Cleverson Guizan Silva

Distinctive sedimentary processes in Guanabara Bay - SE/Brazil, based on the analysis of echo-character (7.0 kHz)

Guanabara Bay bottom sediments and seabed characteristics were analysed using high-resolution (7 kHz) sub-bottom profiles associated with particle size analyses of 92 bottom sediment samples. Eight types of echo-characters were identified revealing the strong relation with the particle size distribution. Sandy bottom areas presented strong echo reflections, without sub-bottom penetration (Echo types I and III), while in muddy areas sub-bottom reflections showed the acoustic basement delineating buried sugar-loaf hills and infilled-valley features (Echo type IV). The presence of shallow gas within the sediments is indicated by acoustic blanket and a series of bottom-multiple reflections (Echo types Va and Vb). Erosion by bottom currents and artificial mechanical dredging are suggested by truncations of sub-bottom reflections and a wrinkled seabed surface (Echo types VI and VII). Crystalline basement outcrops on the seabed are recognized by multiple or single hyperbolae with varying elevations above the bay bottom (Echo type II).

Two-scale gravitational collapse in the Amazon Fan: a coupled system of gravity tectonics and mass-transport processes

Abstract: Gravity tectonics affects the entire marine sedimentary sequence of the Foz do Amazonas basin, including the topmost Amazon Fan. During the various stages of the margins evolution, the sedimentary loading and bathymetric slope induced the formation of a linked extensional–compressional system in which gravitational fold-and-thrust belts form significant structural features on the continental slope. Seismic analysis carried out in this study shows that sea-floor relief created along these thrust belts can trigger recurrent mass-transport deposits in the upper–middle Amazon Fan, suggesting a long-lasting linkage between gravity tectonics and mass-transport processes throughout the sedimentary evolution of the Amazon Fan. Supplementary material: Uninterpreted seismic sections are available at http://www.geolsoc.org.uk/SUP18393.

Architecture and stratigraphic framework of shelf sedimentary systems off Rio de Janeiro state, Northern Santos Basin-Brazil

A analise sismica de dados sparker das Operacoes GEOMAR permitiu a elaboracao de um primeiro arcabouco estratigrafico da secao rasa (~300 msec) da plataforma continental do Estado do Rio de Janeiro, norte da bacia de Santos. Dois conjuntos de sequencias sismicas foram interpretados como sequencias deposicionais induzidas por oscilacoes glacio-eustaticas. O Conjunto I (SqA-SqC), composto por sequencias dominantemente sigmoidais, reflete condicoes de geracao de espaco de acomodacao sedimentar capaz de preservar seus componentes agradacionais-progradacionais; o Conjunto II (Sq1-Sq5), composto principalmente por prismas de regressao forcada, indica diminuicao relativa de espaco de acomodacao. Dados cronoestratigraficos de pocos permitiram posicionar a secao sismica investigada na janela plio-quaternaria: a maior parte do Conjunto I (SqA e parte inferior da SqB) foi atribuida uma idade Plioceno (indiferenciado); a secao estratigrafica que se estende da porcao superior da SqC ate o Conjunto II foi atribuida uma idade quaternaria. A correlacao entre a base de dados e curvas globais de variacoes isotopicas de δ18O permitiu ainda sugerir que as sequencias Sq1-Sq4 registram sequencias regressivas de quarta ordem (ciclos glacio-eustaticos de cerca de 100-120 ka) durante os ultimos 440-500 ka. A sequencia Sq5 representaria a deposicao holocenica, constituida por depositos transgressivos e de sistemas de mar alto.

