The plateaus, the combined size of West Virginia, have long been known to cartographers as the Batavia Seamount and the Gulden Draakâ€”or Golden Dragon.
But not much else was known about the features, other than their location, about 1,000 miles (1,600 kilometers) west of Perth, Australia (map).
Surprising Deep-Sea Island Discovery
To fill in the gaps, an international team of scientists recently mapped the seabed and dredged samples from as deep as 8,200 feet (2,500 meters).
What the scientists found surprised them. Rather than the normal basalt rock of most seabeds, the scientists pulled up chunks of granite, gneiss, and sandstoneâ€”rocks normally found on continents.
Some samples even contained fossils, said team member Joanne Whittaker, a marine geophysicist at the University of Sydney in Australia.
“It’s quite clear that these two plateaus are little fragments of Gondwana left behind as India moved away from Australia,” Whittaker said.
Ancient Continent Pieces Once Rolling Terrain?
Scientists initially thought the plateaus had flat tops, a sign that they’d been above sea level long enough to have been eroded into plains.
But, as mapping continued, it became clear the plateaus’ physical features were rolling, ranging in elevation from as little as 2,600 feet (1,000 meters) to 8,200 feet (2,500 meters) below the surface. That would mean the highest plateau rises up to about 15,000 feet (4,600 meters) above a surrounding abyss.
The fossils found in the fragments were marine bivalves, a type of molluskâ€”indicating that the life-forms had lived in shallow water, not on land.
The animals were also discovered in the deeper regions of the plateaus, not the highest peaks, which may have once been islands. “It’s difficult to tell,” Whittaker said. “But that’s certainly something we’ll be looking at.”
Whittaker and colleagues will also try to match the rock samples with rocks on a nearby geological feature, the underwater Western Australian margin, which may help “pin exactly where these little pieces [of Gondwana] came from,” she said.
Few details are known about how the breakup of Gondwana formed the Indian Ocean about 130 million years ago, she added.
Gondwana Breakup Still a Mystery
Some of the story of the breakup will never be told, since the Gondwana portion of what is now India later collided with Asia.
“In India, the equivalent rocks are probably now squashed beyond recognition somewhere in the Himalayas,” Whittaker said.
As for whether dinosaurs might have once roamed the two plateaus, that depends on whether the features ever extended above sea level, and if so, when.
“Who knows? Whittaker said. At the moment, “anything’s possible.”