Two physical scientists from the University of Tasmania and Mineral Resources Tasmania, both in Australia, have analysed sedimentary rocks from the Rocky Cape Group in North West Tasmania and found that the rocks are very similar to those found in the North American states of Montana, Idaho and British Columbia.
Jacqueline Halpin and Peter McGoldrick dated tiny samples of minerals known as monazite and zircon, which are found in the sedimentary rocks from Rocky Cape, and discovered that they are between 1.45 and 1.33 billion years old—this also makes them the oldest known rocks ever found in Tasmania.
According to the scientists, the minerals must have been deposited in an ancient ocean about 1.45 billion to 1.22 billion years ago. Their finding suggests that Tasmania and Western North America were geographical neighbours about 1.4 billion years ago in the supercontinent Nuna, also known as Columbia.
“As plate tectonics and the supercontinents cycle started to rift Nuna apart, a large sedimentary basin formed that included the Rocky Cape and the Belt-Purcell Supergroup rocks,” explained Dr Hapin in a press release.
Because Tasmania’s rocks are different from the ones in mainland Australia, scientists hadn’t been able to pinpoint the exact location of the state during this prehistoric period.
Previous studies had suggested that Tasmania was part of central Australia and drifted apart when the supercontinent Nuna broke, but the new evidence contradicts this theory.
Halpin told the Guardian: “The rocks of Tasmania don’t look like the rest of Australia’s rocks if you look at those more than 700 million years old. The rocks up the east coast of Australian are much younger than in Tasmania. In terms of the geology, Tasmania is much more like North America.”
The mineral dates have also provided important information about the Horodyskia (string of beads) fossils found recently in the Rocky Cape. These fossils are visible to the naked eye, but are rarely found in rocks older than 635 million years, explained the researchers. This finding, however, suggests that the Horodyskia discovered in Tasmania could be twice this age.
The results of the study were published in the journal Precambrian Research.
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