A new chalcolithic-era tsunami event identified in the offshore sedimentary record of Jisr al-Zarka (Israel)
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abstract
Tsunami field evidence is a critical resource for determining coastal risk. However, in many cases there is low potential for long term preservation of such deposits on land. A growing body of evidence suggests that tsunami deposits can be present in the shallow offshore realm and may present a largely untapped, but important worldwide sedimentological reference set for investigating past tsunami events. Here, different proxies for tsunami sediment identification and differentiation (granulometry, XRD, XRF, FT-IR) were used to determine the presence or absence of such deposits in a core collected offshore at Jisr al-Zarka, midway between Tel Aviv and Haifa. The study aimed to recognize anomalous deposits and test different analytical methods to define their origins. Five anomalous sedimentological horizons were identified, four of which were interpreted as tsunamigenic by comparison to previously identified poorly sorted, shell-rich tsunamites found nearby in Caesarea and contrast to the fine-sand, Nile-derived background sediments. The remaining anomaly was distinctive, but not determined to be tsunamigenic due to a lack of coarse shell in the matrix. The oldest tsunamigenic layer, coinciding with the Chalcholithic cultural period (5.7ka), is the oldest such deposit identified offshore Israel to date and the non-tsunamigenic anomalous horizon may correspond with a transitional climatic phase ( 5.5ka). This research reinforces the importance of offshore investigations as a means of improving tsunami catalogues and identifying environment-altering events.
