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- Exploring offshore sediment evidence of the 1755 CE tsunami (Faro, Portugal): implications for the study of outer shelf tsunami depositsPublication . Kümmerer, Vincent; Drago, Teresa; Veiga-Pires, C.; Silva, Pedro; Magalhaes, Vitor; Mena, Anxo; Lopes, Ana; Rodrigues, Ana Isabel; Schmidt, Sabine; Terrinha, Pedro; Baptista, Maria AnaOuter shelf sedimentary records are promising for determining the recurrence intervals of tsunamis. However, compared to onshore deposits, offshore deposits are more difficult to access, and so far, studies of outer shelf tsunami deposits are scarce. Here, an example of studying these deposits is presented to infer implications for tsunami-related signatures in similar environments and potentially contribute to pre-historic tsunami event detections. A multidisciplinary approach was performed to detect the sedimentary imprints left by the 1755 CE tsunami in two cores, located in the southern Portuguese continental shelf at water depths of 58 and 91 m. Age models based on C-14 and Pb-210(xs) allowed a probable correspondence with the 1755 CE tsunami event. A multi-proxy approach, including sand composition, grain-size, inorganic geochemistry, magnetic susceptibility, and microtextural features on quartz grain surfaces, yielded evidence for a tsunami depositional signature, although only a subtle terrestrial signal is present. A low contribution of terrestrial material to outer shelf tsunami deposits calls for methodologies that reveal sedimentary structures linked to tsunami event hydrodynamics. Finally, a change in general sedimentation after the tsunami event might have influenced the signature of the 1755 CE tsunami in the outer shelf environment.
- Multidisciplinary characterization of Quaternary mass movement deposits in the Portimão Bank (Gulf of Cadiz, SW Iberia)Publication . Silva, Pedro; Roque, C.; Drago, Teresa; Belen, A.; Ercilla, Gemma; Lopes, Ana; Lopez-Gonzalez, Nieves; CASAS, DAVID; Naughton, F.; Vazquez, Juan-Tomas; Henry, B.We present a multidisciplinary study of the seismic stratigraphy, sedimentology, geochemistry and magnetism to characterize the Quaternary mass movement deposits (MMD) and the associated deformation in the Portimão Bank (Gulf of Cadiz, offshore SW Iberia). Two scales of approach have been applied. At large-scale (m to km) approach, were recognized and characterized a series of important and subsequent slide scars (tens of meters high) and MMD (the larger one with 10 km length) related to landslides, more prominent at Portimão Bank's southern flank. At small-scale (cm) approach, we point out on a piston core collected within a scar affected by MMD, a replication of the sedimentary column as evidenced by geochronological results and corroborated by sedimentology, geochemistry and magnetic data. Magnetic fabric data enabled the identification and characterization of the internal structure and deformation of MMD along the sedimentary column. For last, geochronology and the morphology of Portimão seamount are discussed in order to constraint the factors controlling MMD triggering. The multidisciplinary approach is useful in a better characterization of the MMD at different scales and improved the understanding of its dynamics.