Mid-Holocene tectonic geomorphology of northern Crete deduced from a coastal sedimentary archive near Rethymnon and a Late Bronze Age Santorini tsunamite candidate

Abstract

The Late Bronze Age (LBA) tsunami and the A.D. 365 tsunami are supposed to have affected the northern coasts of Crete. However, near-coast sedimentary archives have been rarely investigated in this area, and sedimentary archives including palaeotsunami fingerprints are still unknown. The main objective of our research was to search for appropriate tsunami sediment traps in order to gain detailed insights into the Holocene palaeotsunami history of northern Crete. We found an excellent fine sediment archive near Pirgos, located to the west of Rethymnon. Based on a multi-electrode geoelectrical survey and an 11-m-deep sediment core, we analysed the event-geochronostratigraphical record by means of sedimentological, geochemical, geochronological, geomorphological, and microfossil investigations. The Pirgos record revealed a thick unit of homogeneous mud of a lagoonal environment starting ~6000 years ago. The lagoon was affected by five high-energy events, leaving layers of allochthonous sand. Microfossil analyses of these layers revealed a mixed foraminiferal assemblage including species from brackish habitats but also displaced and transported species from open marine and deep-water environments. Considering sedimentary characteristics, the local wave climate of the Cretan Sea, and the overall geomorphological setting, we interpret these layers as related to extreme wave events (EWE). Based on a local radiocarbon age-depth-model, we identified one EWE layer as a reliable candidate for the LBA Santorini tsunami. Another EWE layer is most probably associated with the A.D. 365 tsunami. This EWE ended abruptly the lagoonal conditions at Pirgos because of to the 1.64 m coseismic uplift at the site. The Pirgos lagoon existed between the first half of the 6th mill. B.C. and (at least) the end of the 2nd mill. B.C. We found that the area around Pirgos has continuously subsided over 3000 or so years, reflecting constant tectonogeomorphological conditions dominated by the nearby subduction zone between the Aegean and African plates.