Geochemical Signatures of Historical Eastern Mediterranean Tsunamis Preserved in Lagoon Sedimentary Sequences

Aquatic environments, particularly coastal lakes and lagoons, offer optimal conditions for preserving depositional records of past tsunami events. Tsunamis are known to transport sediments from shallow nearshore areas and sand spits, redepositing them in lagoon environments. This study investigates the geochemical signatures of historical Eastern Mediterranean tsunamis in two lagoons along the southern coast of Türkiye: Ölüdeniz and Demre lagoons. A total of nine piston cores, ranging from 3.5 to 4.0 meters in length, were analyzed using an ITRAX micro-XRF scanner to obtain high-resolution radiographic and optical images, as well as detailed elemental composition of the sediments. In Ölüdeniz, an oligotrophic lagoon, sedimentary events exhibiting distinct [Ti, Fe, Zn]/Ca anomalies temporally correlate with historical tsunamis. These anomalies are attributed to a sudden influx of sediment from the land into the lagoon, likely originating from the lagoon's sand spit. In contrast, in the hypersaline Demre Lagoon, tsunami deposits are characterized by sediments with lower concentrations of Sr, Cl, and Br compared to the background sedimentation. Due to the lagoon's hypersaline conditions, bio/chemical carbonate and detrital siliciclastic deposition are typically accompanied by salt deposition, which serves as the primary source of Cl and Br in the sediments. However, during the rapid deposition of tsunami sediments, there is insufficient time for salt deposition, resulting in the depletion of Cl, Br, and Sr in these layers. This study in Ölüdeniz and Demre lagoons confirms that lagoons are excellent sites for paleotsunami research.