TASMANIA and parts of western North America were near neighbours about 1.4 billion years ago, according to a just-published study of Tasmania’s oldest rocks by University of Tasmania scientists.

Researchers Dr Jacqueline Halpin and Dr Peter McGoldrick, from UTAS’s Centre of Excellence in Ore Deposits, have found compelling evidence that western North America was once our close geographical neighbour.

The team age-dated tiny grains of monazite and zircon minerals found in sedimentary rocks from the Rocky Cape Group on Tasmania’s North-West Coast.

They found these rocks were deposited in an ancient ocean between 1.45 and 1.33 billion years ago, making them the oldest rocks in Tasmania.

Dr Halpin said the patterns of ages in the Rocky Cape Group strongly resembled those in sedimentary rocks from Montana, Idaho and southern British Columbia, known as the Belt-Purcell Supergroup rocks. It provides strong evidence that Rocky Cape and the Belt-Purcell rocks were geographically close 1.4 billion years ago.

“At this time, both Tasmania and North America were part of a supercontinent called Nuna,” Dr Halpin said.

“As plate tectonics and the supercontinent cycle started to rift Nuna apart, a large sedimentary basin formed that included the Rocky Cape Group and Belt-Purcell Supergroup rocks.”

The continued break-up of Nuna eventually dispersed parts of this ancient sedimentary basin to opposite sides of the Earth.

There was another discovery, too.

Dr McGoldrick said the new mineral dates also provided an age window for the horodyskia (or string of beads) fossils recently discovered in the Rocky Cape Group. These fossils have also previously been found in the Belt-Purcell rocks.

This is significant because horodyskia could be among the world’s oldest multi-celled organisms.

The research has been published in the latest international edition of Precambrian Research.