Chapter 12 - Deep-Sea Homogenites: Sedimentary Expression of a Prehistoric Megatsunami in the Eastern Mediterranean

Abstract

The Bronze-Age catastrophic eruption of the volcanic island of Santorini, which terminated the Minoan civilization on Crete, triggered a megatsunami comparable in size with that of the Krakatoa, which killed some 36,000 human beings in 1883. Well-dated deep-sea turbidites, with sedimentary composition and structures that differ strongly from those of turbidites that are unrelated to tsunamis, and called ‘homogenites’, have been investigated for their sedimentological and acoustic characteristics. The data set consists of 60 piston and/or gravity cores and a few giant cores raised from water depths that range from ∼4100 to ∼2500 m, mostly in the range of ∼3000 m. Type A homogenites, recorded in the Calabrian Ridge and the Mediterranean Ridge (=accretionary complexes), are pelagic turbidites of local provenance: they are attributed to the mobilization and liquefaction of water-saturated, unconsolidated late Quaternary sediments draping the gentle slopes of small perched basins typical of the so-called ‘cobblestone topography’, caused by the passage of tsunami waves near the ocean bottom. Type B homogenites, instead, are megaturbidites of distant, shallow-water provenance (from North Africa) triggered by the largest (third?) tsunami wave that penetrated in the Sirte Gulf of Libya. Type B homogenites have been documented in the Messina and Sirte abyssal plains, but are conspicuously absent in the Herodotus abyssal plain, and off the Nile delta. In a palaeoclimatic and glacio-eustatic context, the Type B homogenite is a paradox: it should not be there. The complex physiographic and structural configuration of the eastern Mediterranean controls the areal distribution of the Bronze-Age homogenites that are—so far—the only known deep-sea tsunamiites except the sediments induced by the bolide impact tsunami.