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Rendiconti Lincei

, 16:137 | Cite as

Prehistoric mega-tsunami in the eastern Mediterranean and its sedimentary response

  • Maria Bianca Cita Sironi
  • Bianca Rimoldi
Article

Abstract

The volcanic island of Santorini that belongs to the trench-arc-backarc Aegean system of the eastern Mediterranean underwent a catastrophic eruption in the Bronze age (circa 3500 y BP), with caldera collapse and creation of a tsunami wave that was funnelled westward. The sedimentary response to this exceptional event in the deep sea was the deposition of resediments called Homogenites. The data set available after almost thirty years of active research consists of 60 sediment cores, including several giant piston cores up to 30 meters long, raised from water depths ranging from 4100 to 2500 m in discrete parts of the Ionian Sea. Two types of Homogenite are recognized. Type A Homogenite consists of pelagic turbidites typically recorded in the Calabrian Ridge and in the western Mediterranean Ridge accretionary prisms, characterized by the «cobblestone topography», only in lows or basinal settings. Their stratigraphic position consistently above the Holocene sapropel S-1 and the depositional base are interpreted as the result of liquefaction of the unconsolidated pelagic sediments draping the nearby slopes caused by the tsunami waves, followed by downslope movement and settling. Type B Homogenite is a megaturbidite of African provenance that expanded throughout the Messina and Sirte abyssal plains originating an up to 24 m thick surficial acoustically-transparent layer calibrated by coring. Type B Homogenite has a coarse and thick sandy base consisting of bioclasts deriving from the continental shelf of North Africa and is interpreted as triggered by the tsunami wave reaching the Sirte Gulf. The Dec. 26, 2004 megatsunami that hit the coastlines of SE Asia provides a real world example of how sediment dispersal can be triggered by a series of gigantic waves. Megaturbidites similar in thickness to Type B Homogenite have been recorded in all the abyssal plains of the Mediterranean, both west and east of the Ionian basin, but their age is older (late Pleistocene) and their emplacement occurred during low sea-level stands corresponding to the last glaciation. The occurrence of a Holocene megabed, postdating the Climatic Optimum, is a paradox in a paleoclimatic scenario. An exceptional event, as the megatsunami originated by the collapse of the Santorini caldera is required.

Key words

Santorini Tsunami Megaturbidite Holocene 

Un megatsunami preistorico nel Mediterraneo orientale e la sua risposta sedimentaria

Riassunto

L’isola vulcanica di Santorini, che fa parte del sistema arco-fossa-bacino di retroarco del Mare Egeo, ha subito una eruzione devastante nell’età del Bronzo (circa 3500 anni fa) con collasso della caldera e creazione di un’onda di tsunami che è stata convogliata in prevalenza verso ovest. La risposta sedimentaria a questo evento eccezionale in mare profondo è stata la mobilizzazione e la rideposizione di sedimenti, chiamati Omogeniti. Dopo quasi trent’anni di ricerca attiva, il data set consiste di 60 carote di mare profondo, comprese diverse carote giganti lunghe fino a 30 metri, raccolte da profondità comprese fra 4100 e 2500 m. Vengono distinti due tipi di Omogeniti. L’Omogenite di Tipo A è costituita da torbiditi pelagiche di provenienza locale che si trovano nelle depressioni dei prismi di accrezione della Dorsale Calabra e della Dorsale Mediterranea caratterizzati dalla cosiddetta «Topografia a Cobblestone». La posizione stratigrafica a tetto del sapropel S-1 olocenico e la base deposizionale sono interpretate come il risultato della liquefazione dei sedimenti pelagici che ricoprivano i pendii circostanti causata dal passaggio dell’onda di tsunami seguita dalla deposizione al fondo dei piccoli bacini sospesi. L’Omogenite di Tipo B è invece una megatorbidite di provenienza africana che si è espansa al fondo delle ampie piane abissali di Messina e della Sirte dando origine a uno strato trasparente superficiale, spesso fino a 24 m, calibrato dai carotaggi. L’Omogenite di Tipo B ha una base spessa e grossolana, costituita da bioclasti provenienti dalla piattaforma continentale nordafricana, ed è interpretata come provocata dalle onde superficiali dello tsunami che hanno raggiunto il golfo della Sirte. Il megatsunami del 26 dicembre 2004, che ha colpito le coste del SE asiatico, fornisce un esempio reale di come la dispersione dei sedimenti possa essere influenzata da onde gigantesche. Megatorbiditi di spessore simile a quello dell’Omogenite di Tipo B sono state documentate in tutte le piane abissali del Mediterraneo, sia a ovest che a est del Mare Ionio, ma la loro età è più antica (Pleistocene superiore) e la loro messa in posto è avvenuta durante stazionamenti bassi del livello del mare, corrispondenti all’ultima glaciazione. La presenza di una megatoribidite nell’Olocene, in un periodo di alto livello del mare, è un paradosso in uno scenario paleoclimatico: occorre un evento eccezionale come il megatsunami provocato dal collasso della caldera di Santorini per spiegame l’esistenza.

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Copyright information

© Springer 2005

Authors and Affiliations

  • Maria Bianca Cita Sironi
    • 1
  • Bianca Rimoldi
    • 2
  1. 1.Dipartimento di Scienze della Terra «Ardito Desio»Università degli Studi di MilanoMilano
  2. 2.INAIL - Direzione Regionale LombardiaConsulenza Tecnica Accertamento Rischi ProfessionaliMilano

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