity parameter was developed based on laboratory experiments in conjunction with observed distributions of pentamethylnaphthalenes.The formation of alkylnaphthalenes and alkylphenanthrenes through a ++ / methylation process is discussed in chapters 8-10. Several crude oils and shales which contain anomalously high concentrations of 1,6-dimethylnaphthalene, 1,2,5-trimethylnaphthalene, 1,2,7-trimethylnaphthalene, 1,2,3,5-tetramethylnaphthalene, 1,2,3,5,6-pentamethylnaphthalene, 2-methyl-6-isopropyl-1(4-methylpentyl)naphthalene, phenanthrene, 1-methylphenanthrene, 1,7-dimethylphenanthrene and retene have been shown to contain relatively high concentrations of their corresponding methylated counterparts. In laboratory experiments carried out under mild conditions, each of the alkylnaphthalenes and alkylphenanthrenes have been shown to be methylated in specific positions when heated with a methyl donor in the presence of a clay catalyst. These observations have been interpreted as evidence for a sedimentary methylation process.The effect of biodegradation on alkylnaphthalenes and alkylphenanthrenes formed from sedimentary methylation is described in chapter 11. Land-plant-derived aromatic hydrocarbons with a range of susceptibilities to reservoir biodegradation have been identified in crude oils. These compounds are the result of reactions of natural products involving aromatisation, rearrangement and methylation in the sediments (chapters 9 and 10). They are therefore suggested as markers for land-plants in severely biodegraded oils in which most of the other biologically derived compounds cannot be recognised. The order of biodegradability of these compounds has been assessed relative to their non-methylated counterparts namely 6-isopropyl-2-methyl-1-(4-methylpentyl)naphthalene and retene. The order of degradation of the four compounds is : retene < 9-methylretene ~ 6-isopropyl-2-methyl-1-(4-methylpentyl)naphthalene > 6-isopropyl-2,4-dimethyl-1-(4-methylpentyl)naphthalene. These results have been used to assess that a crude oil is a mixture of severely biodegraded and ++ / less biodegraded crude oil.

This dissertation presents the detailed results of investigations of the geomorphological and sedimentary processes associated with five Holocene tsunamis reported to have occurred in the Aegean Sea region of Greece. This research considers the effects of the widely quoted and archeologically important Minoan tsunami of the 17th century B.C.; the central southern Aegean tsunami of 66 A.D.; a hugely destructive tsunami reported to have followed a massive earthquake on the 21st July 365 A.D.; a tsunami of volcanic origin which affected the island of Thira on 29th September 1650 A.D.; and the destructive southern Aegean tsunami of 9th July 1965 A.D. The last account is believed to be the first systematic investigation of the geomorphology and sedimentology of a modern Aegean tsunami. This research is primarily concerned with the investigation of Holocene coastal sedimentary sequences in order to identify any geological traces of the former tsunamis and it is hoped that this evidence can be used to supplement the fragmentary historic accounts. This dissertation also considers whether microfossils can be used in the identification of individual stratigraphic horizons associated with tsunami-deposited sediments and investigates whether it is possible to determine the generative origins of individual tsunamis on the basis of the sediments associated with them. Whilst the findings of this research are not intended to provide a definitive account of the tsunamis considered, they do provide important evidence where the prevailing geological conditions of the Aegean Sea region would otherwise combine to limit the data available. Furthermore, it is believed that the results of this investigation do contribute to existing knowledge and will be of value to archaeologists seeking to explore the relationships between archaeological sites, landscape evolution and environmental change.

bold your words your word

Simpson Bay is a turbid, outwash fjord located in northeastern Prince William Sound, Alaska. A high ratio of watershead:basin surface area combined with high precipitation and an easily erodable catchment create high sediment inputs. Fresh water from heavy precipitation and meltwater from high alpine glaciers enter Simpson Bay through bay head rivers and small shoreline creeks that drain the catchment. Side scan sonar, seismic profiling, and high resolution bathymetry were used to investigate the record of modern sedimentary processes. Four bottom types and two seismic faces were described to delineate the distribution of sediment types and sedimentary processes in Simpson Bay. Sonar images showed areas of high backscatter (coarse grain sediment, bedrock outcrops and shorelines) in shallow areas and areas of low backscatter (estuarine mud) in deeper areas. Seismic profiles showed that high backscatter areas reflected emergent glacial surfaces while low backscatter areas indicated modern estuarine mud deposition. The data show terminal morainal bank systems and grounding line deposits at the mouth of the bay and rocky promontories, relict medial moraines, that extend as terrestrial features through the subtidal and into deeper waters. Tidal currents and mass wasting are the major influences on sediment distribution. Hydrographic data showed high spatial variability in surface and bottom currents throughout the bay. Bottom currents are tide dominated, and are generally weak (5-20 cm s-1) in the open water portions of the bay while faster currents are found associated with shorelines, outcrops, and restrictive sills. Tidal currents alone are not enough to cause the lack of estuarine mud deposition in shallow areas. Bathymetric data showed steep slopes throughout the bay suggesting sediment gravity flows. Central Alaska is a seismically active area, and earthquakes are most likely the triggering mechanism of the gravity flows.

