A TEAM of Perth researchers is causing a major rethink on geological history after a study showed major iron formations in Australia, about 1.8 billion to 1.9 billion years old, were synchronous with those found in North America.
The UWA, Curtin University, the Department of Mines and Petroleumâ€™s Geological Survey of WA and Canadaâ€™s University of Manitoba worked together on unravelling why these formations reappeared almost 500 million years after a rise in atmospheric oxygen about 2.4 billion years agoâ€”something that would have stopped iron forming.
A superplume, or massive episode of volcanic eruptions related to extensive melting of the Earthâ€™s mantle, appears to be the cause of the iron formations reappearing.
Australian iron formations were previously thought to be significantly younger than their North American counterpartsâ€”but the new study has dated volcanic ash beds in the Australian formations to show they were deposited at the same time as those in North America.
UWA Centre for Microscopy, Characterisation and Analysis Dr Janet Muhling says, â€śThere were no direct dates on the iron formations in Australia but they were thought to be younger from indirect dating of other rocks in the same areaâ€ť.
â€śWe sampled rocks from the drill core as part of the Exploration Incentive Schemeâ€”no one had found the ash layers before, which were only found by examination of the rocks under a microscope.
â€śThe dating techniques developed at Curtin University by research team leader Professor Birger Rasmussen and Dr Ian Fletcher allowed us to date the ash layers.
â€śSome are only a few millimetres thick so would not be found in surface outcrops.â€ť
The research team has suggested extensive basaltic magmatism related to the superplume released vast volumes of iron into the global ocean, overwhelming the supply of oxygen and promoting the deposition of iron formations across the world.
â€śThe equally dramatic disappearance of iron formations some 40 million years later can be explained as a consequence of rapidly waning volcanic activity that allowed the ocean to become dominated by seawater oxidants once more,â€ť Dr Muhling says.
â€śOur findings not only explain the sudden appearance and disappearance of iron formations circa 1.9 billion years ago but also provide an explanation for the preservation of an oxygen-rich atmosphere above an oxygen-poor ocean.
â€śThe composition of the global ocean was unusual at this timeâ€”itâ€™s too early to relate this to microbial evolution but it is synchronous with other notable events in Earth history, although further research is required to work out the relationships.
The iron formation research has been published in Nature.â€ť