In 2013, divers concluded that the structures of what looked like courtyards, paved floors and colonnades found off the Greek holiday island of Zakynthos were a long lost Greek city. However, a new study from the University of East Anglia in the UK and the University of Athens in Greece reveals that these remains were simply geological formations caused by methane leaking out of rocks.
The findings published on June 3 in the journal Marine and Petroleum Geology state that the gas leak occurred five million years ago during the Pliocene era. Interestingly, the divers did not find any other signs of life at the lost city located two to five meters underwater, including pottery.
After chemical and mineralogical tests, the team concluded that the Greek city remains were due to a gas leak. This phenomenon is usually observed between hundreds and thousands below the ocean’s surface and is very rarely found in shallow waters.
“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 palaeo settings,” adds lead author Julian Andrews from UEA’s School of Environmental Science. “We 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 seabed. The fault allowed gases, particularly methane, to escape from depth.”
The carbon found in methane stood as the fuel for microbes in the sediment. Consequently, in the process known as concretion, the microbes encouraged oxidation that turned the sediment into natural cement called dolomite, which were then exposed on the seabed by erosion.
“These features are proof of natural methane seeping out of rock from hydrocarbon reservoirs,” adds Andrews. “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.”