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Distribuição das associações de Foraminíferos e Ostracodos bentónicos na zona superior do talude continental oeste-algarvio: avaliação da influência do regime de produtividade
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Resumo(s)
Esta dissertação foi desenvolvida com base no estudo de dez amostras recolhidas na parte superior do talude continental oeste algarvio, a sul de Portugal, entre -233m e -511 m, em Janeiro e Junho de 2008. Os objectivos essenciais foram: 1) caracterizar as associações de foraminíferos e ostracodos da zona de estudo, identificando as espécies que as constituem, 2) avaliar a influência do upwelling costeiro, nomeadamente a sua sazonalidade e 3) da Veia de Água do Mediterrâneo na constituição e distribuição destas associações. As amostras foram tratadas em laboratório segundo os métodos clássicos, usados em Micropaleontologia, de lavagem, triagem, identificação taxonómica e contagem das espécies. Para os foraminíferos triaram-se cerca de 300 indivíduos por amostra e para os ostracodos 30 cm3 do resíduo de lavagem (ᴓ>63µm). Obtiveram-se 4 313 espécimens de foraminíferos distribuídos por 100 espécies, pertencentes a 60 géneros entre os quais se destacam: Bolivina, Bolivinellina, Bulimina, Cassidulina, Globocassidulina, Hyalinea, Trifarina e Uvigerina. Foram traídos 3 947 espécimens de ostracodos, distribuídos por 78 espécies, pertencentes a 45 géneros entre os quais se destacam: Buntonia, Bythocypris, Cytherella, Cytheropteron, Henryhowella, Krithe, Paracypris, Parakrithe, Pterygocythereis e Rectobuntonia.
Nas associações de foraminíferos reconheceram-se 5 espécies dominantes: Bolivina ordinária, Bolivina spathulata, Bulimina marginata, Cassidulina carinata e Cassidulina teretis. Nas associações de ostracodos destacam-se Bythocypris obtusata, Cytherella alvearium, Cytherella sp. 1, Henryhowella sarsii, Krithe keyi, Krithe aff. Praetexta, Krithe aff. Pernoides e Paracypris polita como espécies dominantes, das quais se salientam Henryhowella sarsii e K. aff. Praetexta presentes ao longo de todo o talude. As espécies acessórias de foraminíferos perfazem um total de 35 e no caso dos ostracodos de 31. Estas espécies são na sua maioria alóctones, que sofreram transporte, sendo algumas mediterrâneas e outras da zona costeira. A maior abundância de espécies mediterrâneas surge na Estações 19, 20 e 21, que correspondem às amostras em que o sedimento é mais grosseiro (47% a 65% de sedimento fino). As espécies de ostracodos associadas a estas amostras são Anchistrocheles cf. Tenera, Bythocypris obtusata, Cytherella alvearium, Henryhowella sarsii e Rectobuntonia miranda. Entre as espécies mediterrâneas de foraminíferos, a mais abundantes é Uvigerina mediterrânea.
A aplicação da análise de Clusters, modo R e modo Q e da análise de correspondências (CA) permitiu correlacionar as espécies e as amostras com alguns factores do meio. Verificou-se que os ostracodos se correlacionam positivamente com a textura do sedimento e com a profundidade, enquanto os foraminíferos não mostram correlação com estes factores, mas sim com outros factores como a quantidade ou o tipo de matéria orgânica presente no sedimento. Juntando os resultados obtidos com o estudo oceanográfico foi possível reconhecer a influência da Veia de Água do Mediterrâneo, através do upwelling costeiro a estas profundidades.
