Western Australia is often thought as barren land. But in an age before even the rise of the dinosaurs, when the continents were still joined in a great ‘supercontinent’ called Gondwana, a massive river ran the breadth of WA, shaping the land and laying sediments that now host some of Australia’s richest energy reserves.
A group of researchers from Melbourne, Sydney and Monash universities as well as from the Geological Survey of Western Australia and Geoscience Australia have traced this mighty river back to its distant source - in the mountains of East Antarctica. What’s more, they’ve been able to show that this colossal river flowed for over 200 million years, making it a candidate for one of the top ten longest-lived rivers in Earth’s history.
The river’s ancient route was revealed by geochemical analysis of thousands of zircons, a resistant mineral that can act as a geological clock. The dated zircons were once part of rock formations on the river’s headwaters and mountain ranges along the river route. The zircons were then removed by erosion, transported by the river and then deposited on what it is today an ocean. The dated zircons were then traced back to the similarly-aged mountain ranges where they were first formed.
The analysis of zircons from the deposits left behind by this Western Australian mighty river allowed the researchers to build a picture of the regions that river passed through. Their search ultimately led them back to an enormous, Himalaya-like mountain range at the heart of ancient Gondwana.
The river flowed for hundreds of millions of years until the breakup of Gondwana at the beginning of the age of the dinosaurs. With no more mountains to erode, the river dried up, leaving behind its ‘delta’ - a thick deposit of sediments where river meets a body of water. That delta now hosts large deposits of fossil fuels - but it can also teach us how to better care for these vital and fragile coastal environments.
Deltas capture the Earth’s tectonic and landscape history and host a range of resources vital to modern society. More than two thirds of the worlds’ major cities are located in coastal deltas, so geologists can use ancient deltas to understand how modern river systems should be behaving.
The study was published in the journal Geology, the highest-ranking journal for geosciences globally.
Morón, S., Cawood, P. A., Haines, P. W., Gallagher, S. J., Zahirovic, S., Lewis, C. J., and Moresi, L., 2019, Long-lived transcontinental sediment transport pathways of East Gondwana: Geology, v. 47, no. 6, p. 513-516.