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Navegando por Assunto "Holocene"

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    Análise faciológica e estratigráfica da planície costeira de Soure (margem leste da ilha de Marajó-PA), no trecho compreendido entre o canal do Cajuúna e o estuário Paracauari
    (Instituto Nacional de Pesquisas da Amazônia, 2007-06) FRANÇA, Carmena Ferreira de; SOUZA FILHO, Pedro Walfir Martins e; EL-ROBRINI, Maâmar
    Soures's coastal plain, eastern Marajó island (Pará), is formed by muddy and sandy deposits, low gradient areas submitted to tidal and wave processes. The morphological features are tidal flats, estuaries, tidal channels and barrier-beach ridges . The faciological and stratigraphical analysis of six vibra-core with medium deph of four meters and from outcrops allowed a caracterization of depositional environments, temporal sequence and spacial corelation, the elaboration of stratigraphical seccions and column. Were identified five facies associations: (1) tidal flat facies, (2) mangrove facies, (3) tidal channel bar facies, (4) beach facies and (5) dune facies. The sedimentary history of the Soure coastal plain is represented by two stratigraphical successions: (1) progradational succession (tidal flat, mangrove and channel bar facies association) and (2) retrogradational succession (beach and dune facies association). These successions are related to a expansion phase of tidal flats and mangroves with progradation of the coastline (Middle/Late Holocene) and a posterior retrogradation phase with landward migration of the shoreline (Late Holocene). The depositional history of the Soure coastal plain is related to the holocenic evolution model of the northeast coastal plains of Pará.
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    Antropoceno na Amazônia: holoceno em curso ou prelúdio de uma nova época geológica do homem?
    (Universidade Federal do Pará, 2021-08-31) PONTE, Franciney Carvalho da; SZLAFSZTEIN, Cláudio Fabian; http://lattes.cnpq.br/1348005678649555; https://orcid.org/0000-0002-2855-2056
    The Natural Domains of the Brazilian Amazon present a high biogeographic diversity, favored by the complex geological substratum and equatorial climate, both predominant in the Amazonian landscape, located in the northern portion of Brazil, covering an area equivalent to 40% of the national territory (~3.7 million Km2). Human expansion in the Amazon has produced a series of transformations in its natural resources. In this sense, this work aimed to perform a retrospective on the trajectory of human beings in the Amazonian domains, through the spatialization of anthropogenic evidences and analysis of anthropogenic indicators, likely to be associated with precepts of the Anthropocene, made possible by a geographical perspective. The analysis raised the aspects of both morphoclimatic and phytogeographic domains, highlighting their dominant landscapes and natural systems, through biophysical compartmentalization, working as a substrate in the analysis of the dynamics of socio-spatial events and the materialized evidences of human action in the landscapes, under a broad temporal spectrum - the Holocene. The research was based on a holistic and integrative approach of variables, related to both natural and socio-spatial aspects, from a systemic vision, aimed at sizing and measuring the patterns of use of natural resources, the anthropogenization degree of natural domains and the proposition of anthropogenic landscapes/structures. In this sense, the research revealed that these domains currently present a very significant anthropogenic percentage of approximately 70%, the result of a broad and diverse socio-spatial dynamic, which attributed to the region a marked variability of human macrosystems and semi-natural landscapes embedded in apparently natural ecosystems. However, it was detected that this estimate is probably underestimated, if we consider the evidence, according to a cumulative perspective, reaching a value around 150%, that is, 50% above the total area of the study, which denounces a high anthropogenic pressure in the region. Given the above, and considering the Anthropocene precepts, centered on the anthropogenic conception, it is suggested that the Amazon region contains anthropogenic landscapes, substantially altered, for at least four thousand years AP, when much of its domains were already occupied and significantly used and managed by human groups.
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    A evolução dos manguezais nos litorais Nordeste e Sul brasileiros durante o Holoceno
    (Universidade Federal do Pará, 2020-09-30) FREIRE, Neuza Araújo Fontes; COHEN, Marcelo Cancela Lisboa; http://lattes.cnpq.br/8809787145146228
    It is possible that climate changes and sea level fluctuations (allogenic processes) are and will cause major changes in mangrove dynamics. However, other driving forces may be significantly affecting this system. Distinguishing allogenic and autogenic influence on mangroves is a challenging question, because mechanisms related to the natural dynamics of depositional environments (autogenic processes) have strong influences on the establishment and degradation of mangroves. Thus, impacts on mangroves caused by autogenic processes may be erroneously attributed to allogenic mechanisms. Therefore, it is imperative to identify the ‘fingerprint’ of global changes in modern mangrove dynamics. This thesis integrates palynological, geochemical, sedimentological data, 14C dating of sedimentary organic matter, geomorphological and vegetation data in order to evaluate the influence of autogenic and allogeneic processes on Brazilian mangroves during the Holocene. Tropical estuaries from Rio Grande do Norte and southern Bahia, and subtropical estuaries in northern and southern Santa Catarina estates with different climatic, geomorphological and oceanographic characteristics were studied. The Relative Sea-Level (RSL) along the Rio Grande do Norte reached modern level and stabilized at about 7,000 cal yr BP, allowing the mangrove establishment at the edges of the Ceará-Mirim River estuary until the nowadays. However, changes in the spatial distribution of mangroves have occurred since then due to channels dynamics in the region (autogenic processes). Considering the mangroves of the Jucuruçu River in southern Bahia, their horizontal and vertical distribution were controlled by the interactions of the changes in the RSL and fluvial discharge. Therefore, the dynamics of these estuarine mangroves during the Holocene was mainly controlled by changes in sea level and precipitation that affected fluvial discharge. These allogeneic mechanisms were the main drivers of the dynamics of these mangroves. However, during the last 600 years, factors intrinsic to the depositional system gained relevance by controlling the establishment and migration of mangroves by deposition and erosion of muddy tidal flats, abandonment and reactivation of channels (autogenic processes). In the case of Santa Catarina mangroves, the RSL rise up to the middle Holocene was decisive for the establishment of tidal flats appropriate for the expansion of saltmarshes. However, mangroves did not tolerate the Holocene low temperatures in the southern littoral of Santa Catarina. The pollen data indicate the establishment of mangroves with Laguncularia around 1,700 cal yr BP, followed by Avicennia and lastly Rhizophora trees, a cold less tolerant genus, around 650 cal yr BP in São Francisco do Sul, north of Santa Catarina. The mangroves of Laguna, south of Santa Catarina, composed of Laguncularia and Avicennia, were established in the current southern limit of the South American mangroves only in the last decades. No evidence was found for the presence of mangroves in Laguna during the Holocene. The establishment of these mangroves in the region probably started during the Anthropocene, as a consequence of the increase in minimum winter temperatures in southern Brazil. Considering changes in precipitation rates over drainage basins that feed mangrove estuaries, as well as trends in RSL rise and temperatures until the end of the 21st century, tropical estuarine mangroves will likely migrate to higher topographically sectors in the interior of the river valleys, where its extension will depend on the volume of river discharge interacting with the RSL rise. Subtropical mangroves are expected to expand to more temperate zones as minimum winter temperatures increase. This process should cause an increase in the diversity of mangrove species, such as the introduction of the Rhizophora genus in the current southern limit of the mangroves, positioned in Laguna-SC. However, in the case of high rates of RSL rise, the relatively new subtropical mangroves are also expected to migrate to topographically higher sectors of the coast.
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