Heavy metal accumulation in mangrove sediments surrounding a large waste reservoir of a local metallurgical plant, Sepetiba Bay, SE, Brazil

Due to the growing rate of urbanization and a rapid and unplanned development in many tropical coastal areas, there continues to be an increasing concern in relation to the impact of anthropogenic activities on mangrove sediments. In southeastern Brazil, the Sepetiba Bay becomes an example of an ecosystem in the process of accelerated degradation. Previous studies highlighted the activities related with zinc processing by an industry on the Madeira’s Island as one of the main source of heavy metal to Sepetiba Bay. Despite the end of the industrial activities in the area, the waste reservoir became the main source of pollutant to the surrounding area. Analyses of Cd, Pb, Cu, Cr, Hg, Ni, Zn, particle size and nutrients of 20 sediment samples collected in the mangrove of the Madeira Island showed that the waste reservoir is the main source of contaminant to the mangrove. The statistic analyses showed that the moisture content and organic matter play an important role in the geochemical dynamic of heavy metal in the area.

Caracterização morfodinâmica do litoral Norte Fluminense, RJ, Brasil

A morfologia das praias e reflexo da acao hidrodinfunica com o tipo de sedimento disponivel. Esta int~acao se da a partir da base de acao das ondas, tornando-se mais efetiva na zona de arrebentacao onde a energia e dissipada, originando wna zona de surfe que se estende em direcao a linha de costa ate Q limite do espraiamento na face de praia. O objetivo deste trabalho e apresentar as caracteristicas morfodinâmicas do litoral NE do Estado do Rio de Janeiro, baseando-se na analise da variacao espaco Hemporal de perfis de praia, na morfologia da plataforma continental e em fotos aereas. Os perfis de praia foram levantados durante cinco anos pela PETROBRAS S/A, em oito estacoes ao longo do litoral. O comportamento morfodinâmico distinto de setores do litoral estudado e funcao do padrao de ondas e direcao da linha de costa, morfolQgia da plataforma interna controlando a extensao da zona de surfe e o numero de zonas de arrebentacao, caracteristicas dos sedimentos e gradiente da face de praia. Foram reconhecidos quatro compartimentos morfodinâmicos distintos, com base na morfologia dos perfis praiais e plataforma interna, no indice de mobilidade da linha de praia, granulometria x gradiente da face de praia e o parâmetro Q. Os quatro compartimentos sao: Atafona/Foz do Rio Paraiba do Sul - estagio morfodinâmico intermediario a dissipativo, com o maior indice de mobilidade e elevada taxa de erosao; Sul de Atafona-Cabo de Sao Tome - estagio intermediario a refletivo com baixo indice de mobilidade da praia; Cabo de Sao Tome -estagio refletivo a intermediario com alto indice de mobilidade da praia; Cabo de Sao Tome-Cabiunas - estagio refletivo com baixo indice de mobilidade.

Palynological evidence of the replacement of the hygrophilous forest by field vegetation during the last 7,000 years B.P. in the northern coast of Rio de Janeiro, Brazil

Historians claim that European colonizers of the northern coast of Rio de Janeiro State found vast herbaceous fields when arrived in this region. Hypotheses about the origin of these fields include forest burning by the Goitacás indians and periodical floods by the Paraíba do Sul River and the lagoon system. The palynologycal analysis of two lake cores obtained in the municipality of Campos dos Goytacazes revealed opening episodes of hygrophilous forest and the establishment of field vegetation, recorded at ca. 6,500 and ca. 4,000 (14)C yr BP. The partial replacement of forest by field vegetation in the first episode was probably caused by floods of the lower areas during the development of the Holocene lagoon phase. During the second episode, successions of vegetational patterns occurred due to lowering of the sea level. Drying and enlarging of the coastal plain have allowed its colonization by herbs and heliophyte plants. The palynological analysis does not provide any evidence that sustains the theories of use of fire and agricultural activities by indigenous groups during these periods.

Study of pollutant distribution in the Guaxindiba Estuarine System – SE Brazil

The Guaxindiba Estuarine System is located in the northeast portion of Guanabara Bay. Despite the location inside an environmental protection zone, the main affluent of the river runs through the extremely urbanized area of the cities of Niterói and São Gonçalo. In order to understand the contamination levels of the estuary, 35 surface sediment samples were collected along the river and estuarine area and analyzed for the presence of heavy metals, PAHs, organochlorated pesticides, polychlorinated biphenyl and other contaminants. The analyzed data revealed a greatly affected environment with respect to most of these substances. The results suggested propitious deposits of contaminants, with high concentrations of organic matter and fine sediment. The levels of heavy metal in the entire estuarine system were high compared with the local background. The total mean concentrations of As, Cd, Pb, Cu, Zn, Hg, Cr and Ni in the surface sediments were: 3.74; 0.03; 19.3; 15.0; 99.0; n.d.; 29.0; and 22.0mg/kg, respectively, confirming, in certain cases, the high capacity of the environment to concentrate pollution.

