A new study conducted by an international team of scientists has found new evidence that support the hypothesis of the megaflood occurring during the Zanclean period, a giant flood in which water from the Atlantic poured back into the Mediterranean sea and ended the Messinian Salinity Crisis (MSC) 5 million years ago. The study, led by Professor Aaron Micallef from the University of Malta, has been published in the Scientific Reports journal.

Using seismic profiles and borehole data from offshore eastern Sicily, researchers have identified a large body of sediments buried in the subsurface of Sicily Channel which are characterized as being “extensive” and “chaotic”. They have named this mass of material as “Unit 2” .

The study says that this huge mass of sediments is composed of materials eroded and transported by the great flow of water which flooded the Ionian Basin through the Strait of Sicily once the western basin of the Mediterranean was refilled with the contribution of water coming from the Atlantic Ocean that had poured in previously through the Strait of Gibraltar. This event is known as Zanclean megaflood.

The recently identified sediments have been located over a layer of salts originated previously during the partial desiccation of the Mediterranean Sea during the MSC and under another layer of common marine sediments that were deposited after the flood and during the restoration of the normal marine conditions.

“The deposits identified in our study have little reflectivity of the seismic waves, they are seismically transparent, and present a disordered internal structure of the layers which is very similar to the sediments typically originated in catastrophic floods”, explains Daniel García-Castellanos, co-author of the study and researcher at the Institute of Earth Sciences Jaume Almera of the CSIC (ICTJA-CSIC).

The study indicates that the sedimentary body found next to the base of Malta Escarpment, between eastern and western Mediterranean Sea, is wedge-shaped and its estimated thickness is up to 860 meters. According to the researchers, it would be the largest known megaflood deposit on Earth.

“According to the models of the paper that we published in “Nature” journal in 2009, the flood would have lasted only a few years, reaching discharges of up to 100 million cubic meters per second, about a rate thousand times the current flow of the Amazon River”, adds García-Castellanos.

Researchers have also identified a spot in the channel of Sicily as the most likely gateway for the eastern Mediterranean Zanclean flood across the Malta escarpment, the submarine canyon of Noto (south east Sicily). The authors of the study explain that this canyon has a unique morphology, its amphitheatre-shaped head is 6 km wide and is “similar to that of bedrock canyons rapidly eroded by megafloods”. Researchers interpret the Noto submarine canyon as the collector of the cascading flow into the Ionian Basin.

“The study points the abrupt and catastrophic nature of the environmental changes that occurred during the Messinian period, the most important since the dinosaurs’ extinction 65 million years ago”, says Daniel García-Castellanos.

This study has also involved researchers from the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale of Trieste, from the Laboratoire Geosciences Océan of the University of Brest and the CNRS, from the University of Catania, from the Institute für Geowissenschaften of the Christian-Albrechts of Kiel and the GEOMAR Helmholtz Center for Ocean Research of Kiel.

The Messinian salinity crisis: an unrecognizable Mediterranean Sea

About 6 million years ago, the connection between the Atlantic Ocean and the Mediterranean Sea was interrupted. This event led to the partial desiccation of the Mediterranean Sea, which became then into a giant saline lake, with an estimated sea level drawdowns of 1300-2400 meters. This event is known as Messinian salinity crisis (MSC).

A major open question about this period to be answered by researchers is how normal marine conditions were restored. The hypothesis of the Zanclean megaflood proposes that there was a massive inflow of water through the Strait of Gibraltar that first flooded the western Mediterranean Basin and then, through the Strait of Sicily which was then the division between eastern and western basins, flooded Ionian Basin. Some studies indicate that this filling process lasted between a few months and two years.

Original article

Micallef, A., et al. (2018), Evidence of the Zanclean megaflood in the eastern Mediterranean Basin, Scientific Reports, 8(1), 1078, doi: 10.1038/s41598-018-19446-3.