Late Holocene tsunami hydrodynamics, sediment provenance and chronology from Dury Voe, Shetland Islands (UK)

Nel Nussberger , Max Engel , Tasnim Patel, Alexander Varychev, Hans-Peter Meyer, Dominik Brill, Anna Pint, Philipp Kempf, Katharina Hess, Isa Schön, Vanessa M.A. Heyvaert, Sue Dawson

The Shetland Islands are one of the key sites in the Atlantic Ocean to study tsunami deposits, with three major events identified during the Holocene so far. Here, we aim to (i) reconstruct hydrodynamics of the late Holocene Dury Voe tsunami, (ii) constrain the sediment source area, and (iii) refine its age estimate. Onshore sandy deposits bracketed by thick dystrophic peat as well as marine sediment from the intertidal to offshore zone were sampled at Dury Voe and subjected to laser diffraction grain-size analysis, heavy mineral analysis using energy-dispersive X-ray spectroscopy and foraminiferal analysis. Furthermore, we present the first onshore luminescence dating for deposits on Shetland for quartz and feldspar. The combined results from grain-size and heavy mineral analyses indicate that at least two major tsunami waves entrained fine-grained sediment from the intertidal zone down to ~14 m water depth. The proximal deposit, close to the coast, is separated into a massive and an inversely graded subunit, characteristic of deposition in a very high energy, high-density suspension flow, whilst further inland it shows two fining-upward sequences, characteristic of a suspension grading and lower-energy, lower-density flow. Foraminiferal assemblages are diverse and abundant in the shallow-marine source deposits, but entirely missing in the tsunami deposits onshore, possibly due to post-sedimentary chemical dissolution in the very low-pH environment, which also affected the onshore heavy mineral composition. Data from Bayesian age modelling of the luminescence ages, in combination with pre-existing radiocarbon data, indicate tsunami impact at 470–630 CE. Our findings refine tsunami hydrodynamics at Dury Voe and the overall chronology in the Shetland region, and highlight the role of acidic post-depositional environments in modifying palaeotsunami signatures.