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Caracterização sedimentar da plataforma interna do sotavento algarvio
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A plataforma continental algarvia há muito que é objecto de estudo por parte de
investigadores nacionais e estrangeiros, no que se refere a dinâmica sedimentar. O
objectivo deste trabalho é caracterizar a cobertura sedimentar da plataforma interna
algarvia desde Vila Real de Santo António até Olhos de Água. Para tal foram recolhidas
199 amostras em 92 perfis perpendiculares à costa entre os meses de Outubro e
Novembro do ano de 2005. As amostras foram recolhidas com uma draga Petit Ponar
entre os 3 e os 16 metros de profundidade.
Analisou-se a granulometria das 199 amostras através do método da peneiração para as
classes granulométricas cascalhos e as areias e método da pipetagem para as fracções
silto-argilosas. A análise mineralógica foi efectuada em 38 amostras, que se
consideraram ser representativas da zona amostrada.
Na área estudada as amostras eram maioritariamente constituídas por areias quártzicas.
Observaram-se 4 zonas com características granulométricas e mineralógicas distintas:
- A zona entre o Rio Guadiana e Cacela caracterizada por areias finas e onde se
observava grande quantidade de material silto-argiloso resultante da influência
do rio, sendo que o cascalho encontrado nesta zona é de origem biogénica;
- A zona entre Cacela e Cabo de Santa. Maria (Ria Formosa Este) caracterizada
por areias médias de origem quártzicas, influenciada pelas condições
hidrodinâmicas de menor energia;
- A zona entre Cabo de Santa. Maria e Garrão é constituída por areias finas
quartzica influenciada pela maior exposição à onda dominante do que a zona
anteriormente aludida;
- A zona entre Garrão e Olhos de Água, constituída por areias grosseiras e
cascalho de origem quártzica, influenciada pelo contributo das arribas pouco
consolidadas existentes na zona.
The Algarve continental shelf has been the target of research of many foreign and national scientists dedicated to marine sedimentary dynamics. The purpose of this work is to characterizate the sedimentary cover of the Algarve inner continental shelf between Vila Real de Santo. Antonio and Olhos de Água. For that purpose 199 samples were collected along 92 shore normal profiles, between October and November of 2005. The samples have been collected with a Petit Ponar dredge st depths between 3 and 16 meters. . A grain size analysis was performed, with the sand and gravel fractions being sieved and the fine fractions analysed by the Pipette method. For the composition analysis 38 samples were observed, which have been considered to be representative of the study area. Quartzic sands dominate the sedimentary cover of the study area. There are 4 areas with distinct characteristics: - The area between Rio Guadiana and Cacela, characterized by having fine sand, with great amounts of silt and clay resulting from the river influence. The gravel found in this zone has biogenic origin; - The area between Cacela and Santa. Maria Cape (Ria Formosa East) characterized by quartzic sand, that is influenced by the low energy hydrodynamic conditions; - The area between Santa Maria Cape and Garrão is constituted by quartzic fine sand influenced by the exposition to the dominant waves; - The area between Garrão and Olhos de Água characterized by coarse sand and quartzic gravel, influenced by the sediment input due to the existent cliffs.
The Algarve continental shelf has been the target of research of many foreign and national scientists dedicated to marine sedimentary dynamics. The purpose of this work is to characterizate the sedimentary cover of the Algarve inner continental shelf between Vila Real de Santo. Antonio and Olhos de Água. For that purpose 199 samples were collected along 92 shore normal profiles, between October and November of 2005. The samples have been collected with a Petit Ponar dredge st depths between 3 and 16 meters. . A grain size analysis was performed, with the sand and gravel fractions being sieved and the fine fractions analysed by the Pipette method. For the composition analysis 38 samples were observed, which have been considered to be representative of the study area. Quartzic sands dominate the sedimentary cover of the study area. There are 4 areas with distinct characteristics: - The area between Rio Guadiana and Cacela, characterized by having fine sand, with great amounts of silt and clay resulting from the river influence. The gravel found in this zone has biogenic origin; - The area between Cacela and Santa. Maria Cape (Ria Formosa East) characterized by quartzic sand, that is influenced by the low energy hydrodynamic conditions; - The area between Santa Maria Cape and Garrão is constituted by quartzic fine sand influenced by the exposition to the dominant waves; - The area between Garrão and Olhos de Água characterized by coarse sand and quartzic gravel, influenced by the sediment input due to the existent cliffs.
Descrição
Dissertação de Mestrado, Oceanografia, Faculdade de Ciências do Mar e do Ambiente, Universidade do Algarve, 2007
Palavras-chave
Oceanografia Mineralogia Algarve