High resolution geochemical and grain-size analysis of the AD 1755 tsunami deposit: Insights into the inland extent and inundation phases

In this work, we applied successfully high-resolution geochemical and grain-size analyses - XRF core-scanning and image analysis, respectively - to the AD 1755 tsunami deposit. This quartz sand enriched in bioclast deposit (exhibiting high Si/Al and Ca/Ti) was recognized in the coastal stratigraphic sequence of Salgados lagoon due to its contrasting composition when compared with the under and overlying mud layers with scarce bioclasts (exhibiting low Si/Al and Ca/Ti). In the absence of textural evidence, the identification of peaking concentrations of Cl, S and Br (all major constituents of sea salt) in a continuous muddy sequence allowed slightly extending farther inland the limit of inundation. In addition, grain-size analysis data attested the fining inland of the deposit. Furthermore, despite the macroscopic massive structure of the tsunami deposit, throughout the lagoon, grain-size results revealed more complexity and allowed inferring up to four depositional sequences directly associated with the AD 1755 tsunami inundation.