No description available.

Sistemas estuarinos são locais de transição entre ambientes marinhos e fluviais, cujas forçantes influenciam a dinâmica e a distribuição das propriedades químicas, biológicas e sedimentares. Aproximadamente 60 % de todas as grandes cidades se desenvolveram ao redor de estuários que, por serem ambientes abrigados, favorecem a navegação e instalação de portos. O objetivo geral do trabalho foi de identificar os processos sedimentares atuantes em um trecho do canal de acesso ao Porto de Santos (Trecho 1 do Porto organizado), compreendendo 12 km de comprimento desde a embocadura da baía de Santos até a entrada no Canal do Porto, utilizando um conjunto de dados de diferentes períodos (entre 2010 e 2016), provenientes de diferentes fontes acústicas, visando contribuir para a melhor compreensão da dinâmica sedimentar do Sistema Estuarino de Santos. Foram utilizados dados obtidos com um duplo chirp (frequências entre 2-8 kHz e 10-20 kHz) e dados de batimetria multifeixe. A metodologia consistiu na comparação de levantamentos batimétricos (executados em diferentes períodos) e de forma complementar foram utilizados os dados obtidos com a fonte acústica chirp. As análises proporcionaram a identificação de indícios de erosão e de assoreamento no Trecho 1 do canal do Porto de Santos. Em alguns locais, foi possível relacionar os padrões de erosão e de assoreamento com a hidrodinâmica local e, assim, sugerir tendências nos processos sedimentares atuantes na área de estudo. Sem dragagem a tendência do Trecho 1 do Porto de Santos é de assoreamento. O Trecho 1 foi divido em 2 setores com comportamento distintos. O setor A (próximo à embocadura do canal) é, naturalmente, mais profundo, o sedimento de fundo não é depositado em grande quantidade nesse local devido à intensidade da velocidade das correntes que ocorrem no setor. Há indícios de instabilidade das encostas no trecho mais estreito do canal, da ocorrência de lama fluida e de gás raso nesse local. O setor B era, naturalmente, mais raso em 1960, período em que o canal passou a ter a sua configuração atual, sugerindo a formação de um delta de maré vazante no setor, onde a velocidade das correntes são mais lentas, quando comparadas com o setor A. / Estuarine systems are sites of transition between marine and fluvial environments, whose forcing influences the dynamics and distribution of chemical, biological and sedimentary properties. Approximately 60% of all large cities have developed around estuaries because they are sheltered environments, allowed the navigation and harbors installation. The objective of the study was to identify the sedimentary processes in a section of Santos Harbor channel, comprising 12 km in length from the mouth of the bay to the entrance in the Port Channel. It was used a data set from different periods (2010-2016), from different acoustic sources, aiming to contribute to a better understanding the sedimentary dynamics in the Santos Estuary System. It was used a double chirp data with frequencies between 2-8 kHz and 10-20 kHz and multibeam bathymetry data. The methodology consisted in the comparison of bathymetric surveys performed in different periods and in a complementary way used the data obtained from a double chirp. The analyzes allowed an identification of erosion and silting in Section 1 of Santos Port Channel. It was possible to relate erosion and silting patterns to local hydrodynamics and to suggest trends in sedimentary processes in the study region. Without dredging, the trend of Section 1 from the Santos Harbor was of silting. The Section 1 it was divided into 2 sectors with different behavior. Sector A is naturally deeper; the sediment is not deposited in large quantities at this location because of the currents velocities that occurring there. In this site there is evidence of instability of the slopes in the channel\'s narrowest section, the occurrence of fluid mud and shallow gas. Sector B was naturally shallower in 1960, when the canal became its current configuration, suggesting the formation in this site of an ebb tide delta, where the currents velocities are slower when compared to sector A.

