Researchers from Sydney, Tasmania and Macquarie Universities led a team on the voyage to map the seafloor of the Perth Abyssal Plain. The expedition returned after a three-week cruise.
Travelling on the vessel Southern Surveyor, they discovered the islands through detailed seafloor mapping and by dredging rock samples from the steep slopes of the two islands, now in water depths of over 1.5 km, according to a Sydney statement.
“The data collected on the voyage could significantly change our understanding of the way in which India, Australia and Antarctica broke off from Gondwana,” said Joanne Whittaker, post-doctoral fellow at the University of Sydney’s School of Geosciences.
“The sunken islands charted during the expedition have flat tops which indicates they were once at sea level before being gradually submerged,” said Whittaker.
University of Sydney’s Simon Williams, the chief scientist on the expedition, said: “We expected to see common oceanic rocks such as basalt in the dredge but were surprised to see continental rocks such as granite, gneiss and sandstone containing fossils.”
In the Cretaceous period when dinosaurs roamed the Earth (over 130 million years ago), India was adjacent to Western Australia. When India began to break away from Australia, the islands formed part of the last link between the two continents.
Eventually these islands, referred to as ‘micro-continents’ by scientists, were separated from both landmasses and stranded in the Indian Ocean, thousands of kilometres from the Australian and Indian coasts.
“A detailed analysis of the rocks dredged up during the voyage will tell us about their age and how they fit into the Gondwana jigsaw,” Williams said.