This study has been developed on tem samples collected in the upper continental slope of western Algarve, south Portugal, in January and June 2008, between -233 m and -511 m depth. The aims of this work were: (i) to characterize the foraminifera and ostracoda assemblages, identifying the species present in each sample; (ii) verify wheter there is any influence of the seasonal upwelling, the Mediterranean Outflow Water and seasonability itself in the assemblages. The samples were treated in the laboratory according to the classical micropalaentological techniques: washing, picking up, taxonomical identification and scouting of the species. 300 Foraminifera specimens were collected in each sample; 4313 specimens were obtained distributed in 100 species, belonging to 60 genera, the most important being: Bolivina, Bolivinellina, Bulimina, Cassidulina, Globocassidulina, Hyalinea, Trifarina and Uvigerina. For Ostracoda, all specimens contained in each sample (30 cm3) were collected; 3947 specimens were obtained distributed by 78 species, belonging to 45 genera, the most important being: Buntonia, Bythocypris, Cytherella, Cytheropteron, Henryhowella, Krithe, Paracypris, Parakrithe, Pterygocythereis and Rectobuntonia. There are 5 dominant species in the foraminfer assemblage: : Bolivina ordinária, Bolivina spathulata, Bulimina marginata, Cassidulina carinata e Cassidulina teretis. In the ostracoda assemblage the dominant species are: se Bythocypris obtusata, Cytherella alvearium, Cytherella sp. 1, Henryhowella sarsii, Krithe keyi, Krithe aff. Praetexta, Krithe aff. Pernoides and Paracypris polita. The species Henryhowella sarsii and K. aff. Praetexta are present in all the samples all over the continental slope. There are 35 accessory species in the foraminfer assemblages and 31 in the ostracoda ones. These species were mostly transported from Mediterranean Sea or from coastal areas. The majority of the Mediterranean species occurs in the sites 19, 20 and 21 corresponding to the coarser samples (47% to 65% fine sediment). The ostracoda species that are associated with these samples are: Anchistrocheles cf. Tenera, Bythocypris obtusata, Cytherella alvearium, Henryhowella sarsii and Rectobuntonia miranda. The application of Cluster analysis, R and Q mode, and the correspondence analysis (CA) allowed correlating the species and the samples with some environmental factors. It was observed that the ostracoda positively correlate with the sediment texture and with depth. The foraminifera don’t show any correlation with these factors, correlating better with the quantity or even type of organic matter in the sediment. When the obtained results are combined with the oceanographic data it is possible to recognize the influence of the Mediterranean Outflow Water, through the composition of the foraminifera and ostracoda assemblages; and at the same time it is possible to exclude the upwelling influence, at these depths.
This study has been developed on tem samples collected in the upper continental slope of western Algarve, south Portugal, in January and June 2008, between -233 m and -511 m depth. The aims of this work were: (i) to characterize the foraminifera and ostracoda assemblages, identifying the species present in each sample; (ii) verify wheter there is any influence of the seasonal upwelling, the Mediterranean Outflow Water and seasonability itself in the assemblages. The samples were treated in the laboratory according to the classical micropalaentological techniques: washing, picking up, taxonomical identification and scouting of the species. 300 Foraminifera specimens were collected in each sample; 4313 specimens were obtained distributed in 100 species, belonging to 60 genera, the most important being: Bolivina, Bolivinellina, Bulimina, Cassidulina, Globocassidulina, Hyalinea, Trifarina and Uvigerina. For Ostracoda, all specimens contained in each sample (30 cm3) were collected; 3947 specimens were obtained distributed by 78 species, belonging to 45 genera, the most important being: Buntonia, Bythocypris, Cytherella, Cytheropteron, Henryhowella, Krithe, Paracypris, Parakrithe, Pterygocythereis and Rectobuntonia. There are 5 dominant species in the foraminfer assemblage: : Bolivina ordinária, Bolivina spathulata, Bulimina marginata, Cassidulina carinata e Cassidulina teretis. In the ostracoda assemblage the dominant species are: se Bythocypris obtusata, Cytherella alvearium, Cytherella sp. 1, Henryhowella sarsii, Krithe keyi, Krithe aff. Praetexta, Krithe aff. Pernoides and Paracypris polita. The species Henryhowella sarsii and K. aff. Praetexta are present in all the samples all over the continental slope. There are 35 accessory species in the foraminfer assemblages and 31 in the ostracoda ones. These species were mostly transported from Mediterranean Sea or from coastal areas. The majority of the Mediterranean species occurs in the sites 19, 20 and 21 corresponding to the coarser samples (47% to 65% fine sediment). The ostracoda species that are associated with these samples are: Anchistrocheles cf. Tenera, Bythocypris obtusata, Cytherella alvearium, Henryhowella sarsii and Rectobuntonia miranda. The application of Cluster analysis, R and Q mode, and the correspondence analysis (CA) allowed correlating the species and the samples with some environmental factors. It was observed that the ostracoda positively correlate with the sediment texture and with depth. The foraminifera don’t show any correlation with these factors, correlating better with the quantity or even type of organic matter in the sediment. When the obtained results are combined with the oceanographic data it is possible to recognize the influence of the Mediterranean Outflow Water, through the composition of the foraminifera and ostracoda assemblages; and at the same time it is possible to exclude the upwelling influence, at these depths.
Descrição
Tese de mestrado em Geologia do Ambiente, Riscos Geológicos e Ordenamento do Território, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2013
Palavras-chave
Foraminíferos Ostracodos Algarve Talude continental Mar Mediterrâneo Teses de mestrado - 2013