воскресенье, 2 февраля 2020 г.

The Zanclean Megaflood of the Mediterranean – Searching for independent evidence

Beneath the waters of the Alboran Sea, and in the shadow of an underwater volcanic structure, is a body of sediment that seems to have accumulated during a major flood 5.3 million years ago that filled the basin of a partially drained Mediterranean Sea. These sediments are candidates to be added to the list of new evidence found in the last years of the so-called Zancliense mega-flood, according to an article published in the Earth-Sciences Reviews.

The Zanclean Megaflood of the Mediterranean – Searching for independent evidence
Satellite image of the Gibraltar Arc
[Credit: NASA]
The paper reviews the recent findings published so far that support the hypothesis of a mega-flood that put an end to the Messinian Salinity Crisis, an event that occurred some 6 million years ago during which the Mediterranean Sea was isolated from the Atlantic Ocean and became a gigantic salt pan.

"The sedimentary deposits we have identified are compatible with a large flood through the Strait of Gibraltar. It is an elongated sedimentary body that accumulated on the leeward side of the flood thanks to the protection that the volcanic building provided against the force of the water flow that came from the Atlantic Ocean and entered the Mediterranean basin", explains Daniel Garcia-Castellanos, researcher at the Institute of Earth Sciences Jaume Almera of the CSIC (ICTJA-CSIC) and first author of the article.

According to the researchers, this accumulation of sediments has a maximum thickness of 163 metres, extends over about 35 km and is about 7 km wide. The identification of this group of materials has been possible thanks to the images obtained by means of the reflection of seismic waves on the bottom of the Alboran Sea. In these images, the authors of the study detected a series of chaotic and discontinuous stratified reflection profiles located between the Miocene and Pliocene sedimentary layers. In addition, these sediments are arranged parallel to an erosive channel identified in 2009 at the bottom of the Alboran Sea.

This channel, about 390 km long, extended from the Gulf of Cadiz through the Strait of Gibraltar to the Algerian Basin. The canal would have been excavated by the massive influx of water from the Atlantic Ocean once the connection with the Mediterranean Sea through the Strait of Gibraltar was re-established some 5 million years ago.

The Zanclean Megaflood of the Mediterranean – Searching for independent evidence
Isobath map of the eastern Alboran basin with the volcanic edifice location. Orange lines
show the main flood paths [Credit: Garcia-Castellanos et al, 2020]
Once the massive inflow of water entered in the Alboran basin, the channel split into two branches to overcome the topographic obstacles in its path. The volcanic edifice may have been one of these topographic obstacles during the flood leading to the deposition of the recently identified sediments along the seamount lee side.

These sediments identified in the Alboran Sea can be added to the rest of evidence found and published in recent years that support the hypothesis of a massive flood and are summarized in the present article.

The Noto Canyon, in the northern Malta Escarpment, and a body of sediments of up to 860 m in thickness buried at the east of this canyon are two of the other pieces of evidence proposed in this article that may sustain the megaflood hypothesis. Both parts of evidence were analyzed in a previous study published in Scientific Reports in 2018.

However, and despite all summarized pieces of evidence, Daniel Garcia-Castellanos is cautious. "Ten years after publishing the first observations that were related with the Zanclean flood we are still finding new evidences to sustain it, but they are not conclusive. All of the evidences that have been summarized in this article may have other possible interpretations and, before convincing the scientific community it will be necessary to have other studies that consider the hypothesis from other angles."

Researchers from the University of Malta, the Helmholtz Centre for Ocean Research (GEOMAR), the Instituto de Ciencias del Mar (ICM-CSIC), Istituto Nazionale di oceanografia e di geofisica Sperimentale (OGS) and the University of Sevilla also participated in the study.

Source: Institute of Earth Sciences Jaume Almera [January 26, 2020]

* This article was originally published here

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