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Estudo paleoclimático e paleobotânico de Angra do Heroísmo a partir dos fósseis incorporados nas cinzas vulcânicas do Monte Brasil
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Abstract(s)
Esta tese centrou-se na área da paleoclimatologia e paleontologia (mais precisamente a paleobotânica), na tentativa de perceber como o vulcanismo e o clima são capazes de alterar a paisagem e os ecossistemas.
Possui-se neste momento um conjunto muito vasto de fósseis preservados nas cinzas vulcânicas do Monte Brasil, em Angra do Heroísmo, Terceira, Açores, Portugal, que permitiu encetar um estudo paleobotânico e paleoclimático a nível local. O material fóssil estudado foi proveniente das Baías (Falésias) do Fanal e de Angra do Heroísmo, e de um local em Santa Luzia, propriedade da Associação Espeleológica “Os Montanheiros” e de alguns particulares.
Neste estudo, tentou-se verificar se o padrão geométrico de venação de folhas era suscetível de modelação para que, a partir dos modelos encontrados se pudessem identificar fragmentos de fósseis.
Do grande conjunto de fósseis foliares recolhidos foram selecionados apenas 30 exemplares para estudo, sendo que ainda ficou uma significativa quantidade por analisar.
Numa primeira fase, tentou-se a descrição mais completa possível dos espécimes de modo a identificar todo o material fóssil coletado, através da arquitetura foliar dos espécimes. Numa segunda fase, para auxiliar na identificação dos espécimes, optou-se por elencar um conjunto de parâmetros baseados principalmente nas caraterísticas biométricas (e.g. ângulo das nervuras secundárias, densidade, entre outras) de folhas de espécies atuais que se assemelhassem aos fósseis analisados.
Da análise florística efetuada resultou a identificação de 30 morfotipos, sendo que 21 dos quais foram identificados conforme (cf.) a espécie. Conforme Laurus azorica foram identificados 47%; cf. Viburnum treleasei (19%); cf. Picconia azorica (9%); cf. Morella faya (5%); cf. Juniperus brevifolia (5%); cf. Hedera azorica (5%); cf. Polystichum setiferum (5%); cf. Dracaena draco (5%). Dos 7 identificados conforme a família, podese dizer que foram de Lauraceae; Parmeliaceae; Dryopteridaceae. Os restantes 2 morfotipos foram atribuídos a folhas dicotiledóneas indeterminadas.
A coloração da superfície de alguns dos fósseis recolhidos, pode ser associada a processos de silicificação e piritização que de acordo com testes laboratoriais realizados, permite admitir a existência de uma zona muito húmida ou encharcada localizada entre Santa Luzia e a Baía do Fanal. Tais resultados apontam para um ambiente também muito distinto do que é hoje o de Angra do Heroísmo.
Perante os cenários paleoambientais obtidos e tendo em conta as diferentes associações observadas de vegetação, podemos inferir que no Quaternário, o local de estudo aparentemente possuía um clima mais frio e mais húmido do que o atual, de baixa altitude, com um tipo de vegetação, aparentemente heterogénea, e provavelmente constituída por mosaicos casuais e com diferentes associações vegetais.
