Study confirms complex history of Perth’s coastline

A new Curtin University study exploring the complex evolution of two iconic Western Australian landmarks has traced their transformation over millennia and offers a glimpse into their future.

Researchers from the Timescales of Mineral Systems group in the School of Earth and Planetary Sciences collected sediment samples from locations along Perth’s coastline, waterways and even the seabed to track changes that occurred as sea levels rose by tens of meters over thousands of years. .

Study leader Dr Andreas Zametzer said dive teams found certain types of mineral grains at sea, confirming the complex geological history of Rottnest Island (Wadjemup in Noongar) and the Swan River (Derbarl Yerrigan).

A separate group of ancient grains off Rottnest Island is 3.6 billion years old.

These same grains can be found in the modern Swan estuary and in the Avon tributary that delivered and deposited them thousands of years ago.

The article “When River Meets Sea: Transport and Origins in a Long-Living Estuary” was published in the journal Basin studies.

“Perth is located on the edge of a continent that is sinking,” Dr Zametzer said.

“Rottnest Island was the tip of a peninsula some 6,500 years ago – similar to what we see in the Shark Bay area – and because it is still part of a submerged continental margin, the ocean between Perth and Rottnest is hardly deeper than 20 depths. m in most places.

“We also now know for sure that the mouth of the Swan River used to be north of where Rottnest is today.”

Dr Zametzer said the researchers were stunned to find ancient mineral grains carried by the river so far out to sea.

“We expected the grains to break down and wash away because they were in a very turbulent, high-energy environment of waves and tides,” he said.

“But the river’s signature mineral signatures are still there, despite thousands of years of sea level changes and shelf reworking.

“We have an imprint of this river system preserved in the sea, documenting the history of the coast.”

Dr Zametzer said it was important to learn how coastlines had adapted and changed in the past to understand what rising sea levels would mean in the future.

“It’s just shocking to think about how quickly some geological processes actually happen while sea levels continue to rise rapidly.”