Environment

Evidence of one of the largest floods in Earth’s history in the central Mediterranean

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An international team of scientists has uncovered evidence of one of the largest floods in Earth’s history in the central Mediterranean seafloor.

The flood, known as the Zanclean flood, is thought to have ended the Messinian Salinity Crisis (MSC), a period during which the Mediterranean Sea became partially dried up. Due to shrinkage of its connection with the Atlantic Ocean, the Mediterranean Sea was transformed into a giant saline lake that was partially evaporated by the dry climate of the region, six million years ago.

One of the theories proposed to explain the refilling of the Mediterranean Sea at the end of the MSC some 640 000 years later is a catastrophic flood through the Strait of Gibraltar.

By examining the most comprehensive collection of seafloor data from offshore eastern Sicily and the Maltese Islands, an international team of geoscientists has now discovered an extensive buried mass of material that is thought to have been eroded and transported by the Zanclean flood.

This mass covers an area equivalent to that of the island of Crete and is up to 900 m (2 900 feet) thick in places. The passage of the Zanclean flood across the Malta Escarpment – a long submarine limestone cliff – resulted in a 1.5 km (0.9 miles) high waterfall (equivalent to five times the height of the Eiffel Tower).

This water eroded a 5 km (3.1 miles) wide and 20 km (12.4 miles) long canyon on the seafloor that is still preserved underwater offshore the city of Noto (south-east Sicily).

Authors say the discovery is important because it demonstrates that the level of the Mediterranean Sea during the MSC dropped by more than 1 000 m (0.62 miles), and that the end of the MSC coincided with a catastrophic flood that affected the entire Mediterranean Sea.

Reference:

Evidence of the Zanclean megaflood in the eastern Mediterranean Basin – Aaron Micallef et al. – Nature Scientific Reports – January 18, 2018 – DOI: 10.1038/s41598-018-19446-3 – OPEN ACCESS

Abstract

The Messinian salinity crisis (MSC) – the most abrupt, global-scale environmental change since the end of the Cretaceous – is widely associated with partial desiccation of the Mediterranean Sea. A major open question is the way normal marine conditions were abruptly restored at the end of the MSC. Here we use geological and geophysical data to identify an extensive, buried and chaotic sedimentary body deposited in the western Ionian Basin after the massive Messinian salts and before the Plio-Quaternary open-marine sedimentary sequence.

We show that this body is consistent with the passage of a megaflood from the western to the eastern Mediterranean Sea via a south-eastern Sicilian gateway. Our findings provide evidence for a large amplitude drawdown in the Ionian Basin during the MSC, support the scenario of a Mediterranean-wide catastrophic flood at the end of the MSC, and suggest that the identified sedimentary body is the largest known megaflood deposit on Earth.

Featured image credit: University of Malta



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