High resolution geochemical and grain-size analysis of the AD 1755 tsunami deposit: Insights into the inland extent and inundation phases
Moreira, S.; Costa, P.J.M.; Andrade, C.; Ponte Lira, C.; Freitas, M.C.; Oliveira, M.A.; Reichart, G.-J. (2017). High resolution geochemical and grain-size analysis of the AD 1755 tsunami deposit: Insights into the inland extent and inundation phases. Mar. Geol. 390: 94-105. https://dx.doi.org/10.1016/j.margeo.2017.04.007
In: Marine Geology. Elsevier: Amsterdam. ISSN 0025-3227; e-ISSN 1872-6151, meer
In the study of palaeotsunamis it is crucial to decipher the sedimentological record, to derive intensity of pastevents and to infer different inundation phases. To achieve this goal, it is important to apply high-resolutiontechniques that allow magnifying intra-deposit details (at a sub-centimetric scale) that otherwise would not beperceived; consequently, valuable information could be overlooked.In this work, we applied successfully high-resolution geochemical and grain-size analyses – XRF core-scanningand image analysis, respectively – to the AD 1755 tsunami deposit. This quartz sand enriched in bioclastdeposit (exhibiting high Si/Al and Ca/Ti) was recognized in the coastal stratigraphic sequence of Salgadoslagoon due to its contrasting composition when compared with the under and overlying mud layers with scarcebioclasts (exhibiting low Si/Al and Ca/Ti). In the absence of textural evidence, the identification of peakingconcentrations of Cl, S and Br (all major constituents of sea salt) in a continuous muddy sequence allowedslightly extending farther inland the limit of inundation. In addition, grain-size analysis data attested the fininginland of the deposit. Furthermore, despite the macroscopic massive structure of the tsunami deposit, throughoutthe lagoon, grain-size results revealed more complexity and allowed inferring up to four depositional sequencesdirectly associated with the AD 1755 tsunami inundation.
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