Six million years ago the Mediterranean Sea underwent a period of isolation from the global ocean – the Messinian salinity crisis (MSC) – allegedly leading to a km-scale level drawdown by evaporation and widespread salt deposition. One of the competing scenarios for the termination of this crisis consists of a flooding event refilling the Mediterranean through the Strait of Gibraltar: the Zanclean megaflood. This hypothesis is supported by geophysical and well observations, primarily in the western Mediterranean Basin. More recently, a 1500 km³ sedimentary deposit identified in seismic reflection profiles in the western Ionian Sea has been interpreted as the result of the Zanclean megaflood during an overspill from the western to the eastern Mediterranean. Validation of this scenario requires an improved understanding of the direction of flow of the megaflood, its discharge rate and evolutionary stages. The latter can be achieved via:

1. Sampling of the inferred buried megaflood deposit in the Ionian Basin via scientific drilling
2. Mapping and sampling of the terrestrial outcrops of the megaflood deposit in SE Sicily
3. Mapping of a sub-seafloor erosional channel connecting the terrestrial deposits with those offshore
4. High resolution imaging of the internal structure of the inferred buried megaflood deposits in the western Ionian Basin

The goal of our project is to carry out tasks 2-4 by investigating the terrestrial deposits in SE Sicily (fieldwork in March 2023) and mapping those offshore using marine geophysical data (oceanographic expedition in February 2024). If successful, the project will bring to an end decade-long controversies related to the MSC and provide fundamental information on the geography of the Mediterranean at that time. The dimensions of the proposed Zanclean megaflood make it the largest known event of this kind on Earth, one-to-two orders of magnitude larger than well-documented Pleistocene events such as the Bonneville and Altai megafloods or the Missoula floods, and one of the largest known in the solar system. A dedicated investigation of the Zanclean megaflood will shed new light on megaflood erosional/depositional signatures, which can be used to reconstruct the key stages and characteristics of megafloods.

This work is partly supported by the National Geographic Society.

Figure x: Gateway for the passage of the Zanclean megaflood to the eastern Mediterranean. (a) Shaded relief model of SE Sicily showing terrestrial chaotic Zanclean deposits, and seafloor slope gradient map showing Noto Canyon. Isobaths denoted by dotted red lines. Location in (e). (b) Seismic reflection profile CIR-07 showing Noto Canyon head and Messinian erosional surface upslope. Location in (a). Interpretation is based on correlation with nearby wells (shown in (e)). (c) Photograph of terrestrial chaotic Zanclean deposits. Location in (a). (d) Seismic reflection profile C-578, located upslope of Noto Canyon, showing a channel eroded in pre-Messinian limestones. Channel fill is marked by large-scale downlap and sigmoidal internal configuration (denoted by yellow lines), suggesting infilling by high energy deposition, and is sealed by Plio-Quaternary muds. Interpretation and depth conversion based on well Rosa (location in (a)). (e) Messinian topography (above and below present sea-level) across SE Sicily and Malta Plateau, generated using published seismic reflection profiles and well data, overlaid on shaded relief model of present bathymetry. Thickness of Messinian evaporites from well data is included. Potential flow paths of the Zanclean flood are indicated by red arrows (solid = likely; dashed = unlikely). Extent of Zanclean flood deposit (unit 2) is outlined in orange. Dashed black lines denote boundaries of graben structures. Source: Micallef et al. (2018).

Team

Aaron Micallef

Senior Scientist/Marine Geologist

Collaborators:

Angelo Camerlenghi (OGS), Giovanni Barreca (University of Catania), Antonio Caruso (University of Palermo), Paul Carling (University of Southampton), Daniel Garcia Castellanos (CSIC, Barcelona), Christian Huebscher (University of Hamburg)