Oldest on Earth, Australia's Jenolan Caves Date Back 340 Million Years

SYDNEY, Australia, July 31, 2006 (ENS) - The Jenolan Caves in central New South Wales are the world's oldest discovered open caves, formed 340 million years ago, new cave-dating research published by Australian geologists has found.

Until 20 years ago, most scientists thought the Jenolan Caves were no more than a few thousand years old. In 1999 geologists estimated that the caves, which attract thousands of tourists each year, might be between 90 and 100 million years old.

Dr. Armstrong Osborne, a senior lecturer at the University of Sydney, has long suspected that the caves are older than that, but Osborne says even he was surprised to find they dated back to the Carboniferous period - 290 to 354 million years ago.

"We've shown that these caves are hundreds of millions of years older than any reported date for an open cave anywhere in the world," Osborne says.

"Even in geological terms, 340 million years is a very long time, he said. "To put it into context, the Blue Mountains began to form 100 million years ago; dinosaurs became extinct 65 million years ago, and Tasmania was joined to the mainland as recently as 10,000 years ago."

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One entrance to the Jenolan Cave system, just discovered to be 340 million years old (Photo courtesy Jenolan Caves Reserve Trust)
In a study published in the June issue of the Australian Journal of Earth Sciences, scientists from the government research institution CSIRO, the University of Sydney and the Australian Museum in cooperation with the Jenolan Caves Reserve Trust showed that the limestone caves date back more than 340 million years.

"Most people were convinced that caves were quite young," said Osborne, "and those of us who thought they were really old couldn't find any evidence. But no one imagined that they would be more than 300 million years old. This was totally off the planet."

The study used clay-dating methods that CSIRO's Petroleum Resources division developed to help oil exploration companies find oil deposits.

CSIRO Petroleum Resources researcher Dr. Horst Zwingmann says the age of the caves was determined by dating the clay minerals that crystallized when volcanic ash entered the caves. The ash now forms much of the mud in the Temple of Baal and Orient caves.

The technique is a variation of conventional potassium-argon dating, which can calculate the age of minerals by measuring levels of decay caused by radioactive potassium.

"We were able to provide evidence that the clays did form in-situ in the caves and that the sections regularly visited by tourists actually formed in the Carboniferous," Zwingmann says.

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The Persian Chamber in the Orient Cave (Photo courtesy CSIRO)
"This study shows how industry-focused research techniques can also be used to solve more general geological mysteries," he said.

The Australian Museum carried out initial studies using X-ray diffraction and scanning electron microscope imaging to identify clay minerals and their properties to see if they were suitable for dating.

Located 164 kilometers from Sydney, the Jenolan Caves Reserve Trust lands are karst conservation areas. Karst is a landform found in areas with soluble rock, such as limestone. Water carves the limestone into caves, gorges, sinkholes, stalactites and stalagmites.

The Jenolan caves are deep in a valley 793 metres above sea level. The first European to discover the caves was the bushranger and escaped convict James McKeown, who found them in 1838.

There are 22 major caves in the Jenolan system. Of these there are nine - the Imperial, Chifley, Jubilee, Lucas, Pool of Cerberus, River, Orient, Temple of Baal and Ribbon - which are dark caves now open for guided inspection with dramatic lighting on the cave formations.

The Jenolan Karst Conservation Reserve has World Heritage status as part of the Greater Blue Mountains World Heritage Listing and also is listed on the New South Wales State Heritage Register.