Paleoproductivity changes during the Late Quaternary in the southeastern Brazilian upper continental margin of the Southwestern Atlantic

Changes in the Brazilian continental margins oceanic productivity and circulation over the last 27,000 years were reconstructed based on sedimentological and microfaunal analyses. Our results suggest that oceanic paleoproductivity and the supply of terrigenous sediments to the Brazilian continental margin were higher during the Last Glacial Maximum (LGM) than during the Holocene. These changes may have been primarily influenced by significant sea level fluctuations that have occurred since the late Pleistocene. During the LGM, the lower sea level, higher productivity and lower sea-surface paleotemperatures may have been the result of the offshore displacement of the main flow of the Brazil Current. However, during the Holocene, the warm waters of the Brazil Current were displaced toward the coast. This displacement contributed to the increase in water temperature and prevented an increase in oceanic productivity. The decrease in terrigenous supply since the LGM could be related to the increase of the extension of the continental shelf and/or drier climatic conditions.Mudanças na produtividade e circulação oceânica da margem continental Brasileira foram reconstituídas a partir de análises sedimentológicas e microfaunísticas realizadas em sedimentos de um testemunho representativo dos últimos 27 000 anos. Nossos dados sugerem maior produtividade oceânica e suprimento de sedimento terrígeno na área de estudo no Último Máximo Glacial (UMG) do que no Holoceno. Estas mudanças foram principalmente influenciadas por flutuações do nível relativo do mar. Durante o UMG, num cenário de nível relativo do mar mais baixo, a maior produtividade oceânica e menor temperatura da superfície do mar, podem ter sido produtos do deslocamento para o largo da Corrente do Brasil. No Holoceno, o deslocamento para a costa das águas quentes da Corrente do Brasil contribuiu para o aumento na temperatura da água e menor produtividade oceânica. A diminuição do aporte de sedimentos terrígenos desde o UMG pode estar relacionado ao aumento da extensão da plataforma continental e/ou a condições climáticas mais secas no continente.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Radiocarbon geochronology of the sediments of the São Paulo Bight (southern Brazilian upper margin)

The aim of this work was to generate an inventory of the data on radiocarbon datings obtained from sediments of the São Paulo Bight (southern Brazilian upper margin) and to analyze the data in terms of Late Quaternary sedimentary processes and sedimentation rates. A total of 238 radiocarbon datings from materials collected using differents ampling procedures was considered for this work. The sedimentation rates varied from less than 2 to 68 cm.kyr-1. The highest sedimentation rate values were found in a low-energy (ría type) coastal system as well as in the upwelling zones of Santa Catarina and Cabo Frio. The lowest rates were found on the outer shelf and upper slopes. Our results confirm the strong dependency of the shelf currents, with an emphasis to the terrigenous input from the Río de La Plata outflow which is transported via the Brazilian Coastal Current, as well as of the coupled Brazil Current - Intermediate Western Boundary Current (BC-IWBC) dynamics on the sedimentary processes. At least three indicators ofthe paleo sea level were found at 12200 yr BP (conventional radiocarbon age) (103 meters below sea level - mbsl),8300-8800 cal yr BP (13 mbsl) and 7700-8100 cal yr BP (6 mbsl).O objetivo deste trabalho foi a geração de um inventário dos dados de datação de radiocarbono obtidos de sedimentos do Embaiamento de São Paulo (Margem Continental Superior do Sul do Brasil) e analisar os dados em termos de processos sedimentares quaternários e taxas de sedimentação. Um total de238 datações ao radiocarbono de materiais coletados com autilização de procedimentos amostrais diferentes foi considerado neste trabalho. As taxas de sedimentação variaram de menor que 2 a 68 cm.kyr-1. As taxas de sedimentação mais altas foram encontradas em um sistema costeiro de baixa energia (tipo ría), bem como nas zonas de ressurgência de Santa Catarina e Cabo Frio. As taxas mais baixas foram encontradas na plataforma externa e talude superior. Nossos resultados confirmam a forte dependência do sistema de correntes de plataforma, com ênfase no aporte terrígeno oriundo do Rio daPrata, transportado através da Corrente Costeira do Brasil, e da dinâmica da Corrente do Brasil - Corrente de Contorno Intermediária (CB-CCI) nos processos sedimentares. Pelo menostrês indicadores de paleo-níveis marinhos foram encontrados a 12200 anos AP (idade radiocarbônica convencional) (103 metros abaixo do nível do mar atual - manm), 8300-8800 cal anos AP (13 manm) e 7700-8100 cal anos BP (6 manm).Fundação de Amparo à Pesquisado Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