La migration des bancs de vase observée le long des côtes Guyanaises génère des problématiques de navigation, particulièrement pour l'unique port de commerce de Guyane localisé dans l'estuaire du Mahury. La dynamique hydrosédimentaire de cet estuaire mésotidal et l'influence des bancs sur cette dernière sont très peu renseignées. Les principaux résultats de cette étude mettent en évidence l'importance relative du débit et des courants de marée sur la dynamique des sédiments fins. Bien que l'asymétrie de la marée soit dominée par le flot, les courants de jusant sont prédominants en saison humide et équivalents aux courants de flot en saison sèche. La dynamique des sédiments fins est gouvernée par la remise en suspension, bien que des épisodes de stratification puissent fortement atténuer la turbulence durant les premières heures du jusant. Les flux résiduels de sédiments sont généralement orientés vers l'amont durant la saison sèche et vers l'aval en saison humide, excepté lorsque les débits sont inférieurs aux moyennes saisonnières. L'évolution des fonds de l'estuaire sur 20 ans indique néanmoins une stabilité des dépôts et souligne la capacité de l'estuaire à évacuer les sédiments apportés durant la phase d'envasement. L'interdépendance entre l'estuaire du Mahury et le banc de Kaw sera ainsi soumise à discussion. Elle permettra d'évaluer la capacité du banc de Kaw à influencer la sédimentologie de l'estuaire et inversement d'évaluer la capacité de l'estuaire à perturber la migration du banc. / The mud banks migration observed along the Guyanese coastline generates navigating issues, especially for the unique harbor of French Guiana located in the Mahury Estuary. The hydro-sedimentary dynamic of this mesotidal estuary and the influence of the mud banks migration is poorly documented. The main results have brought to light the relative importance of the river discharge and tidal currents on the fine sediment dynamics. Even though the tidal asymmetry is dominated by the flood, the ebb currents are predominant during the wet season and are equivalent to the flood currents during the dry season. The fine sediment dynamics are mainly governed by the resuspension even though some stratification events can highly damp turbulence during the first hours of the ebb. The residual fluxes of sediment are generally landward during the dry season and in the wet season when river discharges are lower than the seasonnal averages. However, the bathymetric evolution over 20 years indicates the stability of the deposits and underlines the estuary's capacity of flushing sediments brought from the mud bank. The interdependence between the Mahury Estuary and the Kaw mudbank will therefore be subject to discussion. It will allow us to evaluate the mud bank influence on the estuarine sedimentology or, inversely, evaluate the capacity of the estuary to interfere with the mud bank migration and slowing down its progression with the currents.

Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2018-03-01T17:33:16Z No. of bitstreams: 1 Dissertação_Julia Duarte Contrera.pdf: 4179003 bytes, checksum: 954048867c122e6fc6c2ef65e6573276 (MD5) / Made available in DSpace on 2018-03-01T17:33:16Z (GMT). No. of bitstreams: 1 Dissertação_Julia Duarte Contrera.pdf: 4179003 bytes, checksum: 954048867c122e6fc6c2ef65e6573276 (MD5) / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geoquímica, Niterói, RJ / A Bacia Amazônica é um importante agente de influência das mudanças climáticas, podendo atuar tanto como sumidouro quanto como emissor de CO2 para a atmosfera. Existem diversos estudos sobre a atuação de sistemas Amazônicos na ciclagem de carbono. Entretanto estudos relacionados à atuação de planícies alagadas amazônicas a cerca do acúmulo de carbono ainda são muito escassos. Nesse contexto o presente trabalho tem como objetivo avaliar as mudanças paleohidrológica, paleoclimáticas que ocorreram no Lago Airo durante os últimos 13 mil anos e como essas mudanças afetaram o acúmulo de carbono em um sistema lacustre localizado na Sub-bacia do Rio Negro. Nesta área de estudo foi coletado um testemunho denominado AIRO12/01, com 1,46 cm de comprimento que apresentou ao longo dos últimos 13300 anos cal AP três fases distintas de sedimentação. Durante o período entre 13300 anos cal AP a 11700 anos cal AP o lago constituía um canal do Rio Negro, durante esse período foi observada a ocorrência de um clima úmido na região evidenciada pela granulometria arenosa (Argila: 0,2%, Silte, 0,1% Areia: 99,63%) que indicou forte influência fluvial. Em 13300 anos cal AP foi observado um evento de sedimentação abrupta que pode ser consequência de fortes chuvas ou pelo aumento da vazão do Rio Negro. Os baixos valores de pigmentos sedimentares (média de 2,9 SPDU) indicaram baixa produtividade lacustre que ocorre devido a forte influência fluvial. Os valores de δ13C indicaram uma maior contribuição de plantas terrestres na constituição da matéria orgânica lacustre. A forte influencia do Rio Negro sobre o lago neste período também foi registrada através de altos valores de C/N (valor médio de 49,4, como reflexo da influência de ácidos húmicos característico deste sistema fluvial) e