Megaslides in the Foz do Amazonas Basin, Brazilian Equatorial Margin

Recent analysis of multi-channel seismic data provides new evidence that mass-transport deposits have been recurrent elements in the Foz do Amazonas Basin during the Middle-Miocene to Recent. In regions located to the NW and SE of the Amazon Deep-sea Fan, mass movement processes remobilized thick siliciclastic series (up to 1,000 m) as huge megaslide deposits over areas up to 90,000 km2. The Para-Maranhao Megaslide in the SE shows a displaced block (>104 km2) in association with large mass transport deposits covering an area of more than 105 km2. These deposits are distally bounded by thrust faults, which propagate upwards eventually offsetting the sea floor. In addition, NW of the deep-sea fan, the Amapa Megaslide Complex presents a series of recurrent megaslides in the stratigraphic succession, bounded by listric normal faults and tear zones on the upper slope. Associated remobilized deposits extend from more than 300 km downslope, partially involving the upper channel-levee units of the Amazon Deep-sea Fan.

O processo de colapso gravitacional da seção marinha da bacia da foz do Amazonas - margem equatorial brasileira

As sequencias marinhas da Bacia Foz do Amazonas sao deformadas pela tectonica gravitacional, incluindo aquelas do Leque do Amazonas. As estruturas associadas ao colapso gravitacional, imageadas por sismica multicanal 2D, foram formadas pelo deslizamento gravitacional da cobertura sedimentar sobre niveis basais moveis, induzido pela sobrecarga sedimentar e pelo gradiente do talude. O deslizamento gravitacional ocorreu ao longo de distintas superficies de descolamento e, aparentemente, em diferentes estagios evolutivos da margem. Ao menos tres niveis estratigraficos principais atuaram como superficies de descolamento, em escala regional ou local. Cinturoes de dobramento e cavalgamento em aguas profundas sao as estruturas mais notaveis deste arcabouco; sua geometria e complexidade variam ao longo da margem em reposta a variacao lateral do desenvolvimento dos depocentros do Leque do Amazonas. Estas estruturas sao mais complexas no Compartimento Noroeste onde os principais depocentros estao presentes, formando multiplas frentes compressivas devido ao mais intenso encurtamento da cobertura sedimentar. No Compartimento Sudeste, o sistema e menos desenvolvido e se limita a um cinturao parcialmente inativo, caracterizado apenas por um par de falhas reversas ativas com menor impacto morfologico. Localmente, falhas normais listricas antiteticas se ancoram sobre a superficie de descolamento mais superior, exercendo um controle estrutural sobre a segmentacao dos depocentros do proprio leque.

Causas e conseqüências do impacto ambiental da exploração dos recursos minerais marinhos

The offshore extraction of marine minerals can cause several environmental impacts to the marine ecosystems, being the habitat destruction the main factor affecting the decline of the number of species around the world. Besides direct interference on the sea-bottom, the marine mineral activities can cause an increase in the water turbidity, affecting the local primary production. These activities can introduce and promote nutrient availability causing eutrophication. Otherwise it can introduce toxic substances that may be incorporated by the organisms, causing growth changes and alterations on the rates of reproduction and survival of the species. Current methods to identify the environmental impacts associated with the offshore mineral exploitation are centered on the reconnaissance of pollutant introduction and bio-availability, on the verification of measurable environmental changes and on the establishment of the relationship among the environmental response and pollutants. These methods apply three approaches: measurement of the pollutant concentration on the physical (water and sediment) and biological (bio-accumulation) environment; laboratory and field determinations of the organisms toxicity responses to pollutants; and field investigations of the ecosystems structure and processes.