When underwater divers discovered what looked like paved floors, courtyards and colonnades, they thought they had found the ruins of a long-forgotten civilisation that perished when tidal waves hit the shores of the Greek holiday island Zakynthos.
But new research published in the journal Marine and Petroleum Geology reveals that the site discovered a few years ago was created by a natural geological phenomenon that took place in the Pliocene era – up to five million years ago.
“The site was discovered by snorkelers and first thought to be an ancient city port, lost to the sea. There were what superficially looked like circular column bases, and paved floors. But mysteriously no other signs of life – such as pottery,” said lead author Julian Andrews , professor at the University of East Anglia in Norwich, England.
The research team 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 between two and five meters under water, and found that it is actually a natural geologically occurring phenomenon,Â” Andrews said.
“The disk and doughnut morphology, which looked a bit like circular column bases, is typical of mineralisation at hydrocarbon seeps – seen both in modern seafloor and palaeo settings,Â” Andrews noted.
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,Â” Andrews explained.