valores de 15N próximos a zero (representativo de forte entrada de material terrestre). Devido a forte influência que o Rio exercia sobre o lago os valores de COT encontrados eram baixos (média de 1,37%). O período entre 11700 e 3000 anos cal AP foi marcado por evidencias de clima mais seco, com um aumento da concentração de micropartículas de carvão com media de 104 μm² e evidência de atividade eólica observada a partir de analise estatística. Contudo foram observados valores mais elevados de pigmentos sedimentares (média de 8,72 SPDU) e uma leve elevação dos valores de COT (média de 2,90%) que sugerem um período de semi-isolamento do Rio. A granulometria nesse período continua arenosa, mas com uma pequena variação na proporção de seus constituintes (Argila: 1,57%; Silte: 5,18%, Areia:93,24%) . Durante os últimos 3000 anos cal AP é possível observar condições climáticas mais úmidas neste registro sedimentar, evidenciadas pelo aumento da concentração de pigmentos sedimentares (média de 13 SPDU) e do COT (média de 34%). A análise granulométrica torna-se mais siltosa (Argila: 13,10%, Silte: 78,31%, Areia: 8,59%) e a razão C/N apresentou acentuado decréscimo (média de 31,2), indicando que a influência fluvial diminuiu a partir desse período. Com a diminuição da influência fluvial foi observado o aumento da produtividade lacustre a partir do aumento do δ15N. O isolamento do lago em relação ao rio pode ter ocorrido devido ao aumento da umidade na região que permite o desenvolvimento da vegetação no entorno do lago Airo como é observado nos dias atuais. A partir do Holoceno Superior também é observado o aumento na concentração de micropartículas de carvão (valor médio de 3x106 partículas por grama) e do tamanho médio das partículas (644 μm²), que podem indicar atividade humana no local. / The Amazon Basin is an important and arguably key component of the carbon cycle due to its role in the carbon storage and also amenable to fast release to the atmosphere throughout land use change or drought-induced feedbacks.Despite the numerous studies about carbon stocks in the Amazonian soils and biomass little is known about the carbon accumulation in the floodplain lakes. In this context, the objective of this work is to evaluate the paleohydrological and paleoclimatic changes in Lake Airo during the last 13,000 years and how those changes affected the carbon accumulation in a floodplain lake located in the Negro river Sub-basin. In this study area a 146 cm core denominated AIRO12/01 was collected. Dated by four AMS-radiocarbon dates, this core has a basal age of 13300 cal years BP and three sedimentary units were identified. During the period between 13300 years cal BP to 11700 years cal BP was observed the occurence of humid climate in the region, evidenced by a grain size with higher proportions of sand (Clay: 0.2%, Silte 0.1 %, Sand: 99.63%) that indicates a strong fluvial influence. In addition an abrupt sedimentation event was observed at 13300 years cal BP interpreted as a consequence of heavy rains. The low values of Chlorophyll derivatives (average of 2.9 SPDU) indicate low lacustrine productivity that occurs due to strong lake influence. The values of δ13C indicated a greater proportion of terrestrial plants in the lacustrine organic matter. The strong influence of Negro river on the river in this period was also recorded by high C/N values (average value of 49.4 as a reflection of the influence of humic acids typical of this river system) and values of δ15N near to zero, representing a strong input of terrestrial material. Due to the strong river influence a extremely low TOC values was observed (average of 1.37%). Between 13300 and 11700 years cal BP the lake constituted a channel of the Negro River. The period between 11700 and 3000 years cal BP was characterized by a dry climate evidenced by an increase in the concentration of microparticles of charcoal (average of 2.4 x 106 particles per gram) and eolian activity observed from statistical analysis. The low charcoal particle size of this period (average of 104 μm2) may suggest the occurrence of regional paleofires. However, higher values of Chlorophyll derivatives (average 8.72 SPDU) and sligth elevation of TOC values (average of 2.90%) were observed suggesting a period of semi-isolation of the River. During this period the grain size was composed by higher concentration of sand, but with a small variation in proportion of its constituents (Clay: 1.57%, Silte: 5.18%, Sand: 93.24%). The last 3000 years BP was characterized by a wetter climate, evidenced by the increase of the chlorophyll derivatives (average 13 SPDU) and TOC (average of 34%). This phase was marked by a transition by a transition from coarse to finer sediments (Clay: 13.10%, Silt: 78.31%, Sand: 8.59%) and C/N ratio showed a significant decrease (average 31.2), indicating a reduction in the river influence. As a consequence a increase in the lacustrine productivity and in the δ15N values was observed during this period. The reduction of the river influence can be due to the increase of humid conditions which allowed the development of vegetation around the Lake Airo, as it is observed today. An increase in the concentration of microparticles of charcoal (mean values of 3 x 106 particles per gram) was observed. In addition the increase in the charcoal particle size (644 m) that characterized this period may indicate human activity around Airo Lake

