BIBLIOS

Document type
Journal articles

Document subtype
Full paper

Title
The AD 1755 tsunami deposits onshore and offshore of Algarve (south Portugal): Sediment transport interpretations based on the study of Foraminifera assemblages

Participants in the publication
Maria Quintela (Author)
Pedro J.M. Costa (Author)
Dep. Geologia
IDL
Francisco Fatela (Author)
Dep. Geologia
IDL
Teresa Drago (Author)
Natalia Hoska (Author)
César Andrade (Author)
Dep. Geologia
IDL
Maria C. Freitas (Author)
Dep. Geologia
IDL

Summary
Tsunamis are amongst the most catastrophic natural hazards affecting worldwide coastal areas. Their\nimpacts are recorded in the geological archives and its study provides crucial insights into the dynamics\nand intensity of these events. The accurate establishment of return periods can also be derived using\nsedimentological data. Onshore tsunami deposits have been extensively described over recent years\nthrough the application of a wide range of sedimentological proxies, including micropalaeontological\nanalysis.\nIn this work, the identification of palaeotsunami evidence, in both the onshore and offshore sedimentary\nrecord of south Portugal, was performed, relying mostly on the study of Foraminifera assemblages.\nThree onshore trenches and one offshore core were analyzed and imprints of the AD 1755\ntsunami were observed based in the identification of allochthonous foraminiferal species, increase in the\nnumber of broken/abraded tests and its correlation with coarser mean grain size. This was possible after\nmicropalaeontological environmental characterization of both low-energy onshore and offshore presentday\nsedimentation regimes.\nIn the onshore record, three distinct sediment transport phases were differentiated within the tsunamigenic\nunit. The basal phase portraying the initial inundation represented by the dominance of\nmarine Foraminifera species in a highly diverse assemblage. The higher energetic character of this phase\nwas also reflected in the identification of the highest number of broken/abraded tests. The intermediate\nphase reflects an unspecified number of inundation and backwash pulses that were recognized based in\nthe well-balanced presence of estuarine (brackish) and marine species, the sharp decrease in the diversity\nindex and in the number of broken/abraded tests. The final phase recorded in the tsunamigenic\nunit registers the imprint of the last relevant backwash which was identified based on the dominance of\nestuarine (brackish) fauna. The overlying unit is dominated by tidal marsh species, demonstrating the\nstart of the coastal system recovery phase.\nIn the offshore record, it was possible to identify 2 distinct historical tsunami events (AD 1755 and AD\n1969). This was achieved through the identification of significant increases in coastal Foraminifera\nspecies coupled with the presence of coarser layers. This interpretation was sustained by indirect ageestimation\nmethods (radiocarbon and 210Pb) that ascribed compatible ages to the historical tsunami\nevents. The results obtained in this study stress the relevance and innovative character of this onshore\nand offshore multiproxy approach in the recognition and understanding of tsunami events.


Institution
FACULDADE DE CIÊNCIAS DA UNIVERSIDADE DE LISBOA

Where published
Quaternary International

Publication Identifiers
ISSN - 1040-6182

Publisher
Elsevier BV



Document Identifiers
DOI - https://doi.org/10.1016/j.quaint.2015.12.029
URL - http://dx.doi.org/10.1016/j.quaint.2015.12.029

Rankings
SCOPUS Q1 (2016) - 1.121 - Earth-Surface Processes
SCIMAGO Q1 (2016) - 1.121 - Earth-Surface Processes