ABSTRACT: This thesis was focus on the area of paleoclimatology and paleontology (more precisely paleobotany) in an attempt to understand how volcanism and climate are capable of altering landscape and ecosystems. At this moment, there is a very vast set of fossils preserved in the volcanic ash of Monte Brasil, Angra do Heroismo, Terceira, Azores, Portugal, which allows the beginning of a paleobotanical and paleoclimatic study at the local level. The fossil material to be studied comes from Fanal, Angra do Heroísmo Bays (Cliffs) and from a location in Santa Luzia, owned by the Os Montanheiros Speleological Association and some individuals. In this study, we tried to verify if the geometric pattern of leaf venation was susceptible to modeling so that, from the models found, fragments of fossils could be identified. From the vast collection of collected leaf fossils, only 30 specimens were selected, and a large amount remain to be analyzed. In the first stage, the most complete description of the specimens was attempted to identify all the fossil material collected through the leaf architecture of the specimens. In a second phase, to assist in the identification of the specimens, it was decided to list a set of parameters based mainly on the biometric characteristics (e.g. secondary rib angle, density, among others) of leaves of current species resembling the analysed fossils. The floristic analysis resulted in the identification of 30 morphotypes, 21 of which were identified according to the species. According to Laurus azorica, 47% were identified; cf. Viburnum treleasei (19%); cf. Picconia azorica (9%); cf. Morella faya (5%); cf. Juniperus brevifolia (5%); cf. Hedera azorica (5%); cf. Polystichum setiferum (5%); cf. Dracaena draco (5%). Of the 7 identified according to the family, it can be said that they were Lauraceae; Parmeliaceae; Dryopteridaceae. The remaining 2 morphotypes were attributed to indeterminate dicotyledonous leaves. The coloring of the surface of some of the collected fossils can be associated with silicification and pyritization processes which, according to laboratory tests carried out, allows to admit the existence of a very wet or waterlogged area located between Santa Luzia and Baía do Fanal. These results point to an environment that is also very different from what Angra do Heroísmo is today. Given the obtained paleoenvironmental scenario and taking into account the different associations of vegetation observed, we could infer that in the Quaternary, the study site apparently had a colder and more humid climate than the current one, of low altitude, with a vegetation type, apparently heterogeneous, and probably constituted by casual mosaics and with different plant associations.
ABSTRACT: This thesis was focus on the area of paleoclimatology and paleontology (more precisely paleobotany) in an attempt to understand how volcanism and climate are capable of altering landscape and ecosystems. At this moment, there is a very vast set of fossils preserved in the volcanic ash of Monte Brasil, Angra do Heroismo, Terceira, Azores, Portugal, which allows the beginning of a paleobotanical and paleoclimatic study at the local level. The fossil material to be studied comes from Fanal, Angra do Heroísmo Bays (Cliffs) and from a location in Santa Luzia, owned by the Os Montanheiros Speleological Association and some individuals. In this study, we tried to verify if the geometric pattern of leaf venation was susceptible to modeling so that, from the models found, fragments of fossils could be identified. From the vast collection of collected leaf fossils, only 30 specimens were selected, and a large amount remain to be analyzed. In the first stage, the most complete description of the specimens was attempted to identify all the fossil material collected through the leaf architecture of the specimens. In a second phase, to assist in the identification of the specimens, it was decided to list a set of parameters based mainly on the biometric characteristics (e.g. secondary rib angle, density, among others) of leaves of current species resembling the analysed fossils. The floristic analysis resulted in the identification of 30 morphotypes, 21 of which were identified according to the species. According to Laurus azorica, 47% were identified; cf. Viburnum treleasei (19%); cf. Picconia azorica (9%); cf. Morella faya (5%); cf. Juniperus brevifolia (5%); cf. Hedera azorica (5%); cf. Polystichum setiferum (5%); cf. Dracaena draco (5%). Of the 7 identified according to the family, it can be said that they were Lauraceae; Parmeliaceae; Dryopteridaceae. The remaining 2 morphotypes were attributed to indeterminate dicotyledonous leaves. The coloring of the surface of some of the collected fossils can be associated with silicification and pyritization processes which, according to laboratory tests carried out, allows to admit the existence of a very wet or waterlogged area located between Santa Luzia and Baía do Fanal. These results point to an environment that is also very different from what Angra do Heroísmo is today. Given the obtained paleoenvironmental scenario and taking into account the different associations of vegetation observed, we could infer that in the Quaternary, the study site apparently had a colder and more humid climate than the current one, of low altitude, with a vegetation type, apparently heterogeneous, and probably constituted by casual mosaics and with different plant associations.
Description
Dissertação de Mestrado, Gestão e Conservação da Natureza, 13 de fevereiro de 2020.
Keywords
Climatologia Fósseis Vegetais Paleobotânica Paleontologia Vegetação Vulcanismo Ilha Terceira (Açores) Paleobotany Paleoclimate Azores
Citation
Machado, Pedro Leando Alves Soares. "Estudo paleoclimático e paleobotânico de Angra do Heroísmo a partir dos fósseis incorporados nas cinzas vulcânicas do Monte Brasil". 2020. 165 p.. (Dissertação de Mestrado em Gestão e Conservação da Natureza). Angra do Heroísmo: Universidade dos Açores, 2019. [Consult. Dia Mês Ano]. Disponível em www:<http://hdl.handle.net/10400.3/5955>.