A terminal Messinian flooding of the Mediterranean evidenced by contouritic deposits on Sicily

Abstract

The evolution of marine gateways and sea straits exerts major control on bottom current depositional systems. A well-known interval in geological history characterized by frequent changes in marine connectivity is the Messinian Salinity Crisis (5.97 to 5.33 Ma) when the Mediterranean allegedly experienced major (>1 km) sea-level drawdown followed by a catastrophic marine replenishment at the base of the Zanclean. Controversy exists around the timing and mode of this event as unambiguous flood deposits have so far never been drilled or recognized in outcrops. In the Sicilian Caltanissetta Basin (Italy), the Messinian/Zanclean boundary is directly underlain by the Arenazzolo Formation. This 5 to 7 m thick sandy sedimentary interval may reveal a genetic link with the abrupt refilling of the Mediterranean, but at present a detailed study to understand its origin is lacking. In this work, the Arenazzolo Formation at Eraclea Minoa has been studied by a multi-method approach, employing detailed facies description, grain-size analyses, petrographic analyses and palaeocurrent analyses. Palaeogeographical reconstructions and facies associations show that the Arenazzolo Formation sands were deposited on the northern flank of the Gela thrust front by persistent bottom currents, flowing parallel to the regional slope physiography, during a transgression. It is hypothesized that these currents are associated with the active circulation of surface and intermediate water masses coeval with a terminal Messinian flood, when basin margins overtopped and a reconnection between western and eastern Mediterranean was created. The Arenazzolo Formation is a unique example of a contouritic deposit formed by bottom currents that establish during the reconnection of major isolated water bodies.