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This study intends to evaluate baseline concentrations of chemical elements for unpolluted sediments of Sepetiba Bay (SE Brazil). It analyzes the concentrations of potentially toxic elements (PTE) and other chemical elements (by Inductively Coupled Plasma Mass Spectrometry and Inductively Coupled Plasma Emission Spectrometry) from the upper part of the SP2 drillcore (or 2-SPT-1-RJ; with 50.30 m length), collected on the margins of Sepetiba Bay (at latitude 22° 55'S and longitude 43° 46'W). This core was described and sampled. Textural, mineralogical and geochemical analyses were performed in 17 sediment levels. The sediment layers of interest were selected, considering the period in which they were deposited, before high anthropic influence in the area, and on sediment grain-size. Only the muddy levels were selected, since fine sediments generally tend to have higher elemental concentrations. Foraminiferal occurrence was also analyzed in the selected layers. The results indicate that the studied sediments were deposited in a transitional marine context, after being exposed to multiple sedimentary cycles and weathering. The baseline concentrations, related to natural sediment sources were estimated for As, Cd, Co, Cr, Cu, Ni, Pb, Zn) and P and for other chemical elements. These results are useful in environmental impact assessment not only in the study area, but also for other coastal regions of Rio de Janeiro State. TÍTULO: CONCENTRAÇÕES DE FUNDO DE ELEMENTOS QUÍMICOS NA BAÍA DE SEPETIBA (SE BRASIL) RESUMO:Este estudo pretende avaliar as concentrações de fundo de elementos químicos, em sedimentos não poluídos, na Baía de Sepetiba (Se Brasil). Analisa as concentrações de elementos potencialmente tóxicos (PTE) e outros elementos químicos (por Espectrometria de Massa Plasma Acoplada Indutivamente e Espectrometria de Emissão Plasma Acoplada Indutivamente) da parte superior do testemunho SP2 (ou 2-SPT-1 RJ; com 50,30 m de comprimento), coletado nas margens da Baía de Sepetiba (à latitude 22° 55'S e longitude 43° 46'W). Este testemunho foi descrito e amostrado a cada 5 cm. Análises estruturais, mineralógicas e geoquímicas foram realizadas em 17 níveis de sedimentos. Os níveis de interesse foram selecionados, considerando o período em que foram depositados, antes da alta influência antrópica na área, e no tamanho do grão do sedimento. Apenas os níveis de lama foram selecionados, uma vez que os sedimentos finos tendem geralmente a ter maiores concentrações de elementos quimicos. A ocorrência de foraminíferos foi também analisada nas camadas selecionadas. Os resultados indicam que os sedimentos estudados foram depositados num contexto marinho de transição, após serem expostos a múltiplos ciclos sedimentares e a intemperismo. As concentrações de fundo, relacionadas a fontes naturais de sedimento foram estimadas para As, Cd, Co, Cr, Cu, Ni, Pb, Zn) e P e para outros elementos químicos. Esses resultados são úteis para a avaliação de impacto ambiental, não apenas na área de estudo, mas também em outras regiões costeiras do Estado do Rio de Janeiro. PALAVRAS-CHAVE: Multi-indicadores. Sedimentos. Registros Holocénicos. Litoral. Atlântico Sul.

This work is based on the study of the core T1 collected in the Guaratiba Mangrove, located on the northeastern margin of Sepetiba Bay. Few studies dealing with the application of benthic foraminifera to study sea level changes during the Holocene have been conducted in Sepetiba Bay, State of Rio de Janeiro, Brazil. In order to fill this gap, the core T1 was studied using textural, geochemical (carbonate, total organic carbon, total sulfur and stable isotopes evaluated in Ammonia tepida) and microfaunal (benthic foraminifera) data, unveiling paleoecological relationships of these organisms and the evolutionary scenario of Guaratiba Mangrove. Radiocarbon results indicate an estimated age of about 2400 yrs cal BP for the core base. Textural, geochemical and benthic foraminifera data suggest that the study area changed significantly during the last 2400 yrs cal BP. It experienced coastal waves action and shoreface processes in the period between ≈2.400-1.400 yrs cal BP; then, this phase gave place to a shallow marine environment similar to that found currently in internal and protected areas of Sepetiba Bay, between ≈1.400-350 yrs cal BP. Thenceforth, the study area evolved to the present mangrove environment. Factors related to climatic oscillations and the formation, evolution and events of rupture of Marambaia sand ridge influenced the late Holocene evolution of the northeast intertidal area of Sepetiba Bay.

Guanabara Bay (GB), located at the coast of Rio de Janeiro State (Brazil), is an ecosystem rich in biodiversity both in terms of mega, macro and microfauna. However, the factors that control their distribution are still poorly understood. This work intends to identify the possible factors affecting the distribution of benthic foraminifera in the bay by comparing living and dead assemblages in selected sediment fractions. Substantial differences in terms of density, diversity and equitability of the species in the living and dead assemblages and in different sediment fractions (63-150 μm, 150-250 μm, 250-500 μm) are identified. Lower similarity (<70%) between the living and dead assemblages are associated with areas impacted by organic matter and may be mainly ascribed to either loss of tests due to dissolution, currents remobilization and abrasion, or inclusion of allochthonous species transported by currents. This work suggests that the use of the living plus dead assemblages or dead assemblages can reduce the accuracy of the results if the work intends to evaluate the environmental conditions.

. Late Holocene closure of a barrier beach in Sepetiba Bay and its environmental impact (Rio de Janeiro, Brazil). Journal of Sedimentary Environments, 2 (1): 65-80. AbstractCore T4 (with 286 cm long) collected in the inner part of Sepetiba Bay is a record of late Holocene evolution of Sepetiba Bay. This core was described and sampled every 2 cm. Textural, geochemical and foraminifera data were analyzed, and two radiocarbon dates were obtained. Estimated ages indicate that core T4 represents the last ≈4,000 years calibrated before present (yrs cal BP). Results of this core suggest that coarse sediments, recorded in the period between ≈4,000-3,400 yrs cal BP, were probably associated with high hydrodynamic conditions in the study area. These sediments should be deposited at an incipient phase of the Marambaia Beach Barrier evolution. The development of this sand barrier resulted in the confinement of the inner region of Sepetiba Bay, leading to the deposition of muddy sediments rich in organic matter. Organic matter enrichment increased especially in the last ≈500 yrs cal BP. Foraminifera assemblages and carbonates content indicate that the studied region should have been affected in the last ≈3,400 yrs cal BP by changes in the water depth column. An increase of the water column depth was recorded for example between ≈850-350 yrs BP. The results obtained in the core T4 show that the confinement and eutrophication process of the internal zone of Sepetiba Bay has been occurring since ≈3,400 yrs cal BP and is being caused by other factors such as geomorphological and climatic changes and human activities.

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