Comparative analysis of the deposits left by the tsunami that followed to the Lisbon ear (1755 ad) o the Castilnovo beach and the old tuna fac tory of La Chança (Conil de la Frontera, SW Spain)

Resumo

On coasts of tectonically active areas, where old tsunami deposits are in a fragmentary state, the study of paleo-tsunamis provides data for interpreting facies and processes. In order to recognize facies, a study has been carried out on a sector of the SW coast of Spain, where some historical tsunamis are documented, such as that caused by the Lisbon earthquake (November 1, 1755 AD). This study is focused on a sector between the Salado River Mouth and Castilnovo Beach (Conil de la Frontera), where depositional morphologies attributed to this event can still be observed. It includes a comparative analysis with well-preserved deposits found inside an old tuna salting factory, La Chança which, albeit severely damaged, survived the tsunami. The sediments deposited by the 1755 AD tsunami record a mixture of older coastal deposits, including sands and muddy-sands, pebbles, mollusc shells, foraminifers, terrestrial gastropods, root features, and archaeological remains. After the tsunami, a part of the deposits were remobilized and mixed with normal coastal sediments, becaming unrecognizable as tsunamites. Several stratigraphic units have been distinguished, corresponding to different sedimentary stages. The results suggest that some depositional features were caused not by this event, but rather are a consequence of the interaction of other factors. Shelly beds intercalated within the deposits have provided a 14C age older than 1755 AD, which have been interpreted as records of other older events or erosion of older deposits followed by deposition during the tsunami event.