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Contribuição dos métodos geofísicos para o modelo evolutivo da região de Santo André desde o último máximo glaciário
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Resumo(s)
Este trabalho visa a reconstituição paleogeográfica da região costeira de Santo André no
Quaternário recente através da aplicação de diversos métodos geofísicos (elétricos, eletromagnéticos
e sísmicos) aliada ao estudo de sondagens geológicas, com o intuito de compreender a resposta deste
sistema costeiro face às alterações climáticas impostas durante o Tardiglaciar e a primeira metade do
Holocénico. Pretende-se, deste modo, contribuir com uma abordagem multidisciplinar, à macroescala
temporal, para a caracterização da resiliência do ambiente estudado com base nas respostas
comportamentais passadas, dados de primordial importância face às mudanças globais e numa
perspetiva de Gestão Integrada da Zona Costeira.
Assumindo as zonas costeiras uma importância estratégica em termos ambientais, económicos,
sociais, culturais e recreativos, torna-se extremamente importante identificar os fatores forçadores e
compreender os processos de evolução da linha de costa, a fim de se efetuar uma correta avaliação
das medidas de gestão a implementar.
No decurso desta investigação foram aplicados quatro métodos geofísicos, designadamente, a
resistividade elétrica e o método eletromagnético transiente sobre as planícies aluviais, o georadar ao
longo do sistema dunar e a sísmica de reflexão na plataforma continental e no corpo lagunar. A
interpretação dos resultados foi validada com base na análise de trabalhos de prospeção coligidos
(manuais e mecânicos) e nos resultados laboratoriais (sedimentológicos e geoquímicos) de amostras
recolhidas em sanjas executadas no sistema dunar.
Os resultados obtidos permitiram reconstruir a paleomorfologia fluvial durante o Último Máximo
Glaciar e no início do Holocénico, determinar a espessura de sedimentos acumulados nos vales
fluviais, caracterizar a estrutura interna do sistema dunar e desenvolver o respetivo modelo
deposicional baseado nas principais etapas evolutivas, bem como identificar variações na posição e
orientação da linha de costa durante os últimos 18 000 anos. A evolução paleogeográfica da área de
estudo foi conseguida através da combinação dos resultados obtidos neste trabalho com a análise
multidisciplinar de sondagens geológicas e as curvas de variação do nível médio do mar previamente
desenvolvidas para o litoral português, sendo apoiada pela informação arqueológica disponível.
This work aims to reconstruct the Late Quaternary paleogeographic evolution of the Santo André coastal area through the application of several geophysical methods (electrical, electromagnetic and seismic) combined with geological data analysis, in order to understand the coastal system response regarding climate changes that occurred during the Lateglacial and the Early Holocene. In addition, the study contributes with a multidisciplinary approach to past behavioral responses in evaluating the large-scale resilience of the costal environment, an issue of primary importance to Integrated Coastal Zone Management, especially when considered under the perspective of global changes. As coastal areas assume a strategic importance from an environmental, economic, social, cultural and recreational point of view, it becomes extremely important to identify forcing factors and to understand the coastline evolution, so that a correct assessment of the required management measures can be made. Current investigation included the application of four geophysical methods, namely, the electrical resistivity and transient electromagnetic method on alluvial plains, the ground penetrating radar along the dune system and seismic reflection on the continental shelf and the lagoon. Data interpretation was validated through the analysis of prospecting works (manual and mechanical) and laboratory analysis (sedimentological and geochemical) of samples collected in trenches excavated on the dune system. The results allowed to reconstruct the fluvial paleomorphology during the Last Glacial Maximum and the Early Holocene, to determine sediment thickness accumulated in the valleys, to characterize the internal structure of the dune system and to develop a depositional model based on the main evolutionary stages, as well as to identify variations in coastline position and orientation during the last 18 000 years. Paleogeographic evolution was achieved by combining the obtained results with the multidisciplinary analysis of geological records and sea level curves previously developed for the Portuguese coast, and is supported by the available archaeological data.
This work aims to reconstruct the Late Quaternary paleogeographic evolution of the Santo André coastal area through the application of several geophysical methods (electrical, electromagnetic and seismic) combined with geological data analysis, in order to understand the coastal system response regarding climate changes that occurred during the Lateglacial and the Early Holocene. In addition, the study contributes with a multidisciplinary approach to past behavioral responses in evaluating the large-scale resilience of the costal environment, an issue of primary importance to Integrated Coastal Zone Management, especially when considered under the perspective of global changes. As coastal areas assume a strategic importance from an environmental, economic, social, cultural and recreational point of view, it becomes extremely important to identify forcing factors and to understand the coastline evolution, so that a correct assessment of the required management measures can be made. Current investigation included the application of four geophysical methods, namely, the electrical resistivity and transient electromagnetic method on alluvial plains, the ground penetrating radar along the dune system and seismic reflection on the continental shelf and the lagoon. Data interpretation was validated through the analysis of prospecting works (manual and mechanical) and laboratory analysis (sedimentological and geochemical) of samples collected in trenches excavated on the dune system. The results allowed to reconstruct the fluvial paleomorphology during the Last Glacial Maximum and the Early Holocene, to determine sediment thickness accumulated in the valleys, to characterize the internal structure of the dune system and to develop a depositional model based on the main evolutionary stages, as well as to identify variations in coastline position and orientation during the last 18 000 years. Paleogeographic evolution was achieved by combining the obtained results with the multidisciplinary analysis of geological records and sea level curves previously developed for the Portuguese coast, and is supported by the available archaeological data.
Descrição
Tese de doutoramento, Geologia (Geologia Económica e do Ambiente), Universidade de Lisboa, Faculdade de Ciências, 2014
Palavras-chave
Geologia económica - Portugal Alterações climáticas Geologia e geofísica - depositos - sedimentologia - Portugal Paleogeografia Lagoa de Santo André Teses de doutoramento - 2014