According to a team of scientists from the United Kingdom and Greece, the underwater ‘archaeological remains’ of a long-lost Greek city were in fact created by a naturally occurring phenomenon.
When divers discovered what looked like paved floors, courtyards and colonnades, they thought they had found the ruins of an ancient Greek city that perished when tidal waves hit the shores of the island of Zakynthos.
But new research, published in the journal Marine and Petroleum Geology, reveals that the site was created by a natural geological phenomenon that took place in the Pliocene era – up to 5 million years ago.
“The site was discovered by snorkelers and first thought to be an ancient city port, lost to the sea,” said lead author Prof. Julian Andrews, from the University of East Anglia.
“There were what superficially looked like circular column bases, and paved floors. But mysteriously no other signs of life – such as pottery.”
The discovery was carefully examined in situ by the Ephorate of Underwater Antiquities of Greece.
Archaeologist Magda Athanasoula and diver Petros Tsampourakis studied the site, together with Prof. Michael Stamatakis from the National and Kapodistrian University of Athens. After the preliminary analyses, a research team was formed.
The scientists went on to investigate in detail the mineral content and texture of the underwater formation in minute detail, using microscopy, X-ray and stable isotope techniques.
“We investigated the site, which is 6.5 – 16.4 feet (2 – 5 m) under water, and found that it is actually a natural geologically occurring phenomenon,” Prof. Andrews said.
“The disk and doughnut morphology, which looked a bit like circular column bases, is typical of mineralization at hydrocarbon seeps – seen both in modern seafloor and paleo settings.”
The research team found that the linear distribution of these doughnut shaped concretions is likely the result of a sub-surface fault which has not fully ruptured the surface of the sea bed. The fault allowed gases, particularly methane, to escape from depth.
Prof. Andrews explained: “microbes in the sediment use the carbon in methane as fuel. Microbe-driven oxidation of the methane then changes the chemistry of the sediment forming a kind of natural cement, known to geologists as concretion.”
“In this case the cement was an unusual mineral called dolomite which rarely forms in seawater, but can be quite common in microbe-rich sediments.”
“These concretions were then exhumed by erosion to be exposed on the seabed today.”
According to the team, this kind of phenomenon is quite rare in shallow waters.
“Most similar discoveries tend to be many hundreds and often thousands of meters deep underwater,” Prof. Andrews said. “These features are proof of natural methane seeping out of rock from hydrocarbon reservoirs. The same thing happens in the North Sea, and it is also similar to the effects of fracking, when humans essentially speed up or enhance the phenomena.”
Andrews, J.E. et al. 2016. Exhumed hydrocarbon-seep authigenic carbonates from Zakynthos island (Greece): Concretions not archaeological remains. Marine and Petroleum Geology, vol. 76, pp. 16-25; doi: 10.1016/j.marpetgeo.2016.05.022
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