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- Benchmarks, sediment source and hydrodynamics of the 1755 Lisbon tsunami deposit at Boca do Rio EstuaryPublication . Font, Eric; Veiga-Pires, C.; Pozo, Manuel; Nave, Silvia; Costas, Susana; Muñoz, Francisco Ruiz; Abad, Manuel; Simões, Nuno; Duarte, SílviaStandardizing the signature of tsunami deposits has been pointed as a major limitation on the identification of paleo-tsunami deposits. This limitation majorly arises from the strongly source-dependent nature of these deposits, which in turn determines their composition and structure, and from the effect of the local morphology of the corresponding depositional environment. Here, we provide new high-resolution mineralogical, geochemical and paleontological data of the 1755 tsunami layer of Boca do Rio estuary (Algarve, Portugal) with the aim of unraveling the signatures of estuarine tsunami deposit and link them to sediment source.
- Identification of Tsunami deposits and their impact on coastal zones : a study case of the Boca do Rio estuary (Algarve , Portugal)Publication . Font, Eric; Veiga-Pires, C.; Pozo, Manuel; Nave, Silvia; Costas, Susana; Muñoz, Francisco Ruiz; Abad, ManuelTsunamis are unforeseeable phenomena and therefore one of the most devastating natural disasters in terms of human and economic losses. Their impact on coastal and nearshore zones is substantial and need to be accurately evaluated to improve their prevention and management. In the last decades, numerous investigations focused on the identification of paleotsunamis in order to evaluate their frequency in the geological record. However, because storm- and tsunami-deposits are generated by similar depositional mechanisms, their discrimination using classic sedimentological methods is an elusive prospect. A promising approach is to couple classic geological criteria with geophysical and geochemical proxies to search for new benchmarks of tsunami deposits and to integrate them into a multi-disciplinary study. To test our method, we investigate the 1755 Lisbon tsunami deposit from the Boca do Rio estuary and other Tsunami-induced deposits from Algarve (Portugal). First results show that, Sr and Ca are enriched in the tsunami layer probably linked to the presence of shelled organism. Contrarily, others marine seawater indicators, such as Ba and Br, which are usually more concentrated in brackish than in fresh water, and heavy minerals, which are generally used as high energy event indicators, are depleted in the Tsunami deposit. Very low magnetic susceptibility values for the Tsunami deposit also indicate a dilution of iron oxides, reworked from the estuarine clays, within the huge volumes of quartz and carbonate (i.e. diamagnetic), issued from the abrasion of the littoral sandy dune and the surrounding carbonated cliffs. Diffusive Reflective Spectrophotometry analyses show changes in the siliclastic fraction on the sediments from above and below the tsunami layer. These apparent colour variations seem linked to the deposition of finer siliclastic particles after the tsunami, rather than to mineralogical composition. These data suggest that the high energy event affected the geomorphology of the estuary in such a way that it could induce a mis-interpretation of the geological record regarding local sea level changes and coastal evolution history.
- Benchmarks and sediment source(s) of the 1755 Lisbon tsunami deposit at Boca do Rio EstuaryPublication . Font, Eric; Veiga-Pires, C.; Pozo, Manuel; Nave, Silvia; Costas, Susana; Ruiz, F.; Abad, Manuel; Simões, Nuno; Duarte, Sílvia; Rodriguez-Vidal, J.Standardizing the signature of tsunami deposits has been identified as a major limitation for the identification of paleo-tsunami deposits. This limitation mostly arises from the strongly source-dependent nature of these deposits, which in turn determines their composition and depositional architecture, and from the effect of the local morphology of the corresponding depositional environment. Here, we provide new highresolution mineralogical, geochemical and micro/macrofauna data of the 1755 tsunami layer of Boca do Rio estuary (Algarve, Portugal) with the aim of unraveling the signatures of estuarine tsunami deposits and linking them to possible sediment sources. We also apply for the first time diffuse reflectance spectrophotometry (DRS) analysis. Our results show that the 1755 tsunami deposit of the Boca do Rio estuary is featured by an enhancement in Sr and Ca, which are linked to the input of biogenic and detrital carbonates (shell fragments and limestone clasts) from the beach foreshore and a strong depletion in most terrestrial- and marine-sensitive indicators. The latter is interpreted as resulting from the reworking of the estuarine clays and subsequent dilution within a huge volume of sand eroded from the coastal barrier. It confirms that in the case of the Boca do Rio estuary, the sediment source is essentially proximal and coastal. Textural and mineralogical features between the base and the top of the tsunami layer suggest the imprint of run-up and backwash currents derived from a unique wave. Micro and macrofauna analysis and DRS data of the siliciclastic fraction show slight but significant environmental changes occurring just after the tsunami, which could be provoked by an eventual closure of the estuary mouth.
- Benchmarks and sediment source(s) of the 1755 Lisbon tsunami deposit at Boca do Rio EstuaryPublication . Font, Eric; Veiga-Pires, C.; Pozo, Manuel; Nave, Silvia; Costas, Susana; Muñoz, Francisco Ruiz; Abad, Manuel; Simões, Nuno; Duarte, SílviaStandardizing tite signature of tsunami deposits has been pointed as a major limitation on the identification paleo-tsunaml deposits. This limitation majorly arises from the strongly source-dependent nature of these deposits, which in turn determines their composition and Structure, and from the effect of the local morphology of the corresponding depositional environmemt. Here, we provide new high-resolution mineralogical, geochemical and paleontological data of the 1755 tsunami layer of Boca do Rio estuary (Algarve-Portugal.
- Testing rock magnetic and AMS methods in tsunami and storm-induced depositsPublication . Font, Eric; Duarte, Sílvia; Veiga-Pires, C.; Simões, Nuno; Muñoz, Francisco Ruiz; Abad, Manuel; Pozo, Manuel; Nave, Silvia; Costas, Susana; Rebelo, LuisStorm- and tsunami-deposits are generated by similar depositional mechanisms making their discrimination hard to establish using classic sedimentologic methods. A promising approach is to use rock magnetism techniques to search for new physical benchmarks of tsunami deposits and to integrate them into a multi-disciplinary study. To test our method, we investigate the 1755 Lisbon tsunami deposit from the Boca do Rio estuary and other Tsunami-induced deposits from Algarve (Portugal) and Huelva (Spain), as well as storm-like deposits for comparison. Magnetic methods repose on bulk (magnetic susceptibility, SIRM, Hc) and directional (AMS, paleomagnetism) magnetic properties.