Photo/Illutration Peculiar rocks can be found in the Izura coastal area in Kita-Ibaraki, Ibaraki Prefecture. (Morikazu Kogen)

KITA-IBARAKI, Ibaraki Prefecture--The Izura coastal area here, a picturesque government-designated treasure, may contain other hidden valuables.

Hisao Ando, a geology professor at the graduate school of Ibaraki University, and scientists from Hokkaido University, said in July that crude oil highly likely exists below the seabed.

Their theory stems from the many unusually shaped rocks formed by natural gas from the seafloor.

According to their July announcement, a huge gas field used to exist under the water off Ibaraki Prefecture.

Layers of solidified calcium carbonate, or carbonate concretion, which were formed 16.5 million years ago, can be widely found along the coastline connecting Izura and Iwaki, Fukushima Prefecture.

The naturally produced cement formation was created with carbon in organic substances combined with calcium in seawater. But the origin of the carbon had been unknown.

The team in 2013 started using a supersensitive detector to study the constitution of small amounts of gas remaining in hollows in rocks. This method identified the traits and composition of hydrogen, methane, ethane and other substances in the gas.

The results showed the carbon there derived from methane in natural gas.

Based on the findings, the scientists concluded the peculiar rocks came into existence when methane in natural gas emitted from the seabed with tectonic movements was dissolved by micro-organisms, reacting with calcium in seawater.

An estimated total of at least 6 million cubic meters of the sedimentary rocks exist around Izura, equivalent to five Tokyo Domes.

That corresponds to the recoverable reserves of Chiba Prefecture-based Kanto Natural Gas Development Co., which are about 100 billion cubic meters, one of the largest volumes of that kind in Japan.

Given that only part of gas contributed to the formation of the rocks, which were later weathered and eroded, the researchers deduced that a much larger amount of gas leaked in Izura.

The team’s gas constitution analysis also revealed the gas was generated when dead zooplankton and phytoplankton in the water were dissolved with terrestrial heat. This indicated that crude oil is most likely there.

The oil is believed to have developed in the geological stratum dating from the Cretaceous Period (145 million years to 66 million years ago) on the seafloor off Ibaraki Prefecture, according to the researchers.

Japan Oil, Gas and Metals National Corp. in fiscal 2019 started a nationwide seabed resource survey using the Tansa 3-D geophysical exploration vessel. It will cover waters off Ibaraki Prefecture and should determine if oil really exists in Izura.

“Mining there will require huge costs, but I hold high expectations for the future resource survey,” Ando said.

The team’s findings were released in May on the online edition of the international geology journal Marine and Petroleum Geology. The printed version was issued on July 14.

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