From sambaquis (shell mounds) to plastic debris: a summary of the geological imprint of human occupation in the coast of São Paulo (Southeast Brazil)

In this work, we present a brief revision of the geological evidence of human activities in the coast of São Paulo (Southeast Brazil), from pre-historical times to the present. We analyze case studies in different sectors of the coast, identifying the main historical causes that resulted in environmental changes with their consequent imprint in the sedimentary column. There was a south-to-north trend inthe occupation at the colonization period (1500 onwards), essentially determined by differences in the geomorphology of the area. Finally, the accumulation of artificial radionuclides and plastic debris in the sediments is discussed

Magnetic fingerprint of the late Holocene inception of the Río de la Plataplume onto the southeast Brazilian shelf.

Measurement of changes in the assembly ofmagnetic particles in sediment records is useful both for paleoclimatic and paleoceanographic reconstructions and for assessing provenance and pathways of sediment transport. In this study we provide detailed rockmagnetic analysis along with scanning electron microscopy (SEM), Ti/Ca ratio and particle size distribution of the decarbonated fraction of sediments to trace terrigenous source changes during the last 6 cal kyr BP in core 7610 collected on the SE Brazilian continental shelf. Magnetic mineralogy data indicate a gradual shift between two distinct sources of sediments: (1) dust fromsouthern South America (Patagonia, central western Argentina and Puna-Altiplano plateau) and (2) sediments eroded fromtheweathered volcanics of Paraná Basin. Thesematerials reached the continental margin off Argentina and Uruguay by different pathways andwere transported northward by the Brazilian Coastal Current (BCC). The chronology of events related to the environmental record of core 7610 indicates that between 6 and 4.7 cal kyr BP dry conditions over continental South America resulted in enhanced eastward eolian transport of the Argentinean loess and a limited discharge of the RdlP river load into the Atlantic Ocean. At this time, the sedimentary magnetic fraction that reached the SE Brazilian shelf reflect predominantly loessic sources transported from the Pampean terraces to the Argentinean and Uruguay shelves and then distributed northward by the shelf current system. From 4.7 to 2 cal kyr BP the climate became gradually wetter over the continent and the contribution of oxidized phases from the weathered Paraná Basin (mainly from the basaltic and acidic volcanics) started to become important. This change in climate overlaps in time awith the late Holocene sea level fall recorded along the SE South American coast. Later, from2 up to 0.9 cal kyr BP even wetter conditions were prevalent in S and SE South America, and the RdlP sedimentary load became themain source of sediments transported to the SE Brazilian shelf by the BCC. The magnetic record of core 7610 reported here together with other paleoenvironmental tracers (palynology, geochemistry and stable isotopes) thus indicates that the inception of the RdlP plume onto the SE Brazilian shelf started as early as 4.7 cal kyr BP and has been strengthened since then mostly due to changes in precipitation over South America and to a smaller extent by sea-level changes

Associações de Foraminíferos em Resposta a Variações Ambientais da Laguna de Aveiro -- Portugal