Sedimentary processes are critical geological phenomena in the evolution of continental margins. Environmental forces from various temporal and spatial scales control these processes. Due to the fast increase of anthropogenic activities in marine environments, these studies on sedimentary processes and their products are becoming increasingly necessary. In this context, geophysical data, such as high-resolution 2D seismic reflection profiles, are efficient tools to characterize sedimentary processes and deposits. This study aimed to map and interpret different types of echo character on the continental shelf of the São Paulo Bight to increase the knowledge of the spatial variability of sedimentary processes in current-dominated shelf settings. With this aim, 120 seismic lines, almost 3200 km in length, have been analyzed in conjunction with 451 surficial sediment samples. Based on the broad-scale seafloor morphology, microtopography and seismic characteristics (e.g., sharpness, amplitude, continuity) of sub-bottom reflections, seven echo types distributed in three echo classes were identified in the study area. Type 1-1 is a flat seafloor with either no or low-amplitude sub-bottom reflectors, mainly observed in the middle shelf; type 1-2 is a flat sea floor with medium to high-amplitude sub-bottom reflectors also found in middle shelf settings; type 1-3 is defined by a transparent acoustic response below the seafloor evolving downsection into a highly reflective pattern that covers most of the inner shelf; type 1-4 presents a flat seafloor molded by regularly spaced undulations, and it is restricted to the outer shelf; type 2-1 consists of mounds with no internal reflectors also located on the outer shelf; type 3-1 is an irregular echo with prolonged internal reflectors found around the São Sebastião Island; finally, type 3-2 is a broad irregular echo with high relief variations mainly found in the outer shelf. The analysis of the seismic survey allowed recognizing that the distribution of the echoes reflects not only the composition of the seabed but also the sedimentary processes that acted during the deposition of the material. In the inner shelf and middle shelves, the Brazilian Coastal Current and the action of waves are the main processes responsible for the echo types found, while the outer shelf echo types are strongly influenced by the Brazil Current. / Processos sedimentares são fenômenos importantes na evolução das margens continentais. Esses processos são controlados por forçantes de várias escalas espaciais e temporais. Devido ao rápido crescimento das atividades antropogênicas em ambientes marinhos, estudos sobre processos sedimentares e seus produtos tem se tornado cada vez mais necessários. Nesse contexto, dados geofísicos, como perfis de sísmica de reflexão de alta resolução, são ferramentas importantes na caracterização desses processos e depósitos. O objetivo do estudo foi mapear e interpretar os tipos de caráter de eco na plataforma continental do estado de São Paulo visando aumentar o conhecimento a respeito da variabilidade espacial dos processos sedimentares em plataformas dominadas por correntes. Para alcançar esse objetivo 120 linhas sísmicas totalizando quase 3200 km em extensão foram analisadas em conjunto com 451 amostras sedimentares. Baseados na morfologia de macro e microescala e características sísmicas do sinal acústico de fundo como nitidez, amplitude e continuidade dos refletores, foram identificados 7 tipos de caráter de eco distribuídos em 3 classes (fundo plano, monticular ou irregular). O tipo 1-1 apresenta fundo plano com refletores de sub fundo ausentes ou de baixa amplitude localizado principalmente na plataforma média; o tipo 1-2 refere-se a um fundo plano com refletores internos com amplitudes médias a altas também presente na plataforma média; o tipo 1-3 é definido por uma camada superficial transparente que é substituída em profundidade por uma camada altamente refletiva que cobre grande parte da plataforma interna; o eco 1-4 apresenta fundo moldado por ondulações com localização restrita na plataforma externa; o tipo 2-1 consiste em montes sem refletores internos localizado próximo a quebra da plataforma; o tipo 3-1 é irregular com refletores internos prolongados e é encontrado ao sul da Ilha de São Sebastião; finalmente, o eco 3-2 é um eco irregular que apresenta grandes variações de relevo presente em grande parte da plataforma externa. A análise dos dados sísmicos permitiu o reconhecimento de que os ecos respondem não somente a composição sedimentar superficial, mas também os processos sedimentares que atuaram durante a deposição do material. Nas plataformas interna e média, a Corrente Costeira Brasileira e a ação de ondas geradas pelos ventos são os principais processos responsáveis pela geração dos ecos encontrados, enquanto na plataforma externa, os tipos de eco são fortemente influenciados pela Corrente do Brasil.