Searching for continental related sediment in Algarve continental shelf sedimentary record as a tool to identify tsunami deposits

• Autor(a) principal: Santos, Jacqueline
• Data de Publicação: 2022
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.1/18647
• topic: Tsunami deposits offshore; Continental shelf; Historical tsunamis events; Sand mineralogical composition; Algarve; Domínio/Área Científica::Ciências Naturais::Outras Ciências Naturais

Records of earthquakes and associated tsunamis are particularly important in a tectonic active zone as it is Portugal, especially the Algarve coast. Studies of geological records allow assessing the information about undocumented tsunami events beyond a wider time frame than historical records. Most of the existing studies are focused especially on onshore deposits but in later years, offshore studies were developed, regarding their better preservation. In this scope, this work aims to add a new proxy to the results of the subtask WP2.2 of the ASTARTE project which the object was to characterize tsunami deposits at continental shelf sedimentary record off Quarteira-Faro coast. The objective of the present work is identify continental related sediments, that may likely to be transported by tsunami backwash. Detailed studies of the texture and sand mineralogical composition of the Algarve coastal zone and of some previously determined potential “high energy events" layers defined in the scope of the subtask WP2.2 in ASTARTE project (core MW107) were performed and compared. Two types of sand mineralogical compositions were identified in both studied layers and in coastal sites, in particular, those from Vale do Lobo and Forte Novo cliffs. They were named “iron-coated quartz”, and “orange clay aggregates”. Their presence in the ASTARTE defined layers coincides with the increased mean grain-size, molluscs, and the lower or absence of mica in these layers, which with other proxies data resulting from ASTARTE project (subtask WP2.2) support the related tsunami nature. Although only the topwards layer (Layer 4) coincides with the known 1755 Lisbon tsunami, the Layer 3 and Layer 1 might be potentially related to a high energy event. Future work should aim to study the sand mineralogical composition of the entire core to define the background sedimentation and confirm if the variations of continental related material from the local coastal areas are associated to high energy events. In addition, its also suggested to study more cores from the ASTARTE project (subtask WP2.2) for lateral correlation and it is further recommended to date above and below the layers of potential high energy events, to determine if the material was deposit immediately after the event or if it is the result of subsequent remobilization and transport in the inner shelf.