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Geochemical proxies and diatom assemblages were used in combination with grain size characteristics not only to describe the deposit left behind by the 27 February 2010, Maule tsunami at Las Cañas, Maule Region, Chile, but also to trace the maximum inundation limit of the event. The sandy deposit was laid down between 160 and 260 m inland behind an eroded sand dune and a lagoon but reached only 60% of the total tsunami inundation distance of 380 m, which was marked by organic debris, pumice clasts and wooden logs. It consisted of coarse to medium sand that thinned and fined inland. At the most seaward point, the 22 cm thick deposit exhibited a fining upward unit overlain by a couplet of coarsening–fining upward units, suggesting deposition by at least two waves, while farther inland the fining upward deposit was probably left behind by only one wave. Chemical proxies (Ca/Ti vs Sr/Ba) allow us to distinguish the deposit from the surrounding soil and indicate that it was sourced from the beach and/or dune area, with diatom assemblages confirming the marine origin of the deposit. Saltwater indicators (e.g. Cl, S) provide evidence for the maximum inundation limit beyond the extent of the sandy deposit, despite dilution and dissolution by 500 mm of rainfall in the six months since the tsunami. Marine and marine/brackish diatom assemblages decreased landward but were found up to the inundation limit and immediately beyond, suggesting the effect of diatom-bearing sea spray at the wave front or redistribution of the detrital assemblage associated with tsunami inundation due to wind. While the latter might result in a slight over-estimation of the inundation distance, they can be used in combination with chemical proxies to trace the maximum inundation distance of recent and past tsunamis, thus allowing for a better estimation of the magnitude of past events. Post-depositional processes were found to have affected the thinner sandy deposits (< 5 cm), suggesting that these are unlikely to be preserved in the geological record. This highlights the need to be able to trace the tsunami inundation limit with geochemical and/or diatom proxies without having to rely on sedimentological evidence, as it is now widely recognised that conventional approaches used by tsunami researchers have led to an under-estimation of previous events. [ABSTRACT FROM AUTHOR]

Three sedimentary sequences from a coastal wetland behind a sand barrier, on the west coast of d'Urville Island, New Zealand, were examined using a multi-proxy approach, including sedimentological, geochemical and microfossil (diatom) analyses, with the chronology established using radiocarbon and 210Pb dating. Data show that a brackish lagoon started developing 7300 year ago after formation of the sand barrier in Moawhitu. This was followed by periods of alternating wetland encroachment and open water, displaying spatial variations, until a peatland was established about 1300 cal. yr BP. The wetland was then partially drained in the early 1900s, leading to compaction of the peat near the surface. A coarse layer containing gravel, sand and shells, with a sharp lower contact, in the northern area of the wetland, is attributed to an overwash about 2500–3000 yr BP, most probably a tsunami generated by the rupture of a local or regional fault. The high-resolution continuous record obtained with XRF core scanning revealed a geochemical signature (Ca and S) for the overwash 600 m inland in the middle area of the wetland, while it was absent from the southern site 1.1 km from the shore. This suggests that, except at the northern end of Moawhitu, the sand dune acted as an effective barrier preventing any sediment from overtopping 2500–3000 yr BP, with only a geochemical evidence marking the extent of seawater inundation. No sedimentological or geochemical evidence could be found in the wetland for the 15th century tsunami that had destroyed almost an entire community in Moawhitu, as recounted in Māori oral tradition (pūrākau), although pebbles at the surface of the dune are likely to be linked to this event. Thus, the sand dune appears to have again acted as an effective barrier for the overwash in the 15th century. However, our study suggests that the area might have been impacted by more than one tsunami in the last 3000 years. It also shows that a high-resolution continuous XRF record can provide the evidence for short-term changes (catastrophic or not) that did not leave any clear sedimentological signature, thus providing a better insight of environmental changes in any depositional environment. [ABSTRACT FROM AUTHOR]