This study is based on the characterization of the sedimentary environment in selected sites, located in Aveiro canals and salt-pans, in the eastern-central and northern part of Aveiro Lagoon. Results of physicochemical parameters measured in water and sediment, as well as grain size, geochemical and microfaunal (benthic foraminifera) data are analyzed. The determinants factors of spatial and seasonal variability of living and dead foraminiferal assemblages were analyzed in two sampling periods, late summer and late winter, in order to study the response of these organisms to the impact caused by pollution and sazonal variation of physicochemical parameters. Biotic and abiotic results are analyzed to discriminate sites with different degree of environmental stress. The conditions of salinity, temperature, pH and Eh in the studied sites vary spatially and seasonally. The sediment in these locations is generally poorly oxygenated, suboxic or even anoxic a few millimeters below the surface. Some of the sites are affected by chemicals derived from industrial effluents and urban contaminants. The most polluted areas by heavy metals such as As, Cr, Cu and Zn are Porto de Salreu, Largo do Laranjo and some locals in the city of Aveiro. Foraminiferal assemblages in the studied sites integrate common lagoonal and estuarine euryhaline and eurythermic species, most of which tolerant to the oxygen reduction. The size of the living foraminiferal communities is reduced and their structure affected by increasing concentrations of heavy metals such as As, Cr, Cu and Zn, as well as by the high variability of environmental parameters such as low Eh, related to depressed levels of oxygen in the sediment, leading to the death of many species. The results also indicate a greater tolerance of some opportunistic species to the Pb enrichment, since the environment offer them abundance and quality of food.Este estudo baseia-se na caracterização do ambiente sedimentar de locais selecionados em canais e salinas da cidade de Aveiro, na zona central leste e na zona norte da Ria de Aveiro. Nessa caracterização foram utilizados os resultados de parâmetros físico-químicos medidos na água e nos sedimentos, assim como dados granulométricos, geoquímicos e microfaunais (foraminíferos bentônicos). Os fatores condicionantes da variabilidade espacial e sazonal das associações viva e morta de foraminíferos foram avaliados em dois períodos de amostragem: no final do verão e no final do inverno, tendo em vista a análise da resposta destes organismos ao impacto causado pela poluição e variação sazonal dos parâmetros físico-químicos. Os resultados bióticos e abióticos foram analisados para discriminar locais com diferente grau de estresseambiental. As condições de salinidade, temperatura, pH e Eh nos locais estudados variam espacial e sazonalmente. O sedimento nesses locais é em geral mal oxigenado, subóxico ou mesmo anóxico em alguns milímetros abaixo da superfície. Alguns dos locais encontram-se afetados por contaminantes químicos derivados de efluentes industriais e urbanos. As zonas mais poluídas por metais pesados como o As, Cr, Cu e Zn incluem o Porto de Salreu, Largo do Laranjo e alguns locais da Cidade de Aveiro. As associações de foraminíferos, nos locais estudados, integram espécies euritérmicas e eurihalinas comuns em ambientes lagunares e estuarinos, sendo majoritariamente tolerantes à redução de oxigênio. A dimensão das comunidades vivas de foraminíferos foi reduzida e a sua estrutura afetada pelo aumento das concentrações de metais pesados como As, Cr, Cu e Zn, assim como, pela variabilidade dos parâmetros ambientais, nomeadamente o Eh, relacionado com as condições de oxigenação do sedimento. Os dados indicam que as condições adversas podem ser causa de morte destes organismos. Sugerem também uma maior tolerância destes organismos ao enriquecimento por Pb, desde que o meio lhes proporcione abundância de alimento

Seismic stratigraphy of the central South China Sea basin and implications for neotectonics

Coring/logging data and physical property measurements from International Ocean Discovery Program Expedition 349 are integrated with, and correlated to, reflection seismic data to map seismic sequence boundaries and facies of the central basin and neighboring regions of the South China Sea. First-order sequence boundaries are interpreted, which are Oligocene/Miocene, middle Miocene/late Miocene, Miocene/Pliocene, and Pliocene/Pleistocene boundaries. A characteristic early Pleistocene strong reflector is also identified, which marks the top of extensive carbonate-rich deposition in the southern East and Southwest Subbasins. The fossil spreading ridge and the boundary between the East and Southwest Subbasins acted as major sedimentary barriers, across which seismic facies changes sharply and cannot be easily correlated. The sharp seismic facies change along the Miocene-Pliocene boundary indicates that a dramatic regional tectonostratigraphic event occurred at about 5 Ma, coeval with the onsets of uplift of Taiwan and accelerated subsidence and transgression in the northern margin. The depocenter or the area of the highest sedimentation rate switched from the northern East Subbasin during the Miocene to the Southwest Subbasin and the area close to the fossil ridge in the southern East Subbasin in the Pleistocene. The most active faulting and vertical uplifting now occur in the southern East Subbasin, caused most likely by the active and fastest subduction/obduction in the southern segment of the Manila Trench and the collision between the northeast Palawan and the Luzon arc. Timing of magmatic intrusions and seamounts constrained by seismic stratigraphy in the central basin varies and does not show temporal pulsing in their activities.Keywords: South China Sea, Neotectonism, Core-well-seismic integration, Seismic facies, Seismic stratigraphy, IODP Expedition 34