Cave system pre-dates dinosaurs, study finds

25 July 2006

The Orient Cave
The Orient Cave

Jenolan Caves - a series of spectacular limestone caves in central New South Wales- date back 340 million years, a University-led study has revealed.

"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," said Dr Armstrong Osborne, cave specialist and science lecturer from the University's Faculty of Education and Social Work.

"The Blue Mountains began to form 100 million years ago; dinosaurs became extinct 65 million years ago, andTasmania was joined to the mainland as recently as 10,000 years ago. Even in geological terms, 340 million years is a very long time," he said. Dr Armstrong worked with Dr Horst Zwingmann from CSIRO and scientists from the Australian Museum to date samples of clay from the Jenolan Caves - "Working out the age of a cave is working out the age of the stuff that's filling it," he said.

The method involves studying tiny amounts of radioactive potassium present in each sample. Small amounts of radioactive potassium exist in the environment alongside normal potassium, and over time radioactive potassium turns to argon, a gas, which remains trapped, explained Dr Osborne. By measuring the ratio between radioactive potassium and argon - the levels of decay - the scientists could determine how long the clay has existed.

The researchers also established that the clay was formed in situ in the caves and that it had not washed in from another source.

"Clay minerals are comprised of stacked sheets. If you find them aggregated - stacked like books - they must have been formed inside the cave. If they had been washed in they would be smashed up," said Dr Osborne.

The dated clays are foundin the Temple of Baal and Orient Caves, formed when clay crystallised after volcanic ash entered the caves.

The discovery has been a long time coming for Dr Osborne. For thirty years he has argued that the caves are much older than has been widely recognised - but even he cannot believe their age. "No-one imagined they would be more than 300 million years old from the Carboniferous period," he said. Until now, the oldest open caves were thought to exist inNew Mexico,dating back 90 million years.

What will this mean for Jenolan Caves tourism? "I think the caves should be nominated for World Heritage listing," he said.

Contact: Jake O'Shaughnessy

Phone: 0421 617 861